WATER QUALITY CONTROL
Part II. Parameters of water.
WATER QUALITY CONTROL
PART II.
Parameters of water
39
WATER QUALITY CONTROL
Part II. Parameters of water.
2. Natural Waters
Natural waters, occurring in the environment, are not chemically pure waters. While
circulating in the environment water contacts with atmosphere, rocks and soil. In this way
many different compounds pass into the water, either inorganic (mineral) or organic. From
physicochemical point of view natural waters are:
a. Multicomponent mixtures containing, apart from the solvent, many dissolved
substances, or
b. Multiphase mixtures containing dispergated solid phase (e.g. suspensions) and liquid
phase (e.g. emulsions).
In aquatic environment naturally occurring compounds are called admixtures (e.g. Ca2+, Mg2+,
Na+, K+, HCO3-, Cl-, SO42- ions, humic substances). The quantity and quality of admixtures
depend on the environment of water circulation. The substances of foreign origin are called
pollutants [4].
•
Inorganic material in natural waters
The quantity of inorganic compounds dissolved in natural waters is differentiated. At the two
common extremes, rainwater may contain as little as a few milligrams of dissolved material
per litre whereas seawater contains approximately 35 g of salt per litre. The presence of even
a few milligrams of dissolved matter in a litre of rainwater is derived from a number of
sources: sulphate from the oxidation of hydrogen sulphide, sulphur dioxide, and
dimethylsulphide, and nitrogenous material from terrestrial vegetation and combustion
emissions.
After falling onto the land, rainwater moves both through and over the soil and underlying
rocks dissolving material as it travels. Such a route may increase the inorganic content of the
water. Organic matter is also picked up during this process but can be removed from the water
if it subsequently travels through the groundwater system [4].
•
Organic material in natural waters
Generally all natural waters contain organic matter. Some of these are living organisms which
size range from that of bacteria to whales; some is decaying matter, and some has been
introduced from external sources such as drainage, factory pollution, and atmospheric fallout.
The naturally dissolved organic matter is made up of the transformation products of biogenic
material and biological excretion products.
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WATER QUALITY CONTROL
Part II. Parameters of water.
Proteins, amino acids, fats, lignines, etc., the structural elements of plants and animals, are
being broken down continuously both whilst the organism is living and as it decays. The
products of degradation and the compounds which are formed by the reassociation of these
fragments, create in water a complex mix of dissolved organic compounds. Organic
compounds are secreted and excreted by all living organisms and these in turn are broken
down into smaller species by bacteria and chemical processes.
This organic matter covers the full range of molecular weight, ranging from totally soluble
low molecular weight organics to high molecular weight polymers of colloidal and particulate
nature.
a. Small organic compounds
In the absence of pollution sources, small organic molecules such as amino acids, sugars, fats,
and chlorophyll are derived from animal and plant metabolism and the decomposition of
larger biologically derived molecules. These in turn are a major source of nutrition for other
organisms. In addition to the naturally occurring compounds there are many which are present
as a result of man's activities, examples of which include pesticides such as DDT and the
polynuclear aromatic hydrocarbons resulting from combustion. The chemical formulas of
exemplary small organic compounds are presented below, in Fig.2.1.
Fig.2.1. Some of the smaller organic molecules found in natural waters [4].
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WATER QUALITY CONTROL
Part II. Parameters of water.
b. Higher molecular weight compounds
Much of the dissolved organic matter is of high molecular weight and falls under the title of
humic matter. Humic matter is a complex mixture of polymeric material. Its solubility and
metal complexing abilities are largely determined by it containing a large number of phenolic
and carboxylic acid groups [4].
2.1. Natural processes affecting the water composition
Any natural water body is a homogenous water solution. Due to circulation in the
environment water continuously undergoes physicochemical transformations from solid,
liquid to gaseous phase, which greatly affect its composition. While travelling in the
environment water contacts different media – soil, rocks and atmosphere, collects and
transports dissolved and insoluble, organic and inorganic compounds. Also biological
processes and activity of organisms contributes to changes in natural waters composition.
When considering composition of natural waters the processes of great importance are
weathering, sedimentation, absorption and evaporation (explained in chapter 1 “Introduction
to Water Quality Control”, point 1.3.1.) and self purification.
2.1.1. Sedimentation and Dissolution
The composition of natural waters is rarely governed purely by homogeneous reactions; there
is a continuous cycling of material between the dissolved and solid phases brought about by a
combination of chemical, physical, and biological processes.
Fig.2.2. The interchange of material between the sediments and water [4].
Some of the solid matter which is suspended in a natural water, or deposited to make up the
top layers of the bottom sediments, is material which has been recently deposited from
solution. This may arise from a purely chemical process such as precipitation or colloidal
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WATER QUALITY CONTROL
Part II. Parameters of water.
aggregation, or may result from the production of solid biomass, such as that which results
from the photosynthetic activity of algae. Some of this solid material will be rapidly returned
to the dissolved phase by changes in solution chemistry or bacterially assisted decomposition;
the remainder will eventually be incorporated into the sediments. Fig.2.2 illustrates the
interaction between dissolved and solid phases.
Most sediment does not consist of one pure component but are made up of mixtures of clay,
silt, sand, minerals, and organic matter. They may be present as a result of local physical,
chemical, or biological processes or may have been washed into the water body from external
sources. The settlement of solid material out of solution onto the floor of a lake or ocean
results in the build up of layers of sediment. If this is not disturbed by movement of the water,
distinct layers can result giving a history of the sediment deposition. In other more turbulent
regions, such as the mouths of estuaries, the energy of the incoming tide can result in the
remobilization of significant depths of sediment during each tidal cycle [4].
2.1.2. Weathering
The intimate contact of rocks and minerals with water is a major factor in their erosion and
the dispersal of solid material in soils and the river, lake, and coastal marine bottom and
suspended sediments. The increased surface area resulting from the breakdown into smaller
particles can enhance the rate of dissolution and change by exposing new surfaces to attack.
This attack not only releases material into the water but can radically change the nature of the
rocks and minerals. There are two main mechanisms which are responsible for these
weathering effects [4]:
•
Hydrolysis - the hydrogen ions are required for the reaction to occur; hydrogen ions
originate from water
•
Oxidation - for the reaction to occur at least one of the elements in the mineral structure
must be in a lower oxidation state which can be readily oxidized. Whilst many elements
fulfil this criterion the most commonly encountered examples contain iron (II), manganese
(II) and sulphide.
Weathering will produce an increase in inorganic salt content. The water composition may be
also affected by interaction with material on the bed of water reservoir.
2.1.3. Colloids and Their Aggregation
Lying between the dissolved state, and particles which precipitate out of solution, there is a
class of very small particles suspended in water, which range in diameter between 1 nm and
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WATER QUALITY CONTROL
Part II. Parameters of water.
1µm. These are colloids. They play a significant role in the aquatic chemistry of both
inorganic and organic compounds. Because they are suspended in the water they are
transported along with moving water bodies. Once destabilized however they rapidly come
together to produce larger particles that can precipitate and drop to the bottom sediments,
carrying with them other adsorbed and co-precipitated material.
The particles are not visible to the naked eye and a colloidal sol (the colloidal equivalent of a
solution) appears completely homogeneous. When allowed to stand, colloids do not settle out
like heavier particles.
Colloidal particles are charged and therefore move in an electric field. This primary charge
may be positive or negative and may change with the solution pH. In aqueous solution
however, there can be no overall charge and the primary charge must therefore be
counterbalanced by the collection of opposite charges around the particles - a double layer
therefore exists at the interface between the solid and the water [4].
2.1.4. Adsorption and Absorption
Adsorption is the preferential partitioning of substances from the gaseous or liquid phase onto
the surface of a solid substrate [23]. The binding to the surface is usually weak and reversible
[22]. The process of adsorption involves separation of a substance from one phase
accompanied by its accumulation or concentration at the surface of another. The adsorbing
phase is the adsorbent, and the material concentrated or adsorbed at the surface of that phase
is the adsorbate. Adsorption is thus different from absorption, a process in which material
transferred from one phase to another (e.g. liquid) interpenetrates the second phase to form a
"solution". Absorption means the penetration of a substance into the body of another. In
natural waters living organisms absorb oxygen, carbon dioxide and nutrients necessary for
growth [23].
2.1.5. Natural Purification
Precipitation that falls onto the surface passes through the layers of soil and infiltrate into the
ground. Due to physical, chemical and biological processes (Table 2.1.) water passing through
the ground undergoes purification. The speed of filtration is very low, that is why the
processes of biochemical and sorption self-purification (spontaneous decrease in degree of
pollution) are complete and ground waters do not reveal physico-chemical and bacteriological
pollution [2].
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Part II. Parameters of water.
Table 2.1. Self-purification processes concerning ground waters.
Physical processes
Chemical processes
Biological processes
Dilution
Coagulation
Precipitation
Sorption (adsorption)
Ion-exchange
Filtration
Degradation
Oxidation
Reduction
Hydrolysis
Biodegradation
Decaying
In case of surface waters they, in time, undergo self-purification as a result of biochemical
processes, due to microbiological activity of organisms in presence of oxygen and
sedimentation. Microorganisms activity leads to decomposition of organic compounds into
simple inorganic ones (carbon dioxide, sulphates, nitrates and water), dilution or removal of
pollutants from water by living organisms. Self-purification processes occur with various
speeds in different environment conditions. The intensity depends on degree of aeration of
water reservoir, microorganisms’ content and type of pollutants [2].
2.2. Classes of Natural Waters
The quality of surface waters is not equal and even, and has to be established. Standards of
permissible pollution of surface waters and conditions of sewage disposal are regulated
according to The Cabinet Decree form 9 June 1970. In Poland surface waters (inland flowing
waters) are divided into 3 classes of cleanness, on the basis of established norms [13]:
a. I class - the cleanest waters; water capable to use as a drinking water directly; waters
suitable for the use in branches of industry requiring high quality water (food and
pharmaceutical industry); water which fulfil requirements for ponds with salmon
b. II class - waters suitable for fish other than salmon, raising of farm animals,
cultivation and recreation
c. III class - waters suitable for the use in industry other than industry which require I
class water; for watering of agricultural and garden areas.
Waters exceeding norms for the III class water are called pose-class waters.
The standards of acceptable surface water pollutants are presented in Table 2.2.
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WATER QUALITY CONTROL
Part II. Parameters of water.
Table 2.2. Standards of acceptable inland surface waters pollution [13].
No.
Indicator or kind of pollution
1.
Dissolved oxygen
Biological Oxygen Demand
(BOD5)
Chemical Oxygen Demand
(COD), (permanganate
Chemical Oxygen Demand
(COD), dichromate
2.
3.
4.
Concentration
Unit
mg O2/dm3
I
6 and above
Clarity class
II
5 and above
III
4 and above
mg O2/dm3
4 and below
8 and below
12 and below
mg O2/dm3
10 and below
20 and below
30 and below
mg O2/dm3
40 and below
60 and below
100 and below
Oligo to
Betamezzo to
betamezzo
alfamezzo
250 and below 300 and below
150 and below 200 and below
350 and below 550 and below
1000 and
500 and below
below
400 and below
250 and below
700 and below
1200 and
below
20 and below
50 and below
5.
Saprobythes
mg O2/dm3
6.
7.
8.
Chlorides
Sulphates
Total hardness
mg Cl/dm3
mg SO4/dm3
G CaCO3/dm3
9.
Dissolved substances
mg/dm3
mg/dm3
11.
12.
13.
14.
15.
16.
17.
Turbidity (total suspensions,
except for sudden water rise)
Ammonia salts
Nitrates
pH
Organic nitrate
Total iron
Manganese
Phosphates
18.
Rhodanic acids
mg CNS/dm3
19.
Cyanides (except for complexes)
mg CN/dm3
20.
Cyanide complexes
mg MeCNx/dm3
mg/dm3
21.
Volatile phenols
10.
22.
23.
Surfactants
Temperature1
24.
Odour
25.
26.
27.
28.
29.
30.
31.
2
Colour
Faecal Coliforms Factor
Pathogenic bacteria
Oils
Ether extract
Lead
Mercury
3
mg NH4/dm
mg NO3/dm3
mg Norg/dm3
mg Fe/dm3
mg Mn/dm3
mg PO4/dm3
1 and below
3 and below
6 and below
1.5 and below
7 and below
15 and below
6.5-8.5
6.5-9.0
6.0-9.0
1 and below
2 and below
10 and below
1.0 and below 1.5 and below 2.0 and below
0.1 and below 0.3 and below 0.8 and below
0.2 and below 0.5 and below 1.0 and below
0.02 and
0.1 and below 2.0 and below
below
0.01 and
0.02 and below 0.05 and below
below
1.0 and below
0.005 and
below
1 and below
22 and below
3
mg/dm
°C
3R and below
3
mg Pt/dm
30 and below
Alfamezzo
2.0 and below
3.0 and below
002 and below 0.05 and below
2 and below
26 and below
natural
3 and below
26 and below
Slight at the
very most
natural
0.1 and above 0.01 and above
Undetectable
Invisible on water surface
5 and below
15 and below
40 and below
0.1 and below 0.1 and below 0.1 and below
0.005 and
0.005 and
0.01 and below
1 and above
mg/dm3
mg Pb/dm3
mg Hg/dm3
1
If natural water temperature is equal to or higher than standard value for particular clarity class of water, the
temperature increase is possible of 2°C
2
In special cases it is possible to change (increase) the value of Pt indicator, for I and II class not more than of
15 mg/dm3 Pt, and for III class not more than of 30 mg/dm3 Pt.
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WATER QUALITY CONTROL
Part II. Parameters of water.
No.
Indicator or kind of pollution
Concentration
Unit
32.
Copper
mg Cu/dm3
33.
Zink
mg Zn/dm3
34.
Cadmium
mg Cd/dm3
35.
36.
37.
Chromium (III)
Total heavy metals
Nickel
mg Cr/dm3
mg/dm3
mg Ni/dm3
38.
Chromium (VI)
mg Cr/dm3
39.
Silver
mg Ag/dm3
40.
41.
Vanadium
Boron
mg V/dm3
mg B/dm3
42.
Arsenic
mg As/dm3
43.
44.
45.
46.
47.
48.
49.
Chloride
Fluoride
Sulphites
Ammonia
Acrylnitrile
Caprolactam
Radioactive substances
mg Cl/dm3
mg F/ dm3
mg S/dm3
mg NH3/dm3
mg/dm3
mg/dm3
50.
Biological test with fish
24 hours
Clarity class
I
II
III
below
below
0.01 and
0.1 and below 0.2 and below
below
0.01 and
0.1 and below 0.2 and below
below
0.005 and
0.03 and below 0.1 and below
below
0.5 and below 0.5 and below 0.5 and below
1.0 and below 1.0 and below 1.0 and below
1.0 and below 1.0 and below 1.0 and below
0.05 and
0.1 and below 0.1 and below
below
0.01 and
0.01 and below 0.01 and below
below
1.0 and below 1.0 and below 1.0 and below
1.0 and below 1.0 and below 1.0 and below
0.05 and
0.05 and below 0.2 and below
below
Undetectable
1.2 and below 1.2 and below 2.0 and below
undetectable
0.1 and below
0.1 and below 0.1 and below 0.1 and below
2.0 and below 2.0 and below 2.0 and below
1.0 and below 1.0 and below 1.0 and below
In quantity determined by different regulations
Positive, water should not cause dead of fish
during 24 hours
The acceptance of particular class of water is made by water administration organ. If water is
for different use the class of water is that of higher requirements.
Drinking water regulations are specified by Decree of Minister of Health and Social Welfare
from 4 May 1990 and are stricter in case of some compounds present in water. They are listed
in chapter 4 “Water for Different Purposes”, point 4.1.
To estimate the class of water it is necessary to make an analysis of physicochemical and
biological water parameters.
2.3. Parameters of Natural Waters
Determination of water parameters is used for description of the quality of water.
Nowadays European countries use 64 parameters to determine water parameters and its
quality. Polish rules require only 51 parameters. The strictest rules considering water
parameters are established by EPA (Environmental Protection Agency 1995). It is equal to
120 parameters.
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WATER QUALITY CONTROL
Part II. Parameters of water.
Tests for the physical/chemical parameters monitor the characteristics that affect the
appearance, taste and odour of water but generally do not cause a health risk, while
microbiological tests are for waterborne organisms that could potentially cause disease.
2.3.1. Organoleptic Parameters
a. Colour
Colour is an optical parameter consisting in absorbing of a part of spectrum of visible
radiation by substances dissolved in water, colloidal substances, and suspended particles
present in water or sewage.
Colour in water may appear as the result of different sources activity. These are:
•
Natural Sources: type of vegetation, decay of plant matter, humic substances, algae
growth, plankton, minerals (iron, manganese and copper).
•
Anthropogenic sources: sewage from paper mills, textile mills, food processing
There are two types of water colour considered: "apparent colour” and "true colour".
True colour is distinguished from apparent colour by filtering the sample. True colour is
mostly found in surface water, although ground water may contain some colour if the aquifer
flows through a layer of buried vegetation, such as from a long buried slough of a
river. Apparent colour is caused by coloured suspensions and dissolved matter.
The unit of colour is the colour developed in 1 dm3 of distilled water by 1mg of dissolved
platinum (potassium hexachloroplatinum (IV) (K2PtCl6)) with addition of 0.5 mg of cobalt
(cobalt chlorate (II) CoCl2 · 6H2O).
Colour measurements are carried out by the use of optical principle, light absorbency and
place detector in direction of incoming light source.
Colour can be removed by activated carbon filters, sometimes marketed as taste and odour
filters. Another treatment method is coagulation and sedimentation using alum or other
chemicals.
There is no direct link between colour and health effects and the colour of water is usually
only an aesthetic problem, both in drinking water and wastewater. However, water colour
may be also an indicator of toxicity and may stain textiles and fixtures. It may be result of the
presence of coloured organic substances, metals (Fe, Mg and Cu) or industrial wastes. Colour
is vital as most water users, be it domestic or industrial, usually prefer colourless water.
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WATER QUALITY CONTROL
Part II. Parameters of water.
According to polish regulations colour in drinking water must not exceed 20 mg(Pt)/dm3. In
case of ground water it should not exceed 25 mg(Pt)/dm3, and in case of surface waters it
should be true colour.
Natural waters are yellowish-green in colour. Waters flowing out of marshy and forest areas,
rich in humic substances, are yellowish-brown. Such colour originates from natural humic
substances and decomposition of plant material taking place in soil, swamps or peat [10].
b. Turbidity
Turbidity is an expression of the optical properties that cause light to be scattered and
absorbed rather than transmitted in a straight line through the water.
Turbidity in water is caused by the presence of dissolved inorganic and organic particles, like:
•
Soluble coloured compounds (iron, manganese and aluminium),
•
Humic acids,
•
Plankton and microscopic organisms (also bacteria and other pathogens),
•
Clay and silt,
•
Suspensions from sewage disposal.
Turbidity depends on a number of factors, such as the quantity, size, shape, and refractive
index of the particles and the wavelength of the incident light [1]. Particles that cause
turbidity in water vary in size between 1 nm and 1 mm [6]. They can be divided into three
classes:
•
Clay particles, which have an upper particle size limit of about 0.002 mm diameter;
produced by the erosion of the land surface constitute the major part of the suspended
material in most natural waters [7],
•
Organic particles, produced by the decomposition of plant and animal debris; Organic
particulates may harbour microorganisms. Thus, turbid conditions may increase the
possibility for waterborne disease. Nonetheless, inorganic constituents have no notable
health effects,
•
Fibrous particles, e.g. those of minerals such as asbestos.
All natural waters are turbid, surface waters generally more than subsurface waters.
Groundwater is usually totally clear due to filtration property of soil. However, after
excavation it very often clouds up, especially in contact with air. This is the result of the
change in chemical composition of water: a part of dissolved carbon dioxide (CO2) passes to
atmosphere causing the calcium-carbon equilibrium to be upset. This leads to gradual
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WATER QUALITY CONTROL
Part II. Parameters of water.
precipitation of calcium, magnesium and iron carbonates and hydroxides, in the following
reactions:
Ca(HCO3) 2 ∆ CaCO3 (↓) + CO2 (↑) +H2O
Fe(HCO3) 2 +2H2O ∆ Fe(OH) 2 (↓) + 2H2CO3
2Fe(OH) 2 + ½ O2 + H2O = 2Fe(OH) 3
Usually after a few hours there is a total sedimentation of precipitates and water becomes
clear again [10].
The series of turbidity-induced changes that can occur in a water body may change the
composition of an aquatic community. First, turbidity due to a large volume of suspended
sediment will reduce light penetration, thereby suppressing photosynthetic activity of
phytoplankton, algae, and macrophytes, especially those from the surface. If turbidity is
largely due to algae, light will not penetrate very far into the water, and primary production
will be limited to the uppermost layers of water. Overall, excess turbidity leads to fewer
photosynthetic organisms available to serve as food sources for many invertebrates. As a
result, overall invertebrate numbers may also decline, which may then lead to a fish
population decline.
If turbidity is largely due to organic particles, dissolved oxygen depletion may occur in the
water body. The excess nutrients available will encourage microbial breakdown, a process
that requires dissolved oxygen. In addition, excessive nutrient content may result in algal
growth. Although photosynthetic by day, algae respire at night, using valuable dissolved
oxygen. Fish kills often takes place because of extensive oxygen depletion.
High turbidity can also reduce the growth of clams and oysters; it can slow or stop egg
development. The comparative unit of turbidity is turbidity developed by 1 mg of silica (SiO2)
added to 1 dm3 of distilled water.
Acceptable turbidity of drinking water consistent with polish regulations must not exceed 5
mg/dm3. For surface waters the requirements are:
I class
-
20 mg/dm3
II class
-
30 mg/dm3
II class
-
50 mg/dm3
Because of microbiological effects it is recommended that turbidity be kept as low as
possible.
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WATER QUALITY CONTROL
Part II. Parameters of water.
•
Turbidity in drinking water
Turbidity can have a significant effect on the microbiological quality of drinking-water. Its
presence can interfere with the detection of bacteria and viruses in drinking water [5];
moreover, turbid water has been shown to stimulate bacterial growth [6] since nutrients are
adsorbed onto particulate surfaces, thereby enabling the attached bacteria to grow more
rapidly than those in free suspension.
The adsorptive capacity of some suspended particulates can lead to the presence of
undesirable inorganic and organic compounds in drinking-water. Most important in this
respect is the organic or humic component of turbidity. In addition, the strength of the bonds
in some metal–humate complexes in the turbidity fraction may complicate the measurement
of trace metals in natural waters, resulting in an underestimation of the metal concentrations.
Turbid water is not suitable for consumption. The consumption of highly turbid water may
constitute a health risk, because excessive turbidity can protect pathogenic microorganisms
from the effects of disinfectants, stimulate the growth of bacteria in distribution systems, and
increase the chlorine demand. In addition, the adsorptive capacity of some particulates may
lead to the presence of harmful inorganic and organic compounds in drinking-water.
c. Suspended Solids
Solids present in water can be divided into three types according to size:
•
Suspended
> 1 mm (larger than bacteria)
•
Colloidal
between 1 mm and 0.001 mm
•
Dissolved
< 0.001 mm
The suspended solids include sand, silt, rust, plant fibres and algae and are an indicator of
possible bacterial or hazardous contamination.
Total Suspended Solids is the mass of solids that can be separated from the water by filtration.
Total Suspended Solids is an indication of the amount of erosion that took place nearby or
upstream. It can also be caused by plankton growth, or wastewater.
d. Dry residues
Dry residue is a residue left after evaporation of water, drying in 105°C and recalculation into
1 dm3 of water or sewage. It makes up for the mass of dissolved and insoluble inorganic and
organic substances present in water. High content of dry residue contribute to the bitter water
taste and have negative impact on the organisms as regards to physiology.
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WATER QUALITY CONTROL
Part II. Parameters of water.
It is advisable that drinking water content of dry residue would not exceed 500 mg/dm3 [2].
e. Taste and odour
Chemically clean water is odourless, while odour of natural waters depends on the type and
quantity of dissolved substances [10].
Taste and odour are usually inter-related. Compounds in water that are perceived as giving it a
taste are generally inorganic substances present at concentrations much higher than those of
organic pollutants. Inorganic chemicals that can affect taste but not cause any odour are salt
(NaCl), minerals and metals. The salt concentration in water should be approximately the
same as in saliva for the water to taste neutral. Of the ions that may be present in water, iron
can be tasted in distilled water at concentration of about 0.05 mg/dm3, copper at about 2.5
mg/dm3, manganese at about 3.5 mg/dm3, and zinc at about 5 mg/dm3. Iron, in particular, is
suspected of affecting the taste of water in practice [14].
A few inorganic chemicals can cause both taste and odour problems. These are ammonia,
chlorine and hydrogen sulphide.
Organic chemicals usually affect both taste and odour: The compounds concerned include
humic
substances,
hydrophilic
Table 2.3. The threshold odour for some chemical contaminants.
acids, carboxylic acids, peptides and
Compound
Threshold [mg/dm3]
amino acids, carbohydrates, and
Chlordane
0.0003
hydrocarbons [14], biological decay
1,4-dichlorobenzene
0.0003
products, petroleum products and
Trichloroethylene
0.5
Phenol
1 - 15.9
4-chlorophenol
0.0005 - 1
2,4-dichlorophenol
0.002 - 0.32
Hydrogen cyanide
0.001
pesticides. These compounds are
detectable
at
extremely
concentrations (Table 2.3).
low
The organisms most often linked to taste and odour problems are actinomycetes and various
types of algae, but other aquatic organisms, such as protozoa and fungi, have been implicated
from time to time.
Earthy-musty tastes and odours are produced by certain cyanobacteria (blue-green algae),
actinomycetes, and a few fungi. Growing algae produce numerous volatile and non-volatile
organic substances, including aliphatic alcohols, aldehydes, ketones, esters, thioesters, and
sulphides.
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WATER QUALITY CONTROL
Part II. Parameters of water.
Occasionally, taste and odour problems in water are caused by other bacteria, fungi,
zooplankton, and nemathelminthes. Ferrobacteria in water-distribution systems may produce
tastes and odours, and some species of Pseudomonas can cause a swampy odour, whereas
others can convert sulphur-containing amino acids into hydrogen sulphide, methylthiol, and
dimethylpolysulfide [14].
Ground waters are usually odourless, however, sometimes they posses a characteristic odour
of hydrogen sulphide (H2S) originating from decomposition of sulphide minerals in presence
of dissolved carbon dioxide [10]:
FeS2 + 2CO2 + 2H2O → Fe(HCO3) 2 + H2S + S
MnS + 2CO2 + 2H2O → Mn(HCO3) 2 + H2S
•
Taste and odour in drinking water
Taste and odour in drinking water can be caused by microorganisms or may be of human
origin. Problems can also be caused by some water-treatment processes or by substances
leached from water pipes or storage facility linings. Odour in potable water may be indicative
of some form of pollution of water, malfunction during water treatment process or distribution
of water. It should not be accepted without knowledge of the exact cause.
Water treatment often includes storage, slow sand filtration or activated carbon filtration.
Microorganisms can grow in the equipment used for these purposes and can then cause tastes
and odours. The biological degradation of organic compounds in raw water can also lead to
the production of substances such as phenols, aldehydes, and alkylbenzenes that cause taste
and odour problems. In addition, the chemicals used in water treatment as coagulants,
oxidants, or disinfectants can interact with organic compounds in water and occasionally
produce tastes and odours [14].
Ozone is one of the most efficient agents in removing tastes and odours, but its use can lead to
the formation of intermediate reaction products. In particular the formation of aliphatic
aldehydes, which has been frequently reported in the literature, leads to the development of
fruity, fragrant, and orange-like odours.
The free halogens used as water disinfectants can produce undesirable tastes and odours in the
water. Taste and odour problems that develop in water-treatment plants are frequently an
indirect consequence of chlorination [14].
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2.3.2. Physicochemical Parameters
a. Temperature
Distribution of temperature is different for surface waters and groundwater. Temperature of
surface waters depends mainly on:
•
Water origin,
•
Climatic zone,
•
Season,
•
Altitude,
•
Degree of riparian coverage,
•
Inflow of industrial and municipal sewage (power plants, industrial cooling) [10].
Water temperature can fluctuate diurnally and seasonally, however, daily variation of air
temperature can hardly affect water temperature. Flowing waters usually have unique
temperature depending on flow velocity. In case of steady reservoirs variations in temperature
can occur due to thermal stratification and restricted mixing of layers (stratification tends to
persist until cooler fall weather). Water layers with dissimilar temperature differ in density
and oxygen content.
Temperature of groundwater depends mainly on the depth of water occurrence. In Poland
temperature of groundwater increases ca.1°C every 33 m going down, due to the increase of
soil temperature.
Temperature can exert great control over aquatic communities, especially influence on
biological activity and growth. If the overall water body temperature of a system is altered,
an aquatic community shift can be expected.
An increase of 10°C in water temperature almost doubles the speed of chemical and
biological reactions occurring in water. Temperature increase leads to:
•
Decrease the amount of dissolved oxygen (DO)
•
Increase biochemical oxygen demand (BOD)
•
Acceleration of nitrification and oxidation of ammonia to nitrates (III) and (V) which
eventually lead to oxygen deficit in water.
Higher temperature also increases toxicity of many substances (pesticides, heavy metals) and
susceptibility of organisms to toxicants. Organisms (including fish) are also sensitive to
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temperature, as must migrate through changing temperature zones. Sudden temperature
changes affects fish more than extremes.
Acceptable temperature of water in Poland is equal to:
•
surface water
I class
-
22°C
II and III class
-
26°C
Temperature of drinking water is not regulated. It does not influence hygienic value of
drinking water; however it is important for taste. Constant temperature 7 - 12°C is
recommended.
b. pH
The pH is a measure of the acidity of a solution (H+ ions) and ranges in scale from 0 to 14
(from very acidic to very alkaline). Water dissociation reaction (see chapter 1, point 1.1.1)
indicates that chemically pure water is neutral. The pH values of natural waters (Table 2.4)
are influenced by different the presence of admixtures (i.e. carbons, hydrocarbons, carbon
dioxide, sulphur dioxide etc.) which alter neutral pH of water. The important factors are
geological characteristics of bottom of a water body, which can contain acidic or basic
compounds as well as vegetation, land use practices, sewage inflow and atmospheric
precipitation.
Table 2.4. pH of natural waters
Water type
Surface water
Groundwater
Acid rain
Lakes damaged by acid rain
pH value
6.5 - 8
5.5 - 7.5
as low as 3
4 or less
Water pH is crucial for living organisms, biochemical processes and industrial water use. The
pH is indicator of the existence of biological life as most of them thrive in a quite narrow and
critical pH range. In too acidic or too basic waters biological life extinct. Low water pH
accelerates heavy meats being washed away from sediments. Acidic waters are highly
corrosive.
According to polish standards permissible values of water pH are the following:
•
drinking water
•
surface water
I class
-
6.5 – 8.5
-
6.5 – 8.5
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II class
-
6.5 – 9.0
III class
-
6.0 – 9.0
c. Alkalinity
Alkalinity refers to the capability of water to neutralize acids. This is really an expression of
buffering capacity. A buffer is a solution to which an acid can be added without changing the
concentration of available H+ ions (without changing the pH) appreciably. It essentially
absorbs the excess H+ ions and protects the water body from fluctuations in pH [20].
Generally, the basic species responsible for alkalinity in water are bicarbonate ion, carbonate
ion and hydroxide ion [3]:
HCO3- + H+ → CO2 + H2O
CO32- + H+ → HCO3OH- + H+ → H2O
The presence of calcium carbonate or other compounds such as magnesium carbonate
contribute to the buffering system [20]. Minor contributors to alkalinity are ammonia and the
conjugate bases of phosphoric, silicic, boric, and organic acids [3].
Alkalinity is often related to hardness because the main source of alkalinity is usually from
carbonate rocks (limestone) which are mostly CaCO3. Since hard water contains metal
carbonates (mostly CaCO3) it is high in alkalinity. Conversely, unless carbonate is associated
with sodium or potassium which do not contribute to hardness, soft water usually has low
alkalinity and little buffering capacity. So, generally, soft water is much more susceptible to
fluctuations in pH from acid rains or acid contamination [20].
It is important to distinguish between high basicity, manifested by an elevated pH, and high
alkalinity, the capacity to accept H+. Whereas pH is an intensity factor, alkalinity is a capacity
factor [3].
Alkalinity (as well as pH) can be determined using inexpensive test strips. However, more
sophisticated electrometric measurement is performed by the computer aided titrimeter (CAT)
and the pH electrode.
Alkalinity is important for fish and aquatic life because it protects or buffers against rapid pH
changes. Living organisms, especially aquatic life, function best in a pH range of 6.0 to 9.0.
For protection of aquatic life the buffering capacity should be at least 20 mg/dm3 [20].
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d. Acidity
Acidity of natural water systems is the capacity of water to neutralize hydroxide ions OH-.
Acidity is generally due to the presence of weak acids such as H2PO4-, CO2, H2S, proteins,
fatty acids, and acidic metal ions, particularly Fe3+. Factors causing acidity of natural waters
can originate from atmosphere (e.g. CO2), soil (CO2 and humic acids), coagulants added to
water during treatment and from industrial sewage inflow.
The term free mineral acid is applied to strong acids such as H2SO4 and HCl in water.
Whereas total acidity is determined by titration with base to the phenolphthalein endpoint (pH
8.2, where both strong and weak acids are neutralized), free mineral acid is determined by
titration with base to the methyl orange endpoint (pH 4.3, where only strong acids are
neutralized).
The acidic character of some hydrated metal ions may contribute to acidity as shown by the
following example:
A1(H2O)63+ + H2O ∆ A1(H2O)5OH2+ + H3O+
Some industrial wastes, for example, pickling liquor used to remove corrosion from steel,
contain acidic metal ions and often some excess of strong acid [3].
e. Conductivity
Conductivity is a measure of the capacity of an aqueous solution to carry an electrical current.
Conductivity depends on the presence of ions (cations and anions) in water, their total
concentration, mobility and valence, and on temperature of water.
In natural waters ions usually origin from inorganic compounds present in water. Organic
compounds dissociate to minimal degree or do not dissociate at all. Conductivity is a good
measure of the total amount of salts in water (e.g., calcium, magnesium, sodium, potassium,
carbonate, bicarbonate, sulphate, chloride, nitrate, and others). It is commonly used to
determine salinity [6].
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High salinity may interfere with the growth of aquatic vegetation. Salt may decrease the
osmotic pressure, causing water to flow out of the plant to achieve equilibrium. Less water
can be absorbed by the plant, causing stunted growth and reduced yields. High salt
concentrations may cause leaf tip and marginal leaf burn, bleaching, or defoliation.
According to polish standards permissible conductivity of drinking water is 1500 mS/cm, and
acceptable amounts of substances dissolved in water are:
•
drinking water
•
surface water
-
should not exceed 800 mg/dm3
I class
-
500 mg/dm3
II class
-
1000 mg/dm3
III class
-
1200 mg/dm3
f. Hardness
The hardness of water is the concentration of ions that will react with a sodium soap to
precipitate an insoluble residue. Water hardness is the result of dissolved minerals presence,
usually total concentration of cations of calcium Ca2+, magnesium Mg2+, iron Fe3+ and
manganese Mn2+. The reaction for calcium is:
2C17H35COO-Na+ + Ca2+ → Ca(C17H35CO2)2 (↓)+ 2Na+
The following types of water hardness are under consideration [2]:
•
Total (temporary) hardness - total amount of calcium and magnesium ions (or other
metals) responsible for water hardness
•
Carbonate hardness - amount of calcium and magnesium hydrocarbons; disappears while
boiling - precipitation of insoluble sediment
Ca(HCO3)2 ∆ CaCO3 (↓) + H2O + CO2(↑)
Mg(HCO3)2 ∆ MgCO3(↓) + H2O + CO2(↑)
MgCO3 + H2O ∆ Mg(OH)2(↓) + CO2(↑)
•
Non-carbonate hardness -difference between total hardness and carbonate hardness;
determine the amount of chlorides, sulphates, nitrates and other soluble salts. Mainly
calcium and magnesium salts.
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Water hardness is given in milimols of calcium and magnesium ions in 1 dm3 of water,
1mmol = 40.08 mg Ca2+ (or 24.32 mg Mg2+) in 1 dm3 of water. It can also be expresses in so
called hardness degrees - German, French, and others.
1mmol = 5.61°n (°DH) or 10 °F,
1 German degree (1°n) = 10 mg CaO (or 7.19 mg MgO) in 1 dm3 of water,
1 French degree (1°F) = 10 mg CaCO3 in 1 dm3 of water.
According to hardness level water is divided into different categories, listed in Table 2.5.
Table 2.5. Typical Hardness Values
Hardness Values
(mmol/dm3)
0 - 0.89
0.89 – 1.87
1.78 – 2.68
2.68 – 3.57
3.57 – 5.35
>5.35
Water type
Very soft
Soft
Moderately hard
Significantly hard
Hard
Very Hard
The effect of hardness mainly consists in causing soap scum and water spots, scaling in
swamp coolers, cooling towers, boilers and pipes.
Hard waters are satisfactory for human consumption as soft waters. [11]
Acceptable water hardness is the following:
should not exceed 5 mmol/dm3 (500 mg CaCO3/dm3)
•
drinking water
-
•
surface water
I class
-
3.50 mmol/dm3 (350 mg CaCO3/dm3)
II class
-
5.50 mmol/dm3 (550 mg CaCO3/dm3)
III class
-
7.00 mmol/dm3 (700 mg CaCO3/dm3)
g. Dissolved Oxygen (DO)
Dissolved oxygen (DO) refers to the volume of oxygen present in water and it is a basic
indicator of ecosystem health. Oxygen enters the water as rooted aquatic plants and algae
undergo photosynthesis, and as oxygen is transferred across the air-water interface. The
amount of oxygen that can be held by water depends on the water temperature, salinity, and
pressure:
•
Gas solubility increases with decreasing temperature (colder water holds more oxygen)
•
Gas solubility increases with decreasing salinity (freshwater holds more oxygen than does
saltwater)
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WATER QUALITY CONTROL
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•
Gas solubility decreases as pressure decreases, thus, the amount of oxygen absorbed in
water decreases as altitude increases because of the decrease in relative pressure.
•
The partial pressure and the degree of saturation of oxygen will change with altitude.
Once absorbed, oxygen is either incorporated throughout the water body via internal currents
or is lost from the system. Oxygen losses readily occur when water temperatures rise, when
plants and animals respire, and when aerobic microorganisms decompose organic matter.
Oxygen levels are also affected by the diurnal cycle. Plants, such as rooted aquatic plants and
algae produce excess oxygen during the daylight hours when they are photosynthesizing.
During the dark hours they must use oxygen for life processes.
Flowing water is more likely to have high dissolved oxygen levels compared to stagnant
water because the water movement at the air-water interface increases the surface area
available to absorb the oxygen. In flowing water, oxygen-rich water at the surface is
constantly being replaced by water containing less oxygen as a result of turbulence. Because
stagnant water undergoes less internal mixing, the upper layer of oxygen-rich water tends to
stay at the surface.
Maximum amount of oxygen in clean water is about 9 mg/dm3. Prolonged exposure to low
dissolved oxygen levels (less than 5 to 6 mg/dm3 oxygen) may not directly kill an organism,
but will increase its susceptibility to other environmental stresses. Exposure to less than 30%
saturation (less than 2 mg/dm3 oxygen) for one to four days may kill most of the aquatic life
in a system [24].
Rules include minimum concentrations of dissolved oxygen which must be met in surface
waters. Polish regulations define that surface waters must meet a minimum dissolved oxygen
standard of:
I class
-
6 mg/dm3
II class
-
5 mg/dm3
III class
-
4 mg/dm3
Oxygen content in drinking water is not regulated [2].
h. Biochemical Oxygen Demand (BOD)
Biochemical Oxygen Demand, or BOD, is a measure of the quantity of oxygen consumed by
microorganisms during decomposition of organic matter. BOD is the most commonly used
parameter for determining the oxygen demand on the receiving water of a municipal or
industrial discharge. BOD can also be used for evaluation the efficiency of treatment
processes, and it is an indirect measure of biodegradable organic compounds in water. High
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WATER QUALITY CONTROL
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BOD is an indication of poor water quality. The lower the BOD the less organic matter is
present in water. A high BOD is often accompanied by a low DO level [25].
BOD is typically divided into two parts:
•
Carbonaceous Biochemical Oxygen Demand - is the result of the breakdown of organic
molecules such a cellulose and sugars into carbon dioxide and water (1st stage of
oxidation)
HCOH + O2 bacteria
 → CO2 + H 2 O
•
Nitrogenous Oxygen Demand - is the result of the breakdown of proteins (2nd stage of
oxidation).
NH 3 bacteria
 ,oxygen
→ NO2− → NO3−
It is estimated that it takes 20 days for biodegradation process to be completed [10].
BOD is a parameter commonly measured by determining the quantity of oxygen utilized by
suitable aquatic microorganisms during a five-day period and is then called BOD5. Though
the choice of a five-day period is somewhat arbitrary, a five-day BOD5 test remains a
respectable measure of the short-term oxygen demand exerted by a pollutant [3].
Determination of BOD5 consists in estimation of dissolved oxygen concentration before and
after five-day incubation. BOD5 is usually as much as 68 – 82% of total BOD.
Water standards for dissolved oxygen include minimum concentrations of dissolved oxygen
that must meet the following [2]:
I class
-
4 mg/dm3
II class
-
8 mg/dm3
III class
-
12 mg/dm3
i. Chemical Oxygen Demand, COD
The Chemical Oxygen Demand (COD) is the amount of oxygen, in mg/dm3, required for
degradation of the organic compounds of waste water to occur. The bigger the COD value of
waste water, the more oxygen the discharges demand from water bodies [26].
The COD test allows measurement of a waste in terms of the total quantity of oxygen required
for oxidation to carbon dioxide and water. It is based upon the fact that all organic
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WATER QUALITY CONTROL
Part II. Parameters of water.
compounds, with a few exceptions, can be oxidized by the action of strong oxidizing agents
under acid conditions. During the determination of COD, organic matter is converted to
carbon dioxide and water, regardless of the biological assimilability of the substances.
One of the chief limitations of the COD test is its inability to differentiate between
biologically oxidizable and biologically inert organic matter. In addition it does not provide
any evidence of the rate at which the biologically active material would be stabilized under
conditions that exist in nature. The major advantage of the COD test is the short time required
for evaluation. The determination can be made in about 3h rather than 5 days required for the
measurement of BOD. For this reason it is used as a substitute for the BOD test in many
instances. COD data can often be interpreted in terms of BOD values after sufficient
experience has been accumulated to establish reliable correlation factors [12]. However, the
values of COD are higher than corresponding values of BOD5, because while making BOD5
test the biodegradation process is not completed [10].
Oxidizing agent that has been found to be the most practical for determination of chemical
oxygen demand is potassium dichromate (K2Cr2O7). It is capable of oxidizing a wide variety
of organic substances almost completely to carbon dioxide and water. In order for potassium
dichromate to oxidize organic matter completely the solution must be strongly acidic and at
elevated temperature. Certain organic compounds, particularly low-molecular-weight fatty
acids, are not oxidized by dichromate unless a catalyst is present. It has been found that silver
ion acts effectively in this capacity. Aromatic hydrocarbons and pyridine are not oxidized
under any circumstances [12]. Another oxidizing agent that can be used in COD test, with
smaller oxidizing properties, is potassium permanganate (KMnO4) [10].
Presence of chloride ions Cl- greatly affects the results of COD test, as they react with both
potassium dichromate and potassium permanganate. The influence is eliminated by addition
of mercury sulphate leading to formation of dissociated compounds like (HgCl2)n or [HgCl4]
which do not take part in reaction [10].
The rules determining permissible values of COD in waters are the following [2]:
•
drinking water
•
surface water3
3
-
should not exceed 3 mg O2 /dm3
I class
-
10 mg/dm3
II class
-
20 mg/dm3
III class
-
30 mg/dm3
According to potassium permanganate (KMnO4) determination method
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WATER QUALITY CONTROL
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j. Carbon dioxide (CO2)
Carbon dioxide is present in atmosphere and all kinds of natural waters. The sources of CO2
in natural waters are atmospheric air, degradation of organic compounds, weathering and
erosion of rocks and metabolic processes of organisms [10].
Carbon dioxide concentration in water depends on temperature, content of organic
compounds and intensity of biochemical processes taking place in water environment.
Decrease in CO2 content results in increase of pH and alkalinity, which eventually leads to
decrease of solubility of some compounds (e.g. CaCO3, Mg(OH)2).
The concentration of carbon dioxide in surface and drinking water is not regulated. It does not
influence hygienic value of drinking water; however influences its taste.
k. Chlorine
Chlorine in elemental form (Cl2) does not exist in natural waters. It can only be delivered with
sewage which undergone chlorination with chlorine or chlorinated compounds.
Chlorine added to water reacts in the following way [2]:
Cl2 + H2O ∆ H+ + Cl- + HOCl
If ammonium nitrate is present in water reaction will lead to formation of chloramines
(NH2Cl, NHCl2, NCl3). Moreover, chlorine causes oxidation of iron (II) compounds,
manganese (II), nitrates (III), sulphides and sulphates (IV) and forms aliphatic and aromatic
chloro-derivatives.
Chlorine present in water is toxic for living organisms.
l. Chlorides
Chloride is generally present in all natural surface waters, from as low concentrations as
fraction of mg/dm3 to thousands of mg/dm3. Chlorides are present in natural waters due to
high solubility of salts of muriatic acid (HCl) (the only exceptions are AgCl, Hg2Cl2, CuCl)
and their common occurrence in the environment. The lowest concentrations of chlorides are
present in rain water and in mountain streams and rivers, while the highest concentration of
salts is recorded in marine waters, however high concentrations may be also found in
groundwater because of naturally high levels of chloride in soils in some areas or
contamination by road salt [10].
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WATER QUALITY CONTROL
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Generally chlorides penetrate into natural waters from soil, natural layers of salt (natural
chlorides), municipal and industrial sewage and wastes of animal origin. Chlorides are not
removed in typical sewage treatment processes and they entirely pass into surface waters
deteriorating their quality.
In case of determination of chlorides content in water it is necessary to define their origin, if
natural or pollution. In case of water pollution together with chlorides high concentration of
nitrogen compounds and increase in quantity of bacteria occurs [10].
High chlorides concentration increase corrosive properties of water. Concentration above 250
mg/dm3 is harmful to vegetation [10].
There is no evidence that ingestion of chlorides is harmful to humans. Although according to
sanitary-hygienic requirements chlorides content in drinking water should not exceed 250
mg/dm3, if natural chlorides. If chlorides are of different source water cannot be consumed.
According to polish regulations permissible concentration of chlorides in surface waters is:
I class
-
250 mg/dm3
II class
-
300 mg/dm3
III class
-
400 mg/dm3
m. Sulphur
Sulphur exists in the environment both in elemental and bonded form. However, in natural
waters sulphur is present in form of dissolved hydrogen sulphide, hydrogen sulphides HS- or
soluble and insoluble sulphides S2-. The form of compound depends on the water pH and
presence of different ions in the solution. At the pH below 6 the main form is dissolved, not
dissociated, hydrogen sulphide, whereas at pH higher than 7 hydrogen sulphides ions HSpredominates. Sulphide ions S2- occur at pH above 9 [10].
Sulphur migrates into natural waters from atmosphere, volcanic gases, industrial dusts, soil,
sewage and decomposition of organic matter of plant, animal and synthetic origin.
n. Sulphates
Sulphates (VI) commonly occur in natural waters, contrary to sulphates which are rarely
present in natural waters. They get into water due to erosion of rocks and soil, biochemical
oxidation of sulphur and its compounds, atmospheric precipitation, biochemical
decomposition of plant and animal proteins (in aerobic conditions) and from industrial
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WATER QUALITY CONTROL
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sewage. Especially high content of sulphates can be present in sewage form chemical
industry.
In surface waters concentration of sulphates usually vary between 10 – 60 mg/dm3. In ground
waters the concentration is higher and very often exceeds 100 mg/dm3 [10].
Sulphates are one of the least toxic anions and large quantities would have to be ingested in
order to health disorders to occur (especially diarrhoea type symptoms). The presence of
sulphate in drinking water can result in noticeable bitter taste.
Acceptable concentration of sulphates (VI) is the following:
•
drinking water
•
surface water
-
200 mg/dm3
I class
-
150 mg/dm3
II class
-
200 mg/dm3
III class
-
250 mg/dm3
o. Silica
Silica does not occur in elemental form in the environment. In natural waters it usually occurs
as colloidal SiO2, silica-metal compounds like Na2SiO3, Ca2SiO3, Mg2SiO3 K2SiO3 and
polynuclear silicate species, such as Si4O6(OH)62-, or silicic acid H4SiO4.
The sources of silica in natural waters are minerals, such as sodium feldspar albite
(NaAISi3O8) present due to erosion of rocks, atmospheric precipitation and industrial sewage.
Silica is present in water at normal levels of 1-30 mg/dm3. From sanitary-hygienic point of
view it is not harmful to plants and animals or humans and its content is not regulated.
p. Calcium
Of the cations found in most fresh-water systems, calcium generally has the highest
concentration. Calcium is a key element in many geochemical processes, and minerals
constitute the primary sources of calcium ion in waters. Among the primary contributing
minerals are gypsum, CaSO4 · 2H2O; anhydrite, CaSO4; dolomite, CaMg(CO3)2; and calcite
and aragonite, which are different mineral forms of CaCO3.
Calcium is present in water as a consequence of equilibrium between calcium and magnesium
carbonate minerals and CO2 dissolved in water. Water containing a high level of carbon
dioxide readily dissolves calcium from its carbonate minerals:
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WATER QUALITY CONTROL
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CaCO3 + CO2 + H2O ∆ Ca2+ + 2HCO3When the above equation is reversed and CO2 is lost from the water, calcium carbonate
deposits are formed. The concentration of CO2 in water determines the extent of dissolution of
calcium carbonate [3].
The content of calcium in drinking and surface waters in not regulated. World Health
Organization recommends concentration of calcium in drinking water for 75 – 200 mg/dm3.
q. Magnesium
Magnesium, like calcium, is a compound commonly found in natural waters, and is present as
Mg2+ ion. The main sources of magnesium ions are sewage inflows and minerals, such as
dolomite, Mg(CO3)2 which are present as a result of soil erosion:
MgCO3 + CO2 + H2O ∆ Mg2+ + 2HCO3Magnesium Mg2+ has similar properties to Ca2+ but its concentration is usually 3 to 4 times
lower than Ca2+, typically 10 mg/dm3. However, with the increase in salinity the content of
magnesium ions increases faster than of calcium and in marine water it can be 3 to 4 times
higher.
The content of magnesium in drinking and surface waters in not regulated. World Health
Organization recommends concentration of magnesium in drinking water for 50–150 mg/dm3.
r. Sodium
The main sources of sodium in natural waters are hydrolytic decomposition of magma rocks
while weathering, erosion of sedimentary rocks, as well as municipal, industrial and
agricultural sewage inflows [x]. In natural waters sodium is present in form of different salts,
mainly as sodium chloride (NaCl), rarely in form of sulphates (Na2SO4), salts of carbonic acid
(NaHCO3, Na2CO3) or nitrates (NaNO3). All salts are well soluble in water. The presence of
sodium hydrocarbons contribute to water hardness [6].
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WATER QUALITY CONTROL
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The concentration of sodium ions in natural surface waters varies between a few to 30
mg/dm3. Ground waters can contain as much as 100 mg/dm3 of sodium and marine waters
even 11000 mg/dm3 [10].
Sodium compounds are not removed in typical sewage treatment processes and they entirely
pass into surface waters [10].
Sodium in certain amounts is an indispensable element for human organism, but higher doses
can be harmful, especially for children. The content of sodium in drinking and surface waters
in not regulated. World Health Organization recommends concentration of sodium in drinking
water for 200 mg/dm3.
s. Potassium
The main sources of potassium in natural waters are hydrolytic decomposition of magma
rocks due to weathering, erosion of sedimentary rocks (mineral matter, as feldspar KAlSi3O8),
forest fire runoff and municipal, industrial and agricultural sewage [10]. In natural waters
potassium is present in form of salts, like sodium chloride (KCl), rarely in form of sulphates
(K2SO4), salts of carbonic acid (KHCO3, K2CO3) or nitrates (KNO3). All potassium salts are
very well soluble in water [6].
The concentration of potassium ions in natural surface waters is much smaller than of sodium
ones, despite the fact that both elements are present in lithosphere almost the same quantity
and solubility of potassium salts in water is better than of sodium salts [6]. It is because K+
ions are adsorbed by soil and rocks better than Na+ and because potassium is one of the macro
nutrient elements necessary for plant growth. Natural waters contain usually less than 20
mg/dm3 of potassium and marine waters about 400 mg/dm3 [10].
Potassium compounds are not removed in typical sewage treatment processes and they
entirely pass into surface water. [10].
Potassium is an essential element in human nutrition and there is no limit on the amount that
can be present in drinking water. World Health Organization recommends concentration of
potassium in drinking water for 200 mg/dm3.
t. Aluminium
Aluminium ions Al3+ are present in surface waters in rather low concentrations due to weak
solubility of aluminium in water. The sources of aluminium are industrial sewage inflow,
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WATER QUALITY CONTROL
Part II. Parameters of water.
corrosion of aluminium tanks and water treatment process (coagulation) with the use of alum
Al2(SO4)3.
Aluminium salts are harmful to humans. The source of its excessive amounts can be drinking
water, diet, aluminium dishes and foil and some of medicines.
World Health Organization recommends concentration of aluminium in drinking water for 0.2
mg/dm3, according to Polish rules it is 0.3 mg/dm3.
2.3.3. Microbiological Parameters
By far the largest health risk from water is from disease-causing (pathogenic) organisms. As
the organisms are small, they are categorised within the field of microbiological parameters.
Microbiological tests are for bacteria that are used as indicators for the presence of
waterborne organisms that could potentially cause disease. The microbiological parameters
causing the greatest risk to humans are those that come from the gut of warm blooded
animals, birds and humans. For these to enter the water, contamination from human or animal
excreta is required, and this needs to come from an infected person or animal.
Monitoring for pathogenic organisms is complex, expensive and the laboratory testing can
take days to identify the pathogens. There is an extensive range of different pathogenic
organisms including bacteria, viruses or protozoa.
Indicator organisms are used as a quick screening mechanism across the water supply system
to determine if there is any possibility of contamination to occur. The indicators used are Coli
Count, Faecal Coliforms and Total Coliforms. The presence of these indicative organisms is
evidence that the water has been polluted with faeces of humans or other warm-blooded
animals. These indicators are also used to test that the water has been effectively disinfected
at each of the entry points of the water supply into our closed pipe system.
a. Coli Count
Coli Count is the smallest volume of water, expressed in cm3, in which 1 coli bacteria is
present by agreement.
Coli _ Count =
100
Coli _ Factor
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WATER QUALITY CONTROL
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Coli Factor is equal to the most probable number of coli bacteria present in 100 cm3 of water.
b. Faecal Coliforms
Faecal Coliforms indicate the presence of pollution from animal or human faeces. Raw
sewage or untreated river water contains high levels of these bacteria. Chlorine used in the
water treatment process kill these bacteria.
Acceptable amount of these bacteria in water is the following:
•
drinking water
•
surface water
-
none
I class
-
1 and above
II class
-
0.1 and above
III class
-
0.1 and above
2.3.4. Parameters Concerning Substances Undesirable in Excessive Amount
a. Nitrates
Nitrate (NO3-) is one of the three common forms of inorganic nitrogen present in water.
Nitrate occurs in water naturally in result of plant or animal material decomposition, but can
also be introduced into water due to human activities, e.g. food production, where used as a
preservative; use of agricultural fertilizers and manure; disposal of domestic and industrial
sewage [17]. Nitrates are also present in municipal sewage after their biological treatment in
aerobic conditions [10].
Extensive application of fertilizers in agriculture can cause nitrates introduction to the
aquifers. Additionally, in rural areas, where high levels of nitric oxide emissions to the air are
observed, this gas is converted to nitrate and then introduced to water with atmospheric
precipitation.
All kinds of surface waters usually contain small amounts of nitrates, less than 1mg/dm3 [6].
Because these ions are necessary for organisms to grow, seasonal changes of nitrates
concentration is observed: in winter the concentration is generally higher than in summer
[10]. Nitrates stimulate the growth of macrophytes and phytoplankton but simultaneously they
make up for the nutrient load in water, leading to eutrophication [17].
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Some studies have shown there may be a relation between nitrates presence in water and
gastric cancer and methemoglobinemia (which in infants is often referred to as blue baby
syndrome), so a maximum guideline of 10 mg/dm3 for drinking water has been set in Poland.
In case of surface waters it must not exceed [17]:
I class
-
1.5 mg/dm3
II class
-
7 mg/dm3
III class
-
15 mg/dm3
b. Nitrites
Nitrite NO2- can be of organic or inorganic origin, and it is a transitional product in nitrogen
cycle taking place in natural waters. Nitrite is less stable than nitrate and generally due to
chemical and biochemical factors it is oxidized to nitrate or undergo reduction to ammonia in
fairly short time [2].
Nitrite is manufactured as a preservative - adding nitrate to meats and fish prevents botulism.
It may also be produced from excess ammonia in drinking water distribution systems that use
chloramines as a disinfectant.
In Poland permissible concentration of nitrates in water is not regulated. However, it is
desirable that the concentration of nitrites in drinking water do not exceed 1 mg/dm3 [2].
c. Ammonia
Ammonia in surface waters can be of organic origin, the product of decomposition of plant
and animal matter, or of inorganic origin, formed due to chemical or biochemical reduction of
nitrate and nitrite.
Ammonia is an indicator of pollution originating from soil (the excessive use of ammonia rich
fertilizers), atmosphere and sewage [2].
Ammonia NH3 is very unstable compound and easily undergoes nitrification:
NH3 + 2O2 → NO3- + H2O + H+
or
NH4+ + 2O2 → NO3- + H2O + 2H+
If buffering capacity of water is not enough to neutralize hydrogen ions made in this reaction
it may lead to a decrease in water pH [6].
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Ammonia is present in all natural waters. Ground water and clean surface waters contain
about 0.1 mg/dm3; marine water - few mg/dm3 and the concentration increases with depth.
The highest concentration of ammonia is observed in waters near crude oil beds, and can be as
high as 100 mg/dm3 [6].
Ammonia is toxic for aquatic organisms. Although it is a nutrient required for life, excess of
ammonia can accumulate in the organism and cause alteration in metabolism or increase body
pH [17].
Drinking water, according to hygienic rules, should not contain ammonia of organic origin. In
case of ammonia of inorganic origin maximum acceptable concentration is equal to [2]:
•
drinking water
•
surface water
-
0.5 mg/dm3
I class
-
1.0 mg/dm3
II class
-
3.0 mg/dm3
III class
-
6.0 mg/dm3
d. Total Organic Carbon (TOC)
Carbon enters the biosphere during photosynthesis:
CO2 + H2O → C6H12O6 + O2 + H2O
and is returned to the biosphere in cellular respiration:
O2 +H2O + C6H12O6 → CO2 +H2O + energy
The principle of determination of the Total Organic Carbon in water consists in combustion of
organic substances at elevated temperature. Combustion results in CO2 formation which is
then determined with the use of instrumental methods (usually spectrophotometric). However,
before the test is done it is necessary to remove inorganic carbon from water sample.
Inorganic compounds are carbonates, hydrocarbonates and dissolved carbon dioxide. To
remove these compounds phosphoric acid is added.
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e. Hydrogen sulphide
Hydrogen sulphide in natural waters can be of inorganic origin and occur in the dissolved
form, or of organic origin in result of anaerobic biochemical decomposition of plant and
animal proteins. Hydrogen sulphide is a weak acid and dissociated in water according to the
reaction [2]:
H2S ∆ H+ + HSHS- ∆ H+ + S2In natural waters and in sewage hydrogen sulphide can occur as dissolved gas, or as HS- and
S2- ions, depending on water pH. Non-ionised hydrogen sulphide will be present if pH below
6, while sulphite ions if pH around 10. Moreover, sulphites can exist in anaerobic conditions,
otherwise they oxidise to sulphur and sulphates [2].
The main sources of hydrogen sulphide in water include sewage and natural processes of
decomposition - sulphur-reducing bacteria are the primary producers of large quantities of
hydrogen sulphide. These bacteria chemically change natural sulphates in water to hydrogen
sulphide. Sulphur-reducing bacteria live in oxygen-deficient (anaerobic) conditions such as
deep wells, plumbing systems, water softeners and water heaters [15]. Hydrogen sulphide in
ground waters can be of geochemical origin (minerals) [10].
Water containing hydrogen sulphide usually does not pose a health risk, but it does give water
a nuisance "rotten egg" smell and taste. The minimum concentration detectable by taste in
drinking waters is 0.05 mg/dm3 [15]. Hydrogen sulphide’s presence in drinking water when
released in confined areas has been known to cause nausea, illness and, in extreme cases,
death. Water supplies with as little as 1.0 mg/dm3 hydrogen sulphide are corrosive, may
tarnish copper and silverware, and occasionally release a black material that stains laundry
and porcelain [16].
Drinking water must not contain any hydrogen sulphite, regardless of the origin, organic or
inorganic.
f. Iron
The main source of iron in natural waters is erosion of minerals from rocks and soil. It is also
introduced to water with acid mine, sewage from metallurgical, dyeing and galvanizing plants
and due to corrosion of pipelines and steal constructions [2].
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Iron is present in water as Fe(II) and Fe(III) in dissolved, colloidal or suspended form. In
presence of oxygen or oxidizing agents Fe(II) compounds easily oxidize to Fe(III) ones,
which precipitate as hydroxides or oxides. Colloids can appear if organic substances are
present in water, e.g. humic substances [2].
Iron is an essential element in human nutrition (blood formation). Large quantities of iron in
drinking water (acceptable 0.5 mg/dm3) cause turbidity, yellowish colour and an unpleasant
taste. Concentrations for surface waters are [2]:
I class
-
1.0 mg/dm3
II class
-
1.5 mg/dm3
III class
-
2.0 mg/dm3
g. Manganese
Manganese in the environment occurs in form of Mn2+ and Mn4+. The original source of
manganese compounds in natural waters is weathering of magma rocks and sedimentary
rocks. Manganese can also get into surface waters with industrial sewage, atmospheric dust
and decomposition of plant material. Concentration of manganese ions in ground waters is
generally higher than in surface waters and varies between 0.1 to 0.4 mg/dm3. This is because
of good oxidation and higher pH of surface water which leads to precipitation of insoluble
MnO2 • H2O and its further sedimentation [10].
Manganese causes water to cloud up. It is connected with precipitation of insoluble sediments.
It also causes undesirable taste of water and is conductive to bacterial growth. At levels above
0.15 mg/dm3, manganese stains plumbing fixtures and laundry [10].
Manganese is an essential component of living organisms, both plant and animal ones, as it
catalyses biochemical reactions [x]. However, in large dose it is toxic to organisms [2].
Acceptable concentration of manganese in water in Poland is set to be not higher than [2]:
•
drinking water
•
surface water
-
0.1 mg/dm3
I class
-
0.1 mg/dm3
II class
-
0.3 mg/dm3
III class
-
0.8 mg/dm3
h. Copper
Copper is widely characterised in chapter 3 “Human Impact on Water Resources”, point 3.4.
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WATER QUALITY CONTROL
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Permissible concentration of copper in drinking water Poland is 0.05 mg/dm3 or less, because
this level is below our taste threshold but contributes to minimum nutritional requirements
[6]. In case of surface waters it is [2]:
I class
-
0.01 mg/dm3
II class
-
0.1 mg/dm3
III class
-
0.2 mg/dm3
i. Phosphorus
Phosphorous occurs in natural waters as anions of orthophosphoric acid H3PO4. The anions
H2PO4- and HPO42- are predominant in normal water pH ranges. It may also be present as
organic phosphorus [3].
Phosphorous is delivered to surface waters with fertilizer runoff form agricultural human
activity, erosion of rocks (also mining), with domestic wastes due to use of detergents,
industrial wastes and as a result of decay of organic matter (plants and animals origin)[2].
Phosphorous is an algal nutrient often contributing to excessive algal growth and
eutrophication [3]. Phosphates are sometimes added to drinking water to reduce corrosion and
precipitation of certain compounds. It is not harmful in clean waters.
Acceptable concentration of phosphates in surface waters is [2]:
I class
-
0.2 mg/dm3
II class
-
0.5 mg/dm3
III class
-
1.0 mg/dm3
j. Fluoride
Fluoride is present in minerals, soils, and is naturally found in different concentrations in
natural waters [19]. It can get into waters also with industrial sewage, agricultural runoff and
due to burning of coal. It forms HF at low pH and in the presence of Ca(II), Ba(II), Sr(II) and
Pb(II) forms insoluble salts. Concentration of fluorides in surface waters is usually less than 1
mg/dm3 [10].
The presence of small quantities of fluoride in drinking water leads to a substantial reduction
of dental cavities, particularly among children (at levels around 1 mg/dm3), and is commonly
added to water for that purpose. However fluoride is harmful to bones and teeth in
concentration above approximately 10 mg/dm3 [3].
According to WHO optimum concentration of fluoride in drinking water is from 0.9 to 1.7
mg/dm3 (depending on temperature). For middle Europe this concentration varies between 0.8
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WATER QUALITY CONTROL
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to 1.5 mg/dm3 [6]. In Poland it is between 0.3 to 1.5 mg/dm3. Permissible concentrations in
surface waters should equal to:
I and II class
-
1.2 mg/dm3
III class
-
2.0 mg/dm3
k. Dissolved or emulsified hydrocarbons - mineral oils
Crude oil is a complex mixture of hydrocarbons (containing up to 90 carbon atoms in a
molecule [8]) with minor proportions of other chemicals such as compounds of sulphur,
nitrogen and oxygen. To use the different parts of the mixture they must be separated from
each other. This separation is called refining [16]. Refining is carried out in different
temperature ranges. Mineral oils are obtained from crude oil as a fraction collected between
330 and 390°C. It is a mixture of nonpolar aliphatic hydrocarbons containing 15 to 22 carbon
atoms in a molecule [8].
Mineral oils occur in natural waters mainly due to inflow of municipal and industrial sewage
(industries using or producing oils), runoff from roads and municipal areas. Also ships and
motorboats can be significant sources of water pollution with oil [8].
Crude oil and its products of refining are practically insoluble in water. However, in presence
of emulgents (e.g. surfactants) emulsions form easily [10].
Oils present in water very often flow on the water surface as a thin layer, showing pollution of
water reservoir [8].
According to polish regulations for all classes of water oils must not be visible on the surface
of water.
l. Phenols
Phenols are benzene derivatives in which hydroxide groups –OH are bounded directly to
carbon atoms in aromatic ring [10]. Some typical phenol contaminants are the following [3]:
OH
CH3
CH3
CH3
OH
OH
OH
OH
OH
OH
OH
phenol
o-cresol
m-cresol
p-cresol
l-naphtol
hydrochinon
chlorophenol
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WATER QUALITY CONTROL
Part II. Parameters of water.
Phenols in natural waters occur in trace concentration, but in case of industrial pollution the
concentration can be as high as few mg/dm3 [8]. They are formed while biochemical
decomposition of plant material and humic substances in bottom sediments. Some amounts of
phenols get into waters with sewage from coking plants, gas-works and petrochemical plants
[10].
Surface waters, contaminated with phenols, after chlorination develop disgusting taste and
odour due to formation of chlorophenols and due to oxidation of phenols to chinons, e.g. [10]:
Phenols are easily biodegradable substances unless they are in concentrations toxic for
microorganisms [8].
The most simple and common compound from the phenolic group is phenol [8]. Phenol is a
toxic substance causing denaturation of proteins [10]. It is a protoplasmic poison that damages
all kinds of cells and is alleged to have caused “an astonishing number of poisonings” since it
came into general use (on wounds and in surgery). The acute toxicological effects of phenol
are predominantly upon the central nervous system and death can occur as soon as one-half
hour after exposure. Acute poisoning by phenol can cause severe gastrointestinal
disturbances, kidney malfunction, circulatory system failure, lung oedema and convulsions.
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WATER QUALITY CONTROL
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Fatal doses of phenol can be absorbed through the skin, by respiration and alimentary canal
[3].
Polish regulations concerning drinking water define that the smell of phenols should be
undetectable.
m. Surfactants (Surface Active Agents)
The surface-active agent is the principal component of a synthetic detergent but is also
assisted in its cleaning agent role by the builders used (sometimes called built detergents). The
surface-active agents are compounds that have two groups present in the molecule: one being
hydrophobic in nature and one being hydrophilic (water-liking) in nature [8].
Surfactants are harmful for aquatic environment (fish, plankton, plants) and in higher
concentrations for humans as well. They cause formation of abundant foam which makes
oxygen diffusion difficult and inhibits self-purification of water. Surfactants in surface waters
act as emulgents facilitating formation of oil emulsions. A part of surfactants containing
phosphates or polyphosphates contribute to eutrophication.
n. Trihalomethanes (THMs)
Trihalomethanes (THMs) are a group of four chemicals that are formed when chlorine, used
to microbial contaminants control in drinking water, react with organic matter naturally
occurring in water. More detailed characteristics is included in chapter 4 “Water for Different
Purposes”, point 4.7.4.
The Environmental Protection Agency has set a Maximum Contaminant Level (MCL) of 100
µg/dm3 for TTHM (total trihalomethanes) in drinking water. The new by-products rule cut
this down to 70 µg/dm3 and will reduce this even further to 40 µg/dm3.
2.3.5. Parameters Concerning Toxic Substances
The term "toxic" refers to the ability of a physical, biological or chemical agent to provoke an
adverse effect or deleterious response in an organism. The term does not include amount or
dose of the substance required to elicit the adverse effect.
A toxic substance is a chemical pollutant that is not a naturally occurring substance in aquatic
ecosystem and above a certain level of exposure or dose has detrimental effects on tissues,
organs, or biological processes. Toxicants in water and sediments are mainly heavy metals,
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WATER QUALITY CONTROL
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persistent organic pollutants (POPs) and radioactive compounds. Waters affected by those
toxicants can have serious influence on the aquatic ecosystems and can make water unsuitable
for human consumption.
Lethal dose (LD) is the amount of a substance (in mg per kg of mass of experimental
organism) or physical agent (radiation) that causes death when taken into the body by a single
absorption [21].
LD50 is an abbreviation for “Lethal Dose 50%.” It is sometimes also referred to as the
“Median Lethal Dose”. The LD50 for a particular substance is essentially the amount (in mg
per kg of mass of experimental organism) that can be expected to cause death in half (50%) of
a group of some particular animal species, usually rats or mice, when entering the animal’s
body by a particular route [27].
The LC(t)50 (lethal concentration 50% for exposure time t) is a similar and widely used
measure for acute toxicity by inhalation. The LC(t)50 is essentially the concentration of a
substance that can be expected to cause death in half of a group of some particular species
when entering the body over the specified period of time [27].
In Poland there is a division for 5 classes of toxicology (Monitor Polski, 1965, Nr 28, poz.
156) and they are shown in Table 2.6.
Table 2.6. Division of toxicology classes
Class of toxicology
LD50 for a rat [ in mg/kg ]
I
to 50
II
51-150
III
151-500
IV
501-5000
V
Above 5000
Level of threat
Highly poisonous (toxic)
Poisonous
Very harmful substances
Harmful substances
Practically harmless
Parameter describing a toxic substance is also persistency. It is explained in chapter 3
“Human Impact on Water Resouces”, point 3.1.1.
Although both natural and synthetic chemicals may cause a variety of toxic effects at high
enough doses, the effect of most concern is cancer.
Cancer is a disease characterized by rapid growth of cells in the body, often in the form of a
tumour. Cancer is invasive - that is, it can spread to surrounding tissues. Although this disease
is a leading cause of death in many countries around the world, research has provided
considerable insight into its many causes. These may include external, environmental factors
comprising 80-90% of the causes of cancer, such as carcinogenic substances, exposure to
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WATER QUALITY CONTROL
Part II. Parameters of water.
irradiation, and, viruses and internal factors, the instances in lowering of immune functions
caused by heredity, agedness and change in lifestyle. According to a report from World
Health Organization (WHO), 35% of carcinogenic substances are derived from food and
drinks,
and
30%
are
from
smoking
as
the
second
rank
[28].
Chemicals which are known to cause cancer are called carcinogens and are divided into 5
groups, listed in Table 2.7.
Table 2.7. Division for groups of carcinogenicity.
Group of carcinogenicity
1
2A
2B
3
4
Characteristics
The agent is carcinogenic to humans; Used only when there is sufficient evidence
of carcinogenicity in humans, eg. Arsenic
The agent is probably carcinogenic to humans; Used only when there is limited
evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in
experimental animals, eg. PCBs
The agent is possibly carcinogenic to humans; Used only when there is limited
evidence of carcinogenicity in humans and insufficient evidence of carcinogenicity
in experimental animals, eg. TCDD
The agent is not classifiable as to its carcinogenicity to humans; If the evaluated
data is insufficient to allow classification into any other group, eg. Cholesterol
The agent is probably not carcinogenic to humans; An agent exhibits evidence
suggesting a lack of carcinogenicity in humans and in experimental animals, eg.
caprolactam
The strongest evidence that a compound is a carcinogenic hazard for man is epidemiological,
although most known human carcinogens are found to be carcinogenic for experimental
animals. There is no evidence that all substances which are carcinogenic for animals are also
carcinogenic for man, but it is difficult to declare any compounds as being non-carcinogenic
for man when it has been shown to be carcinogenic in animal studies.
Up to now, scientists have identified about two dozen chemicals or occupational exposures
which appear to be definitely carcinogenic to humans. In addition, there are a number of
chemicals which cause cancer in animals and are suspected of being human carcinogens. It
must be remembered, however, that as with all toxic effects, the dose or amount of exposure
is critical [29].
Heavy metals presented below (arsenic, cadmium, chromium, lead and mercury) are precisely
characterised in chapter 3 “Human Impact on Water Resources”, point 3.4. This chapter
focuses mainly on some toxic effects caused by drinking water contamination with particular
heavy metal, and permissible concentrations of metals in drinking and surface waters.
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WATER QUALITY CONTROL
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a. Arsenic
Even very low concentrations of arsenic in drinking water appear to be associated with a
higher incidence of lung or bladder cancer [3]. According to WHO arsenic content in drinking
water should not exceed 0.05 mg/dm3. Polish law sets the maximum concentration of arsenic
in drinking water also for 0.05 mg/dm3, and for surface waters:
I and II class
-
0.05 mg/dm3
II class
-
0.05 mg/dm3
III class
-
0.2 mg/dm3
b. Cadmium
In drinking water maximum acceptable concentration of cadmium is 0.005 mg/dm3.
According to polish regulations permissible concentration in surface waters is [6]:
I class
-
0.005 mg/dm3
II class
-
0.03 mg/dm3
III class
-
0.1 mg/dm3
c. Chromium
The Environmental Protection Agency (EPA) established Maximum Contaminant Level
(MCL) to 0.1 mg/dm3 as total chromium [19]. Polish regulations set the value of 0.01 mg/dm3
of chromium (VI) in drinking water. In surface waters maximum permissible concentration of
chromium (VI) is equal to 0.05 mg/dm3 in all classes of waters, and in case of chromium (III)
it is:
I class
-
0.05 mg/dm3
II class
-
0.1 mg/dm3
III class
-
0.1 mg/dm3
d. Lead
Excess quantities of lead may impact human health, especially affecting small children.
Therefore a very conservative limit has been set at 0.05 mg/dm3 of lead in drinking water
(according to WHO) [6]. In Poland the value for drinking water is exactly the same, while in
case of surface waters it is equal to 0.1 mg/dm3 in all classes of water.
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WATER QUALITY CONTROL
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e. Mercury
A very conservative guideline of 0.001 g/m3 of mercury in drinking water has been
established in Poland on the basis of health considerations. In surface waters the maximum
permissible concentration is:
I class
-
0.001 mg/dm3
II class
-
0.005 mg/dm3
III class
-
0.01 mg/dm3
f. Cyanides
Cyanide is a deadly poisonous substance which exists in water as HCN, a very weak acid
[19]. Large quantities of cyanide are used in industry, especially for metal cleaning and
electroplating. It is also one of the main gas and coke scrubber effluent pollutant form gas
works and coke ovens. Cyanide is widely used as a pesticidal fumigant and in certain metalprocessing operations. The presence of cyanide in water is indicative a serious pollution
problem [3].
According to Polish regulations permissible concentration is equal to 0.01 g/m3.
g. Selenium
Selenium naturally occurs in the earth's crust and is commonly found in sedimentary rock.
Much of the selenium in rocks is combined with sulfide minerals or with silver, copper, lead,
and nickel minerals. Selenium can exist naturally:
•
In inorganic forms at different oxidation states: -II (selenide), 0 (elemental selenium), +IV
(selenite SeO32-), +VI (selenate SeO42-);
•
In the form of organic compound and methylated derivatives; each form differing widely
in their nutritional and toxic impact.
Each form differs widely in their nutritional and toxic impact.
The anthropogenic sources of selenium include sewage and wastes disposal [6].
In soil and water selenium exists mainly in form of inorganic ions: Se (IV) and Se (VI). Total
Se levels in environmental samples range from about 0.1 - 400 µg/dm3 in natural waters to 0 80 ng/kg in soils. Selenium transits into organic linkages under biomethylation process, as a
result of microorganisms and plants activity. Well known in our environment organic species
of selenium are associated to aminoacids (e.g. selenocystamine SeCM, selenocystine SeCYS,
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WATER QUALITY CONTROL
Part II. Parameters of water.
selenomethionine SeM). The less toxic forms seem to be volatile methylated selenium
compounds (e.g. dimethylselenide DMSe, dimethyldiselenide DMDSe), which are
metabolised after detoxification processes.
In small amounts selenium is a prerequisite for humans. Sufficient selenium supplementation
can protect against heart disease. Se deficiency can cause many diseases, such as hemolysis,
multiple sclerosis and rheumatic arthritis, and is most critical for the brain and infant growth.
However, transition from required level to toxic dose is quite easy.
Detoxification effects of Se by interaction with other metals are proven and widely described;
the toxicity of Se is modified by complexation with As, Ag, Cu, Hg. In real life the toxicity of
selenium against environment and human being strongly depends on the specific form.
Maximum permissible concentration of selenium in drinking water is 0.01 mg/dm3 (WHO
regulations) and also in Poland is equal to 0.01 mg/dm3 [6]. In case of surface waters it is
equal to 0.01 mg/dm3 in all classes of water.
h. Radioactive compounds
Radioactivity is defined as spontaneous nuclear transformation of nuclide into another
nuclide, accompanied by emission of nuclear radiation, either corpuscular of electromagnetic
[9]. Radioactivity of nuclides naturally occurring in the environment is called natural activity,
while radioactivity of nuclides obtained in nuclear reactions is called artificial radioactivity.
Radioactive elements are spread in rocks, form which they pass into waters. They can also get
into waters with atmospheric precipitation and inflow of radioactive sewage.
Natural radioactivity is caused by
atmosphere – 3H and
14
90
Y,
isotopes:
Sr,
89
Sr,
90
226
Ra,
222
Ru,
238
U,
230Th 210
,
Pb,
40
K and isotopes from the
C. Acquired radioactivity caused by water pollution with radioactive
91
Y,
131
I,
132
I,
137
Cs,
141
Cs,
144
Ce,
32
P [6]. Radio-isotopes the most
commonly found in sewage are: 24Na, 32P, 40K, 60Co, 85Zn, 90Sr, 131I and 137Cs [2].
Naturally radioactive waters are divided into two groups:
•
Waters containing only radon and its emanation – these are radon-waters; most of health
waters are radon-waters;
•
Radium waters with high radium content – these are mainly deep-waters [6].
Radionuclides can be present in waters in form of dissolved ions or complexes, or insoluble
form, depending on pH, redox potential and composition of water [6].
Radionuclides present in waters are absorbed by aquatic organisms, which directly or along
the food chain enter humans [2]. The most common isotopes present in water are radon,
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WATER QUALITY CONTROL
Part II. Parameters of water.
uranium and radium. Their concentration varies between 0.1 to 50 mg/m3. Waters containing
below 10-7 g Ra in m3 are numbered among weakly radioactive, between 10-7 and 10-6 of
average radioactivity, and above 10-6 g/m3 highly radioactive.
Artificial radioactivity originating from human activities (extraction and enrichment of
uranium, exploitation of nuclear reactors) is very dangerous for humans, animals and plants.
The most toxic isotopes are: 90Sr, 90Y, 210Pb, 210Po, 226Ra, 238U. Their maximum concentration
in drinking water must no excess 10-4 µCi/cm3 [6] 4.
In order to protect people against extremely harmful radioactive radiation continuous
monitoring of the level of water and sewage radioactivity is necessary [2].
Radioactivity and radioactive pollution are also described in chapter 3 “Human Impact on
Water Resources”, point 3.8.
i. Persistent Organic Pollutants (POPs)
Persistent Organic Pollutants (POPs) are precisely described in chapter 3 “Human Impact on
Water Resources”, point 3.7. Table 2.8 contains only concise and general information on
POPs.
Table 2.8. Summary of Persistent Organic Pollutants properties.
Type of
pollutant
PAHs
PCBs
Sources in
natural
waters
Industrial
sewage; leaky
Compounds built up of
tanks with
few aromatic rings;
crude oil,
practically insoluble in
fuels; dusts
water, can form
and sooth
suspensions; pile up in
falling onto
sediments [10].
the ground
(runoff); roads
surface [10].
General
characteristics
PCBs include about
200 different
compounds, in water
environment 60 were
determined [8].
Sewage;
surface runoff;
rain [8].
Concentration in
natural waters
little polluted
waters 50 – 250
ng/dm3;
medium polluted
waters 250 – 1000
ng/dm3;
highly polluted
waters above 1000
ng/dm3
[8].
Usually between
0.01 to 10 ng/dm3
[8].
Surface runoff
Used for annihilation
from
agricultural
of pests; divided for
Between 0.001 and
Pesticides
three groups:
areas;
2.8 µg/dm3
insecticides, herbicides, municipal and
industrial
fungicides [10].
sewage [10].
Acceptable
concentration in
drinking water
Maximum
concentration of
PAHs, according
Carcinogenic;
to WHO
[8]
regulations 0.02
bioaccumulate
µg/dm3.
in aquatic
Maximum
organisms [10].
concentration of
benzo(a)pyrene
0.015 µg/dm3 [10].
Harmful to
Maximum
aquatic
environment;
concentration of
bioaccumulate pentachlorophenol
0.01 mg/dm3 [10].
in aquatic
organisms [8].
Toxic effect
Bioaccumulate
in living
organisms;
toxic for
humans [10].
Maximum
concentration of
heptachlor 0.0001
mg/dm3 [10].
4
1 Ci (CURIE) – obsolete unit of radioactivity giving 3.7•1010 disintegrations per second; in SI system 1 Ci = 37
GBq
83
WATER QUALITY CONTROL
Part II. Parameters of water.
Dioxins
By products of:
herbicide production;
municipal and hospital
wastes combustion;
[10]
Can contain between 1
and 8 chloride atoms in
a molecule; practically
insoluble in water.
Industrial
sewage
Depends on the
amount of
chlorine atoms;
Toxic dioxins
are those
containing 4,5
and 6 atoms of
chlorine; skin
irritation; liver
damage;
carcinogenic
and mutagenic
Maximum
concentration of
DDT 0.001
mg/dm3 [10].
References:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
E.L. Katz “The stability of turbidity in raw water and its relationship to chlorine demand”, Journal of
the American Water Works Association, 1986
K. Lipkowaska – Grabowska, E. Faron – Lewandowska “Pracownia chemiczna. Analiza wody i
ścieków”, Warszawa 1998
Stanley E. Manahan “Fundamentals of Environmental Chemistry”, Lewis Publishers, USA 1993
A.G.Howard “Aquatic Environmental Chemistry”, Oxford University Press, Oxford 1998
M.W. LeChevallier, T.M. Evans, R.J. Seidler “Effect of turbidity on chlorination efficiency and
bacterial persistence in drinking water. Applied and environmental microbiology”, 1981
W.F. McCoy, B.H. Olson “Relationship among turbidity, particle counts and bacteriological quality
within water distribution lines”, 1986
Department of National Health and Welfare (Canada) “Guidelines for Canadian drinking water
quality”, 1991
J.R. Dojlido „Zanieczyszczenia wód”
Dictionary of chemical terminology, edited by Dobromiła Kryt, Wydawnictwa Naukowo-Techniczne,
Warszawa 1980
[x]
[x2]
[x3]
[x6]
http://www.aldeaglobal.com.ar/agua/wqsi_taste.htm
On the basis of the following publications:
a. L.M.Bartoshuk “NaCl thresholds in man: thresholds for water taste or NaCl taste?”, Journal of
comparative physiology, 1974
b. Water Research Centre “A guide to solving water quality problems in distribution systems”,
Medmenham, 1981
c. J.M. Cohen „Taste threshold concentration of metals in drinking water”, Journal of the
American Water Works Association, 1960, 52(5):660-670
d. E.J. Thurmann “Organic geochemistry of natural waters”, Amsterdam, Netherlands, Martinus
Nijhoff 1985
e. K.M. MacKenthun, L.E.Keup “Biological problems encountered in water supplies”, Journal of
the American Water Works Association, 1970, 62(8):520-526
f. J.E. Wajon “The occurrence and control of swampy odour in the water supply of Perth,
Western Australia”, Bentley, Western Australia, School of Applied Chemistry, Western
Australia Institute of Technology, 1985
g. F.B. Whitfield, D. Freeman “Off-flavours in crustaceans caught in Australian coastal water”,
Water science and technology, 1983, 15(6/7):85-95.
h. A.C. Linden, G.J.E. Thijsse “The mechanism of microbial oxidation of petroleum
hydrocarbons”, Advances in enzymology, 1965, 27:469-546.
i. W.H. Glaze “Reaction products of ozone: a review”, Environmental health perspectives, 1986,
69:151.
84
WATER QUALITY CONTROL
Part II. Parameters of water.
j.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
C. Anselme “Removal of tastes and odours by the ozone-granular activated carbon water
treatment processes”, Paper presented at the 7th Ozone World Congress, International Ozone
Association, Tokyo, 1985
k. I.H. Suffet “Removal of tastes and odours by ozonation”, Proceedings of the American Water
Works Association Annual Conference, Seminar on Ozonation. Denver, CO, AWWA, 1986
l. R.H. Burttschell “Chlorine derivatives of phenol causing taste and odour”, Journal of the
American Water Works Association, 1959, 51(2):205-214
http://www.ianr.unl.edu/pubs/water/g1275.htm
http://ohioline.osu.edu/lines/search.html
http://www.aaawatertesting.com/nitrogen.htm#EPA
http://www.eco-usa.net/toxics/index.shtml
http://www.clwa.org/chromium.htm
http://water.nr.state.ky.us/ww/ramp/rmalk.htm
http://www.nrc.gov/reading-rm/basic-ref/glossary/lethal-dose.html
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Adsorb/adsorb.htm
http://ias.vub.ac.be/General/Adsorption.html
http://www.deq.state.mi.us/documents/deq-swq-npdes-DissolvedOxygen.pdf
http://www.deq.state.mi.us/documents/deq-swq-npdes-BiochemicalOxygenDemand.pdf
http://www.chemind.fi/english/education/index.html
http://www.ilpi.com/msds/ref/ld50.html
http://www.aboutcancer.info/Food/food.html
http://www.iet.msu.edu/Tox_for_Public/carcin.htm
85