Plumbosolvency: Technical Fact Sheet
Introduction
The Ministry of Health’s Priority 2 Chemical Determinands Identification Programme
(P2 Programme) has established that some/several heavy metals are found at low
concentrations (low microgrammes/litre) in drinking waters throughout New Zealand.
Lead is most frequently found at concentrations exceeding 50% of its (maximum
acceptable value) MAV, but nickel, copper, cadmium and antimony are also found.
Traces of metals, in particular lead, are of concern because over time they pose a
potential health risk, especially if consumed from childhood. Research carried out by
the Institute of Environmental Science and Research for the Ministry has shown some
New Zealand supplies contain minute traces of lead that are near to or exceed the
maximum acceptable level specified in the Drinking-water Standards.
It is important to note that the lead is not coming from the water supplies themselves,
but primarily from metals in some household fittings that may be dissolved and
absorbed by the water. The amount of lead that will dissolve from a fitting depends
on how plumbosolvent the water is; the temperature of the water; the composition of
the plumbing fittings and how long the water has been in contact with it.
The fact that most New Zealand waters are of very good quality and contain little
dissolved substances such as calcium and magnesium salts contributes to their
plumbosolvency, which is widespread in New Zealand. The Ministry of Health
therefore recommends that people do not drink the first mugful of water if their tap
has not been used for several hours; overnight for instance. Instead, people should run
the tap for a second or so, which will quickly flush-away any water that has become
contaminated with lead or any other metals from the plumbing fittings. The Ministry
will work closely with the plumbing industry in New Zealand in developing quality
standards for plumbing fittings.
Drinking water contributes little to the average daily intake of the heavy metals noted
above, except lead. The WHO (World Health Organization) estimates that drinking
water contributes to approximately half the average daily intake of lead. This may be
an over estimate for New Zealanders, because it will have been influenced by data
from North America and Europe, where lead pipes are common.
Health effects of heavy metals
The presence of heavy metals in drinking water is a potential health concern. The
following notes briefly explain the health effects associated with heavy metals that
may be present and ingested via New Zealand’s drinking waters.
Antimony:
Little information is available about the toxicity of this metal when ingested orally.
One compound of the metal, antimony trioxide, is classified by the IARC
(International Agency for Research on Cancer) as a possible human carcinogen, based
on animal inhalation studies. However, there is no evidence to support the
carcinogenicity of antimony’s compounds by the oral route.
Cadmium:
IARC has classified cadmium and its compounds as probable human carcinogens,
based on inhalation studies. There is no evidence of carcinogenicity by the oral route.
The kidney is the main target of cadmium toxicity.
Copper:
Copper is an essential nutrient, but ingesting concentrations that exceed a few mg/L
can have gastrointestinal effects (e.g. vomiting). The long-term effects of copper on
sensitive populations, such as those with disorders that do not allow their bodies to
control its copper levels, are uncertain.
Lead:
Lead is a general toxin that accumulates in the skeleton. IARC classifies it and its
inorganic compounds as possible human carcinogens, but lead also has other toxic
effects. These include interference in metabolic activities, and toxicity to both the
central and peripheral nervous systems, causing neurological and behavioural effects.
There is some evidence that exposure to lead depresses the intellectual capacity of
children.
Nickel:
IARC has classified inhaled nickel compounds as human carcinogens. There is no
evidence of carcinogenicity from oral intake, although it may cause reproductive
effects, e.g., perinatal deaths, in animals.
Like the MAVs for almost all health-significant chemical determinands listed in the
Drinking-water Standards for New Zealand (DWSNZ), the MAVs for heavy metals
are calculated assuming chronic (i.e. long-term – 70 years) exposure to the metals.
Short exposures to concentrations greater than the MAV will not compromise health.
An adult’s bodyweight is used to calculate the MAVs for all of the metals listed,
except lead. Infants, children up to six years of age, and pregnant women are the
most susceptible to the adverse health effects of lead, and consequently its MAV is
calculated using an infant’s bodyweight.
Although the health effects of heavy metals are the primary concern of the DWSNZ,
waters that are highly plumbosolvent also exact an economic toll on the community.
These waters may cause failures in reticulation networks, and domestic or industrial
plumbing systems because of their continual dissolution of materials with which they
are in contact.
Sources of heavy metals in New Zealand’s drinking waters
Data on heavy metals, gathered by the P2 Programme show that, with one or two
exceptions, detectable levels of heavy metals are not found in the source waters of
New Zealand’s drinking-water supplies. Where heavy metals have been found in
source waters, their concentrations are very low and they are probably linked to
natural sources.
Early data from the P2 programme were consistent with the heavy metals in New
Zealand’s drinking waters arising from the dissolution of consumers’ plumbing
systems. This was confirmed by a 1998 study of 154 dwellings in three cities, which
showed that in almost all cases, taps, or fittings close to taps, were the source of these
metals. This finding shows that the source of lead in New Zealand’s drinking waters
is different from the sources in North America and Europe. In the northern
hemisphere, old lead pipe is still present in many reticulation systems, and this is a
major contributor to the metal found in water supplies. All known lengths of lead
pipe in New Zealand’s water systems have now been replaced.
The brass from which taps are made is the source of some of the heavy metals. Lead
is added to some brass alloys to make them more easily machined. Tap components
are made from a range of alloys with differing lead content. In New Zealand, some
brass components used in the manufacture of plumbing fittings have contained up to
4% lead, in the past. In the United States, brass with a lead content of up to 8% is
permitted. The levels of lead leached from brass rise as the lead content increases.
Nickel is the heavy metal that appears at an elevated concentration most frequently
after lead in drinking waters. Some brass alloys may contain traces of nickel, but the
major source is likely to be the nickel- or chromium- plated surfaces of the tap.
Cadmium can be present as a trace impurity in zinc. As the two main components of
brass are copper and zinc, small amounts cadmium may be released from brass. The
source of antimony detected in drinking waters is presently unclear.
Some of the copper that is present in water drawn from a tap will arise from
dissolution of the brass, but unlike the other metals, there is another major source of
copper in (cold water) plumbing systems – copper pipes.
Factors influencing the concentrations of heavy metals in drinking waters
The chemistry that controls the dissolution of metals by water is complex. The
dissolution of different metals by a particular water component may be influenced by
the concentrations of the other water components. In general, waters with low pH and
low alkalinity will cause greater dissolution of metals than waters with higher pH and
alkalinity.
Plumbosolvent waters are often soft (they contain low levels of calcium and
magnesium). Their plumbosolvency arises not as a direct consequence of their low
calcium and magnesium concentrations, but because they are also usually of low
alkalinity. Plumbosolvency does not imply poor water quality. These waters may be
of high chemical quality until they come in contact with metals. It is only the
presence of the metals that adversely affects their quality.
The raw waters of New Zealand’s drinking water supplies are often soft, with low
levels of alkalinity and pH. They are therefore predisposed to being plumbosolvent
unless they are treated to increase the pH and alkalinity levels, or dosed with a
corrosion inhibitor.
The Langelier Saturation Index (LSI), which indicates the tendency for a water to
precipitate calcium carbonate, is often used to assess whether a water will dissolve
metals. The ability of a water to precipitate calcium carbonate is not directly linked to
its ability to dissolve metals. As a result, care should be taken in using the LSI as a
guide to the plumbosolvency of a water.
In addition to a water’s chemistry, several other factors affect the levels of heavy
metals in drinking water:

length of time the metal is exposed to the water;

water temperature;

water flow rate;

composition of the metal where alloys are in contact with the water; and

surface area of the metal exposed to the water.
Minimising exposure to heavy metals
There are three options that will reduce the consumers’ exposure to heavy metals
through drinking water.
i)
Establishment of standards for the composition of materials that may be used
in the manufacture of plumbing fittings.
ii)
Adjustment of the chemistry of the reticulated water to minimise its
plumbosolvency.
iii)
Encouragement of consumers to flush a small volume of water from the tap
before drawing water for drinking, cooking or oral hygiene.
Each of these options has its advantages and disadvantages. The use of all three, not
necessarily simultaneously, is the optimum approach to lowering exposure to heavy
metals in drinking water.
The first two options have the advantage of minimising the release of metals into the
water in the first place. This reduces the levels of heavy metals entering the
environment (through waste water disposal) and reducing the likelihood of material
failure, as well as protecting public health.
The first option takes time to implement. Consumers installing new fittings will gain
protection from heavy metals, but a fraction of the population will not receive this
protection for some period because of the time it will take for older fittings to be
replaced.
Option two could be implemented more rapidly than the first option, but would
require additional treatment expense in terms of both treatment chemicals and
treatment control systems. Furthermore, because of the complex chemistry affecting
metal dissolution, adjustment of the water chemistry to protect consumers from one
type of metal may not provide the same degree of protection for another metal.
The implementation of the first two options should be the long-term goal for
addressing the problem of heavy metals in water. Until such time as they can be set in
motion, a cheaper, more easily implemented approach is required – this is provided by
the third option.
If water has stood in a tap for a period of time, e.g., overnight, the concentration of a
metal in that water may be in excess of its MAV. Provided there is no source of the
metal in the pipes to which the tap is connected, very little of the metal is likely to be
present in the water in the pipe. Safe water can be obtained by emptying the tap of its
water, together with a little extra water to be certain the metals have been flushed
away, before drawing water for use. The volume of water required to do this is not
large – the internal volumes of most taps are less than 100ml. The DWSNZ
recommend a flush of 500 ml to provide a margin of safety.
This volume is small compared with the total estimated usage of water per person per
day of 200–250 L. Moreover, if water wastage is a concern, the water can be
collected and used for purposes that are unaffected by the presence of metals.
Option three will provide adequate protection against the ingestion of metals derived
from taps and fittings close to them. There are some circumstances when flushing
may provide only limited protection.
a) Rainwater supplies
In these supplies, flushing cannot reduce exposure to metals derived from the
dissolution of metals from the roof or guttering. Metals from these sources are
introduced into all the water, including the water in the pipes. Flushing the
taps therefore only draws more water containing the metals. It is necessary to
take care in the selection of roofing materials and to ensure their satisfactory
maintenance to limit exposure to metals from these sources.
b) Protection against copper from copper pipes
Where there are copper pipes, plumbosolvent water that has stood in the pipes
for an extended period may contain high copper concentrations. Flushing
500ml of water in these circumstances will only result in more water that has
been standing in the pipes being drawn for use. Continued flushing will
eventually ensure that uncontaminated water is drawn into the pipes, but a
large volume of water may be required to do this.
Situations where the copper concentration in water exceeds its MAV do not
occur as frequently as for lead and nickel. This is because of copper’s much
lower toxicity, and its consequently higher MAV – copper has a MAV of
2 mg/L, while the MAVs for lead and nickel are 0.01 and 0.02 mg/L,
respectively.
Assessment of plumbosolvency
The plumbosolvency of a water is determined by measuring the concentration of lead
in the first sample of water collected from a brass fitting (i.e. without flushing), and
comparing this result with the concentration of lead in a water sample obtained from
the fitting after a large volume of water has been flushed through it. Lead is used in
the assessment because it is the most frequently occurring heavy metals in drinking
waters.
The first sample contains lead released from the tap and any lead initially contained in
the water supplied to the sampling point. After flushing, the lead in the second
sample taken will contain only lead in the water supplied to the sampling point. The
contribution of lead from the tap, due to plumbosolvency, can therefore be determined
from the difference in concentration between the two samples.
The water is classed as plumbosolvent if the concentration of lead due to dissolution
of material from the tap is greater than 50% of lead’s MAV. A standardised approach
to making this assessment is described in detail in the Ministry of Health’s Guidelines
for Drinking-water Quality Management for New Zealand.
Since New Zealand’s raw waters tend to be plumbosolvent, the DWSNZ assume all
supplies contain plumbosolvent water until the water supplier has shown the water not
to be plumbosolvent.