Hazardous effects of sewage water on the environment
Focus on heavy metals and chemical composition of soil
and vegetables
The Authors
Masood Sadiq Butt, Institute of Food Science and Technology, University of
Agriculture, Faisalabad, Pakistan
Kamran Sharif, Institute of Food Science and Technology, University of Agriculture,
Faisalabad, Pakistan
Babar Ehsan Bajwa, Institute of Food Science and Technology, University of
Agriculture, Faisalabad, Pakistan
Abdul Aziz, Fruits and Vegetables Section, Ayub Agriculture Research Institute,
Faisalabad, Pakistan
Abstract
Purpose – Pakistan is an agricultural country having the world's largest canal irrigation
system. Indus basin that covers 70 percent of irrigated area for crop production is the
major source of water in the country. Owing to rapid increase in population and uncertain
environmental conditions, this water is not adequate to cope with the crop water
requirement and needs additional means to provide extra water for agricultural purposes.
The main source of irrigation is canal and ground water but the quality of ground water is
so poor for the sustainability of agriculture system. To cope with the present demand, use
of municipal sewage water that consists of domestic liquid waste, as well as industrial
effluents, is becoming a common practice. The present study aims to reflect the
hazardous effects of sewage water on the environment, with the main focus on heavy
metals and chemical composition of soil and vegetables.
Design/methodology/approach – Industrial effluent was collected from one ghee mill,
one flour mill, three textile industries and three hosieries located in Faisalabad, an
industrial city of Pakistan highly affected with water pollution. All water samples were
analyzed for pH, EC, SAR and RSC. Water analysis was also carried out for various
nutrients and heavy metals (K+1, P2+, Fe2+, Cu2+, Zn2+, Mn2+, Ni2+ and Pb2+). Soil samples
from various depths (0-15, 15-30, 30-60, 60-90 and 90-120 cm) were taken to analyze
for EC, pH, SAR, Na+1, SO4, K+1, P2+, Fe2+, Cu2+, Zn2+, Mn2+, Ni2+ and Pb2+ after
irrigation with canal water and sewage water. Cadmium, lead and copper concentration
was determined in various vegetables grown in areas irrigated with canal water and
industrial effluents to determine their final concentration in the final product ultimately
affecting the human health.
Findings – Although the sewage water is a source of many nutrients, it also includes a
significant amount of heavy metals like Fe2+, Cu2+, Zn2+, Mn2+, Ni2+, Pb2+ and pathogens.
Extensive use of this effluent for irrigation purpose has resulted in an upsurge of such
metals in soils and various crops, which ultimately resulted in clinical problems in human
beings.
Originality/value – The present study reflects the composition of sewage water and
heavy metal accumulation in soil, as well as crops. It further highlights the different
potential hazards to humans due to these contaminants.
Article Type:
Research paper
Keyword(s):
Metals; Water; Pollution; Pakistan; Trade effluents.
Journal:
Management of Environmental Quality: An International Journal
Volume:
16
Number:
4
Year:
2005
pp:
338-346
Copyright
Emerald Group Publishing Limited
ISSN:
1477-7835
Introduction
Environmental pollution is a worldwide problem. Today, the attention of the whole world
is mainly focused on the problems which result in undesirable changes in the physical,
chemical and biological characteristics of air, water and soil, ultimately affecting human
life and the lives of animals and plants (Misra and Dinesh, 1991). An important segment
of environmental pollution that is directly affecting the health via crops and soil is due to
the indiscriminate use of untreated sewage water. In Pakistan, the pre-disposable
treatment of sewage effluent is not practicable. Sewage is the spent water of a
community, its liquid portion becoming a carrier for the transport of waste in sewers.
This sewage comprises a complex mixture of organic and inorganic matter. It also
contains macro- and micro-organisms and is an excellent vehicle for their dissemination.
Thus it serves as an efficient carrier of human pathogen along with heavy metals that are
hazardous to the environment and human health. There are two basic disposal systems of
sewage in Pakistan. One is its direct application on vegetables and crops, while the other
is disposed of in nearby rivers or lakes.
Pakistan is an agro based country. The agriculture is predominantly dependent on a canal
irrigation network but it is not providing sufficient water to meet the crop water
requirement. To augment the inadequate water supplies of good quality canal water, poor
quality ground water is being used. This causes serious problems of salinity, sodicity and
ultimately reduction in agriculture production (Arif, 1994). In many areas of the country,
the use of alternative sources of water for irrigation is a pressing need. In Pakistan,
unfortunately, most of the industries have given no attention to the control and
management of the industrial waste water, due to lack of proper guidance. So farmers are
using this untreated waste water as such because of expensive water treatment. Most of
the farmers are willing to use this nutrient rich water without treatment.
Although the sewage effluent is considered to be a source of organic matter and plant
nutrients and serves as good fertilizer, it also contains considerable amount of potentially
harmful substances including soluble salts and heavy metals like Fe2+, Cu2+, Zn2+, Mn2+,
Ni2+, Pb2+. Additions of these heavy metals are undesirable (O'Riordan et al., 1983). The
use of sewage effluent as fertilizer has gained much importance in Pakistan. Effluent
users are mainly interested in its visual benefits, like increased agriculture production,
low cost water source, effective way of effluent disposal, source of nutrients, organic
matter and so many others. But they are not well aware of its harmful effects like heavy
metal contamination of soils, crops and quality problems related to health, etc. Studies
have shown that long term use of this sewage effluent for irrigation contaminates the soil
and crops to such an extent that it becomes toxic to plants and causes deterioration of soil
(Quinn and Syers, 1978; Hemkes, et al., 1980).
The heavy metals accumulate in the various food parts of the crop which leads to various
clinical problems in animals and human beings all over the world. Some general toxic
effects of heavy metals are hepatic damaging, renal system damaging, mental retardation,
CNS breakdown, diarrhoea, hookworm infection and degeneration of basal ganglia of
brain and liver (Misra and Dinesh, 1991). Heavy metals in the nutrient cycle have
seriously threatened health and environmental integrity, so this problem of contamination
should be taken up immediately on war footings. Different studies have been carried out
in Pakistan to research the existing situation. The present study is also one of the attempts
to explore the alarming scenario with data collected by different researchers. The main
objective of this paper is to present the composition of sewage water, along with its effect
on soil and crops, where such water is being used. It further focuses on the health risks of
irrigation with the untreated urban waste water due to microbiological contamination.
Materials and methods
Study area
Industrial effluent was collected from one ghee mill (Kashmir); one flour mill (Walayat
Flour Mill); three textile industries (Sattar Dying, Nishat Textile, Chenab Fabrics) and
three hosieries (Kashmir, Abid, Noor) located in Faisalabad, a highly affected industrial
city of Pakistan with water pollution (Figures 1 and 2).
Chemical, nutrient and heavy metals analysis in sewage and industrial effluents
All water samples were analyzed for pH, EC, SAR and RSC. Water analysis was also
carried out for various nutrients and heavy metals (K+1, P2+, Fe2+, Cu2+, Zn2+, Mn2+, Ni2+
and Pb2+).
Chemical, nutrient and heavy metals analysis of soil irrigated with canal water and
industrial effluents
Soil samples from various depths (0-15, 15-30, 30-60, 60-90 and 90-120 cm) were taken
to analyze for EC, pH, SAR, Na+1, SO4, K+1, P2+, Fe2+, Cu2+, Zn2+, Mn2+, Ni2+ and Pb2+
after irrigation with canal water and sewage water.
Heavy metal contamination of vegetables grown with canal and sewage water
For this purpose heavy metals (cadmium, lead and copper) concentration was determined
in various vegetables (tinda, potato, spinach, turnip, tomato and coriander) grown in areas
irrigated with canal water and industrial effluents to determine their final concentration in
the final product ultimately affecting human health.
Results and discussions
Chemical analysis of sewage and industrial effluents
Chemical analysis of sewage water and some industrial effluents is shown in Table I. The
minimum of 2.81 and maximum of 10.0 EC was observed in the water of Walayat Flour
Mills and Kashmir+Abid+Noor Hosieries respectively. The EC of most of the mills'
effluents was highly problematic. About pH, most of the sewage water was within the
permissible limits except Kashmir Ghee Mill, i.e. 11.22 and Abid+Noor+Kashmir
Hosieries (9.24), as 7-9 is considered fit for irrigation. The minimum SAR of 5.93 and
maximum of 32.54 were observed in effluents of Walayat Flour Mills and Kashmir Ghee
Mills respectively. Similarly, RSC of all sewage effluents was problematic and was not
within the safe limits. As water having RSC<2.5 is good, 2.5-5.0 marginal and more than
5.0 is hazardous for irrigation.
Nutrients and heavy metals in sewage and industrial effluents
Nutrients and heavy metal analysis of sewage and industrial effluents (Table II) revealed
that phosphorous and potassium of different industrial effluents was high enough for
growing crops. Cu and Ni were within the permissible limits, while Pb was above the
safe limits in the effluents of Kashmir Ghee Mills and Chenab Fabrics. The iron in the
effluent Pak Foods, Flour Mills and Kashmir Ghee Mill was within the safe limits. The
manganese of all industrial effluents was also safe for use. Zinc in the effluents of Abid
and Noor Hosieries was within the safe limits while it was beyond this limit in the case of
Kashmir Ghee Mills (1.08 ppm).
Effect of sewage effluents on chemical composition of soil
Chemical analysis of heavy metals in soil irrigated with canal water (Table III) shows the
effect of sewage effluents on chemical characteristics of soil (field of cauliflower).
Maximum and minimum EC of 2.41 and 1.94 at 0-15 and 60-90 cm depths was
observed, which is quite higher from canal irrigated soil. It was observed that EC
decreases with depth. There was no significant change in pH with effluent use. The SAR
increased with depth with maximum 8.5 at 60-90 cm and minimum 6.58 at 0-15 cm.
Tables IV and V, reflect comparison between effluent irrigated field and canal
commanded field, there was a significant effect of sewage water and industrial effluents
on soil chemical characteristics, as well as nutrient and heavy metal distribution.
Effect of sewage effluents on nutrients and heavy metals in soil
The distribution of nutrients and heavy metals in canal water irrigated soil and nutrient
and heavy metal distribution in effluent irrigated soil (field of cauliflower) is shown in
Tables V and VI. Results showed that the micronutrients, i.e. Cu, Fe, Mn and Zn were
maximum at 0-15 cm depth while their concentrations were low in the lower depths.
Heavy metals were also high at the top. The concentration of micronutrients and heavy
metals in the sewage-irrigated field was much higher than the canal-irrigated field. It
indicates that sewage water has a clear effect on distribution of heavy metals and
nutrients in the soil throughout the 0-120 cm depth a similar trend was observed in the
case of macronutrients.
Heavy metal contamination in vegetables grown on sewage and canal water
Land application of sewage water is one of the disposal methods of waste products during
recycling the elements contained in the sludge. However, one problem with this approach
is the possible contamination of the human food chain with toxic substances such as
heavy metals, when food crops are grown on sewage treated soils. The influence of
sewage and canal waters on heavy metal contamination of vegetables in Peshawar (Atta
et al., 1997). Heavy metal contents of different vegetables grown with canal and sewage
water (Table VII) showed that the highest concentration of Pb (14.25 and 10.52 μg/g)
was found in spinach and coriander respectively. The maximum amount of Cu
(34.3 μg/g) was found in tinda and the minimum amount (2.65 μg/g) for turnip,
cadmium varied from 0.29 to 2.95 μg/g in these vegetables. Canal irrigated spinach
contained the highest level of Pb (9.72 μg/g) and Cu (10.75 μg/g), while the other
vegetables had varying levels. It was also found that leafy vegetables grown in sewage
water absorbed highest concentration of heavy metals as compared to canal water. Lead
is generally known to persist on materials even at large distances from the road as a
consequence of the transport of aerosol matter, whereas cadmium pollution is an
environmental concern only for leafy crops in close proximity to the edge of the road.
Over the last several years, increasing amounts of sewage sludge and other waste has
been applied to agricultural fields to provide plant nutrients for food crops. From these
results, it is concluded that due to high content of heavy metals and other toxic elements
and organics, untreated sewage water never be used for irrigation purpose.
Water pollution and humans
Water is polluted when it contain materials that make it unsuitable for a given use. The
current situation of Pakistan about irrigation with waste water is quite horrible. Cities
including Lahore, Karachi, and Faisalabad continue to be the major culprits in polluting
water. In Pakistan, like many developing countries, drinking water supply lines and open
sewage drains in the streets are laid side by side. As a result, water is frequently
contaminated when pipes erode. Municipal sewage is a major source of pollution.
Unfortunately, in many urban areas of Pakistan, proper sewage systems are not available.
Domestic waste water collects on the street and in low-lying areas. The situation is
further aggravated by the addition of untreated wastes from small-scale industries. This
contamination includes everything from lead, cyanides, mercury, solvents, hydrocarbon
compounds, hospital and pharmaceutical industry waste.
Health risks
The long-term effect on human health of pesticides and other pollutants include colon
and bladder cancer, birth defects, and deformation of bones. In Pakistan, like many other
developing countries, waste water is used without any treatment, as treatment plants are
expensive and farmers are willing to use this nutrient rich water without treatment.
Knowledge about the costs and benefits of treatment in developing countries is limited, as
is knowledge about the actual environmental and health risks of irrigation with untreated
urban waste water. Therefore, the International Water Management Institute started a
study on benefits and costs of irrigation with urban waste water in Pakistan. This survey
was the part of that study which was conducted around Haroonabad (Feenstra et al.,
2000). The waste water used around Haroonabad contained far more faecal coliform
bacteria and helminthes eggs than advised by WHO (Table VIII). These pose a high
health risk to farmers, their families and crop consumers. The health status of this
community was compared with a farmer community in two peri-urban villages near the
same town that used other water sources for irrigation. In the farmer community exposed
to waste water near Haroonabad, the prevalence of diarrhoea diseases and hookworm
infection was very high. The prevalence of these diseases was especially high among
male farm workers. This group was highly exposed to waste water, as they did a lot of
work in the fields manually and barefooted. In their children, the prevalence of diarrhoea
diseases and hookworm infection was also higher than the control population (Table IX).
For crop consumers, the chance to acquire a hookworm infection seemed slightly
increased.
Conclusions
Over the last several years, increasing amounts of sewage sludge and other waste have
been applied to agricultural fields to provide plant nutrients for food crops, especially
vegetables grown in sewage water in soils located nearby cities. These absorbed the
highest concentrations of heavy metals as compared to canal water. Among the heavy
metals, lead is generally known to persist on materials even at large distances from the
road as a consequence of the transport of aerosol matter, whereas cadmium pollution is
an environmental concern only for leafy crops in close proximity to the edge of the road.
Due to the high content of heavy metals and other toxic elements and organics, untreated
sewage water should not be used for irrigation purposes.