Document(s) 10 of 19

¹International Water Management Institute (IWMI), South Asia Regional Office, Patancheru, India
²IWMI South-East Asia Regional Office, Bangkok, Thailand
³IWMI, Bierstalpad, The Netherland

Abstract

Untreated wastewater is used for irrigation in over 80% of all Pakistani communities with a population of over 10,000 inhabitants. The absence of a suitable alternative water source, wastewater’s high nutrient value, reliability, and its proximity to urban markets are the main reasons for its use. Two case studies in Pakistan studied the impact of untreated wastewater use on health, environment, and income. The results showed a high increase in hookworm infections among wastewater users and a clear over-application of nutrients through wastewater. Heavy metal accumulation in soil over a period of 30 years was minimal in Haroonabad, a small town with no industry, but showed initial signs of excess levels in soil and plant material in Faisalabad, a city with large-scale industry. The impact of wastewater irrigation on household income was considerable as wastewater farmers earned approximately US$300/annum more than farmers using freshwater. Both case studies showed the importance of wastewater irrigation on local livelihoods. The lack of financial resources at municipal and provincial levels for wastewater treatment calls for other measures to reduce the negative impact of untreated wastewater use on health and environment, for example to manage groundwater, regular (canal) irrigation water, and wastewater conjunctively, and regular deworming treatment of those exposed to wastewater.

Introduction

Pakistan has a population of over 140 million and is one of the few countries that is almost completely dependant on a single river system for all its agricultural water demands. The Indus river and its tributaries provide water to over 16 million hectares of land, situated in the mainly arid and semi-arid zones of the country. A rapidly growing population, saline groundwater, a poorly performing irrigation distribution system, and recurrent droughts have led to increased water shortages. Under these conditions, the use of untreated urban wastewater for agriculture has become a common and widespread practice.

Preliminary results from a country-wide survey in the four main provinces showed that untreated wastewater was used in 50 out of 60 visited cities. The three main reasons for the use of wastewater were the high salinity of groundwater, recent droughts that have led to a decline in groundwater tables, and the nutrient value of wastewater. Other important reasons were the proximity of urban markets and the reliability of wastewater, which unlike regular irrigation water is not subjected to a rotational schedule. In more than half of the visited cities some sort of fee was paid by farmers to either the municipality or the local wastewater utility for the use of wastewater. For example, in the city of Quetta, 212 farmers cultivating 800 ha collectively paid US$12,000/ annum for the right to use wastewater. This was 2.5 times more than the fee for regular irrigation water. Land rent in all cities reflected the importance of wastewater with the rent for land that had access to wastewater being at least double and in some cases up to six times that of land without access to wastewater. In the city of Quetta, the average annual rent for land with access to wastewater was US$940/ha, compared to US$170/ha for land irrigated by freshwater.

This chapter presents two ongoing case studies in progress since January 2000 in a small town without major industry (Haroonabad) and a large industrialised city (Faisalabad). The objective of both case studies was to study wastewater use in a holistic way, looking at environmental and health risks together with the economic benefits and costs for a household. To this end, a number of study components were implemented including a cross-sectional health survey to estimate the prevalence of intestinal nematode infections among exposed and unexposed farmers, a nutrient and water balance, an evaluation of the irrigation and nutrient application of wastewater irrigation, a soil and crop survey looking at soil and crop heavy metal concentrations and potential human food chain contamination risks, an entomological study looking at the potential of wastewater bodies to support the life cycle of disease transmitting mosquitoes, and an economic survey comparing the income of households with access to wastewater to that of households without access to wastewater. At both sites, the impacts on water quality and heavy metal uptake were studied by examining locations where untreated wastewater was used exclusively, where freshwater and wastewater were mixed, and where freshwater was used exclusively.

Background

Haroonabad

The town of Haroonabad is located on the edge of the Cholistan desert in southern Punjab province, close to the Indian border. In 1998 the population was 63,000 (Population Census Organization, 2001) and apart from the small-scale seasonal, cotton-related industrial activities such as washing and ginning (separation of seeds and fibre), there was no major industry in the town. The arid climate, with an annual average rainfall of 160 mm, potential evaporation of 2500 mm, and temperatures ranging from 0°C in January to 48°C in July, make agriculture without irrigation virtually impossible. Shortly after the construction of a sewerage system in 1965, farmers started using untreated wastewater pumped from the newly constructed disposal station for irrigation. In 1979 more pumps were installed in and around the town to dispose of blocked wastewater, after the sewerage system had collapsed because of heavy monsoon rains. This resulted in the development of more wastewater-irrigated sites. Currently there are three main sites with a total irrigated area of over 130 ha. The main crops grown with wastewater are vegetables (in particular cauliflower) cotton, and fodder.

Faisalabad

The city of Faisalabad has a population of just over 2 million and is the third largest city in Pakistan. Centrally located in the heart of the Punjab province it was founded in 1900 as an agricultural market town, but has since then rapidly developed into a major agro-based industrial centre. Over 150 different industrial units have been identified by the local Water and Sanitation Agency (WASA), most of which are involved in such cotton processing tasks as washing, bleaching, dying and weaving.

The use of wastewater for agriculture was common, a survey showed that at least nine different sites could be identified, differing in size from a few ha to almost 1,000 ha. Two main sites can be distinguished, the Narwala Road site and the Channel 4 site. Farmers at the first site used wastewater of primarily domestic origin, while farmers at the latter site used a mixture of industrial and domestic wastewater. Common crops at both sites were fodder, wheat, cotton and vegetables (cauliflower, spinach, and aubergine). The aquifer underlying the city was highly saline and could not be used as a source of irrigation or drinking water. Temperatures ranged from 48°C to – 4°C, while annual rainfall has varied between 198 mm and 615 mm over the last 40 years.

Water Quality, Crops and Cropping Intensities

Wastewater used for irrigation in Haroonabad and at both sites in Faisalabad (Table 8.1) was not fit for unrestricted irrigation according to microbiological guidelines set by the World Health Organization (WHO) Health Guidelines for the Use of Wastewater in Agriculture and Aquaculture (WHO, 1989). However, the WHO guidelines state that the guidelines can be relaxed when vegetables are eaten cooked, and in this case, the main vegetables cultivated, cauliflower, spinach and aubergine, are almost exclusively eaten cooked. The high values of electrical conductivity and total nitrogen loads of the wastewater placed medium restrictions on the use of this wastewater for agricultural production as its use could result in limited crop growth and hence yield reductions (Pescod, 1992).

During the course of the studies farmers mentioned that they were limited in their choice of crops, though some crops considered unsuitable by one farmer were grown by another. There seemed to be a consensus among farmers that such root crops as carrots, radishes, onions and potatoes were unsuitable for wastewater irrigation, because as a result of their foul smell, poor colour, and in the case of carrot and radish, the development of several short, not single straight roots, these could not be sold in the local market. The main crops grown were fodder sorghum (Sorghum bicolor), cauliflower, spinach, cotton, wheat, tomatoes and aubergine. The number of crops grown on the same land each year on wastewater-irrigated sites in Faisalabad and Haroonabad was three, compared to less than two grown in fields irrigated with freshwater.

Table 8.1. Water quality parameters of wastewater used for irrigation in Haroonabad and at the Narwala and Channel 4 sites in Faisalabad, Pakistan.

Farmers interviewed along the length of Channel 4 encompassing fully, mixed, and non-Channel 4 water users indicated that ‘excess’ application of Channel 4 water to wheat and sorghum seedlings less than 30 days after emergence resulted in severe ‘burning’ of crops and frequently resulted in expensive re-planting. Further, the long-term application of Channel 4 water has resulted in a significant breakdown in soil structure and visible indicators of soil salinity. In addition, the formation of a compact surface layer has resulted in the delayed emergence of both wheat and sorghum. Prior to reliance on Channel 4 water, the emergence time for wheat was 5–7 days. After relying on Channel 4 water for 5–16 years, emergence now takes place after 15 days.

Nutrient and Water Balance

The original research question about water and nutrient use in both Haroonabad and Faisalabad was whether wastewater was applied according to the plants’ water and nutrient requirements. At both sites, nutrients were over-applied when compared to fertiliser standards set by the Ministry of Food, Agriculture and Livestock, Federal Water Management Cell (1997). Table 8.2 shows the example of cauliflower irrigated with wastewater in Haroonabad and Faisalabad. The differences in nitrogen ratios (N applied/N recommended) between Haroonabad and Faisalabad can be explained by daily and monthly fluctuations in the quality of wastewater.

The over-application of wastewater was reflected in low irrigation performance, as over-application of wastewater led to high percolation (Ensink et al., 2002). In addition, the nitrogen ratio results for both Haroonabad and Faisalabad, indicated a significant ‘inefficient’ over-application of nitrogen (Table 8.2). This resulted in high levels of nitrates, nitrites and Escherichia coli in groundwater under the wastewater-irrigated sites. These levels of nitrates, nitrites and E. coli would be of concern if groundwater were to be used for drinking water purposes [World Health Organization (WHO) Guidelines for drinking-water quality] (WHO, 1993) but the natural salinity of this groundwater has prevented such use.

Heavy Metals

Haroonabad

The results for Haroonabad indicate that because the pH of the soils analysed ranged from 7.72–8.30, the levels of copper (Cu), nickel (Ni), lead (Pb), and chromium (Cr) are within European Economic Community (EEC) maximum permissible (MP) levels (Table 8.3). No MP levels are established for cobalt (Co) and manganese (Mn). However, a significant accumulation of Pb and Cu can be observed within the top 0–15 cm of the 100% wastewater-irrigated soil profiles (Table 8.3). In contrast, Ni, Co, Cr and Mn remained relatively uniform irrespective of depth with mean (n=6) concentrations of Ni 30.2 (±0.4), Co 12.3 (±0.5), Cr 56.3 (±9.5) and Mn 256.3 (±18.4) mg/ kg (Table 8.3).

As with the 100% wastewater-irrigated field, Pb and Cu levels were elevated at the soil surface (0–5 cm) of the conjunctively irrigated field (Table 8.3). However, the surface accumulation of Pb and Cu was restricted to 0–5 cm soil depth compared to 0–15 cm for the 100% wastewater-irrigated field. It is suggested that the elevated levels of Pb could be attributable to deposition from petrol fumes as the 100% irrigated wastewater site is located next to the central bus station. Other metal concentrations remain relatively uniform with depth with mean (n=6) concentrations of Ni 26.9 (±1.1), Co 12.4 (±0.9), Cr 46.5 (±4.6) and Mn 231.9 (±12.5) mg/kg.

Table 8.2. Total nitrogen (TN) application, nitrogen ratios and total amount of wastewater applied to cauliflower in Haroonabad and Faisalabad, Pakistan.

Table 8.3. Vertical distribution of heavy metal concentrations in soil (mg/kg) at varying soil depths in relation to type of irrigation water used at three sites in Pakistan.

^a Sampling depth in parentheses.
^b Standard deviation in parentheses and italicised.
^c The range of European Economic Community (EEC) maximum permissible (MP) levels for Pb, Cu and Ni given in Table 8.3 correspond to soil pH.
  The lower value given corresponds to a soil pH < 5.5 and the higher value a soil pH >7.0.

In contrast, both soil Pb and Cu in the Hakra 4/R (freshwater-irrigated) fields were significantly lower than in the wastewater-irrigated plots (Table 8.3). In addition, no surface accumulation of Pb or Cu was observed. In comparison to the wastewater-irrigated plots, levels of Ni, Co, Mn and Cr remained relatively uniform irrespective of soil depth.

Faisalabad

During April–May 2002 soil and wheat samples were collected from pre-selected fields at 1-km intervals along the length of Channel 4 to evaluate the impact of wastewater use on soil heavy metal accumulation. As a control, samples were also collected from fields receiving freshwater irrigation from the Dhudi Wala Minor. The results indicated that for both the Channel 4 and Dhudi Wala Minor irrigated fields, soil Cd, Pb, Zn, Ni, Cr, and Cu concentrations are all below EEC MP levels irrespective of sampling site (Table 8.4). However, elevated levels of Zn were observed at the 0.2 and 1.3 km sampling locations with values of 90.6 mg/kg at 0.2 km and 92.6 mg/kg at 1.3 km. In addition, elevated levels of Cd were observed between the 1–3 km sampling site with a mean Cd value of 0.40 ± 0.03 mg/kg compared to a mean Cd concentration of 0.14 ± 0.04 mg/kg for the 4–9 km sampling site. Lead, Cr, Ni, and Cu concentrations were relatively uniform irrespective of sampling site and irrigation source.

The wheat grain results indicate trace (<0.05 mg/kg) concentrations of Pb, Cr, and Ni in grain, which reflected the relative immobility of these elements in soils and translocation in the plant. Wheat grain Cu and Zn concentrations for both the Channel 4 and Dhudi Wala Minor irrigated fields were at concentrations indicative of optimum yields (Wells et al., 1996). The wheat grain Cd concentrations exceed the Joint FAO/WHO Expert Committee on Food Additives (JECFA) Codex Committee on Food Additives and Contaminants (CCFAC) draft provisional maximum level (ML) for Cd in wheat grain of 0.1 mg/kg (Codex Alimentarius Commission, 2002). However, Chaney et al. (1996) suggested that a Cd:Zn ratio of <1.5% effectively provides protection against Cd-induced health impacts. For the Channel 4 and Dhudi Wala Minor wheat samples, the Cd:Zn ratio ranged from 0.28–1.05%. Health risks are therefore effectively prevented at this time.

In summary, with the exception of the surface accumulation of Pb and Cu in 100% wastewater and conjunctively irrigated fields in Haroonabad (Table 8.3) heavy metal accumulation in Haroonabad was of minor concern. However, monitoring programmes should be established and the source of contamination confirmed and managed to prevent soil Cu and Pb reaching levels that may prove toxic to crop growth and soil biological functions. In Faisalabad the source of Cd contamination should be identified and managed, monitoring soil and edible portions of crops is essential to ensure protection of the food chain from elevated levels of Cd.

Health Impact

Intestinal nematodes

Preliminary results from a health survey in Faisalabad and a completed study in Haroonabad (Feenstra et al., 2000) show a similar trend (Table 8.5). Wastewater farmers had a 4 to 5 fold higher risk of hookworm infection than a group of non-wastewater users. There was no difference in risk of hookworm infection between children of wastewater farmers and children of non-wastewater irrigators.

Studies in Mexico identified Ascaris lumbricoides as the main source of intestinal nematode infections among wastewater farmers and their children (Blumenthal et al., 2001). Although A. lumbricoides eggs were found in large numbers in wastewater, the studies in Faisalabad and Haroonabad showed very low prevalence of A. lumbricoides among wastewater farmers and their children for as yet unexplained reasons.

Table 8.4. Soil and wheat grain heavy metal concentrations (mg/kg) in relation to irrigation source, Faisalabad, Pakistan.

^a Values in mg/kg ± 1 standard deviation.
^b Range of concentration given in parentheses and italicised.

Vector breeding

Vector studies in Haroonabad and Faisalabad revealed that wastewater stabilisation ponds and other wastewater bodies favoured the breeding of Anopheles and Culex mosquitoes. Within the wastewater-irrigated zones, each vector species was found to be associated with specific breeding site types and environmental characteristics. The presence of potential vectors of human diseases such as malaria, filariasis, West Nile fever, and Japanese encephalitis indicated that wastewater systems could contribute to vector-borne disease risks in addition to other associated health risks among poor human communities that depend on wastewater use for their livelihoods. However, this potential role of wastewater stabilisation ponds to serve as breeding sites for mosquito vectors of human disease has received little attention. Poorly managed wastewater treatment ponds have thick emergent vegetation and floating solid waste along their margins. The vegetation and floating waste offer ideal habitats for the breeding of mosquitoes by attracting them to oviposit and also by providing them with protection against predators. The creation of such perennial water bodies close to large urban areas in an arid environment could pose a significant health risk for communities living around such treatment schemes.

Table 8.5. Hookworm prevalence among wastewater-irrigating farmers and their children compared to a group of unexposed farmers, labourers and their children at two locations in Pakistan.

Household Income and Livelihood

In Haroonabad wastewater farmers spent more money on insecticides, labour and land rent than farmers using regular canal water. The major input cost for regular farmers was for fertiliser and although this was a substantial cost, on average the total costs for regular farmers were less then those for wastewater farmers. However, the average gross margin for a wastewater farmer, about US$173/ha (Rs 10,000/ha), was substantially higher than for a freshwater farmer using canal water, about US$43/ha (Rs 2,500/ha) because of higher cropping intensities and the ability to cultivate crops with higher market values (Fig. 8.1).

Conclusion

Untreated wastewater irrigation poses serious health risks that cannot be ignored. While the risks to consumers may not be excessive, as most vegetables grown in land irrigated with wastewater are eaten cooked, the risks to farmers practicing flood irrigation cannot be ignored. The studies in Faisalabad and Haroonabad show a 5-fold increase in the risk of hookworm infection among wastewater farmers. However many of these farmers have no other option or do not want to use other water. This was illustrated by some farmers in Faisalabad who had access to treated and untreated wastewater but opted for the untreated (black) wastewater as it was considered less saline and better for their crops.

Fig. 8.1. Total cost and gross margin ('000 Rs/ha) for a wastewater farmer and a regular canal water farmer in Haroonabad, Pakistan (Rs.58 = US$1).

In the present situation there seem to be clear gains for both farmers and municipalities. Farmers are willing to pay high water fees, which in turn are used by municipalities to finance the maintenance and operation costs of drinking water and sewerage services. However, the long-term sustainability is at risk as farmers are limited in their choice of crops and heavy metal uptake by wheat as measured in its grain is getting close to critical levels. Groundwater contamination due to extensive irrigation with wastewater has not been an issue for Faisalabad and Haroonabad because the natural saline groundwater there means they have no alternative irrigation water source, but it would be an important issue in cities and towns in the fresh groundwater regions.

Although the use of wastewater is likely to become increasingly important for Pakistan as a combined strategy for water conservation and pollution prevention, management of this resource is in the hands of local farmers and municipalities. There seems to be little awareness of the risks involved in the use of untreated wastewater among local municipalities where the opinion of many is that ‘the farmer knows best’.

It is unlikely that Pakistan will be able to treat all wastewater currently used by farmers up to WHO guideline standards. Enforcement of crop restrictions will deprive many farming families of their livelihoods and there is therefore a need to look at options other than full wastewater treatment or the enforcement of crop restrictions. The need for ways to reduce health and environmental risks while at the same time safeguarding positive impacts on household income is evident. The WHO guidelines offer such other options as partial treatment for irrigation of vegetables eaten cooked, as is predominately the case here, and the use of deworming medication, which could be appropriate for the economic and environmental situation prevailing in Pakistan. Although these strategies have not been implemented, as full wastewater treatment has always been considered the norm, deworming campaigns, with or without partial wastewater treatment, could potentially be very successful, as they have shown to be in programmes established for school children (UNICEF, 1998).

Encouraging farmers to wear footwear and other protective gear, such as gloves and long trousers, has been suggested as a possible additional measure to protect farmer health. Many farmers might consider footwear and gloves impractical and uncomfortable under field conditions, and therefore the acceptability of such an intervention needs to be investigated prior to its implementation.

References

Blumenthal, U.J., Cifuentes, E., Bennett, S., Quigley, M. and Ruiz-Palacios, G. (2001) The risk of enteric infections associated with wastewater reuse; the effect of season and degree of storage of wastewater. Transactions of the Royal Society of Tropical Medicine and Hygiene 96, 131–137.

Chaney, R.L., Ryan, J.A., Li, Y.M., Welch, R.M., Reeves, P.G., Brown, S.L. and Green, C.E. (1996) Phyto-availability and bio-availability in risk assessment for cadmium in agricultural environments. In: Sources of Cadmium in the Environment. Organization for Economic Co-operation and Development (OECD), Paris, France, pp. 49–78.

Codex Alimentarius Commission. (2002) Report of the 34^th Session of the Codex Committee on Food Additives and Contaminants, Rotterdam, The Netherlands, 11–15 March 2002.

Ensink, J.H.J., van der Hoek, W., Matsuno, Y., Munir, S. and Aslam, M.R. (2002) The use of untreated wastewater in peri-urban agriculture in Pakistan: risks and opportunities. IWMI Research Report no. 64, International Water Management Institute, Colombo, Sri Lanka, 22 pp.

Feenstra, S., Hussain, R. and van der Hoek, W. (2000) Health risks of irrigation with untreated urban wastewater in the southern Punjab, Pakistan. IWMI Pakistan Report no.107, International Water Management Institute, Lahore, Pakistan, 13 pp.

Ministry of Food, Agriculture and Livestock, Federal Water Management Cell. (1997) On-farm Water Management Field Manual, volume VI; Irrigation Agronomy. Government of Pakistan, Islamabad, Pakistan, 345 pp.

Pescod, M.D. (1992) Wastewater treatment and use in agriculture. FAO Irrigation and Drainage Paper no. 47, Food and Agriculture Organization of the United Nations, Rome, Italy, 125 pp.

Population Census Organization. (2001) 1998 Provincial Census Report of Punjab. Statistics Division, Government of Pakistan, Islamabad, Pakistan, 324 pp.

UNICEF (United Nations International Children’s Education Fund). (1998) The State of the World’s Children 1998. United Nations Children’s Education Fund, New York, USA, 131 pp.

Wells, B.R., Huey, B.A., Norman, R.J. and Helms, R.S. (1996) Grain Crops: Rice. Part I. In: Bennett, W.F. (ed.) Nutrient Deficiencies and Toxicities in Crop Plants. American Phytopathology Society Press, St. Paul, Minnesota, pp.15–19.

WHO (World Health Organization). (1989) Health guidelines for the use of wastewater in agriculture and aquaculture: Report of a WHO Scientific Group. WHO Technical Report Series 778. World Health Organization, Geneva, Switzerland, 74 pp.

WHO (World Health Organization). (1993) Guidelines for Drinking-water Quality. Volume 1: Recommendations, 2^nd edn. World Health Organization, Geneva, Switzerland, 188 pp.

Document(s) 10 of 19