Policy Interventions Should Focus on Reducing Risk

Conventional wastewater treatment might be viewed as the ultimate risk reduction measure when considering the use of wastewater in irrigation.¹⁴⁵! Establishing and enforcing water quality standards, in conjunction with a wastewater treatment program, can be effective in removing potentially harmful constituents. However, the cost of treating wastewater and enforcing water quality standards will exceed affordability in many developing countries. Recognizing this challenge, the World Health Organization (WHO) recommends shifting the policy focus from reliance on wastewater treatment and water quality standards to establishing health-based targets that might be achieved by implementing a range of risk- reducing interventions.^111,451

The WHO¹⁴⁶¹ describes three sets of health protection measures pertaining to the three groups most susceptible to health impacts of wastewater irrigation: 1) farmers and their families; 2) consumers of farm products; and 3) agricultural communities. We consider each group in turn.

Farmers and Their Families

When delivering irrigation water or working in fields irrigated with wastewater, farmers, family members, and other farm workers can be exposed to microbial pathogens, including viruses, bacteria, helminths (nematodes and tapeworms), and protozoa.¹⁴⁷¹ Wastewater also can contain endocrine-disrupting chemicals, pharmaceutically active compounds, and residuals of personal care products.^148-511 Exposure to wastewater can result in skin irritation and diseases related to pathogens in human waste products. The WHO¹⁴⁶¹ recommends the following protective measures to be considered when designing public policies and intervention strategies:

• 1. Treating wastewater
• 2. Supporting the use of personal protective equipment.
• 3. Providing access to safe drinking water and sanitation on farms
• 4. Promoting good health and hygiene practices
• 5. Providing chemotherapy and immunization
• 6. Controlling disease vectors and intermediate hosts
• 7. Reducing contact with disease vectors

One or more of these measures would be helpful in breaking or disrupting the pathway of contamination from wastewater to farm family members and farm workers. However, success will be determined by how effectively the benefits of these measures are communicated to farmers and how aggressively farm workers adopt them. The farm-level cost of any measure also will be a key determinant of its successful adoption.

Agricultural Communities

In a sense, many residents of agricultural communities are susceptible to the same types of risks as farmers and their families, particularly if they utilize water in irrigation canals or ditches or if they have access to farm fields. In many irrigated areas, community residents use water from irrigation canals or ditches for cleaning clothes, washing livestock, and watering kitchen gardens (Figure 2).¹⁵²¹ Young children often swim or play in irrigation ditches, while some residents rely on irrigation canals as a source of household drinking water.¹⁵³¹ The lack of knowledge regarding the potential health risks in many rural and periurban settings and the scarcity of fresh water supplies create situations in which many residents are at substantial risk. The WHO¹⁴⁶¹ recommends the following measures to protect members of agricultural communities:

• 1. Treating wastewater
• 2. Restricting access to irrigated fields and canals and ditches

FIGURE 2 Community members are at risk of contamination from wastewater carried in local stream, as they withdraw water for cooking, cleaning, and other purposes.

Source: Ben Keraita, IWMI, Ghana.

• 3. Providing safe recreational water, particularly for adolescents
• 4. Providing safe drinking water and sanitation facilities to communities
• 5. Promoting good health and hygiene practices
• 6. Providing chemotherapy and immunization
• 7. Controlling disease vectors and intermediate hosts
• 8. Reducing contact with disease vectors

Several of these measures are similar to those recommended to protect farm families and farm workers, given the similarity in exposure opportunities on farms and in the larger community. Many of the challenges involved in implementing the measures and encouraging sustainable adoption also would be similar.

Consumers of Farm Products

In many settings, in the absence of policy intervention, consumers might be the least informed group regarding the potential health risks due to wastewater irrigation. They might be unaware that farmers using wastewater have produced some of the fruits and vegetables for sale in local markets. They might also be unaware that some of the farm produce carries harmful pathogens and chemicals or that cooking the produce might reduce the likelihood of damage from infectious pathogens. Given these considerations, the WHO¹⁴⁶¹ recommends the following measures to reduce the risk to consumers:

• 1. Treating wastewater
• 2. Restricting the crops that are irrigated with wastewater
• 3. Promoting irrigation practices that minimize contamination of plants
• 4. Implementing withholding periods that allow pathogens to die between the last irrigation and harvest
• 5. Promoting hygienic practices at food markets and during food preparation
• 6. Promoting good health and hygiene practices
• 7. Promoting produce washing, disinfection, and cooking
• 8. Providing chemotherapy and immunization

Although enforcement will be difficult, public agencies might consider disallowing wastewater irrigation of vegetables and other crops that consumers often eat without cooking. Leafy vegetables, such as lettuce and spinach, are particularly prone to accumulating pathogens on edible portions of the plant when wastewater is applied directly over the plants and when irrigators splash contaminated soil particles on the leaves (Figure 3).¹⁵⁴¹ Modifying the spouts of watering cans will reduce contamination by reducing the splashing of soil particles (Figure 4).^I541 Drip irrigation on the soil surface or below ground will minimize contamination,¹⁵⁵¹ but many poor farmers will not have the funds to invest in such systems (Figure 5).

Withholding periods between the date of last irrigation and harvest are sensible approaches as well, but monitoring and enforcement might be problematic in areas where wastewater irrigation is prevalent. Some farmers report that irrigating lettuce on the morning of the day of harvest freshens the crop and enhances its appearance in local markets.¹⁵⁴¹ Encouraging farmers to change such practices will be challenging, particularly given the perishable nature of leafy vegetable crops. Farmers generally want to obtain the highest price possible and to sell their produce quickly, before its appearance and quality begin to fade.

Public efforts to improve hygienic practices and food preparation at homes and in the marketplace also will be challenging. In areas where small-scale farmers sell produce to small-scale vendors who resell the produce in a restaurant or fast-food outlet, individuals have little incentive to assume the extra cost of enhanced food treatment. This situation in which information is limited and asymmetric can be described also an externality involving producers and consumers. The benefits of a cleaner, safer food

FIGURE 3 Leafy vegetables are susceptible to contamination by pathogens in wastewater used for irrigation, particularly when watered with sprinklers or cans, as in this photograph from Ghana.

Source: Ben Keraita, IWMI.

FIGURE 4 Using a watering can spout with many small holes reduces the splashing of soil particles onto leaves of lettuce and other leafy vegetables.

Source: Ben Keraita, IWMI.

FIGURE 5 Drip irrigation minimizes contact of irrigation water with plant foliage, thus reducing the risk of contamination by pathogens in wastewater.

Source: Frank Rijsberman, IWMI.

supply accrue to consumers and communities, rather than to the farmers and food shop owners who will incur higher costs if they implement improved production, washing, and handling practices. Public policy is needed to ensure that farmers and vendors internalize the external costs of their activities.