Editorial: Wastewater use – food safety and health aspects

Abstract

This supplement presents information on food safety and health aspects of wastewater use in agriculture and aquaculture in selected developing countries in Asia and Africa. Wastewater use in agriculture and aquaculture is increasing world-wide as a result of growing water scarcity and its ready availability. In many developing countries, wastewater is discharged untreated and urban and periurban farmers use wastewater directly from sewage drains or indirectly through wastewater-polluted irrigation water. The use of wastewater for food production provides jobs and income for the farmers and in some urban areas is an important food source for the urban populations. At the same time wastewater use systems reduce organic and inorganic nutrient levels in the wastewater as such nutrients fertilize the growth of plants, fish and other produce. The production systems thereby act as natural ‘low-cost wastewater treatment’ systems. Wastewater use areas are often also important in preventing floods and also represent green ‘spaces’ and recreational areas. However, the use of wastewater for agricultural purposes can also pose a significant occupational and public health risk. The major groups at risks include consumers of wastewater irrigated produce, farm workers and their families and nearby communities. Risks may be infectious or non-infectious, e.g. consumption of produce with accumulated toxic elements. Recently the World Health Organization (WHO) published revised guidelines for the safe use of wastewater, excreta and greywater (http:// www.who.int/water_sanitation_health/wastewater/ gsuww/en/index.html). The aim of these guidelines is to maximize public health protection and the beneficial use of important resources and it is stressed that the guidelines should be adapted considering national, sociocultural, economic and environmental factors. In fact, too strict standards are not sustainable and can lead to reduced health protection. A more detailed introduction to the WHO guidelines was recently provided by Ensink, J.H.J. & van der Hoek, W. (Trop. Med. Int. Health. 2007, 12: 575–577). The revised guidelines with their health risk assessment based approach represent a significant improvement compared with previous guidelines. But it is also clear that there remains a strong need for more fieldbased research under different environmental, climatic and socio-economic conditions that combine water and produce quality with epidemiological assessment of health risks in farmers and consumers, as this will improve the risk assessment models and mitigation strategies proposed in the WHO guidelines. The studies included in the Supplement document the microbiological and chemical food safety of vegetables and fish produced in wastewater use systems in Cambodia and Vietnam as well as risks of diarrhoea and helminth infections among wastewater farmers and their families. Evidence is provided that skin problems are a significant occupational health hazard among farmers exposed to wastewater, but that such exposure was not a main risk factor for helminth infections. Studies in Ghana show how simple, cheap and easily adoptable wastewater irrigation methods as well as cessation of irrigation before harvest can reduce faecal contamination of crops. Common indigenous washing methods were also tested for their effectiveness for the reduction of faecal contamination on the surface of wastewater-irrigated vegetables. In Pakistan, it was found that unhygienic post-harvest handling was the major source of produce contamination highlighting that interventions at the market may be better and more cost effective ways to protect public health than wastewater treatment. I hope that the articles will inspire other researchers in their efforts to study and document benefits and health aspects of wastewater use. With the growing water scarcity the challenge is to safely use wastewater even when modern wastewater treatment facilities are not available. Low-cost decentralized treatment alternatives and improved wastewater application methods can significantly reduce human health hazards. This should be combined with treatment of people at high risk of helminth infection and general improvements in personal and food hygiene practices, sanitation and water supply. I would like to thank the researchers who responded positively on providing research results for this Supplement. Thanks also to the organizations and others who provided the funding for the various studies, including the Danish International Development Assistance (Danida), the European Union, The CGIAR – Challenge Program for Water and Food, the International Water Management Institute and the International Foundation of Science in Stockholm.