Fresh produce from wastewater good transportation and refrigerated storage, to import perishable food from far afield. Consequently, millions of farmers cash in on the opportunity to grow and sell crops locally. Given the scarcity of freshwater sources, farmers use the only water available to
IWMI
From Bangladesh to Ghana to Mexico, millions of farmers living in and around cities in developing countries use wastewater to irrigate their crops, according to a new report by the International Water Management Institute (IWMI), a nonprofit research organization supported by 60 governments and other organizations. The report provides the first comprehensive, global analysis of the use of wastewater for irrigationswhich, despite its benefits (providing food and sources of livelihood), poses health risks to farmers and consumers.
“The scene you see is the following,” says Liqa Raschid-Sally, an environmental engineer with IWMI and one of the two A Mexican farmer washes his spring onion crop in a authors of the report. De- containing sewage. veloping countries are experiencing increasing them: sources that are polluted urbanization, causing their cities with partially treated or untreated to consume enormous amounts effluents. As the IWMI report of water. However, the infrafinds, a majority of the crop fields structure for treating wastewater in and around cities are used to is not keeping pace with urban grow perishables, mostly veggrowth, and as a result, most of etables. And the fields are a major the wastewater from cities refood source for city dwellers. Just mains untreated or partially outside her own office building in treated. “If there is a river close Accra, Ghana, says Raschid-Sally, by, they dump it in the river; in small farms grow vegetables using coastal cities, they end up water from a stream that contains dumping it into the ocean; if effluents from her building. there is a lake nearby, they “Sometimes I go and buy vegdump it there. So, if there is a etables from there,” she water source downstream of citconfesses. ies, it’s polluted,” Raschid-Sally As noted in a 1996 report by explains. An overwhelming 85% the World Health Organization of the 53 cities analyzed dis(WHO), the yield is often higher charged untreated or partially in fields irrigated with wastewatreated wastewater; only 15% ter because of the high nutrient treated their wastewater “adlevels. However, there are obviequately”, according to the ous health risks from this pracreport. tice: bacteria, worms, and even harmful chemicals from indusWith urbanization comes intrial effluents pose threats to creased demand for food. Most consumers. developing countries lack adequate infrastructure, including 7732 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / November 1, 2008
It is often difficult to pinpoint sources of infections with epidemiological studies, especially in developing countries, says Raschid-Sally. But a 2002 analysis by WHO of existing studies showed that irrigation with wastewater increases the rates of roundworm and bacterial infections and diarrheal diseases. In the cities the authors studied, 1.1 million farmers with 4.5 million family dependents rely on wastewater for irrigation. Scaling up the numbers to a global level, the report estimates 200 million farmers irrigate at least 20 million hectares with wastewater. “There is this very important livelihood dimension of wastewater agriculture,” she adds. “That’s the other side of the coin.”
Population growth, urbanization, and climate change are threatening the availability of freshwater. As countries develop better ways of treating wastewater, immediate measures should be taken to minimize the health risks to consumers and to farmers who are highly exposed to the constituents of wastewater. WHO has drafted guidelines for safer use of wastewater, and many countries are already adopting them.
river
One indigenous practice at the first level of control is to store the wastewater in ponds before using it. The standing water allows sediments and pathogens, especially worm eggs, to settle to the bottom, leaving the top layer cleaner. A second level of controls can be implemented at the consumer level, says Raschid-Sally, and that can be as simple as educating consumers to wash produce thoroughly before eating. —RHITU CHATTERJEE
10.1021/es8024885
2008 American Chemical Society
Published on Web 09/18/2008
