Fresh produce from wastewater

rom 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 irrigation—which, despite its benefits (providing food and sources of livelihood), poses health risks to farmers and consumers.


INTERNATIONAL WATER MANAGEMENT INSTITUTE
A Mexican farmer washes his spring onion crop in a river containing sewage.

“The scene you see is the following,” says Liqa Raschid-Sally, an environmental engineer with IWMI and one of the two authors of the report. Developing countries are experiencing increasing urbanization, causing their cities to consume enormous amounts of water. However, the infrastructure for treating wastewater is not keeping pace with urban growth, and as a result, most of the wastewater from cities remains untreated or partially treated. “If there is a river close by, they dump it in the river; in coastal cities, they end up dumping it into the ocean; if there is a lake nearby, they dump it there. So, if there is a water source downstream of cities, it’s polluted,” Raschid-Sally explains. An overwhelming 85% of the 53 cities analyzed discharged untreated or partially treated wastewater; only 15% treated their wastewater “adequately”, according to the report.

With urbanization comes increased demand for food. Most developing countries lack adequate infrastructure, including 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 them: sources that are polluted with partially treated or untreated effluents. As the IWMI report finds, a majority of the crop fields in and around cities are used to grow perishables, mostly vegetables. And the fields are a major food source for city dwellers. Just outside her own office building in Accra, Ghana, says Raschid-Sally, small farms grow vegetables using water from a stream that contains effluents from her building. “Sometimes I go and buy vegetables from there,” she confesses.

As noted in a 1996 report by the World Health Organization (WHO), the yield is often higher in fields irrigated with wastewater because of the high nutrient levels. However, there are obvious health risks from this practice: bacteria, worms, and even harmful chemicals from industrial effluents pose threats to consumers.

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.

more from EST online