Food for Thought

Sewage waters a tenth of world's irrigated crops

12:01 18 August 04 - NewScientist.com news service A tenth of the world’s irrigated crops - everything from lettuce and tomatoes to mangoes and coconuts - are watered by sewage. And much of that sewage is raw and untreated, gushing direct from sewer pipes into fields at the fringes of the developing world’s great megacities, reveals the first global survey of the hidden practice of waste-water irrigation. And, however much consumers may squirm, farmers like it that way. Because the stinking, lumpy and pathogen-rich sewage is rich in nitrates and phosphates that fertilise crops free of charge, suggests the survey presented at the Stockholm Water Symposium on Tuesday. “Wastewater irrigation is in an institutional no-man’s land,” said Chris Scott of the Sri Lanka-based International Water Management Institute, co-editor of the study. “Water, health and agriculture ministries in many countries outlaw the practice, but refuse to recognise that it is widespread.” He estimates that 20 million hectares of the world’s farms are irrigated with sewage. A quarter of Pakistan’s vegetables, including salad crops, are grown in sewage effluent, the study found. And business is booming. One farmer in the heart of an un-named West African city grows 12 crops of lettuce a year from his sewage farm. In many fast-growing megacities, clean water is in desperately short supply, where sewage is plentiful. And the sewage pipes keep flowing even in the dry season, when irrigation canals often dry up. Farms hooked up to sewage pipes make big profits. The study found that in parts of Pakistan the price of fields watered by sewage pipes is twice that of neighbouring fields irrigated with clean water. In Mexico, Jordan, Israel and Tunisia, sewage is specially treated to remove pathogens and make it safe for irrigation. But in India, China and Pakistan, the study found that treatment is rare. The sewage is added to fields complete with disease-causing pathogens and toxic waste from industry. Sewage is probably the biggest source of water for urban farming, which provides an estimated one fifth of the world’s food, said Scott. In Hyderabad, the Indian city where he works, “pretty much a 100 per cent of the crops grown around the city rely on sewage,” he said. “There is no other water available.”....

The biological waste products aren't a concern. I mean, we use fertilizer, don't we? No, the big problem is the industrial and household chemical waste that consequently makes its way into the agricultural food chains of these regions. This is a literally deadly situation that must receive the immediate attention of all first-world nations and international relief organizations.