A major health and environmental menace
The use of wastewater to irrigate crops is far more widespread than previously estimated, according to a new study, exposing hundreds of millions of people to health risks and posing a major environmental hazard.
Study results, based on on advanced modeling methods, show that 65% of all irrigated areas within 40 kilometers downstream from urban centers – amounting to about 35.9 million hectares (Mha) worldwide – are affected by wastewater flows to a large degree. Of this total area, 29.3 Mha are in countries where wastewater treatment is very limited, exposing 885 million urban consumers as well as farmers and food vendors to serious health risks.
Five countries – China, India, Pakistan, Mexico and Iran – account for most of this cropland. The new findings supersede a widely cited 2004 estimate, based on case studies in some 70 countries and expert opinion, which had put the cropland area irrigated with wastewater at a maximum of 20 million hectares.
Published this week in the journal Environmental Research Letters, the study was carried out by Anne Thebo, a recent graduate from the University of California, Berkeley, in the USA, with Pay Drechsel, leader of the Rural-Urban Linkages strategic program at the International Water Management Institute (IWMI), as well as colleagues from Stanford University in the USA and Université Catholique de Louvain in Belgium.
The study results feed into a year-long communications campaign through which IWMI and the CGIAR Research Program on Water, Land and Ecosystems (WLE), led by the Institute, are fostering greater recognition of the need to enhance water quality and wastewater management in developing countries. To achieve this requires a dual approach (outlined in a new WLE/IWMI document titled Wastewater reuse in numbers) consisting of practical safety measures along the entire food chain as well as green business solutions that convert waste into valuable resources (like fertilizer and energy), which can be sold to help cover the costs of wastewater treatment.