August 21, 2008 Facing water shortages and escalating fertilizer costs, farmers in developing countries are using raw sewage to irrigate and fertilize nearly 49 million acres (20 million hectares) of cropland, according to a new report—and it may not be a bad thing. While the practice carries serious health risks for many, those dangers are eclipsed by the social and economic gains for poor urban farmers and consumers who need affordable food, the study authors say. Nearly 200 million farmers in China, India, Vietnam, sub-Saharan Africa, and Latin America harvest grains and vegetables from fields that use untreated human waste. Ten percent of the world's population relies on such foods, according to the World Health Organization (WHO). "There is a large potential for wastewater agriculture to both help and hurt great numbers of urban consumers," said Liqa Raschid-Sally, who led the study published by the Sri Lanka-based International Water Management Institute (IWMI) and released this week at the World Water Week conference in Stockholm, Sweden. Health Risks The report focused on poor urban areas, where farms in or near cities supply relatively inexpensive food. Most of these operations draw irrigation water from local rivers or lakes. Unlike developed cities, however, these areas lack advanced water-treatment facilities, and rivers effectively become sewers. When this water is used for agricultural irrigation, farmers risk absorbing disease-causing bacteria, as do consumers who eat the produce raw and unwashed. Nearly 2.2 million people die each year because of diarrhea-related diseases, including cholera, according to WHO statistics. More than 80 percent of those cases can be attributed to contact with contaminated water and a lack of proper sanitation. But Pay Drechsel, an IWMI environmental scientist, argues that the social and economic benefits of using untreated human waste to grow food outweigh the health risks. Those dangers can be addressed with farmer and consumer education, he said, while the free water and nutrients from human wastewater and feces can help urban farmers in developing countries to escape poverty. Waste Into Water Agriculture is a water-intensive business, accounting for nearly 70 percent of global fresh water consumption. In poor, parched regions, untreated wastewater is the only viable irrigation source to keep farmers in business, according to Drechsel. Mark Redwood, a senior program officer with the Canadian International Development Research Centre, said that in some cases, water is so scarce that farmers break open sewage pipes transporting waste to local rivers. Irrigation is the primary agricultural use of human waste in the developing world. But frequently untreated human feces harvested from latrines is delivered to farms and spread as fertilizer. In most cases, the excrement is used on cereal or grain crops, which are eventually cooked, minimizing the risk of transmitting water-borne pathogens and diseases, IWMI's Drechsel noted. With fertilizer prices jumping nearly 50 percent per metric ton over the last year in some places, human waste is an attractive, and often necessary, alternative, Redwood said. In cases where sewage sludge is used, expensive chemical fertilizer use can be avoided, he said. The sludge contains the same critical nutrients—nitrogen, phosphorous, and potassium. Wastewater Recycling It is generally unheard of for untreated wastewater to be used for agriculture in developed countries, simply because farmers there have access to treated water, said Margaret Catley-Carlson of the Global Water Partnership. Instead, farmers in developed countries use recycled wastewater that often meets drinking-water standards. To address health risks associated with wastewater agriculture in developing countries, IWMI recommends education programs for both consumers and farmers. The nonprofit also recommends that such operations adhere to World Health Organization (WHO) standards for safe wastewater usage. WHO, in turn, has made their own standards less stringent. "Overly strict standards often fail," James Bartram, a WHO water-health expert, said. "We need to accept that across much of the planet, waste with little or no treatment will be applied to agriculture for good reason." According to IWMI's report, few developing countries have official guidelines for the use of wastewater for farming. But the fact that authorities are even acknowledging that wastewater agriculture exists is progress, the report says. In the city of Kumasi, Ghana, home to 1.6 million people, IWMI estimates that there are about 12,000 families growing food on 27,000 acres (12,000 hectares) using mostly polluted surface water. Just this year the Ghanaian government began to recognize this type of informal irrigation in its new irrigation policy, according to IWMI's Drechsel, who views the move as a giant breakthrough for addressing related health issues. There are also low-tech solutions for "treating" human waste. IWMI suggests employing appropriate and time-tested indigenous practices. The report cites examples in Indonesia, Nepal, and Vietnam. There, farmers store wastewater in ponds to allow solid feces and worm eggs to settle, possibly reducing bacterial content in the residual water. Composting, in which heat kills much of the bacteria, is another option, according to the report | | 据报道，面对水资源短缺和化肥价格上涨，发展中国家的农民们正在用原污水，对大约4千9百万英亩（2千万公顷）的农田进行灌溉和施肥——也许并非坏事。 研究人员表示，虽然这带来严重的健康危机，但是对社会扩容和经济增涨皆有好处，因为并不富裕的农民工和消费者需要廉价的食品。 在中国，印度，越南，黑非洲和拉丁美洲，大约有2亿农民收获的谷物和蔬菜均使用未经处理的人类粪便作肥料。 据世界卫生组织调查，全世界有10%的人口依赖这种食物。 利卡·瑞斯奇得－萨利负责这项由国际水资源管理所主持的研究，并于本周在位于瑞典首都斯德哥尔摩召开的世界水周大会上公布结果。他说：“依靠废水灌溉的农业，对数量庞大的城填居民具有利与害双重潜在影响。” 健康隐患 调查的地点集中在农产品相对低廉的城区，农田的灌溉水主要从当地的河流或湖泊中抽取。然而，不像发达城市，由于缺少高级水处理设备，这里的河流实际变成了下水道。 脏水用于农业灌溉，农民的健康受到致病细菌的威胁，食用这类且又未经烹调和清洗的农产品的消费者亦会面临同样问题。据世界卫生组织统计，大约2百20万人每年死于与痢疾有关的疾病，包括霍乱。其中超过80%的病例与水污染和环境卫生差有关。不过，国际水资源管理研究所的环境学家佩·德雷克泽尔坚持说，使用未经处理的人类粪便灌溉农田所带来的社会和经济利益大于其带来的健康危害。 他说，这个问题可能通过教育农民和消费者来解决，同时来自人类粪尿的免费水份和营养可以帮助发展中国家的农民摆脱贫困。 粪尿中的水资源 农业离不开水资源，据计算，全球约有70%的淡水资源用于农业。 德雷克泽尔称，在贫困缺水的地区，未处理的粪水是农民们唯一可以用来灌溉的资源。加拿大国际发展研究中心的高级项目官员马克·雷德伍德称，有时候，在水资源奇缺的地方，农民们甚至砸开通向河流的污水管道。 在发展中国家，灌溉是人类粪便的主要农业用途。但是，时不时人们从茅房里获取渣滓当作肥料撒在农田里。 大多数情况下，人类排泄物用于谷类作物。德雷克泽尔表示，这些食物在充分烹饪后，可将水生病原体和疾病的危害降到最低点。 他说，去年有的地方肥料的价格每吨大约上涨了50%，人类粪便顿时大行其道，时常必不可少，别无他选。 有时候，人们用下水道污泥来代替昂贵的化学肥料，其中一样含有重要的营养成分——氮，磷和钾。 污水浄化 通常，很少听说发达国家的农民使用未经处理的污水用于农业。全球水源伙伴组织的玛格丽特·凯利说，原因很简单，他们有能力净化污水。 发达国家的农民使用的净化水有时甚至达到了饮用水标准。 国际水资源管理研究所强调人们重视发展中国家由污水农业引起的健康危害，提议对消费者和农民进行相关的教育。 这个非盈利性组织同时建议，世界卫生组织应该制订污水利用的安全规范。不过，世界卫生组织的标准没有期待中的严格。 “过于严格的标准往往难以实施，”世界卫生组织水资源专家詹姆斯·巴特拉姆说。“我们必须接受一个事实，在这个世界有很多地方，没有经过处理的粪便用于农业是有原故的。”按照国际水资源管理研究所的报告，很少有发展中国家具有污水利用的官方指导方针。不过事实上，有权威部门甚至认为农业用废水的存在是进步的。 加纳国库马西市有160万人口，据国际水资源管理研究所估算，大约1万2千个家庭使用受污染的地表水耕种2万7千英亩（1万2千公顷）的土地。 就在今年，加纳政府开始在其新的政策中认可这种非正式的灌溉方式。德雷克泽尔视此举为普及相关的健康常识的巨大突破。 净化人类粪尿也有土方法。国际水资源管理研究所建议使用恰当的，经得住考验的本地做法。 报告中引用了印度尼西亚，尼泊尔和越南的例子。这些国家的农民将排泄物储存在池子里，其中的固态物和虫卵沉淀下来，也许能够降低残水中的细菌数量。 报告中称，堆制肥料的高温可以杀灭许多细菌，也是一个选择。 |
