The third edition of the WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater in Agriculture and Aquaculture has been announced in Beijing.

Published in four volumes, addressing, respectively, policy and regulatory aspects, wastewater use in agriculture, wastewater and excreta use in aquaculture and excreta and greywater use in agriculture, it supersedes the second edition of the guidelines, which was published in 1989.

"This third edition of the Wastewater Guidelines marks an important departure from the previous edition," says Susanne Weber-Mosdorf, Assistant Director-General for the Cluster of Sustainable Development and Healthy Environments. "The rigid and prescriptive character of the second edition has evolved to a more contemporary and flexible approach based on scientific evidence and process-oriented risk assessment and management. The Guidelines reflect a strong focus on disease prevention and public health principles. Water quality regulators will have to work towards attaining health-based targets through an integrated approach."

The burden of disease caused by infections with food-borne trematodes is considerable: globally, an estimated 40 million people are at risk. Recent studies indicate that in China alone over the period 1995-2004 the incidence of one of the various parasitic infections in this group, clonorchiasis, tripled–some 15 million Chinese were estimated to be infected with Clonorchis sinensis in 2004. A large part of this disease burden is thought to be attributable to excreta and greywater use in fishponds.

In many parts of the world, good quality fresh water resources are becoming increasingly scarce. At the same time, wastewater is produced in ever larger quantities, mainly as a result of the continued growth of the human population and the process of rapid urbanization. In reality, wastewater is a water resource of ever-growing importance, particularly for the urban and peri-urban poor whose livelihoods depend on agricultural products that can be marketed locally. However, its use for crop and fish production carries important health risks and the disease burden that can be attributed to its unsafe use is considerable.

The guidelines clearly reflect regional differences in wastewater use and in associated public health issues. For example, the use of wastewater and excreta in aquaculture in Southeast Asia brings with it region-specific risks, such as the transmission of food-borne trematodes. These parasitic flukes have a complex life cycle that involves aquatic snails and fish as intermediate hosts; water bodies are contaminated by human excreta containing the parasite's eggs. Consumption of raw or fermented fish, a common practice in rural communities of Southeast Asia, from infected ponds closes the infection cycle.

The WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater in Agriculture and Aquaculture reflect the knowledge and experience of a unique group of scientists, regulators and public health specialists brought together by the Water, Sanitation and Health Programme of the World Health Organization. The next step will be their implementation by WHO Member States. To study the obstacles and opportunities that may be encountered in their application and use, WHO and the Canadian International Development Research Centre shortly will start joint research in three countries in North and /or West Africa.

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