Asian agricultural water-reuse risk 'exceeds WHO limits'

Australian researchers have found that wastewater used to irrigate vegetable plots in Asian countries poses health risks that may exceed World Health Organization (WHO) guidelines.

Food systems researchers Hoi-Fei Mok and Andrew J Hamilton of The University of Melbourne made the claim in Exposure factors for wastewater-irrigated Asian vegetables and a probabilistic rotavirus disease burden model for their consumption, which recently appeared in the electronic version of the journal Risk Analysis, published by the Society for Risk Analysis.

They recommend that stricter wastewater regulation may be needed to protect the health of farmers and consumers worldwide. Asia accounts for the majority of the world's reuse of wastewater in irrigation.

The researchers first determined the volume of water retained by three commonly grown Asian vegetables, and then used a statistical model to estimate rotavirus disease burdens associated with wastewater irrigation. Rotavirus is associated with diarrheal disease in children, and was chosen as the focus of the study because diarrheal disease is associated with 74% of wastewater-related deaths, 90% of which occur in children.

Based on their findings, the researchers concluded that the probability curves of the annual disease burden "exceeded the WHO's threshold for acceptable level of risk from wastewater reuse by two to three orders of magnitude." Some vegetables posed greater risk than others, because leaf shape affects the amount of wastewater and contaminants that are retained.

Although there are Chinese national standards and regulations for the reuse of wastewater, they present only threshold concentrations for bacteria such as E coli, not viruses. Furthermore, while there are regulations relating to water quality, there is no guideline for risk management around wastewater reuse in China.

The risk management approach involves more pro-active identification and management of risk, rather than relying on post-treatment testing for managing reuse schemes. Considering the global increase in wastewater use for agricultural irrigation, assessing the health risks from reuse schemes is necessary to develop better wastewater management policies to protect public health, say the researchers.

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