Wastewater irrigation can cause diarrhoeal diseases

Researchers from the University of Melbourne have found that the use of wastewater to irrigate vegetable crops may significantly contribute to deadly health risks such as rotavirus, a major cause of diarrhoeal diseases. The study has been published in the journal Risk Analysis.

“Many farmers in water-scarce regions of developing countries use wastewater to irrigate vegetables and other agricultural crops, a practice that may expand with climate change,” the researchers said. “There are a number of health risks associated with wastewater irrigation for human food crops, particularly with surface irrigation techniques common in the developing world.”

One such risk is diarrhoeal disease - the second leading cause of death globally. More than 99% of deaths of diarrhoeal disease occur in developing countries and 90% of these are in children under five.

Dr Andrew Hamilton, from the Melbourne School of Land and Environment, explained, “There can be lots of microorganisms that cause disease in wastewater. They can be transferred from infected people, travel through the sewerage system and then be eaten from the vegetables. This is a dangerous cycle.”

In particular, Dr Hamilton noted, “There is more wastewater irrigation in China than in the rest of the world combined. Much of this is used growing vegetables.”

The researchers’ study, which focused on the Beijing region, aimed to determine the volume of water left on Asian vegetables and lettuce after irrigation. As Dr Hamilton explained, leaf shape affects the amount of wastewater and contaminants that is retained.

“Choy sum poses the greatest risk, while bok choy poses the least risk,” he said.

But such risk is still too high, with the study finding that the risk posed to children eating vegetables grown with wastewater far exceeded the World Health Organization (WHO) acceptable level. The report concluded that “reduction of pathogen concentration or stricter risk management is necessary for safe re-use” and recommended that China develop its own guidelines for wastewater use.

Meanwhile, said Dr Hamilton, similar situations exist across Asia and other developing countries, where the risk posed by diarrhoeal diseases is highest.

“Vaccination programs for rotavirus are being rolled out globally, but at this stage, they are far from reaching all children in developing countries,” he said.

“When vaccinations cannot be relied upon to stop the spread of rotavirus and other diarrhoeal diseases, research like this is very important to identify other contributing causes.

“This research shows that the use of wastewater in irrigation is a global critical health issue for the Asia-Pacific region and beyond.”

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