A new study says the risk of using wastewater to irrigate vegetable crops is much higher than first thought, and could contribute to the deaths of untold millions.

Researchers say wastewater irrigation, common in many developing countries including China, may significantly contribute to deadly health risks such as rotavirus; a major cause of diarrheal diseases.

Diarrheal disease is the second leading cause of death globally, with over 99 per cent of deaths from diarrheal disease occurring in developing countries. Ninety per cent of those deaths are children under five.

Research published in the journal Risk Analysis, focused on the Beijing region, found that the risk posed to children eating vegetables grown with wastewater far exceeds the World Health Organization (WHO) acceptable level.

“This research shows that the use of wastewater in irrigation is a global critical health issue for the Asia Pacific region and beyond,” said University of Melbourne researcher, Dr Andrew Hamilton from the Melbourne School of Land and Environment.

“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.”

While many Australian farms use wastewater to supplement irrigation, local supplies comply with National Health and Medical Research Council guidelines and exceed the WHO standards.

The research found that some Chinese vegetables posed greater risk than others.

“This was due to leaf shape, which affects the amount of wastewater and contaminants that are retained. Choy sum poses the greatest risk, while bok choy poses the least risk,” said Dr Hamilton.

“There is more wastewater irrigation in China than in the rest of the world combined. Much of this is used growing vegetables.”

The report suggests better protocols be established worldwide, and a specific system just for China, to try and reduce the impact that wastewater irrigation may have.

Dr Hamilton said identifying all aspects of the diarrheal death toll is key to saving millions of lives.

“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 diarrheal diseases, research like this is very important to identify other contributing causes.”

The complete report is accessible here.