Fresh fruit and veg could be contaminated with viruses such as norovirus if it has been exposed to water used to dilute pesticides, a new study has warned.

“Water containing hNoV [human norovirus] used to dilute pesticides may be an important source of infectious hNoV in fresh produce chains,” the report, led by Katharina Verhaelen of the National Institute for Health and the Environment, says. “The application of pesticides may therefore not only be a chemical hazard, but also a microbiological hazard for public health.”

The study found that lettuces and soft berries were particularly susceptible, as viruses can remain infectious on produce even when refrigerated or frozen, The Times reported.

However, the study was criticised by the National Farmers Union as only identifying a “theoretical risk” as it had taken no samples from the food supply chain. “The only positive results [for norovirus] they got were rat and mice noroviruses. Basically they’ve taken their lab results and extrapolated them with what might happen with human norovirus,” said Dr Chris Hartfield, horticulture adviser at the NFU.

Currently, farmers are required to conduct an annual risk assessment on all water sources and carry out microbiological analysis on medium to high-risk sources, he said.

“If you look at the source paper, they are citing papers that are over 15 years old,” Dr Hartfield added. “It doesn’t strike me as a particularly current assessment of what’s going on in the supply chain right now.”

The study was published in the International Journal of Food Microbiology.