Insufficient experimental evidence has been collected to change the way the Pesticides Safety Directorate measures the risk of bystander exposure to pesticides.

Bystanders, who could be anyone in the vicinity of a field that had been or was being sprayed, could be exposed through direct drift, by indirectly touching surfaces that had been drifted onto, or through pesticide vapour inhalation, Clare Butler Ellis of The Arable Group explained.

The current assessment of risk was based on data collected in the 1980s, using a 12m boom set 0.5m above the ground with a forward speed of 8km/h, she said. But there were some holes in the data, not least that typical application equipment had changed. “It means levels of drift might be different.”

Two PSD experiments had been undertaken to compare the data taken under more modern conditions with the original data. But under field conditions the results were very variable, making it difficult to draw any conclusions, she reported.

Some of the results suggested the current risk assessment contamination level of 0.1ml could be exceeded with more modern equipment. But she thought one-off events were more likely than long-term repeated exposure.

A new three-year project (BREAM) was investigating trying to develop a more consistent model of spray drift through experimental work in wind tunnels and through field evaluation, she added.