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New study queries pesticide safety levels

Safe levels Pesticides could be damaging river biodiversity at levels that have been traditionally regarded as environmentally safe by authorities, suggests a new study.

Ecotoxciologist Dr Ben Kefford, of University of Technology, Sydney, and colleagues, report their findings online in Environmental Science & Technology.

"Pesticides are having an effect at 10 to 100 times lower concentrations than traditionally thought," says Kefford.

He says when authorities try to protect our streams and rivers from pesticides they rely on thresholds, under which it is assumed pesticides have no effect.

For example, the European Union recommends the use of a commonly-used safety factor of 100.

This means if a negative effect on an aquatic organism is only seen at a particular concentration of pesticide, then a safe level of that pesticide is regarded as being one hundredth of this concentration.

But, says Kefford, the latest evidence suggests that this safety factor is too small.

The evidence comes from a review of eight field studies which took place in Australia, Europe and Siberia.

Each study looked at the relationship between pesticides and the health of aquatic invertebrates such as insects, worms, crustaceans and snails that make up a key part of river ecology.

The researchers focussed on species that are physiologically sensitive to pesticides, and those that are long-lived and find it hard to 'bounce back' after pesticides are flushed into the river.

It found that when a safety factor of 100 was used for the most toxic of pesticides, there was a 27 to 61 per cent reduction of these species.

Their study also found pesticides also slowed the breakdown of leaves, which feed river ecosystems.

Kefford says a safety factor of 100 is not protective and leads to changes in river biodiversity and ecosystem functions.

He and colleagues recommend the use of a safety factor somewhere between 1000 and 10,000.

Kefford says the evidence reviewed also found that upstream native vegetation and forests reduced the impact of pesticides on streams and rivers.

Australian authorities respond

In a statement provided to ABC Science Online, the Australian Pesticides and Veterinary Medicines Authority says it is aware of the new research and is considering its regulatory implications for Australia.

But it says Australia uses a safety factor of 1000 "when setting the level of concern for a pesticide in aquatic ecosystems if there was only a single-species laboratory test available."

"Our regulatory consideration is usually based on a much more comprehensive assessment in the field and rarely on the effects on a single target species," the APVMA statement says, adding its risk assessment is "more conservative" than that used in the European Union.

Kefford says it's "good to hear" Australia is using a safety factor of 1000, but his study still found problems in Australian rivers.

"Even with their use of a 1000 there are still effects occurring in the field," he says.

Kefford says the study found that larger safety factors were necessary - up to 10,000 - under certain circumstances, that could be relevant to the Australian situation.

But he says there are other explanations for the problem observed in Australia.

"It may not be because of the safety factor. Maybe a factor of 1000 is appropriate but maybe they're underestimating the concentrations in the field," says Kefford. "But for some reason we're detecting effects of pesticides in the field."

He says another possibility is that the interaction between a mixture of pesticides in the field is boosting effects.

The studies reviewed by Kefford and colleagues measured traces of up to 97 pesticides in any one river.

Finally, he says, the problems in Australian rivers could be due to misuse of pesticides by farmers.