COMMON agricultural pesticides are killing off up to one-quarter of aquatic insects in Australia, with their absence attributed to more obvious environmental problems such as habitat loss.
German and Australian researchers have found that pesticides remove up to 42 per cent of the “stream invertebrate” species in Europe, damaging river health and robbing larger animals of food.
Their study, the first of its kind in the world, found pesticides caused wide scale species loss even when they were used legally. “Ecological risk assessment of pesticides falls short of protecting biodiversity,” they report today in the journal Proceedings of the National Academy of Sciences.
The Australian arm of the study focussed on Victoria’s Yarra Valley. It found that in areas with high levels of pesticides, there were no specimens from entire families of species.
Species groups were up to 27 per cent less prevalent in these areas compared to those with little or no pesticides, the researchers found.
Co-author Ben Kefford, of the University of Technology, Sydney, said regulations governing the use of pesticides were based on studies in laboratories or “semi-natural” settings such as simulated river sections. “They’re not doing any studies in the real world,” he said.
“And once the pesticide has been registered, nor are they doing any follow-up monitoring to see whether the assumptions behind their risk assessments are accurate.”
Dr Kefford said the species most affected included mayflies, stoneflies, cattus flies and dragonflies. He said aquatic invertebrates were an important food source for “fish, birds, platypus and the like” as well as being critical to the healthy functioning of streams.
“Some of them eat algae and stop rivers going green, and some contribute to the breakdown of terrestrial matter such as leaves and twigs.
“This is an area of species loss which is essentially being ignored. You can see habitat modification or invasive species just by looking. Pesticides are not something you can see with the naked eye. You have to do complex chemical analysis to work out what’s in the water.”
Dr Kefford said pesticides caused environmental harm in “pulses” when currents funnelled them into particular locations, raising concentration levels. The species most at risk were those that reproduced slowly or couldn’t relocate easily.
“If you’ve got a life cycle of a few weeks, even if your population is drastically reduced by pesticide contamination, the population can recover within a few months. But some organisms last six months, 12 months, even two years. Even if a very occasional pesticide pulse comes down, they will be most affected.”
He said pesticide regulations needed to be informed by real field studies, backed up by regular monitoring. “You could never monitor every creek, but you need some targeted studies where you check whether they are an issue.”