Science & Environment

Banned pesticides may be having wider environmental impacts

bees Image copyright Getty Images
Image caption Neonicotinoid pesticides have been linked to the deaths of bees, but scientists are now concerned about their wider impacts in the environment

A new report indicates that a class of pesticides linked to the deaths of bees may be harming other wildlife species.

Neonicotinoids have now been banned by the European Union because of concerns over bee health.

But this latest review of the scientific data suggests the chemicals pose a risk to soil, water and grain-eating birds such as partridge.

Prof Dave Goulson of Sussex University has published his assessment in the Journal of Applied Ecology.

"It seems to me that we may have been focussing far too much on bees and have missed the bigger picture," he told BBC News.

Neonicotinoids are systemic poisons. They are usually applied as coatings to seeds and as the plant grows, every part of it becomes toxic to insects and other pests.

Introduced in the mid 1990s, the chemicals, which include imidacloprid, were taken up widely in agriculture and are now the world's most prominent group of pesticides.

But although they were heralded as having less of an impact on the environment when they were first developed, concerns have been growing for several years about their impact on bees.

Pervasive problems

Earlier this year, the European Union agreed to a two-year moratorium on their use from December. It would only apply to crops that flower and that are attractive to bees, such as oilseed rape.

Now scientists are looking to see if this group of chemicals pose other threats.

"These compounds are highly toxic to all insects," Prof Goulson said. "They are probably pervasive in the environment, as they last a long time and because they are in water and in soil."

In his review, the Sussex researcher found that 90% of the active ingredients in these chemicals go into the soil and leach into groundwater. They can accumulate in soil at concentrations far higher than those that kill bees and persist there for up to 10 years.

In water, less than one part per billion of imidacloprid is sufficient to kill mayflies.

Birds can also be affected by eating the coated seeds that might spill during sowing. Species such as partridge need only eat a few grains to get a lethal dose.

"When you try and weigh up the evidence, it seems that they harm bees, they might be harming partridge, and that they are probably getting into waterways and harming mayflies," said Prof Goulson.

"And if it turns out that the benefits are insignificant then what's the point in using them?"

Other recent studies have also shown neonicotinoids affecting the environment more than previously thought. Research published in the US looked at the impact on birds while in the Netherlands, data suggested a decline in aquatic populations.

Other scientists described the new work as interesting and stated that Prof Goulson was right to draw attention to the lack of assessment about the sub-lethal effects on insects.

Image copyright Getty Images
Image caption Eating just a few seeds coated with pesticide can be lethal for some birds

As the author himself admits, there are still many unanswered questions, especially about the amount of damage the pesticides can do to species.

"We can show that there is pretty convincing evidence that there is a degree of harm but how big it is, I couldn't tell you, nobody could," said Prof Goulson.

Some researchers, however, are not convinced that the threats from the use of neonicotinoids are as widespread as the new review suggests.

Prof John Pickett from Rothamsted Research said that all commercial pesticides were rigorously tested for impacts on non-target species.

"If you test pesticides out of context, you are likely to find all kinds of effects but that is not necessarily indicative of a wider effect; and strict registration rules exist that are aimed at protecting the environment," he said.

"Pesticides exist to protect our crops and food from pests and while it is very important that scientists do this research, it is also important that we interpret the studies carefully in a way that balances risks and benefits."

Prof Goulson said that his review looked at research from a range of sources, including data from the agrochemical industry. He argued that we urgently needed more work to test soils and waterways for the presence of these chemicals and the levels at which they might be acting.

"There is every reason to believe that lots of insects are exposed to them, and we really don't know what harm they might be doing; we should find out pretty damn quick if you ask me."

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