The world's most widely used insecticides are damaging the environment and risk harming global food production, scientists have said.
Research carried out by the International Union for the Conservation of Nature and due to be published next month suggests that neonicotinoid pesticides are harming a range of species and may be responsible for the global decline of bees.
Details of the report have begun to emerge, with campaigners arguing that use of the offending chemicals should be abandoned.
What are neonicotinoids?
Neonicotinoid pesticides were introduced in the early 1990s to replace "older, more damaging chemicals", the BBC reports. They are used extensively in agriculture to control common pests.
The chemicals differ from other pesticides because, rather than being sprayed over crops as they grow, they are usually used to treat seeds. The result is that the chemical becomes embedded in every part of the plant, including roots, leaves, pollen and nectar.
What is the benefit of using neonicotinoids?
According to reports, $2.6 billion dollars' worth of the long-lasting neurotoxins are sold every year. Neonicotinoids are currently applied routinely rather than in response to specific threats from insects.
Supporters of their use say that the treatment is safe and effective. "Neonicotinoid seed treatments are applied directly to the seed, thus limiting any exposure to non-target organisms while providing valuable protection to the crop," says CropLife, which represents Canadian pesticide manufacturers.
But scientists involved in the new research say that there is a "striking" lack of evidence that the pesticides lead to increased crop yields.
What damage do they do?
According to this research neonicotinoids affect the earth, the air and the water, and harm creatures essential to global food production – from bees to earthworms.
"Overall, a compelling body of evidence has accumulated that clearly demonstrates that the widescale use of these persistent, water-soluble chemicals is having widespread, chronic impacts upon global biodiversity and is likely to be having major negative effects on ecosystem services such as pollination that are vital to food security," the study concluded.
Researchers suspected that the chemicals were having a negative effect on bees, but their research discovered that the environmental impact was significantly more widespread than they had initially thought.
"There is so much evidence, going far beyond bees," Professor Dave Goulson from the University of Sussex told the BBC. "They accumulate in soils, they are commonly turning up in waterways at levels that exceed the lethal dose for things that live in streams.
How was the research conducted?
The international team of scientists spent four years analysing results from 800 peer-reviewed papers that have been published since neonicotinoids came into use 20 years ago.
What does the industry say?
The Crop Protection Association, which represents pesticide manufacturers, criticised the scientists' methodology.
Nick von Westenholz, chief executive of the CPA, told The Guardian: "It is a selective review of existing studies which highlighted worst-case scenarios, largely produced under laboratory conditions. As such, the publication does not represent a robust assessment of the safety of systemic pesticides under realistic conditions of use".
How have legislators reacted?
The EU has already limited the use of neonicotinoids in flowering crops such as oilseed rape. In the US, President Obama has set up a honeybee taskforce to assess the effects of pesticides on bees.
Goulson says he does not support a blanket ban, but says that the efficacy of all pesticides should be constantly monitored, and those that do not have a positive impact should be phased out.
"We have been using these things for 20 years and there's not a single study that shows they increase yield," he said.
"I'm not personally in favour of an outright ban but I think we should use them much more judiciously – if they don't benefit yield we should stop using them". ·
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