Brett Smith for redOrbit.com – Your Universe Online
When they were introduced in the 1990s, a class of insecticides called neonicotinoids was thought to be highly targeted toward pests, but mounting evidence is suggesting that they have had a negative effect on the larger ecosystem.
A new study in the journal Nature has found that use of neonicotinoids is linked to a decline in the populations of farmland birds across Europe.
For the study, scientists from Radboud University in the Netherlands and the Dutch Centre for Field Ornithology and Birdlife Netherlands (SOVON) analyzed long-term data for both farmland bird populations and chemical amounts in surface water. They discovered that in locations where water held high amounts of imidacloprid, a standard neonicotinoid, bird populations were known to decrease by an average of 3.5 percent on a yearly basis.
“In ten years it’s a 35 percent reduction in the local population, it’s really huge,” study author Hans de Kroon from Radboud University told Matt McGrath of BBC News. “It means the alarm bells are on straight away.”
The study team said the insecticide is probably coating seeds that the birds like to eat – as well as leaching into both water and soil around the sprayed areas. They added that neonicotinoids can persist in the environment for up to three years.
“They might be less able to produce their young, or grow their young,” said lead author Caspar Hallman from Radboud University referring to the disappearing farmland birds. “It might increase their mortality by food deprivation, we think this is the most likely mechanism.”
The Dutch researchers also looked to see if the declines in population had started before the widespread use of neonicotinoids and if land use played a role in the declines. Neither was found to be a significant factor.
“I think that the information we have been able to provide is exactly the information that was missing in most studies,” de Kroon said. “In that sense this could be the definite smoking gun, you now see the evidence getting more complete, around the effects of imidacloprid on the environment.”
Bayer, which makes imidacloprid, said the new study doesn’t show a “causal link” between the chemical and the drop in bird populations.
“Neonicotinoids have gone through an extensive risk assessment which has shown that they are safe to the environment when used responsibly according to the label instructions,” a spokesman told the BBC. “Birds living close to aquatic habitats – the species that one could expect to be affected most by concentrations of neonicotinoids in surface water – show no or negligible negative impact.”
“Neonicotinoids were always regarded as selective toxins. But our results suggest that they may affect the entire ecosystem,” de Kroon said. “This study shows how important it is to have good sets of field data, and to analyze them rigorously.”
“Thanks to our partnership with organizations such as Sovon, we can discover ecological effects that would otherwise be overlooked,” he added.
The new Dutch study adds to other research showing the use neonicotinoids is linked to significant decline in bee populations.