GroundTruth Blog

Neonics: More evidence of harm

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by Emily Marquez

PAN has done a lot to spread the word about neonicotinoid pesticides and their adverse impacts on bees. But there are other repercussions for widespread use of neonics too, as an increasing number of studies highlight. Adverse impacts on wild pollinators, birds and other wildlife from neonics have also been in the news lately.

Neonics are the most widely used insecticides in the world, finding their way into ecosystems through water, soil and insects other species rely on for food. These chemicals were released onto the U.S. market without regulators fully understanding their impacts, and scientists continue to uncover more unintended consequences — from harming honey bees to song birds.

A recent study reported in Nature examined the association between high surface-water concentrations of the widely used (and water soluble) neonic imidacloprid and declines in local populations of insect-eating birds in the Netherlands. The authors found avian populations tended to decline by an average of 3.5% annually in areas where imidacloprid contaminated surface waters at concentrations of more than 20 nanograms per liter (ng/L).

This level of 20 ng/L is relatively high among these real-world surface water concentrations of imidacloprid. But that level was by no means the highest amount of imidicloprid found in real-world circumstances. Evidence indicates that neonics pervasively contaminate surface water.

Weighing the factors

The authors' premise for pursuing this line of investigation was based on previous work indicating that there have been adverse impacts of insecticide usage on bird populations in the past.

The authors used statistical analyses to investigate whether two alternative explanations could have caused the association between imidacloprid concentrations and bird population trends from 2003-2010. The first potential confounding factor was whether there already was a decline occurring before imidacloprid was introduced into the environment.

The second potential confounding factor was whether increased land use resulting from agricultural intensification was the factor impacting bird declines. Both of these confounding factors were eliminated by statistics in this study. The only significant correlations in the trends examined were between imidacloprid and bird declines.

Previous studies have mainly examined direct consumption of neonicotinoids by birds, specifically acute toxicity. However, as the Worldwide Integrated Assessment suggested at the end of their review of impacts on vertebrates, there's scientific evidence suggesting that indirect effects of neonics — such as impacts on diet by widespread usage of insecticides — may also constitute a threat to wildlife.

The big picture

The authors of the latest bird study explained that their results are indeed correlative. There could be other direct effects of imidacloprid that may be impacting bird population trends.

But, that doesn't mean their findings should be dimissed. One aspect of agricultural intensification is increased pesticide usage, which the authors of the study cited as a factor "known to be a major threat to farmland birds."

While the results don't mean everything to the field, they are yet another piece of a puzzle that seems to be spelling out a message: widespread use of pesticides that contaminate the environment will invariably lead to larger problems.

Emily Marquez's blog

is PAN's Staff Scientist. Follow @EmilyAtPan

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