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January 7, 2010

Pesticides and the Great Die-Offs

Yale's Environment360 has a new must-read report by Sonia Shah linking pesticides to the high-profile die-offs among amphibians, bees and bats. What makes this news timely isn't necessarily the toxicity of the pesticides per se, it's the indirect effects on these animals of chronic, low-dose exposure to chemicals:

In the past dozen years, no fewer than three never-before-seen diseases have decimated populations of amphibians, bees, and -- most recently -- bats. A growing body of evidence indicates that pesticide exposure may be playing an important role in the decline of the first two species, and scientists are investigating whether such exposures may be involved in the deaths of more than 1 million bats in the northeastern United States over the past several years.

...The recent spate of widespread die-offs began in amphibians. Scientists discovered the culprit — an aquatic fungus called Batrachochytrium dendrobatidis, of a class of fungi called “chytrids” — in 1998. Its devastation, says amphibian expert Kevin Zippel, is “unlike anything we’ve seen since the extinction of the dinosaurs.” Over 1,800 species of amphibians currently face extinction.

It may be, as many experts believe, that the chytrid fungus is a novel pathogen, decimating species that have no armor against it, much as Europe’s smallpox and measles decimated Native Americans in the sixteenth and seventeenth centuries. But “there is a really good plausible story of chemicals affecting the immune system and making animals more susceptible,” as well, says San Francisco State University conservation biologist Carlos Davidson.

Shah goes on to explain a mechanism whereby pesticides applied to fields in California's Central Valley drift into the Sierra Nevada mountains "where they settle in the air, snow, and surface waters, and inside the tissues of amphibians." A scientist who studied the matter "found a strong correlation between upwind pesticide use... and declining amphibian populations."

Meanwhile, bees and bats have suffered a similar fate -- killed off by powerful pathogens that in theory could be novel but in practice seem to have taken advantage of animal populations immuno-compromised by pesticides.

One of the most interesting aspects of the piece was the description of an Italian scientists unpublished research that suggests the "missing link" between neonicotinoids, a powerful pesticide already banned in Europe but still in use in the US, and bee colony collapse. It relates to the practices of using neonicotinoids-coated seeds planted by machines that kick up clouds of pesticide as they work...

READ THE REST OF THIS POST ON GRIST.ORG

Flickr photo: Paul L. Nettles

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