Pesticides loom large in animal die-offs
Yale’s Environment 360 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One of the most interesting aspects of the piece was the description of an Italian scientist’s unpublished research that suggests the “missing link” between neonicotinoids, a powerful pesticide already banned in Europe but still in use in the U.S., and bee colony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:
… In as-yet-unpublished research, [University of Padua entomologist Vincenzo] Girolami has found concentrations of insecticide in clouds above seeding machines 1,000 times the dose lethal to bees. In the spring, when the seed machines are working, says Girolami, “I think that 90 percent or more of deaths of bees is due to direct pesticide poisoning.”
Girolami has also found lethal levels of neonicotinoids in other, unexpected — and usually untested — places, such as the drops of liquid that treated crops secrete along their leaf margins, which bees and other insects drink.
But Shah concludes by observing that this accumulating evidence comes with challenges and caveats that, I would point out, industry ruthlessly exploits:
Proving, with statistical certainty, that low-level pesticide exposure makes living things more vulnerable to disease is notoriously difficult. There are too many different pesticides, lurking in too many complex, poorly understood habitats to build definitively damning indictments. The evidence is subtle, suggestive.
Subtle and suggestive though it may be, it’s extremely unlikely that these chemicals aren’t also acting on us. This news plus the data surrounding the consequences to human health of low-dose exposure to chemicals like atrazine, BPA and phthalates should have us in a panic and our government in a regulatory frenzy. Instead we get paralysis and promises of “further study.” As we wait for a chemical “smoking gun,” I wonder what animal population will die off next. Anyone care to wager?
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