07 JAN 2010: REPORT
Ever since Olga Owen Huckins shared the spectacle of a yard full of dead, DDT-poisoned birds with her friend Rachel Carson in 1958, scientists have been tracking the dramatic toll on wildlife of a planet awash in pesticides. Today, drips and puffs of pesticides surround us everywhere, contaminating 90 percent of the nation’s major rivers and streams, more than 80 percent of sampled fish, and one-third of the nation’s aquifers. According to the
But as regulators grapple with the lethal dangers of pesticides, scientists are discovering that even seemingly benign, low-level exposures to pesticides can affect wild creatures in subtle, unexpected ways — and could even be contributing to a rash of new epidemics pushing species to the brink of extinction.
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
Experimental evidence bolsters Davidson’s findings. In lab experiments, exposure to carbaryl dramatically reduced yellow-legged frogs’ production of fungus-fighting compounds called antimicrobial peptides, which may be crucial to amphibians’ ability to fend off chytrid fungus. Further testing has shown that amphibian species that produce the most effective mixes of antimicrobial peptides resist experimental chytrid infection, and tend to be those that survive most successfully in the wild.
Six years after scientists discovered the fungal assault on amphibians, a mysterious plague began decimating honeybees. Foraging honeybees first started vanishing from their hives, abandoning their broods and queens to certain death by starvation, in 2004. Alarmed beekeepers dubbed the devastating malady “colony collapse disorder.” Between 2006 and 2009, colony collapse disorder and other ills destroyed 35 percent of the
Neonicotinoids came into wide use in the early 2000s. Unlike older pesticides that evaporate or disperse shortly after application, neonicotinoids are systemic poisons. Applied to the soil or doused on seeds, neonicotinoid insecticides incorporate themselves into the plant’s tissues, turning the plant itself into a tiny poison factory emitting toxin from its roots, leaves, stems, pollen, and nectar.
“The companies believe this stuff is safe,” says
And the result could be immediately devastating. In as-yet-unpublished research, 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. (The scientific community has yet to weigh in on Girolami’s new, still-to-be-published research, but Pettis, who has heard of the work, calls it “a good and plausible explanation.”)
As humans encroach on forested lands and as temperatures rise, the transmission of disease from animals and insects to people is growing. Now a new field, known as “conservation medicine,” is exploring how ecosystem disturbance and changing interactions between wildlife and humans can lead to the spread of new pathogens.
Scientists have been trying to identify the cause of a cancer epidemic that is wiping out
Like the mysterious Batrachochytrium dendrobatidis fungus infesting amphibians, Geomyces could be a novel pathogen, newly preying upon defenseless bat species. But scientists have also started to investigate whether pesticide exposure might be playing a role.
Bats are especially vulnerable to chemical pollution. They’re small — the little brown bat weighs just 8 grams — and can live for up to three decades. “That’s lots of time to accumulate pesticides and contaminants,” points out
Which, in the end, is the central dilemma facing pesticide-reliant societies. 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. But with the rapid decimation of amphibians, bees, and bats, it is accumulating, fast.