Pesticide Suspected in Bee Die-Offs Could Also Kill Birds
- 04.12.13
Controversial pesticides linked to catastrophic honeybee
declines in North America and Europe may also kill other creatures, posing
ecological threats even graver than feared, say some scientists.
According to a report by the
American Bird Conservancy, the dangers of neonicotinoid pesticides to birds,
and also to stream- and soil-dwelling insects accidentally exposed to the
chemicals, have been underestimated by regulators and downplayed by
industry.
“The environmental persistence of the neonicotinoids, their
propensity for runoff and for groundwater infiltration, and their cumulative and
largely irreversible mode of action in invertebrates raise environmental
concerns that go well beyond bees,” stated the report, which was co-authored by
pesticide policy expert Cynthia Palmer and pesticide toxicologist Pierre Mineau,
both from the American Bird Conservancy.
Chemical and pharmaceutical company Bayer, a major
neonicotinoid manufacturer, said the criticisms lack solid evidence. “This
report relies on theoretical calculations and exposure estimates that differ
from accepted risk assessment methodologies, while disregarding relevant data
that are at odds with its claims,” the company said in a statement.
The Bees
Neonicotinoids became popular in the late 1990s, largely
replacing earlier insecticides that posed blatant health and environmental
risks. Derived from nicotine, which short-circuits the nervous systems of
insects that try to eat tobacco plants, neonicotinoids at first seemed both
effective and safe.
They now account
for some one-quarter of global insecticide sales, used on hundreds of crops and
also
in gardens and cities. In the last several years, though, it’s become
evident that regulators, especially the Environmental Protection Agency,
overlooked the extreme toxicity of neonicotinoids to honeybees and other
pollinators. Regulatory approvals were partly based on
industry studies now considered unreliable, and sometimes despite the concerns
of the EPA’s own scientists.
Neonicotinoids
subsequently emerged as a
prime suspect in colony collapse disorder, the unexplained malady that since
2005 has annually killed about one-third of the nation’s commercial honeybees,
and may also
affect bumblebee populations. The pesticides are blamed for triggering
collapses outright or making bees vulnerable to to diseases and parasites.
'We’re going to see profound changes in
aquatic and terrestrial ecosystems.'
Early toxicity
studies suggested the
risks were relatively small: Vertebrates don’t have precisely the same
receptors to which neonicotinoids bind so tightly in insects, so higher doses
are needed to cause harm.
It was also assumed that neonicotinoids wouldn’t accumulate in
the environment at levels capable of harming either vertebrates or non-pest,
non-pollinator invertebrates — the countless insect species that are the
foundation of terrestrial and aquatic food webs.
Since then, however, researchers have found widespread
evidence of neonicotinoids spreading beyond their crop targets, and the
methodologies used to establish neonicotinoid safety have come under
question.
“The more studies I see, the more I think the preponderance of
evidence is leaning towards neonicotinoids being tremendously bad for lower
animals in the food chain, especially all the invertebrates,” said Scott Black,
executive director of the Xerces Society, an invertebrate conservation
group.
The Birds
Seeds used to grow crops like corn, sunflowers and canola are
routinely coated in neonicotinoids, which then spread through plants as they
grow. Many species of birds eat seeds. In the absence to date of studies
directly observing farmland birds and their day-by-day fates, the question of
whether neonicotinoids harm them quickly becomes an argument over methods used
to set toxicological guidelines.
In the American Bird Conservancy report, Mineau and Palmer
note that the EPA typically sets guidelines for bird exposures using laboratory
tests on just two species, mallard ducks and bobwhite quail. Their results
become the basis of standards for other birds, but this elides widely varying
sensitivities among hundreds of species.
For example, the LD50 — a standard toxicological measure for a
dose that kills half of exposed animals — for bobwhite and mallards consuming
imidacloprid, the most common neonicotinoid formulation, are 152 and 283
milligrams per kilogram of body weight. For canaries, that number drops to about
35 mg/kg, and for gray partridge it’s just 15 mg/kg.
Were the guidelines calculated more carefully, say Mineau and
Palmer, drawing broadly on peer-reviewed literature and accounting for
heightened sensitivity in certain species, they’d be very different. What are
now considered safe exposure levels would be recognized as poisonous — and many
birds could reach them by eating just a few seeds.
Asked for comment, the Environmental Protection Agency said
the report “uses a method to compare risks across chemicals that differs from
the long-standing peer-reviewed approach EPA uses. The agency will carefully
consider the report’s studies, analytic methods and conclusions.”
David Fischer, director of environmental toxicology and risk
assessment in Bayer’s CropScience division, said the report misrepresented
industry testing. “We tested a lot of species. We did tests beyond what was
required by the EPA,” Fischer said. If neonicotinoids really were killing birds,
said Fischer, it would already have been reported, as were die-offs from the
earlier, more-toxic chemicals that neonicotinoids largely replaced.
“There have been few instances of mortality in the field.
They’re extremely rare,” Fischer said. “I don’t know of any incidents in North
America.” Mineau responded that, even with earlier chemicals, researchers didn’t
find evidence of bird deaths until they actively looked for them. That hasn’t
yet happened with neonicotinoids, he said, and poisoned birds don’t immediately
and visibly drop dead on fields. They may die hours or days later in a tree or
bush, making it unlikely that anyone will even notice.
The report also
notes that chronic toxicity — effects that don’t kill animals outright, but over
time cause health, reproductive and behavioral problems — has largely been
overlooked. Preliminary studies suggest a potential for embryo development
disorders and decreased immune
responses, but guidelines were again set by reference to bobwhite and
mallards. Tests only measured obvious birth defects, ignoring the many other
ways that animals can be impaired.
Mineau thinks
neonicotinoids are at least playing a role in the precipitous decline
of birds that live in or migrate through
agricultural areas. “I believe this is happening right now,” he said. Yet that,
said Mineau, may be just a prelude to other problems. “I think the aquatic and
soil impacts are even greater,” he said. “We’re going to see profound changes in
aquatic and terrestrial ecosystems.”
No comments:
Post a Comment