Pesticide Suspected in Bee Die-Offs Could Also Kill Birds
- 04.12.13
A western meadowlark. Image: Linda
Tanner/Flickr
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.'
A group of beekeepers and
environmental groups have sued the EPA, which now plans to review evidence of
neonicotinoid harms. Yet amidst the honeybee furor, far less attention has been
paid to what the pesticides may do to other creatures.
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.”
Sope Creek near Marietta, Georgia, where high
levels of neonicotinoids have been detected in the water. Image: Timothy J
Carroll/Flickr
Soil and Streams
Neonicotinoids are
what’s known as “systemic” pesticides, which spread through plant tissue,
suffusing it from root to tip. For any given dose, a large proportion of any
dose ends up
in soil, carried there by roots or plant debris. Depending on conditions,
neonicotinoids can remain active for weeks or even months.
What this does to soil-dwelling insects, which would generally
be extremely sensitive to exposure, is uncertain. Fischer said neonicotinoids
bind to particles of clay, effectively removing them from circulation and making
keeping them from being absorbed by other insects. Black said some
invertebrates, such as earthworms, do pick up neonicotinoids, and that the
pesticides are re-absorbed by subsequent generations of plants, creating new and
unintentional exposures.
Soil-bound
neonicotinoids also leach into groundwater, ending up in streams and waterways.
The danger to fish appears low, if not negligible, but
is much higher for aquatic invertebrates. Not only are they neurologically
vulnerable to neonicotinoids, said environmental scientist Jeroen van der Sluijs
of Utrecht University in the Netherlands, but each exposure builds on the last.
Damage caused by neonicotinoids their nervous systems is irreversible, producing
compounded effects from multiple exposures.
The EPA’s own
reviews state that imidacloprid is “acutely very highly toxic” to aquatic
invertebrates, with lethality to common creatures seen at concentrations of .05
parts per million, and chronic damage at even lower concentrations. In the
United States, where just one-fifth
of all streams are considered healthy, systematic watershed testing for
neonicotinoids hasn’t been conducted, but concentrations well above those levels
have been measured in multiple locations.
Surface water measurements of neonicotinoids in the
Netherlands. Green dots correspond to levels at or below European standards of
acceptable risk. Image: Jeroen van der Sluijs
Over a six-month
period at waterways near
Marietta and Whitesburg, Georgia, for example, imidacloprid levels averaged
7.13ppm, or some 142 times higher than what the EPA had considered highly toxic.
Neonicotinoids have also been detected in water in California, Wisconsin,
New York and Quebec.
According to
Bayer, their own laboratory tests show that, even at the reported
concentrations, effects are not significant. “We’ve tested entire aquatic
communities, in microcosm
tests,” with no decline in biomass until well beyond routinely measured
concentrations, said Fischer.
Yet van der Sluijs
argues that real-world effects are visible. Large-scale neonicotinoid in the
Netherlands started around 2004, and preliminary
research from his own laboratory has correlated neonicotinoid levels in
Dutch waterways with large drops in insect populations. “This will likely have
an impact on insect-feeding birds,” said van der Sluijs.
Insect-eating
birds are indeed declining in
the Netherlands and elsewhere, a trend that dates to the 1960s and is blamed
on a variety of factors, including earlier generations of pesticides, habitat
alteration and climate change. Neonicotinoids represent a fairly new threat, but
van der Sluijs is not alone in his concerns.
Ecotoxicologist Christy Morrissey of the University of
Saskatchewan said there is “considerable circumstantial evidence that these
chemicals are causing large-scale reductions in insect abundance. At the same
time, we are observing serious declines in many species of birds in Canada,
particularly aerial insectivores, swifts and swallows for example, that are
highly dependent on insects to raise their young.”
Like the EPA, Canada’s Pest Management Regulatory Agency is
also reviewing neonicotinoids. Morrissey’s research is still preliminary, but in
most of the wetlands she’s sampled, she’s found neonicotinoids. “It is moving
off the seeds in the fields and into the water,” Morrissey said. There appear to
be fewer insects in heavily agricultural sites than elsewhere, she said, and
birds nesting nearby have lower body weights.
The Future
Concerning as these observations may be, correlations are not
proof of causation. Still, the American Bird Conservancy and Xerces Society
think there’s concern enough for the EPA to accelerate their neonicotinoid
review, which is expected to finish in 2018, and consider limiting some uses of
the pesticides immediately.
Though prompted by concerns over pollinators, the EPA’s review
“is not limited to evaluating potential impacts on bees,” but will include
comprehensive ecological assessments, said the agency. Companies will be
required to monitor the environmental presence of neonicotinoids.
Bayer argues that neonicotinoids have become invaluable to
farming, and trying to replace them could backfire. “Without these products, an
additional three million acres of corn would need to be planted to compensate
for the lost productivity,” the company said in the statement. “There would be
pressure to convert land currently set aside for nature to farmland.”
Black said that
integrated pest management, or IPM, which combines precisely targeted chemical
use with other, non-chemical means of pest control, can
deliver industrial-scale yields in an environmentally sustainable way.
“We’ve moved away from IPM, from scouting your farm, putting in habitat for
beneficial insects, and spraying only if there’s damage,” he said. “With
neonicotinoids, you don’t do that any more.”
In coming months, more studies are expected to be published on
the ecological effects of neonicotinoids. These may provide a more conclusive
diagnosis of what’s happening. For Black, the situation resembles what happened
with the pesticide classes they replaced, which were rushed to market to replace
environmentally toxic DDT. Only later were their dangers recognized. “We’ve gone
full circle here,” he said. “We seem to approve these products before we have
all the information.”
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