Pesticide
Suspected in Bee Die-Offs Could Also Kill Birds
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.
12
April, 2013
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.
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.
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 ormigrate
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
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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