There’s already strong evidence that the best-selling pesticides in the world are wreaking havoc on pollinator populations and may play a role in Colony Collapse Disorder among honeybees, but a new study commissioned by the American Bird Conservancy dives deeper into the impact of neonicotinoid pesticides on the food chain, and its findings are grim.
The nearly 100-page study — called The Impact of the Nation’s Most Widely Used Insecticides on Birds and co-authored by environmental toxicologist Dr. Pierre Mineau and American Bird Conservancy Pesticides Program Manager Cynthia Palmer — reviews 200 studies on the effects of neonicotinoids and finds that the pesticides’ persistence, solubility, toxicity and mobility pose a unique threat, particularly to aquatic ecosystems, where agricultural runoff may cause permanent damage to aquatic invertebrate populations and all the organisms that depend on them for food.
And while publicity has focused on the effect of these systemic pesticides — products like imidacloprid and clothianidid that are absorbed by a plant’s roots and then circulate throughout it — on pollinating insects like bees and butterflies, the conservancy’s report alleges that the Environmental Protection Agency (EPA) has simply ignored evidence of toxicity to birds and small mammals, creatures known to eat freshly planted seeds, even those coated in pesticide.
The report states, “Of particular concern to birds are those compounds that are used as seed treatments, primarily imidacloprid, clothianidin, thiamethoxam and acetamiprid. … Seeds are never fully covered with soil, making them easy to find by foraging birds. Spills are commonplace with current machinery. And many species have the ability to scrape and dig for planted seed. Seed treatments, by definition, will result in a high exposure situation for birds….”
The conservancy singles out imidacloprid as acutely toxic to birds at surprisingly low levels, noting that a single kernel of treated corn can kill small birds and sicken large ones, and calls for a ban on its use as a seed treatment.
More alarmingly, the report goes into great detail about agricultural runoff resulting in contamination of aquatic environments, from rivers and streams to groundwater wells and even to “prairie potholes,” which are vital wetlands oases for waterfowl, often set amidst big tracts of commodity cropland. Neonicotinoid pesticides, which act on the central nerve system, can persist in soil for as long as two years, and are highly water soluble.
Contamination through runoff is inevitable, as EPA’s own scientists have repeatedly warned.
How did we get here?
When it comes to understanding the impact of neonicotinoids that have washed into waterways, regulators have simply chosen to strictly adhere to inadequate testing protocols. In short, the EPA’s standard freshwasher invertebrate example species, Daphnia magna, is remarkably insensitive to this class of pesticides. The conservancy’s report spends many pages analyzing exposure rates for different organisms from various studies, and in every cited case, Daphnia species persist at many times the exposure level of most other aquatic invertebrates and crustaceans, sometimes tens or hundreds of times the level. This information is well documented in peer-reviewed research that the EPA has chosen to ignore.
Additionally, EPA and other regulatory bodies conduct testing by exposing organisms to the test chemical, then monitoring the population for a certain period of time following the exposure, usually 24, 48 or 96 hours. The conservancy’s report highlights two studies where the post-exposure monitoring period was increased to a period of two to four weeks. Both studies reported dramatically higher invertebrate mortality beyond the standard post-exposure window.
Another problem that regulators haven’t adequately addressed is that in species mortality evaluations, neonicotinoids score very well on fish toxicity. While they pose little immediate danger to fish species, contamination in waterways threatens many of the food species that fish, as well as waterfowl, avian insectivores, and amphibians rely on. So instead of being poisoned, as they were with older classes of pesticides, fish may now simply experience an environment with fewer species of food organisms available.
So, what do we do now?
Though the report is chock full of bad news, it also contains proposals to mitigate a bleak forecast. Among the American Bird Conservancy’s recommendations:
Ban the use of neonicotinoids as seed treatment.
Suspend all applications for neonicotinoids pending independent review of the impact on birds, aquatic invertebrates and other wildlife.
Require manufacturers to develop testing methodology to diagnose poisoned birds and wildlife.
Expand EPA’s re-registration review beyond honeybees.
Related stories on MNN: