(Beyond Pesticides, June 18, 2013) Neonicotinoid pesticides have broad ranging negative impacts not only on beneficial pollinators, but on overall biodiversity and ecosystem health, according to a new study published in the Journal of Applied Ecology. The study, conducted by David Goulson, Ph.D, of the University of Sussex, provides a detailed overview of the current literature on the economic and environmental risks of neonicotinoid pesticides. Dr. Goulson’s work draws stark and disturbing conclusions about the environmental fate of these systemic insecticides.
First introduced in the early 1990’s as an alternative to the acutely toxic organophosphate and carbamate classes of pesticides, neonicotinoids are now the most widely used insecticides in the world. They can be broadly applied as a spray or soil drench, however, the ability of these chemicals to translocate into a plant as it grows has led to the creation of a large market within conventional agriculture for seeds coated with these pesticides. As Dr. Goulson notes, global acceptance of treated seeds has undermined the adoption of alternative methods of conventional pest control, even integrated pest management (IPM), which can reduce pesticide reliance through monitoring and biological, structural, and cultural strategies. Instead, the treated seed market pushes farmers toward the prophylactic use of these insecticides before any information is available about pest populations in the upcoming year. The chemicals are prohibited in organic production.
The study calls into question the economic benefits of neonicotinoids, noting how yield increases in developed countries have been modest over the past 20 years despite their widespread use. Dr. Gouslon references numerous studies that show that yield increases resulting from using these chemicals, if there are any in the first place, are outstripped by the up-front cost of purchasing these products. He notes, “Studies from the US suggest that neonicotinoid seed dressings may be either entirely ineffective or cost more than the benefit in crop yield gained from their use. We seem to be in a situation where farmers are advised primarily by agronomists involved in selling them pesticides.”
Dr. Goulson’s study provides the public with its first look at Bayer’s own data on the persistence of neonicotinoids in soil. Shockingly, this information shows that the soil half-life of the most commonly used seed treatments can range from 200- 1000 days. In the case of clothianidin, a chemical that Beyond Pesticides and other organizations are suing the Environmental Protection Agency (EPA) to suspend, it is revealed that the chemical has the potential to remain in soil for 6,931 days (nearly 19 years!) before degrading. One study referenced by Dr. Goulson shows that thiamethoxam can persist for nearly a year.* A breakdown product of thiamethoxam is clothianidin; thus, even when these chemicals do begin to degrade, their breakdown products have the potential to be just as toxic as the parent chemical.
Dr. Goulson’s review also highlights a 2005 study which randomly sampled farmland soil in France for the neonicotinoid imidacloprid. While no soil on the organic farms’ sampled contained the chemical, nearly all conventional farmland soils contained detectible levels – even those that had not applied the chemical in the previous year. Of the 67 samples from conventional farms, 9 contained between 10 and 100 ppb imidacloprid, and 3 exceeded 100 ppb.
Once in soil, neonicotinoids have a high propensity to leach into groundwater, streams, and ponds. Dr. Goulson references a 2012 study that found 89% of water samples taken from rivers, creeks and drains in California contain imidacloprid, with 19% of those samples at levels above EPA guidelines.
After neonicotiniods are applied to farmland, their persistence in soil and water can cause broad and far-reaching impacts on ecosystem health; many of which have undergone little scientific scrutiny. Dr. Goulson explains, “Any pesticide that can persist for many years, build up in soil, and leach into waterways is likely to have effects far beyond the pest insects it intends to target. This is particularly so when the pesticide is highly toxic to non-target organisms. For example, less than one part per billion of the neonicotinoid imidacloprid in streams is enough to kill mayflies.”
Dr. Goulson’s also reviews the potential for birds and small mammals to consume lethal doses of neonicotiniods after they are sown into fields. The spillage estimated after a typical sowing for maize and oilseed rape has the potential to kill 100 partridge or 167 mice for every hectare sown, he explains.
The literature concerning the danger that these systemic pesticides pose to pollinators is reviewed in detail in Dr. Goulson’s study. It is determined that there is strong evidence that the concentration of neonicotiniods found in agricultural fields have the potential to cause catastrophic sublethal impacts on colony level success for honey bees and bumblebees. An extensive overview of the major studies showing the effects of neonicotiniods on pollinator health can be found on Beyond Pesticides’ What the Science Shows webpage.
Dr. Goulson asserts that world leaders have failed to meet their commitment made at the 2002 Convention on Biological Diversity — to achieve a significant reduction in the rate biodiversity loss. He points to neonicotinoids as a possible cause of this failure, due to their long-term persistence in soil and water. He specifically points to soil dwelling insects, benthic aquatic insects, grain-eating vertebrates, and pollinators as being in particular danger from the use of these chemicals.
Lastly, it is noted that, given these findings, the EU’s recent 2-year ban on these chemicals may not be enough to truly protect pollinators. As Dr. Goulson explains, “”Neonicotinoids will still be widely used on cereals, so the broader environmental impacts are likely to continue. Given the longevity of these compounds, they would be in our soils for years to come even under an absolute ban, so two years is far too short to produce any benefit, even if there were any clear plan to monitor such benefits — which there is not. It is entirely unclear what this two-year moratorium is meant to achieve.”
While there may be doubts as to the efficacy of EU’s neonicotinoid moratorium on certain crops, the 2-year ban represents a step forward towards protecting pollinators — a step EPA has yet to take. As we ponder these findings and reflect on the importance of pollinators during pollinator week, Beyond Pesticides hopes you will consider doing what you can in your own backyard, neighborhood, and community to create a safe space for these imperiled species. For the latest information on pollinator week events and the steps you can take to BEE Protective of pollinators see Beyond Pesticides’ BEE Protective webpage.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Image Source: The Guardian
*This change was made to reflect the original journal article. The half life of thiamethoxam was corrected: from 46-3001 days to 46-301 days. *