What Are Scientists Saying About Imidacloprid?
The success of imidacloprid as a crop protection product would have been unthinkable had its short and long term impact on the environment brought about any adverse effects or irreversible changes. Assuming a use pattern which guarantees the desired protective effects, the behavior in and between the compartments of the environment, biosphere, soil, water, and atmosphere, depends on physico-chemical and chemical properties defined principally by the chemical structure. Climatic differences and diversities of the soils must also be taken also into account. Which of the theoretical outcomes will predominate following application of a crop protection product, degradation, persistence, binding to soil, volatilisation, translocation into groundwater, runoff into surface due to rainfall after application, must be established either from physico-chemical data or by direct measurements.
In the case of imidacloprid it was proven beyond doubt that persistence of residues in soil due to repetitive application over several years; translocation into deeper soil horizons, groundwater, adjacent crops or surface waters; volatilisation; and transport through the air into other regions can be ruled out. This has been confirmed again and again by world-wide and long-term experience following its use in all major crops.
There is broad evidence from research at Bayer, as well as from independent sources that imidacloprid is degraded continuously though not very rapidly. Practical trials conducted under northern European conditions showed the half-life for dissipation to be less than six months.
Degradation ends with complete mineralization to carbon dioxide, though binding of intermediate degradates to soil also occurs. It is important to draw a line between relatively long lasting residence time and persistence in the soil. Imidacloprid cannot be classified as being persistent as it does not accumulate. Long-term trials under worst case conditions with the repeated use of imidacloprid over several years have demonstrated that maximum concentrations in soil will reach a plateau and will decline if no further applications occur.
The translocation behaviour and particularly the leaching potential of a crop protection chemical from soil into groundwater is equivalent to its inclination for hydrophilic interactions or for interactions especially with water. Imidacloprid contains in its molecular structure substituents which cause a relatively high water solubility and a low affinity to hydrophobic structures found in ordinary organic matter. The parameters, which characterise this affinity, are the partition coefficient for the system octanol-water (Pow-value) and the soil adsorption coefficient normalised to the content of organic carbon (Koc-value). Pow and Koc-values are in a range where, translocation in soil and from soil is still negligible under ordinary conditions, but where the mobility is already sufficiently high for systemic action into the roots of plants or within plants for pest control.
Though imidacloprid is not intended to be applied directly in water, it nevertheless may enter water bodies due to spray drift or in extreme situations by runoff from treated fields after rainfall. It has been shown that no unacceptable harmful effects would occur under these circumstances as the substance will undergo complete elimination from water by photolytic reactions and by microbial activity. Though the substance is stable in sterile water in the dark, it decomposes readily under the influence of light. Biotic processes under the influence of microbes present in natural water and its sediments present another mechanism for the elimination of imidacloprid.”
The untold story (about honey bees) is that these hive losses are simply a capstone to more than a half-century of more prosaic day-to-day losses that beekeepers already faced from parasites, diseases, poor nutrition, and pesticide poisoning.
In the 1980s, two obligate parasites of honey bees were introduced into the U.S., the tracheal mite (Acarapis woodi), first found in the UK, and the varroa mite (Varroa destructor). Varroa mites are native to Asia where the host bee species, Apis cerana [sp] has evolved a resistance to them. Over time, bees in the U.S. developed natural resistance to tracheal mites, but the effects of Varroa destructor have been particularly devastating and hard to overcome. This mite lives up to its name by reducing the lifespan of adult bees, suppressing their immune system, and transmitting viruses as it sucks blood from one bee and moves on to the next (13). Untreated colonies infected with V. destructor die within 6 months to 2 years. Without treatment, 80-90% of hives in the U.S. would likely die within 2-3 years. "
A review of the incidence of CCD around the world points to three or four other factors being more likely explanations. (1) CCD has not diminished in countries where neonicotinoid insecticide use was curtailed, 6 (2) CCD is not found in Australia, where neonicotinoid insecticides are used, but where Varroa mite (a parasite and vector of bee viruses) is also not found,6 (3) 96% of colonies with CCD have been found to harbor a complex of viruses, for which Israeli Acute Paralysis Virus is most strongly implicated; and hive equipment from CCD colonies can be disinfected through irradiation, which implicates involvement of a pathogen. "
Despite the rigors of high-dose testing and the assignment of an extra FQPA safety factor, imidacloprid smells like a rose, thanks in part to its low toxicity and low potential for human exposure.
As for humans, the Material Safety Data Sheet (MSDS) for imidacloprid states, “no specific symptoms of acute overexposure are known to occur in humans” Considering the horrors on the MSDS for naturally occurring substances like acetic acid (vinegar) and sodium chloride (table salt), that’s a pretty mild statement.
Imidacloprid has several registered residential uses. Because there is no evidence of imidacloprid causing toxicity via dermal and inhalational exposure (the usual routes of exposure following home and lawn use), EPA waived consideration of adult residential exposure.
In summary, imidacloprid risk to humans seems nil even when all exposure sources are considered. Since imidacloprid poses no hazard by dermal and inhalational exposure, workers should face minimal risk as well.
Imidacloprid has the appearance of a reduced-risk pesticide with its comparatively low hazards and low exposure potential for humans and nontarget organisms.
Imidacloprid, like nicotine, is a nerve toxin that mimics the action of acetylcholine, and thereby heightens nerve firing with increasing doses. But, unlike nicotine which is extremely toxic in very small doses (smokers, beware!), imidacloprid toxicity to vertebrates is extremely low. Fortunately for mammals, birds, and fish, imidacloprid in contrast to nicotine hardly binds to their nAChRs. Insects, especially sucking bugs, however, are not so lucky. Their nervous systems are not only rich with nAChRs, but imidacloprid is particularly “sticky.” The end result is essentially an insect nervous breakdown.
The most widely used insecticide in the world, imidacloprid has been utilized for many years to control pests of agricultural crops, turfgrass, and landscape plants. Because of its low toxicity to mammals, it is also used to control fleas and ticks on pets.
Imidacloprid soil injections have been widely used in ravines of Smoky Mountain National Park and other forested areas to control hemlock woolly adelgid, an invasive insect that is devastating hemlock trees in the Appalachian Mountains. A risk assessment prepared for the USDA Forest Service (“Imidacloprid — Human Health and Ecological Risk Assessment”) concluded that these treatments pose negligible risk to aquatic organisms when applied as directed to clay or loam soils, and that even a worst-case scenario of a major spill of imidacloprid into a small pond would have negligible effects on fish, amphibians, or tolerant aquatic invertebrates. When used as directed, imidacloprid soil treatments for EAB control are unlikely to impact aquatic organisms.
There has been much concern recently about the potential role of imidacloprid and related neonicotinoid insecticides in colony collapse disorder (CCD). Research is ongoing to investigate the relative effects of pesticides, bee pathogens and parasites, and nutrition on honey bee health. To date there are no conclusive answers, but researchers have not been able to establish a link between imidacloprid and CCD. Stronger evidence implicates a combination of pathogens as well as other pesticides used in hives to control pests that afflict bees