08
Feb
Drinking Water Contaminated with Neonicotinoid Insecticide Byproducts
(Beyond Pesticides, February 8, 2019) Scientists from the U.S. Geological Survey (USGS) and the University of Iowa (UI) have published worrisome news on the neonicotinoid front. The experts discovered two metabolites of imidacloprid (a neonicotinoid insecticide) residues that had not previously been identified in drinking water — desnitro-imidacloprid and imidacloprid-urea. The researchers note both that these metabolites have never been evaluated for their potential risks to human and environmental health, and that there may be potential risks of anthropogenic compounds that can be created when water with neonicotinoid residues, and thus, these metabolites, undergo typical water treatment (often chlorination and/or pH treatment). They note that, “The mammalian toxicity of transformation products formed during water treatment processes remains unknown. It is possible that chlorination of neonicotinoids and their metabolites will . . . alter their bioactivity.”
The joint, federally funded collaboration investigated neonicotinoid pesticides (“neonics”) in tap water to determine whether neonic metabolites are relevant to pesticide exposure through drinking water, and to identify any products of the chlorination of neonics and their metabolites. The scientists simulated realistic drinking water conditions in their research to demonstrate, in laboratory circumstances, that chlorinated disinfection byproduct chemicals are produced. The study, conducted by seven researchers and titled “Chlorinated Byproducts of Neonicotinoids and Their Metabolites: An Unrecognized Human Exposure Potential?” was published in Environmental Science & Technology Letters in mid-January 2019.
Because neonicotinoids are the most widely used category of insecticide, residues are commonly found on surface waters, from which drinking water is not infrequently sourced. Previous work by this group of researchers (by Klarich, K.L., et al., published in 20179 in Environmental Science & Technology Letters) and a Canadian study — by Sultana, T., et al., and published in the journal Chemosphere in 2018 — found the presence of neonic residues in drinking water.
The metabolites of neonics are generated in the environment in microbial breakdown processes and some abiotic processes (photolysis and hydrolysis). Given the ubiquity of these compounds, it is unsurprising that they would now be identified in drinking water. There is additional concern that — because metabolites, such as desnitro-imidacloprid and descyano-thiacloprid, are more than 300 and nearly 200 times more toxic to mammals, respectively, than imidacloprid — even very low levels of exposure may carry risk of harm.
The experts from USGS and UI also warn that these metabolites may morph further into new forms of chlorinated disinfection byproducts (DBPs) during routine water treatment (chlorination) processes. These DBPs have never been tracked or tested and may represent risks to human health. (Other kinds of DBPs in drinking water are highly toxic.) The study authors note increased concern that the DBPs of such metabolites may exhibit enhanced bioactivity — e.g., carcinogenicity and/or genotoxicity. The Results and Discussion section of the published research states: “The greater potential toxicity and the frequent presence in these [subject] water samples of neonicotinoid metabolites demonstrate the need to consider their fate and persistence in drinking water treatment systems (e.g., during chlorination and other treatment processes) and their potential effects on human health. Indeed, neonicotinoids have been measured year-round in streams of impacted watersheds, and our results demonstrate that consumers of drinking water derived from vulnerable sources may be exposed to neonicotinoids and their metabolites.”
The presence of neonics in drinking water is concerning per se, because federal regulators have never addressed what might be “safe” levels of such insecticides in tap water, but the potential harms related to the presence of neonic metabolites in drinking water raises worry to another level. Neonicotinoids are the most widely used category of insecticides, posing both acute and chronic risks for aquatic life and birds; the toxicity of DBPs is unknown, though it may actually be greater than that of the neonic itself. Neonics are poorly regulated by the Environmental Protection Agency (EPA) and other regulators: their toxicity, which was assumed by EPA to be confined to target insects, is actually devastating for beneficial insects (bees and other pollinators), and for aquatic invertebrate species. Neonicotinoids have been linked with neurological effects and with autism-like impacts on children who were exposed prenatally.
In part in response to this emerging research, the Natural Resources Defense Council is asking EPA to include all neonic metabolites and DBPs in its human health risk assessment of the neonic pesticides, due later in 2019. The organization adds that “In addition to including all relevant neonic metabolites in its risk assessment, EPA should also assess the cumulative risks from all the neonic pesticides and their toxic metabolites together. It is alarming that EPA seems to have no plan for conducting a cumulative risk assessment for this toxic and persistent class of pesticides.”
Neonicotinoids are a real problem, certainly for pollinators and other insects, birds, fish, invertebrates, and amphibians, but also, for humans. Because more than 90% of neonicotinoids are used to coat seeds, and thus, represent a huge vector for spread of the insecticide and associated risks, a shift away from this practice is critical. (See Beyond Pesticides’ resource page for growers and gardeners — Companies that Grow and Distribute Organic Seeds and Plants.) There are far-less-toxic ways to deal with pest issues; see Beyond Pesticides’ Managing Pests Safely Without Neonicotinoids, and its advocacy for organic farming practices, which reduce and/or obviate the need for such insecticides, herbicides, and fungicides.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources: https://www.nrdc.org/experts/jennifer-sass/neonic-pesticide-may-become-more-toxic-tap-water and https://pubs.acs.org/doi/abs/10.1021/acs.estlett.8b00706?journalCode=estlcu&
