GreenScreens Show Neonic Pesticides Pose Human Health Hazards: NRDC Asking NTP for An Independent Data Review

After years of frustration with the EPA Office of Pesticide Programs (EPA-OPP) for conducting hazard assessments of pesticides that are almost totally reliant on industry-sponsored toxicity testing data, I contracted ToxServices to review the published scientific hazard data using the GreenScreen® for Safer Chemicals (GreenScreen) method. I chose the GreenScreen method because of its widespread acceptance by governments, industry, and non-governmental organizations alike. The three neonicotinoid pesticides (neonics) assessed were thiamethoxam, imidacloprid, and clothianidin.

In contrast to EPA-OPP's hazard assessment, which relied exclusively on industry-sponsored data for its hazard determinations, GreenScreen assessments include both industry-sponsored data and non-industry scientific studies from the published literature.

Beyond the established very high risks that neonics pose to aquatic and terrestrial invertebrates like bees - even EPA-OPP finally admitted harm to bees last week, years after the scientific community (Goulson et al 2015; Task Force on Systemic Pesticides 2015 report; NRDC fact sheet 2015) - the GreenScreen assessments also identified potential hazards for a number of human health endpoints. GreenScreen identified the following human health endpoints of concern: cancer, reproductive harm, developmental harm, and potential adverse endocrine disruption effects. With these high hazard scores for human health endpoints, all three neonics are classified as a Benchmark 1 chemical, which GreenScreen considers to be a chemical of high concern to be avoided.

Neonic GreenScreen comparisons.png

Note: Hazard levels (Very High (vH), High (H), Moderate (M), Low (L), Very Low (vL)) in italics reflect estimated (modeled) values, authoritative B lists, screening lists, weak analogues, and lower confidence. Hazard levels in BOLD font are used with good quality data, authoritative A lists, or strong analogues. Group II Human Health endpoints differ from Group II* Human Health endpoints in that they have four hazard scores (i.e., vH, H, M, and L) instead of three (i.e., H, M, and L), and are based on single exposures instead of repeated exposures.

For thiamethoxam, EPA dismissed evidence of cancer after receiving an industry-supplied study of a proposed mechanism that was purportedly not relevant to humans, resulting in EPA changing its original classification for thiamethoxam from "likely" to "not likely" carcinogenic in humans (EPA 2000; EPA 2012). Dr. Melnick, retired career NIEHS scientist, warned that serious public health consequences may follow if chemicals are misclassified as less toxic or non-toxic based on untested mechanistic hypotheses, poorly validated tests, or incomplete data sets. "Declaring a chemical as not hazardous, or reducing a level of health protection, should require validation, not speculation." (Melnick et al 2003).

The presence of neonics in food and water makes exposure to these pesticides unavoidable. For this reason, NRDC sent a letter to the National Toxicology Program (NTP), supporting its consideration of a hazard review of the neonicotinoid pesticides through its Office of Health Translation (OHAT) (see Federal Register notice Oct 7, 2015). This review would gather both industry and non-industry data for a robust independent assessment of the scientific evidence of potential harm to human health.

In addition to potential impacts on people and pollinators, there are data linking neonics in milkweed to adverse impacts on the iconic Monarch butterfly, whose population has declined precipitously within the past two decades. Monarchs lay all their eggs exclusively on milkweed - it is the only food source for the larvae. When ingested by the newly born larvae, milkweed makes them toxic to predators. Now data shows that neonics such as clothianidin in milkweed plants can be toxic to Monarch larvae. Sublethal effects that impede normal development of monarchs are observed even at low levels that can be found in milkweed growing adjacent to neonic-treated fields (Pecenka and Lundgren 2015).

Despite these serious risks, neonics have rocketed to the top of the list of the most widely-used insecticides, despite the EPA's inability to demonstrate their safety. Today, even as these chemicals are applied to hundreds of thousands of acres of farmland, the EPA has not issued any plan of action to cancel or even ratchet back the overuse of these toxic and long-lasting pesticides.


NRDC support letter for NTP neonic review:

Imidacloprid GreenScreen:

Thiamethoxam GreenScreen:

Clothianidin GreenScreen:

About the Authors

Jennifer Sass

Senior Scientist, Federal Toxics, Health and Food, Healthy People & Thriving Communities Program

Join Us

When you sign up you'll become a member of NRDC's Activist Network. We will keep you informed with the latest alerts and progress reports.