Researchers have discovered the presence of neonicotinoid insecticides in samples of finished tap water, marking the first such peer-reviewed study in the nation. The study’s announcement comes on the heels of a Gallup poll published in April which revealed Americans are more concerned about water pollution today than they’ve been in the past 16 years.

The study was published in Environmental Science & Technology Letters in March. Scientists from the University of Iowa and U.S. Geological Survey found traces of clothianidin, imidacloprid and thiamethoxam in drinking water samples processed by two water treatment facilities — one in Iowa City and the other serving the University of Iowa.

The concentration of neonicotinoids was lower at the Iowa City treatment plant, and the researchers posited that the differences in filtration processes between the plants were responsible for the variance.

The university’s water is sourced from the Iowa River and its treatment plant uses screening, chemical pretreatment, sedimentation, lime softening, recarbonation, chlorination and sand filtration for treatment. Meanwhile, the city gets water from alluvial wells fed by the Iowa River and treats it with aeration, lime softening, recarbonation, chlorination and granular activated carbon (GAC) filtration.

It’s likely, according to the study’s authors, that the city’s GAC filtration process is superior at removing incescticides.

“Decreases in neonicotinoid concentrations appeared to be greater at the city’s drinking water treatment plant than at the University of Iowa’s drinking water treatment plant,” the study reads. “A notable distinction is that the city’s plant uses GAC filtration compared to rapid sand filtration at the university’s plant; the latter process removes only particles.”

While neonicotinoid insecticides are ubiquitous in surface water throughout the Midwest due to agriculture, this study marks the first instance they’ve been detected in treated tap water. Scientists took intermittent samples of tap water at the university over seven weeks last year from May to July, finding insecticide concentrations between 0.24 and 57.3 ng/L, which is consistent with the levels other studies have found in Iowa’s environment. Those samples did find around 50 percent removal of thiamethoxam, but evidently no removal of clothianidin or imidacloprid.

The levels of all three insecticides were significantly lower in the city, and the researchers used batch experiments to examine that phenomenon. “Thiamethoxam losses are due to base-catalyzed hydrolysis under high-pH conditions during lime softening,” reads the study. “GAC rapidly and nearly completely removed all three neonicotinoids. Clothianidin is susceptible to reaction with free chlorine and may undergo at least partial transformation during chlorination.”

The study concludes there’s a good chance that neonicotinoids are polluting other drinking water systems in the country: 

“Because of their pervasiveness in source waters and persistence through treatment systems, neonicotinoids are likely present in other drinking water systems across the United States. Transformation products formed by chlorination or hydrolysis warrant great consideration because of the potential to form toxic transformation products. For example, the metabolite desnitro-imidacloprid exhibits a mammalian receptor binding affinity 300 times greater than that of imidacloprid because of the loss of the nitro group that confers insect specificity. For management, GAC filtration presents a treatment option for removal of neonicotinoids in resource-constrained communities that rely of agriculturally impacted surface waters or point-of-use systems that is substantially more economical than reverse osmosis or advanced oxidation processes.”

About neonicotinoids

Neonicotinoids are one of the most popular pesticides used by farmers nationwide, and are considered difficult to treat in conventional water treatment processes, according to a press release from the Bluewater Group.

With a chemical structure similar to that of nicotine, neonicotinoids have been blamed alongside habitat loss and disease for a decline in honeybee populations. The pesticides have also been found in insects, microbes and coastal shellfish, prompting several countries in Europe and some U.S. states to restrict their use.