Science to Understand Low-Level Exposures to Neonicotinoid Pesticides, their Metabolites, and Chlorinated Byproducts in Drinking Water

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Scientists reported the discovery of three neonicotinoid pesticides in drinking water and their potential for transformation and removal during water treatment. The research provides new insights into the persistence of neonicotinoids and their potential for transformation during water treatment and distribution, while also identifying granulated activated carbon as a potentially effective management tool for decreasing neonicotinoid concentrations in finished drinking water.

Neonicotinoids are widely used insecticides for control of insects in urban and agricultural areas. These pesticides have gained popularity owing to their potency and their selective toxicity for insects, which limits acute toxicity for nontarget animals. However, because of their widespread use, neonicotinoids commonly are detected in surface waters and groundwaters and have been detected in tap water samples in Iowa and other areas of the United States.

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Neonicotinoids have been reported in treated drinking water.

(Public domain.)

Neonicotinoids break down to metabolites in the environment through microbial degradation and abiotic processes (for example, photolysis and hydrolysis). As a result, metabolites are present in surface waters, some of which are used as sources of drinking water. The U.S. Geological Survey (USGS) reported neonicotinoids in treated drinking water and demonstrated that metabolites can form from select neonicotinoids during disinfection processes where neonicotinoid metabolites and parent compounds react with chlorine, leading to potentially toxic next-generation disinfection byproducts.

University of Iowa and USGS scientists studied neonicotinoid metabolites in raw and treated drinking water samples collected from the University of Iowa and the Iowa City drinking water treatment plants after maize and soy planting. Both of these facilities use free chlorine disinfection. Tap water samples also were collected from two buildings on the University of Iowa campus and three residences in the Iowa City distribution system.

Scientist preparing for granular activated carbon experiments

Scientist preparing for granular activated carbon sorption experiments.

(Credit: Greg LeFevre. Public domain.)

Clothianidin, imidacloprid, and thiamethoxam were detected in finished water samples at concentrations ranging from 0.24 to 57.3 nanograms per liter. Samples collected along the University of Iowa treatment train indicate no apparent removal of clothianidin or imidacloprid, with modest thiamethoxam removal (about 50 percent). In contrast, the concentrations of all neonicotinoids were substantially lower in the Iowa City treatment facility water after using granular activated carbon (GAC) filtration. GAC filtration rapidly and nearly completely removed all three neonicotinoids; however, follow-up studies determined GAC filtration is less effective at removing imidacloprid metabolites than the parent compound. The scientists also determined that clothianidin is susceptible to reaction with free chlorine and may undergo at least partial transformation during chlorination.

Understanding the identity, fate, and bioactivity of transformation products generated in natural and engineered systems is critical to understanding human and wildlife exposure. This work provides new insights into the persistence of neonicotinoids and their potential for transformation during water treatment and distribution.

This study was funded by University of Iowa Center for Health Effects of Environmental Contamination (Grant 18018213 BR05); a National Science Foundation Graduate Research Fellowship; and the USGS Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology), which is part of the USGS Ecosystems Mission Area.