April 01, 2021

A research group recently found dangerous levels of insecticides in English rivers and determined flea control products are likely to blame.

The study joins works published in the U.S. and worldwide on environmental contamination with fipronil, fipronil degradates, and imidacloprid, often linking the contamination with flea and tick products applied to pets and passed through sewers. The studies apply to topical products rather than those administered orally.

An article published Feb. 10 in Science of the Total Environment indicates water samples collected by the U.K. Environment Agency from 20 English rivers almost always contained fipronil and usually contained imidacloprid, both neurotoxic pesticides. The authors, from the University of Sussex, analyzed agency data and found that the mean fipronil concentration was five times the chronic toxicity limit.

While the mean imidacloprid concentration was below its chronic toxicity limit, seven of the 20 rivers had concentrations above the limit.

The samples with the highest concentrations of each chemical came from just downstream of wastewater treatment facilities, and the authors said that finding supports their contention that the chemicals originate from veterinary-use flea control products that wash down household drains.

“These findings suggest the need for a reevaluation of the environmental risks associated with the use of companion animal parasiticide products, and the environmental impact assessments that these products undergo prior to regulatory approval,” the article states. “Reappraisal of current ectoparasite management protocols may also be warranted.”

Studies in United States find link between pet products, pollution

A team from Arizona State University found that fiproles (fipronil and its degradates) were ubiquitous in water samples collected from 2001-16 by the U.S. Environmental Protection Agency. Samples collected from the effluent of 12 wastewater treatment facilities in 2015-16 also contained these compounds at concentrations dangerous for chronically exposed aquatic invertebrates.

The researchers, from Arizona State’s Biodesign Center for Environmental Health Engineering and School of Sustainable Engineering and the Built Environment, described those findings in the February 2019 issue of Water Research.

The Water Research article notes that prior studies suggest fiproles are toxic to aquatic invertebrates and pollinators in parts-per-trillion concentrations and the degradates have half-lives of up to several hundred days. The authors called for further investigation and regulation of nonagricultural fipronil uses, “particularly spot-on treatment for flea and tick control on domestic animals.”

In another study, a California-based research team washed dogs either two, seven, or 28 days after application of a fipronil product and detected fipronil and fipronil sulfone in all samples. They published those findings in 2017 in Science of the Total Environment.

Twenty-eight days after application, the team found fiproles could be dislodged and washed down the drain at a magnitude of milligrams per dog.

“Measurements of dislodgeable pesticide residues during routine bathing confirm spot-on fipronil treatments contribute a substantial mass fraction of total fipronil loading to the wastewater catchment,” the article states.

If groomers and pet owners washed 25% of treated dogs within a week of application, that would account for the entire fiprole load found in sewers—based on measurements from water treatment plants in Northern California, the article states.

Jennifer Teerlink, PhD, environmental program manager for the Surface Water Protection Program at the California Department of Pesticide Regulation and lead author of the 2017 article on fipronil washed off of dogs, said she expects other sources—such as water used to wash clothing or pet bedding—also contribute fipronil to waterways but in lower concentrations. She said the study didn’t examine how often dogs are bathed, and she thinks it would be good to examine data from professional groomers in particular.

Dr. Teerlink said she and her colleagues in the Surface Water Protection Program continue studying the sources and concentrations of pesticides in wastewater, mostly imidacloprid, fipronil, and pyrethroids. That work includes modeling what proportion of fipronil that reaches aquatic environments comes from wastewater.

Pesticide concentrations in waterways have already raised enough ecological concerns to prompt changes in how some products are used. In 2017, the state changed the registrations of fipronil-containing sprays used outside of buildings to keep out ants or termites. In doing so, the state prohibited application during the November through February rainy season, decreased the maximum concentrations and width of sprays outside buildings, and prohibited applications to some impervious surfaces linked with runoff.

No fipronil-containing products are registered for agricultural use in California, Dr. Teerlink said. The Arizona State team separately found no links between fiprole concentrations and agricultural fipronil use.

Kelly D. Moran, PhD, senior scientist for the San Francisco Estuary Institute, co-authored a 2016 article, published in Environmental Toxicology and Chemistry, that indicates most of the fipronil and imidacloprid that enters sewage treatment plants passes through them into surface waters, and flea and tick products likely were the primary sources in sewage. The team found stunning consistency of contamination per capita, she said. Dr. Teerlink was among the authors of that paper as well.

Dr. Moran also has worked as a consultant on wastewater treatment, and she has found that fipronil and imidacloprid concentrations in wastewater could hamper efforts by some cities to perform the purification needed to recycle wastewater into drinking water. Disposing of waste from that process becomes more difficult with higher pesticide concentrations, she said.

Pesticides endanger ecosystem health

U.S. Geological Survey and EPA researchers, in an article published in May 2017 in Environmental Science and Technology, indicated fipronil and imidacloprid were among the pesticides endangering aquatic life in 38 streams across the U.S., as shown through analysis of samples collected November 2012-June 2014. The researchers tested the samples for human-source organic contaminants—especially pesticides, antimicrobials, pharmaceuticals, and degradates of those substances—and found 389.

“Invertebrates comprise most animal biomass in aquatic ecosystems and the current results suggest substantial potential for adverse contaminant impacts,” the article states. “For example, the phenylpyrazole insecticide, fipronil, blocks GABA-gated chloride channels of insect central nervous systems leading to reduced reproduction and survival and at least two fipronil degradates (sulfide, sulfone) are reported to be more toxic to sensitive aquatic invertebrates than the parent compound.”

One fipronil degradate, desulfinylfipronil, was the most frequently detected contaminant, occurring at 32 of 38 stream sites. The researchers found at least two fipronil-related compounds at 19 sites and imidacloprid at 37%.

EPA officials are reviewing the approved uses of fipronil through a program that reevaluates all registered pesticides at least once every 15 years, and, in May 2020, EPA officials issued a draft risk assessment that noted concentrations of fipronil and fipronil degradates found in wastewater treatment plant effluent, according to a statement provided by an EPA spokesperson.

“If EPA determines there are urgent human or environmental risks from pesticide exposures that require prompt attention, the Agency will take appropriate regulatory action, regardless of the registration review status of the pesticide,” the statement says.