Veterinary flea products in widespread pesticide contamination of English rivers

• The environmental impact of pesticides used in veterinary flea treatments is largely unknown. This is an analysis of potential sources of fiprole and imidacloprid pollution in 20 English rivers. 
• Seven out of 20 sites exceeded the chronic toxicity limit for Imidacloprid. 
• Sewage worksare indicated as a possible route to rivers for fiproles and imidacloprid. 
• Veterinary flea products are a potential source of pollution and ecosystem harm and a reevaluation of the environmental risks is needed. 

Perkins, R., Whitehead, M., Civil, W., & Goulson, D. (2021) Potential role of veterinary flea products in widespread pesticide contamination of English rivers. Science of The Total Environment, 755, 143560. https://doi.org/10.1016/j.scitotenv.2020.143560 

Little is known about the environmental fate or impact of pesticides used to control companion animal parasites. Using data from the Environment Agency, we examined the occurrence of fipronil, fipronil metabolites and imidacloprid in 20 English rivers from 2016 to 2018, as indicators of the potential contamination of waterways from their use as ectoparasiticides on pets. Water samples were collected by the Environment Agency as part of their chemical surveillance programme and analysed using Liquid Chromatography Mass Spectrometry / Quadrupole-Time-of-Flight Mass spectrometry (LC/Q-TOF-MS) methods. A total of 3861 chemical analyses were examined, and the significance and potential sources of this contamination were assessed. Fipronil, fipronil sulfone, fipronil sulfide (collectively known as fiproles) and imidacloprid were detected in 98.6%, 96.5%, 68.7% and 65.9% of samples, respectively. Across the river sites sampled, the mean concentrations of fipronil (17 ng/l, range <0.3–980 ng/l), and fipronil sulfone (6.5 ng/l, range <0.2–39 ng/l) were 5.3 and 38.1 times their chronic toxicity limits of 3.2 and 0.17 ng/l, respectively. Imidacloprid had a mean concentration of 31.7 ng/l (range <1–360 ng/l), which was below its chronic toxicity limit of 35 ng/l, however seven out of 20 sites exceeded that limit. Chronic risk quotients indicate a high environmental risk to aquatic ecosystems from fiproles, and a moderate risk from imidacloprid. Sites immediately downstream of wastewater treatment works had the highest levels of fipronil and imidacloprid, supporting the hypothesis that potentially significant quantities of pesticides from veterinary flea products may be entering waterways via 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 risk assessments that these products undergo prior to regulatory approval.