Friday September 4, 2026
Bay Nature —
Walk into any pet store and you’re likely to see shelves of topical products aimed at killing and repelling fleas and ticks on dogs and cats from brands such as Frontline, Advantage, and Seresto. Almost all of them contain the pesticides fipronil or imidacloprid. They are, as you might expect, toxic to invertebrates.
But they don’t stay on your furry companions.
When you wash your dog or its bedding, or pet your cat and wash your hands, the chemicals go down the drain, where they head to a wastewater treatment plant—a facility that was not designed to remove pesticides.
Studies show that fipronil and imidacloprid are ubiquitous in Bay Area wastewater effluent at levels that the EPA has deemed may be harmful to aquatic life. That means they end up in the Bay, where, scientists say, they may pose risks to invertebrates such as shrimp, amphipods, and isopods—bottom-dwelling creatures that provide important food for fish, birds, and marine mammals.
The data is worrying enough that California’s Department of Pesticide Regulation is currently considering limiting the use of fipronil. (Fipronil is also classified as a possible human carcinogen based on animal studies.) DPR plans to release possible mitigation options for public comment before October 1.