Both laboratory studies and extensive field studies have shown that chlorpyrifos breaks down quickly in water. In laboratory studies, chlorpyrifos was added to pure water with a neutral pH factor. As with soil, chlorpyrifos’ half-life was about a month — with water and light (photolysis) contributing to its detoxification and breakdown. And, as with soil, more alkaline conditions resulted in faster breakdown — half-life was around two weeks.
In field studies, where samples of natural water from streams and canals were analyzed, chlorpyrifos often broke down significantly faster than in the laboratory — as much as 16 times faster. In fact, half-lives in the water of less than one day are typical, due to a combination of breakdown by microbes and plants, evaporation, and bonding with organic matter and sediments.
Racke, K.D. “Environmental Fate of Chlorpyrifos.” Reviews of Environmental Contamination and Toxicology, 1993, Volume 131:1-154.
Giddings, J.M. et al. “Fate of chlorpyrifos in outdoor pond microcosms and effects on growth and survival of bluegill sunfish.” Environmental Toxicology and Chemistry, 1997, Volume 16(11): 2353–2362.