How Chlorpyrifos Breaks Down in the Environment

Chlorpyrifos is a degradable pesticide, and it undergoes breakdown in the environment as a result of biological, chemical and physical forces. In all systems (soil, water, plants and animals), the major pathway of degradation begins with cleavage of the phosphorus ester bond to yield the breakdown product trichloropyridinol (TCPy). This first step is a detoxification, as TCPy has no insecticidal activity and is considered toxicologically insignificant by regulatory authorities. In soil and water, TCPy is further degraded via microbial activity and sunlight to carbon dioxide and organic matter. In animals, TCP may be excreted directly or following conjugation (bonding with other chemicals); in plants TCP conjugates are stored.

Breakdown of Chlorpyrifos

Persistence

Because chlorpyrifos is a degradable product, it is not considered persistent in the environment. Residues of chlorpyrifos may be initially present in soil, in water or in plant foliage following application, but they decline with time as the molecule is acted upon by chemical, biological, and physical forces. The first generation of insecticide products introduced in the 1940’s and 1950’s (e.g., DDT, lindane, etc.) had a tendency to be resistant to breakdown and might last for many months or years in the environment. This long persistence led to the potential for other problems to develop (e.g., accumulation in living organisms). However, chlorpyrifos and other modern insecticide products have been designed to be degradable and their persistence is most often measured more in terms of days, weeks, or several months depending on type of environmental compartment.

Further Resources

Racke, K.D. “Environmental Fate of Chlorpyrifos.” Reviews of Environmental Contamination and Toxicology, 1993, Volume 131:1-154. http://www.ncbi.nlm.nih.gov/pubmed/7678349

Racke, K.D. et al. “Is Chlorpyrifos a Persistent Organic Pollutant?” Dow AgroSciences Issues Paper