A brief review of the environmental fate and metabolism of pyrethroids

Pyrethroids are a class of lipophilic insecticide very easily degraded in the natural environment. The two main routes of degradation, photo‐ and biodegradation, are often superimposed. Pyrethroids developed for use in agriculture are much more photostable than the natural pyrethrins or early synthetic derivatives but they are still sensitive to sunlight, which triggers many alterations such as isomerisation or ester cleavage. The basic pathways of pyrethroid metabolism include hydrolysis of the central ester linkage and oxidation of both acid and alcohol moieties. The rate of these metabolic transformations and the nature of the metabolites depend mainly on the organism involved. Birds and mammals metabolise and excrete more rapidly than insects and fishes. In plants, initial metabolic processes are identical to those known in animals. In soil, pyrethroids undergo the same type of transformation, hydrolysis and oxidation. Neither degradation products nor intact parent compounds are leached.