The behavior of cyphenothrin (1) [(RS)-α-cyano-3-phenoxybenzyl (1RS)-cis-trans-2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylate] in an aquatic environment was investigated by using the 14C-labeled trans and cis isomers. In parallel with the rapid partition from water phase to bottom sediment, 1 was degraded with the first-order half-lives of 2.0 (trans-1) and 7.3 days (cis-1) in the water-sediment system under dark conditions. 1 underwent extensive microbial degradation via ester cleavage to form 3-phenoxybenzoic acid, finally forming bound residues and mineralizing to CO2. Aqueous photolysis significantly accelerated the degradation of 1 with a half-life of <1 day, mainly via photo-induced oxidation at the 2-methylprop-1-enyl group and ester cleavage without cis-trans isomerization. These results strongly suggest that 1 is unlikely to persist in the actual aquatic environment due to its rapid photolysis and extensive microbial degradation.
Keywords: biodegradation; cyphenothrin; photodegradation; soil adsorption; water-sediment.