Improved Assessment of Soil Nonextractable Residues of the Pyrethroid Insecticide Cyphenothrin.

The metabolic fate of pyrethroid insecticide cyphenothrin () [()-α-cyano-3-phenoxybenzyl (1)---2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylate] in soils was investigated using C-labeled (1)-/ isomers at the cyclopropane ring. Both isomers degraded with half-lives of 19.0-47.4 days, and 48.9-56.0% and 27.5-38.7% of the applied radioactivity (AR) were mineralized to CO and incorporated into nonextractable residues (NER), respectively, after 120 days at 20 °C. NER analyses revealed 37.5-42.2% (-) and 44.9-54.1% (-) of each residue at 30/120 days were comprised of C-amino acids (AAs) as microbial products. Assuming that 50% of microbial biomass is AAs, it was estimated that 11.3-22.9%AR (- 75.0-84.4% of NER) and 13.9-30.4%AR (- 89.8-108.2% of NER) were nonhazardous biogenic NER (bio-NER), while type I/II xenobiotic NER (xeno-NER) characterized by silylation was insignificant at 0.9-1.0%/2.8-3.3%AR (-). Detailed C-AA quantitation indicated a high relevance of the tricarboxylic acid cycle and pyruvate pathway during bio-NER formation, offering new insights into the microbial assimilation of the chrysanthemic moiety.