Improved Assessment of Soil Nonextractable Residues of the Pyrethroid Insecticide Cyphenothrin

The metabolic fate of pyrethroid insecticide cyphenothrin ( 1 ) [( RS )-α-cyano-3-phenoxybenzyl (1 RS )- cis - trans -2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylate] in soils was investigated using 14 C-labeled (1 R )- cis / trans 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 2 and incorporated into nonextractable residues (NER), respectively, after 120 days at 20 °C. NER analyses revealed 37.5–42.2% ( cis - 1 ) and 44.9–54.1% ( trans - 1 ) of each residue at 30/120 days were comprised of 14 C-amino acids (AAs) as microbial products. Assuming that 50% of microbial biomass is AAs, it was estimated that 11.3–22.9%AR ( cis - 1, 75.0–84.4% of NER) and 13.9–30.4%AR ( trans - 1, 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 ( cis - 1 ). Detailed 14 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.