Light mediated effects of algae on the aquatic persistence of fenitrothion.

The fate and persistence of the pesticide, fenitrothion (O,O-dimethyl-O (3-methyl-4-nitrophenyl)phosphorothioate) was monitored in the presence of the alga Chlamydomonas segnis Ettl. Under natural sunlight (800 w m$\sp{-2}$) and Vita Lite$\sp{\rm R}$ high intensity fluorescent lamps (Dura Test, 50 w m$\sp{-2}$, 290-700 nm), there was 10 to 20 times the uptake of $\sp $C ring-labelled fenitrothion into live and freeze-killed algae as compared to dark conditions. The accumulated label in both the live and freeze-killed algae (with nonfunctioning electron transport systems) was identified as polar metabolites of fenitrothion, their identical percentages suggesting photophysical reactions. As a consequence of increased uptake and degradation of fenitrothion by live algae, the fenitrothion half-life in the media decreased by approximately one half in the presence of algae and light, as compared to lighted media controls. When accumulation experiments were repeated under anaerobic conditions, polar metabolites were reduced by 50%. Further, as increased pigment chlorosis correlated with increased polar metabolites, it is suggested that photooxidation of fenitrothion by singlet oxygen could have been a degradation route. Fenitrothion photolysis was accelerated by the aquatic alga, Chlamydomonas segnis