Abstract
The persistence of the photolytically degradable pesticide fenitrothion (O,O-dimethyl-O-(3-methyl-4-nitrophenyl) phosphorothioate) in aquatic systems was examined to determine whether its t½ could be modulated by the algae Chlamydomonas segnis (Ettl). Sorption of 14C ring labelled fenitrothion into live and freeze-killed algae was monitored under lighted and darkened conditions.
In living algae held under natural sunlight (800 wmࢤ2), an optimal uptake of 9.4 ug 14C ring label mgࢤ1 algae was obtained following 3.75 hours compared to 0.7 µg 14C ring label mgࢤ1 uptake by algae maintained in the dark. Live algae maintained under Vita Lite high intensity fluorescent lamps (Dura Test, 40 wmࢤ2, 290-700 nm) sorbed fenitrothion more slowly. Optimal uptake of 16.6 µg 14C ring label mgࢤ1 algae was obtained after 24 hours compared to 0.8 µg 14C ring label mgࢤ1 algae in sets in the dark. The same phenomenon was observed with freeze-killed cells, where uptake in natural sunlight and Vita Lite® lamps was significantly enhanced (15.7 and 28.8 μg 14C ring label mgࢤ1 algae, respectively) compared to cells maintained in the dark (1.6 and 2.3 µg 14C ring label mgࢤ1 algae, respectively).
The t½ of fenitrothion in the aquatic media without algae was 30.7 hours whereas with live algae in the media the t½ decreased to 15.8 hours.
Photolytic degradation and sorption of fenitrothion were both augmented in the light exposed sets containing algae, thus significantly affecting the t½ of the fenitrothion in the water compartment.