Variation in acute toxicity between technical grade and commercial formulation of cypermethrin to some non-target freshwater organisms

Static bioassays were conducted in laboratory to evaluate variation in acute toxicity between technical grade (92 % a.i) and commercial formulation (10 % EC) of cypermethrin to four freshwater organisms viz. the crustacean Cyclops viridis, the oligochaete worm Branchiura sowerbyi, the gastropod Pila globosa, and one week old tadpole larva of the toad Duttaphrynus melanostictus. Commercial formulation (F) of cypermethrin was found more toxic than the technical (T) grade cypermethrin. Based on 96h LC50 values of T and F cypermethrin C. viridis was found most sensitive (0.08 and 0.04 μg/L) and P. globosa as most tolerant (1416 and 545 μg/L) to cypermethrin. Toxicity of T cypermethrin in water existed up to 48h except for C. viridis and B. sowerbyi, in which toxicity existed till 72h exposure. Toxicity of F cypermethrin existed till 96h in all species except C. viridis in which F cypermethrin became non-toxic after 72h. It was concluded from this study that acute toxicity of cypermethrin to aquatic organisms varied with the formulation and 10% EC of cypermethrin remained viable in freshwater aquatic ecosystem for longer period.