EVALUATION OF A DAPHNIA-MAGNA RENEWAL LIFE-CYCLE TEST METHOD WITH DIAZINON

Acute and chronic toxicity tests with diazinon (diethyl 2-isopropyl-6- methyl-4-pyrimidinyl phosphorothionate) were conducted on Daphnia magn a. The 24-hr static LC50 was 0.86 mu L.L-1. The sublethal effects of 0 .05, 0.1, 0.5, 0.75 and 1.0 ngL(-1) of diazinon concentrations on the survival, reproduction and growth of D. magna were monitored for 21 da ys. The algae Nannochloris oculata (5 x 10(5) cellsmL(-1)) was used to feed the daphnids. The parameters used to determined the effect of th e pesticide on D. magna were: mean total young per female, mean brood size; days to first brood; intrinsic rate of natural increase (r); gro wth; and survival. Reproduction as well as survival was significantly reduced at diazinon concentrations of 0.10 ngL(-1) and higher. The int rinsic rate of natural increase (r) decreased with increasing concentr ations of diazinon. Growth, as measured by body length, was depressed significantly at 0.05 ngL(-1) of diazinon and higher concentrations. T he maximum acceptable toxicant concentration (MATC) was calculated. Th e chronic data was used to formulate an acute/chronic ratio.