AN ATTEMPT TO USE THE Daphnia magna - ACUTE TOXICITY ASSAY FOR PREDICTING ENZYME ALTERATION INDUCED BY HEAVY METALS AND PESTICIDES

In acute toxicity bioassay of some heavy metals and pesticides against Daphnia magna-juveniles, the estimated 24 h-LC50 values for Cu, Cd and Pb were 0.0002, 0.25 and 0.41 mg/L, respectively. The 24 h-LC50 values of 0.0027, 0.0093 and 0.014 mg/L were obtained for Chlorpyrifos-methyl, Triazophos and Profenofos, respectively. The established regression lines were used to estimate LC25, LC50 and LC75 values for each tested toxicants. Batches of juvenile daphnids were exposed to these concentrations for 24h, and then the survived daphnids were counted, weighted and subjected to some biochemical determinations, such as superoxide dismutase (SOD), lipid peroxidation in terms of malondialdehyde (MDA), total antioxidant capacity (TAC) and cholinesterase (ChE). Compared to control values, SOD and ChE showed high significant decrease, while MDA and TAC showed the opposite trend, and in all cases the observed alterations were occurred in a dose-dependent manner. At LC50 values of the tested toxicants, alteration in SOD level ranged between (-18.12%) and (- 45.39%); 20.68% - 31.32% for MDA; 717.00% - 1283.02% for TAC; and between (-12.30 %) and (-28.33%) for ChE. In conclusion, the established “curves” from plotting LC values versus enzyme level could be suggested as a “reference” for predicting the enzyme level of a given toxicity value (e.g., LC50) by extrapolation, without need to repeat conducting of enzymatic assay. However, such suggestion may be better to subject it for further validation.