The use of biomarkers in Daphnia magna toxicity testing II. Digestive enzyme activity in Daphnia magna exposed to sublethal concentrations of cadmium, chromium and mercury

The effect of 48h and 96h exposure to sublethal concentrations of CdCl2, HgCl2 and K2Cr2O7 on the digestive enzyme activity of Daphnia magna was assessed. Five different digestive enzymes were investigated: cellulase, amylase, β-galactosidase, trypsin and esterase. Both inhibition (CdCl2 and HgCl2) and increase (K2Cr2O7) of the enzyme activities were noted after short-term (48h) exposure. No inhibition, however, was observed after prolonged exposure (96h) to HgCl2 and K2Cr2O7 and even an increase in activity was noted for CdCl2. The increased digestive enzyme activity probably reflects the test organismʹs altered food assimilation efficiency in order to cope with the reduced food uptake. The observed changes in the digestive enzyme activity were furthermore evaluated as alternative effect criteria for chronic effect concentrations. Comparison of the enzymatic effect concentrations (1 and 2 enzyme LOECʹs) with the LOECʹs obtained for chronic reproduction tests (data taken from literature) shows that the concentration where at least 1 enzyme was significantly affected after only 48h exposure, was predictive of the 21 day chronic toxicity values.