PHOTOSYNTHETIC AND POPULATION-GROWTH RESPONSE OF THE TEST ALGA SELENASTRUM-CAPRICORNUTUM PRINTZ TO ZINC, CADMIUM AND SUSPENDED SEDIMENT ELUTRIATES

Short-term C-14-fixation (4 h) Selenastrum capricornutum algal toxicit y tests were conducted with Cd (n = 8), Zn (n = 9) and suspended sedim ent aqueous elutriates (n = 28) and the results were compared to those obtained in a 48 h population growth test. In order to provide more r ealistic experimental conditions, toxicity tests were carried out in p refiltered nutrient-spiked Lake Geneva water. The population growth in hibition test was significantly more sensitive than the C-14-fixation test for Cd (median EC50-4h and EC50-48h values of 600 and 118 mu g L- 1, respectively) whereas no significant difference was measured for Zn toxicity (median EC50-4h and EC50-48h values of 97 and 96 mu g L-1, r espectively). With suspended sediment aqueous elutriates, the relative sensitivity of the two different end points is sample dependent, with ratios of the EC25 for the C-14-fixation: population growth test rang ing from < 0.26 to > 53.3. Elutriate toxicity shows no apparent relati onship between the acute and chronic test, indicating that population growth inhibition cannot be derived directly or predicted from C-14-fi xation. Both tests with their specific advantages and limitations prov ide valuable complementary information to measure the impact of single toxicants or complex mixtures on aquatic plants.