COMPARISON OF DIFFERENT METHODS FOR QUANTITATIVE TOXICITY MEASUREMENTS ON NATURAL-WATERS USING S-CAPRICORNUTUM

Toxicity, in terms of growth inhibition of the green alga Selenastrum capricornutum, was measured on a series of 26 river water samples taken over a period of 19 months. The aim was to verify if the measured effect was influenced by nutrient enrichment, and by the subsequent biomass increase. For each sample, the three values of percent inhibition measured on the untreated sample, on the enriched sample and on the additional yield due to enrichment were calculated. Significant differences were observed between these three sets of data. The relationship between the measured values was expressed mathematically by means of an equation correlating their differences. The biological explanation of the difference between the responses of the enriched samples and the unenriched ones lies in the fact that a drop in toxicity seems to correspond to the increase in biomass which occurs in the enriched sample.