Evaluation of a novel short-term algal toxicity assay by the development of QSARs and inter-species relationships for narcotic chemicals

A novel short term toxicity assay utilising the unicellular green alga Chlorella vulgaris is described. The test is based upon the premise that all living organisms contain nonspecific esterase enzymes, the activity of which can be assessed by the measurement of the disappearance of the ester, or appearance of the product. The novel assay described utilises fluorescein diacetate which is metabolised to fluorescein. The appearance of fluorescein, after 15 minutes exposure to the toxicant, was measured fluorimetrically. The concentration causing a 50% decrease in fluorescence, as compared to a control, was determined for 10 non-polar and 10 polar narcotics. Toxicity was related significantly to hydrophobicity for both mechanisms of action, with the QSAR for polar narcosis having a lower slope and higher intercept than that for non-polar narcosis. Significant inter-species relationships of the toxicity data with those for a 6 hour Chlorella vulgaris, and 40 hour Tetrahymena pyriformis, toxicity assay were also observed.