The combined toxic effects of nonpolar narcotic chemicals to Pseudokirchneriella subcapitata

This paper presents the toxicity data of 10 nonpolar narcotic chemicals on Pseudokirchneriella subcapitata (green algae) assessed by a new algal toxicity testing technique conducted under air-tight environment. Based on DO production, median effective concentration (EC50) varies from 1.73 mg/L (1-octanol) to 8040 mg/L (2-propanol). The endpoint of algal growth rate reveals similar sensitivity as that from DO production. Compared to literature data, Pseudokirchneriella subcapitata and Nitrosomonas are apparently more sensitive to nonpolar narcotics than other organisms such as minnow, daphnia, and Tetrahymena pyriformis. Furthermore, good correlations between toxic effects observed from Pseudokirchneriella subcapitata and other aquatic organisms were found. Hence, algal toxicity test can be considered as a surrogate test for estimating the toxicity of nonpolar chemicals to fathead minnow, Microtox, activated sludge, Daphina magna, and Tetrahymena pyriformis. The combined effects of 13 binary mixtures of nonpolar chemicals were investigated using both additive-index method and isobologram analysis. Overall speaking, the joint actions between these chemicals are strictly additive. Model analyses indicate that these compounds act on identical reaction sites or receptors, which verify that these chemicals are of the same toxicity mechanism (narcosis).