A comparison of sensitivity of spirotox biotest with standard toxicity tests

The Spirotox test utilizes a large ciliate protozoan, Spirostomum ambiguum, as a bioindicator. Two kinds of test responses were observed after 24 and 48 h of incubation: different deformations and lethal response. The toxicity of 78 organic compounds evaluated by the Spirotox-volatile procedure varied over six orders of a magnitude from -log (24-h LC(50)) = -3.0 (methanol) to 3.0 (pentachlorophenol). Deformations of the S. ambiguum were two to three times more sensitive toxic response than lethality. The sensitivity of the Spirotox test was compared to four bioassay systems used worldwide: Tetrahymena pyriformis, Microtox, Daphnia magna, and Pimephales promelas. The toxicants were sorted according to the mechanism of action. The toxicity data for both protozoa. T. pyriformis and S. ambiguum were almost identical. Microtox, D. magna, and P. promelas were in general six- to eightfold more sensitive than the 24-h LC(50) Spirotox. The best agreement of toxicity data appeared in the group of nonpolar narcotics. In contrast the toxicity data for all tests only slightly correlated for polar narcotics. Very low slope for polar narcotics indicates that the toxicity range was much broader for the Spirotox test comparing to the others. The most toxic polar narcotics were even more toxic to Spirotox than to Microtox, Daphnia, and fish.