Chemosensory responses of ciliates: A sensitive end point in xenobiotic hazard assessment

It is known that ciliates exhibit chemosensory behavior. An assay implementing this response was performed with Tetrahymena thermophila, a well-studied representative of the ciliates. A concentration-dependent avoiding reaction was observed for all substances of the test battery, comprising a heterogeneous set of 43 compounds from the European Inventory of Existing Chemicals. Comparisons were made between toxic data from this chemosensory test and chemical concentrations leading to effects on Tetrahymena growth, and EC values from recommended aquatic toxicity tests. Low correlation coefficients indicate that the chemosensory response reflects chemical interactions, which cannot be adequately explained by these other tests. The chemosensory assay proved to be more sensitive in the majority of cases than the Tetrahymena growth test and standard tests with fish and Daphnia. Tetrahymena is able to recognize and avoid about half the substances at concentrations lower than those effective in the algae growth inhibition test. The behavioral response of Tetrahymena could provide further lexicological information and serve as a complementary sublethal end point for ecotoxicological screening purposes. © 1994 by John Wiley & Sons, Inc..