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Abstract
A short-term, static protocol using the common freshwater ciliate Tetrahymena pyriformis (strain GL-C) is reported. The 50% impairment growth concentration (IGC 50) is the endpoint of choice. Cultures are reared in 50 mL of a semi defined medium in 250-mL Erlenmeyer flasks. Definitive test replicates consist of a minimum of 5 different concentrations of each test material. Duplicate flasks are inoculated to an initial density of 2500 cells/ mL with log-growthphase ciliates. Following 40 h of incubation at 27 1 C, population density is measured spectrophotometrically and 50% effect levels are determined. Toxicity data for 250 chemicals representing several mechanisms of toxic action are reported and compared to fish toxicity data. As demonstrated by the relationship, log (IGC50-1) =0.77 log (LC50-1) - 0.40; r 2 =.750; s =.546; F =744, there is favorable similarity in toxic potency between T. pyriformis (log \[IGC50-1]) and fish, Pimephales promelas, survivability (log \[LC50-1]). However, toxicokinetics and/or toxicodynamic differences between the two systems result in either potency or mechanism of action variances for several chemical classes.