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The TETRATOX database is a collection of toxic potency data for more than 2,400 industrial organic compounds of which more than 1,600 have been published. The assay {Schultz, T.W. 1997. TETRATOX: Tetrahymena pyriformis population growth impairment endpoint-A surrogate for fish lethality. Toxicol. Methods 7: 289-309}is a short-term, static protocol using the common freshwater ciliate Tetrahymena pyriformis (strain GL-C). The 50% impairment growth concentration (IGC50) is the recorded endpoint.

Briefly, cultures are reared in 50 ml of a semi-defined medium in 250 ml Erlenmeyer flasks. In the TETRATOX assay, a range-finding assay followed by three replicate definitive tests is performed on each test material. Definitive test replicates consist of a minimum of five different concentrations of each test material with duplicate flasks of each concentration. Thus, a minimum of 30 data points comprises each analysis. Duplicate controls, which have no test material but were inoculated with T. pyriformis, and a blank are used to provide a measure of the acceptability of the test by indicating the suitability of the medium and test conditions, and a basis for interpreting data from other treatments. While several different time points were used over the course of more than 15 years, each was used with a medium and test condition regime to allow for 8 to 9 cell cycles in controls. Duplicate flasks are inoculated with an initial density of 2,500 cells/ml with log-growth-phase ciliates. Following 40 hours of incubation at 27 1C, population density is measured spectrophotometrically and 50% effect levels determined.

The 50% inhibitory growth concentration in mg/l (IGC50) and the 95% fiducial interval are determined for each test compound. The IGC50 is calculated by probit analysis using the percent control-normalized absorbance as the dependent variable and the toxicant concentration in mg/l as the independent variable. Both the slope and intercept of the probit regression equation is recorded as well as the Chi-squared value. The latter is an indicator of the fit of the data to the probit model. Normally the Chi-squared value is greater than 0.9.

In the majority (> 85%) of the more than 2,100 tests completed, it is possible to generate a statistically valid concentration-response curve. However, some chemicals (e.g., neutral organics with 1-octanol/water partition coefficients greater than 5.0) are not toxic at saturation; others do not attain the measured 50% effect endpoint at saturation, and still other chemicals (e.g., highly bioreactive toxicants) have a very narrow concentration-response range that precludes proper statistical analyses.

  Toxicity and chemical descriptor data for 500 aliphatic chemicals



Schultz, T.W., M. S., Ph.D.
Department of Comparative Medicine
College of Veterinary Medicine
The University of Tennessee
2407 River Dr.
Knoxville, TN 37996- 4500

Tel: 1- 865- 974- 5826
Fax: 1- 865- 974-5640

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