Background variability in whole effluent chronic toxicity test statistics for Ceriodaphnia dubia and Pimephales promelas
Conference
·
OSTI ID:31785
- Chadwick and Associates, Inc., Littleton, CO (United States)
Past studies have shown considerable variability in whole effluent toxicity tests in terms of LC{sub 50}`s and NOEC`s from reference toxicant tests. However, this approach cannot differentiate between variability in test organisms themselves from the variable response to a toxicant. A data base of control treatments in chronic WET tests was constructed allowing evaluation of mean performance of WET test organisms Ceriodaphnia dubia and Pimephales promelas not subjected to chemical stress. Surrogate test series were then constructed by randomly selecting replicates from this control data base. These surrogate test series were analyzed using standard EPA statistical procedures to determine NOEC`s for survival and both NOEC`s and IC{sub 25} for reproduction and growth. Since NOEC`s have a significance level (p) of 0.05, it follows that approximately 5% of the tests could ``fail`` simply due to chance and this was, in fact, the case for these surrogate tests. The IC{sub 25} statistic is a linear interpolation technique, with 95% confidence intervals calculated through a bootstrap method. It does not have a statistical check for significance. With the IC{sub 25} statistic, 10.5% of the Ceriodaphnia tests indicated toxicity (i.e. an IC{sub 25} of less than 1 00% ``effluent``), while this increased to 37% for fathead minnows. There appear to be fundamental flaws in the calculation of the IC{sub 25} statistic and its confidence intervals, as currently provided in EPA documentation. Until these flaws are addressed, it is recommended that this method not be used in the analysis of chronic toxicity data.
- OSTI ID:
- 31785
- Report Number(s):
- CONF-9410273--
- Country of Publication:
- United States
- Language:
- English
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