Due to the increased emphasis on the use of aquatic toxicity tests to evaluate the quality of complex effluents, there is a need to objectively evaluate the precision of effluent toxicity test methods. Based upon an extensive search of the published and unpublished literature (available through April 1985), the intralaboratory and interlaboratory precision of effluent toxicity test methods was evaluated. Most of the inter- and intralaboratory studies obtained address the acute toxicity of effluents to three standard test organisms: Daphnia spp. (water fleas); Salmo gairdneri (rainbow trout); and the marine bacterium Photobacterium phosphoreum (Microtox). Only limited data exist for Pimephales promelas (fathead minnows); Mysidopsis bahia (opposum shrimp); and Cyprinodon variegatus (sheepshead minnows). Based on LC50 or EC50 values for 141 effluents for which interlaboratory data were available, 81.6% had coefficients of variation ≤40%, and 74.5% had coefficients of variation ≤30%. For 46 effluents for which intralaboratory data were available, 89.2% had coefficients of variation ≤40%, and 89.2% also had coefficients of variation ≤30%. To put this variability in perspective, coefficients of variation for these replicated toxicity tests with effluents are compared to published precision estimates for analytical chemistry methods.

A new field of analysis has arisen for the evaluation of wastewater samples in response to forthcoming regulations. Instead of using current methodology to determine if target compounds are present in environmental water samples (for example, priority pollutant analysis), Monsanto's Environmental Sciences Center (ESC) has developed a scheme to identify compounds that are either toxic to aquatic organisms or major sources of total organic carbon in wastewaters. This procedure may be necessary with the upcoming toxicity reduction evaluation (TRE) program sponsored by the United States Environmental Protection Agency (USEPA). The ESC scheme uses simple column chromatography techniques to initially fractionate the wastewater into separate inorganic and organic constituents. Each fraction is evaluated for toxicity to a common test organism, Daphnia magna. The fraction containing the toxicity is then analyzed to identify the sources of toxicity. Several case studies are presented to show how the ESC fractionation and chemical analysis scheme has been used to isolate and identify the factors responsible for wastewater toxicity.