Use of a miniaturized test system for determining acute toxicity of toxicity identification evaluation fractions

A miniaturized test system was developed and used to determine the acute toxicity of effluent fractions separated by HPLC to Daphnia magna and Pimephales promelas. The miniaturized test system consists of exposing test organisms in 1 ml of test solution using 48-well microtiter plates for the test vessels. Several factors were investigated to determine the acceptability of this test system. These factors included organism biomass to test solution ratio, toxicity of the microtiter plates to the organisms, dissolved oxygen in the test solution, partitioning of the test chemicals to the walls of the test vessels, and dilution of the test solution when the organisms are transferred. Toxicity of four reference chemicals to D. magna and P. promelas was also determined using the miniaturized test systems. It was concluded that the test system could be miniaturized and still provide results comparable to those obtained when standard U.S. EPA test procedures were used. The major benefit of using the miniaturized test system is that less solution is required for conducting a toxicity test. This becomes important when only a small amount of test solution is available, as might occur during a toxicity identification evaluation, after an effluent has been fractionated by HPLC. Other benefits include less space required to conduct a test, less time necessary to prepare test solutions, and a reduced volume of waste for disposal.