Examination of procedures for acute toxicity tests with the fathead minnow and coal synfuel blends

Static and flow-through procedures were examined for conducting acute toxicity tests with the fathead minnow, Pimephales promelas Raf., and water-soluble fractions of a liquid synfuel blend derived from coal. Static conditions were characterized by declines in levels of dissolved oxygen (DO) and total dye-complexable phenolics over the 96-hr test period. Renewal of exposure solutions each 12 or 24 hr retarded, but did not prevent, dissolved oxygen and phenolic declines and periodic disturbance of fish caused stress. Flow-through test conditions, particularly 9.0 volumetric turnovers daily, provided suitably stable levels of DO and phenolics. Mortality reached or exceeded 50% when fish were exposed to about 8.6-8.9 mg l-1 total phenolics during static or renewal tests, but was less than 25% under flow-through conditions. Microorganism development in static solutions was primarily responsible for declines in DO and phenolic levels. Differences in fish mortality between static and flow-through tests suggested the latter was most useful for evaluating toxicity of aqueous extracts from liquified coals. Results of laboratory tests, however, may not accurately portray field conditions where biodegradation or other environmental interactions occur.