Use of whole body sodium loss from the fathead minnow (Pimephales promelas) as an indicator of acid and metal toxicity.

The use of an easily measured physiological change as a method of detecting the effect of toxic mine effluent (acidity, heavy metals) on a standard aquatic test organism was examined. Changes in whole body sodium concentration of Pimephales promelas after exposure for eight hours to mine water in the field were assessed as a physiological indicator of acid and metal pollution from coal mines. Static 96-h lethality tests were also performed in the laboratory in water collected from severely acidic (pH 3.49), moderately acidic (pH 4.65) and circumneutral (pH 6.25) mine effluent impacted streams as well as an artificially prepared (reconstituted) water (RMW) at three similar pH's (but lacking potentially toxic metals). This allowed comparison of the two assays in their sensitivity and ability to detect interactions between heavy metals and acidity. Exposure of P. promelas to severely acidic mine water caused the same mortality as exposure to RMW, although in the latter the fish died more rapidly (2 vs. 3 h); moderately acidic water was more toxic than RMW lacking metals. No mortality was observed in circumneutral mine water or corresponding RMW. Toxicity as estimated by changes in whole body sodium levels of P. promelas followed a pattern similar to toxicity as determined by the 96-h lethality tests. Exposures of P. promelas to moderately acidic mine water at two pHs and trace metals concentrations resulted in significantly different body sodium concentrations and net sodium efflux between groups of fish within six hours. The results suggest that the whole body sodium assay is a useful indicator of coal mine pollution.