Laboratory Investigation on the Effects of Conductivity on the Sensitive Early Life Stages of Fishes from the Appalachian Region

While it is known there is a link between land disturbance and elevations in ionic constituents in streams, the relationship between elevated conductivity and aquatic taxa impairment is harder to define. Multiple field studies demonstrating correlations between conductivity and fish or benthic macroinvertebrate communities have not described the mechanisms of impairment and impairment has not been demonstrated with traditional toxicity testing. In an effort to explore more sensitive sub-lethal endpoints for evaluation of instream effects of mining effluent, chronic toxicity testing was conducted on eggs and early life stages of trout species and the fathead minnow, utilizing a simulated mining discharge with elevated conductivity. Chronic toxicity testing conducted with the native taxa and sub-lethal endpoints were utilized to evaluate the relationship between conductivity and organism fitness without the variability associated with field studies. Embryo-larval and standard chronic larval toxicity testing was conducted on sensitive life stages of brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) using a high sulfate synthetic mine effluent. Testing was also conducted using the standard test organism, fathead minnows (Pimephales promelas). Comparison of the response between taxa and between life stages of individual taxa were made. Conductivities ranged from 100-2400 µS/cm in the exposures with mortality and teratogenesis being the endpoints in embryo-larval testing. Embryo exposures were initiated at fertilization in the fathead minnow tests and at 3 days old for rainbow trout, with both having EC50s greater than 2400 µS/cm. Generally, there was little sensitivity in the embryo or larval exposures with endpoints consistently \u3e2400 µS/cm. Estimated effect concentrations (IC20s) were variable between the species and the life stages indicating that not only are the tolerance levels of each species different, but the tolerance of the life stages of each species is also variable