This study was conducted to determine long-term toxic effects, on selected species of fish and invertebrates, of mine depressurization at concentrations non-lethal in acute toxicity tests. The study also includes chronic toxicity experiments, studies of sublethal effects of groundwater, and a literature review. The results of groundwater monitoring indicate that during 6 mo of storage, there was a decline in concentration of almost all chemical parameters tested. However, in contrast to previous studies, some heavy metals (iron, lead, nickel, and zinc) showed an increase in concentration with storage time. Mine depressurization groundwater was acutely toxic to the three species of invertebrates tested. The 96 h LCso for the two mayfly species, Caenis simulans and ParaZeptophZebia cornuta, was 68.75 and 64.28%, respectively. The 96 h LC so for the amphipod, Hyalella azteca, was 50%. Results of chronic toxicity tests for the three invertebrates species indicated that percent survivorship was highest in control and 3% groundwater concentrations. The mine depressurization groundwater had an inhibitor effect on the larval growth and emergence of the two mayfly species tested. The result was less obvious in the experiment with H. azteca. Cannibalism appeared to be an important factor contributing to higher mortalities in amphipods. The salinity of mine depressurization groundwater affected the osmoregulatory function of the two mayfly species. Chloride cell density was of some predictive value in determining osmoregulatory stress in the test animals. Accumulation of both Cu and Zn occurred in tissues of Caenis and Hyalella, particularly after chronic exposure to the higher concentrations of groundwater.
The 90 d LC50 was 8.5 to 9% for rainbow trout, 13.2% for lake chub, and 5.8% for white suckers. Initial exposure to sublethal levels of groundwater caused significant elevation of operculate pumping frequency and coughing rate. Significant depression of opercular pumping frequency occurred during chronic exposure. Measurement of both operculate pumping and coughing rates might constitute a practical biomonitoring method because of the speed of response and ease of measurement. A 1 h exposure to mine depressurization water was toxic to fertilized lake whitefish eggs at concentrations as low as 10%. Mortality increased with time.
The review of the literature available on the components and effects of mine depressurization groundwater is presented. The review includes sections on chemical properties of groundwater, the effects of storage on groundwater, acute toxicity studies done using groundwater, studies of sublethal effects of groundwater, and a summary of work done on individual components (heavy metals, cations, and anions) commonly found in groundwater. Because more data are available on the acute toxicity of mine depressurization groundwater, the determination of tolerance limits should be made with greater reliance on this test. Information from other sources should be used to verify decisions derived from acute toxicity data.