Abstract
Erosion and leaching of abandoned deposits of lead-mine tailings in southeast Missouri have resulted in the heavy metal contamination of surface waters, sediments and aquatic biota. We examined how cover materials added to stabilize tailings deposits might influence the mobilization of metals in mine tailings leachates by monitoring metal bioaccumulation and toxic effects in aquatic invertebrates (Orconectes nais, Hexagenia limbata and Chironomus riparius) exposed to leachates from test plots of tailings that had been given various cover treatments. Bioaccumulation of lead and cadmium increased significantly, and survival, growth and development were impaired in one or more invertebrate taxa during chronic (10–120 d) exposures to leachates from cover treatments of vegetation and organic mulches. Metal bioaccumulation and toxicity were greatest in a maple leaf cover treatment. Leachate from the leaf treatment had high metal concentrations because of the formation of metal/organic complexes. Lesser responses were observed in treatments of seed + fertilizer, bluegrass sod and dried sewage sludge, all of which resulted in the establishment of varying amounts of vegetative cover on the tailings. Bioaccumulation of lead, but not cadmium, was significantly correlated with the dissolved metal concentrations in the leachates. Toxic effects on invertebrate survival, growth and development were significantly correlated with the metal concentrations in leachate samples and, for lead, with body burdens in invertebrates. The results indicated that leachates from mine tailings deposits can adversely affect aquatic invertebrates, and that cover materials that release organic complexing agents can increase the mobilization of toxic metals in leachates. Vegetative cover would probably reduce future runoff and erosion from tailings deposits, but conditions similar to those in this study may favor the mobilization of metals from tailings already present in riparian habitats and stream sediments.
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