Biological impacts and recovery from marine disposal of metal mining waste

Abstract

Waste from coastal, metal mining operations may be disposed of in the ocean. Studies were conducted using tailings and wastewater (effluent) from a proposed gold mine that is located near Juneau, Alaska, USA. The ability of invertebrates to colonize tailings after obliteration by submarine tailings disposal (STD) was assessed through a field experiment. Trays of tailings and reference sediment were placed on the sea floor and retrieved over a 22 month period. The taxonomic composition, abundance, and biomass of invertebrates that colonized tailings and reference sediment were similar. Therefore, recolonization of invertebrates after obliteration by STD should not be inhibited by the presence of these tailings as a bottom substrate. In a laboratory study, the toxicity of effluent from the milling process was compared for early life stage fish and crustaceans. Common reference species and species that are indigenous to southern Alaska were exposed to effluent. The relationship between effluent concentration and organism response was established for immobilization, paralysis, and death. For each response, the sensitivity of the reference species bracketed that of the indigenous species. An overall ranking of species sensitivity could not be made because it depended on the response that was compared. The source of effluent toxicity was determined for one of the reference species, a crustacean. A simulated effluent was created to duplicate the ionic composition of the actual effluent. Toxicity was compared in effluent, effluent with increased salinity, simulated effluent, and solutions with adjusted concentrations of ions. Calcium was in excess in the effluent, relative to seawater, and was isolated as the source of toxicity. Sodium deficiency in the effluent, relative to seawater, reduced calcium toxicity.