Investigation of Cause for MMER Using Hyalella azteca: Results from the Birchtree Mine
CIM Montreal 2011
Malcolm Stephenson, Dave McDonald,
The Metal Mining Effluent Regulations require operating mines to conduct environmental effects monitoring (EEM) programs to assess the effects of effluent discharges on the aquatic environment. Successive phases of study identify first, if there is an effect on fish and fish habitat (benthic invertebrates), next, the geographic extent of any effects, and then an investigation of the cause of the effect.
We discuss results of successive phases of EEM studies at the Birchtree Mine, a Vale Inco nickel mine in Thompson, Manitoba. At this mine, effects on benthic invertebrate community structure were identified in two successive cycles. A relatively simple procedure for investigation of cause was developed using a small amphipod (Hyalella azteca) known to be less abundant in the exposure area than the reference area. Metal toxicity is well understood for this animal, and there are published values for several metals for lethal body concentrations at which 25% mortality of exposed Hyalella will occur (the LBC25). Stantec measured metals concentrations in tissues of Hyalella collected from the field and found higher levels of most metals in composite tissue samples collected from the reference area than from the exposure area. This was likely due to higher calcium concentrations in the exposure area, also originating from the mine effluent, which would tend to reduce uptake of those metals. Two trace metals for which critical body burden values are available showed higher concentrations in amphipods collected from the exposure area. For cobalt, the difference was small and the measured concentration in Hyalella from the exposure area was less than 20% of the LBC25 value. For nickel, amphipods from the exposure area exhibited tissue concentrations (11 mg/kg) that were 96% of the LBC25 value (11.4 mg/kg), and more than two times higher than the concentration measured in the reference area. Although the mine complies with the effluent quality requirements of the MMER, nickel concentrations were higher in water samples collected from the exposure area than in samples from the reference area. Based on a weight of evidence it is considered likely that exposure to nickel is responsible for alteration of the benthic invertebrate community in the exposure area.
Metals, Toxicity, Monitoring, Environment, Hyalella