Second national assessment of environmental effects monitoring data from metal mines

Second National Assessment of Environmental Effects Monitoring Data from Metal Mines Subjected to the Metal Mining Effluent Regulations

February 2012

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We would like to thank Lisa Taylor for her significant contribution to this report. We would also like to thank the members of the Environmental Effects Monitoring National Team and Science Committee for providing comments and scientific expertise during the preparation of this report.

Executive Summary

Under the Fisheries Act, the 2002 Metal Mining Effluent Regulations (MMER) require the owners or operators of metal mines to conduct environmental effects monitoring (EEM) to assess effects potentially caused by metal mine effluents. Specifically, the EEM comprises

  • a fish population survey to assess fish health,
  • a benthic (bottom-dwelling) invertebrate community survey to assess effects on fish habitat, and
  • a study of mercury levels in fish tissue to assess effects on the usability of fisheries resources when conditions specified in the MMER are met.

Metal mines also collect supporting data through sublethal toxicity testing, water and sediment quality monitoring, and effluent characterization. Results of EEM are used to evaluate the effectiveness of the MMER, including the effects of metal mine effluents on the environment. EEM information provides a basis for current and future water pollution prevention and control technologies, practices and programs within the mining sector.

The MMER EEM reporting period is structured into “phases,” whereby a mine conducts an EEM study every two to six years according to conditions specified in the Regulations. The sequence of EEM studies is based on a tiered approach to monitoring from one phase to another. Initial field surveys are followed by studies to determine the extent, magnitude and cause of effects where effects are detected and confirmed, or by a reduced level of monitoring where effects are not found.

The metal mining EEM program has now completed two national assessment periods of monitoring. The purpose of this report is to present and discuss the major findings of the MMER EEM results, using data collected by metal mines across Canada. Several lines of analysis, based now on two national assessments, indicate that effects related to the discharge of effluent from metal mines tend to be more inhibitory than stimulatory. That is, effluent exposure was more often associated with reductions rather than increases in the indicators (endpoints) such as growth rate of fish, which are used to assess effects.

During at least one of the national assessment periods, fish collected in areas exposed to effluent, referred to as exposure areas, showed significantly1 reduced condition, relative liver size, and growth rate. Other effects included some reductions in gonad (reproductive organ) size and a significantly increased age structure. In other words, fish collected in areas exposed to effluent were, on average, older, thinner and slower-growing, with smaller livers and with more of a tendency toward reduced gonad size. These generally inhibitory response patterns may reflect direct inhibitory effects of the effluent on fish, and/or food limitation resulting from habitat alteration and inhibitory effects on prey organisms, such as benthic invertebrates.

Data for benthic invertebrates collected in exposure areas from both national assessment periods showed significantly reduced taxon richness. That is, there were fewer kinds of benthic invertebrates found in exposure areas. The Bray-Curtis endpoint, which measures differences in community structure, revealed different groupings of benthic invertebrates in exposure areas compared to reference areas. Relative to the first assessment period, a national average increase in benthic invertebrate density (number of individuals per unit area) was observed during the second national assessment period, which could indicate that some mine effluents may have stimulatory effects on benthic invertebrates.

Reduced growth rate of fish collected in exposure areas was most strongly associated with metal mines that discharge effluent to lake and river habitats, and with base metal and iron ore mine types. Smaller gonads in fish collected in exposure areas were mostly associated with mines that discharge effluent directly into river habitats, as well as precious and base metal mines. The presence of older fish in exposure areas was associated with metal mines that discharge effluent to lake and river habitats, as well as precious metal and uranium mine types. Increased benthic invertebrate density was associated with all habitat and ore types, with the exception of river erosional habitat types.

Analyses of benthic invertebrate community data in relation to effluent flow data generally did not indicate that changes in effluent flow had an influence on changes in magnitudes and patterns of effect for either density or taxon richness, although site-specific exceptions may exist.

At this time, the available data do not suggest that metal mine effluents were broadly linked to high mercury levels in fish tissue.

To supplement the primary field surveys, sublethal toxicity testing is conducted on effluent from the mine’s final discharge point. This testing monitors effluent quality by measuring survival, growth and/or reproduction endpoints for organisms in a controlled laboratory environment. The tests showed fairly similar effluent quality over the two national assessment periods, though future tests may prove useful in determining whether effluent quality is improving.

Although a substantial amount of data for a large number of mines is summarized in this report, these data represent just two monitoring periods, and some of the variations between phases may have been partly due to factors other than effluent exposure. Further rounds of data collection and analysis will help to shed light on how constant or variable these response patterns are through time. Of particular interest, some mines are entering the investigation of cause phase, which is expected to further elucidate the nature of metal mining effluent effects on receiving waters in Canada.

1 In this context, significance refers to a statistically significant difference at a national level when
comparing monitoring results collected in effluent exposure areas to results collected in reference
areas not exposed to effluent.

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