Environment Canada is currently undertaking a 10-year review of the Federal Metal Mining Effluent Regulations (MMER) that guide the effluent deposition activities of 105 metal mines active in Canada (as of 2010.) Roughly 60 additional new mines are in various stages of approval and will likely be added to the program in coming years.
The MMER not only stipulate contaminant discharge limits for arsenic, copper, cyanide, lead, nickel, zinc, total suspended solids, and radium 226, but require mines to perform Environmental Effects Monitoring (EEM) field biological studies every three years. In these studies, mines test endpoints such as fish age, weight, condition, and gonad and liver size downstream of mines to assess whether their activities are having an effect on the receiving environment. In particular, the EEM studies are designed to detect whether there’s an effect on the downstream environment, even when the mines are in compliance with the regulations. The results from these studies, when considered on the national level, allow for continuous improvement of the MMER guidelines.
The EEM studies address two important but separate questions:
1) Is any one particular mine having an effect on the receiving environment?; and,
2) are metal mines nationally having an effect on downstream environments?
As part of the 10-year review of the MMER, Environment Canada convened a multi-stakeholder group that has been tasked with providing advice to the Minister of Environment regarding changes to the Metal Mines Effluent Regulations.
To address this question, Environment Canada has undertaken two major reviews of environmental data gathered by mining companies over the course of the last decade. In 2010, it was determined that the metal mining sector was in compliance with MMER permitted discharge limits for arsenic, copper, nickel, zinc, radium 226 and pH 99% of the time (Environment Canada, 2012c). However, in the Second National Assessment of Environmental Effects Monitoring Data from Metal Mines Subjected to the Metal Mining Effluent Regulations (Environment Canada, 2012b) a meta-analysis of all EEM studies found that fish downstream of metal mines were, on average, thinner, older, and slower growing.
In the original EEM program, an effect is defined as a simple statistically significant difference between a reference and exposed site. The current technical guidance document requires only one reference and exposed site. Because it is pseudo-replicated, with sufficient power it is very likely that the study will find a statistically significant difference between the reference and exposed sites. Thus, EC recommended the implementation of Critical Effects Sizes, or a threshold difference between reference and exposed sites. The 2012 Discussion Paper states: “As statistically significant difference may not necessarily be indicative of the level of risk to the environment, from the conception of the EEM program, it was envisioned that increased monitoring efforts such as investigative studies should be focused on facilities demonstrating effects of greatest concern. Critical Effect Sizes (CES), defined as thresholds above which effects may be indicative of a potential higher risk to the environment, have been developed for the fish population and benthic invertebrate community components of the MMER-EEM program.” (Environment Canada 2012c).
Given these challenges, there have been questions as to whether the conclusions drawn from the Second National Assessment are sufficiently informative, and what changes can and should be made to the EEM program.
The Mining Association of Canada undertook two further studies on the EEM data. Though neither study replicated the meta-analysis of the Second National Assessment, both questioned the methodology of the EEM studies, and suggested that the findings of the Second National Assessment were due to confounding factors. Both reports supported implementing CES, but also suggested other changes to the EEM studies, such as utilizing a Bonferroni Correction on the level of significance to account for performing multiple tests.
In order to inform our policy recommendations, we undertook our own meta-analysis of these same data to determine whether the MMER guidelines are protective of the receiving environment nationally, and how methodological changes suggested by Environment Canada and the Mining Association of Canada would affect interpretation of monitoring results. Our meta-analysis results largely confirm Environment Canada’s findings regarding reduced fish condition downstream of base metal (Phase 1, 2 and 3/4) and precious metal (Phase 2 and 3/4) mines, though we find reduced weight-at-age only in Phase 2 data in base metal mines (Table 1). Contrary to Environment Canada’s finding in the Second National Assessment, we found enlarged livers in Phase 1 and 2 in base metal mines and in Phase 2 in precious metal mines. The effects on gonad size were variable between phases (Table 1). We were significantly hampered by insufficient data to assess iron ore, uranium, and other metal mines in Phases 1 and 2, though results from Phase 3/4 show no effects across endpoints for other metal or uranium mines (incomplete data to assess gonad size and weight-at-age), and reduced liver size and increased condition in iron ore mines. When pooled across mine type and phase, our analysis shows lowered condition, reduced weight-at-age, and increased liver size. This effect is likely driven by base metal and precious metal mines. That the effects are detectable given the wide variety of receiving environments that are subject to MMER and thus included in this study is striking. However, caution must be afforded in interpreting these results: we were hampered by a number of data quality issues, and some mines entered the program more recently, thus our data set is under-represented by iron ore, uranium and other metal mines.
Our analysis also indicates that utilizing Critical Effects Sizes would reduce the number of failed tests by more than half. This will have a large impact on the rate of false positives in the EEM program. It has been suggested that the Bonferroni correction should also be utilized in order to correct for the inflation of false positives due to undertaking multiple tests. However, our analysis does not support the conclusion that the rate of endpoint failure of mines across Canada is driven by chance, and thus require a Bonferroni correction. Most mines that fail EEM studies do so by more than one end-point, and the number of endpoint failures, even once corrected for CES, is much higher than would be expected by chance. Furthermore, the Bonferroni correction is known to be very conservative, particularly as the number of tests increases, and inflates Type II error.
We conclude that there are measurable biological effects downstream of metal mines across Canada, particularly for base and precious metal mines. We also conclude that implementing Critical Effects Sizes will do a great deal to address the rate of false positives in EEM studies, but that there is no evidence to suggest that the rate of endpoint failure in EEM studies is driven by stochasticity, therefore implementing a Bonferroni correction is likely overly conservative and would result in the reduction of protection for the environment.
