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Third national assessment

Executive Summary

The Metal Mining Effluent Regulations (MMER) came into force in 2002 under the Fisheries Act. They prescribe end-of-pipe (discharge) limits for specified substances, and provide a national standard that is intended to protect fish, fish habitat and the use of fisheries resources. The metal mining sector is achieving over 95% compliance with the prescribed discharge limits and meeting the requirement that effluent not be acutely lethal to rainbow trout (Environment Canada 2015). In addition to complying with end-of-pipe limits, Canadian mines subject to the MMER are required to conduct environmental effects monitoring (EEM) studies of the potential effects of mine effluent on the aquatic environment. Information obtained through EEM supports the evaluation of the effectiveness of the Regulations in protecting the aquatic environment and of current and future pollution prevention and control technologies, practices and programs within the mining sector. The purpose of this report is to present the main findings of the EEM studies conducted by mines across Canada.

The EEM studies required by the MMER consist of biological, effluent and water quality monitoring studies. Biological monitoring studies are conducted on three components: fish populations, fish habitat (represented by the benthic invertebrate community) and the use of fisheries resources by humans (represented by mercury concentrations in fish tissue). Effluent and water quality monitoring studies, consisting of chemical characterization and sublethal toxicity (SLT) testing of final effluent and water quality monitoring in the environment, contribute to the assessment of effluent quality and aquatic environment conditions at individual mine sites. This report focuses on the biological components of EEM studies in order to provide a national assessment of the potential effects of metal mining effluents on aquatic environments.

The third national assessment report summarizes the biological monitoring studies undertaken to assess the presence or absence of effects that were submitted to Environment and Climate Change Canada (ECCC) before October 1, 2013 and the biological monitoring studies conducted to investigate the magnitude, geographic extent and cause of observed effects that were submitted before June 2014. The results of the SLT and effluent characterization studies that were carried out from 2003 to 2012 are also summarized in order to provide supporting information.

In the MMER, an “effect” is defined as a statistical difference between specific data collected from an area exposed to mine effluent and from a similar reference area not exposed to mine effluent. There are five effect indicators associated with the fish population component, four effect indicators associated with the fish habitat component and one criterion associated with an effect on the use of fisheries resources. The presence or absence of an effect is considered “confirmed” when a similar type of effect or the absence of an effect has been observed in two consecutive studies. If effects are observed in one study and different effects or no effects are observed in the second study, the presence or absence of effects is considered “unconfirmed” and further studies are required to obtain confirmation.

Although the metal mining sector is achieving over 95% compliance with the prescribed discharge limits, a decade of EEM results have shown that impacts do occur on fish and fish habitat downstream from metal mines, but rarely do effluents impact the consumption of fish by humans.

Most mines (62/82 or 76%) that have completed two consecutive studies to assess effects confirmed at least one effect, and 52% (32/62) of these mines confirmed effects on both fish and fish habitat. One mine confirmed the absence of effects on fish, fish habitat and the use of fisheries resources. Almost all mines (57/62 or 92%) with confirmed effects observed at least one effect of a magnitude that may be indicative of a higher riskFootnote 1 to the environment.

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For fish, changes (increases and decreases) in the relationship between body weight and length, known as body condition, were the most prevalent effect observed, but changes in survival, growth, reproduction and liver condition were also observed. Survival, growth and liver condition indicators were more often larger in the area exposed to effluent, and reproduction and body condition indicators were more often smaller in the exposure area.

In the case of fish habitat, the most prevalent effect was a change in the benthic invertebrate community structure (measured using a similarity index), followed by a decrease in the number of species present (taxon richness). Changes in the total number of individuals (increases and decreases in density) and changes in the number of individuals of each species (measured with an evenness index) were less prevalent. The number of mines with an increased density in the area exposed to effluent was higher than the number of mines with decreased density in the exposure area. Effects observed on the number of individuals of each species were equally increases or decreases in the area exposed to effluent.

Monitoring studies conducted to assess the impact of metal mining effluents on mercury concentrations in fish tissue (use of fisheries resources) did not indicate that metal mining effluents were linked to high levels of mercury in fish tissue.

Results from EEM studies indicate that the overall sublethal toxicity (SLT) of mine effluent remained stable during the first 10 years of MMER implementation. In SLT tests, metal mining effluent had the greatest effect on invertebrate reproduction and aquatic plant growth and the least effect on fish larval growth. Mining effluent stimulated growth in plants and algae in some SLT tests.

When the presence of effects was confirmed, mines were required to conduct sampling in additional locations within the exposure area to assess the magnitude and geographic extent (M&E) of the confirmed effects. Most mines (25/29 or 86%) assessing the magnitude and geographic extent (M&E) of effects confirmed in the exposure area near the point of effluent discharge (near-field area) observed one or more of the same effects in the exposure area farther from the point of effluent discharge (far-field area). Half (14/25 or 56%) of the mines assessing the M&E of multiple confirmed effects observed the same multiple effects in far-field areas. In more than 50% of cases, fish effects occurring in additional locations were smaller in magnitude than effects occurring close to the discharge point. The magnitude of fish habitat effects was mainly indicative of a higher risk to the environment in both the area near the point of discharge and in additional locations within the exposure area. The distance of the additional exposure locations from the point of discharge did not influence the occurrence or magnitude of same effects.

Once the M&E of confirmed effects have been determined, mines are required to carry out a biological monitoring study designed to determine the causes of confirmed effects. Thirty-five mines conducted investigation of cause (IOC) studies. Two general categories of effects were investigated: inhibitory effects that can be caused directly by toxicity and habitat alteration or indirectly by food limitation or toxic substances contained in prey organisms; and stimulatory effects that can be caused by eutrophication due to nutrient addition to the environment. About half of the mines carrying out IOC studies examined predominantly inhibitory effects and the remaining mines examined predominantly stimulatory effects or a mix of inhibitory and stimulatory effects. Some mines have completed their IOC studies and other mines have completed part one of a two-part IOC study.

Of the 26 mines that had completed IOC studies, 77% (20/26) identified current mine effluent as a primary or possible contributing cause of effects. Two mines identified mine-related substances as a cause, but did not indicate if current mine effluent was the source, and four mines indicated that effects were caused by non-mine related factors. Major ions and phosphorus in effluent tended to be associated with stimulatory effects, whereas metals, selenium and total suspended solids in effluent were more often associated with inhibitory effects. Nitrogen compounds in effluent were associated with both stimulatory and inhibitory effects.

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