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Third national assessment

Third National Assessment of Environmental Effects Monitoring Information from Metal Mines Subject to the Metal Mining Effluent Regulations


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Metal mines in Canada are required to conduct environmental effects monitoring (EEM) studies of the potential effects of mine effluent on the aquatic environment as a condition governing their authority to deposit effluent under the Metal Mining Effluent Regulations (MMER) pursuant to the Fisheries Act. The results of EEM studies conducted by regulated mines represent an important source of information for assessing the adequacy of the regulations for protecting the aquatic environment. Although the metal mining sector is achieving over 95% compliance with the prescribed limits (Environment Canada 2015), a decade of EEM results has 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.

In the MMER, an “effect” is defined as a statistical difference between specific data collected from an area exposed to mine effluent and data collected from a similar reference area that is not exposed to mine effluent. 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.

Eighty-two mines have completed at least two consecutive studies to assess the effects of mine effluent. Of these mines, 76% (62/82) confirmed the presence of effects on fish or fish habitat, or both. Ninety-two percent (57/62) of mines that confirmed effects observed at least one effect of a magnitude that may be indicative of a higher risk to the environment. One mine confirmed the absence of effects on fish, fish habitat and the use of fisheries resources. The presence or absence of effects remained unconfirmed for 23% (19/82) of mines that completed two or more studies, because the results of these studies were variable (an effect observed in one study, but a similar type of effect not observed in the second study).

The types of effects identified by this third national assessment were similar to those identified by the previous national assessments. Fish in the exposure area were thinner or fatter, older or younger and had smaller or larger livers and gonads than fish in the reference area. Fish habitats exposed to effluent had experienced a change in benthic invertebrate community structure, contained more or fewer individuals and had fewer species present.

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 these effects. Most mines (25/29 or 86%) that assessed the M&E of confirmed effects observed one or more of the same effects within the exposure area farther from the point of effluent discharge. To date, effluent from current mining activities has been shown to cause or contribute to effects in 77% (20/26) of studies completed to determine the causes of effects. The effluent substances associated with effects were major ions, metals, nitrogen, total suspended solids, phosphorus and selenium.

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