Projecting Fish Mercury Levels in the Province of Ontario, Canada and the Implications for Fish and Human Health

Fish mercury levels appear to be increasing in Ontario, Canada, which covers a wide geographical area and contains about 250 000 lakes including a share of the North American Great Lakes. Here we project 2050 mercury levels in Ontario fish, using the recently measured levels and rates of changes observed during the last 15 years, and present potential implications for fish and human health. Percentage of northern Ontario waterbodies where sublethal effects of mercury on fish can occur may increase by 2050 from 60% to >98% for Walleye (WE), 44% to 59–70% for Northern Pike (NP), and 70% to 76–92% for Lake Trout (LT). Ontario waterbodies with <i>unrestricted</i> fish consumption advisories for the <i>general population</i> may deteriorate from 24–76% to <1–33% for WE, 40–95% to 1–93% for NP, and 39–89% to 18–86% for LT. Similarly, Ontario waterbodies with <i>do not eat</i> advisories for the <i>sensitive population</i> may increase from 32–84% to 73–100% for WE, 9–72% to 12–100% for NP, and 19–71% to 24–89% for LT. Risk to health of Ontario fish and humans consuming these fish may increase substantially over the next few decades if the increasing mercury trend continues and updated advisories based on continued monitoring are not issued/followed

Assessing fish consumption Beneficial Use Impairment at Great Lakes Areas of Concern: Toronto case study

<p>Beneficial use of fish consumption was designated impaired in the 1980s in many Areas of Concern across the North American Great Lakes. Remedial Action Plans have guided the restoration of beneficial use impairments with the goal of delisting the Areas of Concern. Here we present generic re-designation criteria and a three-tier Assessment Framework to assess the status of the fish consumption beneficial use impairments using the Toronto and Region Area of Concern as a case study. Tier 1 assessment identified that consumption advisories for many resident fish on the Toronto waterfront are non-restrictive (8+ meals month⁻¹). Advisory assessments in Tier 1 found that most migratory fish species, Carp and White Sucker are still restrictive in some cases preventing a ‘not impaired’ re-designation. Tier 2 Comparison with Reference Sites found that the advisories for most local fish are either non-restrictive or similar to reference locations in Lake Ontario, but some advisories due to elevated levels of polychlorinated biphenyl are still more restrictive for the Toronto waterfront and do not favour a ‘not impaired’ re-designation. An evaluation of multiple lines of evidence in Tier 3 including fish contaminant trend analyses, time to reach target fish levels, sediment concentrations and fish consumption patterns resulted in outcomes ranging from <i>neutral</i> (not conclusive) to <i>not impaired</i>. As a precautionary approach, the impaired status of the beneficial use impairment should be maintained to ensure continued polychlorinated biphenyl declines in fish. It is recommended that the Remedial Action Plan team update the fish consumption survey, investigate where additional feasible actions can be taken including examining potential polychlorinated biphenyl sources on the Humber and Don Rivers, and collect new data to undertake a future assessment.</p