Journal Article

Managing mercury exposure in northern Canadian communities

Lemire, Melanie, Muckle, Gina, Pirkle, Catherine McLean

2016

Overview

Although high mercury levels (> 100 μg/L in blood) have occasionally been reported in Canadian adults since the 1970s, mercury-induced signs and symptoms have never been comprehensively studied. Consequently, it is virtually impossible to establish diagnostic criteria for mercury intoxication at exposure levels relevant to northern Canada. Moreover, the evidence base for the health effects of long-term mercury exposure in Canadian adults is limited in scope and methodology. For example, among 135 Quebec Cree adults less than 40 years old, tremor was significantly associated with increasing mercury concentrations when measured by a general clinical examination but not by a specialized neurologic examination.40 The study was the result of a lawsuit, which may have compromised internal validity because participants with symptoms may have self-selected into the study. In a crosssectional study with a control group of nonexposed Japanese residents, First Nations adults from Grassy Narrows, Ontario, exhibited neurologic symptoms consistent with mercury poisoning, but the study lacked biomarker data of actual mercury exposure.41 Other cross-sectional studies conducted outside of Canada have also documented neurologic abnormalities in fisheating populations with comparable mercury exposure levels.42 In contrast to children, in whom the developing brain is a critical target of mercury toxicity, the cardiovascular system may be most sensitive in adults.1 Representative surveys of Nunavik Inuit and Cree adults documented associations between increasing blood mercury concentrations and risk markers for cardiovascular disease.43,44 Although the studies used crosssectional designs and had low response rates (< 50%), they had large samples (> 600) and adjusted extensively for confounders.43,44 It is possible that chronic conditions influence mercury metabolism and excretion, and thus affect exposure concentrations observed in crosssectional studies (e.g., reverse causality). In addition, cross-sectional studies cannot determine whether the observed mercury-induced cardiovascular damage occurred prenatally or postnatally. Two well-conducted nested case-control studies analyzing data from large prospective US cohorts found no association between mercury exposure and hypertension, nonfatal myocardial infarction, coronary artery disease or stroke in adults free of cardiovascular disease at baseline; however, exposure levels in these cohorts were lower than those typically observed in northern Canada.45,46 In the absence of prospective studies among adults with greater exposure levels, it may be justifiable to advise people with elevated cardiovascular risk to reduce mercury exposure as a precaution. We searched Embase, MEDLINE, Scopus and Google Scholar from 1994 to 2015 for English- and French-language epidemiologic studies conducted in Canada using the following search terms: \"mercury\" or \"methylmercury,\" and \"Canada,\" \"Nunavik,\" \"Nunavut,\" \"Northwest Territories,\" \"Yukon,\" \"Inuit,\" \"Cree,\" \"Dene,\" \"Metis,\" \"First Nations,\" \"indigenous,\" \"Aboriginal\" and \"fishermen.\" We conducted a cited reference search on all review articles on the topic. In addition, we reviewed books and technical reports from the National Academy of Sciences, the Arctic Monitoring and Assessment Programme and the World Health Organization.

• Publisher: Elsevier Inc,CMA Impact Inc,Joule Inc,CMA Impact, Inc
• Subject: Animals / Aquatic ecosystems / Canada / Cerebral palsy / Child development / Congenital diseases / Counseling / Diet / Environmental aspects / Environmental Exposure - prevention & control / Fetuses / Fish / Fishes / Food contamination & poisoning / Food Supply / Health aspects / Health Promotion / Human exposure / Humans / Indians, North American / Intellectual disabilities / Marine mammals / Mass Screening / Medical personnel / Mercury / Mercury (Metal) / Mercury - adverse effects / Mercury - blood / Mercury poisoning / Mercury Poisoning - diagnosis / Mercury Poisoning - physiopathology / Mercury Poisoning - prevention & control / Nutrition Policy / Pregnancy / Prenatal Care / Prevention / Review / Risk factors / Selenium