Mercury, selenium and arsenic concentrations in Canadian freshwater fish and a perspective on human consumption intake and risk

Mercury (Hg) and arsenic (As) contamination of fish can be toxic and limit safe human consumption, whereas selenium (Se) can potentially protect fish and consumers from the adverse effects of Hg and As. We assembled datasets of the above-mentioned elements in Canadian freshwater fish and compare them with risk assessment thresholds. We further assessed linkages between the elemental concentrations and anthropogenic activities and ecozones. Mercury concentrations exceeded the retail fish Canadian threshold (0.5 & mu;g/g wet weight) in 31% of all Walleye; this proportion rose to 64% in reservoirs. Reservoirs and lakes impacted by logging and urbanization had higher fish [Hg] than other types of impacted systems. Se and As concentrations exceeded Canadian guidelines in 5% (aquatic life) and 0.2% of all fish, respectively. In mining areas, fish [Hg] were low and negatively correlated with [Se], and fish [Se] were positively correlated with [As]. In all areas, we observed an important overall and previously unpublished negative relationship between mean fish [As] and [Hg], suggesting an inverse consumption risk for these two elements. The ratio Se/Hg was lower than the protective value of 1 for 14% of all fish and was negatively correlated with fish length. However, the benefit-risk value (BRV) threshold, which accounts for the Se intake from other food products, did not suggest any fish consumption limitations, except for few very contaminated top predators ( > 2 & mu;g/g ww). More studies need to assess the role of Se against Hg toxicity and adjust fish consumption guidelines accordingly.