Mercury (Hg) found in country foods can pose a health risk to Canadians from communities relying on fishing and hunting to complete their diet. Current equations used to estimate human exposure to Hg from country food assume (1) that all Hg is present as methylHg (MeHg), the neurotoxic form; (2) that Hg levels remain constant during food preparation; (3) that all MeHg in food is absorbed by humans; (4) that Hg interactions with selenium and arsenic do not alter human exposure. These assumptions have been recently challenged in the literature (Ha et al., 2016). For instance, it is now well established that the proportion of MeHg in fish varies with age, size and species (Lescord et al. 2018) and with tissues (e.g. liver vs muscle; Khadra et al., 2019). There is also a growing body of evidence that metal levels in tissues vary in concentrations and speciation during cooking (Mieiro et al., 2016) although there are diverging results on this effect, and the mechanisms occurring during cooking are not well understood. Further, experiments simulating human digestion are indicating that not all MeHg in fish is bioaccessible to humans, and that cooking strategies may alter our exposure to metals (Afonso et al., 2015; Clemente et al., 2017; Girard et al., 2018). Such experiments have also been conducted with country food in Canada (Laird et al. 2009). Finally, current studies are increasingly considering the molar ratio of selenium (Se) and mercury to assess risk (Burger et al. 2013) although the protective effect of this ratio is a subject of debate.
The goal of this project is to test some of the assumptions of the equations currently used by Health Canada (HC) to assess exposure to metal of Indigenous communities whose diet partly rely on country food. We plan to use ring seal liver and whitefish muscle tissue. These two types of food items are likely different in the % of MeHg and in the preparation method by Indigenous people and will therefore represent two contrasting cases. We will consider Hg, since its presence in country foods is often the reason for the development of advisories and consumption guidelines. We will also consider selenium (Se), because of its potential protective effect on Hg absorption. Arsenic (As) will also be investigated because it can be an antagonist of Se, thereby potentially decreasing its protective effect towards Hg. We will not only consider total concentrations of these metals, but also their speciation (in the case of Hg and As), since speciation is an important factor in processes occurring during food preparation and digestion.
The objectives of this proposal are to:
- Measure the concentration of Hg, As and Se in country food samples – ring seal liver and whitefish tissues are being proposed but it will depend on sample availability (see Proposed Approach and Steps section below);
- Document changes in these metals’ concentration and speciation during traditional food preparation; and
- Document changes in their concentration and speciation during in vitro digestion of prepared vs unprepared food.