Mercury is a global contaminant that accumulates in organisms, including humans, and can result in many health problems. Eating fish is the primary route by which humans are exposed to mercury, and mercury levels tend to be high in northern regions due to global atmospheric circulation patterns and atmospheric deposition of mercury. Our aim is to understand what the key drivers of fish mercury concentrations are in traditional fishing lakes in the Dehcho region, and how/if these drivers vary predictably among lakes. Furthermore, the water quality, sediment quality, fish tissue and fish health results have informed consumption guidelines of the fish in the waterbodies being studied, as fish are a valuable traditional food resource to First Nations. During a study conducted over the last three years funded by CIMP (#00154), Northern Contaminants Program, Health Canada, and NSERC, we found that some Dehcho lakes have high mercury concentrations in top predator food fish species, such as Northern Pike (exceed Health Canada consumption guidelines), whereas other lakes have relatively low mercury concentrations in these species. Our results found that among-lake variability in fish mercury concentrations are not fully explained by any of the variety of variables we investigated, including fish growth rates, fish trophic position, fish age, and fish size. We also found an interesting decoupling between mercury concentrations in water and mercury concentrations in fish, and that lakes with high fish mercury concentrations do not necessarily have high rates of mercury biomagnification through the food web. The water quality and fish data also establish reference conditions for the area relative to future development and a changing climate.

To assess chemical parameters standard 1-litre grab water sample bottles were collected at discrete depths using a peristaltic pump, acid-washed Teflon tubing and following standard best practices. Water was collected for ultra-trace Hg analysis using EPA protocols 1631 and 1669 (US EPA, 1996a&b). The clean-hands dirty-hands technique will be used to collect unfiltered water samples. All fish tissue and water were collected following best practices of Quality Assurance and Quality Control in the field and laboratory.