Exposure characterizations are a critical component of human health risk assessments, providing key insights into to the environmental determinants of health. Contaminant exposure is spatially and temporally dependent and can be influenced by natural and anthropogenic factors that impact air and water quality, and the integrity of locally harvested food sources. In remote subarctic Indigenous communities of the Northwest Territories, Canada, the ongoing reliance on country foods, such as locally-harvested land mammals, fish, birds and plants, may influence people’s exposure to environmental contaminants, potentially causing significant differences in exposure profiles relative to the general population of Canada.
With funding from the Northern Contaminants Program, which is jointly supported by Health Canada and Indigenous and Northern Affairs Canada, this research investigated levels of contaminant exposure among participating First Nations communities of the Canadian subarctic. The aims of the project are to provide baseline reference levels for this region and to assess the risks and benefits of country foods consumption in terms of contaminant and nutrient exposure.
Methodology
Six First Nations communities of the Dehcho region participated in the project. The researchers sampled proportional to community population size, with a minimum target of 10 per cent of the population per community, and aimed for a sample representative of the sex and age distribution of the combined population.
In each of the project years (2016–2018), sampling and data collection were completed during the winter months (November to March), to reduce the potential impact of seasonal variability in the results. Participants were invited to complete two dietary surveys: i) a 24-hour recall survey to detail what they had eaten over the previous 24 hours, including traditional country foods and market foods, and ii) a food frequency questionnaire to gather information about country food consumption patterns over the previous year. In addition, participants were invited to complete a health messages survey that evaluated awareness and understanding of health messages on country foods and contaminants, and the perception of risks related to contaminant exposure.
Hair, blood, and urine samples were collected from participants. In accordance with the Northern Contaminants Program, biological samples were analyzed for several metals (e.g. mercury, lead, cadmium) and nutrient biomarkers (e.g. selenium, n-3 polyunsaturated fatty acids) associated with country foods, and persistent organic pollutants (e.g. PCBs, organochlorine pesticides) that undergo long-range transport. In addition, and as a result of community consultations, the study included a broader set of contaminants.
For the majority of contaminants, no defined healthbased tissue guidance (HBTG) values were available. The main exceptions to this included mercury, cadmium, and lead. For contaminants without established HBTGs, the research team compared the participants’ levels of exposure with those normally observed in nationally representative Canadian biomonitoring studies.
Outcomes
A total of 283 participants were recruited, representing 8.3 per cent of the residents from this region and 20.6 per cent of the six communities. Participants included 51 per cent female and 49 per cent male, with a mean of 39, a median of 42, and an age range from 6 to 79 years old.
Moose (92 per cent), whitefish (89 per cent) and rabbit (57 per cent) were consumed by the largest number of participants. Although the majority of participants reported eating fish only from waterbodies that did not have a Government of the Northwest Territories consumption notice, 33 per cent of participants reported eating fish from a specific waterbody that had a consumption notice for mercury. Results from the 24 hour dietary recall survey showed that, on the day prior to sample/data collection, 5.1 per cent of total calories consumed in the community were from wild-harvested country foods. Results from the health messages survey showed that 98 per cent of the respondents reported consuming country foods, and that at least 27 per cent would prefer to solely eat country foods. More than half (59 per cent) of the respondents reported that they were concerned about the quality and safety of the country foods they consume. More specifi cally, 68 per cent of the respondents heard about a public health message on mercury in fish, and 55 per cent reported that since hearing this message they were more concerned about the fish they eat.
A total of 231 hair, 136 blood and 85 urine samples were collected. For a few participants (n = 5), mercury levels in hair and blood were higher than the HBTG values and required a regular follow-up. Table 1 provides biological results for the contaminants for which thresholds were established. Of these, only blood lead and blood cadmium had a geometric mean above those reported in the Canadian Health Measures Survey.
Table 1: Observed average contaminant levels for which guidance values were established during the Human Biomonitoring in the Dehcho Region of the Northwest Territories (2016–2017)
Conclusions
Country foods provide the people of the Northwest Territories with many benefits which have nutritional, economic, social, and cultural importance. It is, therefore, important that messages about contaminants and country foods are carefully crafted in a way that balances benefits and risks. The biomonitoring results in the Dehcho show that participants’ heavy metal exposure was generally low, with relatively few participants (2.1%) providing samples above available health guidelines. Although some country foods occasionally have elevated levels of mercury and cadmium, most peoples’ exposures in the territory have typically remained low.
Levels of some metal nutrients (e.g. selenium and zinc) and omega-3 fatty acids were also documented. High levels of omega-3’s may help protect against heart disease and some country foods (e.g., Lake Whitefi sh, Cisco) are particularly rich in these important nutrients. Country foods are generally low in saturated fat and rich in nutrients and signifi cantly contribute to Arctic and sub-arctic dietary quality. These results reinforce the important message that the benefi ts of country food consumption generally outweigh contaminant risks.
Human biomonitoring can document aggregated exposures across sources, but alone can rarely detail the relative importance of various exposure sources. A co-located, ongoing project monitoring contaminants in fish is generating in-depth information on mercury exposure sources and the fi sh that are most strongly associated with nutrient status. The data from the dietary surveys are being used to reconstruct exposures according to frequency of consumption, the portion size and preparation methods. In addition, a statistical approach is being developed to estimate the relationship between risk factors (e.g. diet, lifestyle, demographics) and biomarker levels. The outputs of this project will serve to support the development of public health interventions and health policies minimizing the contaminant exposure in Dehcho communities of the Northwest Territories.
Ratelle, M., Skinner, K., Laird, M.J., Majowicz, S., Brandow, D., Packull-McCormick, S., Bouchard, M., Dieme, D., Stark, K.D., Aristizabal Henao, J.J., Hanning, R., Laird, B.D. (2018). Implementation of human biomonitoring in the Dehcho region of the Northwest Territories, Canada
Contact: Brian Laird, School of Public Health and Health Systems
For more information about WaterResearch, contact Julie Grant.
