4. Mercury and Human Health

4.1 - Human biomonitoring results

The most direct way to measure human exposure is through human biomonitoring. Measurements of mercury levels or concentrations are usually taken in blood or urine but can also be taken in other tissues and fluids such as hair, nails and breast milk. The measurement indicates how much of a chemical is present in a person.

Canada has biomonitoring programs for mercury in the general population, First Nations populations and Inuit populations. These measurements can be compared to the Health Canada blood guidelines.

Health Canada set guidelines for acceptable levels of methylmercury in blood at 20 micrograms^{Footnote 1} per litre (µg/L) or lower for men over 18 and for women 50 and older (Health Canada, 1999). In 2010, an acceptable level of 8 μg/L or lower was developed for children 18 years of age and under, women of childbearing age (19 to 49 years), and pregnant women, recognizing that the developing nervous systems of the fetus and of young children place them at greater risk of health effects from methylmercury (Legrand et al., 2010).

Trends in blood levels may be seen when measurements are taken at more than one point in time. The data below was taken from the Canadian Health Measures Survey (Statistics Canada 2013 & 2017) and a number of recent comprehensive reviews including the Canadian Mercury Science Assessment (2016) and the Arctic Monitoring and Assessment Programme’s Human Health Assessment (2015).

4.1.1 - Canadian general population

Total mercury in the general Canadian population is measured on an ongoing basis as part of the nationwide Canadian Health Measures Survey^{Footnote 2}. This survey began in 2007 and is led by Statistics Canada in partnership with Health Canada and the Public Health Agency of Canada. The survey includes assessment of blood, urine, and hair collected from survey participants for a wide variety of environmental chemicals (Health Canada, 2017; Statistics Canada, 2017).

As shown in Figure 5, for 2007 to 2009 the mean level of mercury in blood was 0.88 μg/L, for 2009 to 2011, 0.92 μg/L; for 2012 to 2013, 0.92 μg/L; for 2014 to 2015, 0.77 μg/L. Therefore the majority of Canadians have mercury levels well below the Canadian blood guidelines and their levels are not changing over time (Statistics Canada, 2017). As shown in Figure 6, younger Canadians have lower levels of mercury compared to older Canadians.

In the 2007 to 2009 Canadian Health Measures Survey, less than 1% of the general population (6–79 years old) had mercury concentrations above the 20 µg/L guideline (Health Canada, 2010). In the same survey, 1.61% of Canadian pregnant women, women of childbearing age, and children were above the 8 µg/L guideline (Lye et al., 2013). As mercury levels in the general Canadian adult population have not changed significantly between 2007 and 2015 (Statistics Canada, 2017), the percentage of Canadians with mercury blood concentrations above acceptable levels has also remained constant. Almost all Canadians are expected to have blood mercury concentrations below the 8 µg/L and 20 μg/L guidelines. Public health risk to the general population continues to be low. Health advisories and interventions may have contributed to this outcome.

4.1.2 - Indigenous communities

Mercury exposures are generally higher among those whose diet is high in fish or sea mammals, such as members of many Indigenous communities, especially Inuit communities. Although traditional diets consisting of harvested country foods have significant nutritional benefits, they may also increase exposure to mercury (Arctic Monitoring and Assessment Programme, 2011).

As part of the First Nations Biomonitoring Initiative (PDF) (the Initiative) average total blood mercury levels of First Nations adults (20 years old or above) living on reserve in southern Canada were studied. Mean levels of total mercury in blood in this subpopulation were not significantly different than those of the general Canadian population measured in the Canadian Health Measures Survey, although there was much more individual variability within the subpopulation. As well, six of the thirteen First Nations communities who participated in this initiative showed statistically higher mercury levels than the general Canadian population. The Initiative demonstrated that the mean level of mercury in blood for 95% of the population was less than 9.28 µg/L, well below the 20 µg/L blood guideline. The mean level for 90% of all females was less than 6.42 µg/L. However, by broadening the range to 95% of females, the mean level increased up to 9.85 µg/L, which is above the 8 µg/L blood guideline for women of childbearing age (Assembly of First Nations, 2013).

For Inuit, blood mercury levels are higher than populations in southern Canada, with mean levels ranging from 2.8 µg/L to 12 µg/L across the Inuvialuit Settlement Region, Nunavut, Nunavik, and Nunatsiavut communities. For women of childbearing age in these areas, mean levels range from 1.7 µg/L to 8.4 µg/L (Arctic Monitoring and Assessment Programme, 2015). For Nunavut, the relative frequency of mercury levels above Health Canada’s guidance value of 20 μg/L in whole blood was higher for men, all women, and women of childbearing age, than in other regions of northern Canada. Specifically, for women of childbearing age in all regions surveyed, exceedances of the 8 µg/L blood guideline for this age group ranged from 9.3 to 36% (Figure 7) (Arctic Monitoring and Assessment Programme, 2015).

Nonetheless, mercury blood levels have decreased over time in certain Inuit populations, including those most susceptible to effects. For example, there has been:

• a 47% decrease in mercury blood levels in Inuit mothers from the Inuvik region of the Northwest Territories between 1998/99 and 2005/06 (Arctic Monitoring and Assessment Programme, 2009)
• a 40% decrease in mercury blood levels in Inuit mothers from the Qikiqtaaluk (Baffin) region of Nunavut between 1997 and 2005/07 (Arctic Monitoring and Assessment Programme, 2009)
• a 57% decrease in mercury blood levels in pregnant Inuit women from the Nunavik region of Quebec between 1992 and 2013 (Figure 8) (Arctic Monitoring and Assessment Programme, 2015)

An examination of the various human biomonitoring studies previously discussed was undertaken to determine the presence of trends in mercury levels in Canadians. This is summarized in Table 2. Also included in this table are proportions of populations that were found to exceed Canadian blood guideline levels for mercury. While levels of mercury appear to be decreasing over time in Inuit populations, populations in Canada’s North continue to exceed mercury guideline levels at much higher percentages than the general population. The general decrease seen in the Inuit population’s exposure to mercury may be because of changes in their diets, in particular, a move away from their traditional diets, rather than a change in the levels of mercury in fish and sea mammals that make up this diet. No trend can be determined for First Nations populations, and levels in the general Canadian population are basically unchanged from 2007 to 2015.

^aStatistics Canada, 2017

^b Assembly of First Nations, 2013

^c Arctic Monitoring and Assessment Programme, 2015

^d Lye et al., 2013

Sea mammals in the Arctic have significantly elevated levels of mercury making these country foods an important contributor to mercury levels in the Inuit. Among Nunavut children, dietary intake of these mammals has been shown to be the biggest contributor to methylmercury in their bodies. Furthermore, biomonitoring results showed that 25% of these children exceeded the World Health Organization reference value for mercury in hair (Arctic Monitoring and Assessment Programme, 2011). Accordingly, the Nunavut government issued dietary advice for women of childbearing age to lower their intake of ringed seal liver in June 2012 (Government of Nunavut, 2012). Laird et al. (2013) further documented the ringed seal liver as the major source of mercury among Inuit in Nunavut. Additionally, the Nunavik government issued dietary advice for beluga meat, which is the major source of mercury for Inuit (Lemire et al. 2015).

4.1.3 - Conclusion

The biomonitoring results show that progress is being made towards minimizing human exposure to mercury. Levels of mercury in the general Canadian population are low and relatively stable. Regarding southern First Nations, mercury levels observed were similar to levels observed in the general Canadian population. However, there are limitations in the comparison of southern First Nations data with that of the general Canadian population. This is because there is a wide range of mercury blood concentrations from individual to individual in southern First Nations communities, a range not seen within the general Canadian population. A statistical comparison performed on a community basis was possible in six of the thirteen First Nation communities. In this case, the six First Nation communities had statistically higher levels than the Canadian population. Northern Inuit populations have higher levels of mercury than the general Canadian population, but their levels have been decreasing over time. These decreases may be due to a decrease in consumption of certain country foods. Given the nutritional, cultural, and spiritual benefits of traditional diets, efforts need to continue to decrease mercury levels in these food webs, as much as possible, to protect human health. (Statistics Canada, 2017.)