Human Health Assessment (2017)
The Northern Contaminants Program (NCP) undertook this assessment to address concerns about potential human health risks associated with exposure to environmental contaminants from a diet that includes traditionally prepared and harvested foods from local northern ecosystems. Traditional food, also known as country food, is central to the social, cultural, economic, and spiritual well-being of Inuit, Dene, and Métis in the North and, for many, is essential for their overall food security.
This report is the fourth human health assessment as part of the Canadian Arctic Contaminants Assessment Reports (CACAR) that summarizes the state of knowledge on contaminants and human health in northern Canada. The overall objective of this report is to provide the most up-to-date knowledge on contaminant exposure patterns in northern Canada, methods for describing these human exposures, potential health outcomes related to contaminants, and contaminant management and communication efforts that concern Indigenous people living in northern Canada.
Traditional food and the northern diet
Traditional foods such as marine mammals, fish, terrestrial animals, and birds are nutritious dietary choices for children and adults living in northern Canada. When northern diets include traditional foods, intakes of protein and many dietary nutrients tend to be higher. This is especially important for young people and children. The collection of traditional foods also has economic benefits. For people with access to hunting and fishing equipment, these foods are often more affordable than market food. However, the current Inuit diet across the Arctic is suboptimal, where about one quarter to one third of total calories consumed come from high sugar foods and drinks. Although country food use is culturally specific and varies widely throughout the Arctic, the overall trend shows that younger generations are consuming less traditional food than their elders.
Traditional food can also be a main source of exposure to environmental contaminants in the North. Dietary choice in northern Canada, and therefore extent of exposure to contaminants from traditional food, is a complex issue because the substantial benefits of collecting and consuming traditional foods may be offset by concern about contaminants. Dietary substitutions may help northerners to reduce contaminant exposures. For instance, in the case of mercury, substituting traditional foods high in mercury for others lower in mercury is one way to lower mercury intake, while still promoting consumption of healthy levels of important nutrients like selenium and omega-3 fatty acids. It is critical that dietary substitutions and intervention strategies are designed at the regional level to make sure they are relevant to the different contaminant sources, dietary preferences, and food availability scenarios for people across northern Canada.
Human exposure and contaminant levels
Findings from this assessment show that levels of Persistent Organic Pollutants (POPs) have declined by up to 80% across the 20 years (1992–2013) that contaminants have been measured in blood samples from pregnant Inuit women from Nunavik. At the same time, blood concentrations for total mercury and lead have decreased by about 60% in these pregnant women. The proportion of Inuit pregnant women (and Inuit women of childbearing age) from Nunavik exceeding the provisional interim blood guidance value for methylmercury has been decreasing overall since 1992. Similarly, the proportion of these women who are exceeding the blood lead intervention level and the guideline for lead in whole blood of pregnant women has been decreasing steadily over time in Nunavik, with exceedances approaching zero since 2004.
It is generally expected that differences in contaminant body burdens will usually reflect differences in traditional lifestyles and especially dietary habits. When blood data was examined for Inuit women of childbearing age from across northern Canada, POP and metal levels were generally higher for Inuit from coastal communities in Nunavik (in northern Québec) and Nunavut, where marine mammals were more likely to be consumed, compared with Inuit from Nunatsiavut (in northern Labrador) and the Inuvialuit Settlement Region (in the Northwest Territories). During the Inuit Health Survey conducted in 2007-2008, Inuit men reported eating larger portions of traditional foods and ate these foods more frequently than Inuit women. As well, older adults often ate more traditional food than younger adults. When contaminants were measured in the blood of participants from the Inuit Health Survey, body burdens of many POPs and metals were frequently higher in Inuit men compared with Inuit women, often by as much as two- or three-fold, and older people tended to have higher contaminant body burdens than younger people.
Mechanistic modelling studies can help to explain findings from northern studies by simulating the exposure of Indigenous Arctic populations to contaminants. Some mechanistic modelling studies have observed that the main determinant of some relationships between body burden and age is the length of time elapsed since the peak in exposure for long-lived contaminants whose production and use are subject to international agreements, such as PCBs. These age trends are often more pronounced among Arctic populations, as older generations of northerners tend to have a higher dietary intake of traditional food than younger generations, implying a higher intake of contaminants throughout life. Mechanistic modelling studies have also predicted that Inuit living in northern Canada may have potentially greater POP exposures due to the presence of some marine mammals in their diet.
These findings from mechanistic modelling studies may help to explain the observation that levels of several POPs (and also some metals) were generally between two- and eleven-fold higher among Inuit men and women from the Inuit Health Survey (2007-2008) and the Nunavik Inuit Health Survey (2004) compared to the general Canadian population in southern Canada (2007-2009). Results from the Nunavik Child Development Study also suggest that Inuit children from Nunavik experienced higher exposures to mercury and lead than children from the general Canadian population during the period 2000 to 2009.
Future work in exposure studies
Northern studies have observed that the developing fetus is sensitive to some contaminant exposures, and there is on-going concern with mercury exposures in particular. Some traditional foods are significant dietary sources of mercury, namely predatory fish and specific parts of marine mammals, but many of these traditional foods are also rich sources for selenium and other nutrients. While time trends for contaminants have been determined for pregnant Inuit women from Nunavik through continued sampling of maternal blood, additional studies are required to ascertain contaminant trends for women of childbearing age and pregnant women from the other three Inuit regions. The co-location of biomonitoring studies in people and wildlife is also encouraged, as this would permit researchers to create direct links between site-specific exposures and measured body burdens.
The importance of consuming specific traditional foods that may contain high concentrations of mercury is also a knowledge gap. On-going consideration of the interests of northern communities during future studies that examine contaminants in traditional food will ensure these specific exposures are being investigated within the context of the regional exposure issue. As well, this approach would ensure that any important health, dietary, or contaminant issues that may arise will be addressed with the communities in the most appropriate cultural health context.
Some research suggests that traditional food may not be the only source of contaminant exposures for northerners. Routes of exposure to polybrominated diphenyl ether (PBDE) (a group of chemicals used as flame retardants) appear to vary across the Arctic, and the association between PBDE concentrations in human blood and the consumption of traditional food is unclear. The contribution of dietary and non-dietary sources to PBDE exposures in northern Canada warrants further investigation to improve the understanding of PBDE exposures from traditional food compared to other sources, such as dust in the home.
As noted in prior assessments, cadmium is also an exception, where Inuit men and women have shown similar blood concentrations within each of the four northern Inuit regions. Smoking, a major source of cadmium exposure, was highly prevalent amongst participants from the Inuit Health Survey (2007-2008) and the Nunavik Inuit Health Survey (2004), with about 70% of people smoking. Blood cadmium levels among non-smoking study participants from the Inuit Health Survey were about 3 to 10 times less than for than for the general Inuit population. Sustained efforts on anti-smoking campaign are needed to address this on-going public health issue.
The identification and measurement of new chemicals in commerce that might be transported to the Arctic and bioaccumulate in wildlife and northern people are on-going research needs that will require substantial investment of resources to ensure methods are available to measure these chemicals in people. The expansion of northern biomonitoring to include chemicals that are studied under other national programs would support public health efforts of risk management groups, potentially permit the examination of chemical exposures from local sources, and, overall, provide a better understanding of the full chemical exposure profile of northern populations.
In general, the interpretation of human levels of contaminants is a complex undertaking that often requires using computational tools to increase the understanding of data from exposure studies. There are numerous potential applications for these tools in the Arctic that may assist northerners in managing risks of exposure and for making informed dietary choices. The on-going investment of resources for the development of appropriate computational tools is encouraged.
Health outcomes related to contaminant exposures
The measurement of elevated contaminant levels among northerners has raised concern because many of these widespread environmental contaminants are known for their adverse effects on neurodevelopment. In response to this concern, several prospective longitudinal cohort studies of pregnant women, infants, and children have been conducted globally, some on Arctic populations, to assess the effects of prenatal exposures to mercury, polychlorinated biphenyl (PCB), and lead.
In this assessment, many key findings involving the effects of prenatal contaminant exposures on child health in Canada come from the Nunavik Child Development Study, a prospective mother-child cohort study. Between 2005 and 2010, nearly 300 eleven-year-old children in Nunavik were tested for growth, visual, motor, cognitive, and behavioural development. Comparisons have been made with results from this cohort obtained at a younger age and also to results reported from child cohort studies in other circumpolar Arctic countries.
Additionally, findings for the effects of contaminants on health outcomes for adults in northern Canada have primarily come from two cross-sectional health surveys conducted in Nunavik in 1992 and 2004. Some preliminary data are also available from the Inuit Health Survey (2007-2008) in the other three northern Inuit regions in Canada.
The results from the Nunavik Child Development Study suggest that the composition of PCB congeners found in people in northern Canada may have less toxicity than those in southern populations. With the implementation of the Stockholm Convention, environmental PCB concentrations are expected to now be in decline. The combined effects of these two factors may change the concern of PCB exposure on the health of northerners in the future. Health studies that examine on-going and future PCB exposures for Indigenous people in northern Canada could provide confirmation of these assumptions.
At the same time, some new and emerging contaminants, such as perfluorooctane sulfonate (PFOS) and PBDEs, are now being found in Arctic biota and humans. There is preliminary evidence that both groups of chemicals have potential effects on the thyroid and the endocrine system. NCP studies that include new and emerging contaminants will permit the NCP to assess whether the next generation of chemicals may become a health concern in the North.
New data related to the role of mercury and POPs on cardiovascular disease risk factors collected from several cross-sectional studies conducted in the circumpolar Arctic have also been inconsistent. These inconsistencies may be due to the relatively small number of samples collected during each separate study; however, combining datasets may provide more power to elucidate potential effects of contaminants on health. As well, circumpolar studies outside of Canada have examined associations between Type 2 diabetes and POP exposures. It is recommended that Canadian studies also examine this association.
There is increasing evidence that some chemical forms of selenium found in traditional food (with naturally high concentrations of selenium) may be of lower toxicity than other chemical forms of selenium that are often found in selenium dietary supplements, in drinking water, or in occupational settings. More research is needed on the chemical forms of selenium present in selenium-rich traditional northern diets. While selenium is an essential nutrient for human health, it can also be toxic at elevated exposures, leading to selenosis. However, in some cases, selenium has been found to be a beneficial cofactor for mercury and POP effects on risk of cardiovascular disease. Selenosis has not been specifically observed or monitored in Canadian Inuit populations. Both the benefits and potential risks of elevated selenium consumption from a traditional diet warrant further investigation.
Communication about contaminants
The NCP is a best practice program model that supports capacity building, and it ensures participation of northern Indigenous people in program management, research, and information dissemination. Since the early years of the NCP, benefit-risk communication has been undertaken by Indigenous partners and territorial and regional health authorities. Health messages created during NCP projects have focused on the amount and types of traditional food consumed, as well as the benefits of traditional food consumption. However, the communication of research results and advisories to northern communities remains a challenging task due to the complexity of balancing the social, cultural, economic, spiritual, and nutritional benefits of consuming traditional foods with the potential health risks from contaminant exposures.
Positive experiences in communicating research results in the North have been found when studies are designed and completed through a partnership approach between researchers and northern communities. Effective northern communication tools include those that permit easy understanding of research results and make results accessible past study completion, such as through the creation of visual banners or signs posted in public locations. On the other hand, communication tools that contain complex scientific language are sometimes difficult for community members to understand.
Overall, local health advisories in northern regions are important interim measures to address contaminant exposures until concentrations in traditional food decline to safe levels. However, the rapid dispersal of messages meant for one group or location can create anxiety and confusion in other areas where an advisory does not apply, or is not intended. Moreover, key information can be misconstrued if language is changed during subsequent reporting through the media and social media. Continuous communication is therefore required locally to reinforce the validity of messages for specific audiences and to prevent confusion in other communities. There is also a need to conduct evaluations after risk communication activities, to ensure that messages were released and received as planned and expected.
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