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Environmental exposures come with costs and benefits for workers, families, industries and communities. When exposures are potentially adverse, ethically, what should be the burden of proof of harm versus proof of safety? Will scrutiny be scrupulous, and how will evidence be weighed to ensure The Right to a Healthy Environment under a newly-amended Canadian Environmental Protection Act (CEPA) or the Pest Control Products Act (PCPA)?
A lot of work over extended periods of time is generally in place before authorities reach a conclusion that an environmental exposure causes harms, particularly for high use and/or lucrative products. Numerous scientific challenges may be met, however, with modern data capabilities and sophisticated methods with powerful computing.
Determining causality in human epidemiology is complex, with several possible routes of arguments. In addition to plausibility on the basis of laboratory studies, research that will result in policy change requires a combination of longitudinal exposure and health data, and forensic investigations of exposures and mechanisms of harms as outlined, for example, in the Halifax Project1 and investigation of workers’ breast cancer.2 Indeed, how to conduct and to synthesize such studies is its own field of study.
Longitudinal studies capture temporality – that an exposure preceded a health outcome – so these resource-intensive datasets may provide powerful evidence that certain exposures cause related outcomes. Canada has some longitudinal studies with limited data on well-known toxicants as well as biobanking. These include the national Maternal-Infant Research on Environmental Chemicals (MIREC), as well as regional studies such as the Ontario Health Survey and Atlantic PATH (with its helpful collection of toe nail samples), and some efforts with Aboriginal (particularly northern) populations.
The Canadian Health Measures Survey (CHMS) was initiated after it was decided that Canada would not join the larger National Health and Nutrition Examination Survey (NHANES) effort in the US. CHMS “cycles” are periodic “snapshots” in largely healthy people of a particular sample of toxicants in blood and urine for each cycle, as well as some basic health information from a physical examination and questionnaire. Some chemicals or metabolites are repeated in subsequent cycles, and some are one-time assessments. Importantly, unlike longitudinal studies, measures are not repeated in an identified cohort; each cycle is a cross-section of Canadians who have access to the facilities for the testing. Participants are not Aboriginal or in the North; there are separate smaller projects for them.
Caution is warranted in comparing CHMS cycles because detection limits are not always consistent. Finally, the CHMS may not assess regrettable substitutions as seen for example with:
Additional information sources would be needed beyond the CHMS to establish causality of exposure and health outcome, as temporality cannot be determined in one-off studies, and ongoing state of health is not followed.
Occupational and regional clusters in workers, and vulnerable, disadvantaged, racialized and marginalized individuals and communities, such as investigated by Brophy, Keith, Gilberson, Rochon-Ford and others, can be informative; unfortunately with higher exposures and higher incidence of harms.2,4
Surrogate exposure data may apply locally or according to occupation, such as air quality or drinking water quality from municipal supplies or geological survey data for groundwater determined by postal code, or nutritional intake with questionnaires. CANadian Urban Environment (CANUE) works on air quality, “greenness” and urban form.
Information infrastructure needs to be developed, to mine data on health outcomes and environmental exposures (beneficial and adverse) – in the air, water, food, at home, work, school and during leisure. Some means to fill “exposure” gaps include accessing under-utilized data sources such as geological groundwater data and legacy lead pipe infrastructure, a clinical environmental exposures questionnaire, and facilitating access to testing for toxicants in certain populations when environmentally-linked conditions are being investigated.5 Collecting, confederating and conducting ongoing analyses of exposure and health data may facilitate identification of exposures that contribute to morbidity, disability and premature mortality in Canada (and associated burdens on society and costs to the public purse). The Pan-Canadian Health Data Strategy6 is gaining ground, and should include health data that may be related to contaminants. Uncovering links between exposures and adverse health outcomes could prevent great costs to Canadians, their caregivers and the health care system, as well as vast lost opportunity.
1. Goodson WH, Lowe L, Carpenter DO, Gilbertson M, Manaf Ali A, Lopez de Cerain Salsamendi A, et al. Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: the challenge ahead. Carcinogenesis [Internet]. 2015 Jun [cited 2018 Mar 13];36(Suppl 1):S254–96. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4480130/
2. Gilbertson M, Brophy J. Causality Advocacy: Workers’ Compensation Cases as Resources for Identifying and Preventing Diseases of Modernity. New Solut [Internet]. 2018 Nov 22 [cited 2018 Dec 10];1048291118810900. Available from: https://doi.org/10.1177/1048291118810900
3. Canada H. Sixth report on human biomonitoring of environmental chemicals in Canada [Internet]. 2021 [cited 2022 Jan 15]. Available from: https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/environmental-contaminants/sixth-report-human-biomonitoring.html
4. Gilbertson M. Index of Congenital Minamata Disease in Canadian Areas of Concern in the Great Lakes: An Eco-Social Epidemiological Approach. Journal of Environmental Science and Health, Part C [Internet]. 2009 Nov 30 [cited 2018 Jun 8];27(4):246–75. Available from: https://doi.org/10.1080/10590500903310120
5. Marshall L, Weir E, Abelsohn A, Sanborn MD. Identifying and managing adverse environmental health effects: 1. Taking an exposure history. CMAJ [Internet]. 2002 Apr 16 [cited 2017 Aug 11];166(8):1049–55. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC100881/
6. Public Health Agency of Canada. Moving Forward on a Pan-Canadian Health Data Strategy [Internet]. 2022 [cited 2022 Apr 28]. Available from: https://www.canada.ca/en/public-health/programs/pan-canadian-health-data-strategy.html