Emerging Issues

CAREX Canada has developed profiles and estimates of occupational and environmental exposure for a total of 73 agents evaluated by the International Agency for Research on Cancer (IARC) as known, probable, and possible carcinogens, and classified by the CAREX team as important exposures in the Canadian setting. As part of our ongoing surveillance of these exposures, the CAREX team also monitors substances of growing concern to Canadians. This includes substances scheduled for future evaluations by IARC, which may or may not be classified as known or suspected carcinogens. We’ve summarized the status of many of these agents below, and provide links to further information about their known or suspected health effects.


3-D printing, which is also known as additive manufacturing, is a process that creates three-dimensional objects by depositing a specific material layer by layer. Different materials with varying properties are used in 3-D printing, including thermoplastics (the most popular of which are acrylonitrile butadiene styrene (ABS) and polylactic acid), metals, ceramics and glass, resins, and flexible materials (e.g. polypropylene, rubber). Typically, the material is deposited in its liquid or powdered form. Given its potential for streamlining production (e.g. in manufacturing, aerospace, and healthcare) and its growing accessibility, 3-D printing is increasingly used by industry and the general public. This has potential implications for occupational and environmental exposure. Over the past few years, there has been an increased interest in assessing this exposure. Preliminary studies show that 3-D printers may produce elevated levels of ultrafine particles, which are believed to impact respiratory functioning and cardiovascular outcomes. They may also produce volatile organic compounds (VOCs), which encompass a large group of compounds implicated in eye and nose irritation, and liver, kidney, or central nervous system damage. In particular, styrene, which is a possible carcinogen, is the primary VOC released when ABS is used. Furthermore, some metal powders that are used in 3-D printing (e.g. cobalt and nickel alloys) have been classified as possibly carcinogenic by IARC and are associated with health effects including neurotoxicity and lung complications.



Bisphenol A (BPA) is a synthetic compound widely used in epoxy resins, such as paper sales receipts and protective linings of many canned foods and beverages, as well as plastics, such as beverage bottles and food containers. The World Health Organization reviewed the carcinogenicity of BPA in 2010 and concluded that there was insufficient evidence to assess its carcinogenic potential at that time. Since then, several studies have provided enough new information to warrant a review and IARC has included BPA in their list of high priorities for review by 2019.

Based on BPA’s status as a potential endocrine disruptor, Health Canada’s Food Directorate recommends that the general principle of ALARA (as low as reasonably achievable) be applied to continue efforts on limiting BPA exposure to infants and newborns, specifically from pre-packaged infant formula products used as a sole source of food.



Blue light is a range in the visible light spectrum with the highest energy and shortest wavelength. Due to the use of artificial lights, periods of light and darkness are no longer solely controlled by the sun. The use of white LED lights (i.e. in streetlights, indoor lighting) and light emitting devices (i.e. TVs, cellphones, computers, e-books) has greatly increased people’s exposure to blue light. Exposure to any light at night is known to disrupt the body’s circadian rhythms, and blue light causes the greatest disruption. Circadian rhythms are biological processes that generate the sleep-wake cycle and are responsive to the solar light-dark cycle.

By disrupting circadian rhythms, light at night suppresses melatonin production. The short wavelengths of visible light (i.e. blue light) are known to have the greatest impact on melatonin suppression. Melatonin is a hormone that relays environmental light and darkness information from the eye to the brain, and then to all body tissues. Researchers hypothesize that melatonin suppression could be related to an increased risk of breast and prostate cancer.

Several studies show a link between circadian rhythm disruption at work and increased risk of breast and prostate cancer. The International Agency for Research on Cancer has classified shiftwork that involves circadian disruption as a probable carcinogen (Group 2A), based on sufficient evidence in experimental animals and limited evidence in humans. Recent reports show that these hormone dependent cancers may also be positively associated with outdoor artificial blue light exposure. Exposure to blue light at night while indoors has not yet been investigated in relation to breast and prostate cancer.



Canadians are exposed to a mixture of chemical substances in our workplaces and communities; these substances may be naturally occurring or human-made. Once in the environment, these substances can enter the body through a variety of pathways and routes of exposure, including inhalation of indoor and outdoor air, ingestion of food and water, and use of consumer products. It is challenging to accurately characterize these complex exposures and to measure the impact they may have on human health, especially in combination. Some scientists hypothesize that chemical mixtures may have carcinogenic effects even when their constituents are not known to be carcinogenic. Much of the current research on the health impacts of chemical exposures has been conducted one chemical at a time, which limits our understanding of how mixtures may operate in combination.

Many national regulatory agencies and institutes in Canada and abroad have recognized the challenges of chemical mixtures. The World Health Organization (WHO) has developed a framework to assess chemical mixtures, to support international efforts, and to help facilitate agreement. They also define a variety of terms relevant to discussing chemical mixtures, for example:

  • Aggregate exposure: An exposure scenario that considers one substance in multiple routes or pathways (also known as ‘single chemical, all routes’).
  • Antagonistic: When exposure to substances present in a mixture has toxicity lesser than what would be expected from the sum of their parts.
  • Cumulative exposure: An exposure scenario that considers multiple substances in multiple routes or pathways (also known as ‘multiple chemicals, all routes’).
  • Synergistic: When exposure to substances present in a mixture has toxicity greater than what would be expected from the sum of their parts.

Researchers are developing new approaches to better assess exposure to mixtures. For example, some have used the results of large-scale biomonitoring studies to identify the most common chemical co-exposures in a population. This is useful to narrow the scope of which mixtures could be prioritized for further investigation. Others are using computer modeling and screening databases to predict if an exposure to a mixture is expected to produce an additive, synergistic, or antagonistic effect. Several new research initiatives combine exposure monitoring with internal exposure science (e.g. genomics, metabolomics) in an approach called exposomics, which attempts to characterize a person’s exposure in a more comprehensive way. Although these are encouraging developments, researchers generally agree that our understanding of our exposures to mixtures is still emerging.



Electronic Waste (e-waste) is a term used to describe all types of electrical and electronic equipment and its parts that have been discarded by the owner without the intention of re-use. When e-waste is recycled, heavy metals and organic pollutants (e.g. flame retardants, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs)) can be released into the environment. These materials are known to cause adverse health effects, such as cancer and impaired thyroid, lung, and/or reproductive functions. Common substances released during e-waste recycling that have also been classified by the International Agency for Research on Cancer as carcinogenic to humans (Group 1) include cadmium, PAHs, and PCBs.

Due to international conventions and regulations that limit the export of e-waste to developing countries, the e-recycling industry is growing within Canada. Studies from low- and middle-income countries identified adverse health effects to those working at or living near informal e-waste processing sites, however few studies have investigated the occupational health and safety of workers at formal e-recycling facilities. Formal e-recycling facilities are licensed and process e-waste indoors with varying degrees of industrial hygiene, worker protection, and pollution control. Studies investigating formal e-recycling facilities often found levels of heavy metal exposure above occupational guidelines and flame retardant levels higher than reference group levels. Two Canadian studies are currently focusing on the occupational health and safety of workers at formal e-recycling facilities. One study by the Institut de recherche Robert-Sauvé en santé et en sécurité du travail focuses on occupational exposure and associated health risks to chemical contaminants, metals, and flame retardants within Quebec e-recycling facilities. Preliminary results from this study found that exposure levels for metals were below occupational exposure limits. The second study by the Occupational Cancer Research Centre is estimating workers inhalation exposure to flame retardant chemicals within an Ontario-based e-recycling facility.



Hydraulic fracturing (or fracking) is an oil and gas extraction process that injects large volumes of fluid containing chemicals and agents, such as sand, at high pressure into rock formations. This process fractures the rock and releases trapped oil and gas.

Several of the chemicals employed in fracturing, including acetaldehydenaphthalene, and crystalline silica (sand), have been classified by IARC as known or suspected carcinogens; silica exposure in workers, in particular, has been documented at levels above allowable workplace inhalation standards. Air emissions from the oil and gas industry, such as diesel exhaustparticulate matter, and polycyclic aromatic hydrocarbons (PAHs), are another source of carcinogen exposures during construction of well pads, drilling, and flaring/venting. The main route of workers’ exposures to carcinogens is inhalation. Communities located near wells can also be exposed to contaminants through air and water.



Perfluoroalkyl substances (PFAS) are a large group of synthetic chemicals that include perfluorooctanoic acid (PFOA) or C8, perfluorooctanesulfonic acid (PFOS), and GenX. They have been used extensively since the 1940s in a wide variety of consumer and industrial products including adhesives, cleaning products, cosmetics, and fire-fighting foams. They’re also used in water-, soil-, and grease-repellant surface coatings for cookware, carpets, fabrics, leather goods, paper, and cardboard packaging. PFAS are not manufactured in Canada, but are present in an assortment of imported goods. In 2008, Canada prohibited the sale, use, and import of PFOS or PFOS-containing products with exception of firefighting and military products.

PFAS are persistent in the environment and are ubiquitous worldwide as contaminants in air, soil, and surface, and ground water. They are also bioaccumulative in humans and animals, and have been detected in blood serum, umbilical cord blood, and breast milk. The main route of exposure is thought to be ingestion from various sources, including food and food packaging migration, water, dust, and hand-to-mouth transfer from treated carpets (particularly in children). Health Canada’s Guidelines for Canadian Drinking Water Quality list maximum allowable concentrations (MAC) of 0.2 and 0.6 µg/L for PFOA and PFOS, respectively.

A large number of epidemiological studies have evaluated associations between PFAS (most focusing on PFOA or PFOS) and a variety of cancers and non-cancer health outcomes including dyslipidemia, thyroid disease, pre-eclampsia, and liver function in children. In 2017, IARC classified PFOA as Group 2B: possibly carcinogenic to humans, based on limited evidence of carcinogenicity in humans and experimental animals and a positive association for cancers of the testis and kidneys. Most recently, IARC flagged some perfluorinated compounds (e.g. PFOA) as a high priority for evaluation by 2022.



Polybrominated diphenyl ethers (PBDEs) are a group of flame retardant compounds used in televisions, computers, electronics, motor vehicles, carpets, and furniture. These chemicals are released into the environment during manufacturing and when products containing them are discarded. As products degrade, PBDEs also end up in household dust, where they can be inhaled and ingested. They persist in the environment, so are considered bioaccumulative, persistent organic pollutants.

IARC has reviewed one PBDE, deca-BDE and classified it as group 3, not classifiable as to its carcinogenicity to humans. No other PBDEs have been reviewed for their potential carcinogenicity. However, a review panel struck by the National Toxicology Program in the U.S., which looked at a mixture of six PBDE compounds, described clear evidence of carcinogenic activity in male and female rats and mice. The Canadian Cancer Society has a useful summary on how to reduce exposures to these PBDE compounds, included below.



Sedentary work is defined as activities that require little physical movement and expend low metabolic energy. Sedentary work can be measured in a number of ways, including time spent sitting, job title, and direct measurement using an accelerometer. One meta-analysis from 2014 demonstrated a positive association between occupational sitting time and colon cancer. Another study found that participants who spent 10 or more years in sedentary work had almost twice the risk of distal colon cancer and almost one and a half times the risk of rectal cancer than those who did not do any sedentary work. This study also reported that the risk from sedentary work was independent of recreational physical activity, which means that being sedentary for long periods of time can increase cancer risk even in people who exercise regularly.

IARC has included sedentary work on their list of high priorities for evaluation by 2019 and will include these and other studies in their comprehensive review.



Indoor farming facilities provide a controlled environment that allows farmers to grow produce and other plants year-round. The increasing number of indoor farming facilities is related to advances in technology; particularly, advances in light technology. In these facilities, horticulture lighting (or grow lamps/lights) produces the wavelengths of the light spectrum that plants use for photosynthesis (i.e., photosynthetically active radiation [PAR] in the range of 400-700 nanometers [nm]). Horticulture lighting may also be used to supplement natural sunlight in large scale greenhouse operations.

Conventional horticulture lighting emits relatively small to negligible amounts of ultraviolet radiation (UVR). However, these lights are now being designed to emit increased UVR compared to conventional varieties. While UVR wavelengths are not in the range of PAR, it is biologically relevant as it helps regulate plant growth.

UVR is a potential hazard to workers in indoor farming facilities. UVR with wavelengths in the range of 100 to 400 nm has been classified by IARC as Group 1, known human carcinogen. Exposure is associated with skin cancer and ocular melanoma, and may also have other adverse health effects on the skin (e.g., burns) and eyes (e.g., photokeratitis). UVR-emitting lights also produce infrared radiation (IR), which may also damage the skin and eyes.

Currently, there has been little research conducted in indoor farming facilities to evaluate workplace exposure to UVR. Research in cannabis growing facilities revealed that worker exposure to UVR from horticulture lights is possible. However, the authors concluded that more research is needed to fully characterize workers’ exposure to UVR, particularly as increased UVR-emitting grow light are utilized.

Simpson (2018) also reported that germicidal lamps are being introduced into the indoor cannabis cultivation practice to help control powdery mildew. These lamps emit high levels of UVR, typically in the UV-C portion of the spectrum, which is the most harmful component of UVR. Simpson (2018) found that UVR overexposure could occur within seconds to minutes for a worker approximately 3 feet away from a germicidal lamp, when comparing the average dose of effective UV light to an occupational exposure limit of 3 mJ/cm2 for an 8-hour shift.

As UVR-emitting technologies are introduced into indoor farming facilities, additional research should be conducted to properly assess worker exposure and hazard levels.


Photo: Flickr, AgriLife Today


Wildfires, including fires in forests, shrublands, and grasslands, typically occur between April and early October in Canada and cause approximately 7,300 fires that consume 2.5 million hectares of land each year (1,2). The frequency of fires is expected to increase as climate change creates weather conditions that increase the risk of wildfires (3).

During wildfire season, elevated levels of fine particulate matter (PM2.5) in smoke is the main concern for public health. In addition to particulate matter, wildfire smoke contains several known or suspected carcinogens, including benzene, polycyclic aromatic hydrocarbons (PAHs), 1,3-butadiene, acrolein, formaldehyde, and others (4). It also contains a variety of other gases and substances including ozone (O3), carbon monoxide (CO), sulphur dioxide (SO2), volatile organic compounds (VOCs), mercury, and nitrogen dioxide (NO2) (5).

Wildfire smoke can cause symptoms such as eye irritation, headaches, sore throat, coughing, and runny nose (1,6). Some populations are more vulnerable to adverse health effects following wildfire smoke exposure including seniors, people working outdoors, children, pregnant people, and those with existing health conditions (1,6). Exposure can exacerbate existing cardiovascular and lung diseases and is associated with increased mortality and respiratory morbidity (7,8). The long-term health effects from acute, periodic exposures to wildfire smoke are still unknown, and are a focus of emerging research as wildfire season in Canada continues to become longer and more extreme (9-11). The International Agency for Research on Cancer classifies outdoor air pollution and associated particulate matter as carcinogenic to humans, and cites wildfire smoke as a contributing source (12).

Some workers may be at higher risk of exposure to wildfire smoke and associated health effects. In particular, wildland firefighters’ exposure is greater than the general public’s due to proximity, increased respiration, and inconsistent and sometimes inadequate respiratory protection 13,14). Their exposure varies with wildfire season length and number of seasons being exposed. Navarro et al. estimated that US wildland firefighters have an increased risk of lung cancer mortality (8% – 43%) in addition to increased risk of cardiovascular diseases (15). Other occupations with the potential to be exposed to wildfire smoke at work include first responders attending to wildfire related emergencies and outdoor workers (12,14,16,17).

  1. Government of Canada. Wildfire smoke and your health (2021)
  2. Natural Resources Canada. Forest fires (2021)
  3. Natural Resources Canada. Climate change and fire (2020)
  4. International Agency for Research on Cancer (IARC). IARC Monographs. Painting, Firefighting, and Shiftwork: Volume 98(2010) (PDF)
  5. BC Centre for Disease Control. Evidence Review: Wildfire smoke and public health risk (2014) (PDF)
  6. BC Centre for Disease Control. Health Effects of Wildfire Smoke (2021) (PDF)
  7. Cascio WE. “Wildland fire smoke and human health.” Sci Total Environ 2018;624:586–595.
  8. Reisen F, Duran SM, FlanniganM, Elliott C, Rideout K. “Wildfire smoke and public health risk.” Int J Wildland Fire 2015;24(8):1029–1044.
  9. Coogan SCP, Robinne FN, Jain P, Flannigan MD. “Scientists’ warning on wildfire — a Canadian perspective.” Can J For Res 2019; 49(9):1015–1023).
  10. Government of Canada. Climate change and fire (2020)
  11. Wang X, Thompson DK, Marshall GA, Tymstra C, Carr R, Flannigan MD. “Increasing frequency of extreme fire weather in Canada with climate change.” Climatic Change 2015;130(4);573–586.
  12. International Agency on Research for Cancer (IARC). IARC Monographs. Outdoor Air Pollution: Volume 109(2016) (PDF)
  13. Cherry N, Barrie JR, Beach J, Galarneau JM, Mhonde T, Wong E. “Respiratory Outcomes of Firefighter Exposures in the Fort McMurray Fire: A Cohort Study From Alberta Canada.” J Occup Environ Med 2021;63(9):779-786.
  14. Navarro K. “Working in Smoke: Wildfire Impacts on the Health of Firefighters and Outdoor Workers and Mitigation Strategies.” Clin Chest Med 2020;41(4):763-769.
  15. Navarro KM, Kleinman MT, Mackay CE, Reinhardt TE, Balmes JR, Broyles GA, Ottmar RD, Naher LP, Domitrovich JW. “Wildland firefighter smoke exposure and risk of lung cancer and cardiovascular disease mortality.” Environ Res 2019;173:462-468.
  16. Moitra S, Tabrizi AF, Fathy D, Kamravaei S, Miandashti N, Henderson L, Khadour F, Naseem MT, Murgia N, Melenka L, Lacy P. “Short-Term Acute Exposure to Wildfire Smoke and Lung Function among Royal Canadian Mounted Police (RCMP) Officers.” Int J Environ Res Public Health 2021;18(22):11787.
  17. National Institute for Occupational Safety and Health. Outdoor Workers Exposed to Wildfire Smoke (2021)

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As a national organization, our work extends across borders into many Indigenous lands throughout Canada. We gratefully acknowledge that our host institution, the University of British Columbia Point Grey campus, is located on the traditional, ancestral and unceded territories of the xʷməθkʷəy̓əm (Musqueam) people.