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.

3D PRINTING

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.

References

ACROLEIN

Acrolein is a highly volatile liquid that is registered for use in Canada as a pesticide. It is used to control weeds and algae in irrigation canals and in water injection systems during crude oil extraction. Acrolein can also be formed and released to the environment from natural sources (e.g. forest fires, fermentation processes), and other human-made sources (e.g. combustion of organic matter and fuel, tobacco smoke, high-temperature cooking, and the forestry industry).

Exposure to acrolein takes place by inhalation and is highest in those who smoke or are exposed to second-hand smoke, work closely with sources of wood and plastic smoke, and live or work in high traffic areas.

Currently classified as a Group 3 carcinogen, acrolein is flagged by IARC as a high priority agent for further assessment by 2019. This is because of new information regarding acrolein’s mechanism of action and its potential role in causing bladder cancer. Other health effects associated with acrolein include changes in lung function and irritation of the respiratory tract.

References

BISPHENOL A

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.

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BLUE LIGHT AT NIGHT

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.

References

CHEMICAL MIXTURES 

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.

References

ELECTRONIC WASTE RECYCLING (E-RECYCLING)

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.

References

HYDRAULIC FRACTURING 

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.

References

POLYBROMINATED DIPHENYL ETHERS

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.

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SEDENTARY WORK

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.

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