Chromium (Hexavalent) Occupational Exposures
Chromium (Hexavalent) Occupational Exposures
Overview
Inhalation and dermal contact are the most important routes of occupational exposure to hexavalent chromium (VI).[1] CAREX Canada’s estimates indicate that approximately 85,000 Canadians are occupationally exposed to chromium (VI). Most exposures (87%) occur in the low exposure category. However, many workers are exposed to moderate or high levels of chromium (VI) in fabricated metal products, transportation equipment manufacturing, and machinery manufacturing.
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The industries with the largest numbers of exposed workers are automotive maintenance and repair and printing and support activities. Other industries with larger numbers of workers exposed to chromium (VI) include building equipment contractors and commercial and industrial machinery and equipment repair and maintenance.
In terms of occupation, the groups with the largest number of exposures to chromium (VI) are welders (who are exposed when welding stainless steel), printing press operators, construction millwrights and industrial mechanics, and automotive service technicians, truck and bus mechanics, and mechanical repairers.
According to the Burden of Occupational Cancer in Canada project, occupational exposure to chromium (VI) leads to approximately 50 lung cancers, and less than five possible sinonasal cancers each year in Canada, based on past exposures (1961-2001).[2,3] This amounts to 0.2% of all lung cancers and 0.5% of all sinonasal cancers diagnosed annually. Most chromium(VI)-related cancers occur among workers in the manufacturing sector.[3]
Prevalence Estimate
Results show that approximately 85,000 Canadians are occupationally exposed to chromium (VI); 92% of these workers are male. The largest industrial group exposed is the automotive repair and maintenance industry.
When examining exposure to chromium (VI) by occupation, the largest exposed group is welders (where exposure to chromium (VI) occurs during the welding of stainless steel) (19,000 workers exposed), printing press operators (9,500 workers exposed), construction millwrights and industrial mechanics (8,300 workers exposed), and automotive service technicians, truck and bus mechanics, and mechanical repairers (7,300 workers exposed).
There was significant variation in job title by gender; the largest groups for women are printing press operators (approximately 1,500 women exposed), followed by dental technologists and technicians (approximately 1,200 exposed), while many more men exposed to chromium (VI) are welders, construction millwrights and industrial mechanics, printing press operators, and automotive technicians.
The number of workers exposed to hexavalent chromium decreased by approximately 19,000 workers from 2006 to 2016 (a 19% decrease). This was primarily driven by a decrease in the number of workers in the manufacturing industry and in the number of workers in repair and maintenance jobs. The proportions of workers exposed to hexavalent chromium through CCA treated wood were also adjusted to account for fewer wood preservation facilities using CCA in 2016 compared to 2006.
Workers exposed to hexavalent chromium by industry in 2016
Workers exposed to hexavalent chromium by region in 2016
Click the second tab to view total number of workers exposed.
* = < 50 workers
Level of Exposure
In total, approximately 85,000 Canadians are exposed to chromium (VI) in their workplaces. The majority of workers exposed to chromium (VI) are in the low exposure category. A substantial number of chromium (VI)-exposed workers are at risk for moderate exposure, while very few are in the high exposure category.
Workers exposed to hexavalent chromium by exposure level in 2016
Level of exposure by industry
Identifying industries with either 1) workers exposed to high levels of chromium (VI) or 2) a larger number of workers exposed to chromium (VI) is important in guiding cancer prevention efforts to prioritize exposed groups and target resources most effectively.
The table below shows the number of workers exposed by industry group and level of exposure to chromium VI. These results highlight industries with the most number of workers, as well as industries with the highest levels of exposure.
For example, in the repair and maintenance industry (which is the largest industrial group exposed to chromium (VI)), all of the exposed workers are in the low category. However, in the fabricated metal product manufacturing and transportation equipment manufacturing industries, we see substantial groups of workers potentially exposed at moderate or high levels. Depending on the goals of a prevention campaign, exposure reduction in the large industrial group might be a useful strategy, or reducing exposure to those at highest risk of exposure could be seen as a priority.
Workers exposed to hexavalent chromium by exposure level and industry in 2016
*Numbers may not add up due to rounding
Methods and Data
Our Occupational Approach page outlines the general approach used to calculate prevalence and exposure level estimates for workplace exposures.
Data Sources
Data used in developing the occupational estimates for chromium (VI) were collected from several sources:
- The Canadian Workplace Exposure Database (CWED) contains 4,400 measurements for chromium (VI) exposure. These measurements were collected during the years 1981 to 2004 in Ontario and British Columbia workplaces.
- Canadian and US scientific peer reviewed publications that addressed chromium (VI) exposure in Canada and the United States.
- Grey literature including technical reports from governments and international bodies.
Prevalence Estimate Method
CAREX defines exposure to chromium (VI) as inhalation and/or dermal exposure to chromium at work above levels expected to be encountered in the general environment (i.e. from food or drinking water sources).
To determine the number of workers potentially exposed to chromium (VI) at work, CAREX occupational exposure experts used methods previously established in other peer-reviewed CAREX projects in Europe. A series of steps were taken to assign exposure proportions to occupations and industries at risk of exposure to chromium (VI).
- Occupations and industries at risk of possible exposure to chromium (VI) were identified using any combination of data sources described above.
- The total number of workers in each identified occupation and industry intersection was obtained from Statistics Canada 2016 census data.
- A percentage of workers exposed was assigned to that occupation and industry intersection. Percentages were determined by consultation with existing evidence in the data sources, previously established methods from the Europe CAREX estimates and the expert judgement of CAREX occupational hygienists.
- The number of workers in the identified group is multiplied by the assigned percentage to calculate the prevalence estimate of workers exposed to chromium (VI).
Exposure Level Method
CAREX uses available workplace exposure measurements in the CWED to create exposure level categories by industry and occupation. For chromium (VI), these categories are:
Category 1: Low Exposure
A group of workers (people in the same job category and industry) is put in this exposure category for one of two reasons:
- The are no valid measurements, but a hygienist identified this group as typically exposed during literature and other reviews;
- There are valid exposure measurements in the CWED and a hygienist review determined that exposure is plausible; AND EITHER:
- There are less than 10 samples available in the CWED, OR
- There are ≥10 measurements available but they do not meet the criteria for Moderate Exposure.
Category 2: Moderate Exposure
A group of workers is put in this exposure category if:
- There are at least 25 individual samples in the CWED, AND
- 20% or more samples have a value higher than 0.01 mg/m3 (which is the current occupational exposure limit for insoluble chromium (VI) compounds).
OR
- There are at least 10, but less than 25, individual samples in the CWED, AND
- 20% or more samples have a value higher than 0.05 mg/m3 (which is the current occupational exposure limit for water-soluble chromium (VI) compounds).
Category 3: High Exposure
A group of workers is put in this exposure category if:
- There are at least 25 individual samples in the CWED, AND
- 20% or more samples have a value higher than 0.05 mg/m3 (which is the current occupational exposure limit for water-soluble chromium (VI) compounds).
Sources
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