Workplace exposure to carcinogens such as diesel exhaust, asbestos and silica are together causing thousands of cancer cases in Ontario each year, says a new study that reveals the toll of on-the-job hazardous substances.
Asbestos leads them all, causing an estimated annual burden (cases that could be prevented) of 630 cases of occupational lung cancer and 140 of mesothelioma in the province, says the paper formally released on Wednesday by the Occupational Cancer Research Centre and Cancer Care Ontario.
Estimates on numbers of workers exposed to carcinogens have been produced before in Canada. This study is the first to estimate the number of cancer cases from workplace exposure in Ontario and is part of a four-year national project, OCRC director Paul Demers said.
"I can't count the number of times that I have talked about how important it is to prevent exposure to carcinogens, but raising awareness doesn't always lead to action," said Dr. Demers, who is leading the study. "I think the numbers are important to make this real and push action towards preventing exposure to these causes of cancer."
This is the first publication in the project; a national picture is expected within about a year.
Workers in Ontario spend on average a third of their waking hours on the job, although little research has been done until now on the impact of cancer-causing exposure in the workplace, the paper said.
The study examined a range of known or suspected carcinogens, including radon, wood dust and shift work. It identified four key carcinogens: Asbestos, diesel-engine exhaust, silica and solar ultraviolet radiation, or outdoor sun exposure.
These four "should be prioritized for exposure prevention and control because they present the best opportunity for making a large health impact," the paper said.
Asbestos also causes an estimated 15 laryngeal cancers in Ontario each year, as well as some ovarian cancers. By industry, most workplace exposure to asbestos is in construction, largely through maintenance and renovations of homes and buildings, as well as in manufacturing.
"Asbestos is still our worst carcinogen, or nightmare, depending upon your choice of words," Dr. Demers said. "It's one that has had such a big impact that we're going to be living with it for a while."
Canada will ban asbestos in 2018. However, it is still in products such as insulation, tiles and brake pads and was widely used in construction of homes and public buildings such as schools and universities.
Other substances also hurt workers' health. Exposure to fine crystalline silica dust – the most common form of which is quartz – causes an estimated nearly 200 work-related lung cancer cases each year. Workers in construction and manufacturing are most exposed.
Exposure to diesel exhaust accounts for an estimated 170 lung cancer cases and 45 bladder cancer cases each year. Workers in mining and transportation have the highest level of exposure.
Solar radiation causes an estimated 1,400 non-melanoma skin cancer cases a year, with workers in agriculture and construction most exposed.
The paper also examined shift work that disrupts circadian rhythms as a potential carcinogen, saying studies since 2007 have found this type of work may be associated with breast cancer. Although cautioning that additional research is needed, the paper said shift work "may be responsible" for 180 to 460 new cases of breast cancer in Ontario a year.
These cancers are almost entirely preventable, Dr. Demers said. The study recommended strengthening rules on workplace exposure limits, reducing or eliminating the use of toxic substances on the job, and creating registries of worker exposures to occupational carcinogens.
Researchers in Britain and at the World Health Organization have done similar studies. The Canadian study estimated the cancer burden using data from Carex Canada (a research project) on the prevalence of workplace exposure to different carcinogens, along with Statistics Canada labour force survey data. Funding was from the Canadian Cancer Society.