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Safeguard Magazine

How work can give you cancer

ANDREA ‘t MANNETJE reports on recent New Zealand research which shows more awareness of workplace carcinogens is urgently needed.

It has been estimated that yearly in New Zealand from 200 to 400 people die from a work-related cancer. This is an estimate based on epidemiological studies which show that people working in jobs where known carcinogens are likely to be present have a higher risk to develop cancer, compared to people not exposed to carcinogens at their job. This increased risk is not explained by lifestyle factors such as smoking, and we know this from epidemiological studies conducted in the US, UK, Europe, Australia, and also New Zealand.

A carcinogen is defined as a cancer-causing substance or agent. Our knowledge on what causes cancer in humans is based on animal studies as well as epidemiological studies in human populations. It generally takes a large number of such studies before sufficient evidence has accumulated to classify a certain substance or agent as carcinogenic to humans. There are agencies that periodically review the evidence regarding the carcinogenicity of certain exposures, and one of them is the World Health Organisation’s International Agency for Research on Cancer (IARC). Experts in the field meet for a week to discuss the scientific evidence after which the agent is classified into:

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    group 1 (carcinogenic to humans);
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    group 2A (probably carcinogenic to humans);
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    group 2B (possibly carcinogenic to humans); or
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    group 3 (not classifiable).

Common carcinogens

Currently, IARC has classified 113 agents as carcinogenic to humans. Among these, more than 50 commonly occur in the New Zealand workplace. The most common occupational carcinogens include asbestos, chromium VI compounds, diesel engine exhaust fumes, formaldehyde, involuntary smoking, crystalline silica, solar radiation and wood dust.

There are more than an additional 100 possible or probable human carcinogens present in New Zealand workplaces. For these agents insufficient scientific evidence is currently available to classify them as carcinogenic to humans. Examples include very common workplace exposures such as certain chlorinated solvents, welding fumes, and shiftwork involving circadian disruption.

However, scientific evidence continues to accumulate, which periodically results in an agent being re-classified by IARC from a possible or probable human carcinogen, to carcinogenic to humans. A recent example is diesel engine exhaust. Only last year this very common occupational and environmental exposure was moved from group 2A (probably carcinogenic), in which it was classified since 1988, to group 1 (carcinogenic). This does not mean that diesel engine exhaust is as potent a carcinogen as other proven carcinogens (such as asbestos for example), but it means that there now is scientific consensus that this substance causes cancer in humans.

Exposures by industry

Exposure to occupational carcinogens is not equally distributed in the working population, with some industries having a higher prevalence of carcinogen exposure compared to others. This is reflected in epidemiological studies showing increased cancer risks for certain industries and occupational groups compared to the general population.

The industries for which an increased cancer risk has been observed repeatedly and which in New Zealand have a high number of potentially exposed workers include agriculture, construction, health services, machinery & equipment manufacturing, metal product manufacturing, and wood & paper product manufacturing.

Some of these industries may generally not be thought of as involving carcinogen exposure. Work in the agricultural sector, for example, is widely regarded as healthy employment but exposure to potential carcinogens can nonetheless be common. Of the agricultural chemicals currently in use in New Zealand’s agricultural sector, none are known human carcinogens, but numerous of them are suspected to be carcinogenic to humans. Other very common exposures in agriculture include solar radiation and diesel engine exhaust, both confirmed human carcinogens.

In the construction industry, solar radiation and diesel engine exhaust are also common exposures, as well as exposure to asbestos and silica. Although asbestos is one of the most notorious occupational carcinogens for which awareness is high, exposure studies in the New Zealand building industry have shown that exposures to asbestos above the exposure standard can still occur in demolition.

The health sector also represents a large industry in terms of numbers employed where exposure to carcinogens may be more common than generally thought. For example, many anti-cancer drugs are classified as human carcinogens. Workers can be exposed to these compounds during preparation of the drugs, and also by handling treated patients and laundry.

Other exposures in the health sector include sterilizing agents (eg ethylene oxide is a group 1 carcinogen) and ionizing radiation. In the health sector shiftwork involving the disruption of circadian rhythm is also common, which has been classified as probably carcinogenic to humans (group 2A) since 2010.

In the wood conversion industry exposure to wood dust is common, as well as group 1 carcinogens such as chromium VI compounds, formaldehyde, arsenic and solar radiation. There is room for improved exposure control, illustrated by an exposure study among New Zealand joinery and furniture workers indicating that a majority is exposed to inhalable wood dust levels in excess of international exposure standards.

Intervention barriers

These examples illustrate that exposure to carcinogens remains common in the workplace, and that there is still a lot of opportunity to reduce exposure and thereby reduce the burden of occupational cancer in new Zealand. A number of barriers for the implementation of intervention strategies can however be identified.

Firstly, there is a lack of awareness of which agents commonly present in the workplace are carcinogenic. For example, wood dust is not often regarded as a carcinogen, although it has been classified as such by IARC since 1995. Silica dust is another example: it is widely known to cause silicosis but since 1997 there has been sufficient evidence that silica can also cause lung cancer in exposed workers. Several commonly used chlorinated solvents are classified as probably carcinogenic to humans, but little awareness of this exists.

Another limitation is the lack of awareness of the presence of the carcinogen in the workplace, even for exposures for which the awareness of their carcinogenicity is high. Asbestos is an example of such an exposure. Knowledge of how to recognize the presence of asbestos is limited in the building industry, particularly because few workers today would have installed asbestos themselves. Even for clearly visible exposures, such as wood dust, there is limited awareness of how high these exposures are and whether they exceed the exposure standard. In both examples, exposure measurements are needed to detect and quantify the levels of exposure.

Controlling exposures

Even if the awareness of the carcinogenicity as well as its presence in the workplace is high, there may be insufficient awareness of how to effectively control the exposure. In situations where the carcinogen cannot be replaced by a safer agent (for example in the situation of wood dust) there is a clear need for access to control tools and methods to evaluate their effectiveness. Workplace exposure measurements and video exposure monitoring can play an important part in removing barriers for implementation and evaluation the effectiveness of control measures.

Even for occupational carcinogens for which there is awareness of its carcinogenicity, and awareness of its presence in the workplace, and awareness of how to control the exposure, there is still room for improvement. This is for example the case for one of the most common occupational carcinogens in the workplace: solar radiation (ie UV from the sun).

Awareness then action

In summary, occupational exposure to carcinogens remains very common in New Zealand workplaces and improved awareness is urgently needed. Carcinogens are not simply limited to “chemicals”, but rather represent a wide variety of agents including dusts, radiation, pharmaceutical agents, infectious agents and working circumstances such as shiftwork.

Action is particularly needed for those agents known to be carcinogenic to humans, but for the many possible and probable carcinogens in New Zealand workplace, the precautionary principle should apply.

By reducing exposure to workplace carcinogens, a significant health benefit can be achieved through the prevention of a large number of occupational cancer deaths, and through reducing risks for many other work-related diseases also associated with these common workplace exposures.

DR ANDREA ‘T MANNETJE works as a senior research fellow at Massey University’s Centre for Public health Research. This article was based on the findings of a research project titled “Workplace exposure to carcinogens in New Zealand” which was funded by the Department of Labour and the Health Research Council of New Zealand, and aimed to give an overview of the carcinogens present in New Zealand industries and identify key industries and key carcinogens for which intervention would result in marked reductions in occupational cancer.

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