Occupational cancers in the chemical sector

Nigel Bryson OBE considers why occupational cancers receive little public attention in relation to other work-related fatalities.

During 2012, the Health and Safety Executive (HSE) published a series of research reports regarding occupational cancers. Using previous studies on occupational health, the HSE generally estimated that around 6000 people a year died from work-related cancers. Having funded these studies in the UK, by 2008, the HSE estimated that around 8000 people per year died from occupational cancers. In addition, there were around 13,500 new cancers being registered annually that are likely to have work-related causes.

An increase in the annual number of work-related fatal injuries usually causes much discussion about whether standards are dropping or improving. During 2011/12, there were 173 workers killed at work. Yet around 50 times as many people are estimated to have died from occupational cancers. These deaths hardly get a mention. So why are occupationally related cancers generally invisible?

In this article the issue of occupational cancers will be reviewed and the need to devote more attention to them will be explored.

Cause and effect

As with many ill-health issues, the key factors to consider are as follows.

  • The time lag: Often, the time taken for the onset of symptoms from initial exposure to a carcinogen (cancer-causing agent) to the cancer being diagnosed can take many years. For example, the asbestos-related disease mesothelioma can take up to 50 years to develop from initial exposure.

  • Safe level: For carcinogens it is often impossible to establish a safe exposure level. In the face of no safe limit being identified, a reasonably practicable control limit may not protect some people.

  • Work cause: The use of epidemiology as a main statistical tool to identify if specific substances at work can cause cancer has limitations. The reason that mesothelioma has been directly linked with asbestos exposure is due to the high numbers of recorded deaths within specific occupations. Smaller numbers of cancer deaths are more difficult to separate out to specific occupations.

  • At point of death: Death certificates may record the last occupation of a person but this may not reveal former occupations where they may be exposed to carcinogens.

These factors mean that people may not associate the cancer they now have with the work they did previously or — indeed — may still be doing. Consider the following example.

4,4’-methylene-bis-ortho-chloroaniline (MbOCA)

MbOCA is a Class 1 carcinogen as defined by the International Agency for Research on Cancer (IARC). The workplace exposure limit for MbOCA (8-hour Time Weighted Average (TWA)) is 0.005mg/m3. MbOCA also has a biological monitoring guidance value (BMGV) of 15µmol MbOCA/mol creatinine in urine samples collected at the end of shift. The main route of entry of the substance is through the skin, hence biological monitoring is important in identifying if workers are being exposed to MbOCA.

In the review done for the HSE, both MbOCA and Isocyanates controls were reviewed. They found the following.

  • Using biological monitoring as a measure, MbOCA exposures in the polyurethane industry had not fallen between the intervention made by the HSE in 2006 and the survey taken in 2008.

  • Using the Health and Safety Laboratory’s (HSL) biological monitoring database as a reference, there had been “no discernible downward trend in urinary MbOCA levels since 1996”. During 1996 to 2008, the vast majority of urinary MbOCA data from the HSL’s biological monitoring database “has remained around the range of 5 to 10μmol/mol creatinine, against a UK biological monitoring guidance value (BMGV) of 15µmol/mol creatinine”.

  • The 90th percentile of urinary MbOCA results from the 2008 survey were at a level of 10µmol/mol creatinine. It was argued that, while this was below the limit value, it was “not associated with good occupational hygiene practice in all cases”. The researchers concluded “that there was scope for improvements in exposure controls and working practices at a number of the sites visited”.

  • The data from the 2008 Disease Reduction Programmed (DRP) survey showed that 70% of urinary values were below 5µmol/mol creatinine. The researchers indicated that if the biological monitoring limit was based on the 2005/6 and 2008 data, it would “likely be less than 10µmol/mol creatinine”.

  • At 7 of the 18 sites visited urinary, MbOCA results above the biological limit were measured “with 11 of the 83 workers providing samples exceeding the BMGV on at least one occasion”.

In addition, deficiencies in the COSHH assessments were found at 11 sites. The researchers stated the following.

“Deficiencies relating to COSHH assessments included no information on groups of workers exposed, an inadequate description of the tasks with exposure potential, an inadequate description of the exposure controls and the measures used maintain these controls and a failure to consider available information on exposures, in the form of biological monitoring results, in the assessment.”

The results from the survey showed that control measures in most of the surveyed workplaces — around 70% — could reduce blood levels of MbOCA to below 5µmol/mol creatinine. Yet at seven sites, measurements above 15µmol/mol creatinine were recorded. Given that the main route of exposure was through the skin, the researchers thought that working practices in the use of gloves could help reduce exposure.

This highlights one of the central difficulties in dealing with carcinogens. As noted in the Approved Code of Practice associated with the Control of Substances Hazardous to Health (COSHH) Regulations 2002: “So in the present state of knowledge it is usually not possible to specify any wholly ‘safe’ limits’.”

In the guidance on the COSHH Regulations in Appendix 1, reference is made to the importance of adequately reducing exposure, where it cannot be eliminated: “For carcinogens or mutagens, it is particularly important that employers control exposure to as low a level as is reasonably practicable. This is because of the high risk of death associated with many forms of cancer, and the fact that the level of exposure affects only the probability of cancers occurring in any exposed population, not the severity of the disease in individuals.”

The COSHH Regulations require employers to prevent exposure to hazardous substances or — where this is not reasonably practicable — adequately control exposure. The Regulations establish the general principles of prevention that must apply. MbOCA has a Workplace Exposure Limit (WEL) of 0.005mg m3 (8-hour TWA). However, this is not a safe limit and employers need to achieve the lowest level that is “reasonably practicable”.

With biological monitoring in 70% being below 5µmol/mol creatinine, it could be argued that most of the sector should be able to comply with this limit and reduce exposure accordingly.

This example has been used to highlight an approach taken with a carcinogen within the chemical sector that was studied in depth.

Carcinogens in the chemical sector

In the study of carcinogens done for the HSE, the deaths of workers were identified by the sectors they worked in. For the chemical sector, the following carcinogens were estimated as a cause of death in 2004 and 2005.

  • Asbestos: 272 deaths.

  • Silica: 22 deaths.

  • Diesel fumes: 4 deaths.

  • 2,3,7,8-Tetrachlorodibenzodioxin (TCDD): 19 deaths.

The Chemical Downstream Oil Industry Forum has established a working group to review occupational health in the sector. The statistics for estimated cancers in the chemical sector identified above have been recognised and the forum is likely to promote action to improve preventative measures.

Given the failings in the COSHH assessments and some controls identified with a carcinogen that was the subject of a HSE intervention, managers would be well advised to review the issue of occupational cancer now.