Cancer risks amongst workers exposed to tetrafloroethylene

A recently published study of workers exposed to tetrafloroethylene has failed to identify any risk of cancer [1]. However, despite efforts to include as many exposed workers as possible the study had little power and so more research is needed to clarify whether there is a risk to worker health from exposure.

Tetrafluoroethene Molecular formula C2F4 Molar mass 100.02 g/mol Density 1.519 g/cm3 at -76 °C Melting point -142.5 °C, 131 K, -225 °F Boiling point -76.3 °C, 197 K, -105 °F

Tetrafluoroethylene (TFE) is used to make fluorinated polymers including polytetrafluoroethylene (PTFE). It is a colourless, odourless gas that is unstable and tends to form explosive peroxides when in contact with air.

There is good evidence from studies in rats and mice showing increased incidence of liver and kidney cancers along with leukaemia. On the basis of these data, in 1999 the International Agency for Research on Cancer (IARC) classified TFE as possibly carcinogenic to humans. At that time there was insufficient epidemiological data to be informative.

Our study was carried out in six PTFE production plants in five countries, which at the time the study was initiated were all of the relevant production facilities in Europe and North America. We constructed a job-exposure matrix (covering the period 1950–2002) for TFE and ammonium perfluoro-octanoate (APFO), a chemical used in the polymerization process [2]. We also identified the vital status of the cohort and cause of death for the deceased. National reference rates were used to calculate standardized mortality ratios (SMRs).

Among the almost 5,000 workers ever exposed to TFE, we found a statistically significantly lower risk of death from all causes combined and for all cancers. This is often described as the “healthy worker” effect”.  There were non-statistically significantly increased risks for cancer of the liver (SMR = 1.3, based on 8 deaths) and kidney (SMR = 1.4, 10 deaths) and for leukaemia (SMR = 1.5, 12 deaths), and a non-significant upward trend of the SMR for liver cancer with estimated cumulative exposure to TFE. The estimated TFE and APFO exposures were highly correlated, and so it was difficult to separately identify health effects from these chemicals.

So we concluded that the study, “narrows the range of uncertainty on potential TFE carcinogenicity but cannot conclusively confirm or refute the hypothesis that TFE is carcinogenic to humans.” Given that the follow-up of the majority of the subjects ended around 12 years ago it seems that the best strategy for reducing the uncertainty will be to update the study to include more recent deaths.

References

1. Consonni, D. et al., 2013. Cancer Risk Among Tetrafluoroethylene Synthesis and Polymerization Workers. American Journal of Industrial Medicine.

2. Sleeuwenhoek, A. & Cherrie, J., 2012. Exposure assessment of tetrafluoroethylene and ammonium perfluorooctanoate 1951-2002. Journal of environmental monitoring : JEM, 14(3), pp.775–781.