Bladder cancer and oil mists: a prospective cohort study in populations of workers from the steel industry in the Nord-Pas de Calais Region

Outline of reasons and objectives
Oil mists are aerosols of cutting fluids comprising straight oils or aqueous fluids (soluble oils or synthetic fluids). Certain chemicals can be present in such fluids or can form while they are being used: in particular polycyclic aromatic hydrocarbons (PAHs) (straight oils and soluble fluids), and nitrosamines (aqueous fluids). The concentration of these pollutants has changed over time due to improvements made in the composition and in the nature of the cutting fluids. Past epidemiological studies have suggested that bladder cancers are more frequent in populations who use cutting oils that are unrefined or relatively unrefined. However, studies per type of fluid show discordant results.
The objective of this study was to seek to determine whether a risk of bladder cancer is associated with occupational exposure to oil mist, resulting from the more recent use of straight oils or of aqueous fluids, while taking into account other occupational and extra-occupational carcinogens. This risk was studied in the steel industry.

Approach
A case-control study was put in place in a cohort constituted by all of the employees hired from 1960 to 1997 in 6 steel works in the Nord–Pas-de-Calais Region. The cases of bladder cancers occurring in the subjects of the cohort, during the period 2006-2012, were identified based on data from the French National Health Insurance scheme, and on information from 21 public and private hospitals in the Nord-Pas-de-Calais Region. The controls were selected from the subjects of the cohort using the counter-matching method. The medical information, tobacco consumption, job history (job titles, dates, tasks performed, exposures) was gathered by questionnaires filled in face-to-face at the subjects’ homes. The occupational exposures from 1960 to 2012 were assessed by experts from INRS and from the Laboratoire Interregional de Chimie de l’Est (LICE, the Eastern Interregional Chemistry Laboratory).

Main results
This study showed a relationship between occurrence of bladder cancer and occupational exposures to cutting fluid mists of all types, as well as to straight-oil cutting fluid mists. The relationship observed for straight-oil cutting fluids results from exposures dating back over the last 30 years. This study did not show any relationship between bladder cancer and exposures to aqueous fluids (soluble oils or synthetic fluids).

Discussion
Since the straight oils were mainly constituted by mineral oils, this result would appear to argue in favour of the presence of carcinogens contained in mineral oils, whether they be new or used. This study shows that prevention remains necessary in the sectors in which cutting fluids are used. However, effective prevention presupposes improved knowledge of the composition of cutting fluids, be they new or in the process of being used.
Multi-disciplinary studies designed to determine the composition of cutting fluids (new and used), the current atmospheric levels, and their relationships with early-effect biomarkers, would make it possible to improve the targeting of the prevention actions and thus to reduce the frequency of bladder cancers related to exposures to cutting fluids.