Thermal spraying: biological and atmospheric assessments of occupational exposure to chromium and nickel

Thermal spraying is a process during which a coating is applied at high temperature and at high speed onto an object in order to improve the surface properties of that object. Existing thermal spraying processes differ from one another by the systems used for melting the material to be sprayed. Those differences directly influence the quantity of aerosols produced and their particle size distribution (the high-temperature systems produce ultrafine particles), and thus directly influence their toxicity. Protecting the operatives requires atmospheric and biological exposure evaluation that is adapted to these specificities. A study has thus been initiated by the Biomonitoring Laboratory of INRS's Toxicology and Biomonitoring Division, and is planned to run for 5 years as from July 2016. The objectives of this study consist in evaluating occupational exposure to chromium (Cr) and to nickel (Ni) during thermal spraying and welding operations, and in proposing a biomonitoring strategy suitable for being used by occupational medicine professionals. Welding is being monitored in order to compare the biological uptake of welders and of metal coaters for equal quantitative exposures. The utility of studying the Ni-Cr alloy lies in the fact that it cuts across the various existing processes. Furthermore, in terms of occupational risk prevention, Cr remains an element to be watched in particular because of the presence of Cr VI, a carcinogenic form of Cr. The campaign to evaluate exposures out in the companies will be based on atmospheric measurements, urinary assays of exposure biomarkers, and also assays of urinary biomarkers of early effects of renal injury such as beta-2-microglobulin (â2M), N-acetyl glucosaminidase (NAG), and Kidney Injury Molecule 1 (KIM-1), and of oxidative stress such as malondialdeyhde (MDA) and 8-hydroxy-2'-deoxyguanosine (8-OHdG). In parallel, samples taken from work surfaces and skin surfaces will make it possible to determine objectively whether or not the two metals are present on surfaces that might be sources of cutaneous exposure, and on the skin of the operatives. The data from the study should provide information on the levels of urinary excretion of the Cr and Ni used during the various thermal spray and welding processes, and should make it possible to study firstly the relationships between the atmospheric measurements and the urinary levels excreted, and secondly the relationships between the biomarkers of exposure and of early effects. The ultimate aim is to propose biological limit values (BLVs) and, at the very least to assess the effectiveness of the personal protective equipment used.