The SAM-Krom biomonitoring study shows occupational exposure to hexavalent chromium and increased genotoxicity in Denmark

Background

Hexavalent chromium (Cr(VI)) is a carcinogen. Exposure to Cr(VI) may occur in different industrial processes such as chrome plating and stainless steel welding. The aim of this study was to assess occupational exposure to Cr(VI) in Denmark.

Methods

This cross-sectional study included 28 workers and 8 apprentices with potential Cr(VI) exposure and 24 within company controls, all recruited from six companies and one vocational school. Use of occupational safety and health (OSH) risk prevention measures were assessed through triangulation of interviews, a questionnaire and systematic observations. Inhalable Cr(VI) and Cr-total were assessed by personal air exposure measurements on Cr(VI) exposed participants and stationary measurements. Cr concentrations were measured in urine and in red blood cells (RBC) (the latter reflecting Cr(VI)). Genotoxicity was assessed by measurement of micronuclei in peripheral blood reticulocytes (MNRET).

Results

At announced visits, a consistent high degree of compliance to OSH risk prevention measures were seen in ‘chromium bath plating’ for both technical devices (e.g. ventilation, plastic balls, sheet coverings) and in the use of personal protective equipment (e.g. gloves, respirators), yet a lesser degree of compliance was observed in ‘stainless steel welding’. The geometric mean of the air concentration of Cr(VI) was 0.26 μg/m³ (95% confidence interval (CI): 0.12–0.57) for the Cr(VI)-exposed workers and 3.69 μg/m³ (95% CI: 1.47–9.25) for the Cr(VI)-exposed apprentices. Subdivided by company type, the exposure levels were 0.13 μg/m³ (95% CI: 0.04–0.41) for companies manufacturing and processing metal products, and 0.81 μg/m³ (95% CI: 0.46–1.40) for bath plating companies. Workers with occupational exposure to Cr(VI) had significantly higher median levels of urinary Cr (2.42 μg/L, 5th-95th percentile 0.28–58.39), Cr in RBC (0.89 μg/L, 0.54–4.92) and MNRET (1.59 ‰, 0.78–10.92) compared to the within company controls (urinary: 0.40 μg/L, 0.16–21.3, RBC: 0.60 μg/L, 0.50–0.93,MNRET: 1.06 ‰, 0.71–2.06). When sub-dividing by company type, urinary Cr (4.61 μg/L, 1.72–69.5), Cr in RBC (1.33 μg/L, 0.95–4.98) and MNRET (1.89 μg/L, 0.78–12.92) levels were increased for workers with potential Cr(VI) exposure in bath-plating companies, and when subdividing by work task, workers engaged in process operation had increased levels of urinary Cr (8.51 μg/L, 1.71–69.5), Cr in RBC (1.33 μg/L, 0.95–4.98) and MNRET (1.89 μg/L, 0.82–12.92) levels.

Conclusion

This biomonitoring study shows that bath platers were highly exposed to Cr(VI), as suggested by relatively high levels of urinary Cr, Cr in RBC and increased levels of micronuclei. The urinary Cr concentrations were high when compared to the French biological limit value of 2.5 μg Cr/L, corresponding to the Danish occupational exposure limit of 1 μg/m³. This, in turn, indirectly suggests that additional exposure routes than via air may contribute to the exposure. For welders, no statistically significant increases compared to within company controls were observed, however, the observed urinary Cr levels were similar to the levels observed in a European study (HBM4EU), and were higher than the levels observed for welders in Sweden (SafeChrom). In spite of a high degree of self-reported and observed compliance to OSH risk prevention measures during announced visits, the biomarkers of exposure reflecting recent exposure (urinary Cr) or exposure during the last four months (Cr in RBC) may point to variation in compliance to OSH risk prevention measures in general. Reduced occupational exposure to Cr(VI) may be achieved by applying the hierarchy of controls in eliminating or substituting Cr(VI), and the use of more effective technical solutions (e.g. automation).