Background China is the world's largest producer and consumer of cobalt. Skin exposure to excess cobalt can cause symptoms such as contact dermatitis. At present, there are few studies on skin contact of cobalt and its compounds.

Objective To investigate the skin contact characteristics of cobalt and its compounds.

Methods A cross-sectional study was conducted in February 2024 involving 70 workers from a hard metal tool manufacturing company and the workers were divided into four groups according to their job positions: powder mixing, sintering, automatic pressing, and grinding processing. General demographic information was collected through questionnaires. Workplace air samples were collected using personal samplers, and cobalt concentrations in workplace air were measured by inductively coupled plasma optical emission spectrometry (ICP-OES). Skin samples were collected from the workers' foreheads using cotton swabs, and urine samples were collected within 30 min after the end of their shift. Urine specific gravity was measured immediately after collection, and disqualified samples were discarded. Cobalt concentrations in the swab extracts and urine were determined by inductively coupled plasma mass spectrometry (ICP-MS). Statistical analysis was performed using Kruskal-Wallis test for multiple group comparisons, Mann-WhitneyU test for pairwise comparisons, Chi-square test for categorical variables, and Spearman's rank correlation analysis to examine the correlations among air, dermal, and urinary cobalt levels.

Results The 8 h time-weighted average (TWA) cobalt concentration was (2.30±2.15) μg·m⁻³ ( \barx\pm s ). The median skin exposure level was 53.8 ng·cm⁻², with a range of 4.25 ng·cm⁻² to 1090.2 ng·cm⁻². The median urinary cobalt level was 3.74 µg·L⁻¹, with a range of 0.83 to 382.9 µg·L⁻¹. Statistically significant differences in TWA cobalt concentration, skin exposure levels, and urinary cobalt levels were found between different work positions (H=9.012, P=0.029; H=16.348, P＜0.001; H=11.078, P=0.011). A positive correlation was observed between skin exposure levels and urinary cobalt levels (r=0.537, P＜0.01).

Conclusion Skin contact may be one of the main sources of cobalt levels in urine. Therefore, it is essential for workers to improve skin protection and hygiene practices.