[Preliminary study on occupational biological exposure limits of soluble nickel compounds]

Objective: To analyze the relationship between nickel level of post-shift urine and individual exposure level of soluble nickel compounds in nickel exposed workers, and to explore the feasibility of using urine nickel as a biomarker. Methods: In November 2020, a typical sampling method was employed to select 301 employees from a nickel salt-using enterprise in Jiangmen City as study subjects, including 257 nickel-handling workers as the exposure group and 44 non-exposed administrative and logistics staff as the control group. The time-weighted average concentration (C(TWA)) of soluble nickel in workplace air was measured using individual sampling and fixed-point sampling methods. Urinary nickel levels were detected before and after shifts using inductively coupled plasma mass spectrometry (ICP-MS). Occupational health examination results were collected, and Spearman rank correlation analysis was employed to assess the correlation between urinary nickel levels and nickel exposure levels. The biological exposure limit was calculated through linear regression analysis. Results: The median nickel concentration in the workplace C(TWA) for the exposure group was 3.52 (0.03-587.06) μg/m(3), with concentrations exceeding the action level (250 μg/m(3)) observed in positions such as vibrating screen iron removal and electric furnace automatic line operation. Pre-shift and post-shift urinary nickel levels in the exposure group were 0.46 (0.20-30.30) and 4.41 (0.24-56.34) μg/L, respectively, both significantly higher than those in the control group (0.27、0.46 μg/L, P<0.01), with post-shift levels showing a significant increase compared to pre-shift levels (P<0.01). Post-shift urinary nickel levels exhibited a positive correlation with individual exposure levels to nickel and its compounds (r(s)=0.36, P<0.01). The linear regression equation for the natural logarithm of median post-shift urinary nickel levels (ŷ) versus the natural logarithm of median individual exposure levels to soluble nickel compounds (x) across different positions in the exposure group was: ŷ=0.463+0.371x (R(2)=0.511, F=11.45, P<0.01). The recommended biological contact limit for post-shift urinary nickel levels among workers exposed to soluble nickel is 30 μg/L. Conclusion: There was a linear correlation between the nickel level of post-shift urine and the occupational nickel exposure level of nickel-exposed workers. Urinary nickel can be used as a biomarker of occupational nickel exposure.