Adjustment of urinary mercury in health risk assessment of mercury.

The determination of adjustment method of urinary mercury in spot urine is one of the important issues in assessing the health risks of mercury workers. But there have been debates about whether creatinine or other forms of correction for urinary concentration are better in reducing the variation of urinary mercury. We evaluated four adjustment methods-specific gravity, creatinine, log creatinine and excretion rate-by correlation between values adjusted by the four methods and individual exposure levels which were the geometric mean of daily air mercury level for 2 or 5 days, and mercury concentrations in 24 hour urine were also investigated to compare the results of spot urine. The correlation between values of spot urine and mercury exposure level was over 0.8 in all adjustment methods for workers who worked over 1 year. All four adjustment methods for urinary mercury were found to be similar in assessing the exposure, log creatinine and excretion rate method however were not practical to use due to lack of reference values, and variable standard values of specific gravity. And the creatinine adjusted values were more sensitive in low mercury exposure level. We therefore recommend the creatinine adjustment method for adjustment of urinary mercury.