Increasing interest in the health effects of manganese exposure has focused attention on suitable manganese biomarkers, but identifying appropriate biomarkers has proved difficult. Blood and urine manganese are questionable biomarkers, and toenail manganese, which may reflect longer term exposure, has not been validated. This study aimed to examine the correlation between manganese exposure and these biomarkers.

Personal air monitoring data during different tasks and work histories were collected from welders and used to determine manganese exposure over a workshift and estimate cumulative exposure over the past year. The welders provided toenail samples (n = 49), and blood and urine were collected before (n = 27) and after (urine, n = 26; blood, n = 24) a workshift.

Toenail manganese, adjusted for age and dietary manganese, was significantly correlated (Spearman correlations) with cumulative exposure in months 7-9 (r = 0.35, p = 0.02), 10-12 (r = 0.32, p = 0.03), and 7-12 (r = 0.32, p = 0.03) before the toenail clipping date, but not months 1-6. Toenail manganese did not correlate with blood (r = 0.11, p = 0.66) or urine (r = -0.18, p = 0.46) manganese, but blood and urine manganese were reasonably well-correlated (Pearson's r = 0.33, p = 0.10). Manganese exposure over a work shift was not correlated (Pearson's correlations) with changes in blood (r = -0.06, p = 0.80) nor urine (r = 0.21, p = 0.32) manganese.

Toenail appeared to be a valid measure of manganese exposure 7 to 12 months earlier. In populations with more consistent external manganese exposures than welders, toenails likely reflect other exposure windows as well. Neither change in blood nor urine manganese appeared to be suitable indicators of manganese exposure over a typical work shift.

( Published in Journal of Occupational and Environmental Medicine, 2011; 53(5): 506-510 )