Manganese in plasma: a promising biomarker of exposure to Mn in welders.  A pilot study. 
There is raising concern about the potential neurotoxic effects of manganese (Mn) inhalation exposure in welders.  Because most of the airborne particles in welding fume are in the respirable fraction, their bioavailability is likely to be higher than for coarser dust exposure.  No well-validated biomarker for Mn exposure is available.  To investigate the interest of measuring Mn in plasma (Mn-P) and urine (Mn-U) as biomarkers of exposure in a group of 28 welders whose tasks were only welding-related.  Ambient air exposure to Mn (Mn-air) was determined by personal full-shift measurements on Monday and Tuesday.  On the same days, blood and urine samples were collected before and after the shift.  Mn-air varied from 1.3 to 729 μg/m(3) (GM 27.7).  For Mn-U 65% of the values in welders were below the LOQ (0.20 μg/L).  Compared to controls, the welders' Mn-P averaged 33% higher (1.5 vs 2.0 μg/L).  In welders, the after-shift Mn-P values correlated well with Mn-air above 10 μg/m(3).  In spite of similar Mn-air exposure on Monday and Tuesday, the relationships between Mn-air and after-shift Mn-P strikingly differed on Tuesday in that the inflection in the relationship was less obvious and the slope of the regression line (Mn-P after-shift/logMn-air) for a doubling of logMn-air was 2.3 times lower than on Monday.  On Monday (the first day of the workweek), a Mn-P value of 2 μg/L could distinguish Mn-air exposure above or below 20 μg/m(3) with a sensitivity of 69% and a specificity of 82%.  This preliminary study indicates that Mn-P is a promising biomarker of current exposure to Mn in welders and lends biological plausibility to the intended change for the Mn TLV-TWA of 20 μg/m(3) proposed by ACGIH for respirable Mn particulate.