Blood manganese as an exposure biomarker: state of the evidence

Abstract

Despite evidence of adverse health effects resulting from exposure to manganese (Mn), biomarkers of exposure are poorly understood. To enhance understanding, mean blood Mn (MnB) and mean air Mn (MnA) were extracted from 63 exposure groups in 24 published papers, and the relationship was modeled using segmented regression. On a log/log scale, a positive association between MnA and MnB was observed among studies reporting MnA concentrations above about 10 μg/m(3), although interpretation is limited by largely cross-sectional data, study design variability, and differences in exposure monitoring methods. Based on the results of the segmented regression, we hypothesize that below the concentration of about 10 μg/m(3), Mn in the body is dominated by dietary Mn, and additional inhaled Mn only causes negligible changes in Mn levels unless the inhaled amount is substantial. However, stronger study designs are required to account for temporal characteristics of the MnA to MnB relationships that reflect the underlying physiology and toxicokinetics of Mn uptake and distribution. Thus, we present an inception cohort study design we have conducted among apprentice welders, and the analytical strengths this study design offers. To determine if blood could be a useful biomarker for Mn to be utilized by industrial hygienists in general industry requires additional time-specific analyses, which our inception cohort study design will allow.

FIGURE 1

Group-based relationships between mean MnA and mean MnB from the literature on (A) native scale; and (B) log transformed with outliers removed

FIGURE 2

Measured MnA concentration by weld type in inception cohort study of apprentice welders

FIGURE 3

Inception cohort study design of apprentice welders Trainees progress through the welding program in the order indicated: Oxyacetylene, SMAW (shielded metal arc welding, or stick), FCAW (flux core arc welding, encompassing inner and dual shield), GMAW (gas metal arc welding, or MIG), and GTAW (gas tungsten arc welding, or TIG). The baseline measurement occurs the morning of trainees first day in the program. With the exception of the follow-up week at the end of quarter 5, each week blood and urine sampling occurs both Monday and Friday, in both the morning and afternoon, for a total of 4 samples a week, and 8 samples a quarter.