In vivo neutron activation analysis of bone manganese in workers

Objective: Manganese (Mn) is a neurotoxin. However, the impact of elevated, chronic Mn exposure is not well understood, partially due to the lack of a cumulative exposure biomarker. To address this gap, our group developed a compact in vivo neutron activation analysis (IVNAA) system to quantify Mn concentration in bone (MnBn). Approach: In this study, we used this system and determined MnBn among male Chinese workers and compared results to their blood Mn (MnB), a measure of recent exposure, and the years of employment, a measure of cumulative exposure. A cross-sectional study was conducted with 30 ferroalloy smelters (exposed) and 30 general manufacturing workers (controls). MnBn was assessed using IVNAA, MnB was measured with inductively coupled plasma mass spectrometry, and occupational history and demographics were obtained via questionnaire. Mn-doped phantoms were used to generate a calibration curve; spectra from these phantoms were consistent with in vivo spectra. Main results: The median (interquartile range (IQR)) values for Mn biomarkers were 2.7 µg g^-1 (7.2) for MnBn and 14.1 µg l^-1 (4.0) for MnB. In regression models adjusted for age and education, the natural log transformed MnBn (ln(MnBn)) was significantly associated with the exposed/control status (β = 0.44, p = 0.047) and years of employment (β = 0.05, p = 0.002), but not with natural log transformed MnB (ln(MnB)) (β = 0.54, p = 0.188). Significance: Our results support the use of IVNAA to quantify MnBn and the use of MnBn as a biomarker of cumulative Mn exposure.