title: Using exposure windows to explore an elusive biomarker: blood manganese.
abstract: OBJECTIVE
  We sought to understand the time course between exposure to manganese (Mn) and uptake into the blood, to allow a more meaningful interpretation of exposure biomarker data, and to determine the utility of blood as a biomarker of Mn exposure.
  
  
  METHODS
  Welder trainees were monitored over the course of a five-quarter training program. Each quarter, trainees gave eight blood samples and had personal air monitoring four times. A mixed model was fit to obtain estimates of airborne exposure by welding type (fixed effect), adjusted for subject (random effect). Considering weekends and days absent as zero exposure, estimated exposures were summed over various exposure windows and related to measured blood manganese (MnB) using a mixed model.
  
  
  RESULTS
  A relationship consistent with zero was found between MnB and modeled 1 or 7 days of exposure. After 30 days of preceding exposure, a 1 mg-days/m(3) increase in air Mn is associated with a 0.57 ng/mL increase in MnB (95% CI -0.04, 1.19). Considering a 90-day exposure window and a cumulative exposure window, a 1 mg-days/m(3) increase in air Mn is associated with a 0.26 (95% CI 0.005, 0.51) and 0.09 (95% CI 0.006, 0.17) ng/mL increase in MnB, respectively.
  
  
  CONCLUSIONS
  From this analysis, MnB may begin to act as a biomarker of Mn exposure over longer time periods, or at higher levels of exposure. This novel study design allowed investigation of how MnB relates to different time windows of exposure, representing the most robust Mn exposure assessment in the biomarker literature.
authors.affiliation: Department of Environmental and Occupational Health Sciences, University of Washington, 4225 Roosevelt Way NE, Suite 100, Seattle, WA, 98105, USA. bakermg@uw.edu.
authors.forename: Marissa G
authors.initials: MG
authors.lastname: Baker
authors.affiliation: Department of Environmental and Occupational Health Sciences, University of Washington, 4225 Roosevelt Way NE, Suite 100, Seattle, WA, 98105, USA.|Department of Health Services, University of Washington, Seattle, WA, USA.|Department of Family Medicine, University of Washington, Seattle, WA, USA.
authors.forename: Bert
authors.initials: B
authors.lastname: Stover
authors.affiliation: Department of Environmental and Occupational Health Sciences, University of Washington, 4225 Roosevelt Way NE, Suite 100, Seattle, WA, 98105, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Simpson
authors.affiliation: Department of Environmental and Occupational Health Sciences, University of Washington, 4225 Roosevelt Way NE, Suite 100, Seattle, WA, 98105, USA.|Department of Biostatistics, University of Washington, Seattle, WA, USA.
authors.forename: Lianne
authors.initials: L
authors.lastname: Sheppard
authors.affiliation: Department of Environmental and Occupational Health Sciences, University of Washington, 4225 Roosevelt Way NE, Suite 100, Seattle, WA, 98105, USA.
authors.forename: Noah S
authors.initials: NS
authors.lastname: Seixas
mesh_terms: D000328:Adult; D000395:Air Pollutants, Occupational / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D005260:Female; D006801:Humans; D008297:Male; D008345:Manganese / Q000097:blood*; D016273:Occupational Exposure / Q000032:analysis*; D013997:Time Factors; D014896:Welding / Q000379:methods
chemical_list: D000395:Air Pollutants, Occupational; D015415:Biomarkers; D008345:Manganese
keywords: Biomarker of exposure; Exposure assessment; Exposure modeling; Exposure windows; Manganese; Welding