Project title: Bioavailability of Inhaled Chromium VI in Occupational Settings
Completed in: 2010
In industrial environments, chromates in primers, paints, and chrome-plating solutions are released into the workplace environment when paint is sprayed and plating tanks produce mist. Metallic chromium is incorporated in stainless steel alloys to improve color and increase resistance to corrosion. During welding it is oxidized and released as hexavalent chromium. All Cr(VI) compounds are considered to be potential carcinogens by the National Institute for Occupational Safety and Health (NIOSH).
Particle size and respiratory protection fit and use influence bioavailability and systemic uptake of inhaled chromium. Historically, systemic exposure to chromium was assessed via concentration of total chromium in urine. However, as occupational exposures continue to decrease, questions arise whether urinary chromium concentration is sufficiently sensitive to distinguish occupational exposures from background.
Fifteen workers in three industries with hexavalent chromium exposure were studied and added to a growing dataset of forty-one subjects. The study assessed bioavailability of inhaled chromium and evaluated urinary chromium concentration (U-Cr) as a biomarker of inhaled chromium. Personal air samples using IOM inhalable fraction samplers or Marple Cascade Impactors were collected each day for five consecutive days for each of the participants. Urine samples were collected on Monday, prior to the shift and Friday, following the shift. A brief survey was administered Monday and Friday to assess confounding factors and other determinants of urinary chromium concentration.
Mean change in U-Cr between Monday and Friday, when grouped by operation (plating, painting, welding), was not statistically distinguishable from zero. Using simple linear regression, airborne chromium concentration (A-Cr) explains U-Cr for workers in plating operations. A positive correlation between A-Cr and U-Cr was found for platers (r=0.65). For painters and welders, A-Cr did not account for U-Cr and negative correlations were found between A-Cr and U-Cr (r=-0.19 and -0.31, respectively). Adjusting for respiratory protection use did not improve the association for welders or painters. Further analysis is required to determine if years in chromium industry or smoking and drinking confound the weekly change in U-Cr. Analytical error when measuring U-Cr at low concentrations is proportionately high; duplicate samples differed by up to 27%. The analytic error could mask small fluctuations in U-Cr from occupational exposure. U-Cr may not be sufficiently sensitive to detect occupational chromium exposure among painters and welders in a new era of lower occupational exposures to chromium.