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Abstract
The National Institute for Occupational Safety and Health has conducted an occupational exposure assessment study of manganese (Mn) in welding fume of construction workers rebuilding tanks, piping, and process equipment at two oil refineries. The objective of this study was to evaluate exposures to different Mn fractions using a sequential extraction procedure. Seventy-two worker-days were monitored for either total or respirable Mn during stick welding and associated activities both within and outside of confined spaces. The samples were analyzed using an experimental method to separate different Mn fractions by valence states based on selective chemical solubility. The full-shift total particulate Mn time-weighted average (TWA) breathing zone concentrations ranged from 0.013–29 for soluble Mn in a mild ammonium acetate solution; from 0.26–250 for Mn0,2+ in acetic acid; from non-detectable (ND) – 350 for Mn3+,4+ in hydroxylamine-hydrochloride; and from ND – 39 micrograms per cubic meter (μg/m3) for insoluble Mn fractions in hydrochloric and nitric acid. The summation of all Mn fractions in total particulate TWA ranged from 0.52–470 μg/m3. The range of respirable particulate Mn TWA concentrations were from 0.20–28 for soluble Mn; from 1.4–270 for Mn0,2+; from 0.49–150 for Mn3+,4+; from ND – 100 for insoluble Mn; and from 2.0–490 μg/m3 for Mn (sum of fractions). For all jobs combined, total particulate TWA GM concentrations of the Mn(sum) were 99 (GSD = 3.35) and 8.7 (GSD = 3.54) μg/m3 for workers inside and outside of confined spaces; respirable Mn also showed much higher levels for welders within confined spaces. Regardless of particle size and confined space work status, Mn0,2+ fraction was the most abundant followed by Mn3+,4+ fraction, typically >50% and ∼30–40% of Mn(sum), respectively. Eighteen welders’ exposures exceeded the ACGIH Threshold Limit Values for total Mn (100 μg/m3) and 25 exceeded the recently adopted respirable Mn TLV (20 μg/m3). This study shows that a welding fume exposure control and management program is warranted, especially for welding jobs in confined spaces.
ACKNOWLEDGMNTS
The authors wish to acknowledge the company, contractor management, and union staff who provided valuable input for the success of this endeavor, and the workers who provided their voluntary consent prior to their participation in this exposure monitoring study. The authors would also like to acknowledge Kevin Dunn and Kenneth Sparks (NIOSH), and Timothy Carter (Battelle, Inc.) for laboratory and field assistance with equipment preparation and sample collection; Bureau Veritas North America Laboratories for analytical services; Lian Luo (SRA International) for programming, and Cheryl Estill and Brian Curwin (NIOSH) for article review prior to submission to the journal.
The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health (NIOSH), National Institute of Environmental Health Sciences (NIEHS), and Battelle, Inc. It does not represent and should not be construed to represent any agency determination or policy. Mention of company names and internet websites does not constitute an endorsement by NIOSH, NIEHS, and Battelle, Inc. This article is not subject to US copyright law.
FUNDING
This study was partially funded by an interagency agreement between the National Toxicology Program (NTP), National Institute of Environmental Health Sciences (NIEHS) and the National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention (CDC) [NIEHS/NIOSH Interagency Agreement No. Y1-E5-9018-02].