The National Institute for Occupational Safety and Health (NIOSH) conducted a field study at a electronic printed circuit assembly manufacturing plant where n-propyl bromide (nPB) was used as a vapor de greasing and liquid cleaning solvent. Workers' breathing zone, and exhaled breath concentrations of nPB and isopropyl bromide (iPB) were measured on two consecutive days, as were urinary metabolite concentrations of bromide (Br) and propyl mercapturic acid (PMA). n-Propyl bromide has been marketed to replace ozone depleting solvents 1,1,1-trichloroethane and freons, as well as suspect carcinogens trichloroethylene and methylene chloride; chemicals commonly used in industry. Sparse data are currently available to evaluate human exposure to nPB. However, there is concern that nPB may be a hematological, reproductive, or neurological toxin, based on analogy to other Br-propanes, animal studies, and a few case studies. Full-shift time weighted average (TWA) exposure to nPB collected in workers' breathing zone air samples ranged from 1.3 to 14 parts per million (ppm) and from 1.6 to 21 ppm, respectively for day 1 and day 2. All of the workers were exposed to nPB at levels below the industrial guideline of 25 ppm published by the EP A in their proposed rulemaking to accept nPB under the Clean Air Act. However, four (out often) TWA nPB measurements exceeded the American Conference of Governmental Industrial Hygienist (ACGIH) Threshold Limit Value of 10 ppm; workers' average TW A exposure for both days was 9.7 ppm. Exhaled breath concentrations of nPB ranged from 0.13 to 4.0 ppm and 0.3 to 6.6 ppm, respectively, for pre- and post-shift samples. Isopropyl bromide, a low level contaminant in nPB, was not detected in any of air or breath samples. Average urinary Br concentrations measured before the work week began and during both workdays, as measured by 24 hour sample durations, were approximately ten times higher for all workers combined than for unexposed controls who were not employed by this company. Although the worker with the lowest exposure to nPB had urinary Br levels within or near the range measured from control specimens, the levels were still several times higher than the control average. Bromide in urine can be influenced by non-occupational factors such as diet and medications, including over the counter medications. Propyl mercapturic acid is a more specific metabolite for measuring exposure to nPB. The 24-hour average PMA concentrations for both workdays were over two orders of magnitude higher than the average PMA concentration in controls. The assembler with the lowest breathing zone concentration of nPB had the lowest PMA urinary metabolite levels but these levels were still over five and nine times higher than the average control concentrations for day 1 and day 2, respectively. Workers were observed to periodically contact nPB solvent with unprotected hands; dermal absorption of nPB may contribute to urinary metabolite concentrations in addition to inhalation exposure. Recommendations include substitution of nPB solvents with a less toxic solvent, periodic exposure monitoring, ventilation modifications, implementation of a respiratory protection program, impermeable gloves to nPB, and routine medical examinations.
National Institute for Occupational Safety and Health, Division of Surveillance, Hazard Evaluations and Field Studies, Industrywide Studies Branch, 4676 Columbia Parkway, Cincinnati, OH 45226