The National Institute for Occupational Safety and Health (NIOSH) conducted a field study at a prism and optical assembly manufacturing plant where n-propyl bromide (nPB) was used as a vapor de greasing 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 0.52 to 9.8 parts per million (ppm) and from 0.12 to 11 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 EPA in their proposed rulemaking to accept nPB under the Clean Air Act. However, five (out of 14) TWA nPB measurements exceeded or approached (> 75%) the American Conference of Governmental Industrial Hygienist (ACGIH) Threshold Limit Value of 10 ppm. The average TWA exposure for all workers on both days combined was 4.9 ppm. Exhaled breath concentrations of nPB ranged from 0.035 to 0.59 ppm and 0.067 to 2.5 ppm, respectively, for pre- and post-shift samples. Isopropyl bromide (iPB), a low level contaminant in nPB solvents, was only detected in three air samples in very low quantities; iPB was not detected in any of the breath samples. Average urinary bromide (Br) concentrations measured before the work week began and during both workdays, as measured by 24 hour composite samples, were approximately three times higher for all workers combined than for unexposed controls who were not employed by this company. Mill technicians had the highest workday urinary Br levels (range: 7.5 - 26 milligrams per liter; average = 15 mg/l). Bromide in urine can be influenced in general and working populations by non-occupational factors such as diet and medications, including over the counter medications. Propyl mercapturic acid (PMA) is a more specific metabolite for measuring exposure to nPB. The 24-hour average PMA concentrations determined for both workdays combined was fifty times higher than the average PMA concentration in controls. The mill technicians, who spent the most time using the de greaser or who were in closest proximity to the de greaser, had urinary PMA concentrations approximately 66 and 95 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, in addition to inhalation exposure, may contribute to the observed urinary metabolite concentrations. Recommendations provided in this report include substitution of nPB solvents with a less toxic solvent, periodic exposure monitoring, local exhaust ventilation, degreaser 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