The National Institute for Occupational Safety and Health (NIOSH) conducted a field study at an adhesive and coating manufacturing plant where n-propyl bromide (nPB) was used as a solvent carrier. 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 brominated-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 0.072 to 19 parts per million (ppm) and from 0.077 to 9.1 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, three (out of 22) 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 2.5 ppm. The cement makers and packagers working directly with nPB based adhesives had the highest breathing zone exposures; they wore air purifying or air-supplied respirators for protection. Exhaled breath concentrations of nPB ranged from non-detectable (N) to 0.056 ppm and ND to 0.32 ppm, respectively, for pre- and post-shift samples. Isopropyl bromide (iPB), a low level contaminant in nPB solvents, was detected in all but one of the air sample TWA measurements and ranged from 0.006 to 1.0 ppm; iPB was not detected in any of the breath samples. However, the highest iPB levels were found in workers who were remote from the nPB adhesives operation, and their iPB concentrations were close to or greater than their nPB exposure levels. The workers who worked directly with the nPB adhesive had the highest nPB exposures, but also had much lower iPB levels than the highest that were measured. This suggests that a chemical mixture other than the nPB solvent was the source of the iPB, or there was a positive interference with the analytical method. Workers' average urinary Br concentrations, as measured by 24 hour composite samples, were slightly higher than for unexposed controls who were not employed by this company (0.52 versus 0.4 milligrams per liter (mg/l)). The low urinary bromide concentration in exposed workers may be due, in part to the infrequent manufacturing schedule for nPB adhesives at this faculty (approximately every 45 days). 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 is a more specific metabolite for measuring exposure to nPB. The workers' 24-hour PMA concentrations determined for both workdays ranged from ND to 2370 micrograms per liter (microg/l) and the average was nearly an order of magnitude greater than the average PMA concentration in controls. Dermal absorption, in addition to inhalation exposure, may contribute to the observed urinary metabolite levels. Recommendations provided in this report include substitution of nPB solvents with a less toxic solvent, periodic exposure monitoring, improved exhaust ventilation, continued use of respiratory protection, 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