Derivation of an occupational exposure limit (OEL) for n-propyl bromide using an improved methodology

Severe neurotoxicity associated with exposure to the solvent 1-bromopropane (n-propyl bromide)

BACKGROUND

1-bromopropane was recently substituted for traditional ozone-depleting solvents in the industrial setting.

CASE SERIES

We report a cohort of six cases of 1-bromopropane neurotoxicity occurring in foam cushion gluers exposed to 1-bromopropane vapors from spray adhesives. Patients 1-5 were exposed 30-40 hours per week over three years; patient 6 had been employed for the previous three months. Exposure had peaked over the previous month when ventilatory fans were turned off. All patients complained of subacute onset of lower extremity pain or paresthesias. Five of six complained of difficulty walking and on examination had spastic paraparesis, distal sensory loss, and hyperreflexia. Three patients initially had nausea and headache. Serum bromide concentrations ranged from 44 to 170 mg/dL (reference 0-40 mg/dL). Apparent hyperchloremia was present with serum chloride concentrations of 105 to 139 mmol/L (reference 98-107 mmol/L). Air samples taken at the workplace during gluing operations revealed the mean air concentration of 1-bromopropane to be 130 ppm (range 91-176 ppm) with a seven hour time-weighted average of 108 ppm (range 92-127 ppm), well above the EPA-proposed limit of 25 ppm. Two years after exposure, the two most severely affected patients had minimal improvement of function and they, with a third patient, continued to experience chronic neuropathic pain.

CONCLUSION

This report supports the growing recognition of 1-bromopropane neurotoxicity in humans consisting most commonly of headache, nausea, and subacute spastic paraparesis with distal sensory loss. The pathogenesis of 1-BP neurotoxicity in humans has yet to be fully elucidated but may reflect a central distal axonopathy syndrome.

Severe Illness in Furniture Makers Using a New Glue: 1-Bromopropane Toxicity Confounded by Arsenic

OBJECTIVE

To describe the illnesses of four workers with high concentrations of serum bromide after exposure to glue containing 1-bromopropane (1-BP).

METHODS

We reviewed all available clinical records, examined the workers, and obtained additional urinary arsenic values. We used standard autoanalyzer and other routine methods for blood and urinalysis.

RESULTS

All four workers had symptoms and abnormal physical findings when hospitalized, remaining symptomatic with abnormal examinations 3 months later. Milder symptoms persisted in two workers, 8 years after their initial illnesses. Both have returned to work. Follow-up was unavailable for the other two workers.

CONCLUSIONS

Severe illness occurred in four gluers after 1-BP exposures associated with elevated levels of serum bromide. All had elevated urinary arsenic concentrations, the source of which remains unknown, but which confound interpretation of the abnormal bromide levels and clinical findings present during the acute illnesses.

Development of an occupational exposure limit for n-propylbromide using benchmark dose methods

This paper presents the development of an occupational exposure level (OEL) for n-propylbromide (nPB) using benchmark dose methods. nPB is a non-ozone depleting solvent, proposed under the Significant New Alternatives Policy (SNAP) for use as a precision vapor degreaser. OELs have generally been developed on the basis of a NOAEL or LOAEL and application of uncertainty factors; this paper represents a departure from historic methods. Six recently completed toxicological studies were critically reviewed to identify (1) toxicologically significant endpoints, (2) dose-response information on these endpoints, and (3) uncertainties and limitations associated with the studies. Dose-response data were compiled and entered into the USEPA's benchmark dose software for calculation of a benchmark dose (BMD) and a benchmark dose low (BMDL). Once values were estimated for all relevant studies, they were then incorporated into a weight-of-evidence approach to develop a single BMD and BMDL representative of nPB. This approach is similar to that recently taken by USEPA to develop their own recommended OEL for nPB. USEPA's approach is compared and contrasted with ours, particularly in relation to the application of uncertainty factors (UFs) to generate a final OEL. There are no published criteria for application of UFs in developing an OEL. Although USEPA recommends utilizing a UF of 9, based on intraspecies variability and pharmacokinetic differences between rats and humans, to meet the goal of protecting healthy adult in a workplace setting, no uncertainty factor was deemed necessary for nPB in this paper. Therefore, the BMDL was recommended as the OEL.