New study disputes TLV for nPB
A detailed comprehensive review of 1-bromopropane studies confirm current recommendations by EnviroTech for occupational exposure levels for safe usage of EnSolv® as a vapour degreasing solvent.
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Update on a safe occupational exposure level for 1-Bromopropane
Prepared for EnviroTech Europe, Ltd.
Prepared by Dr. Mark Stelljes
SLR International Corporation
This paper re-evaluates EnviroTech Europe’s (ETE’s) current occupational exposure level recommendation of 100 ppm for 1-bromopropane (1-BP) [106-94-5] in the vapor degreasing industry in light of the recent lowering of the ACGIH Toxicity Threshold Value (TLV) from 10 ppm to 0.1 ppm. The 0.1 ppm value is based on a study of 86 workers exposed to 1-BP during its manufacturing in China in four different facilities. The authors reported significant effects at all 1-BP exposure levels down to 1.28 ppm. The 1-BP in these facilities had concentrations of the isomer 2-bromopropane [75-26-3] (2-BP) present as a contaminant at about 10-20 times the level sold for vapor degreasing.
There are several factors that undermine the conclusions reached in the paper that a concentration of 1.28 ppm resulted in toxicity in exposed workers. These factors were related to:
(1) Exposure measurements – passive rather than active samplers were used, and concentrations varied by more than tenfold for the same activity.
(2) Exposure via other routes in addition to inhalation – described worker activities indicate substantial dermal exposure, which increases the overall dose of the chemical relative to just inhalation exposure.
(3) Exposure to other chemicals – at least 20% of the workers were previously exposed to 2-bromopropane
(2-BP), and no testing was done for other chemical exposure.
(4) Statistical methods and interpretations – instead of using paired patient-exposure data, authors categorized exposure into groups (e.g., high, low); this resulted in apparent statistical relationships that may not be biologically relevant.
(5) Lack of robust dose-response relationships – when evaluating typical doseresponse relationships, only a single parameter (vibration sense in the toes, a subjective parameter) was shown to be significantly different across all dose levels.
(6) The outcome of the subjective vibration sense test was in part dependent on the testing doctor – this dependency should remove the test and its results from consideration in the paper as a scientifically defensible endpoint.
When all of this information is considered as a whole, it is unlikely that the 1.28 ppm lowest effect concentration reported in the paper is accurate. The interpretations in the Li et al. study are inconsistent with expectations based on the ways in which 1-BP acts in rodents relative to humans. Studies on how 1-BP acts in the body of rats and mice and studies on metabolism of the chemical in humans indicate that humans should be no
more sensitive to 1-BP than either of these rodents.
Based on the weight of evidence available for the toxicity of 1-BP in humans and rodents, there is no credible scientific reason to target an occupational concentration as low as 10 ppm or 0.1 ppm. ETE’s current recommendation of 100 ppm should be maintained, and employers together with vapor degreasing personnel should not be concerned about the much lower levels recommended by the ACGIH.
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