Butyl acetate (n-butyl) and its isomers – sec-butyl acetate and isobutyl acetates. Documentation of proposed values of occupational exposure limits (OELs)
Journal Title: Podstawy i Metody Oceny Środowiska Pracy - Year 2015, Vol 31, Issue 4
Abstract
Butyl acetates, or acetic acid esters and a suitable butyl alcohol, are four compounds with identical molecular formulas which differ from each other by sequence of bonding of atoms. These are n-butyl acetate with a straight carbon chain and its three isomers: isobutyl acetate, sec-butyl and tert-butyl acetate. The subjects of this documentation are n-butyl acetate and isomers: sec- and iso-, because they have similar physical and chemical properties, route of metabolism and critical effect. Isomer tert- was described in separate documentation.n-Butyl, sec-butyl and isobutyl acetates are colorless, flammable liquids with a fruity odor. They are mainly used as organic solvents and as ingredients of solvent blends for resins, waxes, varnishes, perfumes, fats, inks, adhesives, camphors and in the production of nitrocellulose lacquer.The median lethal concentration for n-butyl acetate is in the range from 750 mg/m3/4h to 45000 mg/m3/4h for rats and depends on the method of its generation. LD50 values after intragastric administration of n-butyl acetate amounts to approx. 14130 mg/kg for rat and 7100 mg/kg for mice. The minimum value of LD50 for isobutyl acetate is 4800 mg/kg. While in the case of sec-butyl acetate LD50 value is within the range of 3200 ÷ 6400 mg/kg.Acetates cause irritation to mucous membranes of the respiratory tract. For n-butyl acetate and isobutyl acetate RD50 values are 3470 mg/m3 and 3890 mg/m3, respectively.n-Butyl acetate, sec-butyl acetate and isobutyl acetate are similar in structure, physicochemical properties and metabolic pathway. Most of the quantitative data are available only for acetate of straight carbon chain. Hence, it is proposed to establish an equal limit value for these three substances.In humans, weak irritation of eye, nose, throat, esophagus were observed in the concentration of n-butyl acetate of 1000 mg/m3 at 5-min exposure. n-Butyl acetate at a concentration of 1449 mg/m3 in most individuals exposed for 2 to 5 min caused irritation of eyes, nose and throat rated as sharp. In volunteers exposed for 20 min for n-butyl acetate, the highest concentration at which no irritation to eyes, nose, throat, skin, respiratory system were observed was of 1050 mg/m3. Although in the same study, significant differences compared with the control group which include irritation to throat, difficulties in breathing, sensing odor were observed at a concentration of 700 mg/m3 for 4 h.SCOEL and ACGIH proposed TWA of 240 mg/m3 and STEL at 720 mg/m3 for all isomers of butyl acetates.To calculate the MAC value for butyl acetates The Expert Group adopted the study on volunteers (Iregren et al. 1993) as a starting point. Assuming that the concentration of 700 mg/m3 is the LOAEC value for irritation on the mucous membranes of the respiratory tract and the respective uncertainties, The Expert Group proposed MAC-NDS for n-butyl, sec-butyl and isobutyl acetate of 200 mg/m3. Due to the mild irritant of butyl acetates and the possibility of ceiling concentrations in workplace, The Expert Group proposed STEL of 3 times higher than the MAC-NDS of 600 mg/m3.After discussion and voting, the Interdepartmental Commission for Maximum Admissible Concentration and Intensities for Agents Harmful to Health in the Working Environment at its 79th meeting adopted the MAC value of n-butyl acetate and its isomers sec-butyl and isobutyl proposed by SCOEL of 240 mg/m3 and STEL value of 720 mg/m3.n-Butyl acetates are slightly absorbed through the skin (1.6 ± 0.1 g/m2·h), hence it is not recommended to label them as skin (absorption of substances through the skin can be just as important as for inhalation). It is recommended to label this substance as I (irritant).
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MAŁGORZATA KUPCZEWSKA-DOBECKA
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