Ethyl tertiary-butyl ether. Documentation of suggested occupational exposure limits (OELs)

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Ethyl tertiary-butyl ether. Documentation of suggested occupational exposure limits (OELs)

Journal Title: Podstawy i Metody Oceny Środowiska Pracy - Year 2014, Vol 30, Issue 2

Abstract

Ethyl [i] tertiary[/i]-butyl ether (ETBE, 2-ethoxy-2-methylpropane, CAS: 637-92-3) is a colorless, flammable liquid with a characteristic odor, which is obtained in a reaction of isobutene with ethanol. ETBE is used in an amount up to 15% as an additive, which improves the oxidizing properties and the octane number of gasoline. In Poland, PKN ORLEN SA and LOTOS Group produce ETBE (more than 170000 tonnes per year). Exposure of workers (usually by inhalation) occurs during manufacturing of ETBE, blending gaso-lines, and its transport and distribution. There are no data on the number of people exposed to ETBE in Poland and the concentrations, to which they are exposed. ETBE is readily absorbed into the body by inhalation. Its elimination from the blood is a four-phase process (the first two phases are very fast, t1/2 = 2 and 18 min). ETBE is rapidly metabolized by oxidation involving cytochrome P-450 to tert-buthyl alcohol (TBA), 2-methyl-1,2-propanediol (MPD) and 2-hydro-xybutyric acid (HBA). In the second phase of metabolism, TBA is coupled, mainly with glucuronic acid. Unchanged ETBE is excreted in the expired air (about 45 – 50% of the dose) or as TBA (about 3% of the dose). The metabolites (representing approximately 40 to 70% of the dose) in the urine are excreted. There is little data on the effect of ETBE in humans. In volunteers exposed to ETBE by inhalation at the concentration of 106 or 212 mg/m3 (25 or 50 ppm), the mucous membrane of the nose and upper respiratory tract were irritated. After exposure to ETBE at the concentration of 212 mg/m[sup]3[/sup] irritation and slight changes in the parameters defining the functions of the lungs were recorded.After intragastric administration of ETBE to rats, LD50 values 2000 mg/kg of body weight were exceeded. The compound was irritant to the skin and eyes of rabbits. No allergic effect was noted (maximization test on guinea pigs). In short-term experiments on animals, regard-less of the route of exposure (inhalation or intragastric), dose-related (600 – 1800 mg/kg/day for 14 days) or concentration (2090 – 16720 mg/m[sup]3[/sup] for 4 weeks) increases in the relative weight of the liver and kidneys, but without histopathological changes in these organs were reported. After subchronic inhala-tion of rats to ETBE at the concentrations 2090 – 20900 mg/m[sup]3[/sup], reduced body weight gain and an increase in the mass of the liver and kidneys were observed. In the kidneys of males, histopathological changes and disorders in the functioning of the kidneys caused by the accumulation of α2-microglobulin in proximal tubular cells were reported. ETBE at the concentrations 7315 – 20900 mg/m[sup]3[/sup] caused an increase in urea ni-trogen (BUN) in the blood of rats. After 13- -week exposure of rats to ETBE at the concentra-tions 2090 – 20900 mg/m[sup]3[/sup], effects of neurotoxicity were noted. On the basis of a two-year study, in which ETBE was administered to animals in drinking water, the LOAEL value (kidney damage in rats) was 625 ppm (625 μg/l of water). No genotoxic nor carcinogenic effects were noted. ACGIH classi-fies ETBE as group 4A. ETBE did not affect the fertility and reproductive in laboratory animals, and did not cause embryotoxicity and teratogenicity. The value of the maximum admissible concentration (MAC) for ETBE was based on the results of tests carried out on vol-unteers. After exposure to ETBE at the concen-tration of 212 mg/m[sup]3[/sup] (LOAEL), the irritation of the mucous membranes of the eyes, nose and upper respiratory tract and a slight dysfunction of the lungs were observed. The Expert Group for Chemicals Agents suggest a MAC-TWA value of 100 mg/m[sup]3[/sup]. Due to the irritant potential of ETBE, a MAC-STEL value of 200 mg/m3 (2 x MAC-TWA) has been proposed. It has been also proposed to label the substance with I (irritant).<br/><br/>

Authors and Affiliations

Jadwiga SZYMAŃSKA, Elżbieta BRUCHAJZER

Keywords

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EP ID EP224581
DOI 10.5604/1231868X.1111930
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