A new IRIS review has been issued for public comment by the EPA, describing the scientific basis for the human health hazard and dose-response assessments of the petrol additive ETBE.

Exposure is primarily expected through inhalation of vapours or ingestion of contaminated groundwater. Absorption following direct skin contact is also possible, particularly in occupational settings. Considering effects other than cancer, EPA derived a chronic oral reference dose (RfD) of 0.5 mg/kg bw/day based on kidney effects (specifically, urothelial hyperplasia) observed in a long‑term study in rats. The point of departure from this oral study was converted into a chronic inhalation reference concentration (RfC) of 9 mg/m3.

EPA considered there to be “suggestive evidence of carcinogenic potential” of ETBE in humans from all routes of exposure, based on liver tumours in (male) rats in a 2-year inhalation study. Although no liver tumours were induced in 2-year oral studies in rats, there was an increased incidence of tumours of the liver, thyroid, colon, forestomach, urinary bladder and kidney in male rats in an initiation-promotion study (long-term oral administration of ETBE after a 4-week initiation with a known mutagen). In this instance, EPA calculated the benchmark dose associated with a 10% incidence of the liver tumours, from which an oral slope factor (OSF) of 9 x 10-4/(mg/kg bw/day) was derived. This slope factor is equivalent to an excess human cancer risk of 1 in 100,000 from a lifetime daily intake of 0.011 mg ETBE/kg bw/day. The equivalent risk factor for inhalation exposure was 8 x 10-5/(mg/m3), corresponding to a 1 in 100,000 excess cancer risk from lifetime exposure at 0.125 mg/m3.

US Environmental Protection Agency (EPA) (2016). Toxicological review of ethyl tertiary butyl ether (CASRN 637-92-3) in support of summary information on the Integrated Risk Information System (IRIS). August 2016. EPA/635/R-16/184a. http://ofmpub.epa.gov/eims/eimscomm.getfile?p_download_id=528998


The above items were taken from the October 2016 issue of Toxicology and Regulatory News which is sent automatically to members of bibra (click here)

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