Benzene, carcinogen risk assessment

The lARC has concluded that epidemiological studies have established the relationship between benzene exposure and the development of acute myelogenous leukemia and that there is sufficient evidence that benzene is carcinogenic to humans. Although a benzene-leukemia association has been made, the exact shape of the dose-response curve and/or the existence of a threshold for the response is unknown and has been the source of speculation and controversy. Some risk assessments suggest exponential increases in relative risk (of leukemias) with increasing cumulative exposure to benzene. At low levels of exposure, however, a small increase in leukemia mortality cannot be distinguished from a no-risk situation. In addition to cumulative dose other factors such as multiple solvent exposure, familial connection, and individual sus-... 

OSHA has in the past decade completed a number of rulemakings on occupational carcinogens, including arsenic, benzene, asbestos, ethylene oxide and acrylonitrile. The agency conducted risk assessments and concluded that occupational exposure standards - so-called Permissible Exposure Levels, PELs - were too high and had to be reduced. 

Hard, G. C. (2002). Significance of the renal effects of ethyl benzene in rodents for assessing human carcinogenic risk. Toxicol Sci 69, 30 1. 

Occnpational Safety and Health Administration, Identification, Classification and Regnlation of Potential Occupational Carcinogens, 45 Fed. Reg. 5001 (1980) American Petroleum Institute v. Industrial Union, AFL-CIO, 448 U.S. 607 (1980) Thomas O. McGarity, The Story of the Benzene Case Judicially Imposed Regulatory Reform through Risk Assessment, in Environmental Law Stories 141 (Richard Lazarus Oliver Houck, eds. 2005). 

Carcinogenic Effects. Specific hydrocarbon indicator compounds that have EPA cancer risk estimates are assessed these are benzene and benzo(a)pyrene. EPA relative potency factors can be used for benz(a)anthracene, indeno(l,2,3-cd)pyrene, dibenz(a,h)anthracene, chrysene, benzo(b)fluoranthene, and benzo(k)fluoranthene. 

Inhalation Exposure. The available inhalation MRLs for each of the BTEXs, and the EPA cancer risk for benzene, can be used to assess the potential for health effects for each of these indicator compounds individually. This is consistent with current practice. These MRLs and their associated effects, as well as the EPA cancer assessments, are summarized in Table 6-3. Health effects that are common to the BTEXs are neurological effects. Developmental effects appear to be a sensitive effect of inhalation exposure to ethylbenzene and xylene. Benzene has hematological and immunological/ lymphoreticular effects and is classified in EPA Group A (human carcinogen). 

The above represent the most widely available generic approach to hydrocarbon assessment. Risks from carcinogenic components (BTEX PAH) are assessed first as they usually drive die risks. The remaining petroleum hydrocarbons are assessed as a series of 13 fractions defined on the basis of Equivalent carbon (EC) numbers rather than carbon numbers . The EC number is related to the boiling point of individual compounds and retention time on a GC column. For example, the EC number of benzene is 6.5 because its boiling point and GC retention time are approximately halfway between those of 77-hexane (6-carbon chain) and 77-heptane (7-carbon chain). The TPHCWG chose the concept of EC numbers because these values are more logically related to compound mobility in the environment than carbon numbers. 

Albert, R.E., et al. Carcinogen Assessment Group s Final Rep. on Population Risk to ambient Benzene Exposure, EPA 1978... 

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