Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels (1996) / Chapter Skim
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7 RISK ASSESSMENT
7 RISK ASSESSMENT
Pages 123-140
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From page 123... ...
It also contains an evaluation of the scopes of the two reports, the data and methods used in each, and recommendations for further development of the risk-assessment portion of the federal government's comprehensive evaluation of oxygenated fuels now being undertaken under the aegis of the NSTC's Committee on Environmental and Natural Resources. -The final part of this chapter contains recommendations for research efforts that could improve the scientific basis of risk assessment.
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From page 124... ...
Data gaps are noted, and judgments are made regarding risks about which some conclusions could be reached (i.e., those in Table 7.~. Although there are animal-carcinogenicity data on unoxygenated gasoline, these are appropriately considered by HEI to be inadequate for evaluation of human risk, because the test animals were exposed to totally vaporized gasoline, a mixture to which humans are not exposed.
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From page 125... ...
1 25 v Ct Cal q)
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From page 126... ...
The potential health effects from exposure to gasoline containing MTBE include (1) headaches, nausea, and sensory irritation in some, possibly sensitive, individuals, based on reports after exposure tO oxygenates; (2)
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From page 127... ...
In addition to its conclusions about possible health effects, the Oxygenates Evaluation Committee noted a general lesson to be learned from introducing oxygenates to the general public. Although it is not possible to have complete information about a substance before it is used, the diverse experiences after introducing oxygenated fuels argue strongly that any future new use of a substance should (1)
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From page 128... ...
In effect, the OSTP report is devoted entirely to the possible health risks associated with MTBE exposures resulting from its use in gasoline, in isolation from all other risks. DATA, METHODOLOGY, AND CONCLUSIONS The OSTP report presents a review and analysis of available data concerning human exposures to MTBE and the compound's health effects as reported in the currently available human and animal database.
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From page 129... ...
These potency estimates are combined with estimates of potential population exposures to MTBE Presented in Chapter 2 of the OSTP report and discussed by our committee) to yield estimates of upper-bound, excess lifetime cancer risks from inhalation of MTBE.
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From page 130... ...
1 30 a_ ED ad ad Cal o .
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From page 131... ...
1 3 1 o as o a)
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From page 132... ...
The OSTP report does not deal with the ingestion associated with MTBE, as might exist from consumption of contaminated water. In addition to its characterization of MTBE's cancer risks, the OSTP report concludes that "it is not known whether the cancer risk of oxygenated gasoline containing MTBE is substantially different from the cancer risk of conventional gasolines." The report also notes that "data were generally inadequate to evaluate the health risks of oxygenates other than MTBE." GENERAL COMPARISON OF THE TWO REPORTS WITH RESPECTTO RISK ISSUES It is obvious that the two reports differ substantially regarding scope and methods for risk assessment.
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From page 133... ...
EVALUATION OF EXISTING ASSESSMENTS AN D RECOM M EN DATIONS FOR Fl NAL ASSESSM ENT GENERAL COMMENTS ON RISK ASSESSMENT AND TREATMENT OF UNCERTAINTIES Both reports appropriately emphasize the substantial uncertainties associated with the problem of developing a comprehensive, comparative assessment of the health risks associated with oxygenated fuels. Indeed, it is clear that the database for certain oxygenates is so meager that no useful analysis can be undertaken.
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From page 134... ...
Such an argument fails on at least two grounds. First, although comprehensive data on the above mentioned mixtures are not available, a substantial amount of data do exist for selected components of those mixtures that are known to present potential health risks.
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From page 135... ...
Nevertheless, there are substantial quantitative toxicity data on each of the chemicals, and there is no reason why the federal government cannot adopt reference concentrations, reference doses, and cancer potency factors that have been prepared or developed for all the chemicals using federal guidelines for risk
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From page 136... ...
but was not used in any explicit way in the risk assessment. Without some attempt to provide an indication of the magnitudes of the risks associated with the potential constituents of oxygenated and nonoxygenated fuels, it is difficult to accept the final conclusions of the HE!
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From page 137... ...
With respect to noncancer health effects resulting from MTBE inhalation, the EPA's reference concentration (RfC)
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From page 138... ...
The committee sees no value in presenting such estimates. CONCLUSIONS _ The committee has made a number of recommendations for refinements and improvements in the assessment of potential human health risks associated with prolonged exposures to gasoline containing MTBE and for assessment of the comparative risks associated with oxygenated and nonoxygenated fuels.
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From page 139... ...
Rag ASSESSMENT i 3g _ ~ Spears that HTBE-co~~ning Ads do not pose bomb asks suLstanti~ly Vibrant Gom those associ~eJ with nonoxygenated bead but this conclusion ~ less Bed establLbed and should become the centerpiece for the government? comprehensive assessment.
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