Science and Judgment in Risk Assessment (1994) / Chapter Skim
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Appendix G: Improvement in Human Health Risk Assessment Utilizing Site- and Chemical-Specific Information: A Case Study
Appendix G: Improvement in Human Health Risk Assessment Utilizing Site- and Chemical-Specific Information: A Case Study
Pages 479-502
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From page 479... ...
human carcinogen.4 Conservative screening level cancer risk estimates reported by EPA to rank sources and prioritize regulatory action associated emissions of butadiene from the Texaco Chemical Company, Port Neches, Texas facility with a maximum individual risk of 1 in 10. Although the agency emphasized that these screening level estimates should be viewed only as rough estimates of the relative risks posed by the facility under evaluation, and should not be interpreted to represent an absolute risk of developing cancer, the risk estimate generated a high level of concern.
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From page 480... ...
Butadiene emissions have been reduced more than 90 percent. Repeating the prior EPA screening level analysis predicts a maximum individual cancer risk after completion of this project in the range of 5-10 in 1000 based on a 70 year exposure to the maximum predicted annual-average ground level concentration 200 meters from the center of the plant.
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From page 481... ...
Risks were characterized for the conventional "worst case" 70year exposure, the 30-year upper bound exposure, the 9-year average residential exposure, and the 95th percentile fraction of life exposed (FLE) based on national human activity pattern distributions.
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From page 482... ...
This model utilized meteorological data in the format of a STAR summary. The STAR summary is a joint-frequency distribution of wind speed, wind direction, and stability classification, processed from discrete hourly observations.
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From page 483... ...
3.3 Alternative Meteorological Data Set Comparison for the ISCLT Model Two quality-assured sets of meteorological data were evaluated for use in this analysis: 1) a 14-year composite annual joins frequency distribution of wind speed, wind direction, and stability class (STAR)
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From page 484... ...
No Butadiene Decay
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From page 485... ...
Low Butadiene Decay ~ If x^CO i,'`Of'ff2,trS ~ J _ ....
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From page 486... ...
. Median Butadiene Decay C^hlD USE: O L ...~ ' '~ ?
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From page 487... ...
High Butadiene Decay ,,
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From page 488... ...
To characterize potential carcinogenic effects, estimated risks that an individual will develop cancer over a lifetime of exposure to butadiene were calculated from projected intakes and the cancer slope factor. The cancer slope factor converts estimated daily intakes directly to an estimate of incremental risk as follows: Dose (mg/kg-day)
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From page 489... ...
Some of these, particularly the slope factor, have a high level of uncertainty. 4.1.1 Effect of Exposure Assumptions Realistically, very few people remain in the same location for a lifetime.
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From page 490... ...
EPA Slope Factor Adjusted by a Factor of 30 EPA slope Factor Adjusted by a Factor of 590 As defined by U.S. EPA, 1989 SCIENCE AND JUDGMENT IN RISK ASSESSMENT TABLE 4-1 KEY VARIABLES THAT DESCRIBE THREE CASES Base Case Worst Case Best Case National statistics are available on the upper-bound (30 years)
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From page 491... ...
average FLE based on national human activity pattern distributions. Figure 4-1, 4-2, and 4-3 illustrate the areal extent encompassed by several risk levels using traditional "worst case", reasonably maximum, and average exposure assumptions.
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From page 492... ...
\ |1 ma/ 1/500.000 ~-it- ~ // 1/1 00.000 ~' _ /; \/ // ~ \ 1/50,000 i: at- - - /~: 1/ \> Hi,', j 1'1' Hi' ( , . SCAM: IJETEOS 0 5000 FIGURE 4-1 Area Encompassed by Specific Risk Levels-Traditional Worst Case Exposure Assumptions
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From page 493... ...
~ / // 1 /50,000 SCAL-: ~tT~RS C 5000 - ~,-/f ': · /; ~ ~__ - - - ~ LAND USP: o TEXACO PROPERTIES ~ ::: :-, ~ -- :~ :-:4 RCSIDENTIAL AREA L ~ INDUSTRIAL AREA . , UNDEVELOPED LAND FIGURE 4-2 Area Encompassed by Specific Risk Levels-Reasonable Maximum Exposure Assumptions (Base Case)
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From page 494... ...
IN5USTRIAL ~R UN3_VELOP=D LAND FIGURE 4-3. Area Encompassed by Specific Risk Levels-Average Exposure Assumptions
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From page 495... ...
In the current analysis, however, risk estimates were also generated using alternative slope factors based on research that the EPA slope factor may overpredict risks to the human population.5 Cancer slope factors can be converted to unit risk estimates to determine the risk per unit air or water concentration. The inhalation unit risk can be calculated by dividing the slope factor by 70 kg (average body weight for an adult)
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From page 496... ...
. Since risks change proportionally to changes in the butadiene slope factor, the risks using the alternative slope factors are lowered by a factor of 30 to 590.
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From page 497... ...
-D >NC | e FIGURE 4-4. Area Encompassed by Specific Risk Levels-EPA Slope Factor (Base Case)
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From page 498... ...
_D FIGURE 4-5. Area Encompassed by Specific Risk Levels-EPA Slope Factor Adjusted by a Factor of 30
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From page 499... ...
RESIDENTIAL AREA _ ~ ~ INDUSTRIAL AREA ~ UNDEVE' OPED LAND FIGURE 4-6. Area Encompassed by Specific Risk Levels-EPA Slope Factor Adjusted by a Factor of 590
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From page 500... ...
Monte Carlo simulation calculates risk through numerous iterations using randomly generated values from the defines probability functions. The resulting distribution of risk estimates makes greater use of the scientific evidence and data related to exposure and theoretical risk without sacrificing conservatism.
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From page 501... ...
An examination of some of the key variables that influence estimates of theoretical risk indicates that the maximum individual risk at the nearest residences may be as low as 1 in 10,000,000. Risk estimates in this report should be considered in comparison to the approximate 1 in 4 background fatal cancer risk in the U.S.
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From page 502... ...
Site-Specific Evaluation of Potential Cancer Risk Associated with 1,3-Butadiene Emissions from the Texaco, Port Neches Facility. Addendum I-Probabilistic Monte Carlo Simulation.
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