TPM-C1 - Risk Assessment Orlando VI 14:30 - 15:30
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| Chair(s): Wayne Gaul
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TPM-C1.1
14:30 A Methodology for Investigating the Impact of Biological Countermeasures on the Risk of Exposure Induced Death CM Werneth*, NASA
; TC Slaba, NASA; SR Blattnig, NASA; JL Huff, Wyle Laboratories, Inc.; RB Norman, NASA
Abstract: The space radiation environment is composed of ionizing particles that may pose health risks to crew members during space missions. NASA has established astronaut career radiation limits of 3% Risk of Exposure Induced Death (REID) at the 95% confidence level. The REID is the increased lifetime risk of cancer death due to radiation exposure in comparison to an unexposed background population and has been traditionally mitigated by passive shielding design concepts. Additional reduction in radiation exposure risk may be achieved with Biological Countermeasures (BCM). Recent studies have demonstrated the efficacy of aspirin in the reduction of the background colorectal cancer incidence and mortality rates for specific cohorts. Furthermore, a recent cohort study of warfarin-users indicates significant cancer incidence reduction for stomach, prostate, bladder, brain, and lung cancers as compared to the control group. In this presentation, a general methodology for incorporating BCM into the NASA Space Radiation Cancer Risk model will be described and includes modifications of the background mortality rates (hazard rates) and the radiation risk coefficients. As examples of the method, aspirin and warfarin will be employed as BCM to compute the REID for astronauts embarking on a one-year deep space mission scenario.
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TPM-C1.2
14:45 US EPA Superfund Model for Assessing Radon and Thoron Intrusion SA Walker*, US Environmental Protection Agency
Abstract: The U.S. Environmental Protection Agency (EPA) Superfund remedial program is developing a new Radon Vapor Intrusion Screening Level (RVISL) calculator that is expected to be finished in 2019, similar to the Vapor Intrusion Screening Level (VISL) for chemical calculator that was finished in 2018. Currently, there is no U.S. EPA guidance on correlating soil or groundwater levels of radon with indoor radon concentrations at Superfund sites. The RVISL calculator will be an online tool that (1) lists three radon isotopes (Rn-219, Rn-220 and Rn-222) known to pose a potential cancer risk through the inhalation pathway; (2) provides generally recommended risk and Applicable or Relevant and Appropriate Requirements (ARAR) based preliminary remediation goals (PRG) for groundwater, soil gas (exterior to buildings and sub-slab) and indoor air for default target risk and ARAR-based levels and exposure scenarios; and (3) allows calculation of site-specific PRGs based on user-defined target risk, ARAR levels, and exposure scenarios. The RVISLs are calculated using the recommended approaches in existing guidance and are based on current understanding of the vapor intrusion pathway. The screening levels for groundwater and soil gas (either sub-slab gas or soil gas collected exterior to buildings) are calculated from the target indoor air concentrations using empirically-based conservative "generic" attenuation factors that reflect generally reasonable worst-case conditions as described in the EPA’s draft RVISL User Guide. The default, generic RVISL in this calculator are based on default exposure parameters and factors that represent Reasonable Maximum Exposure (RME) conditions for long-term/chronic exposures from either the PRG calculator when a risk based, or the DCC calculator when a dose based, ARAR exists at the site. The calculator also includes target levels based on the indoor radon standards of 0.002 Working Levels established under the Uranium Mill Tailings Radiation Control Act (UMTRCA) that are in 40 CFR 192.12(b)(1). Site-specific criteria that can be input to the calculator include exposure scenario (either residential or indoor worker), target risk or dose for radon and average in situ groundwater temperature (stabilized temperature measured during well purging prior to groundwater sampling).
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TPM-C1.3
15:00 US EPA Superfund Assessing Risks and Doses of Homegrown Food at Contaminated Sites SA Walker*, US Environmental Protection Agency
Abstract: The U.S. Environmental Protection Agency (EPA) Superfund remedial program has developed the Preliminary Remediation Goal (PRG) and Dose Compliance Concentration (DCC) internet-based calculators for radiation risk and dose assessment for contaminated soil and water at Superfund sites. Both calculators have 10 land uses for potential receptors. The residential scenario has a large potential garden that may be included in risk and dose assessments, and the farmer scenario adds potential farm animals to the produce found in the residential scenario. The PRG and DCC calculator's resident and farmer scenarios include exposures from 24 specific subcategories of produce. The produce intake rates are derived from 24 individual produce items, found in the 2011 Exposure Factors Handbook, that contribute to the overall produce ingestion PRG. Mass loading factors (MLFs) are incorporated for each produce category so that the 24 individual MLFs that correspond with the 24 individual produce items that make up the new produce intake rates. The user is able to select four climate zones (temperate, subtropical, tropical, humid) and up to seven soil types (e.g., default, sand, loam, clay, organic, coral sand, other) depending upon the climate zone to use a more appropriate soil to plant transfer factor from IAEA when available. In the farmer scenario for the PRG and DCC calculators, their 9 animal product categories (Beef, Eggs and Poultry, Fish, Dairy, Swine, Goat Milk, Mutton Milk, Goat Meat, and Mutton) that users may select as appropriate for their site-specific risk/dose assessment. The user is also able to choose between fresh weight intake rates which may be more appropriate for some sensitive subgroups that consume the entire produce or animal product, or pick intake rates that assume cooking and preparation more typical for the U.S. population. In the farmer scenario, when poultry is selected, the user is able to specify which type of poultry (chicken, duck, turkey, or goose) which will affect the fodder, water, and soil ingestion intake rates for the farm animal.
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TPM-C1.4
15:15 Minimum Provable Risk Considering the Variation in Background Risk M Sasaki*, Central Research Institute of Electric Power Industry
; H Ogino, Central Research Institute of Electric Power Industry; T Hattori, Central Research Institute of Electric Power Industry
Abstract: In order to prove a small increment in a risk of concern in an epidemiological study, a large sample of a population is generally required. Since the background risk of an end point of interest, such as cancer mortality, is affected by various factors, such as lifestyle (diet, smoking, etc.), adjustment for such factors is necessary. However, it is impossible to inclusively and completely adjust for such factors; therefore, uncertainty in the background risk remains for control and exposed populations, indicating that there is a minimum limit to the lower bound for the provable risk regardless of the sample size. In this case study, we developed and discussed the minimum provable risk considering the uncertainty in background risk for hypothetical populations by referring to recent Japanese statistical information to grasp the extent of the minimum provable risk. Risk of fatal diseases due to radiation exposure, which has recently been the focus of radiological protection, was also examined by comparative assessment of the minimum provable risk for cancer and circulatory diseases. It was estimated that the minimum provable risk for circulatory disease mortality was much greater than that for cancer mortality, approximately five to seven times larger; circulatory disease mortality is more difficult to prove as a radiation risk than cancer mortality under the conditions used in this case study.
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