Outside High Level Reviews of US EPA Superfund Remediation Program Approach for Radiation Risk Assessment

The Superfund program generally addresses radioactive contamination in a consistent manner as it addresses chemical contamination, except where there are technical differences between radionuclides and other chemicals. For example, when selecting cleanup levels for radioactively contaminated sites, they are generally expressed in terms of risk levels (e.g., 10^-4), rather than millirem or millisieverts, as a unit of measure. Although EPA and other US agencies have issued millirem based regulations under other statutory authorities, under CERCLA EPA promulgated a risk rang of 10^-4 to 10^-6 as a standard of protectiveness for all carcinogens including radionuclides. CERCLA guidance recommends the use of slope factors when estimating cancer risk from radioactive contaminants, rather than converting from millirem. Current slope factors are based on risk coefficients in Federal Guidance Report 13 using ICRP 107 data. The Superfund remedial program uses 10^-6 as a point of departure and establishes Preliminary Remediation Goals (PRGs) at 1 × 10^-6. PRGs, not based on other environmental standards known as Applicable or Relevant and Appropriate Requirements (ARARs), are risk-based concentrations, derived from standardized equations combining exposure information assumptions with EPA toxicity data.

EPA’s approach of addressing radiation and chemicals in a similar approach has received outside high- level review: both risk management/policy review, and scientific review. These reviews will be discussed below.

Blue Ribbon Commission

In 1997 the Presidential/Congressional Commission on Risk Assessment and Risk Management developed a report to Congress on the appropriate uses of risk assessment and risk management in Federal regulatory programs. In “The Presidential/Congressional Commission on Risk Assessment and Risk Management Final Report Volume 1 1997”, the commission described their mandate on page i in the Executive Summary as “in the 1990 Clean Air Act Amendments, Congress mandated that a Commission on Risk Assessment and Risk Management be formed to: ‘…make a full investigation of the policy implications and appropriate uses of risk assessment and risk management in regulatory programs under various Federal laws to prevent cancer and other chronic human health effects which may result from exposure to hazardous substances.’

In the Final Report Volume 2, “Risk Assessment and Risk Management In Regulatory Decision-Making” the commission recommended that:

1. Radiation and chemicals should be addressed consistently, particularly when co-located, stating on page 82 “A concerted effort should be made to evaluate and relate the methods, assumptions, mechanisms, and standards for radiation risks to those for chemicals to clarify and enhance the comparability of risk management decisions and investments, especially when both types of hazards are present.”
2. Superfund should continue to use the 10^-4 to 10^-6 cancer risk range and reasonably anticipated land use, stating on page 121 that for Superfund “Risk assessments and remedy selection should be based on reasonably anticipated current and future uses of a site. As EPA’s Land Use Directive of 1995 states, reasonable assumptions about future land uses should be developed early in a process of seeking consensus with local officials and community representatives.”

National Academy of Science

In 1999 the National Academy of Science (NAS) issued a report “Evaluation of Guidelines for Exposures to Technologically Enhanced Naturally Occurring.” NAS compared EPA’s approach for risk assessment (slope factors) and NRC’s approach (use EDE then convert to risk) and found NAS found EPA’s approach methodologically more rigorous for assessing risks from chronic exposure to radionuclides, stating on page 222 that:

“…the Nuclear Regulatory Commission's approach to estimating risk posed by chronic radiation exposure of the public normally is based on ICRP recommendations on estimating doses per unit exposure and the risk per unit dose. ... Lifetime risk is estimated by multiplying the annual effective dose equivalent from external and internal exposure by the assumed exposure time (for example, 70 y) and the nominal risk of fatal cancers caused by uniform whole body irradiation of 5 × 10^-2 per sievert… EPA has developed a methodologically more rigorous approach to assessing risk posed by chronic lifetime exposure to radionuclides, which is particularly important for internal exposure and differs in several respects from the simple approach described above.” NAS further notes on page 224 that “aspects of EPA's approach to risk assessment for radionuclides described above have been used in several regulatory activities, including development of radionuclide-specific slope factors for use in risk assessments at contaminated sites subject to remediation under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).”

On page 225 NAS further states that:

“EPA's approach should provide more realistic estimates of risk than the approach used by the Nuclear Regulatory Commission. All the factors described in the previous section—the use of organ-specific risks for many organs instead of risks based on the effective dose equivalent and a nominal risk from uniform whole-body irradiation, the use of updated biokinetic models in estimating dose from ingrowth of decay products in the body, the use of organ specific RBEs for alpha particles, and the use of age-specific dose rates from internal exposure in conjunction with age-specific cancer risks—should result in more realistic estimates of risks associated with chronic lifetime exposure.”

NAS goes on to compare EPA and NRC risk management approaches and determined differences were a matter of policy and not science, and should reflect societal values by noting on pages 233-234 that:

“…this committee finds that the differences between EPA and other guidance’s for TENORM do not have a scientific and technical basis but, rather, result essentially from differences in policies for risk management. …This committee offers the following comments on the issue of a limit on acceptable risk and, therefore, acceptable dose. First, the determination of an acceptable risk for any exposure situation clearly is entirely a matter of judgment (risk-management policy) which presumably reflects societal values.”

Although the focus of this report was on TENORM, NAS did state on page 221 that:

“…in general, there should be no difference between NORM and any other radioactive materials with regard to suitable approaches to estimating doses and risks related to external or internal exposure.”

EPA Science Advisory Board

In 1992 the EPA Science Advisory Board sent a letter to the EPA Administrator “Commentary on Harmonizing Chemical and Radiation Risk-Reduction Strategies.” SAB viewed the harmonization of radionuclides to the chemical approach as scientifically valid, stating on page 11 that one set of:

“…alternative approaches would strive for clear consistency between the radiation and chemical risk reduction strategies”, including to “regulate radiation risks exactly as chemical risks are now regulated. Use 10^-4 as a standard criterion for remediation or regulation.”

SAB noted on page 12 after describing several alternatives, that:

“…clearly, all choice among these options - and others that may exist - is a policy choice that transcends scientific analysis. The leadership of the Environmental Protection Agency has the authority and the responsibility to make the choice. We urge the choice to be articulated clearly so that the scientists who assess the risks of radiation ·and chemicals can understand the basis for subsequent decisions about risk reduction.”

In the letter the SAB acknowledged that EPA guidance for Superfund sites, including DOE sites under CERCLA, would use a consistent risk-based approach for addressing radiation and chemical contamination in both risk assessment methodology and cleanup levels (e.g., no more than 10^-4 cancer risk), by stating on page 9 that:

“a second area of discordance grew out of the recognition of waste problems involving radioactive materials that were under the purview of EPA or state environmental agencies rather than the Nuclear Regulatory Commission or the nuclear/radiation safety agencies in agreement states. The most striking of these are the radioactive or mixed waste problems at sites that have been placed on the National Priority List for attention by the Superfund Program. ... The facilities of the Department of Energy that are part of the nuclear weapons complex form another group of problem sites where radionuclides are a significant or even dominating part of the cancer risk equation. Whether these facilities are treated as Superfund (CERCLA) problems or current waste disposal sites under the Resource Conservation and Recovery Act (RCRA), the treatment of radioactive materials is seen as necessarily being subject to the same types of risk analyses and remedial responses that EPA has used for chemicals. The document "Risk Assessment Guidelines for Superfund" (RAGS), for example, contains a section on how to assess the cancer risks from exposure to radionuclides, but does not suggest any different risk-reduction strategies than for carcinogenic chemicals. The implication is that remediation is expected if the lifetime risks from radionuclides are calculated to exceed about 10^-4 (or lower in some proposals for radiation sites).”

Interagency Steering Committee

The Interagency Steering Committee on Radiation Standards (ISCORS), has federal agencies as members, including includes EPA, NRC, DOE, and DOD. In 2002 ISCORS issued entitled “A Method for Estimating Radiation Risk from Total Effective Dose Equivalent (TEDE).” ISCORS noted that the simple method of converting dose to risk is insufficient for a complex risk assessment such as those for CERCLA sites. ISCORS recommended that slope factors should be used when a complex risk assessment is needed for assessing radionuclides, such as at a CERCLA sites. The report stated on page 1 that:

“…for external sources of low linear energy transfer (LET) radiation that provide nearly uniform irradiation of the body, the risk of cancer incidence (morbidity) and mortality as a function of external dose can be closely approximated using the conversion factors of 8 × 10^-2 risk per sievert and 6 ×10^-2 risk per sievert respectively. The documentation for these conversion factors can be found in ‘Estimating Radiogenic Cancer Risks’ and its ‘Addendum: Uncertainty Analysis.’ These conversion factors can also provide a generally high-sided, but less accurate, estimation of risk from internal dose. A discussion of the sources and limits of this conservatism is presented in the discussion below. Using these factors to convert internal effective dose equivalent to cancer risk may be appropriate when radionuclide-specific data is missing. The conversion of dose to risk referred to in this document refers primarily to a conversion of total effective dose equivalent (TEDE, as defined by the Department of Energy in 10 CFR 835.2) to lifetime cancer incidence and mortality risks. The conversion of TEDE to cancer risks using these conversion factors will not satisfy the requirements for a comprehensive radiation risk assessment, but may be of use for making less rigorous comparisons of risk. For situations in which a radiation risk assessment is required for making risk management decisions, the radionuclide-specific risk coefficients published in "Federal Guidance Report No. 13 should be used. For radiation risk assessments required by EPA’s Superfund Program, the risk coefficients in EPA’s Health Effects Assessment Summary Tables (HEAST) should be used.”