Review of the US Navy's Human Health Risk Assessment of the Naval Air Facility at Atsugi, Japan (2001)

Review of the US Navy's Human Health Risk Assessment of the Naval Air Facility at Atsugi, Japan

This report was prepared by the Subcommittee on the Atsugi Incinerator, a subcommittee of the National Research Council's Committee on Toxicology, in response to a request from the US Navy for an independent review of the Navy Environmental Health Center (NEHC) report NAF Atsugi, Japan Human Health Risk Assessment Summary of Findings, Conclusions and Recommendations, Draft Final, January 2000 (NEHC 2000). In reviewing the NEHC draft summary report, the subcommittee also studied a number of supporting documents, including a risk-assessment draft report prepared by Pioneer Technologies Corporation (Pioneer 2000); sampling plans, sampling results, and summaries prepared by Radian International (Radian 1998a,b,c,d, 1999a,b,c,d, 2000a,b,c,d); statistical analyses prepared by Research Triangle Institute (RTI 1999); and quality-assurance reports (IT 1999; UAI 1999). A brief summary of the subcommittee's review of the risk assessment is provided below and is followed by a detailed evaluation of the planning of the risk assessment, data analyses, interpretation of the results of the risk assessment, data gaps, some suggestions for improving the NEHC draft summary report itself, and the responses of NEHC to comments from previous National Research Council committees. Specific examples of some of the problems associated with the NEHC draft summary report and other issues are presented in appendixes.

The Enviro-Tech incinerator facility, formerly called the Shinkampo or Jinkanpo incinerator complex, is adjacent to the US Naval Air Facility (NAF) at Atsugi, Japan, southwest of Tokyo. Enviro-Tech is a privately owned waste-combustion facility that consists of three incinerators, a waste-staging area, and an ash-holding area. Concerns have been raised by the residents of NAF Atsugi—US Navy personnel and their families—regarding the health effects of exposure to emissions from the incinerators and to chemicals resulting from the storage, handling, and disposal of waste material at the facility.

At the Navy's request, the National Research Council's Committee on Toxicology (COT) previously reviewed preliminary health risk assessments of NAF Atsugi that had been conducted by Navy Environmental Health Center (NEHC 1995, 1998). COT concurred with NEHC's overall recommendation that a comprehensive health risk assessment of NAF Atsugi be conducted (NRC 1995, 1998). NEHC conducted a comprehensive health risk assessment of NAF Atsugi and issued a draft summary report in 2000, NAF

Atsugi, Japan Human Health Risk Assessment Summary of Findings, Conclusions and Recommendations, Draft Final, January 2000¹ (NEHC 2000). That draft report is a summary of more-detailed reports prepared by Pioneer Technologies Corporation, Radian International, and other contractors, which performed the sampling and risk assessment. Reports prepared by those contractors, together with quality-assurance audits and a statistical analysis report, constitute the supporting documentation for the NEHC risk-assessment draft summary report.

NEHC then asked the National Research Council to review the comprehensive risk assessment. In response, the Research Council convened the COT Subcommittee on the Atsugi Incinerator. The subcommittee members were selected for their expertise in toxicology, epidemiology, industrial hygiene, engineering, exposure assessment, and risk assessment. Specifically, the subcommittee was asked to

1. Review the adequacy of the methods used to assess risk, the uncertainties identified, the risks to susceptible subpopulations (such as pregnant women and young children), and the scientific validity of the conclusions drawn.

2. Recommend, depending on its evaluation, research to fill data gaps and options for mitigating the risks associated with exposure to the incinerator emissions.

   Although not all the recommendations in the 1998 Research Council report (NRC 1998) were followed by NEHC, the subcommittee concludes that NEHC did an excellent job of addressing some of the recommendations:

• The NEHC risk assessment included a rigorous quality-assurance and quality-control program, and the subcommittee therefore has confidence in the accuracy of data collected.

• As recommended previously, risks of acute- and chronic-toxicity end points for different subpopulations were calculated separately in the current risk assessment.

• In addition to previously monitored air pollutants, ozone, nitrogen dioxide, carbon monoxide, sulfur dioxide, particulate matter smaller than 10µm in diameter (PM₁₀), and particulate matter smaller than 2.5 µm in diameter (PM_2.5), were monitored.

• Soil-trend analysis was conducted at sites where high exposures could occur.

• Extensive meteorologic data were collected.

Despite those improvements, the subcommittee has some concerns with the NEHC risk assessment.

A lack of proper planning was evident in the risk assessment and appeared to cause inconsistencies in the objectives of the data collection and risk assessment. The purpose and objectives of the risk assessment were not consistent and not clearly stated. Statistical analysis at the planning stage was not adequate to determine the number of samples and the sampling frequency needed for indoor and outdoor air. Data from the previous screening risk assessments could have been used to design the sampling program. For future risk assessments of this nature, NEHC should follow a general risk-assessment framework, such as those discussed in Science and Judgment in Risk Assessment (NRC 1994), and Framework for Environmental Health Risk Management and Risk Assessment and Risk Management in Regulatory Decision-Making (Presidential/Congressional Commission on Risk Assessment and Risk Management 1997a,b) and should consider the use of independent peer reviewers to oversee the entire assessment process, including the planning stages.

The subcommittee has confidence in the quality of the sampling techniques and meteorologic monitor

ing, but NEHC's analyses of the resulting data do not consistently meet the objectives of estimating the potential health risks to people living at NAF Atsugi and determining the contribution of the incinerator to those risks. The most appropriate methods were not used to determine the contribution of the incinerator complex to health risks at NAF Atsugi. The excellent and innovative air-dispersion modeling, used in conjunction with correlation analyses, would be the most appropriate method to determine the contribution of the incinerator complex to the health risks at NAF Atsugi.

NEHC used outdoor-air samples as surrogates for indoor air, but such substitution is not appropriate for determining the overall health risks to people living at NAF Atsugi. At almost all sites, air sampling was conducted for 14 months, with the last 2 months of sampling apparently being collected at times when the contribution of the incinerator was expected to be high. The potential biases in that collection protocol are not discussed in the draft summary report or accounted for in the data analysis. Reference concentrations (RfCs) are converted to reference doses (RfDs) for compounds for which such a conversion is inappropriate. Exposures to inhaled pollutants are converted from concentrations to doses in milligrams per kilogram per day. The previous Research Council report recommended against such conversions, and this subcommittee reiterates that recommendation.

The interpretation of the risk-assessment results by NEHC is not appropriate, given that a Superfund type of risk assessment was conducted. In such a risk assessment, the use of RfCs or RfDs is adequate to determine safety but not to determine health effects. Interpreting those risk values as thresholds for effects or “bright lines” can be useful for setting goals for decision-making; but, because of uncertainty inherent in them, they should not be accepted rigidly as exact values. For example, NEHC translates noncancer and cancer risks into absolute exposure durations that pose a cancer risk of 1 in 10,000 (10⁻⁴), such as 32 months for children younger than 6 years old and 98 months for adults. That interpretation ignores the stochastic and continuous nature of risk. The derivation of the values, including uncertainty factors and assumptions, should be considered when interpreting them.

The NEHC draft summary report should characterize the uncertainties in the risk assessment, including all the principal uncertainties identified in the supporting documents. The conclusions of the risk assessment should be presented in such a way that uncertainties in the data and process that led to the conclusions are evident. The potential effectiveness of some of NEHC's recommended actions is not evident, and, as is acknowledged by NEHC in Appendix B , there is no analysis of their effect. For example, the recommendation to stay indoors with the windows closed when the incinerator plumes are blowing onto NAF Atsugi is not consistent with the observation that the concentrations of many chemicals are higher in indoor air than in outdoor air. It is also evident from Appendix B that risk-reduction strategies are being used before an adequate evaluation and peer review of such recommendations; this is not an appropriate risk-management sequence.

Some potentially useful data were not collected by NEHC or not included in its draft summary report. Indoor-dust samples should be analyzed for heavy metals, including lead. The report should discuss the health-surveillance studies that have been conducted at NAF Atsugi. Information on Japanese standards should be included in the report. Susceptible subpopulations are not adequately addressed.

The subcommittee recommends changes in the NEHC draft summary report to make it more useful to readers. The report should begin with a clear statement of the purpose and objectives of the risk assessment, and it should include more details of the methods, assumptions, uncertainties, and limitations of the risk assessment. The report should be thoroughly referenced, including references to specific sections of the many supporting documents.

When drawing conclusions and making recommendations, NEHC should clearly distinguish between those based on science and those based on policy. NEHC should also describe the ways in which stakeholders have been involved in the policy decisions as recommended by many advisory groups for appropriate risk management practice.