PART B – HEALTH RISK ASSESSMENT

B.1  INTRODUCTION

The Office of the Special Assistant to the Secretary of Defense for Gulf War Illnesses, Medical Readiness, and Military Deployments (OSA) conducted a health risk assessment (HRA) for pesticides and related products used by or in proximity to ground troops deployed to the Kuwait Theater of Operations (KTO) during the Gulf War. Risk assessment, as defined by the US Environmental Protection Agency (EPA), Office of Pesticide Programs (OPP), is the process used to estimate the likelihood and magnitude of health effects from environmental exposures.[109] "Exposure" is defined here as the contact of a chemical with the outer boundary of a human or test animal.[110] The outer boundary means the skin, the lining of the alimentary canal (stomach, intestines, etc.), and the lining of the airways. Most exposures to pesticides are harmless; however, exposures of sufficient concentration and duration may elicit adverse physical symptoms, indicating overexposure.

The purpose of the HRA is to provide an estimate of the likelihood and magnitude of various specific effects from pesticide exposures during deployment. Such effects would have been limited to the time of deployment, and may or may not have implications for long-term health effects. While the HRA alone cannot prove either that overexposures occurred during deployment, or that any connection exists between pesticide exposures and chronic health effects months or years after exposure, the goal of the analysis is to answer the question, "Is it possible that some US personnel were exposed to concentrations of pesticides which exceeded reasonable risk-based levels?" The answer is yes; however, significant uncertainty is inherent in the overall analysis and limts the extent to which the analysis can be used.

This HRA was conducted in a manner that would allow it to be as comprehensive as possible, taking into account exposures due to supervised and unsupervised pesticide applications. Supervised applications were pesticide applications conducted under the supervision of DoD-certified pesticide applicators. Unsupervised applications were those not supervised by DoD-certified pesticide applicators. The HRA also addresses the cumulative health effects of various combinations of pesticide active ingredients.

The HRA is based on information from a number of sources. Foremost among these were the veterans of the Gulf War. RAND personnel contacted veterans in the course of a scientific survey. OSA investigators interviewed preventive medicine personnel, personnel with specific knowledge of fly bait use, and personnel who participated in or witnessed delousing of enemy prisoners of war. Investigators also conducted searches of military records. Additionally, Health Effects Division (HED), a division of the EPA Office of Pesticide Programs, provided much helpful assistance during the preparation of the HRA. HED personnel met with OSA staff on numerous occasions, and otherwise communicated on an ongoing basis from 1997 to 2000. HED personnel reviewed preliminary draft portions of the HRA in depth, and provided many helpful comments, suggestions, and recommendations.

While the risk assessment is quantitative, it is associated with significant levels of uncertainty. No real-time monitoring data exist for pesticide usage during the Gulf War, consequently the HRA must rely heavily on limited written records and on veteran recall of events which occurred 7 to 9 years prior to discussions with investigators. Thus, the descriptions of the HRA findings in Section A.6 are qualitative. However, investigators employed standard quantitative risk assessment methodology to arrive at the conclusions. The HRA follows four steps commonly employed in risk assessments:

The HRA's data collection and evaluation section summarizes and evaluates the data used such as from the survey, interviews, and records searches. The HRA presents and screens pesticides and related products against specific criteria to determine which will be evaluated in detail. In the exposure assessment, investigators estimated possible human doses for the pesticide products retained for detailed evaluation. The toxicity assessment comprises hazard identification and dose-response evaluation. Hazard identification is the process of determining whether exposure to a pesticide can cause an adverse health effect relevant to humans. Dose-response evaluation is the process of quantitatively characterizing the relationship between dose and one or more defined effects, which may or may not be accurately characterized as truly "adverse." Finally, risk characterization combines the information from the exposure assessment and the toxicity assessment to estimate noncancer hazards and cancer risks. However, it must be emphasized that the HRA relies on many assumptions, associated with varying levels of uncertainty, to arrive at the estimates of hazard and risk. The hazards and risks so determined may be considered "hypothetical" in that while they reflect known use and application practices as determined from the veteran interviews, we do not have the benefit of data that characterize application rates and the actual levels of the pesticides to which the applicators were exposed. Therefore, while the risk estimates may indicate areas of potential concern for large groups, investigators cannot know with confidence the full extent to which the estimates reflect the actual hazards and risks to any particular individual.

It is possible to carry out toxicity assessment and risk characterization using a "toxicological approach," and/or an "epidemiological approach." We employed both. The toxicological approach combines the doses estimated in the exposure assessment with the "standard" toxicity values identified in the toxicity assessment. These standard toxicity values are reference doses (RfDs) derived from controlled laboratory studies of animals or humans. Most of the values listed were derived by EPA, or investigators extrapolated them from EPA-derived values. The epidemiological approach compares the doses estimated in the exposure assessment to the available benchmarks from human studies (see Tab C-8). The relevant studies include epidemiological studies of exposed individuals. The latter benchmarks have not been verified by an appropriate agency, such as EPA, for purposes of risk assessment, but provide another means of comparison. It should be noted that the epidemiological approach does not constitute an epidemiological study of Gulf War veterans.

Investigators used the toxicological approach to determine whether or not specific biological effects would be hypothetically likely at the possible exposure levels encountered. The epidemiological approach was used to relate doses to specific human health effects. The appropriateness in the present case of the epidemiological approach is self-evident; that is, troops were exposed to pesticides and comparison of estimated exposure levels to published levels believed to be associated with specific health outcomes is a relevant analysis. The toxicological approach is called for, given the lack of hard data on exposure, the number and variety of chemicals involved, and the need to assess potential cumulative effects. Additionally, the toxicological approach addresses, to a limited extent, the potential for future health problems. Each approach has its own strengths and weaknesses, as summarized in Table 6.

Table 6. Toxicological and epidemiological approaches

Approach

Strengths

Weaknesses

Toxicological
  • Laboratory studies in animals are generally better controlled than "real-world" studies in humans.
  • Dose levels are constant and reliable.
  • Study populations are exposed only to the pesticide formulation of interest.
  • Study populations are sufficiently large and are homogeneous.
  • Animal data must be extrapolated to humans.
  • Human reactions may vary markedly from those of test animals.
  • Some toxicity values are derived from very high doses.
  • Humans are rarely exposed to a pesticide active ingredient the way test animals are.
  • Exposure conditions may be unrealistic.
Epidemiological
  • Directly comparable, high-quality human data would be the most relevant.
  • Interspecies extrapolation is not an issue.
  • Exposure conditions are realistic, and may more nearly approximate the conditions encountered by Gulf War veterans.
  • Directly comparable, high-quality human data are available sometimes, but are likely to be unavailable in most cases.
  • Actual dose levels are unknown; estimates are associated with a high level of uncertainty.
  • Exposures may have been sporadic and/or have fluctuated widely.
  • Study populations are exposed to many risk factors.
  • Study populations may be small and highly heterogeneous.
  • The actual dose form may not be known.

Throughout the HRA various assumptions, inputs, and the analysis in general are frequently referred to as "conservative." In the HRA, consistent with conventional risk assessment methodology, conservative means "marked by moderation or caution." A conservative assumption is one that is used due to the uncertainty present, and is more likely to overestimate than it is to underestimate exposure and/or risk. A conservative analysis, containing one or more conservative assumptions, is conducted in order to estimate an upper limit on exposure and/or risk. In a regulatory environment, where risk assessment is used to determine (future) pesticide tolerances, or drive cleanup at contaminated sites, conservative means health protective. To the extent that the HRA is an evaluation of past exposures, "health protective" is not an appropriate description. However, given that some recommendations for future pesticide use by DoD may result from the HRA, there is potentially a health-protective component.


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