Investigators used a total of 60 interviews to evaluate exposure to lindane dust during delousing of enemy prisoners of war (EPWs). The best information available indicates that lindane, 1% powder was virtually the only formulation used by US servicemembers for delousing EPWs. UK troops reportedly used a malathion formulation. Twenty-five of the 252 preventive medicine interviews provided information about delousing. To better capture the details of the process, investigators completed 35 additional interviews of servicemembers likely to be knowledgeable about delousing, from November 1998 through December 1999 (Tab H). Table 17 summarizes exposure data from all 60 delousing interviews.

Table 17 confirms that lindane was the most widely-used formulation for delousing. In the course of the 60 interviews, lindane was the only product identified, although some responses did not specify the active ingredient. The dispersal equipment most frequently used included power devices and manual pumps. No one could recall the output rates used. Army guidance required applicators to wear specific PPE components, including BDUs, respirators, and gloves.^[159] The appropriate respirator would have been a half-face respirator with organic vapor cartridges and pesticide prefilters, while the appropriate gloves would have been natural or synthetic rubber gloves.^[160] The answers to Question 5, and the detailed responses provided to the interviewers indicate 25% of applicators wore respirators and gloves together. Whether the referenced respirators and gloves met military standards is unknown, as the interview questions were not specific to this level of detail. At least 18% of personnel reportedly wore no PPE, and about 45% did not wear respirators.

Question 6 answers indicate about 50% of applicators inhaled lindane, and/or had dermal contact with lindane. Applicators conducted delousing in a tent about half the time (Q. 7). About 22% of respondents indicated that applicators made some efforts to clean up prior to breaks (Q. 8), and 8% did nothing; however, 70% of interviewees did not answer the question. Only one interviewee said he was aware of incidents where US troops experienced an immediate reaction ("…it burned their skin") to lindane (Q. 10). The interviews did not produce usable information on the approximate weight of lindane applied to each EPW (Q. 11). Only 10% of interviewees answered Question 11, and the answers appear to be unreasonably high based on military guidance. For example, according to the percentile values calculated for Question 11 responses, 10% or fewer interviewees stated that 3 oz of lindane dust were applied to each EPW, while 90% or fewer interviewees stated that 24 oz of lindane dust were applied to each EPW. In fact, 24 oz was the maximum reported, and was reported by a single interviewee.

The summary statistics for exposure time (Q. 14), exposure frequency (Q. 15), and exposure duration (Q. 16) are associated with a moderate to low level of uncertainty. Note, however, that the 90^th percentile value of 3 months is not a value calculated based on the interviews (which is considerably higher), but is based on the known maximum length of time (in months) that EPW processing occurred.

2. Screening Pesticide Products for Risk Assessment

Most of the pesticides and related products identified as potentially used during the Gulf War are well known to produce adverse health effects in animals and/or humans if applied at sufficient concentrations under certain conditions, and are recognized by EPA as being at least moderately toxic. However, most of them posed little or no health threat given the combinations of their prevalence, toxicity, and the ways in which they would have almost certainly been handled in the field.

Table 18 presents 64 pesticides and related products identified from specific sources as possibly used during the Gulf War. Such sources include the survey, PM interviews, and records searches described above. Where possible, investigators listed pesticide products by the probable formulations used; thus, there are many trade names not listed in Table 18. However, Table 18 also lists a number of infrequently cited miscellaneous products from the PM interviews. Investigators identified a subset of 15 pesticides for thorough evaluation in the HRA, known as the "pesticides of potential concern" (POPCs) from the complete set listed in Table 18. The POPCs are the ones which would have posed the greatest potential hazard to servicemembers during the Gulf War due to their prevalence, toxicity, and manner of use.

Investigators retained a pesticide product if it was cited in greater than 5% of the survey sample and/or PM interviews, and if it had a significant potential for toxicity under the conditions of use that most likely existed during the Gulf War.^[161]

Table 18. Screening summary of pesticides and related products

Investigators eliminated a pesticide product if it was deemed to have a low potential for toxicity under the conditions of use that most likely existed during the Gulf War. Details regarding the toxicity of the pesticide products listed in Table 18 may be found in a variety of sources, including the RAND Pesticides Literature Review, ^[162] Tab E, and four websites, as follows:

• EPA Office of Pesticide Programs, ^[163]
  
  
• Extension Toxicology Network (Extoxnet) at Oregon State University,^[164]
  
  
• National Library of Medicine (Toxnet), Hazardous Substances Data Bank (HSDB),^[165] and
  
  
• Agency for Toxic Substances and Disease Registry (ATSDR) of the US Department of Health and Human Services.^[166]

Investigators eliminated several types of formulations, chemicals, or other products identified as "pesticide products," at least partly, because of low toxicity under the conditions of use that most likely existed during the Gulf War. Such types included:

• anticoagulants,
  
  
• various traps,
  
  
• bait stations, and
  
  
• non-specific/unknown/misidentified.

PM personnel used anticoagulants for rodent control; anticoagulants exert toxicity only following ingestion. Products containing low concentrations of anticoagulants were provided as baits, placed near locations where rodents were expected to appear, such as rodent burrows. Some of the active ingredients and products include brodifacoum, warfarin, pindone, and "rat poison." While it is possible to describe a scenario where troops could have been exposed to anticoagulants via ingestion, we are justified in assuming that the amounts that could have been ingested would have been too small to be of consequence. For example, it is possible that rodents transferred contaminated material from paws to food, food storage areas, or food preparation surfaces, but the mass of material would be very small.

PM personnel used various traps to hold insects fast or kill them by slowly releasing a chemical in the immediate vicinity of the trap. The majority of these traps worked exclusively by holding the insect fast, and contained no pesticide active ingredient. Furthermore, those traps containing pesticide active ingredients would have released far too little chemical to have been of any health consequence to humans. The products (generic terms) included flystick, stick paper, one-way fly trap, and sticky trap.

Bait stations were small containers that contained baits attractive to the target pests. The bait stations were provided in closed containers, which had small holes opened immediately prior to placement in a location where they would be readily accessible to the pests. The pests would then crawl inside and consume the bait. There would have been little opportunity for human contact with the active ingredients. A typical example of such a bait station contained amidinohydrazone (Combat�) and was placed on floors for control of cockroaches.

Some personnel provided information on products referred to here as "nonspecific/unknown/misidentified." There are few reports in this category, and partly for this reason, they are of little consequence. In any case, investigators identified insufficient information from these reports to include these products in the HRA. Examples of products in this category include Kuwaiti organophosphate (OP) powder, carbamate, pyrethroids, red jelly, and chlorophyll.

C. EXPOSURE ASSESSMENT

The objective of this exposure assessment is to estimate the type and magnitude of exposures to the 15 pesticides of potential concern (POPCs), containing 12 different active ingredients, that servicemembers may have been exposed to during deployment. The exposure assessment evaluates the potentially-exposed population only, which is a subpopulation of the deployed population. Investigators have combined the results of the exposure assessment with toxicity data to characterize risk in Tab D, Section E, "Risk Characterization."

The movement of a pesticide active ingredient from the source to a human receptor is described in terms of an exposure pathway. A complete exposure pathway consists of all four of the following elements:

• a source and mechanism for pesticide active ingredient release,
  
  
• an environmental transport medium,
  
  
• an exposure point, and
  
  
• a human receptor and a feasible route of exposure at the exposure point.

Investigators have determined that each of the 15 pesticide formulations retained for detailed evaluation in the exposure assessment were associated with one or more completed pathways during deployment.

Investigators developed three to six exposure scenarios for each of the 15 POPCs for detailed evaluation in the pesticide exposure assessment. Table 19 presents a general description of all exposure scenarios evaluated for the POPCs. "Detailed" evaluation means that investigators used the specific scenarios and quantitative methods to estimate human intakes (doses); however, there is a moderate to high level of uncertainty associated with many of the exposure factors used to make the estimation. Wherever possible, investigators developed KTO-specific assumptions; otherwise investigators used standard generic EPA assumptions.

The EPA’s Office of Pesticide Programs (OPP) commonly conducts similar risk assessments in order to decide how to regulate pesticide products. OPP seeks to develop realistic exposure scenarios, and has developed highly detailed, sophisticated, and validated exposure models, in order to estimate doses. The models, which have been developed using an abundance of actual field monitoring data, can be used to make estimates for actual or hypothetical situations where monitoring data do not exist. Many of these models are incorporated into the following two sources:

• EPA: Pesticide Handlers Exposure Database (PHED) Surrogate Exposure Guide.^[167]
  
  
• EPA: Standard Operating Procedures (SOPs) for Residential Exposure Assessments.^[168]

Both sources have extensive applicability in estimating potential pesticide formulation exposures to Gulf War veterans. The HRA discusses PHED in more detail later in the exposure assessment.

While it is impossible to identify and evaluate all exposure scenarios which actually occurred, the HRA develops exposure scenarios that are representative of the range of exposures. Each exposure scenario is associated with the low exposure level, medium exposure level, or high exposure level. These exposure levels are hypothetical, depending entirely on the assumptions presented for each throughout the HRA.