C.  Exposure Scenarios and Analysis

1.  Exposure Estimates

In the HRA we estimated the dose of each pesticide a veteran may have received. To calculate the dose for those who were exposed, we developed exposure scenarios—descriptions of how a veteran might have been exposed to a pesticide, such as breathing pesticide fumes in a tent, or touching a surface on which a pesticide was sprayed. We developed separate exposure scenarios for the general military population and for pesticide applicators, to account for the different types of exposure. For each exposure scenario, there are three possible routes of exposure: dermal (pesticide touches skin), inhalation, and oral (pesticide swallowed after unintentional hand-to-mouth contact). There are an infinite number of possible exposure scenarios; therefore, investigators developed exposure scenarios representative of the range of exposures that may have occurred for each of the 15 pesticide products (known as "pesticides of potential concern" or POPCs). Data collection indicated that between 10 and 40 percent of Gulf War veterans had little to no exposure to pesticides. For the population that was exposed to pesticides, investigators developed low, medium, and high exposure scenarios for each pesticide product. The low scenario covers that portion of the population who were least exposed (about 10 percent of the exposed population); the medium scenario covers the bulk of the exposed population (about 80 percent); and the high scenario covers those veterans who were exposed to the highest pesticide concentrations (about 10 percent). Investigators attempted to develop realistic exposure scenarios, but when in doubt, made assumptions that tended to overestimate exposures.

2.  Toxicity

The Environmental Protection Agency (EPA) supplied the toxicity information on most of the active ingredients contained in 14 of the 15 POPCs. The manufacturer supplied the information for azamethiphos. For each POPC and exposure scenario, and various combinations of exposure scenarios, we defined a "level of concern" using the toxicity information we acquired. The higher the exposure above the level of concern, the greater the likelihood of health effects occurring. Exposures at or below the level of concern are unlikely to produce health effects. Additionally, exposures above the level of concern do not mean that health effects are guaranteed. The development of levels of concern is discussed in detail in Part B, Section B.5,  Risk Characterization.

3.  General Military Population

a. Personal-Use Pesticides

1) DEET

According to the RAND pesticides survey, about half of the servicemembers in the Gulf used DEET repellents. The preparations most commonly available in the Gulf were a stick (33% DEET), a lotion (33% DEET), and a liquid (75% DEET). Similar preparations have been widely available to the American public for many years as a repellent for numerous pests (e.g., mosquitoes and ticks).

In the low exposure scenario, the servicemember applied DEET once a day, four days each month for two months. In the medium exposure scenario, the servicemember applied DEET twice a day, 15 days each month over a period of four and a half months. In the high exposure scenario, the servicemember applied DEET seven times a day, 24 days each month for eight months.

We relied on various sources to construct the DEET exposure scenarios. The number of applications came from the RAND pesticides survey. We assumed DEET covered one-fourth of the entire body, based on information from EPA. The number of days per month DEET was used came from the survey, and the number of months DEET was used came from the preventive medicine interviews. We are using DEET as an example of how the scenarios for all the pesticides were developed; the specifics for other pesticides are provided in the Health Risk Assessment, Part B.

The HRA indicates that DEET exposures were below levels of concern and used alone would have been unlikely to cause toxicity under any of the three exposure scenarios examined. Simply put, DEET applied to the skin of a normal, healthy adult is not very toxic, even upon repeated application.

2) Permethrin

About 44% of servicemembers in the Gulf used permethrin spray—mainly on battle dress uniforms (BDUs), tents and mosquito nets. Normally, servicemembers waited two to four hours for the permethrin spray to dry before wearing the uniform. According to the label, servicemembers should have applied permethrin outside only; however, some veterans indicated to investigators that they did apply permethrin inside their tents.

In the low exposure scenario, the servicemember applied one can of permethrin each day, two days each month for one month. In the medium exposure scenario, the servicemember applied one can a day, four days per month for four months. In the high exposure scenario, the servicemember applied one can a day, eight days per month for eight months. We assumed servicemembers were exposed to vapors one, five, or 15 times per month in tents, since different individuals could have been spraying on different days. Servicemembers had skin exposure to permethrin present in their uniforms every day.

None of the scenarios examined for permethrin exceeded the levels of concern.

3) Area Spray (d-Phenothrin)

Up to 28% of servicemembers in the Gulf may have used d-phenothrin aerosol spray to control flies and mosquitoes inside tents and other structures. The label advised the user to spray the area for no more than 10 seconds (1/6 of a can) per 1,000 cubic feet, to then close the area for 30 minutes, and finally to ventilate the area before personnel reentered. Individuals used this pesticide with little or no supervision. Since we lacked specific information about how well servicemembers followed label instructions, we assumed that they remained inside the structures during and after application.

In the low exposure scenario, the servicemember sprayed a tent or other enclosed area with about three-fourths of a can per day, two days per month for two months. In the medium exposure scenario, the servicemember sprayed about three-fourths of a can per day, every day of the month for four months. In the high exposure scenario the servicemember sprayed a tent with three cans per day, every day of the month for six months.

None of the scenarios examined for d-phenothrin exceeded the levels of concern, despite assuming that servicemembers remained inside structures during and after applications (contrary to label directions).

b. Fly Baits (Azamethiphos and Methomyl)

The most commonly used fly baits in the Gulf were one percent methomyl (purchased locally and issued by the military) and one percent azamethiphos (the locally purchased Snip). Fly baits may have been used in any of the areas where personnel worked, ate, and slept, and were often placed in open containers inside and outside buildings and tents, or spread on the ground. Military guidance and the labels on the EPA-registered products authorized outdoor use only. The label on Snip (not registered with EPA) said, "…suitable for use in villas, markets ... apply Snip on ... floor, pathways, window sills, [and] partitions." Fly baits were applied variously by trained pesticides personnel, field sanitation teams, and by untrained personnel (e.g., food service personnel, and individual servicemembers).

Approximately 12% of servicemembers in the Gulf applied or were exposed to fly baits. The preventive medicine interviews showed that the Army used azamethiphos fly baits about as often as methomyl. The Marine Corps and the Navy used methomyl-based fly baits more than twice as often as azamethiphos-based baits. The Air Force apparently used methomyl almost exclusively. Fly bait exposures occurred both when the bait was applied and when servicemembers were in the vicinity of the applied baits. Investigators developed the exposure scenarios from survey information and preventive medicine interviews.

In the low fly bait exposure scenario, the servicemember distributed one pound per day, one to four days each month for one to three months (the ranges cover the different fly baits used). In the medium fly bait exposure scenario, the servicemember distributed two pounds per day, 22 days per month for five months. For this scenario, investigators assumed that the servicemember could either inhale the pesticide dust or absorb the pesticide contacting the skin. In the high fly bait exposure scenario, the servicemember distributed four pounds per day, 30 days per month for nine months, and investigators assumed that the servicemember could inhale the pesticide, absorb it through the skin, or ingest it via unintentional hand-to-mouth contact.

The medium scenario for azamethiphos fly baits produced exposures slightly exceeding the levels of concern. The high scenarios for both azamethiphos and methomyl produced exposures exceeding the levels of concern. Servicemembers who were exposed to—but did not handle or apply fly baits—were exposed below the levels of concern.

c. Pest Strips (Dichlorvos 20%)

Approximately seven percent of servicemembers in the Gulf were exposed to pest strips containing 20% dichlorvos hung in various indoor locations to control flying insects. The pest strip label recommended one strip per 1000 cubic feet, equating to one strip per small general-purpose tent or two strips per medium general-purpose tent.

In the low exposure scenario, the servicemember inhaled pest strip fumes three hours per day, 23 days per month for two months. In the medium exposure scenario, the servicemember inhaled the fumes 11 hours per day, 27 days per month for four months. In the high exposure scenario, the servicemember inhaled the fumes 16 hours per day, 30 days per month for six months.

Because servicemembers spent long periods in areas where pest strips hung, all three scenarios produced exposures above the levels of concern.

d. Field Use Pesticides

In addition to repellents, area sprays, fly baits, and pest strips, the general military population was exposed to pesticides applied by applicators (including professional certified and trained applicators and field sanitation teams).

1) Sprayed Liquids:

Chlorpyrifos 45%
Diazinon 48%
Malathion 57%
Propoxur 14.7%

Applicators sprayed liquid pesticides on the outside base of walls or tents, the outside of garbage containers, and other places where pests congregated. Applicators also sprayed pesticides inside structures such as in and around cracks and crevices where walls met the floors. In small structures, like latrines, the spray may have covered much of the interior surface of the structure below waist level.

All the services used all of these liquid pesticides. Army applicators used mostly chlorpyrifos and diazinon. Navy and Marine applicators used mostly chlorpyrifos and malathion. Air Force applicators used mostly diazinon. All used propoxur and to a lesser extent malathion.

Under the low and medium exposure scenarios, exposure to chlorpyrifos, diazinon, and malathion occurred only outdoors. Since treated areas outside would have usually been limited to building and tent foundations, and garbage containers, there would have been little opportunity for exposure following application. In the high exposure scenario, servicemembers were exposed for two and a half-hours a day for up to nine months in dining facilities and latrines. Exposure occurred by skin contact with treated surfaces, and inhalation of vapors.

Propoxur was applied outdoors only under the low exposure scenario. In the medium exposure scenario, servicemembers were exposed to propoxur for two and a half-hours a day, four days per month for three months. In the high exposure scenario, servicemembers were exposed to propoxur for two and a half-hours a day, ten days a month for seven months.

For the general military population, investigators found that the sprayed liquid pesticide scenarios exceeding levels of concern were those in the mess and the latrine. Servicemembers inhaled the vapors resulting from sprayed liquids in both locations, and particularly in the latrine, where servicemembers touched treated surfaces and absorbed the pesticides through the skin.

The high scenarios for chlorpyrifos, diazinon, and malathion produced exposures exceeding the levels of concern. None of the scenarios for propoxur produced exposures reaching the levels of concern.

2) Sprayed Powder:

Bendiocarb 76%

Bendiocarb powder was mixed with water and sprayed on the outside base of walls or tents, the outside of garbage containers, and other places where pests congregated. Bendiocarb was also sprayed inside structures in cracks and crevices where walls met the floors. In small structures, like latrines, the spray may have covered much of the interior surface of the structure below waist level. Servicemembers were exposed through inhalation of the vapors and skin contact on pesticide-contaminated surfaces in dining facilities and latrines.

Under the low exposure scenario for bendiocarb, exposure occurred only outdoors. Since treated areas outside would have usually been limited to building and tent foundations, and garbage containers, there would have been little opportunity for exposure following application. In the medium exposure scenario, bendiocarb was applied indoors, servicemembers were exposed for two and a half-hours a day, six days per month for four months. In the high exposure scenario, servicemembers were exposed for two and a half-hours a day, 12 days a month for seven months.

The medium and high scenarios for bendiocarb produced exposures exceeding the levels of concern.

3) Fogging Agents:

Chlorpyrifos 19%
Malathion 91%

Pesticides were applied outdoors as a fog to control filth flies, sand flies, and mosquitoes. Fogging trucks discharged the fog outside living quarters, mess tents, or latrines. The Navy/Marines and the Air Force primarily used fogs. The general population may have been exposed by inhalation.

In the low exposure scenario, servicemembers had a single 30-minute exposure. In the medium exposure scenario, servicemembers were exposed for a half-hour each day, four days per month for four to five months. In the high exposure scenario, servicemembers were exposed for a half-hour per day, 16 days per month for eight months.

None of the fogging scenarios produced exposures reaching the levels of concern.

e. Summary of General Military Population Exposures Which Exceeded the Levels of Concern

Investigators determined that the personal-use pesticides (DEET, permethrin, and d-phenothrin) did not produce exposures exceeding the levels of concern. Table 4 summarizes the exposures for the general military population that exceeded the levels of concern.

Table 4. General military population exposures which exceeded the levels of concern

Pesticide Type

Affected Group

Active Ingredient/Class

Scenarios

Fly baits Only individuals who handled (applied) fly baits

Azamethiphos (OP)

Medium, High

Methomyl (C)

High

Pest strips

General military population

Dichlorvos (OP)

Low, Medium, High

Sprayed liquids General military population

Chlorpyrifos (OP)

High

Diazinon (OP)

High

Malathion (OP)

High

Sprayed powders

General military population

Bendiocarb (C)

Medium, High

OP = organophosphate
C = carbamate

4.  Pesticide Applicators

a. Field Use Pesticides

1) Sprayed Liquids:

Chlorpyrifos 45%
Diazinon 48%
Malathion 57%
Propoxur 14.7%

Applicators obtained these liquid pesticides in concentrated form, mixed them with water, and then applied them using either a two-gallon handwand sprayer (Figure 7) or a backpack sprayer. These pesticides were used predominantly outdoors to control filth flies, sand flies, mosquitoes, fleas, and ticks. Outside, applicators applied liquid pesticides to the base of walls or tents, garbage containers, and other places where pests congregated. Applicators also applied pesticides inside structures along cracks and crevices, such as where the walls met the floors. In small structures, such as latrines, much of the interior surface of the structure below waist level may have been treated. Investigators calculated applicator exposures separately for the two-gallon handwand sprayer and the backpack sprayer. Applicators who handled and applied liquid pesticides were exposed when filling the sprayer and during use.

In the low exposure scenarios, applicators were exposed while wearing appropriate personal protective equipment (PPE), and preparing and applying 1 gallon of diluted pesticide on a single occasion. In the medium exposure scenario, applicators were exposed while wearing appropriate personal protective equipment (PPE), preparing and applying five gallons of spray per day for 4-13 days per month over a period of four to five months. Under the high exposure scenario, unprotected (inadequate PPE) applicators prepared and applied 40 gallons of spray per day, every day for seven to nine months.

The propoxur scenarios produced no exposures reaching the levels of concern. The medium and high scenarios for chlorpyrifos, diazinon, and malathion produced exposures exceeding levels of concern.

2) Sprayed Powder:

Bendiocarb 76%

Applicators mixed bendiocarb powder with water then applied the mixture with a two-gallon handwand sprayer. Otherwise, the use and exposure scenarios are very similar to the sprayed liquid pesticides. Bendiocarb was used almost exclusively by Navy, Marine Corps and Air Force applicators.

In the low exposure scenario, applicators wore appropriate personal protective equipment (PPE) while preparing and applying one gallon of bendiocarb spray on a single occasion outdoors. In the medium exposure scenario, applicators wore appropriate PPE while mixing and applying five gallons of bendiocarb spray indoors each day, six days per month for four months. In the high exposure scenario, unprotected (inadequate PPE) applicators mixed and applied 15 gallons of bendiocarb each day, 12 days per month for seven months.

All three bendiocarb scenarios produced exposures exceeding the levels of concern.

3) Fogging Agents:

Chlorpyrifos 19%
Malathion 91%

Applicators used fogging pesticides outdoors to control flies and mosquitoes. Applicator exposure began when they poured the pesticide liquid into the tank of a fogging truck. Fogging occurred outside living quarters, mess tents, and latrines. The area treated determined the low, medium, and high application scenarios. The Navy, Marine Corps and the Air Force applicators primarily used fogs.

In the chlorpyrifos low exposure scenario, applicators wore appropriate personal protective equipment (PPE) while mixing and applying three and a half gallons of chlorpyrifos on a single occasion. In the medium exposure scenario, applicators wore appropriate PPE while mixing and applying seven gallons of pesticide each day, eight days per month for four months. In the high exposure scenario, unprotected (inadequate PPE) applicators mixed and applied 14 gallons of chlorpyrifos each day, 21 days per month for eight months.

In the malathion low exposure scenario, applicators wore appropriate PPE while mixing and applying eight gallons of pesticide on a single occasion. In the medium exposure scenario, applicators wore appropriate PPE while mixing and applying 52 gallons of malathion each day, 10 days per month for five months. In the malathion high exposure scenario, unprotected (inadequate PPE) applicators mixed and applied 120 gallons of malathion each day, every day for eight months.

The high scenarios for both fogging pesticides produced exposures exceeding the levels of concern.

b. EPW Delousing with Lindane

US forces used lindane primarily for delousing enemy prisoners of war (EPWs). Some servicemembers used lindane for purposes other than EPW delousing, (e.g., individual treatment of clothing to control body lice), and it is likely that these exposures were significantly lower than during the EPW delousing operations. US personnel conducted delousing both outdoors and inside tents. Most EPWs were processed between February 24 and April 30, 1991. US-operated EPW camps processed 69,822 EPWs at four camps, with peak processing rates of 1,500 EPWs per day, per camp.[99] Investigators estimate that 100 Army personnel assigned to military police units, medical units, and possibly a few other units participated in the delousing process.

Delousing procedure specified applying one or two ounces of lindane powder to clothed individuals,[100]spraying the powder beneath the clothing at the neck, sleeve, and waist openings, and then whitening the head and hair with dust, and dusting the inside of the hat.

In the low exposure scenario, the servicemember applied lindane in the proper manner outdoors while processing 35 EPWs a day, four hours a day (the exposure time) for six days, at a rate of one ounce of lindane powder per EPW. In the medium exposure scenario, the servicemember applied lindane indoors while processing 35 EPWs a day, nine hours a day for 32 days at one and two-tenths ounce of lindane powder per EPW. In the high exposure scenario, the servicemember applied lindane indoors while processing 150 EPWs a day, 12 hours a day for 90 days at two ounces of lindane powder per EPW. The applicators were not applying lindane continuously during the exposure time, but were near enough to be exposed continuously. We assumed that two and a half percent of the lindane powder applied became airborne (part of which could be inhaled). The high scenario produced exposures above the levels of concern.

c. Summary of Applicator Exposures Which Exceeded the Levels of Concern

Besides being exposed while preparing and applying pesticides, applicators were also subject to the same exposures as the general military population. The exposures that are unique to applicators, and which exceed the levels of concern, are summarized in Table 5.

Table 5. Applicator personnel additional exposures which exceeded the levels of concern

Pesticide

Active Ingredient/Class

Scenarios

Sprayed liquids

Chlorpyrifos (OP)

High

Diazinon (OP)

Medium, High

Malathion (OP)

High

Sprayed powders

Bendiocarb (C)

Low, Medium, High

Fogs

Chlorpyrifos (OP)

High

Malathion (OP)

High

Delousing

Lindane (OC)

High*

OP = organophosphate.
C = carbamate.
OC = Organochlorine.
*Lindane use also may increase the risk of cancer.

D.  Possible Cumulative Effects

The HRA addresses some of the effects of being exposed to more than one pesticide at a time, which is certainly relevant for some individuals. The focus is on combinations of organophosphates and the carbamate bendiocarb, since they act on the nervous system in the same way. Investigators conducted the analysis by combining results from the medium-exposure scenarios as these are the most reliable, and pertain to potentially the largest numbers of personnel. While we could have combined the results from high-exposure scenarios, this would produce an extremely unlikely result, due to the compounding of conservatism associated with each pesticide active ingredient.

For the general military population, investigators assumed exposure to fly baits, resin strips, chlorpyrifos fog, and either propoxur EC or bendiocarb WP, depending on branch of service. Additional effects from DEET, permethrin, and d-phenothrin would be negligible under the analysis as conducted. The cumulative results for the general military population were above the level of concern for the Army, Navy, Marines, and Air Force.

For pesticide applicators, investigators assumed exposure to chlorpyrifos liquid used for fogging, fly bait, and either diazinon EC or bendiocarb WP, depending on branch of service. Investigators also added in results for the general military population. Additional effects from DEET, permethrin, d-phenothrin, and lindane would also be negligible under the analysis as conducted. The cumulative results for applicators were above the level of concern for the Army, Navy, Marines, and Air Force. The results for applicators were also higher than the levels estimated for the general military population, which is not surprising since applicators were assumed to have the same exposures as the general military population plus additional exposures while performing their assigned tasks of pesticide application.

 

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