1.  Application Scenarios

a.  Common Elements

Servicemembers applied the four emulsifiable concentrates to control pests such as: flies, mosquitoes, ticks, and/or fleas. They applied different ECs for different pests. Investigators evaluated application by low-pressure 2-gallon handwand sprayer and by backpack sprayer, as applicators used both methods. Application took place both outdoors and indoors. Outdoor applications were broadcast treatments typically made to the near-ground portions of buildings and tents, as well as to garbage containers, animal carcasses, and other places where the target pests congregated. Indoor applications would normally have been crack and crevice type treatments of locations such as mess and latrine facilities. In the course of such treatments the applicator directs a stream or cone of spray at cracks and crevices, such as commonly occur where a wall meets a floor. Investigators assumed applicators treated surfaces adjacent to the cracks, and that overspray could have been substantial. Additionally, building size, condition, and configuration impacted the relative fraction of surface area treated. Investigators assumed that applicators treated a much greater fraction of surface area in a small latrine as opposed to a large rectangular mess hall. For this assessment, rigid structures serve as the models. Applicators probably treated some tent interiors, but investigators did not specifically address these treatments, as they have no reason to believe that the exposures would be any higher. EC use by service is presented in Section A.4,  Pesticide Use and Exposure.

Investigators employed the following clothing scenarios based on review of military guidance and the PM exposure interviews:

• Low and medium exposure: long pants, long-sleeve shirt, gloves, half-face respirator with organic vapor cartridges and pesticide prefilters (respiratory protection factor = 90%).^[228]

• High exposure: long pants, long-sleeve shirt ("single layer, no gloves" from the PHED Guide).

The low- and medium-exposure levels represent normal and proper use of ECs, while the high-exposure level includes limited misuse (e.g., inadequate PPE).

As implied previously, one cannot take the percentile values listed for servicemembers wearing PPE on Table 13 at face value. For ECs, the percentile values presented would seem to indicate that 73-100% of servicemembers wore "adequate" PPE; however, much uncertainty surrounds these values: 1) adequate PPE was not defined in the interviews; 2) there is a low response rate for ECs (no higher than 64%); and 3) the data do not reflect the many qualitative statements provided by interviewees indicating that some applicators had little or no PPE.

Table 55 presents the common assumptions for application of ECs. The unit exposure values presented are from the PHED Guide. All values used to calculate the doses to applicators are presented in the following subsections. The equations used to calculate two of the values presented are as follows (refer to the following subsections for details):

where,

VF = volume of formulation used daily^[229]
VS = volume of spray prepared daily
FC = finished concentration
WD = density of water
CS = concentration of active ingredient in formulation

W_A = CS x VF

where, WA = weight of active ingredient handled daily

All other equations used in dose calculations are provided in the associated tables in the following subsections.

b.  Chlorpyrifos, 45% Liquid (EC)

Twenty-five percent of the PM exposure interviews cited use of chlorpyrifos, 45% liquid (EC) (Table 13). Note that "chlorpyrifos, 45% liquid (EC)" as used throughout this health risk assessment means the 42% and/or 45% formulations; the difference being negligible in this assessment. Chlorpyrifos EC was used to control filth flies, sand flies, and mosquitoes, predominantly outdoors. Chlorpyrifos EC reportedly had some use indoors (cited by 8% of PM exposure interviews), in structures such as mess and latrines. TIM 24 lists both indoor and outdoor uses for chlorpyrifos EC, although it specifies outdoor use only for biting flies.^[235] Table 56 presents the formulation-specific assumptions used for the application exposure assessment of chlorpyrifos EC.

c.  Diazinon, 48% Liquid (EC)

Fifteen percent of the PM exposure interviews cited use of diazinon, 48% liquid (EC) (Table 13). Diazinon EC was used to control ticks and fleas, predominantly outdoors. Diazinon EC reportedly had some use indoors (cited by 13% of PM exposure interviews), in structures such as mess and latrines. TIM 24 lists both indoor and outdoor uses for diazinon EC.^[241] Table 57 presents the formulation-specific assumptions used for the application exposure assessment of diazinon EC.

Table 57. Diazinon, 48% liquid (EC) assumptions for application^a

d.  Malathion, 57% Liquid (EC)

Seventeen percent of the PM exposure interviews cited use of malathion, 57% liquid EC (Table 13). Malathion EC was used to control filth flies, sand flies, mosquitoes, and ticks, predominantly outdoors. Malathion EC was reportedly used indoors as well (cited by 17% of PM exposure interviews), in structures such as mess and latrines. TIM 24 lists outdoor uses, but no relevant indoor uses, for malathion EC.^[247] The label does mention use inside homes.^[248] Thus, while indoor use of malathion may not have constituted misuse, it was not encouraged by military guidance. Table 58 presents the formulation-specific assumptions used for the application exposure assessment of malathion EC.

Table 58. Malathion, 57% liquid (EC) assumptions for application^a

e.  Propoxur, 14.7% Liquid (EC)

Six percent of the PM exposure interviews cited use of propoxur, 14.7% liquid EC (Table 13). Propoxur EC was used to control filth flies, sand flies, mosquitoes, and fleas, predominantly outdoors. Propoxur EC reportedly had a substantial level of use indoors as well (cited by 36% of PM exposure interviews), in structures such as mess and latrines. TIM 24 does not list propoxur EC; but it does list both indoor and outdoor uses for a propoxur, 70% solid (WP) and a 1% oil solution.^[254] The 14.7% EC formulation (Baygon^�) was ordered from the Defense Logistic Agency by units deploying to the KTO, and was reported by eleven Navy PM interviewees and three Army EAC interviewees. Table 59 presents the formulation-specific assumptions used for the application exposure assessment of propoxur, 14.7% liquid (EC).

Table 59. Propoxur, 14.7% liquid (EC) assumptions for application^a

f.  EC Doses — Application

Table 60 presents doses potentially resulting from exposure during application of ECs. There are three types of doses presented for each of two cases; all for the evaluation of noncarcinogenic effects: PDR_D, AD_D, and PDR_I. The two cases are when a handwand sprayer was used and when a backpack sprayer was used. Doses for the two cases differ somewhat for dermal exposure, but are identical for inhalation exposure because the respective UIE values listed in the PHED Guide are identical.

Table 60. ECs, dose rates – application, for evaluation of noncarcinogenic effects^a

Table 61 presents the application doses for the evaluation of carcinogenic effects for propoxur EC. Carcinogenic activity for chlorpyrifos EC, diazinon EC, and malathion EC is unlikely or unquantifiable (see Section B.4,  Toxicity Assessment). Table 61 presents two types of doses: LADD_D and LADD_I. Once again, the dermal doses calculated for the handwand sprayer differ from those calculated for the backpack sprayer, while the inhalation doses are identical.

Table 61. ECs, lifetime average daily doses – application, for evaluation of carcinogenic effects

2.  Post-Application Scenarios

a.  Common Elements

The post-application scenarios below address servicemembers who were exposed to ECs on surfaces inside mess and latrine facilities. In mess facilities, inhalation was the only consequential exposure route, while in latrines, both dermal and inhalation exposure were consequential. Air modeling for the post-application exposure to ECs is presented below. Investigators presume that opportunities for dermal contact in the mess were minimal, given that the only treated surfaces were normally limited to the intersections of walls and floors. The assumptions associated with the model mess and latrine structures are as follows:

• Model mess. The surface area treated was 608 ft². The interior dimensions were 50 ft long x 35 ft wide x 8 ft high. Crack and crevice application covered 25% of the floor surface, and the wall surface 1 ft above the floor. The interior breathing-space volume was 14,000 ft³.

• Model latrine. This was a "three-holer" latrine. The surface area treated was 78 ft². The interior dimensions were 7 ft long x 6 ft wide x 7 ft high. The dimensions of the sitting box were 7 ft long x 2 ft wide x 2 ft high. Application resulted in 100% coverage of the floor, sitting box, and 1 ft up the walls. The interior breathing-space volume was 266 ft³.

Investigators estimated potential dermal post-application exposure to pesticide active ingredient residues on hard surfaces using a method provided by EPA.^[262] In the method, the amounts of residues transferred to hands, legs, and feet are calculated, being representative of areas that may have contacted treated surfaces in latrines. The actual parts exposed probably varied substantially. If servicemembers wore shoes, then feet were not exposed; however, the buttocks may have been exposed. At some camps, applicators may have treated shower areas, in which case feet might have been exposed. The assumptions provided by EPA used for both ECs and the wettable powder (WP; bendiocarb) are presented in Table 62.

Based on the PM exposure interviews, investigators presumed outdoor exposure was inconsequential and so did not estimate it. Applicators sprayed ECs outdoors around building and tent foundations, and around garbage containers. This would have provided little or no opportunity for post-application exposure.

b.  Chlorpyrifos, 45% Liquid (EC)

Table 63 presents the formulation-specific assumptions investigators used for the post-application exposure assessment of chlorpyrifos, 45% liquid (EC). The table presents values for the high-exposure level only, since this level is associated with indoor exposure.

Table 63. Chlorpyrifos, 45% liquid (EC) assumptions for post application^a

c.  Diazinon, 48% Liquid (EC)

Table 64 presents the formulation-specific assumptions investigators used for the post-application exposure assessment of diazinon, 48% liquid (EC). The table presents values for the high exposure level only, since this level is associated with indoor exposure.

Table 64. Diazinon, 48% liquid (EC) assumptions for post application^a

d.  Malathion, 57% Liquid (EC)

Table 65 presents the formulation-specific assumptions investigators used for the post-application exposure assessment of malathion, 57% liquid (EC). The table presents values for the high exposure level only, since this level is associated with indoor exposure.

e.  Propoxur, 14.7% Liquid (EC)

Table 66 presents the formulation-specific assumptions investigators used for the post-application exposure assessment of propoxur, 14.7% liquid (EC). The table presents values for both the medium- and high-exposure levels, since both are associated with indoor exposure,

Table 66. Propoxur, 14.7% liquid (EC) assumptions for post application^a

f.  Air Modeling for ECs

Investigators conducted indoor air modeling to estimate indoor concentrations of emulsifiable concentrates that might occur as a result of crack and crevice treatment. Investigators estimated post-application air equilibrium concentrations for a model mess building and a model latrine. A description of the model mess and latrine is provided in Section B.3.G.2.a,  Common Elements, above.

Investigators calculated long-term average emission rates for pesticide active ingredients offgassing from treated surfaces using an empirical relationship for evaporation time based on the vapor pressure and molecular weight of the active ingredient by the method of Chinn, as recommended by EPA.^[289] This relationship is based on the evaporation of pure substances under artificial conditions and may overestimate the emissions from substances in mixtures.

In this approach, investigators first calculated the Chinn evaporation time using the following formula:

t_e = 145/[(mw)(vp)]^0.9546

where,

t_e = Chinn evaporation time (h)
mw = molecular weight of pesticide active ingredient (unitless)
vp = vapor pressure of pesticide active ingredient (mm Hg)

Next, investigators calculated a long-term emission rate using the following formula:

E = mass/t_e

where,

E = emission rate (mg/h)
mass = mass of active ingredient (mg)

Investigators calculated the mass of active ingredient for each scenario by multiplying the application rate (mass per area) by the application area. Investigators assumed the resulting constant emission rate to apply for the duration of the calculated evaporation time. In effect, investigators calculated concentrations for a single event.

The possible cumulative effects on airborne concentrations due to repeated applications on emission rate are not included in the calculation of concentrations. Investigators assumed that repeated applications to the same treatment area will largely restore or maintain the long-term average emission rate.

Investigators calculated indoor concentrations using a standard box model approach. One can develop the box model equation from the same mass balance considerations as described for permethrin, and employ the following differential equation:

V(dCA_in/dt) = E + CA_outIV – CA_inIV - K(CA_in)V

where,

CA_in = final indoor concentration (mg/m³)
CA_out = ambient (outdoor) concentration (mg/m³)
E = emission rate (mg/h)
I = air changes per hour in room
V = room volume (m³)
t = time (h)
K = decay rate (h^-1)

This equation has the following general solution:

CA_in = [1/(I+K)][(E/V) + (CA_out)(I)][1 – exp{-(I+K)(t)}] + CA₀ exp{-(I+K)(t)}

where,

CA₀ = initial concentration in room (mg/m³)

Investigators assumed: 1) the active ingredients to be nonreactive (K = 0), and 2) contributions from outdoors to be negligible (CA_out = 0); the rationale is provided under permethrin.

With these assumptions, the equation for concentration within the room simplifies to:

CA_in = [E/(I)(V)][1 – exp{-(I)(t)}] + CA₀ exp{-(I)(t)}

For an initial concentration of zero (CA₀ = 0), this equation for concentration at time t simplifies to the following expressions:

CA_in = [E/(I)(V)][1 – exp{-(I)(t)}]

This equation yields estimated concentrations that asymptotically approach an equilibrium concentration given by:

CA = E/[(I)(V)]

The time in hours (t_f) required to reach a given fraction (f) of the equilibrium concentration is:

t_f = -[ln(1-f)]/I

Although EPA recommends the use of the MCCEM in conducting high-end exposure assessments, investigators used the simple box model for the same reasons discussed under permethrin. Investigators modeled each structure examined for the application scenarios under consideration here (a mess and latrine) as a single chamber structure.

Investigators assumed ventilation rates of 2 and 4 air changes per hour for the high and medium indoor inhalation exposure scenarios, respectively, where applicable. Investigators believe these rates to be reasonable given reports that strong winds readily penetrated the structures under consideration.

For a ventilation rate of 2 air changes per hour, investigators estimated indoor concentrations to reach 50% of the equilibrium concentration in about 0.35 hours, 90% in 1.15 hours, 95% in 1.5 hours, and 99% in 2.3 hours. For a ventilation rate of 4 air changes per hour, the indoor concentrations are estimated to reach 50% of the equilibrium concentration in 0.17 hours, 90% in 0.58 hours, 95% in 0.75 hours, and 99% in 1.15 hours.

In accordance with draft EPA guidance for conducting residential exposure assessments, investigators also calculated saturation concentrations to ensure that the estimated indoor concentrations do not exceed the associated saturation concentration. Investigators estimated saturation concentrations using the following equation:

CA_sat = (vp/760)(mw)(10⁶)/[(R)(T)]

where,

vp = vapor pressure (mm Hg)
mw = molecular weight (g/mole)
R = 0.0821 liter atmosphere/mole ^oK, the universal gas constant
T = temperature of air (^oK)

Investigators assumed an ambient temperature of 293^o K (20^o C) for the calculation of the saturation concentrations. The sensitivity of saturation concentration to temperature is relatively low over the range of temperatures one would expect inside a mess or latrine, since the saturation concentration is inversely proportional to the absolute temperature.

Calculated air equilibrium concentrations of ECs for the exposure scenarios of interest are summarized in Table 67. More detailed tables documenting the calculation of equilibrium concentrations and saturation concentrations for each EC and exposure scenario appear in Tables 68 through 71. The tables present the saturation concentrations solely to ensure that the estimated equilibrium concentrations do not exceed the corresponding saturation values. The saturation concentrations should not be used to represent ambient levels. In all cases, the estimated equilibrium concentrations are well below the associated saturation values.

As discussed previously, the modeled constant emission rate for each EC is based on a Chinn evaporation calculation recommended by EPA and represents emissions for a single event. Although some increase in the effective emission rate might occur as a result of the cumulative effects from repeated applications, there are no on-site measurements available to quantify this effect. As stated previously, investigators assumed that repeated applications to the same treatment area restore or maintain the long-term calculated emission rates.

Information in the literature about studies involving the four ECs under consideration here show that although ECs may remain active for extended periods of time following indoor application, the measured airborne indoor concentrations generally decrease fairly rapidly with half-life values on the order of several hours to 1.5 days. Therefore, the use of an assumed constant, long-term average emission rate (without the incorporation of any consideration of decay) should, on balance, provide a conservative estimate of equilibrium concentrations.

Average airborne concentrations of chlorpyrifos measured in dormitory rooms receiving spray applications to cracks and crevices were 100, 1100, 1100, 800, and 300 ng/m³ before treatment, immediately after treatment, 1 day after, 2 days after, and 3 days after treatment, respectively.^[290] In another study, airborne concentrations of chlorpyrifos receiving spray or aerosol application to cracks and crevices decreased from 2700 ng/m³ immediately following application to 50 ng/m³ 3 days later.^[291] In a third study, airborne levels of chlorpyrifos following crack and crevice treatment in food preparation areas ranged from 20 - 1488 ng/m³ immediately after spraying to 4 – 361 ng/m³ after 24 hours.^[292]

If chlorpyrifos is released to the air in vapor phase, it will react with photochemically-produced hydroxyl radicals at an estimated half life of approximately 6.34 hours.^[293] Diazinon has an estimated vapor phase half-life in the atmosphere of 4.1 hours due to reactions with photochemically produced hydroxyl radicals.^[294] Malathion has an estimated vapor phase half life in the atmosphere of 1.5 days resulting from hydrogen abstraction by photochemically produced hydroxyl radicals.^[295]

One study measured airborne concentrations after application of propoxur to a dormitory room.^[296] Concentrations decreased from 15.4 m g/m³ following application, to 2.7 m g/m³ after 1 day, to 1.8 m g/m³ after 2 days, and to 0.7 m g/m³ after 3 days. Propoxur is primarily released to the atmosphere in the form of an aerosol during its use as an insecticide and would subsequently be subject to gravitational settling. The resulting vapor phase propoxur will react with photochemically-produced hydroxyl radicals with a half-life of about 4.3 hours.^[297] However, one would expect the half-life at indoor locations to be longer due to the generally lower concentration of hydroxyl radicals.

g.  EC Doses — Post Application

Table 72 presents doses potentially resulting from the post-application exposure to ECs. There are three types of doses presented for the evaluation of noncarcinogenic effects: PDR_D, AD_D, and PDR_I. Table 73 presents the post-application doses for the evaluation of carcinogenic effects for propoxur EC. Carcinogenic activity for chlorpyrifos EC, diazinon EC, and malathion EC is unlikely or not quantifiable (see Section B.4,  Toxicity Assessment). The two types of doses shown are LADD_D and LADD_I.

Table 73. ECs, lifetime average daily doses, post application for evaluation of carcinogenic effects^a

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