I.  Products Used for Fogging

The term "fogging" as used here covers two distinct types: ultra low volume (ULV) application, and high volume (HV) application. Fogging was conducted throughout some camps mainly to control flying insects such as filth flies, sand flies, and mosquitoes. US servicemembers appear to have employed ULV application to a much greater extent than HV application, although both methods are discussed briefly below. However, investigators evaluated only ULV application in detail because there were few reports of HV application, none of which came from the survey or PM interviews.

ULV application disperses much less pesticide active ingredient than HV application. Armed Forces technical guidance[320] describes the ULV insecticide application process. The undiluted ULV insecticide formulation is dispersed from the truck sprayer as fine droplets (less than 50 microns diameter) mixed with air. The material discharged is a fine mist that does not obscure visibility. The truck travels at 5-10 miles per hour while dispensing the insecticide in a 300-foot-wide swath. The droplets must be generally in the 5-25 micron size range to be effective. Less than 10% of the droplets should be smaller than 5 microns (small droplets do not impinge on the insects and are not effective). ULV application may have also been made by backpack-mounted and/or hand-held equipment. ULVs were used predominantly outdoors (Table 13).

HV fogging disperses more pesticide active ingredient. Additionally, HV equipment requires the use of "inert" carrier substances. For example, the pesticide active ingredient (e.g., malathion) may be diluted with diesel fuel or other petroleum-based solvent prior to discharge. Thermal fog applicators discharge pesticide product in a smoke.[321] The fog generated during HV application obscures visibility. Common dispersal equipment includes truck-mounted fog generators.

1.  Application Scenarios

a.  Common Elements

Table 78 presents the common assumptions for ULV fog application. 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.

Table 78. ULV fogging, common assumptions for application

Factor Units Definition/Explanation

Assumptions by Level

Source/Rationale

Low

Medium

High

UE

mg/lb a.i.

Unit dermal exposure

0.023

0.023

2.9

1998 PHED Guide: Aerosol[322]
UIE

mg/lb a.i.

Unit inhalation exposure

0.00012

0.00012

0.0012

1998 PHED Guide: Aerosol[323]

The PPE considerations and rationale are essentially the same as for ECs.

The percentile values listed for servicemembers wearing PPE on Table 13 cannot be taken at face value. For ULV fogs, the percentile values presented would seem to indicate that 75-100% of servicemembers wore "adequate" PPE; however, much uncertainty surrounds these values: 1) adequate PPE was not defined in the interviews; 2) 22-39% of servicemembers who cited ULV fogs did not answer the question on PPE; and 3) the data do not reflect qualitative statements provided by interviewees indicating that some applicators had little or no PPE.

One of the important pesticide active ingredient-specific assumptions needed to calculate dose is the amount of active ingredient handled daily (WA). In order to calculate WA, it is first necessary to estimate the area treated per hour (AH), as follows:

AH = (VT x SW x CF1)/CF2 = 273 ac/h

spacer

where,

spacer

VT

= velocity of truck = 7.5 mi/h

SW

= width of fog swath = 300 ft

CF1

= unit correction factor 1 = 5,280 ft/mi

CF2

= unit correction factor 2 = 43,560 ft2/ac

For the ULV fogging exposure assessment, AH is rounded to 275 ac/h. Then the area treated per day (AD) = AH x exposure time. All other equations used in dose calculations are provided in the associated tables in the following subsections.

b.  Chlorpyrifos, 19% Liquid (ULV)

Eleven percent of the PM exposure interviews cited use of chlorpyrifos, 19% liquid (ULV) (Table 13). Table 79 presents the formulation-specific assumptions used for the application exposure assessment of chlorpyrifos ULV.

Table 79. Chlorpyrifos ULV assumptions for applicationa

Factor Units Definition/Explanation

Assumptions by Level

Source/Rationale

Low

Medium

High

AD

ac/d

Area treated per day

275

550

1,100

ET x 275 ac/h (see text)
AR

fl oz/ac

Application rate of formulation

1.6

1.6

1.6

TIM 24[324]
V

gal/d

Volume handled daily

3.44

6.88

13.8

A x 0.0125 gal/ac
CS

lb a.i. /gal

Concentration of a.i. in formulation

1.5

1.5

1.5

Product label[325]
WA

lb a.i./d

Weight of a.i. handled daily

5.2

10.3

21

V x CS
ABS

--

Dermal absorption factor

0.03

0.03

0.03

ATSDR[326]
ET

h/d

Exposure time

1

2

4

PM interviews (Table 13)
EF

d/mo

Exposure frequency

1

8

21

PM interviews (Table 13)
ED

mo

Exposure duration

1

4

8

PM interviews (Table 13)
a) A dash ("--") indicates inconsequential exposure, or that the item is otherwise not applicable.

c.  Malathion, 91% Liquid (ULV)

Thirteen percent of the PM exposure interviews cited use of malathion, 91% liquid (ULV) (Table 13). Table 80 presents the formulation-specific assumptions used for the application exposure assessment of malathion ULV.

Table 80. Malathion ULV assumptions for applicationa

Factor Units Definition/Explanation

Assumptions by Level

Source/Rationale

Low

Medium

High

AD

ac/d

Area treated per day

275

825

1,925

ET x 275 ac/h (see text)
AR

fl oz/ac

Application rate of formulation

8

8

8

TIM 24[327]
V

gal/d

Volume handled daily

17

52

120

A x 0.0625 gal/ac
CS

lb a.i. /gal

Concentration of a.i. in formulation

9.33

9.33

9.33

Product label[328]
WA

lb a.i./d

Weight of a.i. handled daily

159

485

1,120

V x CS
ABS

--

Dermal absorption factor

0.1

0.1

0.1

EPA[329]
ET

h/d

Exposure time

1

3

7

PM interviews (Table 13)
EF

d/mo

Exposure frequency

1

10

30

PM interviews (Table 13)
ED

mo

Exposure duration

1

5

8

PM interviews (Table 13)
a) A dash ("--") indicates inconsequential exposure, or that the item is otherwise not applicable.

d.  ULV Doses — Application

Table 81 presents doses potentially resulting from exposure during application of ULV fogs. There are three types of doses presented for the evaluation of noncarcinogenic effects: PDRD, ADD, and PDRI. Toxicity values were not available for the assessment of the potential carcinogenic effects of chlorpyrifos and malathion (see Section B.4,  Toxicity Assessment), so investigators did not calculate LADDs.

Table 81. ULVs, dose rates – application, for evaluation of noncarcinogenic effectsa

Formulation

Exposure
Group

Exposure
Point

ABS

PDRD
(mg/kg/d)

ADD
(mg/kg/d)

PDRI
(mg/kg/d)

Chlorpyrifos,
19% liquid (ULV)
Low

Outdoor

0.03

1.71E-03

5.13E-05

8.91E-06

Medium

Outdoor

0.03

3.38E-03

1.02E-04

1.77E-05

High

Outdoor

0.03

8.70E-01

2.61E-02

3.60E-04

Malathion,
91% liquid (ULV)
Low

Outdoor

0.1

5.22E-02

5.22E-03

2.73E-04

Medium

Outdoor

0.1

1.59E-01

1.59E-02

8.31E-04

High

Outdoor

0.1

4.64E+01

4.64E+00

1.92E-02

Malathion,
91% liquid (ULV)
Formulasb:
(1) PDRD = (UE x WA)/BW
(2) ADD = PDRD x ABS
(3) PDRI = (UIE x WA)/BW
a) ABS = dermal absorption factor.
PDRD = potential dose rate for dermal contact.
ADD = absorbed dermal dose.
PDRI = potential dose rate for inhalation.
UE = unit dermal exposure.
WA = weight of a.i. handled.
BW = body weight.
UIE = unit inhalation exposure.
b) Formulas 1 and 3 adapted from EPA, 1997.[330]

2.  Post-Application Scenarios

a.  Common Elements

The post-application exposure scenarios address servicemembers who were exposed to ULV mist downwind of spraying operations for 30 min. The only consequential exposure route was inhalation. While it is possible limited post-application dermal contact occurred, investigators presumed this to have been inconsequential. There would have been few outdoor surfaces conducive to frequent and/or prolonged and/or extensive dermal contact (i.e., small skin surface area exposed); primarily, there would have been little high vegetation that servicemembers would have been frequently rubbing against. Some mist undoubtedly drifted indoors, and there was undoubtedly some dermal contact, but with ULV fog application the surface concentrations should have been very low.

Two reports, from non-applicators, will serve to illustrate pesticide product fogging operations during the Gulf War in a way which is relevant for post-application exposure assessment. Although the reports appear to address HV fogging, some of the information is useful in the assessment of post-application ULV fog exposure. The first report describes fogging with malathion at an Air Force base in Saudi Arabia with over 5,000 servicemembers.[331] According to the report, the entire camp was fogged with a mixture of malathion in diesel fuel at least twice a week from March 1991 through early July 1991 to control flies. The trucks drove along all the streets of the base between the rows of tents. Prior to fogging, the troops were warned via a public address system to stay away, although the announcements were not necessarily always audible to everyone, and some servicemembers may have ignored the announcements. The second report (also Air Force) describes the fogging of a base in the United Arab Emirates.[332] The report states that the base was fogged by truck twice a day every day for 6 months. During the fogging operations the entire camp was reported to be completely engulfed in mist. The latter contact did not know what pesticide product was used, and did not know whether the fogging was done by US servicemembers or local contractors.

Based on the two reports described above, and the PM exposure interviews (Table 13), investigators selected exposure frequencies (EFs) of 1, 4, and 16 days per month for low, medium, and high exposure for evaluation of ULV fogs. Some of the PM interviews indicated that fogging occurred but was rare. Investigators consider the second report above, indicating an EF of 60 times per month as unique and unrepresentative of the majority of ULV fog exposures. It is noteworthy that the reported exposure durations (EDs) of 5-6 months from the two non-applicator reports are close to the average values for ULV fogs from the PM interviews. It is also noteworthy that the two non-applicator reports describe a readily visible fog, and presumably servicemembers would be more likely to see this, and move to an upwind location. In the case of a ULV mist, it is less likely that servicemembers would be aware of its presence if they did not observe the applicator's truck or missed instructions to change location.

b.  Chlorpyrifos, 19% Liquid (ULV)

Table 82 presents the formulation-specific assumptions used for the post-application exposure assessment of chlorpyrifos, 19% liquid (ULV).

Table 82. Chlorpyrifos ULV Assumptions for post application

Factor Units Definition/Explanation

Assumptions by Level

Source/Rationale

Low

Medium

High

CA

mg/m3

Concentration of a.i. in air

0.009

0.009

0.0183

Air modeling; 30-minute averages
ET

h/d

Exposure time

0.5

0.5

0.5

Air modeling[333]
EF

d/mo

Exposure frequency for inhalation.

1

4

16

See text
ED

mo

Exposure duration

1

4

8

PM interviews (Table 13)[334]

c.  Malathion, 91% Liquid (ULV)

Table 83 presents the formulation-specific assumptions used for the post-application exposure assessment of malathion, 91% liquid (ULV).

Table 83. Malathion ULV assumptions for post application

Factor Units Definition/Explanation

Assumptions by Level

Source/Rationale

Low

Medium

High

CA

mg/m3

Concentration of a.i. in air

0.287

0.287

0.5817

Air modeling; 30-minute averages
ET

h/d

Exposure time

0.5

0.5

0.5

Air modeling[335]
EF

d/mo

Exposure frequency for inhalation.

1

4

16

See text
ED

mo

Exposure duration

1

5

8

PM interviews (Table 13)[336]

d.  Air Modeling for ULVs

For the purpose of air modeling, investigators assumed that a 400,000-square-meter (99-acre) area is treated with the insecticide formulation sprayed as an aerosol or mist from a ULV fogging truck. The treated area is assumed to be rectangular (1,000 meters long x 400 meters wide). The truck traverses the area, gradually applying the formulation in four, sequential, 100-meter wide swaths until the entire area is treated. The direction of source movement alternates oppositely for each swath (e.g., north, south, north, south). The entire application takes 30 minutes (450 seconds per swath).

Two different formulations were applied. One formulation was 19% chlorpyrifos, consistent with the label for a representative chlorpyrifos ULV concentrate.[337] Investigators assumed chlorpyrifos to be applied at the rate recommended in Armed Forces technical guidance[338] for a similar 25% chlorpyrifos ULV formulation (1.6 ounces per acre). The other formulation was 91% malathion, consistent with the material safety data sheet (MSDS) for a representative malathion ULV concentrate[339] and Armed Forces technical guidance.

Exposure to insecticides applied via ULV fogging is a potential concern for individuals downwind of the application area. To estimate air concentrations downwind of the application area, investigators made the following assumptions:

Investigators estimated the ambient air concentrations resulting from these scenarios using the EPA INPUFF dispersion model (Version 2.5).

e.  General Model Description

Investigators conducted the modeling of ULV fogging impacts downwind of the treatment area using the EPA's INPUFF model. INPUFF is a Gaussian integrated puff model that was designed to simulate dispersion from semi-instantaneous or continuous point sources. Source emissions are treated as a series of individual puffs. Wind direction, speed, and atmospheric stability class are assumed to be constant during each time step, and the Gaussian puff diffusion equation is used to calculate the contribution to the concentration at each receptor from each puff for every time step.

EPA developed the INPUFF model in response to requests for modeling impacts downwind of moving incineration ships. Investigators selected INPUFF for use for estimating impacts downwind of a ULV fogging truck since it was the only available model that captured the intrinsic nature of the source term (i.e., a moving point source). For this analysis, the ULV fogging truck was simulated as a moving point source within a spatially constant wind field.

Other models investigators considered were less appropriate. Although investigators conducted some initial analysis using the EPA SCREEN model, the representation of the source in SCREEN as a continuous area source did not conform as well to the scenario under consideration. In addition, SCREEN is a Gaussian plume model (rather than a puff model) that assumes a release at a constant rate for a period of an hour and was not able to account directly for the more limited duration (30 minutes) of the spraying and subsequent exposure. Other puff models, such as CalPUFF, are designed for mesoscale analyses and do not incorporate the capability of simulating moving sources. Models such as CalPUFF are more appropriate for analyzing the long-range transport of pollutants rather than for the more limited microscale analysis for the ULV fog application.

The INPUFF model is documented in its computer code (available from EPA) and, in part, in a user’s guide[340] for an earlier version of the model.

f.  Model Application

Each of the four swaths was represented by a moving point source that emits the insecticide formulation only during the 450-second interval representing the coverage of the particular swath. Each source started at one end of a swath and traveled towards the other end of the swath at a rate of 2.222 m/s (5 miles per hour).

Investigators assigned each point source an emission height of 1 m. Investigators also assigned nominally small parameter values for stack gas temperature, stack diameter, stack gas velocity, and stack gas volume flow rate in order to minimize any modeled plume rise. In essence, the model treats the release as inert and nonbuoyant. Investigators set deposition and settling velocities both to zero, so that the model neglected any depletion of the airborne portion of plume material.

Investigators assigned initial horizontal and vertical dispersion parameters for the point sources based on the user’s guide for sources located near the ground. Investigators defined the initial horizontal dispersion parameter by dividing the initial horizontal scale (100 meters) by 4.3, and defined the initial vertical dispersion parameter by dividing the initial vertical scale (1 meter) by 2.15. Investigators set the source update parameter so that a new puff was emitted each second.

Investigators defined the modeling domain as a sufficiently large area to ensure that the model would continue tracking emitted puffs over the area in which source impacts were of interest.

An emission rate was calculated for and assigned to each source for the period when the particular swath was being treated. The calculated emission rate was consistent with the recommended insecticide application rate and the assumption that 10% of the applied material remained airborne. Table 84 presents the emission rate calculated.

The assumption that 10% of the applied material remains airborne is based on the droplet size description provided in military guidance,[341] as follows:

Thus, investigators assumed that a maximum of 10% of all ULV droplets would be less than 5 microns in diameter. We estimated the deposition (settling) rates of malathion ULV droplets of various sizes under the modeled conditions (400 m x 1,000 m application area, 1 m release height, 1 m/s wind speed). This analysis indicated that the 5 micron droplets would tend to remain airborne downwind of the application area, but the larger droplets would tend to deposit. Based on these results, 10% of the ULV aerosol released was estimated to remain airborne downwind of the application area (similar to the total maximum acceptable mass of 5 micron droplets).

The actual model runs used a unit emission rate of 1.0 g/s. The investigators scaled model estimates in the output files scaled to account for the emission rates for chlorpyrifos (0.046 g/s) and malathion (1.46 g/s), respectively. This approach is valid since the estimated concentration is directly proportional to the emission rate.

Table 84. Calculation of emission rate of ULV fogs for air modelinga

Parameter

Units

Chlorpyrifos, 19% Liquid

Malathion, 91% Liquid

AR

oz/ac

1.6

8

A

ac

99

99

r

g/cm3

0.93

1.23

Cai

dimensionless

0.19

0.91

Fe

dimensionless

0.10

0.10

k

cm3/oz

29.57

29.57

t

sec

1800

1800

Effective emission rate of a.i.

g/sec

0.046

1.46

a) Emission rate (g/s) = (AR)(A)(r )(Cai)(Fe)(k)/t
where,where,
AR = volumetric application rate (ounces/acre).
A = surface area treated (acres).
r = density (g/cm3).
Cai = concentration of active ingredient in applied formulation (fraction).
Fe = fraction of applied formulation remaining airborne (fraction).
k = units conversion factor (cm3/ounce).
t = duration of application (seconds).

The modeling considered a range of standard screening meteorological conditions. Table 85 presents the combinations of stability class and wind speed for each as analyzed in a separate model execution. These combinations fully span the range of conditions that would yield maximum concentrations near the surface. Higher wind speeds would only yield lower concentrations due to the increased dilution effect of the wind. Wind speeds lower than about 1 m/s are considered to be calm and are not appropriate for Gaussian models.

Table 85. ULVs, meteorological parameters for air modeling

Stability Class

10-meter level wind speeds (m/s)

A

1, 3, 5

B

1, 3, 5

C

1, 3, 5

D-day

1, 3, 5

D-night

1, 3, 5

E

1, 3, 5

F

1, 3

Investigators set the anemometer height to a standard 10-meter level for screening purposes. Given the low level of the release and the definition of source release parameters to minimize any estimate of plume rise, the effect of mixing height on estimates will be negligible.

Investigators modeled two wind directions: one parallel to the long axis of the treatment area and one parallel to the short axis of the treatment area.

Investigators placed model receptors downwind of the treatment area. The closest model receptors were located 10 meters beyond the downwind edge of the last swath. Receptors were also placed at various lateral positions beyond the downwind edge of the last swath.

Investigators assigned a receptor height of 1.25 meters above ground level to represent a typical breathing zone height.

Investigators ran the model for a total duration of 1-hour beginning at the onset of insecticide application and ending 30 minutes after the application was completed. For each modeled meteorological condition, the model provided concentrations at each model receptor for each of two 30-minute averaging periods as well as 1-hour concentrations for the entire period of modeling. For most wind speeds and receptors, most of the insecticide exposure was estimated to occur during the first 30-minute averaging period. However, for the lowest modeled wind speeds, comparable exposure was estimated to occur during the second 30-minute period at more distant receptors.

The model estimated maximum concentrations for light wind (1 m/sec), stable (class F) conditions. These are the conditions that typically yield maximum estimated concentrations for ground-level or low level releases without appreciable plume rise.

For the scenario in which winds were perpendicular to the direction of insecticide application (Condition A), the model estimated maximum concentrations at the nearest receptors (i.e., those located 10 meters beyond the downwind edge of the application area) and varied laterally. The maximum 1-hour average concentration estimated for the modeled unit emission rate was 98.3 m g/m3, and the maximum 30-minute average concentration was approximately 196.6 m g/m3. After adjusting for emission rates, this corresponds to maximum average 30-minute concentrations of 9.0 m g/m3 for chlorpyrifos and 287.0 m g/m3 for malathion.

For the scenario in which winds were parallel to the direction of insecticide application (Condition B), the model again estimated maximum concentrations to occur at the nearest receptors (i.e., those located 10 meters beyond the downwind edge of the application area) and varied laterally. The maximum 1-hour average concentration estimated for the modeled unit emission rate was 199.2 m g/m3, and the maximum 30-minute average concentration would be no greater than 398.4 m g/m3 (assuming that the entire 1-hour exposure occurred within a 30-minute period). After adjusting for emission rates, this corresponds to maximum average 30-minute concentrations of 18.3 m g/m3 for chlorpyrifos and 581.7 m g/m3 for malathion.

INPUFF model output files for the maximum estimated impact conditions (F stability with 1 m/second winds) were generated. These conditions would generally be expected to only occur in the period after sunset until shortly after sunrise. Solar heating of the surface and the lower atmosphere would lead to more unstable atmospheric conditions and lower estimated concentrations.

Investigators assumed all chlorpyrifos and malathion that remains airborne to have existed in the vapor phase (or as fine droplets which behave similarly) during exposure. Therefore, separate particulate modeling was not conducted.

g.  ULV Doses — Post Application

Table 86 presents doses potentially resulting from the post-application inhalation exposure to ULV fogs, for evaluation of noncarcinogenic effects. Toxicity values were not available for the assessment of the potential carcinogenic effects of chlorpyrifos and malathion (see Section B.4,  Toxicity Assessment), so investigators did not calculate LADDs.

Table 86. ULV fogs, dose rates – post application, for evaluation of noncarcinogenic effectsa

Formulation

Exposure
Group

Exposure
Point

ABS

PDRD
(mg/kg/d)

ADD
(mg/kg/d)

PDRI
(mg/kg/d)

Chlorpyrifos,
19% liquid (ULV)
Low

Outdoor

0.03

--

--

1.03E-04

Medium

Outdoor

0.03

--

--

1.03E-04

High

Outdoor

0.03

--

--

2.09E-04

Malathion,
91% liquid (ULV)
Low

Outdoor

0.1

--

--

3.28E-03

Medium

Outdoor

0.1

--

--

3.28E-03

High

Outdoor

0.1

--

--

6.65E-03

Malathion,
91% liquid (ULV)
Formulab:
PDRI = (CA x IRA x ET)/BW
a) ABS = dermal absorption factor.
PDRD = potential dose rate for dermal contact
ADD = absorbed dermal dose
PDRI = potential dose rate for inhalation
A dash ("--") indicates that the item is not applicable.
BW = body weight.
CA = a.i. concentration in air from modeling
IRA = inhalation rate.
ET = exposure time


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