### 2



### non

- listed f

reshwater and estuarine/marine invertebrates ( risk quotients or RQ s = 11 and 20,

respectively ) when the aerial ULV spray was modeled at 100 ft flight altitude with 500 ft swath

width under 1 mph wind speed . To further explore these risk concerns, EFED performed a n

additional wind speed analysis for prallethrin typical end

- use product (TEP) application by a

fixed wing aircraft using AGDISP (v8.26)

. The prallethrin percent deposition into a water body

was modeled based on the scenarios of 5 wind speed s (1, 2, 3, 4 and 5 mph)

, 2 flight altitude s (75

and 100 ft) and 2 spray lines ( 1 and 2 swaths ).

Based on the current analysis, it is concluded that prallethrin deposition into a water body can be

minimized by increasing the wind speed and manipulating spray altitude s

. W hen wind speed

reached 5 mph at the flight altitude of 75 ft or ≥ 3 mph at the flight altitude 100 ft , the percent

deposition (or percent application efficacy) under a single 500 ft flight swath (or percent aquatic

deposition) approaches zero (Table 1) with corresponding RQ value ≤ 0.001, a level which is

less than level of concern (LOC = 0.05) for both non

- listed and listed estuarine/marine and

freshwater invertebrates, respectively (Table 2).

However, for two flight swaths over a water body, when the wind speed reaches 5 mph at 100 ft

flight altitude, the percent aquatic deposition is 1.19 (Table 1), which is equivalent to 0.91 ppb in

water with corresponding RQ values 0.62 (>LOC = 0.5) for estuarine/marine and 0.39 (>LOC =

0.05) for freshwater invert ebrates respectively (Table 2). The analysis indicates that multiple

swaths (≥ 2 swaths) over a water body may pose a risk to aquatic invertebrates

. One uncertainty

related to the AGDISP modeling is that the m odel prediction s on multi

- swath deposition have

not been validated.



## A dditional Analysis on the Mosquito Adulticide Deposition

Using AGDISP (v8.26) Model

AGDISP (v8.26) Model ing Method

AGDISP (version 8.26) is a science

- based model that predicts spray drift from application sites.

The model was developed by the USDA Forest Service. AGDISP was designed to optimize

agricultural spraying operations and has detailed algorithms for characterizing th e release,

dispersion, and deposition over and downwind of the application area. This model can be used in

estimating downwind deposition of spray drift from aerial and ground boom applications. In

addition, it can be used in estimating downwind deposition of spray drift from forestry and

adulticide/mosquitocide applications.

The prallethrin percent deposi tion into a water body was simulated by a fixed wing aircraft based

on scenarios of 5 wind speed (1, 2, 3, 4 and 5 mph)

, 2 flight altitude s ( 75 and 100 ft ) and 2 spray lines ( 1 and 2 swaths )

. O ne spray line ( single swath ) wa s assumed to be 500 ft. The methods for

calculation s of surface water estimated environmental concentrations (EECs) and risk quotients

( RQs ) were same as the previous assessment (USEPA 2014, DPs 417461, 417581, 417582)

.

### 3



### Results

Flight Altitude

T he highest percent of

prallethrin deposition in the

a pplication site s are 51 % and

73 % at a 75 ft altitude with 1

mph wind speed for a single

swath and two flight swaths

respective ly

. The percent of

deposition decrease s following an increase of the

spraying altitude ( Fig. 1).

F light altitude above 100ft is

not modeled due to the

limitation s of AGDISP

( v 8.26).

Wind Speed

The percent of prallethrin application efficiency ( deposition ) under spray swath(s) is heavily

influenced by the wind speed a s well as spraying altitude discussed above . The deposition

decrease s as wind speed increase s (Fig .1 and Table 1 )

. The simulation modeling show s that a single swath of the mosqu ito aerial ULV spray under ≤ 2 mph wind speed at 100 ft spray

altitude

, and ≤ 4 mph at 75 ft produces substantial deposition, which results RQ values above the

level of concerns for both listed (LOC = 0.05) and non

- listed species (LOC = 0.5) ( see Table 2

for EECs and RQ calculations ) for aquatic invertebrates

. However, when the wind speed reaches

5 mph at 7 5 ft flight altitude or ≥ 3 mph at 100 ft

, the deposition in the water body approach es

zero for a single flight swath ( Fig 1. a nd Table 2 ) with corresponding RQ values (≤0.001) below

the level of concerns for both liste d (LOC = 0.05) and non

- listed (LOC = 0.5) aquatic

invertebrates (Table 3 ).

Flight Swaths over Water Body

As indicated above, th ere are not risk concerns for a single swath application over the water body

when the wind speed reaches 5 mph at 75 ft flight altitude or ≥ 3 mph at 100 ft. However, the

analysis also indicates that multiple swaths (≥ 2 swaths) over a water body may pose a risk to

aquatic invertebrates. Table 2 shows that 2

- swaths of adulticide application over a water body at
5 mph wind speed and 100 ft flight altitude , the aquatic deposition is reduced to 1.19% with

corresponding RQ values 0.62 (≥ LOC = 0.5) and 0.39 (≥ LOC = 0.05) for estuarine/marine and

freshwater invertebrates (Tab le 3 ). T here is an uncertainty , ho wever, related to multiple swaths

using the AGDISP model to predict adulticide deposition behavior. The m odel prediction h as

not been validated for multi ple swath s

. 0 10 20 30 40 50 60

1 2 3 4 5 % Aquatic Deposition

Wind Speed (mph) 

## % Aquatic Deposition Influenced by

Wind Speed and Spray Altitude

75 ft 100 ft

### 4



### Table 1

. Comparison of Application Efficiency of Fixed Wing Aircraft at Five Wind Speeds

and Two Spray Altitudes with 500 ft Swath Using AGDISP Model (v8.26 )

Swath

width

(ft) No. of

Swath Release

Height (ft) Wind

Speed

(mph) Application

efficiency (%) a 

### Downwind

Deposition (%) b 

### Airborne

Drift (%) c

500 1 75 1 51.33 48.67 0.0

500 1 75 2 24.14 75.86 0.0

500 1 75 3 5.59 82.6 11.87

500 1 75 4 1.14 80.88 17.99

500 1 75 5 0 d 76.12 24.42

500 1 100 1 36.04 63.96 0

500 1 100 2 19.19 80.81 0

500 1 100 3 0 d 81.77 18.66

500 1 100 4 0 d 73.82 28.15

500 1 100 5 0 d 65.21 37.08

500 2 75 1 73.18 26.82 0

500 2 75 2 49.72 50.28 0

500 2 75 3 27.93 62.93 9.14

500 2 75 4 15.57 68.31 16.12

500 2 75 5 9.81 68.25 21.94

500 2 100 1 63.92 36.08 0

500 2 100 2 39.89 60.11 0

500 2 100 3 13.05 71.01 15.94

500 2 100 4 4.18 70.58 25.24

500 2 100 5 1.19 65.15 33.66

a % Application Efficacy

– the percent of prallethrin deposited directly under the 500 ft flight swath or deposited into

the water when an aircraft sprays over a water body. The focus of EFED’s analysis is to reduce the percent of

a quatic deposition (or the % application efficacy), which is used to calculate the aquatic EEC and RQ.

b % Downwind Deposition

– the percent of prallethrin drift downwind and deposited on land. For this assessment,

EFED did not use percent drift deposition in the aquatic RQ calculation. However, this parameter is still considered

because a higher percent downwind deposition may represent a lower percent mosquito control efficacy because of

reduced opportunities to come into contact with flying mosquitoes.

c % Airborne Drift

– the percent of prallethrin fine droplets that stay aloft downwind. A higher percent of airborne

drift ma y indicate a higher amount of prallethrin retained in the air for better control efficacy against flying

mosquitoes.

### 5 d Bolded application scenarios with estimated RQs below the LOC while the spray deposit approaching to zero.



### Table 2 . Estimate Environm ental Concentrations (EECs) and Risk Quotients (RQs) after

Mosquito Adulticide ULV Application a 

### over a Water Body ( Rice Paddy )

No. of

Swath Release

Height (ft) Wind

Speed

(mph) Application

efficiency

(%) Peak EECs b

( μ g/L) RQs Freshwater

Invertebrate

EEC / EC 50 ( EC 50(TEP)

= 2. 3 2 μ g /L) c RQs Estuarine/

marine

Invertebrate

EED / EC 50 ( EC 50( TEP )

= 1.46 μ g /L) d

1 75 1 51.33 39.18 16.89 ** 26.83 **

1 75 2 24.14 18.43 7.94 ** 12.62 **

1 75 3 5.59 4.27 1.84 ** 2.92 **

1 75 4 1.14 0.87 0.38 * 0.60 **

1 75 5 0 ≤ 0.001 ≤ 0.001 ≤ 0.001

1 100 1 36.04 27.51 11.86 ** 18.84 **

1 100 2 19.19 14.65 6.31 ** 10.03 **

1 100 ≥ 3 0 ≤ 0.001 ≤ 0.001 ≤ 0.001

2 75 1 73.18 55.86 24.08 ** 38.26 **

2 75 2 49.72 37.95 16.36 ** 25.99 **

2 75 3 27.93 21.32 9.19 ** 14.60 **

2 75 4 15.57 11.88 5.12 ** 8.14 **

2 75 5 9.81 7.49 3.23 ** 5.13 **

2 100 1 63.92 48.79 21.03 ** 33.42 **

2 100 2 39.89 30.45 13.12 ** 20.85 **

2 100 3 13.05 9.96 4.29 ** 6.82 **

2 100 4 4.18 3.19 1.38 ** 2.19 **

2 100 5 1.19 0.91 0.39 * 0.62 **

a Maximum single application rate at 0.07 lb formulation ( Multicide 2922 ) per acre

b Calculation based on: 0.17 ( t otal lb formulation applied to 1 ha ) x (application efficiency/100 ) x

(453.6*1,000,000) ( gram * 10 ha water pond volume) . For multiple sprays ( ≥ 2 spray lines), only a single ap plication

rate (0.17 lb per ha ) is used to calculate the EEC.

c endpoint for water flea ( D. magna ) to acute MU LTICIDE Fogging Concentrate 2 798

d endpoint for mysid ( M. b ahia ) to acute MULTICIDE Fogging Concentrate 2922

e estimated RQ (< 0.01) with simulated zero deposition in water

* exceeds aquatic listed species acute LOC (=0.05)

** exceeds aquatic non

- listed species acute LOC (=0.5)

### 6



### References

USEPA. 2014. Prallethrin: Revised ecological risk assessment to support proposed new use

over, near, and around agricultural areas. Environmental Fate and Effects Division, USEPA,

Washington, DC. PC Code 128722; DP Barcodes 417461, 417581, 417582; February, 2014.