Sethoxydim Risk Assessment

Worksheet B04 [KP_CHEM]: Calculation of dermal permeability rate (K
p
) in cm/hour for sethoxydim 
1
. 
Parameters 
Value 
Units 
Reference 
Molecular weight 
327.5 
g/mole 
K
o/w 
45.1 
unitless 
log
10
 K
o/w 
1.65417654188 
Column vector a for calculating confidence intervals 
a_1 
1 
a_2 
327.5 
a_3 
1.65417654188 
Calculation of  a' 
A
 (X'X)
-1 
A
 a 
Term 1 
0.00714617 
Term 2 
0.0212279437 
Term 3 
-0.008898365 
a' 
A
 (X'X)
-1 
A
 a 
0.0195 
log
10
 K
p
 =  0.706648 log
10
(k
o/w
) - 0.006151 MW - 2.72576 
log
10
 of dermal permeability 
Central estimate 
-3.57129195504 
± 
t
0.025 
× 
s 
× 
a'
A
(X'X)
-1
A
a
0.5 
Lower limit 
-3.77030651145 
-
1.9600 
× 
0.727129 
× 
0.13964240044 
Upper limit 
-3.37227739862 
% 
1.9600 
× 
0.727129 
× 
0.13964240044 
Dermal permeability 
Central estimate 
0.0002684 
cm/hour 
Lower limit 
0.0001697 
cm/hour 
Upper limit 
0.0004243 
cm/hour 
1
 See Worksheet A07a for details of method. 
WS-16  

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Worksheet B05 [DERM]: Summary of chemical specific dermal absorption values used for sethoxydim dermal 
absorption. 
Description 
Code 
Value 
Units 
Reference/Source 
Zero-order absorption (K
p
) 
Central estimate 
Lower limit 
KpC 
KpL 
0.00027 
0.00017 
cm/hour 
cm/hour 
Worksheet KPMODEL, values 
rounded to two significant figures 
Upper limit 
KpU 
0.00042 
cm/hour 
First-order absorption rates (k
a
) 
Central estimate 
Lower limit 
AbsC 
AbsL 
0.0011 
0.00047 
hour
-1 
hour
-1 
Worksheet KAMODEL, values 
rounded to two significant figures 
Upper limit 
AbsU 
0.0025 
hour
-1 
Worksheet B06 [AMBWAT]: Estimates of the concentration of sethoxydim in ambient water per pound 
applied per acre based on monitoring data and the resulting estimated concentrations in ambient water that are 
used in the chronic contaminated water exposure assessments. 
Scenario 
GLEAMS model runs were conducted at rainfall rates of 5 to 250 
inches per year and an application rate of 1 lb/acre with a 10 acre 
square plot adjacent to a 10 acre pond that is 1 meter deep. 
ID 
WCR 
(mg/L) ÷ 
(lb/acre) 
Short-term Peak Concentrations in Streams 
(See Section 3.2.3.4.1 for details) 
Central 
The typical rate is taken as 200 µg/L.  This is about the peak 
concentrations that could be expected at rainfall rates of about 100 
inches per year from sand. 
AWPT 
0.200 
Lower 
The lower limit is about the peak concentration from sandy soil at 
an annual rainfall rate of 15 inches per year. 
AWPL 
0.020 
Upper 
The upper limit is approximately the peak concentration from loam 
soils at rainfall rates of 250 inches per year. 
AWPU 
0.500 
Longer-term Concentrations in Lakes 
(See Section 3.2.3.4.2 for details) 
Central 
The typical WCR is taken as 0.0008 mg/L.  This is about the 
average concentration that could be expected at rainfall rates of 
about 100 inches per year from loam. 
AWT 
0.0008 
Lower 
The lower limit of the WCR is taken as 0.00002 mg/L, the average 
concentration from loam soil at an annual rainfall rate of 10 inches 
AWL 
0.00002 
per year. 
Upper 
The upper limit is taken as 0.0012 mg/L, approximately the 
longer-term average concentration from loam soils at rainfall rates 
of 250 inches per year. 
AWU 
0.0012 
WS-17  

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WORKER EXPOSURE ASSESSMENTS 
Worksheet C01a: Worker exposure estimates for directed foliar (backpack) applications of sethoxydim 
[WkBkExp01] 
Verbal Description: The absorbed dose for the worker is calculated from the amount handled per day and the 
generic absorbed dose rate from several field studies on worker applications of a number of herbicides.  The 
amount handled per day is calculated from the application rates as well as estimates of the hours worked per day 
and acres treated per hour. 
Parameter/Assumption 
Value 
Units 
Source/Designation 
Application rates (R) 
Central 
0.3 
lb/acre 
APPL.TYP 
Lower 
0.09375 
APPL.LOW 
Upper 
0.375 
APPL.HI 
Hours of application per day (Hrs) 
Central 
7 
hours 
USDA 1989a,b,c 
Lower 
6 
USDA 1989a,b,c 
Upper 
8 
USDA 1989a,b,c 
Acres treated per hour (Acres) 
Central 
0.625 
acres/hour 
USDA 1989a,b,c 
Lower 
0.25 
USDA 1989a,b,c 
Upper 
1 
USDA 1989a,b,c 
Acres treated per day (ATD): Hrs × Acres 
Central 
4.375 
acres/day 
Lower 
1.5 
Upper 
8 
Amount handled per day (AHD): R × ATD 
Central 
1.3125 
lb/day 
Lower 
0.140625 
Upper 
3 
Absorbed dose rate (ADR): 
Central 
0.003 
(mg agent/kg bw) 
SERA 2001 
Lower 
0.0003 
÷ (lbs agent 
Upper 
0.01 
handled per day) 
Absorbed dose [D
Abs
]: AHD × ADR 
Central 
3.94e-03 
mg/kg bw/day 
Lower 
4.22e-05 
Upper 
3.00e-02 
WS-18  

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