Sethoxydim Risk Assessment

Worksheet F04b: Consumption of contaminated fruit by a small mammal, chronic exposure scenario off-site 
[VegChSmMam02]. 
Verbal Description: A 20 g mammal consumes contaminated fruit for a 90 day period starting shortly after 
application of the chemical.  Food consumption is estimated from allometric relationships.  The concentration 
of the chemical in fruit at time zero (C
0
) is estimated from the application rate (A), the proportion of drift 
(Drift), and empirical residues rates (rr) summarized in HK.  Drift is estimated for distances of 25 to 100 feet 
from the application site.  The foliar halftime (t
50
) is used to estimate the foliar decay coefficient (k): k = 
ln(2)÷t
50
.  The concentration on the vegetation after time t (C
t
) is calculated as C
t
= C
0
e
-kt
.  The time-weighted 
average of the concentration on vegetation (C
TWA
) is calculated as the integral of the concentration after time t 
(C
t
) divided by the duration (t).  The daily dose is calculated as the product of  food consumption and the 
proportion of the diet that is contaminated divided by the body weight. 
Parameters/Assumptions 
Value 
Units 
Source/Reference 
Duration of exposure (T) 
90 
days 
N/A 
Body weight (W) 
0.02 
kg 
Section 4.2.1 
Allometric coefficients for food consumption in g based on body weight in g 
a 
0.621 
U.S. EPA/ORD 1993, p. 3-6 
b 
0.584 
Food consumed per day (A): a×(W×1000)
 b
÷1000 
0.0035718 
kg 
Foliar halftimes (t
½
) 
Central 
3 
days 
CHEM.FrT12C 
Lower 
3 
CHEM.FrT12L 
Upper 
3 
CHEM.FrT12U 
Application rates (R) 
Central 
0.3 
lb/acre 
APPL.Typ 
Lower 
0.09375 
APPL.Low 
Upper 
0.375 
APPL.Hi 
Residue rates (rr): 
Central 
7 
mg/kg fruit 
HK.FRT2 
Lower 
7 
per lb/acre 
applied 
HK.FRT2 
Upper 
15 
HK.FRU2 
Drift (Drift): 
50 feet 
0.0101 
unitless 
Estimated from AgDRIFT 
100 feet 
0.0058 
for low-boom applications. 
See Worksheet A06. 
25 feet 
0.0187 
Decay coefficient (k): ln(2)/t
50 
Central 
0.2310491 
day
-1 
Upper estimate of t
50
 used to 
Lower 
0.2310491 
calculate lower limit of k and 
lower estimate of t
50
 used to 
Upper 
0.2310491 
calculate upper limit of k. 
WS-48  

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Worksheet F04b (continued): Consumption of contaminated vegetation by a small mammal, chronic off-site 
exposure scenario . 
Initial Concentration on Vegetation (C
0
): C
0
 = R × rr × Drift 
Central 
0.02121 
mg/kg veg. 
Lower 
0.0038063 
Upper 
0.1051875 
Concentration on Vegetation at time T (C
T
): C
T
 = C
0
 e
-kT 
Central 
1.98e-11 
mg/kg veg. 
Lower 
3.54e-12 
Upper 
9.80e-11 
Time-weighted Average Concentration on Vegetation (C
TWA
): C
0
 (1 - e
-k T
) ÷ (k T) 
Central 
1.02e-03 
mg/kg veg. 
Lower 
1.83e-04 
Upper 
5.06e-03 
Proportion of Diet Contaminated (Prop)
1
: 
Central 
0.1 
unitless 
See footnote. 
Lower 
0.05 
Upper 
0.2 
Dose estimates (D): C
TWA
 × A × Prop ÷ W 
Central 
1.82e-05 
mg/kg bw/day 
Lower 
1.63e-06 
Upper 
1.81e-04 
1
 Based on data on the shrew (U.S. EPA/ORD 1996, p. 2-214,), the vegetation accounts for about 5% of the diet. 
This is used as the lower limit.  The typical and upper values are judgementally set to account for incidental 
contamination of other food items such as insects as well as different feeding preferences among other small 
mammals. 
WS-49  

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Worksheet F05: Consumption of contaminated water by a small mammal, acute exposure scenario for an 
accidental spill. [DWAcERA01]. 
Verbal Description: An animal of a specified weight consumes contaminated water shortly after an accidental 
spill into a small pond.  No dissipation or degradation is considered.  The amount of water consumed is 
estimated from allometric relationships 
Parameters/Assumptions 
Value 
Units 
Source/Reference 
Surface area of pond [SA] 
1000 
m
2 
N/A 
Average depth [DPTH] 
1 
m 
N/A 
Volume of pond in cubic meters [VM] 
1000 
m
3 
N/A 
Volume of pond in Liters [VL] 
1000000 
L 
1 m
3
 = 1,000 L 
Volume of spill [VS] 
200 
gallons 
N/A 
757 
liters 
1 gallon = 3.785 Liters 
Concentrations in field solution (C
Fld  (mg/L)
) 
Central 
3600 
mg/L 
APPL.TypDR × 1000 
Lower 
560 
APPL.LowDR × 1000 
Upper 
9000 
APPL.Hi_DR × 1000 
Concentrations in ambient water (C
Wrt
): C
Fld
 × VS
(Liters)
 ÷ VL) 
Central 
2.7252 
mg/L 
Lower 
0.42392 
Upper 
6.813 
Body weight (W) 
0.02 
kg 
Section 4.2.1 
Allometric coefficients for water consumption in L based on body weight in kg 
a 
0.099 
All mammals. U.S. 
EPA/ORD 1993, Eq. 3-17, p.
b 
0.9 
3-10. 
Water consumed per day (A): a×W
 b 
0.002928 
L 
Dose estimates (D): C
wrt
 × A ÷ W 
Central 
3.99e-01 
mg/kg bw 
Lower 
6.21e-02 
Upper 
9.97e-01 
WS-50  

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