Sethoxydim Risk Assessment

Worksheet A07b [KPMODEL]: Estimate of dermal permeability (K
p
 in cm/hr) and 95% confidence 
intervals (data from U.S. EPA/ORD 1992). 
Model parameters 
ID 
Value 
Coefficient for k
o/w 
C_KOW 
0.706648 
Coefficient for MW 
C_MW 
0.006151 
Model Constant 
C 
2.72576 
Number of data points 
DP 
90 
Degrees of Freedom (d.f.) 
DF 
87 
Critical value of t
0.025
 with 87 d.f.
1 
CRIT 
1.96 
Standard error of the estimate 
SEE 
45.9983 
Mean square error or model variance 
MDLV 
0.528716 
Standard deviation of model (s) 
MSD 
0.727129 
MDLV
0.5 
X
N
X, cross products matrix 
0.0550931 
-0.0000941546 
-0.0103443 
-0.0000941546 
0.0000005978 
-0.0000222508 
-0.0103443 
-0.0000222508 
0.00740677 
1
 Mendenhall and Scheaffer, 1973, Appendix 3, Table 4, p. A31. 
NOTE: The data for this analysis is taken from U.S. EPA/ORD (1992), Dermal Exposure Assessment: Principles 
and Applications, EPA/600/8-91/011B, Table 5-4, pp. 5-15 through 5-19.  The EPA report, however, does not 
provide sufficient information for the calculation of confidence intervals.  The synopsis of the above analysis was 
conducted in STATGRAPHICS Plus for Windows, Version 3.1 (Manugistics, 1995) as well as Mathematica, 
Version 3.0.1.1 (Wolfram Research, 1997).  Although not explicitly stated in the EPA report, 3 of the 93 data 
points are censored from the analysis because they are statistical outliers: [Hydrocortisone-21-yl]-hemipimelate, n­
nonanol, and n-propanol.  The model parameters reported above are consistent with those reported by U.S. EPA 
but are carried out to greater number of decimal places to reduce rounding errors when calculating the confidence 
intervals.  See notes to Worksheet A07a for details of calculating maximum likelihood estimates and confidence 
intervals. 
WS-12  

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CHEMICAL SPECIFIC VALUES 
Worksheet B01 [APPL]: Anticipated Application and Dilution Rates for sethoxydim 
Item 
Code 
Value 
Units 
Source 
Application rate (R) 
Central 
Typ 
0.3 
lb/acre 
Section 2.4 
Lower 
Low 
0.09375 
Section 2.4 
Upper 
Hi 
0.375 
Section 2.4 
Dilution (Dil) 
Central 
CDil 
10 
gal./acre 
Section 2.4 
Lower 
LDil 
5 
Upper 
HDil 
20 
Concentration in field solutions
1
: R
(lb/acre)
 ÷ Dil
(gal/acre)
 × 119.8 mg/mL÷lb/gal 
Central 
TypDr 
3.6 
0.56 
9 
mg/mL 
Lower 
LowDr 
Upper 
HI_Dr 
The typical concentration in applied solution is calculated as the typical application rate (lbs/acre) divided by 
the typical dilution (gal/acre), yielding units of lbs/gallon.  This is converted to mg/mL using the relationship of 
lb/gal = 119.8 mg/mL from Worksheet A01.  The lowest estimated concentration is calculated as the lowest 
application rate divided by the highest dilution.  The highest estimated concentration is calculated as highest 
application rate divided by the lowest dilution. 
NOTE ON UNITS FOR APPLICATION RATE: In all cases, lb/acre refers to 
lb a.i./acre. 
WS-13  

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Worksheet B02 [CHEM]: Summary of chemical specific values used for sethoxydim in exposure assessment 
worksheets. 
Parameter 
ID 
Value 
Units 
Source/Reference 
Molecular weight 
MW 
327.50 
grams/mole 
Table 2-1 
Water Solubility, pH 7 and 20°C 
WS 
4700 
mg/L 
Table 2-1 
K
o/w
, pH 7 
Kow 
45.1 
unitless 
Table 2.1, log  K
o/w
 = 1.65 
Foliar half-time ( t
½
 ) 
FT12 
3 
days 
Table 2-1 
central 
FrT12C 
3 
days 
lower 
FrT12L 
3 
days 
upper 
FrT12U 
3 
days 
Dissipation coefficients on vegetation 
central 
VgKC 
0.231049 
day
-1 
ln(2)/half-time. 
The upper limit on half-
lower 
VgKL 
0.231049 
day
-1 
time is used to calculate 
the lower limit on 
upper 
VgKU 
0.231049 
day
-1 
dissipation coefficient. 
Bioconcentration factor, edible 
BCFT 
1.2 
L/kg fish 
Section 3.2.3.5. 
portion, acute exposure 
Bioconcentration factor, edible 
BCFCh 
7 
L/kg fish 
portion, chronic exposure 
Bioconcentration factor, whole fish, 
BCFWA 
3.6 
L/kg fish 
acute 
Bioconcentration factor, whole fish, 
BCFWC 
21 
L/kg fish 
chronic 
Chronic RfD
a 
RfDP 
0.09 
mg/kg bw/day 
Section 3.3.3 
Acute RfD 
RfDA 
0.6 
mg/kg bw/day 
Section 3.3.3 
WS-14  

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Worksheet B03 [KA_CHEM]: Calculation of first-order dermal absorption rate (k
a
) for sethoxydim
1
. 
Parameters 
Value 
Units 
Reference 
Molecular weight 
327.5 
g/mole 
K
o/w
 at pH 7 
45.1 
unitless 
log
10
 K
o/w 
1.65 
Column vector a for calculating confidence intervals 
a_1 
1 
a_2 
327.5 
a_3 
1.65 
Calculation of  a' 
A
 (X'X)
-1 
A
 a 
Term 1 
-0.016549475 
Term 2 
0.0808133318 
Term 3 
-0.0142359975 
a' 
A
 (X'X)
-1 
A
 a 
0.05 
log
10
 k
a
 =  0.233255 log
10
(k
o/w
) - 0.005657 MW - 1.49615 
log
10
 of first order absorption rate (k
a
) 
Central estimate 
-2.96297255072 
± 
t
0.025 
× 
s 
× 
(a'
A
(X'X)
-1
A
a)
0.5 
Lower limit 
-3.32488467153 
-
2.0560 
× 
0.787218 
× 
0.22360679775 
Upper limit 
-2.60106042992 
% 
2.0560 
× 
0.787218 
× 
0.22360679775 
First order absorption rates (i.e., antilog or 10
x
 of above values). 
Central estimate 
0.00109 
hour
-1 
Lower limit 
0.00047 
hour
-1 
Upper limit 
0.00251 
hour
-1 
1
 See Worksheet A07a for details of method. 
WS-15  

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