Sethoxydim Risk Assessment

Table 3-3: Pesticide specific parameters used in GLEAMS modeling and estimation of 
concentrations in ambient water 
Parameter 
Clay 
Loam 
Sand 
Comment/ 
Reference 
Halftimes (days)
 Aquatic Sediment 
190 
190 
190 
Note 1
 Foliar 
3 
3 
3 
(Knisel et al.  1992)
 Soil 
22 
22 
22 
Note 2
 Water 
155.2 
155.2 
155.2 
Note 3 
Ko/c 
100 
100 
100 
Knisel et al.  1992 
K
d 
0.03 
0.84 
0.06 
Soeda and Shiotani 1988d.  See Note 4. 
Water Solubility, mg/L 
4700 
4700 
4700 
pH 7 and 25°C
. 
USDA/ARS 1995 
Note 1   The mean of halftimes of 141 and 247 days for the generation of C0
2
 from sethoxydim in an anaerobic 
aquatic environment (Shiotani 1990b).  See Section 3.1.9.2. 
Note 2   15% trapped as CO
2
 over a 61 day incubation period (Shiotani.  1989).  Corresponds to a k 
(degradation rate in soil) of 0.031 day
-1
 and a halftime of 22.2 days. 
Note 3  
Hydrolysis at 25°C, pH 7 from Soeda and Shiotani (1988a) 
Note 4   Value of 0.84 is for sandy clay loam.  Value of 0.03 is for clay loam. 
3-24  

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Table 3-4: Estimated concentrations of sethoxydim in a small stream based on GLEAMS 
modeling with different soil types and annual rainfall rates and using a normalized application 
rate of 1 lb/acre. 
Concentrations in Ambient Water (µg/L per lb/acre) 
1 
Annual 
Clay 
Loam 
Sand
Rainfall 
Average 
Maximum 
Average 
Maximum 
Average 
Maximum 
5 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
10 
0.00 
0.00029 
0.02 
3.99 
0.03 
7.81 
15 
0.03 
4.62 
0.08 
14.7 
0.07 
19.8 
20 
0.06 
10.1 
0.14 
28.7 
0.11 
32.0 
25 
0.09 
16.7 
0.19 
44.2 
0.15 
43.9 
50 
0.24 
54.9 
0.45 
128 
0.30 
95.7 
100 
0.51 
141 
0.81 
306 
0.49 
174 
150 
0.72 
229 
1.01 
406 
0.63 
226 
200 
0.89 
320 
1.14 
455 
0.74 
269 
250 
1.03 
411 
1.23 
491 
0.83 
304 
1
 The maximum concentration is the highest concentration modeled.  This occurs on the day after the first 
rainfall.  The average is calculated as the average value over a four year period assuming one application per 
year. 
3-25  

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Table 3-5: Estimated concentrations of sethoxydim in a small pond based on GLEAMS 
modeling with different soil types and annual rainfall rates and using a normalized application 
rate of 1 lb/acre. 
Concentrations in Ambient Water (µg/L per lb/acre) 
1 
Annual 
Clay 
Loam 
Sand
Rainfall 
Average 
Maximum 
Average 
Maximum 
Average 
Maximum 
5 
0.00 
0.00 
0.00 
0.00 
0.00 
0.00 
10 
0.00 
0.000040 
0.16 
0.75 
0.26 
1.24 
15 
0.15 
0.83 
0.50 
2.57 
0.59 
2.92 
20 
0.30 
1.73 
0.89 
4.70 
0.91 
4.50 
25 
0.48 
2.78 
1.28 
7.01 
1.21 
5.93 
50 
1.31 
8.40 
2.94 
17.9 
2.38 
12.2 
100 
2.72 
19.3 
5.31 
38.4 
3.93 
22.1 
150 
3.81 
28.3 
6.61 
50.9 
5.00 
28.8 
200 
4.69 
39.5 
7.39 
57.0 
5.84 
34.2 
250 
5.41 
50.7 
7.95 
61.5 
6.52 
38.7 
1
 The maximum concentration is the highest concentration modeled.  This occurs on the day after the first 
rainfall.  The average is calculated as the average value over a four year period assuming one application per 
year. 
3-26  

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Table 3-6: Summary of risk characterization for workers
1 
Acute RfD 
0.6 
mg/kg/day 
Sect. 3.3.3. 
Chronic RfD 
0.09 
mg/kg/day 
Sect. 3.3.3. 
Scenario 
Hazard Quotient Based on Chronic RfD 
Exposure 
Assessment 
Worksheet
Central 
Lower 
Upper 
General Exposures [using Chronic RfD] 
Directed ground spray 
(Backpack) 
4e-02 
5e-04 
3e-01 
C01a 
Broadcast ground spray 
(Boom spray) 
7e-02 
7e-04 
6e-01 
C01b 
Aerial applications 
N/A 
Accidental/Incidental Exposures [using Acute RfD] 
Scenario 
Hazard Quotient Based on Acute RfD 
Exposure 
Assessment 
Worksheet
Typical 
Lower 
Upper 
Immersion of Hands, 
1 minute 
3e-04 
3e-05 
1e-03 
C02a 
Contaminated Gloves, 
1 hour 
2e-02 
2e-03 
8e-02 
C02b 
Spill on hands, 
1 hour 
6e-04 
4e-05 
4e-03 
C03a 
Spill on lower legs, 
1 hour 
2e-03 
1e-04 
9e-03 
C03b 
1
 Hazard quotient is the level of exposure divided by the provisional RfD then rounded to one significant 
decimal place or digit. See Table 3-1 for summary of exposure assessment. 
3-27  

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