Sethoxydim Risk Assessment

the concentration of sethoxydim - equivalent to the lower dilution of sethoxydim - the greater the 
risk.  For this risk assessment, the lowest dilution is taken as 5 gallons/acre, the minimum 
recommended for ground applications.  The highest dilution is based on 20 gallons of water per 
acre, the highest application volume specifically recommended for ground applications.  A typical 
dilution rate is taken as 10 gallons/acre, the minimum volume recommended in the west and 
southwest regions of the United States.  Details regarding the calculation of field dilution rates are 
given in worksheet B01. 
In addition to dilution rates, the area that the Forest Service might treat has a major impact on the 
estimates of concentrations of sethoxydim that could occur in ambient water.  Given the projected 
and limited use of Poast by the Forest Service, this risk assessment models a 10 acre square plot 
rather than a right-of-way. 
2.5. USE STATISTICS 
Poast as well as many of the other commercial formulations of sethoxydim are used extensively in 
agriculture.  A summary of the agricultural use of sethoxydim is presented in Figure 2-1 (USGS 
1992).  As indicated in this table, over 1,000,000 lbs of sethoxydim are applied to crops annually, 
primarily to soybeans and cotton in the mid-west.  By comparison, the uses of sethoxydim by the 
Forest Service are trivial - i.e., a total of 3.8 lbs in 1999 (USDA/FS/FHP 2000). 
2-4  

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Table 2-1.  Selected physical and chemical properties of sethoxydim 
Synonyms and trade names 
U.S. EPA Reg. No. 
CAS number 
Molecular weight 
Specific Gravity 
Appearance, ambient 
Odor 
Vapor pressure 
pKa  
Water solubility (mg/L)  
log K
ow 
Henry’s law constant 
Soil sorption, K
oc 
Soil mobility, K
ads
 (mL/g) 
Field dissipation half-time  
(days)  
Foliar half-time (days)  
Soil half-time (days)  
Anaerobic sediment (aqueous)  
half-time (days)  
Water half-time (hydrolysis)  
(days)  
Photolysis halftime (days)  
Aljaden, Alloxol S, BAS 9052H, BAS 9052 06H, BAS 562 05H, Checkmate, Expand, 
Fervinal, Grasidim, Nabu, NP-55, Poast, Tritex-Extra, and Vantage (BASF 2000, 
Extoxnet 2000) 
7969-58  
74051-80-2 (BASF 2000)  
327.50 (BASF 2000)  
0.935 g/mL (BASF 2000); 1.043 @ 25°C (technical) (WSSA 1989)  
amber-colored, oily, odorless liquid (Kidd and James 1991)  
aromatic (BASF 2000)  
<0.1 mPa @ 20°C (EXTOXNET 2000); 2 mmHg @ 20° (BASF 2000); 1.67x10
-7
 mm  
Hg @ 25°C (USDA/SCS 1990; WSSA 1989); 4.55x10
-10
 mm Hg @ 25°C (estimated)  
(SRC 2001). 0.02 mPa (USDA/ARS 1995).  
5.0 (Brudenell et al.  1995)  
25 mg/L @ pH 4 and 20°C (experimental) (SRC 2001); 4700 mg/L @ pH 7 and 20°C  
(Extoxnet 2000); forms an emulsion (BASF 2000),  4700 mg/L @ pH 7 and 25°C, 4390  
mg/L @ pH 7 and 20°C  (USDA/ARS 1995); 4390 mg/L (Knisel et al.  1992)  
1.65 [reported as  K
ow
 = 45.1] (Bryceland et al.  1997) 
4.38 (experimental) (SRC 2001) (probably at low pH) 
3.99 (estimated) (SRC 2001) (undissociated) 
1.32-1.43 [reported as  K
ow
 = 21-27] (Sczerzenie et al.  1989) 
1.47x10
-11
 atm-m
3
/mol (Bryceland et al.  1997)  
1.39x10
-6
 Pa-m
3
/mol (USDA/ARS 1995)  
50 (BCPC 1983)  
100 (Knisel et al.  1992)  
0.03-0.94 (Bryceland et al.  1997)  
0.02-0.84 (Soeda and Shiotani 1988d)  
1 to 10 (USDA/ARS 1995) 
3 (Knisel et al.  1992)  
1-3 (aerobic) (USDA/ARS 1995)  
5 (Knisel et al.  1992)  
biphasic and highly variable in field (Koskinen et al.  1994, see Section 3.2.3).  
<1 (aerobic) (Bryceland et al.  1997)  
>60 (anaerobic) (Bryceland et al.  1997)  
0.7 to 0.9 (aerobic, sandy loam and sandy clay loam)(Shiotani 1989) 
1-3 (USDA/ARS 1995) 
0.7-1 (Shiotani 1990a) 
39.9 (Bryceland et al.  1997) 
25-40 (Soeda and Shiotani 1989) 
2.8 (25°C, pH 3) (USDA/ARS 1995) 
46.2 (25°C, pH 6) (USDA/ARS 1995) 
439 (25°C, pH 9) (USDA/ARS 1995) 
0.7-1 (Bryceland et al.  1997) 
8.8 (25°C, pH 5) (Soeda and Shiotani 1988a) 
155.2 (25°C, pH 7) (Soeda and Shiotani 1988a) 
283.7 (25°C, pH 8.6) (Soeda and Shiotani 1988a) 
43.3 (aqueous) (USDA/ARS 1995) 
5.23 (aqueous) (Bryceland et al.  1997) 
5.53 (aqueous) (25°C, pH 8.7) (Soeda and Shiotani 1988b) 
0.16 (soil) (3.8 hrs, 25°C) (Soeda and Shiotani 1988c) 
2-5  

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Table 2-2: Commercial liquid formulations of sethoxydim
a
 (C&P Press 1999) 
Commercial 
Name 
Supplier 
Active Ingredients 
Inerts 
Conclude G 
BASF Corporation 
sethoxydim (1.5 lbs/gal) 
petroleum solvent (57%) with 
naphthalene (7%); other inerts 
(25%) 
Conclude Xact 
BASF Corporation 
bentzon, sodium salt (2.67 
lbs/gal); acifluorfen, 
sodium salt (1.33 lbs/gal); 
sethoxydim (2.0 lbs/gal) 
inerts (65.1%) 
Manifest G 
BASF Corporation 
sethoxydim (1.5 lbs/gal) 
petroleum solvent (74%) with 
napthalene (7%); non-ionic 
emulsifier (7%); impurities (1%) 
Poast 
BASF Corporation 
sethoxydim (1.5 lbs/gal) 
petroleum solvent (74%) with 
napthalene (7%); non-ionic 
emulsifier (7%); other inerts (1%) 
Poast Plus 
BASF Corporation 
sethoxydim (1.0 lbs/gal) 
napthalene (1.3%); other inerts 
(85.7%) 
Rezult G 
BASF Corporation 
sethoxydim (1.0 lbs/gal) 
napthalene (1.3%); other inerts 
(85.7%) 
Torpedo 
BASF Corporation 
sethoxydim (1.0 lbs/gal) 
napthalene (1.3%); other inerts 
(85.7%) 
Vantage 
TopPro 
sethoxydim (1.0 lbs/gal) 
napthalene (1.3%); other inerts 
(85.7%) 
2-6  

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