Sethoxydim Risk Assessment

3.4.3. General Public.  The quantitative hazard characterization for the general public is 
summarized in Table 3-7.  Like the quantitative risk characterization for workers, the quantitative 
risk characterization for the general public is expressed as the hazard quotient using the U.S. EPA 
chronic RfD of 0.09 mg/kg/day for longer-term exposures and the U.S. EPA acute RfD of 0.6 
mg/kg for acute exposures. 
None of the longer-term exposure scenarios exceed a level of concern.  Although there are several 
uncertainties in the longer-term exposure assessments for the general public, as discussed in 
Section 3.2, the upper limits for hazard indices are below a level of concern by factors of 25 
(longer term consumption of contaminated fruit) to 2000 (longer-term consumption of fish by the 
general population).  The risk characterization is thus relatively unambiguous: based on the 
available information and under the foreseeable conditions of application, there is no route of 
exposure or exposure scenario suggesting that the general public will be at risk from longer-term 
exposure to sethoxydim. 
The exposure scenario for drinking water following an accidental spill results in a modest 
excursion about the RfD at the upper limit of exposure – i.e, a hazard quotient of 1.3.  As detailed 
in Section 3.2.3.4.1, this exposure scenario is extreme to the point of limited plausibility.  This 
sort of scenario is routinely used in Forest Service risk assessments as an index of the measures 
that should be taken to limit exposure in the event of a relatively large spill into a relatively small 
body of water.  For sethoxydim, this standard exposure scenario may have only very limited 
applicability because the amount spilled, about 15 lbs, is about 4 times more sethoxydim than the 
Forest Service used in all of 1999.  The acute drinking water scenario for water contamination of 
a small stream after a rainfall is much more plausible (although still highly conservative) and leads 
to very low hazard quotients – i.e., 0.008 to 0.04. 
3.4.4.  Sensitive Subgroups.  There is no information to assess whether or not specific groups or 
individuals may be especially sensitive to the systemic effects of sethoxydim.  As indicated in 
Section 3.1.3, the mechanism of the acute and chronic toxicity of sethoxydim is unclear but may 
be related to the ability of sethoxydim to uncouple oxidative phosphorylation.  Other effects noted 
in experimental mammals include decreases in food consumption as well as decreased body 
weight and the occurrence of liver pathology. 
3.4.5.  Connected Actions.  No data are available on the combined toxicity of sethoxydim with 
other pesticides.  As noted in Section 2, Poast does contain a petroleum solvent as well as a 
polyoxyethylene nonylphenol emulsifier.  While these agents have a substantial impact on the 
ecological risk assessment (Section 4), there is no information suggesting that these agents have a 
substantial impact on the toxicity of sethoxydim to humans or experimental mammals. 
3.4.6. Cumulative Effects.  This risk assessment specifically considers the effect of both acute as 
well as chronic exposures to sethoxydim.  Consequently, the risk characterizations presented in 
this risk assessment encompass the potential impact of long-term exposure and cumulative effects. 
3-21  

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Table 3-1: Summary of Worker Exposure Scenarios 
Scenario 
Central 
Dose (mg a.i./kg/day or event) 
Lower 
Upper 
Exposure 
Assessment 
Worksheet 
General Exposures (dose in mg/kg/day) 
Directed ground spray 
(Backpack) 
3.94e-03 
4.22e-05 
3.00e-02 
C01a 
Broadcast ground spray 
(Boom spray) 
6.72e-03 
6.19e-05 
5.67e-02 
C01b 
Aerial applications 
N/A 
C01c 
Accidental/Incidental Exposures (dose in mg a.i./kg/event) 
Immersion of Hands, 
1.94e-04 
1.90e-05 
7.56e-04 
C02a 
1 minute 
Contaminated Gloves, 
1.17e-02 
1.14e-03 
4.54e-02 
C02b 
1 hour 
Spill on hands, 
3.80e-04 
2.53e-05 
2.16e-03 
C03a 
1 hour 
Spill on lower legs, 
9.36e-04 
6.23e-05 
5.32e-03 
C03b 
1 hour 
3-22  

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Table 3-2: Summary of Exposure Scenarios for the General Public 
Target 
Dose (mg a.i./kg/day) 
Worksheet 
Scenario 
Central 
Lower 
Upper 
Acute/Accidental Exposures 
Direct spray, entire body 
Child 
1.44e-02 
9.54e-04 
8.15e-02 
D01a 
Direct spray, lower legs 
Woman 
1.44e-03 
9.59e-05 
8.19e-03 
D01b 
Dermal, contaminated 
Woman 
7.38e-04 
8.94e-05 
2.10e-03 
D02 
vegetation 
Contaminated fruit 
Woman 
3.53e-03 
1.10e-03 
7.00e-02 
D03 
Contaminated water, spill 
Child 
2.05e-01 
1.94e-02 
7.68e-01 
D05 
Contaminated water, stream 
Child 
4.51e-03 
8.60e-05 
2.11e-02 
D06 
Consumption of fish,  general 
Man 
7.38e-03 
1.15e-03 
1.85e-02 
D08a 
public 
Consumption of fish, 
Man 
3.60e-02 
5.60e-03 
8.99e-02 
D08b 
subsistence populations 
Chronic/Longer Term Exposures 
Contaminated fruit 
Woman 
1.70e-04 
5.30e-05 
3.37e-03 
D04 
Consumption of water 
Man 
6.86e-06 
3.75e-08 
1.54e-05 
D07 
Consumption of fish, general 
public 
Man 
2.40e-07 
1.88e-09 
4.50e-07 
D09a 
Consumption of fish, 
subsistence populations 
Man 
1.94e-06 
1.52e-08 
3.65e-06 
D09b 
3-23  

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