              OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460
              OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460
                                       
                                       
                                       
                                       
                                       
                                March 31, 2015

                                                                PC Code: 121011
MEMORANDUM	DP Barcode: 425767

SUBJECT:	Clethodim: Drinking Water Exposure Assessment for Proposed New Uses and Crop Group Conversions regarding Stevia, Pome Fruit Group 11-10, Stone Fruit Group 12-12, Bulb Onion Subgroup 3-07A, Low-growing Berry Subgroup 13-07G, Rapeseed Subgroup 20A, Sunflower Subgroup 20B, Cotton Seed Subgroup 20C, and Fruiting Vegetable Group 8-10

FROM:	Greg Orrick, Environmental Scientist
	ERB2/EFED (7507P)

THROUGH:  Brian Anderson, Branch Chief
	ERB2/EFED (7507P)

TO:	Meheret Negussie, Risk Assessor
	Christine Olinger, Branch Chief
	RAB3/HED (7509P)

		Sydney Jackson, Risk Manager
		Barbara Madden, Team Leader
		MUERB/RD (7505P)

		Aswarthy Balan, Risk Manager
		Shaja Joyner, Team Leader
		FHB/RD (7505P)

      This Environmental Fate and Effects Division (EFED) memorandum is a drinking water exposure assessment (DWA) of proposed labeled uses of clethodim (listed in Table 2).  In light of the following three bullets, this DWA recommends use of the estimated drinking water concentrations (EDWC) of the previous DWA (USEPA, 2013), which are 1,430 ug/L (acute) and 1,150 ug/L (chronic) (also listed in Table 1).
      
         *       The previous DWA assessed a maximum annual application rate of 4.5 pounds of active ingredient per acre (lbs a.i./A) using Tier I screening models.
         *       Representative uses have been assessed previously for most of the proposed crop groups.
         *       All of the proposed uses are limited to a seasonal application rate of 0.5 or less lbs a.i./A, which is less than the maximum assessed annual application rate of 4.5 lbs a.i./A.
Table 1. Screening-Level ROC EDWCs for Clethodim Uses [A]
Source (Tier: Model)
Use Site
(Max. Annual App. Rate)
                              Acute EDWC (μg/L)
                             Chronic EDWC (μg/L)
Surface water (Tier I: FIRST)
Non-cropped  (4.5 lbs a.i./A)
                                      330
                                      137
Ground water (Tier I: PRZM-GW)
Non-cropped  (4.5 lbs a.i./A)
                                     1,430
                                     1,150
Ground water (Tier I: SCI-GROW)
Non-cropped  (4.5 lbs a.i./A)
                                     <=27
[A] Maximum values in bold.
      
      The clethodim residues of concern (ROC) include clethodim and degradates with 5-(2-ethylthiopropyl)-5-hydroxycyclohexene-3-one or 5-(2-ethylthiopropyl)cyclohexene-3-one moieties.  The maximum use pattern for clethodim is for non-cropped areas, fallow ground, and alfalfa.  Table 2 lists the proposed uses and crop group conversions and their maximum use patterns.
      
Table 2. Proposed Use Patterns of Clethodim [A]
                             Proposed Use Pattern
                          Similar Current Use Pattern
                               Single App. Rate
                                 (lbs a.i./A)
                            Reapp. Interval (days)
                           Max. No. of App. per Crop
                        Seasonal App. Rate (lbs a.i./A)
                                  App. Method
                            Additional Restrictions
                                    Stevia
                                     Herbs
                                     0.125
                                      14
                                      NS
                                     0.50
                                      NS
                                       - 
                            Pome fruit group 11-10
                                    (None)
                                     0.125
                                      14
                                      NS
                                     0.50
                                      NS
                                       - 
                            Stone fruit group 12-12
                                     Peach
                                     0.125
                                      14
                                      NS
                                     0.50
                                      NS
                                       - 
                       Low-growing berry subgroup 13-07G
                                  Strawberry
                                     0.125
                                      14
                                      NS
                                     0.50
                                      NS
                                       - 
                             Rapeseed subgroup 20A
                               Rapeseed/ canola
                                     0.094
                                     None
                                      NS
                                     0.094
                                      NS
         Do not apply after crop has begun bolting. Not for use in CA.
                            Sunflower subgroup 20B
                                   Sunflower
                                     0.25
                                    NS [B]
                                      NS
                                     0.50
                                      NS
                                       - 
                              Cotton subgroup 20C
                                    Cotton
                                     0.25
                                    NS [B]
                                      NS
                                     0.50
                                      NS
                                       - 
                         Bulb onion subgroup 3-07A [C]
                            Onion, garlic, shallot
                                     0.125
                                      14
                                      NS
                                     0.50
                                      NS
                                       - 
                         Fruiting vegetable group 8-10
                              Fruiting vegetables
                                     0.125
                                      14
                                      NS
                                     0.50
                                      NS
                                       - 
NS = "not stated"
A  Listed use patterns represent those of the maximum use pattern and do not represent all labeled use patterns for that use.
B Reapplication interval on 12.6% a.i. label is 14 days, on 26.4% a.i. label is not stated.
C Bulb onion subgroup 3-07A appears on 12.6% a.i. label, not on 26.4% a.i. label.


USEPA. 2013. Orrick, G. Clethodim: Drinking Water Exposure Assessment for Registration Review. DP barcode 412704. U.S. Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention, Environmental Fate and Effects Division. Memorandum to the Health Effects Division and Pesticide Re-evaluation Division. Jun. 24, 2013.

