Document ID: EPA-HQ-OPP-2016-0651-0013
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2018-04-12T04:00Z

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
                                       
                                       
                                       
                                       
                                       
                                 June 24, 2013

                                                                PC Code: 121011
MEMORANDUM	DP Barcode: 412704

SUBJECT:	Clethodim: Drinking Water Exposure Assessment for Registration Review

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

THROUGH:  R. David Jones, Ph.D., Senior Agronomist	
            Brian Anderson, Branch Chief
	ERB2/EFED (7507P)

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

	Ricardo Jones, Chemical Review Manager
	Neil Anderson, Branch Chief
	RMIB1/PRD (7508P)

      This Environmental Fate and Effects Division (EFED) memorandum is a drinking water exposure assessment based on currently labeled uses of clethodim (listed in Table 2) to support the registration review of the active ingredient.  This assessment provides screening-level estimated drinking water concentrations (EDWC) of the residues of concern (ROC), which include clethodim and degradates with 5-(2-ethylthiopropyl)-5-hydroxycyclohexene-3-one or 5-(2-ethylthiopropyl)cyclohexene-3-one moieties.
      
      The maximum screening-level acute and chronic EDWCs (1,430 and 1,150 ug/L, respectively) are based on the maximum use pattern for clethodim (which includes non-cropped areas, fallow ground, and alfalfa), which includes a maximum annual application rate of 4.5 lbs a.i./A.  The EDWCs are estimated with PRZM-GW to occur in an area of Wisconsin that is vulnerable to ground water contamination.  These EDWCs are 43-53x greater than screening-level EDWCs for ground water from SCI-GROW and 4-8x greater than screening-level EDWCs for surface water from FIRST (Table 1).  The variance with SCI-GROW may be due, in part, to 1) PRZM-GW being mechanistic, whereas SCI-GROW is empirical, and 2) differences in modeling assumptions such as the duration of the modeling scenario.

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.
      
      Uncertainty regarding PRZM-GW outputs results from the extended time period of ground water flow and the model's underlying assumptions, including that soils are sterile below a 1-meter depth.  Bacteria in soils greater than one meter below the surface may degrade the ROC (potentially at a slower rate than on the surface) and may potentiate over years or decades in order to degrade the ROC at a faster rate.  Clethodim ROC have an average breakthrough time of only 4.3 years with the Wisconsin scenario.  Breakthrough times for PRZM-GW have been up to one order of magnitude shorter than observed for bromide (USEPA, 2012a) and up to one order of magnitude longer than observed for oxamyl (MRID 45591605).  With an error of approximately one order of magnitude, average breakthrough of clethodim ROC may occur after 0.4-40 years of use, which is a considerable uncertainty, compounded by variable usage that is not expected to occur at the maximum labeled rate annually.
      
      Also, the one-dimensional model represents a drinking water well that is surrounded by a large pesticide-treated area.  Most drinking water wells are not surrounded by large pesticide-treated areas.   Therefore, in most wells, horizontal convection and dispersion may attenuate persistent, dissolved residues such as these over time.
      
      The main uncertainties with clethodim ROC exposure estimates are the toxicities of the degradates of concern and the actual usage rates.  If actual annual application rates are an order of magnitude lower than those assumed in this assessment (e.g., 0.5 versus 4.5 lbs a.i./A), then exposure estimates for the actual rates are an order of magnitude lower as well (e.g., 158 versus 1,430 ug/L).  If the degradates of concern were shown to be much less toxic than clethodim, then exposure estimates for clethodim alone would be <=3.2 ug/L at pH 7 and <0.1 ug/L in acidic (pH 5) aquifers.

 Use Characterization

      Clethodim is applied with aerial, ground, hand-held, and irrigation equipment to a variety of agricultural and non-agricultural use sites.  Approximately 67 uses and use groups (i.e., use sites) are listed on dozens of end-use labels registered by 21 registrants.  These uses and use groups are organized into the following 26 maximum use patterns listed in Table 2 that are ranked by annual application rate.  The use sites are not grouped by similarity and are not meant to be used as surrogates for other use sites that share the same use pattern.
      
      Many use sites have application rate limits on a seasonal or crop basis, not on an annual basis.  Annual application rates were assumed for use sites with multiple seasons per year, when not specified on labels, based on estimates in USEPA, 2007 for California agriculture.  These estimates are more applicable to the lower latitudes of the United States and their applicability is complicated by the common practice of crop rotation.  A reapplication interval of 14 days is labeled for a variety of uses.  In the absence of label directions, a reapplication interval of 7 days is assumed.  This is the minimum interval assumed to be practical for control of re-emerged weeds following an earlier treatment.
      
Table 2. Maximum Use Patterns for Current Uses of Clethodim [A]
                                  Use Pattern
                               Single App. Rate
                                 (lbs a.i./A)
                           Reapp. Interval B (days)
                           Max. No. of App. per Crop
                        App. Rate per Crop (lbs a.i./A)
                        Annual App. Rate C (lbs a.i./A)
                                App. Method [D]
                           Geographic Applicability
             Fallow land, golf course turf, non-cropped areas [E]
                                     0.25
                                     NS F
                                      NS
                                      NS
                                     4.5 G
                                    Aerial
                                 United States
                                  Alfalfa [I]
                                     0.25
                                      NS
                                      NS
                                     0.50
                                    4.5 [J]
                                    Aerial
                                 United States
Ornamentals, landscaped areas, non-bearing food crops [H], around buildings, bare soil, mulched areas
                                     0.25
                                      14
                                      NS
                                      NS
                                     4.5 G
                                    Ground
                                 United States
                            Grass forage/fodder/hay
                                     0.19
                                      NS
                                      NS
                                      NS
                                     3.4 G
                                    Sprayer
                                    MO only
                                    Clover
                                     0.25
                                      NS
                                      NS
                                     0.25
                                    2.25 J
                                    Aerial
                                 United States
                             Herbs, turnip greens
                                     0.125
                                      14
                                      NS
                                     0.50
                                     2.0 N
                                    Aerial
                                 United States
                              Mustard, vegetables
                                     0.12
                                      14
                                      NS
                                     0.485
                                     1.9 N
                                    Aerial
                     ID only (and OR & WA for mustard)
                                   Radishes
                                     0.125
                                      14
                                      NS
                                     0.25
                                   1.25 [M]
                                    Aerial
                                 United States
                                     Mint
                                     0.25
                                      14
                                      NS
                                     0.50
                                     1.0 K
                                    Aerial
                                 United States
                                   Sod farms
                                     0.25
                                      NS
                                      NS
                                     0.50
                                    1.0 [L]
                                    Aerial
                            AL, FL, GA, NC, SC only
Beets, brassica vegetables, carrots, cranberries, cucurbit vegetables, fruiting vegetables, leafy vegetables, strawberries
                                     0.125
                                      14
                                      NS
                                     0.50
                                    1.0 [L]
                                    Aerial
                                 United States
Dried beans, Christmas trees, cotton, forest trees, peanuts, potatoes, root & tuber vegetables, sainfoin, soybeans, sugar beets, sunflowers, sweet potatoes, tomatoes, trefoil, yams
                                     0.25
                                      NS
                                      NS
                                     0.50
                                     0.50
                                    Aerial
                                 United States
                                    Lentils
                                     0.25
                                      14
                                      NS
                                     0.50
                                     0.50
                                    Aerial
                                 United States
                                Garlic, onions
                                     0.25
                                      NS
                                       2
                                     0.50
                                     0.50
                                 Chemi-gation
                             Except ID, MT, OR, WA
          Tree fruits, tree nuts, asparagus, hops, safflower, sesame
                                     0.125
                                      NS
                                      NS
                                     0.50
                                     0.50
                                    Aerial
                                 United States
                                     Sage
                                     0.24
                                      NS
                                      NS
                                     0.485
                                     0.485
                                    Ground
                                    NC only
                                   Shallots
                                     0.24
                                      14
                                      NS
                                     0.485
                                     0.485
                                    Aerial
                                 United States
      Artichokes, bushberries including cranberries, caneberries, peaches
                                     0.12
                                      14
                                      NS
                                     0.485
                                     0.485
                                    Aerial
                                 United States
                                     Flax
                                     0.125
                                      NS
                                      NS
                                     0.25
                                     0.25
                                    Aerial
                                   Except CA
                                  Meadowfoam
                                     0.125
                                      NS
                                      NS
                                     0.25
                                     0.25
                                    Aerial
                                    OR only
                                     Seeds
                                     0.125
                                      NS
                                      NS
                                     0.25
                                     0.25
                                    Aerial
                                  MN, ND only
                                     Kenaf
                                     0.125
                                      NS
                                      NS
                                     0.25
                                     0.25
                                    Ground
                                    NC only
                                    Canola
                                     0.10
                                      NS
                                      NS
                                     0.25
                                     0.25
                                    Aerial
                                 United States
                              Wildlife food plots
                                     0.24
                                      14
                                      NS
                                     NA F
                                     0.24
                                  Not stated
                                 United States
        Succulent beans, legume vegetables, dried & succulent peas
                                     0.125
                                      NA
                                       1
                                   0.125 [O]
                                     0.125
                                    Aerial
                                 United States
                                 Corn (field)
                                     0.045
                                      NA
                                       1
                                     0.045
                                     0.045
                                    Aerial
                                 United States
A  Listed use patterns represent those of the maximum use pattern and do not represent all labeled use patterns for that use.
B  Reapplication intervals of 14 days were labeled for a variety of uses.  In the absence of label directions, a reapplication interval of 7 days is assumed for control of emerged weeds.
C  The annual application rate accounts for how many crops may occur per year.  For perennial crops (e.g., alfalfa), the number of cuttings per year was used.  Source: USEPA, 2007.
D  Aerial application is assessed unless it is not allowed for the use.
E  Non-cropped areas include fallow agricultural land, rights-of-way, around airports, electric utilities, commercial buildings, manufacturing plants, storage yards, rail yards, fence lines, parkways, golf courses, uncultivated areas, and beneath greenhouse benches.
F  NS means "not stated."  NA means "not applicable."
G  For non-cropped areas, fallow land, golf course turf, and hay, eighteen applications were assumed in the absence of a labeled annual application limit.
H  Non-bearing crops include apples, berries including strawberries, citrus fruits, grapes, olives, pears, stone fruits, and tree nuts.
I  Alfalfa use pattern includes an alfalfa plus clover mixture.
J  For alfalfa, nine cuttings may occur per year in California.  Nine cuttings were assumed for clover as well (USEPA, 2007).
K  Annual application rate is 1.04 lbs a.i./A for spearmint and 0.52 lbs a.i./A for peppermint.
L  Two crops of sod, beets, and most brassica and leafy vegetables may be grown per year (USEPA, 2007).
M  Radishes may have 5 crops per year (USEPA, 2007).
N  Turnip greens and mustard greens may have 4 crops per year (USEPA, 2007).
O  The seasonal application rate limit is stated as 0.50 lbs a.i./A; however, no more than one application of 0.125 lbs a.i./A may be applied per season.  Therefore, the practical seasonal rate limit is 0.125 lbs a.i./A.

 Environmental Fate Characterization

      Clethodim is microbially oxidized to moderately persistent degradates within days of application.  Clethodim is soluble in water up to 29 mg/L and will not appreciably volatilize or bioconcentrate in fish.  The compound and its degradates are mobile in soil and may be transported to surface and ground waters.  The available environmental fate data for clethodim are listed in Table 3.  The information in this section is provided to expand the brief characterization provided in the 2008 problem formulation for registration review (USEPA, 2008).
      
Table 3. Chemical Properties and Environmental Fate Parameters of Clethodim
Parameter
Value
Source
                     Selected Physical/Chemical Parameters
Molecular mass (molecular formula)
359.92 g/mol (C12H10ClN3O)
(Calculated)
Vapor pressure (25 °C)
<1 x 10[-][7] torr
MRID 48881401
Aqueous solubility (20C)
29 mg/L
MRID 48881405
Henry's Law Constant (25 °C)
<2 x10[-][9] atm-m[3]/mol
(Calculated)
Log octanol-to-water partition coefficient (log KOW)
4.81
MRID 48881405
Dissociation constant (pKa)
4.62
MRID 48881405
                             Persistence in Water
Hydrolysis half-life (25C) [A]
pH 5: 28 days
pH 7: 289 days
pH 9: 305 days
MRID 40974520
Aqueous photolysis half-life (25C)
pH 5: 1.5-1.7 days
pH 7: 2.5-6.8 days
pH 9: 6.0-9.6 days
MRID 41030133,
41030134
Anaerobic aquatic metabolism half-life (25C)
233 days
MRID 41652301
                              Persistence in Soil
Aerobic soil metabolism half-life (25°C)
1.2 days
MRID 41376801

2.5 days
MRID 40974522
Photolysis half-life in soil (13-23C)
7 days
MRID  41030135
                                   Mobility
Freundlich soil-water partition coefficients (KF); Freundlich organic carbon-normalized coefficients (KFOC)
0.08, 0.15, 0.46, 0.51, 1.57 L/kg;
4.9, 65, 68, 132, 271 L/kgOC
MRID 40974523
                               Field Dissipation
Terrestrial field dissipation half-life
Half-lives and leaching depths could not be calculated due to high LOQs (20 ppb) relative to dose rates (MS cotton; CA cotton; NC soybean; and IA soybean sites)
MRID 41030207

MRID 41030208

(MRID 41030209) [B]

(MRID 41030210) [B]
                             Fish Bioconcentration
Fish bioconcentration factors (steady-state, total residues); depuration rate
0.7-2.1 (edible), 3.0-4.0 (inedible), 2.3-3.6 (whole fish); >70% depuration in 3 days
MRID  40974524/ 40974531
[A] Technically, clethodim underwent nonhydrolytic, abiotic, thermal degradation in the presence of aqueous buffers.  Half-life values only represent the propyl-labeled studies because allyl-labeled clethodim was not studied at pH 9 and was studied at an elevated concentration at pH 5 and 7.
[B] Studies with MRIDs in parentheses are provisional until reviewed.

      Clethodim and many of its degradates have multiple types of isomerization.  The compound is an equilibrium mixture of four tautomers, which are predominantly two keto-enol tautomers at the cyclohexene ring (MRID 41376801).  The other two tautomers, which are cyclohexane diones with tautomerization at the oxime, may be intermediates.  Clethodim also has two chiral centers along the thiopropyl side chain and two double bonds that can form cis-trans isomers.  Clethodim and its degradates include only the E-isomer of the chloropropenyl group.  Clethodim is a racemic mixture, however, of the sixteen combinations of the other two cis-trans isomers, four enantiomers, and two predominant tautomers.  MRID 41376801 Appendix D provides a more complete discussion of the complex isomerism in clethodim and its degradates.  Isomerism complexity often complicates study results because multiple observed chromatograph peaks may represent isomers or tautomers of the same compound.
      
      In the fish bioconcentration (BCF) studies, clethodim and its sulfoxide were identified and quantified in the tank water and identified in the fish.  Residue concentrations were too low to quantify clethodim or its sulfoxide in fish or to identify any other metabolites in fish that may have been present at lower concentrations than the sulfoxide.  Total-residue fish BCF values for whole fish were 2.3-3.6x.  Allyl-labeled residues depurated from fish by 72% in 14 days.  Cyclohexenone-labeled residues depurated from fish faster, by >70% in 3 days.  Due to the low bioconcentration of clethodim residues and their relatively rapid depuration, bioaccumulation of clethodim residues of concern in aquatic organisms is not expected.
      
      Degradates of clethodim and their amounts formed in submitted studies are listed in Table 5.  Clethodim sulfoxide is the main degradate of clethodim, formed in soil at up to 75% of the applied compound three days after application.  Clethodim sulfone forms up to 16% of the applied 30 days after application.  These degradates are more persistent than the parent compound, but not expected to generally persist, with 0.4-0.9% of the applied remaining 380 days after application.  Clethodim oxazole sulfone does persist, with up to 10% of the applied at study termination, 380 days after application.  Nine additional major photolysis degradates are formed in shallow, clear, well-lit water bodies; however, most of the applied clethodim is likely to biodegrade prior to reaching a water body, prior to photolyzing, or both.

Clethodim's sulfoxide and sulfone are more mobile than clethodim in soil.  However, clethodim's oxazole sulfoxide is less mobile in soil than the parent compound.  Table 4 lists the available environmental fate information for degradates of clethodim, which is only focused on soil mobility.
      
Table 4. Environmental Fate Parameters of Clethodim Degradates
Parameter
Degradate
Value
Source
Freundlich organic carbon-normalized coefficients (KFOC)
Clethodim sulfoxide
12, 27, 38, 57, 86 L/kgOC
MRID 40974523

Clethodim sulfone
6, 13, 19, 29, 43 L/kgOC

Clethodim oxazole sulfoxide
50, 135, 429, 460, 771 L/kgOC

Table 5. Chemical Names and Structures of Clethodim and Its Environmental Degradates [A]
Code Name/ Synonym
Chemical Name
                              Chemical Structure
Study Type
Ref. [B]
(MRID)
                               Maximum %AR (day)
                           Final %AR (study length)
                                    PARENT
Clethodim
RE-45601
(Z-isomer is RE-46116)
(5RS)-2-{(1EZ)-1-[(2E)-3-chloroallyloxyimino]propyl}-5-[(2RS)-2-(ethylthio)propyl]-3-hydroxycyclohex-2-en-1-one

CAS No.: 99129-21-2
Formula: C17H26ClNO3S
MW: 359.92 g/mol
SMILES:C1C(CC(=C(C1=O)\C(CC)=N\OCC=CCl)O)CC(C)SCC
                                       
                                       

                            TRANSFORMATION PRODUCTS
Clethodim sulfoxide
RE-45924
CLSO
SOX
(5RS)-2-{(1EZ)-1-[(2E)-3-chloroallyloxyimino]propyl}-5-[(2RS)-2-(ethylsulfinyl)propyl]-3-hydroxycyclohex-2-en-1-one

Formula: C17H26ClNO4S
MW: 375.92 g/mol
SMILES:C1C(CC(=C(C1=O)\C(CC)=N\OCC=CCl)O)CC(C)[S](CC)=O
                                       
Hydrolysis  - pH 5
Hydrolysis  - pH 7
Hydrolysis  - pH 9
40974520
                                  2.6% (0 d)
                                  3.0% (14 d)
                                  5.3% (14 d)
                                  1.7% (32 d)
                                  2.0% (32 d)
                                  4.5% (32 d)

                                       
Aq. photo. -  dark
Aq. photo. -  light
41030133
                                  5.2% (3 d)
                                   14% (3 d)
                                  1.4% (10 d)
                                   nd (30 d)

                                       
Aq. photo. -  dark
Aq. photo. -  light
41030134
                                  3.6% (3 d)
                                  14% (30 d)
                                  2.7% (10 d)
                                  14% (30 d)

                                       
Aq. photo. -  dark
Aq. photo. -  light
44066701
                                  4.6% (25 d)
                                  7.6% (1 d)
                                  4.4% (30 d)
                                   nd (30 d)

                                       
Soil photo. -  dark
Soil photo. -  light
41030135
                                   64% (7 d)
                                   74% (4 d)
                                   64% (7 d)
                                   71% (7 d)

                                       
Aerobic soil
40974522
                                   65% (7 d)
                                  nd (380 d)

                                       
Aerobic soil
41376801
                                   75% (3 d)
                                 0.9% (121 d)

                                       
Anaerobic aquatic
41652301
                              23-38% [B] (181 d)
                              23-38% [B] (181 d)
Clethodim sulfone
RE-47253
ONE
(5RS)-2-{(1EZ)-1-[(2E)-3-chloroallyloxyimino]propyl}-5-[(2RS)-2-(ethylsulfonyl)propyl]-3-hydroxycyclohex-2-en-1-one

Formula: C17H26ClNO5S
MW: 391.92 g/mol
SMILES:C1C(CC(=C(C1=O)\C(CC)=N\OCC=CCl)O)CC(C)[S](CC)(=O)=O
                                       
Aerobic soil
40974522
                                  12% (62 d)
                                 0.4% (380 d)

                                       
Aerobic soil
41376801
                                  16% (30 d)
                                 5.6% (121 d)

                                       
Anaerobic aquatic
41652301
                                  0.6% (42 d)
                                  nd (181 d)
Clethodim oxazole
RE-47365
CLOX
OX
(+-)-6,7-dihydro-2-ethyl-6-[2-(ethylthio)propyl]-4(5H)-benzoxazolone

Formula: C14H21NO2S
MW: 267.39 g/mol
SMILES:C12=C(OC(=N1)CC)CC(CC2=O)CC(C)SCC
                                       
Hydrolysis  - pH 5
Hydrolysis  - pH 7
Hydrolysis  - pH 9
40974520
                                  54% (32 d)
                                  7.3% (32 d)
                                  5.1% (32 d)
                                  54% (32 d)
                                  7.3% (32 d)
                                  5.1% (32 d)

                                       
Aq. photo. -  dark
Aq. photo. -  light
41030134
                                  14% (2.5 d)
                                  5.5% (3 d)
                                  14% (2.5 d)
                                  0.5% (14 d)

                                       
Aq. photo. -  dark
Aq. photo. -  light
44066701
                                  34% (30 d)
                                  12% (1.5 d)
                                  34% (30 d)
                                   nd (30 d)

                                       
Aerobic soil
40974522
                                  2.1% (3 d)
                                  nd (380 d)

                                       
Anaerobic aquatic
41652301
                                 1.2% (181 d)
                                 1.2% (181 d)
Clethodim oxazole sulfoxide
RE-47796
OXSO
OXSOX
(+-)-6,7-dihydro-2-ethyl-6-[2-(ethylsulfinyl)propyl]-4(5H)-benzoxazolone

Formula: C14H21NO3S
MW: 283.39 g/mol
SMILES:C12=C(OC(=N1)CC)CC(CC2=O)CC(C)[S](CC)=O
                                       
Aq. photo. -  dark
Aq. photo. -  light
41030134
                                 1.2% (2.5 d)
                                  5.9% (10 d)
                                  1.0% (14 d)
                                   nd (30 d)

                                       
Aq. photo. -  dark
Aq. photo. -  light
44066701
                                  1.9% (30 d)
                                  8.9% (6 d)
                                  1.9% (30 d)
                                  2.2% (30 d)

                                       
Aerobic soil
40974522
                                  6.1% (90 d)
                                 3.0% (380 d)

                                       
Aerobic soil
41376801
                                  5.3% (30 d)
                                 4.9% (121 d)

                                       
Anaerobic aquatic
41652301
                                  10% (70 d)
                                 7.7% (181 d)
Clethodim oxazole sulfone
RE-47797
OXONE
(+-)-6,7-dihydro-2-ethyl-6-[2-(ethylsulfonyl)propyl]-4(5H)-benzoxazolone

Formula: C14H21NO4S
MW: 299.39 g/mol
SMILES:C12=C(OC(=N1)CC)CC(CC2=O)CC(C)[S](CC)(=O)=O
                                       
Aerobic soil
40974522
                                  10% (380 d)
                                  10% (380 d)

                                       
Aerobic soil
41376801
                                 8.6% (121 d)
                                 8.6% (121 d)

                                       
Anaerobic aquatic
41652301
                                 5.1% (181 d)
                                 5.1% (181 d)
Clethodim imine
RE-47686
CLIM
IMINE
(+-)-5-[2-(ethylthio)propyl]-3-hydroxy-2-(1-iminopropyl)cyclohex-2-enone

Formula: C14H23NO2S
MW: 269.41 g/mol
SMILES:C1C(CC(=C(C1=O)C(CC)=N)O)CC(C)SCC
                                       
Aq. photo. -  light
41030134
                                  18% (2.5 d)
                                  18% (2.5 d)

                                       
Aq. photo. -  dark
Aq. photo. -  light
44066701
                                1.4% (25-30 d)
                                   28% (2 d)
                                  1.4% (30 d)
                                   nd (30 d)

                                       
Anaerobic aquatic
41652301
                              1.3-17% [B] (181 d)
                              1.3-17% [B] (181 d)
Clethodim imine sulfoxide
RE-47718
IMSO
IMSOX
(+-)-5-[2-(ethylsulfinyl)propyl]-3-hydroxy-2-(1-iminopropyl)cyclohex-2-enone

Formula: C14H23NO3S
MW: 285.41 g/mol
SMILES:C1C(CC(=C(C1=O)C(CC)=N)O)CC(C)[S](CC)=O
                                       
Aq. photo. -  light
41030134
                                  23% (21 d)
                                  20% (30 d)

                                       
Aq. photo. -  dark
Aq. photo. -  light
44066701
                                  0.5% (25 d)
                                  30% (10 d)
                                  0.4% (30 d)
                                  11% (30 d)

                                       
Aerobic soil
40974522
                                1.1% (14-30 d)
                                  nd (380 d)

                                       
Aerobic soil
41376801
                                  2.1% (3 d)
                                 2.0% (121 d)

                                       
Anaerobic aquatic
41652301
                                 1.6% (181 d)
                                 1.6% (181 d)
Clethodim imine ketone
IMK
(+-)-5-[propyl-2-one]-3-hydroxy-2-(1-iminopropyl)cyclohex-2-enone

Formula: C12H17NO3
MW: 223.27 g/mol
SMILES:C1C(CC(=C(C1=O)C(CC)=N)O)CC(=O)C
                                       
Aq. photo. -  light
41030134
                                12% (15, 25 d)
                                  9.5% (30 d)

                                       
Aq. photo. -  light
44066701
                                  15% (2-4 d)
                                  5.8% (30 d)
Clethodim trione
TRIONE
(+-)-5-[2-(ethylthio)propyl]-3-hydroxy-2-(1-oxopropyl)cyclohex-2-enone

Formula: C14H22O3S
MW: 270.39 g/mol
SMILES:C1C(CC(=C(C1=O)C(CC)=O)O)CC(C)SCC
                                       
Aq. photo. -  light
44066701
                                  2.9% (7 d)
                                   nd (30 d)
Clethodim trione sulfoxide
RE-47386
TRISO
(+-)-5-[2-(ethylsulfinyl)propyl]-3-hydroxy-2-(1-oxopropyl)cyclohex-2-enone

Formula: C14H22O4S
MW: 286.39 g/mol
SMILES:C1C(CC(=C(C1=O)C(CC)=O)O)CC(C)[S](CC)=O
                                       
Aq. photo. -  light
41030134
                                 4.4% (0.5 d)
                                 2.7% (2.5 d)

                                       
Aq. photo. -  light
44066701
                                 18% (20-30 d)
                                  18% (30 d)
Clethodim trione ketone
(+-)-5-[propyl-2-one]-3-hydroxy-2-(1-oxopropyl)cyclohex-2-enone

Formula: C12H16O4
MW: 224.26 g/mol
SMILES:C1C(CC(=C(C1=O)C(CC)=O)O)CC(=O)C
                                       
Aq. photo. -  light
41030134
                                  5.3% (20 d)
                                  4.8% (30 d)
Clethodim imine ketone
IMK
(+-)-5-[propyl-2-one]-3-hydroxy-2-(1-iminopropyl)cyclohex-2-enone

Formula: C12H17NO3
MW: 223.27 g/mol
SMILES:C1C(CC(=C(C1=O)C(CC)=N)O)CC(=O)C
                                       
Aq. photo. -  light
41030134
                                12% (15, 25 d)
                                  9.5% (30 d)

                                       
Aq. photo. -  light
44066701
                                  15% (2-4 d)
                                  5.8% (30 d)
DME sulfoxide
RE-52453
DMESO
(+-)-3-[2-(ethylsulfinyl)propyl]pentanedioic acid

Formula: C10H18O5S
MW: 250.32 g/mol
SMILES:C(C(CC(=O)O)CC(C)[S](CC)=O)C(=O)O
                                       
Aq. photo. -  light
41030134
                                  49% (30 d)
                                  49% (30 d)

                                       
Aq. photo. -  light
44066701
                                 11% (20-30 d)
                                  11% (30 d)
DME sulfone
DMESO2
(+-)-3-[2-(ethylsulfonyl)propyl]pentanedioic acid

Formula: C10H18O6S
MW: 266.32 g/mol
SMILES:C(C(CC(=O)O)CC(C)[S](CC)(=O)=O)C(=O)O
                                       
Aq. photo. -  light
41030134
                                  7.4% (30 d)
                                  7.4% (30 d)
Unknown-2
(+-)-3-[propyl-2-one]pentanedioic acid
 (proposed chemical name)
                                       
                         (proposed chemical structure)
Aq. photo. -  light
41030134
                                  7.4% (30 d)
                                  7.4% (30 d)
3-chloroprop enal

(E)-3-chloropropenal

Formula: C3H3ClO
MW: 90.51 g/mol
SMILES:O=CC=CCl
                                       
Aq. photo. -  light
41030133
                                  31% (2.5 d)
                                  31% (2.5 d)
Chloroallyl alcohol
RE-46261
(E)-3-chloroallyl alcohol
 
Formula: C3H5ClO
MW: 92.53 g/mol
SMILES:OCC=CCl
                                       
Hydrolysis  - pH 5
Hydrolysis  - pH 7
40974520
                                  35% (30 d)
                                  5.3% (30 d)
                                  35% (30 d)
                                  5.3% (30 d)

                                       
Aq. photo. -  dark
Aq. photo. -  light
41030133
                                  11% (2.5 d)
                                  31% (15 d)
                                  11% (2.5 d)
                                  29% (30 d)
Unextracted residues
(not applicable)
                               (not applicable)
Soil photo. -  dark
Soil photo. -  light
41030135
                                  5.5% (7 d)
                                  6.2% (7 d)
                                  5.5% (7 d)
                                  6.2% (7 d)

                                       
Aerobic soil
40974522
                                  23% (183 d)
                                  18% (380 d)

Aerobic soil
41376801
                                  29% (125 d)
                                  29% (125 d)

                                       
Anaerobic aquatic
41652301
                                  11% (181 d)
                                  11% (181 d)
Carbon dioxide
Carbon dioxide

Formula: CO2
MW: 44.01 g/mol
SMILES:O=C=O
                                       
Aq. photo. -  light
41030133
                                  12% (30 d)
                                  12% (30 d)

Soil photo. -  dark
Soil photo. -  light
41030135
                                  3.7% (7 d)
                                  4.2% (7 d)
                                  3.7% (7 d)
                                  4.2% (7 d)

Aerobic soil
40974522
                                  54% (380 d)
                                  54% (380 d)

Aerobic soil
41376801
                                  57% (121 d)
                                  57% (121 d)

Anaerobic aquatic
41652301
                                 0.1% (181 d)
                                 0.1% (181 d)
[A] nd means "not detected".  AR means "applied radioactivity".  MW means "molecular weight".  Bolded values are laboratory study values >10%AR.
[B] These values have a range because portions of the sulfoxide and imine degradates co-eluted and the proportions of the mixture are unclear, i.e., whether the residue was one degradate, the other, or both.

 Exposure Modeling
      
      The available physical/chemical and environmental fate properties of clethodim and its degradates of concern were used to calculate exposure model input parameters to estimate potential drinking water concentrations (EDWC).  The compounds of concern include those with 5-(2-ethylthiopropyl)-5-hydroxycyclohexene-3-one or 5-(2-ethylthiopropyl)cyclohexene-3-one moieties.  Half-lives calculated for the residues of concern (ROC) are listed in Table 6.  Also listed is the soil mobility of the most prominent residue of concern, clethodim sulfoxide, which is used to represent the residues of concern.
      
Table 6. Environmental Fate Parameters of Clethodim Residues of Concern (ROC)
Parameter
Value
Source
                             Persistence in Water
Hydrolysis half-life (25C)
pH 5: 414 days
pH 7: 3,660 days
pH 9: 45,000 days
MRID 40974520
Aqueous photolysis half-life (25C)
pH 5: 2.1-8.0 days
pH 7: 4.1-24 days
pH 9: 7.5-27 days
MRID 41030133,
41030134
Anaerobic aquatic metabolism half-life (25C)
1217 days
MRID 41652301
                              Persistence in Soil
Aerobic soil metabolism half-life (25°C)
44 days
MRID 41376801

87 days
MRID 40974522
Photolysis half-life in soil (13-23C)
No observable degradation
MRID  41030135
                                   Mobility
Freundlich organic carbon-normalized coefficients (KFOC)
12, 27, 38, 57, 86 L/kgOC
MRID 40974523
      
      The Total Residue (TR) modeling approach was used to estimate aquatic exposure with the ROC half-lives (from Table 6), the soil mobility of clethodim sulfoxide (from Table 6), and the physical/chemical properties of clethodim (from Table 3).  The TR approach is appropriate because there are multiple degradates of concern, for none of which a full environmental fate data profile is available.  Because up to 75% of clethodim oxidizes to its sulfoxide, the sulfoxide is the most prominent degradate of concern.  With a mean KOC value of 44 L/kg, clethodim sulfoxide is more mobile in soil than clethodim and its oxazole sulfoxide, but less mobile in soil than clethodim sulfone; therefore, use of its KOC value in modeling may be representative and may be conservative, but is not a worst case assumption.
      
 Surface Water
      
      Surface water sourced drinking water exposure was estimated using the Tier I screening model FIRST (v1.1.1; Mar. 26, 2008).  Input parameters for FIRST follow in Table 7.  The modeled use pattern represents the maximum labeled use pattern for alfalfa, fallow land, and non-cropped areas (aerial application at 0.25 lbs a.i./A), with eighteen applications per year assumed in the absence of an annual application rate limit.  A reapplication interval of 7 days was modeled in the absence of label directions because it is the minimum interval assumed to be practical for control of re-emerged weeds.

Table 7. FIRST Input Parameters for Clethodim ROC [A]
Input Parameter
Value
Comments
Source
Application rate (lbs a.i./A)
0.25
Maximum labeled single application rate
Current labels
Number of applications per year
18
Maximum number of applications per year assumed in the absence of label directions
Current labels
Application interval (d)
7
Reapplication interval assumed in the absence of label directions
Current labels
Percent cropped area
100%
Default for agricultural plus non-agricultural uses
USEPA, 2012c
Organic Carbon Partition Coefficient (KOC) (L/kg)
44
Represents the mean KFOC value (n=5) for clethodim sulfoxide, the most prominent degradate of concern 
MRID 40974523
Aerobic soil metabolism half-life (days)
132
Represents the upper 90% confidence bound on the mean of two half-lives for the residues of concern
MRIDs 40974523 and 41376801
Wetted in?
No
Not required
Current labels
Method of application
Aerial
Allowed application method
Current labels
Solubility in water (ppm)
29
Solubility in water at 20°C
MRID 48881405
Aerobic aquatic metabolism
half-life (days)
264
Represents the aerobic soil metabolism half-life input times two in the absence of data
(calculated)
Aqueous photolysis half-life (days)
24
Represents the maximum aqueous photolysis half-life at pH 7 for the residues of concern
MRID 41030134
 [A]  Source data are in Tables 2, 3 and 6.

      Chemical property input values were chosen in accordance with current input parameter guidance (USEPA, 2009).  Based on analysis of total residues of concern, the 90% confidence bound on the mean half-life for aerobic soil metabolism (132 d) was selected.  In the absence of data, the aerobic aquatic metabolism half-life input (264 d) was selected to be two times the soil metabolism input value.  The aqueous photolysis half-life input represents the maximum study value at pH 7.  The KOC input (44 L/kg) represents the mean value for clethodim sulfoxide, which is the most prominent residue of concern.
      
      Standard percent cropped areas (PCA) are used as conservative default estimates of the extent of watershed on which agricultural crops of unknown specific PCA are grown (USEPA, 2012c).  Because clethodim is labeled for use on both agricultural and non-agricultural sites, PCA values cannot be used to modify clethodim exposure estimates.
      
      Table 8 presents the ROC EDWCs in surface water from FIRST.

Table 8.  Screening Surface Water EDWCs for Clethodim
Source (Tier: Model)
                           1-in-10-year Peak (μg/L)
                       1-in-10-year Annual Mean (μg/L)
Surface water (Tier I: FIRST)
                                      330
                                      137
      
 Ground Water
      
 SCI-GROW
      
      Current modeling methodology is to estimate exposure in ground water using both SCI-GROW (v2.3, Jul. 29, 2003) and PRZM-GW (v1.01, Dec. 26, 2012) (USEPA, 2012d).  Input parameters for SCI-GROW appear in Table 9.  The lowest Freundlich organic carbon partition coefficient for clethodim sulfoxide (KFOC = 12 L/kgOC) was selected because the sulfoxide is more mobile in soil than the parent compound and is the most prominent degradate of concern.  The mean total residue half-life (66 d) from two aerobic soils was selected to approximate the biodegradation kinetics of the residues of concern in aerobic soil environments.
 
Table 9. SCI-GROW Input Parameters for Clethodim ROC [A]
Input Parameter
Value
Comments
Source
Application Rate
(lbs a.i./A)
0.25
Maximum labeled single application rate
Current labels
Applications per Year
18
Maximum number of applications per year assumed in the absence of label directions
Current labels
Organic Carbon Partition Coefficient (KOC) (L/kgOC)
12
Represents the lowest KFOC value for clethodim sulfoxide, the most prominent degradate of concern, chosen because of the greater than three-fold variation in values
MRID 40974523
Aerobic Soil Metabolism Half-life (days)
66
Represents the mean of two half-lives for the residues of concern
MRIDs 40974523 and 41376801
 [A]  Source data are in Tables 2 and 6.
      
      The SCI-GROW output represents the highest 90-day running mean concentration following one year of application.  The output value is 27 ug/L.
      
 PRZM-GW
      
      PRZM-GW model inputs are listed in Table 10.  Application inputs represent the maximum use pattern of 4.5 lbs a.i./acre applied per year.  PRZM-GW currently is limited to 11 application events per year.  Therefore, starting May 1[st], 11 applications of 0.41 lbs a.i./A (4.5 lbs a.i./A / 11) were applied with a fourteen-day reapplication interval that spreads the applications across the growing season to September 19[th].  These dates of application are within the weed-growing season and selected to result in high-end concentrations in ground water due to vulnerability to precipitation.
      
      Chemical inputs for the residues of concern follow the PRZM-GW Input Parameter Guidance (USEPA, 2012b).  The aerobic soil metabolism half-life model input (132 days) is the upper 90[th] percentile confidence bound on the mean of two residue-of-concern half-lives from studies conducted at 25°C.  The organic carbon partition coefficient (44 L/kgOC) is the mean of five values for clethodim sulfoxide, which is the most prominent degradate of concern and more mobile in soil than clethodim.
      
Table 10. PRZM-GW Input Parameters for Clethodim ROC [A]
                                Input Parameter
                                     Value
                                 Justification
                                    Source
                               Application Rate
                                0.46 kg a.i./ha
Maximum annual application rate divided by 11 applications per year due to PRZM-GW limitations
                                Current labels
                             Applications per Year
                                11; every year
                                       
                                       
                            Reapplication interval
                                    14 days
                  Spreads applications from May 1 to Sep. 19
                                 Current label
                           Initial application date
                                     May 1
Selected within growing season and for high-end vulnerability due to precipitation
                                 (calculated)
                             Hydrolysis Half-life
                                    3660 d
        Represents the value at pH 7 for clethodim residues of concern
                                 MRID 40974520
                            Aerobic Soil Metabolism
                                   Half-life
                                     132 d
Represents the upper 90% confidence bound on the mean of two half-lives for the residues of concern
                          MRIDs 40974523 and 41376801
                  Organic Carbon Partition Coefficient (KOC)
                                    44 L/kg
Represents the mean KFOC value (n=5) for clethodim sulfoxide, the most prominent degradate of concern
                                 MRID 40974523
 [A]  Source data are in Tables 2 and 6.
      
      All six available scenarios were modeled as surrogates for non-cropped, fallow, or alfalfa use sites with the maximum annual application rate of 4.5 lbs a.i./A.  The Wisconsin corn scenario produced the highest EDWCs, which is typical, with the other scenarios resulting in EDWCs 41-84% less.  PRZM-GW outputs are listed in Table 11.

Table 11. PRZM-GW Output for Clethodim Uses [A]
                                   Use Site
                               Modeled Scenario
                           Max. Daily Conc. (ug/L)
                         Mean Breakthrough Time (yrs)
                        Post-breakthrough Mean (ug/L)
                              Non-cropped/alfalfa
                                   DMV corn
                                      828
                                      1.6
                                      602
                              Non-cropped/alfalfa
                                   FL citrus
                                      845
                                      1.6
                                      608
                              Non-cropped/alfalfa
                                   FL potato
                                      225
                                      3.2
                                      194
                              Non-cropped/alfalfa
                                   GA peanut
                                      314
                                      4.7
                                      271
                              Non-cropped/alfalfa
                                   NC cotton
                                      686
                                      3.9
                                      555
                              Non-cropped/alfalfa
                                    WI corn
                                     1430
                                      4.3
                                     1150
[A] Maximum values are in bold.
      
      Figure 1 displays concentrations in ground water over time for the Wisconsin corn scenario.  EDWCs were not highly sensitive to application dates, which is expected for residues in ground water since the medium typically moves slower than surface water.  For example, the maximum daily concentration for the Wisconsin scenario was 1,390 ug/L (3% less) for applications beginning on April 1[st] rather than May 1[st].
      
                                       
Figure 1. Ground Water EDWCs (ppb) per Time (years) for the Wisconsin Scenario
      
 Modeling Results Summary
      
      Table 12 summarizes the screening-level exposure model results for clethodim ROCs.  
      
Table 12. 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.
      
      Because eighteen applications of clethodim per year are not expected to be applied on any use site, including non-cropped areas and alfalfa, reduced use patterns were modeled to explore the resulting exposure estimates that may better characterize typical use patterns and could be the result of the exposure assessment if use directions on current labels are updated to reflect the reduced use patterns.  If the Wisconsin scenario in PRZM-GW is re-run with a maximum annual application rate of 2.0 lbs a.i./A (8 applications per year at 0.28 kg a.i./A each) rather than 4.5 lbs a.i./A, then the acute EDWC is reduced 57% from 1,430 ug/L to 613 ug/L.  A maximum annual application rate of 1.0 lb a.i./A (4 applications per year at 0.28 kg a.i./A each), which is consistent with the current use on mint, results in an acute EDWC of 295 ug/L.  A maximum annual application rate of 0.5 lbs a.i./A (2 applications per year at 0.28 kg a.i./A each), which is consistent with many current uses including cotton, peanuts, and potatoes, results in an acute EDWC of 148 ug/L (158 ug/L if the initial application date is moved to April 1[st]).  Note that the explored reductions in annual application rate reflect reductions in the number of applications per year and not reductions in the single application rate.
      
      Note, also, that clethodim biodegrades within days of application.  If the degradates of concern are shown to be much less toxic than clethodim, then exposure estimates would be greatly reduced.  The acute EDWC of 1,430 ug/L for the ROCs is reduced to 3.2 ug/L if clethodim alone were the residue of concern.  In shallow, acidic aquifers that are common on the east coast, clethodim-only EDWCs would be <0.1 ug/L, if clethodim's degradates were not of concern.
      
 Monitoring Data
      
      Clethodim does not appear to be an analyte in the following water monitoring programs: the California Department of Pesticide Regulation (CDPR) surface water database (http://www.cdpr.ca.gov/docs/emon/surfwtr/surfcont.htm, the USGS NAWQA surface and ground water database (http://infotrek.er.usgs.gov/apex/f?p=136:1:0::NO:::), the USEPA STORET Data Warehouse (http://www.epa.gov/storet/), and the  USDA Pesticide Data Program drinking water monitoring analyses (http://www.ams.usda.gov/AMSv1.0/ams.fetchTemplateData.do?template=TemplateG&navID=&rightNav1=&topNav=&leftNav=ScienceandLaboratories&page=PDPDownloadData/Reports&resultType=&acct=pestcddataprg).
      
 References

USEPA. 2007. Kaul, M. Maximum Number of Crop Cycles per Year in California for Methomyl Use Sites. U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic Substances, Biological and Economic Analysis Division. Memorandum to the Environmental Fate and Effects Division. Feb. 28, 2007.

USEPA. 2008. Dean, R. and J. Angier. Registration Review  -  Preliminary Problem Formulation for the Ecological Risk Assessment of Clethodim. DP barcode 349758. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Memorandum to the Special Review and Reregistration Division. Aug. 13, 2008.

USEPA.  2009.  Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides.  Version 2.1.  U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division, Oct. 22, 2009.  http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

USEPA. 2012a. Identification and Evaluation of Existing Models for Estimating Environmental Pesticide Transport to Groundwater. Final Report (Draft). U.S. Environmental Protection Agency; Health Canada. Jan. 27, 2012.

USEPA. 2012b. Guidance for Selecting Input Parameters for Modeling Pesticide Concentrations in Groundwater Using the Pesticide Root Zone Model. Version 1.0. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division; Health Canada, Pesticide Management Regulatory Agency, Environmental Assessment Directorate. Oct. 15, 2012.

USEPA. 2012c. Guidance on Development and Use of Percent Cropped Area and Percent Turf Area Adjustment Factors in Drinking Water Exposure Assessments: 2012 Update. Internal Environmental Fate and Effects Division memorandum. U.S. Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention. Mar. 16, 2012.

USEPA. 2012d. Approval of PRZM-GW for Use in Drinking Water Exposure Assessments. Internal Environmental Fate and Effects Division memorandum. U.S. Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention. Dec. 11, 2012. http://www.epa.gov/oppefed1/models/water/przm_gw/wqtt_przm_gw_guidance.htm
      
 Submitted Environmental Fate and Product Chemistry Studies

MRID
Citation Reference

40974520
Pack, D. (1988) Hydrolysis Study on RE-45601: Project ID: MEF-0013/ 8703899. Unpublished study prepared by Chevron Chemical Co. 52 p. 
40974522
Pack, D. (1988) The Aerobic Soil Metabolism of ?Propyl-1-?carbon 14|Clethodium: Project ID: MEF/0014/8721028. Unpublished study prepared by Chevron Chemical Co. 54 p. 
40974523
Pack, D. (1988) Freundlich Soil Adsorption/Desorption Coefficients of Clethodim and Three Metabolites: Project ID: MEF-0102/ 8829844. Unpublished study prepared by Chevron Chemical Co. 122 p. 
40974524
Rose, A.; Suzuki, J. (1988) Characterization of |carbon 14| Residues in Bluegill Sunfish Treated with (Allyl-2-|Carbon 14|- Clethodim or (Cyclohexene-1-One-4,6-?carbon 14|)-Clethodim: Pro- ject ID: MEF-0020. Unpublished study prepared by Chevron Chemi- cal Co. 109 p. 
40974531
Forbis, A. (1987) Uptake, Depuration and Bioconcentration of Allyl-2 |carbon| and Cyclohexene-1-One-4,6|carbon| RE-45601 to Bluegill Sunfish (Lepomis macrochirus): Project ID: S-2827. Un- published study prepared by ABC Laboratories, Inc. 87 p. 
41030133
Chen, Y. (1988) Allyl-2-Carbon 14|-Clethodim Photodegradation in Water: Project ID MEF-0025. Unpublished study prepared by Chev- ron Chemical Co. 93 p. 
41030134
Chen, Y. (1988) 4,6-Ring-Carbon 14|-Clethodim Photodegradation in Water: Project ID MEF-0024. Unpublished study prepared by Chev- ron Chemical Co. 97 p. 
41030135
Chen, Y. (1988) Clethodim Photodegradation on Soil: Project ID MEF- 0022. Unpublished study prepared by Chevron Chemical Co. 44 p. 
41030207
Ho, B. (1989) Field Dissipation Study with Clethodim on Cotton in Mississippi--T7227: Project ID 1641-88-7227. Unpublished study prepared by Chevron Chemical Co. 512 p. 
41030208
Ho, B. (1989) Field Dissipation Study with Clethodim on Cotton in California--T7226: Project ID 1641-88-7226. Unpublished study prepared by Chevron Chemical Co. 427 p. 
41030209
Ho, B. (1989) Field Dissipation Study with Clethodim on Soybean in North Carolina--T7229: Project ID 1641-88-7229. Unpublished study prepared by Chevron Chemical Co. 501 p. 
41030210
Ho, B. (1989) Field Dissipation Study with Clethodim on Soybean in Iowa--T7228: Project ID 1641-88-7228. Unpublished study prepar- ed by Chevron Chemical Co. 536 p. 
41376801
Pack, D. (1990) The Aerobic Soil Metabolism of Clethodim Using ?Ring-4,6-(Carbon 14)|- and ?Allyl-2-(Carbon 14)|-Clethodim Revised January 5, 1990: Lab Project ID: MEF-0015/0016/8914823. Unpublished study prepared by Chevron Chemical Co. 161 p. 
41652301
Tucker, B. (1990) The Anaerobic Aquatic Metabolism of Ring-4,6- ?carbon 14||Clethodim: Lab Project Number: MEF-0141/9004983. Unpublished study prepared by Chevron Chemical Co. 85 p. 
45591605
Hiscock, A., R. Warren, and B. Patterson. A Small-Scale Prospective Groundwater Monitoring Study for Oxamyl. DuPont Report No. AMR 4318-97. Unpublished study conducted by Stone Environmental, Inc., Ecologic, Inc., Agricultural Systems Associates, AGVISE Laboratories, Centre Analytical Laboratories, Inc., and E.I. du Pont de Nemours and Company; submitted by E.I. du Pont de Nemours and Company, Wilmington, DE. Jan. 14, 2002.
48881401
Gregory, A. (2012) Clethodim TGAI: Summary of Product Properties Test Guidelines. Project Number: ALB12/14. Unpublished study prepared by Albaugh, Inc. 8p.
48881405
Li, H. (2012) Chemical and Physical Characterization of Clethodim TGAI: Color, Physical State, Odor, Stability, pH, Oxidation/Reduction, UV-Vis, Boiling Point, Density, Viscosity, Dissociation Constant, Partition Coefficient and Solubility: Final Report. Project Number: NC/2011/083. Unpublished study prepared by Nutrichem Laboratory Co., Ltd. 87p.

Appendix A. Exposure Model Input/Output Files