UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON. D.C. 20460 

MEMORANDUM 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

November 26,2013 

PC Code: 105401 

DP Barcode: 408647 

SUBJECT: Clomazone: Ecological Risk Assessment for IR-4 Proposed New Uses for 

Brassica (Head and Stem Subgroup SA , Peas, and Rhubarb 

FROM: Kristina Garber, Senior Biologist 

f...rJames Lin, Environmental Engine 

ERB2/EFED (7507P) 

THROUGG;-R. David Jones, Ph.D. Senior Agronomist JS-A 

Jean Holmes, Risk Assessment Process Leader 

Brian Anderson, Branch Chief h A.O/ It, 

ERB2/EFED (7507P) f/try' -

TO: Sidney Jackson, Risk Manager Reviewer 

Barbara Madden, Risk Manager, RM 05 

Erik Kraft, Risk Manager Reviewer, RM 25 

Kable Davis, Risk Manager RM 25 

RSB/RD (7504P) 

I. Risk Conclusions 

For the proposed new uses on peas, brassica and rhubarb, the primary risks of clomazone are for 

non-target plants in terrestrial and wetland habitats. Clomazone exposure via spray drift, runoff 

and volatilization poses a risk of effects to growth of plants in non-target terrestrial and semiaquatic habitats. This risk is supported by available ecological incidents indicating that 

clomazone exposure may have caused effects to terrestrial plants hundreds of feet to 2 miles 

from treated sites after volatilizing. 

There is also some concern for mammals, since some application rates result in exposures of 

concern for some mammals. Clomazone applied at 1.5 lb a.i./A poses a risk of acute exposure to 

small listed mammals (that consume short grass) and of chronic exposure to mammals (that 

consume grass). Application rates of0.81 lb a.i./A would not pose risk concerns for mammals. 

This indicates that the proposed use on rhubarb poses a risk to mammals and the proposed uses 

on peas and brassica do not pose a risk of concern. 
Estimated exposures resulting from the proposed new uses are not expected to impact survival, 

growth or reproduction of birds, terrestrial-phase amphibians, reptiles, fish, aquatic invertebrates 

and aquatic plants. 

II. Use Information 

This IR-4 Petition, 2E8136, proposes the following new uses to Command 3ME label (Reg. No. 

279-3158): 

(1) Brassica (head and stem subgroup 5A)- Apply broadcast at 0.67 pints per acre (0.25 lb 

ai/ac); This group includes broccoli, Chinese broccoli, Brussels sprouts, cabbage, Chinese 

(or napa) cabbage, Chinese mustard cabbage, cauliflower, cavalo broccoli, and kohlrabi. 

(2) Rhubarb- Apply broadcast at 4.0 pints per acre (1.5 lb ai/ac) to dormant rhubarb prior to 

leaf emergence; and 

(3) Southern pea- Apply broadcast at 1.3 pints per acre (0.49lb ai/ac). Southern peas (Vigna 

unguiculata) are also known as black-eyed peas, field peas, and cow peas. 

The following precautions and restrictions are notes in the label: 

• Do not apply aerially or through irrigation equipment. 

• Observe all buffer restrictions. 

• Do not apply Command 3ME within 1,200 feet of the following areas: towns and housing 

developments, commercial fruit/nut or vegetable production, commercial greenhouses or 

nurseries. 

• Before application, determine air movement and direction. 

• Do not apply in winds above 10 miles per hour. 

• Do not apply Command 3ME herbicide to non-field areas including fence rows, 

waterways, ditches, and roadsides. 

• When moving spray equipment to noncontiguous sites, do not apply spray or drip from 

tanks, hoses, fittings or spray nozzles and tips. 

• Do not apply when weather conditions favor drift. 

• Use a minimum spray volume of 10 gallons per acre. 

• Use the lowest possible boom height while maintaining a uniform spray pattern, in 

conjunction with nozzle type, size, operating pressure and volume that meet a droplet size 

classification of coarse or greater. 

III. Environmental Fate Summary 

Clomazone is a semi-volatile compound of low to high persistence in various environmental 

compartments and of moderate mobility in soil. The major exposure route of concern is 

displacement of sorbed clomazone from soil by water vapor after rain or during episodes of high 

humidity, volatilization from the soil, and downwind transport of clomazone vapors. Once 

displaced from soil clomazone is not expected to be persistent in air for more than a couple of 

days. 
IV. Risks to Terrestrial Animals 

T-REX was used to estimate upper bound exposure to birds and mammals to clomazone through 

consumption of food items located directly on the treated area. An application rate of 1.5 lb 

a.i./ A was simulated to represent the highest of the proposed new uses considered in this 

assessment. The default foliar dissipation half-life of35-d was used. Note that this value is likely 

an overestimate of the true dissipation of clomazone due to volatility; however, since only one 

application rate is simulated, the half-life does not impact estimated environmental 

concentrations (EECs) and risk quotients (RQs). To represent exposure, the highest EECs 

generated by T-REX are used below. These values are representative of small animals that 

consume short grass. The acute and chronic endpoints used to represent birds and mammals are 

listed in Table 1. Detailed descriptions of these studies are provided in the registration review 

assessment for clomazone. For this assessment, birds are used as surrogates to represent 

terrestrial-phase amphibians and reptiles. 

Table 1. Summary of Specific Measurement Endpoint Values Selected to Calculate RQ 

V a I ues t E o va I ua t e s Ri k ~ or o· tr d d M san amma I A t ssessmen E n d IP01D . ts . Test Species Value ACC/ Classificati 

Assessment Measurement MRIO on 

Endpoint Endpoint 

Survival and Acute mortality: Mallard duck (Anas >2,230 mg ai/kg-bw Ace II Acceptable 

Reproduction of most sensitive p/atyrhynchos) 248475 

Birds, Reptiles avian acute oral 

and toxicity, LD.so 

Amphibians (single-dose) 

Mortality: most Bobwhite quail > 4,990 mg ai/kg-diet Ace II Acceptable 

sensitive subacute (Colinus virginianus) (ppm ai) 248475 

avian LC.so and Mallard duck 

Reproduction: Bobwhite quail I ,020 mg ai/kg-diet (or MRlD Acceptable 

most sensitive ppm ai) 45178101 

avian reproductive 

NOAEC 

Survival and Acute mortality: Norway rat (Rattus I ,369 mg ai/kg-bw Ace# Acceptable 

Reproduction of most sensitive norvegicus) (female) 00117121 

Terrestrial acute oral toxicity, 

Mammals LD.so (single-dose) 

Reproduction: Norway rat I 000 mg ai/kg-diet Ace II Acceptable 

most sensitive 00151108 

reproductive 84.4 mg a.i./kg-bw 

NOAEC/NOAEL 

[based on 

decreased body 

weight in adults 

and offspring) 

Acute dose-based exposures of birds to clomazone at 2230 mg!kg-bw (LDso >2,230 mg ailkgbw) did not cause mortality or sublethal effects. This test dose was an order of magnitude above 

the highest dose-based EEC that would be predicted for this use, which is 410 mg/kg-bw. 
Similarly, for dietary-based sub-acute exposure, no mortality or sublethal effects were observed 

in birds dosed with 4990 mglkg-diet, which is well above the highest EEC predicted by T-REX 

for this use, which was 360 mg/kg-diet. 

The maximum acute dose-based EEC for mammals estimated by T-REX was 343 mglkg-bw, 

which is also an order of magnitude below the unadjusted LDso for rats, i.e., 1369 mglkg-bw. 

Dividing the EEC by the adjusted LDso for small mammals (3009 mg/kg-bw) yields an RQ of 

0.11, which is below the acute LOCs for non-listed mammals (O.S) but exceeds the LOC for 

listed mammals (0.1). This RQ applies to listed small (15 g) mammals that consume 100% short 

grass at the upper bound exposure value. No other food items (i.e., tall grass, broadleafplants, 

seeds, arthropods) yield risk concerns for small, medium (35 g) or large (1000 g) mammals 

(listed and non-listed species). 

On a chronic exposure basis, the NOAEC values for birds and mammals exposed to clomazone 

were 1020 and 1000 mg/kg-diet, respectively. The highest dietary-based EEC generated by TREX for this proposed use is 360 mglkg-diet. This EEC generates chronic RQs for birds and 

mammals of 0.4, which is below the LOC of 1. Dose-based RQs for mammals exceed the LOC 

for small and medium mammals that consume short grass (Table 2). An application rate of0.81 

lb a.i./ A would not exceed any LOCs for mammals. 

Table 2. Dose-based chronic RQs for mammals exposed to clomazone applied at 1.5 lb 

a. i./A. 

Food item SmaU(ISg) Medium (35 e:) Large (1000 g) 

Short Grass 1.9• 1.6* 0.85 

Tall Grass 0.85 0.72 0.39 

Broadleaf plants 1.0 0.89 0.48 

Fruits/pods 0.12 0. 10 0.05 

Arthropods 0.72 0.62 0.33 

Seeds O.Q3 0.02 O.oJ 

*RQ exceeds chrome LOC. 

V. Risks to Aquatic Animals 

The model input parameters for PES based on the general chemical and environmental fate data 

for clomazone are listed in Table 3. The model input parameters used in PES to simulate 

clomazone application and crop management practices are provided in Table 4. The proposed 

highest rate is l.S lb ai/ac for rhubarb use. Rhubarb belongs to the Crop Group 4B for leaf 

petioles subgroup. The representative modeling scenario is MI beans. Clomazone should be 

applied during dormant prior to leaf emergence. The scenario assumes the emergency date of 

June 1, so the application rate is adjusted to May 1S. The EECs of clomazone are provided in 

Table 5. Table 6 includes the acute and chronic endpoints used to derive RQs for fish and 

invertebrates inhabiting fresh and salt water areas (Table 7). Acute and chronic RQs for aquatic 

animals do not exceed LOCs. 
T a e bl 3 . PES Ch emu~ . a II npu tP arame t ers ti or Cl omazone. 

Input Parameter Value Source/comment 

Molecular weight 239.70 

Vapor pressure 1.44 x 10-4 torr Ahrens, 1994 (Herbicide 

Handbook, WSSA, 7th ed.) 

Solubility in water 1100 mg/L Ahrens, 1994 

Hydrolysis half-life stable at pH 5, 7, 9 Ace. No. 2484 76, ref. 29 

Aqueous Photolysis half-life 87 days Ace. No. 073672 

Aerobic Soil metabolism half- 80 days (90% UCL on mean Ace. No. 248476, ref. 30 

life of35, 65, 74 days) 

Anaerobic aquatic metabolism 44 days for total system MRJD 44348403 

half-life 

Aerobic Aquatic metabolism 79 days (90% UCL on mean MRID 44348404, 44348405 

half-life of75, 64, 40.3 days) 

Organic carbon norrnalized 300 Ahrens, 1994 

soil partition coefficient Koc 

Henry's Law Constant 4.13 x 10-8atm-m3

/mol Calculated from vapor 

pressure and solubility 

Air Diffusion Coefficient 3802 cm

2

/day Calculated from molecular 

weight, Da= 

l.SS/((MW)0.65) 

(Schwarzenbach, Gschwend, 

Imboden, 1993, p. 195) 

Enthalpy of Vaporization 20 kJ/mol PRZM default value 

Chemical Application Method 1 (broadcast, surface applied) 

Spray Drift 1% for ground application Guidance for ground 

applications 

Application Efficiency 9~/o Guidance for soil applications 

without incorporation 

Table 4. PRZM Scenario and Input Parameters Describing the Maximum Proposed 

Clomazone Use Patterns. 

Application App. Rate App. Depth, CAM IPSCND Application 

Use Scenario per Efficiency/ Date (lbs a.i.!A) Year em Input Input Spray Drift 

Rhubarb MI Beans 05/15 1.68 1 4 1 I 0.99/0.01 

T a e bl S . PE 1. -m-10 -year A .quatic . EEC so fCI omazone 

Use Scenario Peak (llg/L) 21-day Mean 60-day Mean 

(f.lg/L) (f.li/L) 

Rhubarb Ml Beans 16.40 15.53 13.98 

Sediment Pore Water 

Rhubarb Ml Beans 6.44 6.40 6.30 
Table 6. Summary of Speci.fic Measurement Endpoint Values Selected to Calculate RQ 

VI a ues tE o va I ua tRik e s f< or fib IS an d aqua ti. c mverte b rate A ssessment Ed n lpomts. 

Selected Measurement Endpoint Value and Source 

Assessment Measurement Species Toxicological Endpoint1 Source I 

Endpoint Endpoint and Effect(s) Study 

(ppb a.i. or !Jg a.iJL) Classification 

Survival and Acute mortality: Rainbow trout 19,000 Ace# 248475 

reproduction of most sensitive (Oncorhynchus Rhoderick, 1982 

freshwater acute freshwater mykiss) Acceptable 

vertebrates (fish, fish 96-h LC$0 

amphibians) Reproduction: 2290 Ace# 073830 Anon, 1985 

most sensitive Acceptable 

early life stage 

(ELS)NOAEL 

Survival and Acute mortality: Sheepshead 40,600 Ace# 073830 and 

reproduction of most sensitive minnow 073671 Surprenant 1985 

marine/ acute freshwater (Cyprinodon I 

estuarine fish fish 96-h LCso variegatus) Supplemental 

Reproduction: 4,890 Based on ACR (8.30) 

most sensitive from rainbow trout data 

early life stage 

(ELS)NOAEL 

Survival and Acute mortality: Water flea 5,400 Ace# 248475 Graney, 

reproduction of most sensitive (Daphnia 1982 I 

freshwater acute freshwater magna) 

invertebrates invertebrate 48-h Acceptable 

or 96-h ECso or 

LCS<l 

Reproduction: 2,200 Ace# 073997,073616 

most sensitive Spare and Graney, 1982 

reproductive Acceptable 

NOAEL 

Survival and Acute mortality: Mysid shrimp 566 Ace # 263080 Williams, 

reproduction of most sensitive (Americamysis 1986/ 

marine/ acute invertebrate bahia) 

estuarine 48-h or 96-h ECso Acceptable 

invertebrates or LCso 

Reproduction 231 Based on ACR (2.45) 

NOAEC from D. magna data 

T bl 7 A t d h .k a e . cue an c rome r1s . quo tients for aquatic animals. 

Taxa Acute Chronic 

FW fish 0.00086 0.0061 

SW fish 0.00040 0.0029 

FWinverts 0.0030 0.0071 

SWinverts 0.029 0.067 
VI. Risks to Plants 

Applications of domazone may result in offsite transport via spray drift, volatilization and 

runoff. As a result, non-target plants may be exposed to this herbicide. Table 8 summarizes the 

most sensitive seedling emergence endpoints for monocots and dicots. These values are used to 

determine risks of non-target plants exposed to clomazone through off site transport via spray 

drift and runoff RQs generated using the TerrPlant model are provided in Table 9. RQs exceed 

the LOC for listed and non-listed species of plants inhabiting terrestrial and semi-aquatic habitat. 

RQs for aquatic plants (also provided in Table 9) do not exceed the LOC for non-listed or listed 

species. 

At this time, EFED does not have a standard approach for estimating the amount of clomazone 

that redeposits on non-target areas after volatilization. Therefore, exposure of plants to 

clomazone through volatilization and redeposition is not quantified. Based on available 

ecological incidents indicating that clomazone exposure may have caused effects to terrestrial 

plants hundreds of feet to 2 miles from treated sites after volatilizing, this exposure pathway is of 

concern. 

Table 8. Summary of Spetific Measurement Endpoint Values Selected to Calculate RQ 

V a I E I ues to va uat e Ri s k fi or T . I d A errestna an quattc . PI ant A E d ssessment n lpomts 

Selected Measurement Endpoint Value and Source 

Assessment Measurement Species Toxicological Endpoint Source I 

Endpoint Endpoint and Effect(s) Study 

Classification 

Survival and Monocots: the most Onion Seedling Emergence MRlD 4155750 I 

biomass of non- sensitive seedling (Allium cepa) IC25 = O.Q31 lbs ail A Chetrem, 1990 I 

target plants in emergence or vegetative NOAEC = 0.0062 lbs ail A 

terrestrial and vigor IC25 for non-listed Acceptable 

semi-aquatic and its associated Most sensitive endpoint was height 

areas NOAEC for listed 

species 

Dicots: the most sensitive Lettuce Seedling Emergence MRlD 42165705 

seedling emergence or (Lactuca sativa) 1C25 = 0.0037 lbs ail A Chetrem, 199 I I 

vegetative vigor IC25 for NOAEC "' 0.0008 lbs ail A 

non-listed and its Acceptable 

associated NOAEC for Most sensitive endpoint was dry 

listed species weight 

Survival and Non-vascular species: the Freshwater 5-d ICso = 167 ppb ai MIRD 4499480 I 

biomass of most sensitive biomass diatom (Navicula 5-d NOAEC = 23.6 ppb ai Kranzfelder and 

aquatic vascular ICso for non-listed and its pel/icu/osa) Goble, 1999/ 

and non- associated NOAEC for 

vascular plants listed species Acceptable 

Vascular species: the Duckweed 7-d ICso = 30,200 ppb ai Michel et al., 2004 

most sensitive biomass (Lemna 7-d NOAEC = 7,300 ppb ai (Published) I 

IC50 for non-listed and its paucicostata) 

associated NOAEC for Supplemental 

listed species 
T a bl e 9 . RQ s I or plan t s. 

Habitat Plant Type Listed Status Brassica Peas Rhubarb 

Monocot non-listed 0.48 0.95 2.9* 

Terrestrial 

Monocot listed 2.4* 4.7* IS* 

Dicot non-listed 5.6* 11* 33* 

Dicot listed 19* 37* 110* 

Monocot non-listed 4.1* 8.1* 25* 

Semi-Aquatic Monocot listed 21* 40* 120* 

Dicot non-listed 47* 93* 280* 

Dicot listed 160* 310* 960* 

Non-vascular non-listed 0.10 

Aquatic Non-vascular listed 

Not calculated 0.69 

Vascular non-listed 0.00054 

Vascular listed 0.0022 

*Exceed plant LOC (1.0).