UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: August 16, 2012 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: Acetochlor. PP#2F7996. Request to Establish a Rotational Tolerance for 

Inadvertent Residues In/On Rice. Request to Add Rice as a Rotational Crop to an 

Acetochlor ME Label. 

PC Code: 121601 

Decision No.: 461987 

Petition No.: 2F7996 

Risk Assessment Type: Chemistry 

TXRNo.:NA 

MRID No.: 48720001 

From: Susan V. Hummel, Senior Chemist 

Risk Assessment Branch 4 

Health Effects Division (7509P) 

/ 

DP Barcode: D401205 

Registration No.: 524-591 

Regulatory Action: Section 3 

Case No.: 7230 

CAS No.: 34256-82-1 

40 CFR: 180.470 

Through: Thurston G. Morton, Senior Chemist ~ / .L0.~ /J~ Risk Assessment Branch 4 U /7 tl t!' """( 

Health Effects Division (7509P) 

To: Hope Johnson/Kable Davis, PM 25 

Herbicide Branch 

Registration Division (7505P) 

Executive Summary 

Monsanto Company has submitted a pesticide petition (PP#2F7996) requesting the removal of 

"except rice" from the established tolerance for inadvertent residues of acetochlor (2-chlor-N-

(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide) in/on grain of cereal grain at 0.05 ppm 

and straw of cereal grain group 16 at 0.3 ppm, and a supplemental label to add rice as a rotational 

crop to MON 63410 Herbicide (EPA Reg. No. 524-591 ), a microencapsulated formulation (ME). 

In support of the petition, Monsanto has cited a summary of previously submitted rotational crop 

data for acetochlor on grains (MRID 48720001 ), using an emulsifiable concentrate (EC) 

formulation. No new residue data were submitted with this request. 

Tolerances for acetochlor are currently established under 40 CFR §180.470(a) and (d) and are 

expressed in terms of acetochlor and its metabolites, to be analyzed as acetochlor, ethyl methyl 

aniline (EMA), and hydroxyethyl methyl aniline (HEMA), and expressed as acetochlor 

Page I of 12 
equivalents. Tolerances for field corn, pop com, sweet com, cotton, sorghum, and soybean 

commodities are established under 180.470(a) and range from 0.05 ppm for field and pop com 

grain, sweet com kernels plus cob with husk removed, and sorghum grain, to 3.0 ppm for field 

com forage. Tolerances for rotational crops are established under 180.470(d) and include 

tolerances for nongrass animal feeds, sugar beet root and tops, cereal grain commodities, peas 

and beans, potato, soybean forage and hay, sunflower seed, and wheat commodities. No 

tolerances have been established for livestock commodities. 

The qualitative nature of acetochlor residues in com is adequately understood based on a com 

metabolism study. HED concluded that the residues of concern in com include parent and any 

metabolites containing the EMA moiety or the HEMA moiety, expressed in acetochlor 

equivalents. The nature of the residue in rotational crops is adequately understood based on the 

results of confined rotational crop studies in lettuce, radishes and wheat. HED concluded that 

rotational tolerance should be expressed as acetochlor and its EMA and HEMA producing 

metabolites, and residues of hydroxymethyl ethyl aniline (HMEA) type metabolites would not be 

included in the tolerance expression, but should be included in the risk assessment. 

An adequate HPLC/oxidative coulometric electrochemical detector (OCED) method is available 

for enforcing tolerances of acetochlor and its metabolites in plant commodities. For this method, 

residues are solvent-extracted into aqueous acetonitrile (ACN), and then base-hydrolyzed to 

yield EMA and HEMA. The resulting residues are steam-distilled into dilute acid, adjusted to a 

basic pH, and then partitioned into dichloromethane (DCM). HEMA is methylated, then 

residues of EMA and methylated HEMA (MEMA) are separated, and determined via 

HPLC/OCED. Residues ofEMA and HEMA are expressed in acetochlor equivalents; the 

validated method limits of quantitation (LOQs) are 0.020 ppm for each analyte. 

HED previously reviewed a confined rotational crop study submitted by Acetochlor Registration 

Partnership (Monsanto/Zeneca) in support ofPP#3F2966/PP#lF4011 (08/23/93, M. Flood). The 

study was considered adequate. The study indicated that 14C residues accumulated at levels > 

0.01 ppm, inion all commodities oflettuce, radish, and wheat that were planted 30, 120, and 365 

days after [phenyl-14C] acetochlor was applied to sandy loam soil at IX the proposed maximum 

rate. Because the three confined rotational crops all showed significant (>0.01 ppm) acetochlor 

residues, even at the 365 days, then HED requested that tolerances be established for inadvertent 

residues on rotational crops for which field rotational crop studies have been completed. Field 

rotational crop studies for sorghum, soybean, and wheat were also reviewed in the above cited 

memo. HED recommended rotational crop tolerances for sorghum, soybean, and wheat 

commodities (01111/94, M. Flood). These tolerances are established under 40 CFR §180.470(d). 

HED reviewed field trial data from the application of a ME formulation on field com at the same 

maximum rate (3.0 lb a.i./A) as the registered use for an EC formulation (08/01194, M. Flood). 

At that time, HED recommended the registration of this ME formulation for use on com, 

providing a restriction be added against rotating crops other than sorghum, soybean, and wheat. 

In addition, HED has recently reviewed several Section 3 registrations for the use of acetochlor 

on cotton, sorghum, and soybean. All field trial data were produced using ME formulations 

(11121/06, W. Drew; 06/17/09, S. Hummel). Use ofrotational crops are allowed on these ME 

Page 2 of 12 
formulation labels. However, HED has not reviewed rotational crop field data in which the 

primary crop was treated with a ME formulation prior to planting any rotational crop. 

Executive Summary 

HED recommends for the establishment of the requested tolerances for the inadvertent residues 

on rice as a rotational crop (removal of"except rice" from the established tolerance). The field 

trial data as a result of application of an acetochlor EC formulation on a primary crop are 

adequate to support the tolerance request, and a request to add rice as a rotational crop to an 

acetochlor EC label. However, there are inadequate field trial data to support rotational crops on 

an acetochlor ME formulation label. 

The petitioner was recently reminded of the need for rotational crop data using an acetochlor ME 

formulation on the primary crop. (PP#OF7703, D387534, J. Stokes, 5/5/11, and ChemSAC 

meeting of 04/20111.) If it is the intent of the petitioner to add peanut to the label of the ME 

formulation, then the petitioner must submit a full set of rotational crop data for peanut using the 

MEformulation (EPA Reg. No. 524-591) at the maximum application rate. 

The request to remove rice as an exception from the current grain and straw of cereal grain 

tolerances without additional data has been discussed by ChemSAC (10/5/11). ChemSAC found 

this proposal to be acceptable, primarily because there were non-quantifiable residues on the 

other cereal grains, there were limited areas where this rotation would occur, and because rice 

straw had been removed as a livestock feed stuff in the most recent Table I. There was no 

request from the registrant, nor discussion of allowing rice as a rotational crop on acetochlor ME 

labels. 

Although data are inadequate for rotational crops on acetochlor ME labels, it is unlikely that use 

of the acetochlor ME formulation will result in finite residues on grains, so the amendment may 

be allowed while data are being developed as a condition of registration. 

A revised Section F is required, stating the proposed tolerances as follows: 

Grain, cereal, forage, fodder and straw, group 16, except com, grain sorghum, and wheat, straw 

at 0.3 ppm 

Grain, cereal, group 15, except com, grain sorghum, and wheat, grain at 0.05 ppm 

Note to PM: Concurrent with the establishment of the proposed tolerance for 

Grain, cereal, forage, fodder and straw, group 16, except corn, grain sorghum, and wheat, 

straw at 0.3 ppm, and 

Grain, cereal, group 15, except corn, grain sorghum, and wheat, grain at 0.05 ppm 

under 180.470(d), the tolerances for 

Grain, cereal, forage, fodder and straw, group 16, except corn, grain sorghum, rice and 

wheat, straw at 0.3 ppm 

Grain, cereal, group 15, except corn, grain sorghum, rice, and wheat, grain at 0.05 ppm 

listed under 180.470(d) should be removed. 

Page 3 of 12 
The alachlor metabolite HEMA must be replenished prior to publication of the tolerance. 

A human health risk assessment is forthcoming (dietary assessment only). 

Background 

The chemical structure and nomenclature of acetochlor, the EMA and HEMA moieties, and 

Metabolite 57 are presented in Table 1. The physiochemical properties of the technical grade of 

acetochlor are presented in Table 2. 

Table 1. Acetochlor Nomenclature. 

Chemical structure 

lLC/"-...0 0 ~ 

l~cl N 

H3C ~ CH3 

I 

// 

Common name Acetochlor 

Company experimental name None 

IUPAC name 2-chloro-N-ethoxymethyl-6'-ethylacet-o-toluidide 

CAS name 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide 

CAS registry number 34256-82-1 

End-use product (EP) 3 lb/gal Mcap formulation (MON 63410 Herbicide, EPA File Symbol No. 524-

LOR) 

Chemical structure of EMA NH2 

moiety 

lLC -;::/ CH3 

J I ~ 

CAS Name: 2-ethyl-6-methylaniline 

Acetochlor EMA-type 0 

metabolites 1 

Rl-......... )l 

N R2 

H3C ~ CH3 

I 

// 

Page 4 of 12 
Table 1. Acetochlor Nomenclature. 

Chemical structure of HEMA 

moiety 

Acetochlor HEMA-type 

metabolites 1 

Acetochlor Metabolite 57 

CAS Name: 2-(1 -hydroxyethyl)-6-methylaniline 

0 

R3......._ RI .........._ Jl 

0 N R2 

H,C 

0 

HNJlCOOH 

OH 

N-(6-ethyl-3-hydroxy-2-methylphenyl) oxamic acid 

For the acetochlor EMA- and HEMA-type metabolites, the Rl functional group can consist of - H or -

CH20CH2CH3 and the R2 functional group may consist of many different moieties. The R3 functional group for 

acetochlor HEM A-type metabolites can consist of - H or a variety of components such as sugars. 

Table 2. Physicochemical Properties of Acetocblor. 

Parameter Value Referenc.e 

Melting point/range 163 °C at I 0 mm Hg; decomposition Residue Chemistry Chapter 

occurs before the boiling point at of the Acetochlor TRED 

atmospheric pressure (calculated by (DP# 297062, 5/31 /05, S. 

extrapolation of vapor pressure at lower Ary) 

temperature) 

pH 4.41 , 1% solution in acetone:water (I: 1, 

v:v) 

Density 1.123 g/mL at 20 °C 

Water solubil ity 223 mg/L at 25 oc 

Solvent solubility Infinitely soluble in acetone, benzene, 

carbon tetrachloride, ethanol, chloroform, 

and toluene at 25 °C 

Vapor pressure 0.045 11m Hg (4.5 x 10"

5 mm Hg) at 25 °C 

Dissociation constant, pKa Not applicable because acetochlor is 

neither an acid nor a base. 

OctanoVwater partition coefficient, 970 (Dow study) or 1082 (Monsanto 

Log(Kow) study); differences are likely due to 

experimental error 

Page 5 of 12 
Table2. Physicochemical Properties of Acetochlor. 

Parameter Value Reference 

UV /visible absorption spectrum Not available 

860.1200 Directions for use 

Monsanto has submitted a supplemental label to add rice as a rotational crop to MON 63410 

(EPA Reg. No. 524-591) a ME formulation (3 lb a.i./gal). The field treated with this product may 

be rotated the next season to rice. Note: The crop field trial data for rotational grains were 

collected using an EC formulation on the primary crop (See 860.1900, this memo). 

860.1900 Field Accumulation in Rotational Crops 

The Acetochlor Registration Partnership (ARP), comprised of Monsanto and Dow AgroSciences, 

submitted a petition (PP#6F4791) in 1996 supporting the direct use on sweet com of acetochlor, 

formulated as an EC formulation. In addition, under the sweet corn petition and a second 

petition (PP#IF6263) submitted in 2001, ARP requested revision to their current acetochlor 

labels to allow for replanting of the following rotational crops: potatoes; sugar beets; dried peas 

and beans (subgroup 6C); cereal grains (except rice), alfalfa, clover, and sunflowers. 

The submitted rotational crop field trials, were accompanied by full data sets using an acetochlor 

EC formulation on potatoes, sugar beets, dried peas and beans, oats, sunflowers, alfalfa and 

clover, were considered adequate to add these uses to the label and for the establishment of 

tolerances for inadvertent acetochlor residues((§ 40 CFR 180.470a). For each rotational crop, 

an adequate number of field trials were conducted in the appropriate geographic regions. 

Acetochlor (EC formulation only) was applied to the primary com crop at the current maximum 

seasonal application rate (3 lb ai/A), and the rotational crops were planted the spring (9-12 

months) following application (06/20/06, D. Davis). 

Monsanto has requested a waiver from the requirement of a full set of field rotational crop trials 

for acetochlor on rice. Monsanto originally requested tolerances for inadvertent residues of 

acetochlor on the cereal grains crop group (except corn and rice). In their original petition for 

establishment of inadvertent (rotational crop) tolerances, they specifically requested that rice be 

excluded from the crop group, and provided no field trials on rice. Com was originally excluded 

from the tolerance for inadvertent residues of acetochlor on the cereal grain crop group because 

corn was registered as a primary crop. Full data sets (860.1500) are available for the other 

representative commodities of the cereal grain crop group. Residues are non-quantifiable in the 

grains, but finite residues are found in the forages, hays, and straws. 

Now Monsanto has requested that the exclusion of rice from the crop group be deleted, but 

without providing field trial data for rice. Corn, sorghum, and wheat are now excluded from the 

crop group tolerance for inadvertent residues on cereal grains, because there are primary crop 

tolerances on those commodities. 

Page 6 of 12 
ChemSAC found this proposal to be acceptable, primarily because there were non-quantifiable 

residues on the other cereal grains, there were limited areas where this rotation would occur, and 

because rice straw had been removed as a livestock feed stuff in the most recent Table I. 

Conclusion: 

HED has noticed that all current rotational tolerances have been established from field crop 

residue data generated from use of EC formulations. The petitioner has requested the addition of 

rice as a rotational crop to a ME formulation, e.g., MON 63410 (EPA Reg. No. 524-591). 

According to OPPTS Residue Chemistry Test Guidelines 860.1500, the use of a slow- release 

encapsulated formulation may lead to higher residues than conventional formulations. Thus, if 

the use of a slow-release formulation is proposed, then residue data reflecting this type will be 

required. It is further stated that this type of formulation will normally require a full set of field 

trials to include the same number of trials as needed to obtain an original tolerance regardless of 

the timing and mode of application and the amount of data available on other formulation 

classes. 

Available extensive rotational crop field trials conducted at 3.0 lb ai/A (lx the maximum 

proposed seasonal application rate) with an EC formulation have been submitted and these data 

support the PBis (plantback intervals) specified on the EC product labels, and the tolerances for 

indirect or inadvertent residues of acetochlor inion the commodities of nongrass animal feeds; 

sugar beets; cereal grains except corn, sorghum, rice, and wheat; dried shelled peas and beans; 

potatoes; soybeans; sunflower seed; and wheat (D193048, 11/23/93, M. Flood; D275019, 

6/20/06, D. Davis.). Currently these rotational crops are listed on the ME formulation MON 

63410. Note: However, HED has not reviewed rotational crop field data in which the primary 

crop was treated with a ME formulation prior to planting rotational crops. 

There are inadequate field trial data to support the request to add rice as a rotational crop to an 

acetochlor ME formulation label, and to support the current rotational crops on the acetochlor 

ME label. The issue of rotational crops being added to a acetochlor ME formulation label has 

been discussed by ChemSAC (04/20/ 11 ), and the following is needed to add a crop as a 

rotational crop to a ME formulation label: The petitioner must submit a full set of rotational crop 

data for the crop using the ME formulation (EPA Reg. No. 524-591) at the maximum application 

rate. 

860.1550 Proposed Tolerances 

The current tolerance expression for acetochlor inadvertent tolerances is: 

Tolerances are established for indirect or inadvertent residues of acetochlor, including its 

metabolites and degradates, in or on the raw agricultural commodities in the table to this 

paragraph when present therein as a result of application of acetochlor to the growing crops 

in the table to paragraph (a) of this section. Compliance with the tolerance levels specified 

below is to be determined by measuring only acetochlor, 2-chloro-2'-methyl-6-ethyl- Nethoxymethylacetanilide, and its metabolites containing the ethyl methyl aniline (EMA) 

moiety and the hydroxyethyl methyl aniline (HEMA) moiety. Both parent and the named 

metabolites shall be determined as ethyl methyl aniline (EMA) and hydroxyethyl methyl 

Page 7 of 12 
aniline (HEMA), and calculated as the stoichiometric equivalents of acetochlor, in or on the 

following commodities. 

The wording of the tolerance expression is in accord with our recent guidance (S. Knizner, 

5/27/09). 

The petitioner has requested changing the inadvertent tolerances for grains from the current 

Grain, cereal, forage, fodder and straw, group 16, except com, grain sorghum, rice and wheat, 

straw at 0.3 ppm 

Grain, cereal, group 15, except com, grain sorghum, rice, and wheat, grain at 0.05 ppm 

to remove the exception for rice as follows: 

Grain, cereal, forage, fodder and straw, group 16, except com, grain sorghum, and wheat, straw 

at 0.3 ppm 

Grain, cereal, group 15, except com, grain sorghum, and wheat, grain at 0.05 ppm 

The change in the tolerance is supported. However, in Section F of the petition, the proposed 

tolerances still include rice as an exception. A revised Section F is required. 

860.1650 Submittal of Analytical Reference Standards 

Analytical standards for acetochlor and its EMA and HEMA metabolites are currently available 

in the EPA National Pesticide Standards Repository (personal communication with Theresa 

Cole, ACB, 8/20/12), with expiration dates as shown below 

acetochlor, expiration date 10/31/2013 

acetochlor ESA, (tert-sulfonic acid na salt), expiration date 4/30/2013 

acetochlor metabolite (EMA) 2-ETHYL-6-METHYLANILINE, expiration date 

5/31/2015 

acetochlor metabolite (HEMA) 2-( 1-hydroxyethyl)-6-methylaniline, EXPIRED 

7/3112012 

acetochlor tert oxanilic acid, expiration date 4/30/2014 

acetochlor tert-sulfinyl acetic acid, Na salt, expiration date 1131113 

The alachlor metabolite HEMA must be replenished now. 

Analytical standards must be replenished, as requested, by the Pesticide Repository. Analytical 

standards should be sent to the attention of either Theresa Cole or Thuy Ngygen at the following 

address: 

USEPA 

National Pesticide Standards Repository/ Analytical Chemistry Branch!OPP 

701 Mapes Road 

Fort George G. Meade, MD 20755-5350 

Page 8 of 12 
Page 9 of 12 
International Residue Limits 

A cetoc hl or (PC C d o e 121601 D t fR t 8/9/12) ' a eo eques 

Summary ofUS and International Tolerances and Maximum Residue Limits 

Residue Definition: 

us Canada Mexico2 Codex3 

40 CFR 180.470 None None 

Plant & Livestock: acetochlor, 2-chloro-2'-

methyl-6-ethyl- N -

ethoxymethylacetanilide, and its 

metabolites containing the ethyl methyl 

aniline (EMA) moiety and the 

hydroxyethyl methyl aniline (HEMA) 

moiety. Both parent and the named 

metabolites shall be determined as ethyl 

methyl aniline (EMA) and hydroxyethyl 

methyl aniline (HEMA), and calculated as 

the stoichiometric equivalents of acetochlor 

Commodity' Tolerance (ppm) /Maximum Residue Limit (mg/kg) 

us Canada Mexico.t Codex3 

Grain, cereal, group 15,except 0.05 

com, grain sorghum, and 

wheat, grain 

Grain, cereal, forage, fodder 0.3 

and straw, group 16, except 

com, grain sorghum, wheat, 

straw 

Completed: M. Negussie; 08/20/2012 .. Includes only commodJtJes of mterest for th1s actJOn. Tolerance values should be the HED recommendatiOns and 

not those proposed by the applicant. 2 Mexico adopts US tolerances and/or Codex MRLs for its export purposes. 3 * = absent at the limit of quantitation; Po = postharvest treatment, such as treatment of stored grains. PoP = 

processed postharvest treated commodity, such as processing of treated stored wheat. (fat) = to be measured on the 

fat portion of the sample. MRLs indicated as proposed have not been finalized by the CCPR and the CAC. 

Page 10 of 12 
References 

DP Barcode: D189047 

Subject: PP#3F2966.PP#1F4011. Acetochlor Registration Partnership. Acetochlor EC 

Herbicide for Use on Field Com. Confined Rotational Crop Study. Field 

From: 

Dated: 

MRID(s): 

DP Barcode: 

Subject: 

From: 

Dated: 

MRID(s): 

Rotational Crop Studies. 

M. Flood 

08/23/93 

42549908,42549914,42549919, 42591501 

D193048 

Acetochlor. Rotational Crop Tolerances for Soybeans, Wheat, and Sorghum 

M. Flood 

01/ 11194 

None 

DP Barcode: D275019 

Subject: Acetochlor: Petitions for Tolerances on Sweet Com and Rotational Crops of 

Nongrass Animal Feeds (Group 18), Sugar Beets, Dried Shelled Beans and Peas 

(Subgroup 6C), Sunflowers, Potatoes, Cereal Grains (Group 15), and Forage, 

Fodder, and Straw of Cereal Grains (Group 16). Summary of Analytical 

From: 

Dated: 

MRID(s): 

Chemistry and Residue Data. Petition Numbers: 6F4791 and 1F6263 

D. Davis 

06/20/06 

44107101,44107102,44107103, 44107104, 44107105, 44107106, 44107107, 

45322102,45322103,45322104, 45322105,45322106,45322107,45322108, 

45322109, 45322110,45322111,45322112,45483301 

DP Barcode: D316496 

Subject: Acetochlor. Tolerance PetitionRequesting the Establishment of Permanent 

From: 

Dated: 

MRID(s): 

DP Barcode: 

Subject: 

From: 

Dated: 

MRID(s): 

Tolerances Associated with Section 3 Registration for Food Use of the Herbicide 

Acetochlor on Sorghum. Summary of Analytical Chemistry and Residue Data. 

W. Drew 

11121106 

46507101,46507102 

none 

Interim Guidance on Tolerance Expressions 

S. Knizner 

5/27/09 

none 

Page 11 of 12 
DP Barcode: D359990 

Subject: Acetochlor. Petition Request for New Uses on Cotton (PP#8F7443) and Soybean 

(PP#8F7448). Summary of Analytical Chemistry and Residue Data. 

From: S. Hummel 

Dated: 06117/09 

MRID(s): 47695701,47552201,47555601 

DP Barcode: 0387534 

Subject: Acetochlor. PP#OF7703. Request to Establish a Rotational Tolerance for 

Inadvertent Residues In/On Peanut. Request to Add Peanut as a Rotational Crop 

to an Acetochlor ME Label. Request for Label Restriction on Feeding Peanut 

From: 

Dated: 

MRID(s): 

Forage to Livestock. 

J. Stokes 

5/5/11 

41338503 

RDI:SHummel:8/16/12:RAB4Chemists:8/22/12 

Petition Number: 2F7996 

DP Barcode: 0401205 

PC Code: 121601 

Page 12 of 12