UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

PC Code: 125203 

DP Barcode: 409558 

May 2, 2013 

MEMORANDUM 

SUBJECT: 

TO: 

FROM: 

THRU: 

The Environmental Fate and Effects Division Response to Comments Posted to the 

Registration Review Docket for Clodinafop-propargyl; Docket ID EPA-HQ-OPP-2012-

0424. 

Wilhelmena Livingston 

Chemical Review Manager 

Pesticide Re-evaluation Division (7508P) _ /. ~ s/2-)13 

Melanie Biscoe, Environmental Pro~~tion Specialist~~ Tanja Crk, Biologist /~L (_JfiL S/'2-/(3 

Environmental Risk Branch~ 

Environmental Fate and Effects Division (7507P) 

Dana Spatz; Branch Chie :c::;:~~ibt!~ 

Rosanna Louie-Juzwiak, Risk As .r;:;:~ot_:~ 

Environmental Risk Branch 3 

Environmental Fate and Effects Division (7507P) 

This document contains the Environmental Fate and Effects Division's (EFED) response to comments on 

the Clodinafop-propargyl Problem Formulation (Docket ID EPA-HQ-OPP-2012-0931). Other than the 

corrected Koc value pointed out by Syngenta, which indicates greater mobility than originally stated in 

the Problem Formulation, none of the public comments w ill materially impact the ecological risk or 

drinking water exposure assessments to be completed in Registration Review. 

COMMENT SOURCE: SVNGENTA 

EPA Statement 

Page 2, Section 1, Table 1 Percent Crop Treated for wheat: Avg: 5, Max: 10. 

Syngenta Comment 1: Syngenta believes the Percent Crop Treated for wheat should be 7.4 

(average) and 15.1 (maximum). 

EFED Response 1: EFED defers questions about use or usage to the Biological and Economic 

Analysis Division. 

Page 1 of 6 
Page 2 of 6

EPA Statement 

Page 3, Table 2, 

application Method 

Timing, WHEAT, (6.4% 

a.i., Emulsifiable 

Concentrate)

Stated application method timing was Foliar, Tillering.

Syngenta Comment 2: Syngenta would like to respectfully revise Foliar to Foliar, Postemergence.

EFED Response 2: EFED defers questions about use or usage to the Biological and Economic 

Analysis Division. 

EPA Statement

Page 4, Section 2.2, 

paragraph 1, 1st 

sentence

“...drinking water EECs....”.

Syngenta Comment 3: Syngenta would like to respectfully revise EECs to EDWCs.

EFED Response 3: EFED acknowledges that "EDWCs" should be used in place of "EECs" in this 

context.

EPA Statement

Page 4, Section 2.2, 

paragraph 1, 2nd 

sentence

In this DWA, the surface water values were modeled using PRZM 

EXAMS based on the North Dakota wheat scenario....”.

Syngenta Comment 4: Syngenta would like to respectfully revise to add “based on the North 

Dakota and Oregon wheat scenarios...”. Values (1-in-10 year annual Mean) cited in Table 4 

(page 4) were derived from the Oregon wheat scenario (2006 EPA DWA, DP324688).

EFED Response 4: EFED acknowledges that the Oregon wheat scenario should be added to the 

sentence as indicated by Syngenta. The PRZM-EXAMS Oregon wheat scenario resulted in a 1-

in-10 year annual mean surface water EDWC of 2.5 μg/L, as indicated in Table 4 of the Problem 

Formulation (2006 EPA DWA, DP324688).

EPA Statement

Page 7, Table 5, 

Degradation Product 

Formation in

Environmental Fate 

Studies

For degradation product CGA-193469, Study-Aerobic Soil, the 

maximum percentage formed is stated as 79.9% of applied (2 

hours).
Page 3 of 6

Syngenta Comment 5: Syngenta believes the actual percentage formed for the degradate, 

CGA-193469 is 79.7% of applied (2 hours).

EFED Response 5: EFED agrees that with Syngenta that, based on data from aerobic soil 

metabolism study MRID 46012931, the maximum percentage formed is 79.7% of applied (as an 

average of two samples at hour 2 of the study).

EPA Statement

Page 7, Table 5, 

Degradation Product 

Formation in 

Environmental Fate 

Studies

For degradation product CGA-193468, Study-Aerobic Soil, the 

maximum percentage formed is stated as 10.7% of applied (3 

days).

Syngenta Comment 6: Syngenta believes the actual percentage formed for the degradate, 

CGA-193468 is 5.4% of applied (3 days).

EFED Response 6: Based on data presented in aerobic soil metabolism study MRID 46012931, 

the maximum percentage formed for degradation product CGA-193468 is 10.7% of applied (as 

an average of two samples on day 3). Based on the latter data and anaerobic aquatic 

metabolism data (as referenced in Table 5 of the Problem Formulation), EFED considers CGA193468 to be a major degradate of clodinafop-propargyl.

EPA Statement

Page 8, 4. Receptors “Table 7 and Table 7 provide a summary.....” .

Syngenta Comment 7: Syngenta believes that the reference should be Table 6 and Table 7.

EFED Response 7: EFED agrees with Syngenta's editorial comment regarding Table 6 and Table 

7.

EPA Statement

Page 8, 4.1 Effects to 

Aquatic Organisms, 

paragraph 1, 4th 

sentence

“A comparison of non-vascular aquatic plant data suggests that the 

green algae (S. subspicatus) is less sensitive to the degradate CGA302371 than it is to the parent...”.

Syngenta Comment 8: The alga tested in the study with the CGA-302371 metabolite was 

Pseudokirchneriella subcapitata (Selenastrum capricornutum) rather than S. subspicatus. Table 

6 (page 9) and Appendix E (page 43) also list S. subspicatus rather than P subcapitata. P. 

subcapitata was less sensitive to the degradate CGA-302371 (MRID 44399161) than to the 

parent compound (MRID 44561104). In addition, Syngenta will submit additional algal data for 

the primary degradate, CGA-193469, by the end of 1st Quarter 2013.
Page 4 of 6

EFED Response 8: Syngenta pointed out that the study cited in the problem formulation was 

not referencing the correct species. Indeed, the algae study, MRID 44399161, using the 

metabolite CGA-302371 as the test compound, used Selenastrum capricornutum (new name: 

Pseudokirchneriella subcapitata) and not Scenedesmus subspicatus. The text (paragraphs in 

section 4.1 and Appendix E, and Table 6) where this species is cited under this MRID number is 

an error in the problem formulation; however, the conclusions from the study are the same 

and the sentence pointed out should read as follows: “A comparison of non-vascular aquatic 

plant data suggests that the green algae (S. capricornutum) is less sensitive to the degradate 

CGA-302371 than it is to the parent...”

EPA Statement

Page 13, 5. Conceptual 

Modal, paragraph 1, 4th 

sentence

“Clodinafop acid and its transformation products are persistent,...”.

Syngenta Comment 9: Under aerobic conditions, metabolites CGA-193469, CGA-302371 and 

CGA-193468 degrade with half-lives of 1 to 2.4 days (MRID 46012931 and 46012930), 11 days 

(MRID 46012930) and 1.1 days (MRID 46012931), respectively. Therefore, Syngenta believes 

that the transformation products of clodinafop are not persistent to persistent, depending on 

the environment.

EFED Response 9: EFED agrees that clodinafop acid and its transformation products are not 

persistent to persistent, depending on the environment. Regardless of the individual half-lives 

of clodinafop-propargyl transformation products, EFED will use the half-life of the totality of 

the toxic residues identified in the Problem Formulation for the Preliminary Ecological Risk and 

Drinking Water Assessments for registration review.

EPA Statement

Page 15-16, Table 8, 

Vapor Pressure and 

Aqueous Solubility

The referenced source for these studies is MRID 44399101.

Syngenta Comment 10: Syngenta believes the referenced source should be MRID 44399103.

EFED Response 10: EFED agrees that MRID 44399103 is the appropriate source for data 

concerning the aqueous solubility and vapor pressure of clodinafop-propargyl.

EPA Statement

Page 16, Table 8, 

Anaerobic Aquatic

The referenced source for this study (MRID 46012933) was in 

duplicate.

Syngenta Comment 11: Syngenta believes the referenced sources should be MRID 46012933 

and 44399177.
Page 5 of 6

EFED Response 11: EFED agrees that MRID 44399177 is the appropriate source for data 

concerning anaerobic aquatic metabolism, in addition to MRID 46012933.

EPA Statement

Page 16, Table 8, 

Mobility

The Koc values for metabolite CGA-193468 are stated as (average 

of “..........832, 2133, 647, 998, 718, 577”) (MRID 46012936).

Syngenta Comment 12: The study report (MRID 46012936) cites Koc adsorption values for 

metabolite CGA-193468 as 289, 630, 363, 378, 367 and 352.

EFED Response 12: EFED acknowledges that MRID 46012936 reports adsorption Kfoc values for 

metabolite CGA-193468 as 289, 630, 363, 378, 367 and 352. The Kfoc values for CGA-193468 

that EFED listed in Table 8 were the desorption Kfoc values for this metabolite reported in 

MRID 46012936. Because EFED uses the adsorption Kfoc values to estimate exposure, the 

average Koc value that should be listed in Table 8 on Page 16 of the Problem Formulation is 

144.4. EFED intends to use this average Koc value in the Preliminary Ecological Risk and 

Drinking Water Assessments for registration review. 

EPA Statement

Page 19, Section 7.1, 

Environmental Fate, 

Table 9, Submitted 

Studies (MRID)

For OCSPP Guideline 835.4100, Aerobic Soil Metabolism, MRID 

46012931 is cited in duplicate.

Syngenta Comment 13: Syngenta believes that one of the references should be MRID No. 

46012930.

EFED Response 13: EFED agrees that the duplicate entry for MRID 46012931 should be MRID 

46012930.

EPA Statement

Page 19, Section 7.1, 

Environmental Fate, 

Table 9, Submitted 

Studies (MRID)

For OCSPP Guideline 835.4400, Anaerobic Aquatic Metabolism, 

MRID 4399176.

Syngenta Comment 14: Syngenta believes that the reference should be MRID No. 44399176.

EFED Response 14: EFED agrees that this reference should be should be MRID 44399176.

EPA Statement

Page 28, Appendix A, 

EFED Label Data Report

Reg# 100-907, the Original (Product/A.I.) Max App Rate is listed as 

“1 unspecified”.

Syngenta Comment 15: The maximum application rate for Discover Herbicide (EPA Reg. No. 

100-907) is 4 fl oz/A.

EFED Response 15: See EFED Response 16 below.
Page 6 of 6

EPA Statement

Page 28, Appendix A, 

EFED Label Data Report

Reg# 100-907, the A. I. Max App Rate is listed as NDC, No Dosage 

Conversion.

Syngenta Comment 16: The active ingredient (A.I.) maximum application rate for Discover 

Herbicide (EPA Reg. No. 100-907) is 0.0625 lb/A.

EFED Response 16: Based on the information provided on the Discover Herbicide product (EPA 

Reg. No. 100-907) label approved November 23, 2009, (i.e., product contents of 2 lb active 

ingredient (a.i.) per gallon, maximum single application rate of 4 fl oz per acre) EFED agrees 

that the maximum single application rate for this product is 0.0625 lb a.i./acre.

EPA Statement

Page 31, Appendix A, 

Screening Level 

Estimates of Agricultural 

Uses of Clodinafoppropargyl

Percent Crop Treated for Wheat: Avg: 5, Max:10.

Syngenta Comment 17: Syngenta believes the Percent Crop Treated for wheat should be 7.4 

(average) and 15.1 (maximum).

EFED Response 17: EFED defers questions about use or usage to the Biological and Economic 

Analysis Division.