2

applied through various ground methods, such as ground booms and soil incorporation equipment.” None of the end use products containing isoxaflutole are manufactured as

emulsifiable concentrates. The end use products are suspensi on concentrates or dry flowables.

Also on page 4 of the Summary Document (and as noted in the Ecological Problem Formulation Document) the Agency notes that the most recent isoxaflutole ecological risk assessment was conducted in April 2010 for an Experim ental Use Permit (EUP) for use on soybeans. An

assessment conducted in 1997 was the next most current assessment.

EFED Response: The comment is noted.

#2 Bayer Comment:

BCS would like to remind the Agency of the extensive additional ecotoxicology stud ies, environmental fate studies, and environmental monitoring studies that were conducted after the 1997 assessment as summarized by Allen et al. (2004, MRID 46330201). Examples would include a comment made on page 9 of the Ecological Problem Formulation Document

wherein EPA states : Isoxaflutole’s terminal metabolite, RPA 203328 is expected to persist and accumulate. The results of the field dissipation, ground water, tile drain, and surface water studies as summarized by Allen et al. (2004, MRID 46330201) do not support the statement that RPA 203328 persists and accumulates in the environment.

EFED Response: EFED will re

- examine existing data and information on the physical

chemical and fate properties of the RPA 203328 degradate. Any changes in EPA‟s characterization of that degradate will then be reflected in the forthcoming drinking water and ecological risk assessments in support of registration review.



### Environmental fate data gaps

GLN 835.4100.

- Aerobic soil Metabolism

#3 Bayer Comment:

As described in Allen et al. (2004, MRID 46330201), three aerobic soil metabolism studies have been conducted on a total of six different soils (Ferreira et al.

, 1994, MRID 43588006; Ferreira

et al. , 1996, MRID 45658805; Burr, 1996a; MRID 45 658804). Kinetics evaluations conducted by Hardy et al. (2002, MRID 45658807) for all six soils are also summarized in Allen et al. (2004, MRID 46330201). This information should be sufficient to meet the aerobic soil metabolism study requirements. EPA ma y not have considered Ferreira et al. , 1996, MRID 45658805, such that only the data from three soils were considered for aerobic soil metabolism

results.

EFED Response : As noted in Table 9 of the Isoxaflutole Summary Document MRID‟s

43588006 and 45658804 are categorized as „supplemental‟. As such they may contain useful information that may be used in the Agency‟s assessment of parent isoxaflutole but do not fully meet the requirements of Guideline No. 835.4100 . More specifically, the individual stud y results are not based on the analyses of four soil samples. Collectively, however, since the total number of studies account for four or more soils then no additional data is needed.3

GLN 835.4300.

- Aerobic Aquatic metabolism

#4 Bayer Comment: As summarized by Allen et al. (2004, MRID 46330201), an aerobic aquatic metabolism study on two water sediment systems was conducted by Ayliffe and Newby (1995, MRID 44291502). Isoxaflutole was rapidly degraded in both systems and no longer detected after 7 days. This study should satisfy the requirements for an aerobic aquatic metabolism study.

EFED Response: The Agency completed a review of an aerobic aquatic metabolism stud y by Ayliffe and Newby (MRID) 44291502) in February 1998 and found it to be acceptable with one notable exception. The analysis only satisfied the data requirements for the parent and the metabolite RPA 202248; it did not include the metabolite RPA 203328

. As a result , the analysis was considered incomplete. Subsequent to that review the Agency has determined that the RPA 203328 metabolite is not a chemical of toxicological concern. Therefore

, no additional data are

needed

.



### For degradate RPA 202248

# 5 Bayer Comment: In the Ecological Problem Formulation Document, EPA stated that “There have been no registrant submitted environmental fate studies for the compound‟s primary degradate.” Numerous studies for RPA 202248 have been submitted for review by the Agency. For example, three of the adsorption/desorption studies cited in Table 9 of the formulation document used RPA 202248 degradate as the test material. In many of the degradation studies, the

behavior of the RPA 202248 degradate can be determine d from the studies starting with parent

isoxaflutole.

EFED Response: EPA will change the above language to note that data have been submitted.



### Anticipated data requirements for degradate RPA 202248

Guideline No. 835.1230

- Adsorption/desorption (batch equilibrium)

#6 Bayer Comment: Three of the studies listed in Table 9 of the formulation document (Burr, 1995, MRID 43940301; Burr, 1996b, MRID 44065801; and Lowden et al. , MRID 48108103) were conducted with RPA

202248. These studies have been classifie d as acceptable in Table 9.

EFED Response: No additional adsorption/desorption study data (GLN 835.1230) are requested for the RPA 202248 degradate

.4

Guideline No. 835.1240

- Leaching Studies

#7 Bayer Comment: The study cited for parent isoxaflutole (MRID 43588008) should satisfy the requirement for RPA 202248 since the parent isoxaflutole had degraded to RPA 202248 before the start of the leaching phase of the study.

EFED Response: No additional leaching study data (GLN 835.1240) are requested for the RPA 202248 degradate.

Guideline No. 835.4100

- Aerobic Soil Metabolism

#8 Bayer Comment:

As described in Allen et al. (2004, MRID 46330201), three aerobic soil metabolism studies have

been condu cted on a total of six different soils (Ferreira et al.

, 1994, MRID 43588006; Ferreira

et al. , 1996, MRID 45658805; Burr, 1996a, MRID 45658804) starting with parent isoxaflutole. Kinetics evaluations conducted by Hardy et al. (2002, MRID 45658807) for all six soils are also

summarized in Allen et al. (2004, MRID 46330201). In these studies the degradation rate for RPA 202248 has been determined, so these studies should be sufficient to meet the aerobic soil metabolism study requirements for the RPA 202248 degradate.

EFED Response: See response to BCS comment #3. No additio nal aerobic soil metabolism data

are needed.

Guideline No. 835.4200

- Anaerobic Soil Metabolism

#9 Bayer Comment: The study starting with parent isoxaflutole is not being required since “additional data are not expected to change risk conclusions.” Giv en the relatively rapid degradation of RPA 202248, the same reasoning applies to RPA 202248 and therefore an anaerobic soil metabolism with RPA 202248 should not be required.

EFED Response: No additional anaerobic soil metabolism study data (GLN 835.4200) are needed to assess the RPA 202248 degradate.

Guideline No. 835.4300

- Aerobic Aquatic Metabolism

#10 Bayer Comment: As summarized by Allen et al. (2004, MRID 46330201), an aerobic aquatic metabolism study on two water sediment systems was conducted by Ayliffe and Newby (1995, MRID 44291502). Since isoxaflutole was rapidly degraded in both systems to RPA 202248, this study should satisfy the requirements for an aerobic aquatic metabolism study with RPA 202248. Note that in5

response to t he slow degradation rate encountered in the laboratory study, an outdoor mesocosm study was also performed (Lui et al. , 2003, MRID 46081105; also Rupprecht et al. , 2004). This study should also be considered as fulfilling this requirement.

EFED Response: See response to BCS comment #4. No additional aerobic aquatic metabolism study data (GLN 835.4300) are needed to assess the RPA 202248 degradate

.

Guideline No. 835.4400

- Anaerobic Aquatic Metabolism

#11 Bayer Comment: As summarized by Allen et al. (2004, MRID 46330201), an anaerobic aquatic metabolism study on one water sediment system was conducted by Burr et al. (1995, MRID 43588007). This study was found to be acceptable to satisfy the requirement for parent and so should also satisfy the requi rement for RPA 202248 since isoxaflutole was rapidly degraded to RPA 202248, which remained stable throughout the remainder of the study.

EFED Response: The comment is noted

. No additional anaerobic aquatic metabolism study

data (GLN 835.4400) are needed to assess the RPA 202248 degradate

.

Guideline No. 835.6200

- Environmental Chemistry Analytical Methods and ILV (Water)

#12 Bayer Comment: The methods and associated independent laboratory validations that apparently were acceptable for parent i soxaflutole (since there was no data requirement in this area) also include RPA 202248. Therefore, no additional work is needed to meet this guideline for RPA 202248.

There are three methods that include parent and RPA 202248 that have undergone indepen dent laboratory validations. The first was an enforcement method (Hunt and Lopes, 1997, MRID 44399901) with three associated independent laboratory validations (Wickremesinhe, 1997, MRID 44399902; Davis, 1997, MRID 44399903; Hughes, 1997, MRID 44399904). T he second method was the method based on internal standards that was used in the monitoring work conducted by the registrant during the period of the conditional registration (Smitley, 1999, MRID 44830501). The independent validation of the second method w as conducted by Zheng (1999, MRID 44830502). A later revision of this method (Smitley et al. , 2000) does not seem to be listed independently in the list of MRID values, but was included in its entirely in the reports of several monitoring studies (for exam ple pages 320 to 360 in Lee and Nandihalli, 2002, MRID 45696003). The third method was an immunoassay method required by EPA as a condition of registration and internal (Nandihalli, 2006, MRID 47171602) and independent (Perez, 2006, MRID 47171603) laborato ry validations have been submitted to the Agency. The instructions for applying the immunoassay methods are included in the validation reports.

EFED Response: No additional environmental chemistry methods and independent laboratory

validation documentation (GLN 835.6200) are needed for the RPA 202248 degradate

.6



### For degradate RPA 2033 28, General comment on EFED’s recommendations to request chronic toxicity data

#13 Bayer Comment: “ All available data indicate that RPA 203328 is not of toxicological significance as indicated in the recent assessment for soybean uses (USEPA, 2010). No or limited toxicity has been observed with all species (plants, fish, Daphnia, algae, Lemna, birds, soil microgranisms, earthworms and rats) tested to date with RPA 203328. In the few cases where a toxicological response has been observed, it has been at high dose levels. Requiring

extensive chronic e cotoxicity testing of a metabolite solely based on the potential for trace levels in the environment, when data exists to demonstrate the lack of toxicity, appears to a major policy shift by the Agency. Based on how the Agency has historically handled met abolites, in general and specifically in this case, and the available Agency guidance on this topic, Bayer believes that additional testing is not warranted with RPA 203328.

“As summarized in Allen et al. , 2004 and Allen et al. , 2010, an extensive set of monitoring data are available for RPA 203328, RPA 202248 and parent isoxaflutole. In the vast majority of samples, RPA 203328 concentrations were below 0.3 ppb. A comparative example from these data indicate that the lowest EC50 value (for algae) was es timated by EPA to be 5900 ppm. Even the EECs estimated by the Agency using PR Z M

- EXAMS in 1997 (EPA, 1997) are 1000x lower than the lowest toxicity value. Based on the depth and breadth of available information, Bayer requests that the Agency reconsider th eir request for additional e cotoxicity testing with RPA

203328.”

EFED Response: In order to evaluate the utility of degradate toxicity data, EFED uses both exposure potential and available toxicity data to determine if additional data would be useful to

t he risk assessment process. In the case of isoxaflutole, the two major degradates are converted at fairly high rates, and they are expected to be persistent and mobile. Therefore, evaluating potential risks from these degradates is considered an importan t aspect of the risk assessment. In light of comments received from the registrant, EFED has re

- evaluated the utility of obtaining additional data on the two degradates as explained in the following sections. EFED notes that monitoring data rarely captur es high

- end exposure values from vulnerable areas.



### For degradate RPA 202248, Guidelines 850.4100 and 850.4150

- Terrestrial plant toxicity, Tier II (seeding emergence and vegetative vigor)

#14 Bayer Comment: “ The agency has request ed tier II seeding emergence and vegetative vigor studies with RPA 202248. With respect to the vegetative vigor study request, it is difficult for BCS to come up with a scenario where plants would be directly oversprayed with RPA 202248, which makes such a study irrelevant to the risk assessment. If additional data is necessary, then it would seem that exposure via the soil (seedling emergence study design) would be the more relevant route of exposure for any additional NTTP testing with RPA 202248.

“As st ated by EPA, a non

- target terrestrial plant (NTTP) screening study with RPA 202248 exists, and Bayer has acknowledge d that RPA 202248 is herbicidally active at a level similar to
parent. We believe the toxicity of RPA 202248 is covered in studies with par ent, since it is so7

rapidly formed in plants and soils after application of the parent isoxaflutole

. A large number of NTTP studies, lab and field, are available with isoxaflutole, its formulations and to a lesser

extent metabolites. Additional standard N TTP studies are unlikely to change the characterization
of isoxaflutole’ s risk to terrestrial plants. With the exception of more recent studies, this work has been summarized in Cappy, et al. , 2002 and Dobbs et al. , 2002.”

EFED Response: EFED agrees with the comment that vegetative vigor studies conducted with parent isoxaflutole would also include exposures of plants to degredate 202248. Since toxicity endpoints from vegetative vigor studies are expressed in terms of the amount of parent applied to

the p lant and they are intended to be compared to exposures of non

- target plants to pesticide exposures through spray drift, existing studies with parent isoxaflutole are sufficient to characterize the effects of spray drift transport of isoxaflutole and its herbicidally active degradate , RPA 202248.

EFED recommends that PRD request seedling emergence data for RPA 202248 because 1) RPA 202248 may form on the treated field for days before runoff events occur, leading to an exposure of non

- target plants to RPA 202248 through runoff transport and 2) the a vailable seedling emergence studies with isoxaflutole may have a smaller proportion of RPA 202248 than could be found on non

- target areas exposed to this degredate through runoff. Therefore, it is important to have an understanding of the effects of RPA 2 02248 to the seedling emergence of non

- target plants.



### For degradates RPA 202248 & RPA 203328, Guideline No. 850.2300

- Avian reproduction

#15 Bayer Comment: “ The agency has requested 3 avian reproduction studies that include a

mallard duck and bobwhite quail study with RPA 203328, and a mallard study with RPA 202248 (a quail study already exists). While BCS believes that the available information is adequate to assess the risk to birds, BCS agrees to perform a mallard reproduction study with RPA 202248 as requested. However, as previously mentioned, BCS strongly disagrees that additional testing of RPA 203328 is necessary.”

EFED Response: Given that the available reproduction test with the bobwhite quail exposed to degradate 202248 did not show reproductive effects at 500 mg/kg

- food, which is an order of magnitude below the expected environmental concentration (EEC) of isoxaflutole on poten tial food items of birds ( if 100% conversion of isoxaflutole to degradate 202248 is assumed, the most conservative EEC is 34 mg/kg

- food ), EFED recommend

s that PRD waive the avian reproduction study with the mallard duck exposed to RPA 202248.

In regards to degradate RPA 203328, EFED no longer considers this a degradate of toxicological concern for avian reproductive effects. This conclusion is based on three lines of evidence. First, this degradate would need to be at least an order of magnitud e more toxic that degradate 202248 to pose a concern for birds on a chronic exposure basis. Second, a developmental toxicity study in rats conducted with RPA 203328 has been submitted to the Agency (MRID 45655906). The results of the study show that in th e presence of material toxicity at the highest doses tested (750 mg/kg/day), there was no teratogenicity or developmental8

toxicity. Third, the Health Effects Division (HED) has determined that degradate RPA 203328 is not of toxicological concern for human s

. Therefore, EFED recommends that PRD does not require avian reproduction studies with this degradate.



### For degradates RPA 202248 & RPA 203328, Guideline No. 850.1300

- Freshwater invertebrate life cycle

#16 Bayer Comment: “The Agency expressed concern about the lack of chronic invertebrate

studies with isoxaflutole or its metabolites. Three studies are available to address this concern and will be submitted for review by the Agency. These studies include two Daphnia magn a studies that examined the impact of isoxaflutole around the practical limit of solubility and a

limit test with Chironomous riparius at much lower concentration.

“The first Daphnia magna study was a flow

- through study (McElligott, 1995; M

- 213123

- 01

- 1)

w here undissolved test material, that likely confounded the study results, was present at the two high test concentrations (0.75 and 1.5 mg/L nominal). The rapid addition of a concentrated stock to water with insufficient mixing time likely led to precipit ate formation and continual delivery

to the test chambers. Survival was impacted (65 and 73%) at the two high treatment levels where undissolved test substance was observed, but not at any of the treatment levels (0.09, 0.9, and 0.38 mg/L) where the test compound appeared to be fully in solution. No treatment related effects on reproduction were observed.

“A second Daphnia chronic study (Putt, 1998; M

- 210464

- 01

- 1) was conducted with isoxaflutole, using a static renewal study design. Nominal test levels is this study were 10, 3.1, 0.98, 0.31, 0.095, and 0.030 mg/L. Undissolved test material was observed at the highest treatment of 10 mg/L after mixing of new test solution, but prior to distribution to individual replicates, consistent with the reported s olubility limit for isoxaflutole of 6.2 mg/L. No treatment related effects were observed at any test level, resulting in a NOEC of 5.7 mg/L based on measured

concentrations.

“A water

- sediment study (Odin

- Feurtet, M., 1997; (M

- 211474

- 01

- 1) with Chironom ous riparius

is available. There was a single treatment level of 100 ug/L of isoxaflutole spiked to the water. The isoxaflutole did degrade to predominately RPA 202248 during the 28 study. No negative effects were observed during the study.

“The 1997 s tudies showed no negative effect to aquatic invertebrates due to chronic exposure of

solub i lized isoxaflutole. Acute exposure testing of parent isoxaflutole, and the two primary metabolites, indicated no toxicity to Daphnia. While BCS believes there is su fficient information available to conclude that RPA 202248 and RPA 202328 pose minimal risk to aquatic invertebrates, BCS is willing to conduct a Daphnia magna chronic study with RPA 202248 to increase the Agency confidence in the risk assessment.

EFED Re sponse: When the chronic invertebrate studies conducted with isoxaflutole that were referenced by Bayer are submitted, EFED w ill review them and determine whether or not they are sufficient for risk assessment under the guideline requirement. EFED agrees that submission of chronic toxicity data for RPA 202248 would increase the Agency‟s confidence in the risk9

assessment for isoxaflutole. If these studies are acceptable, EFED will consider using the submitted chronic toxicity studies involving exposures of D. magna to isoxaflutole to derive

ACRs

. These ACRs may be applied to the acute toxicity data for RPA 202248 and RPA 203328 to estimate the chronic toxicities of these degradates to freshwater invertebrates.



### For degradates RPA 202248 & RPA 203328, Guideline No. 850.1350

- Saltwater invertebrate life cycle

#17 Bayer Comment: “ The Agency has requested chronic mysid studies with RPA 202248 and

RPA 203328. A mysid chronic is available for isoxaflutole, along with acute mysid studies with parent and both metabolites. As noted by the Agency in the problem formulation document, the metabolites are over two and close to four orders of magnitude less toxic to shrimp than parent.

The 96

- hr mysid LC 50 values are 0.0178, 3.6. and 1 45 mg/L for isoxaflutole

. The acute values for the two metabolites are above the 1 mg/L criteria as listed in the 40 CFR Part 158 guidance and the expected EECs for the metabolites are well below the LC50 values. The statement by the Agency that the chro nic mysid study with parent suggests the potential for reproductive

effects is difficult to understand. Survival was the most sensitive endpoint in mysid chronic with parent and there were not significant effects on reproduction. Even at the two highest test levels,(where survival was 13 and 48 percent, respectively), reproduction on an offspring/female/reproductive day was comparable to the control.

“BCS requests the Agency to reconsider their request for mysid chronic studies with two metabolites, or p ossibly provide a more detail explanation as to why these studies are triggered based on existing guidance.”

EFED Response: Available acute toxicity data for isoxaflutole and RPA 202248 indicate that

this degradates is less toxic (on an acute exposure bas is) than isoxaflutole by two orders of magnitude. If the available ACR for available toxicity data for the mysid shrimp exposed to isoxaflutole (17.8) is applied to the acute toxicity endpoint for RPA 202248 (3600 ppb), the estimated chronic toxicity endpo int for mysid shrimp exposed to this degradate would be 200 ppb. In the most recent ecological risk assessment of isoxaflutole ( DP Barcode 370959), EFED

derived a 21

- d EEC of 7.6 ppb for RPA 202248. If this EEC and the estimated chronic toxicity endpoint w ere used to determine risk to estuarine/marine invertebrates, this degradate would not be of concern. In order to pose a risk to estuarine/marine invertebrates, RPA 202248 would have to be 2 orders of magnitude more toxic on a chronic exposure basis to be of concern.

Available acute toxicity data for isoxaflutole and RPA 203328 indicate that this degradates is less toxic than isoxaflutole by four orders of magnitude. Using the ACR for isoxaflutole (17.8) and the acute toxicity endpoint for RPA 203328, the estimated chronic toxicity endpoint for this degradate is 8300 ppb. Given that the EEC for isoxaflutole‟s other degradate, i.e., RPA 202248 is orders of magnitude below this level, it is not expected that degradate RPA 203328 will be

present at levels sufficient to pose a risk.

EFED believes that available acute and chronic toxicity data for isoxaflutole are sufficient to

derive ACRs that may be used to estimate the chronic toxicities of degradates 202248 and10

203328 to estuarine/marine inverte brates. EFED does not believe that it is necessary to require chronic toxicity studies involving exposures of mysid shrimp to degradates 202248 and 203328.



### For degradates RPA 202248 & RPA 203328, Guideline No. 850.1400

- Freshwater and saltwater fish ea rly life stage

#18 Bayer Comment: “ BCS will conduct a freshwater fish ELS study with RPA 202248 as requested by Agency, but requests that an estuarine fish ELS study be held in reserve contingent

on the outcome of the freshwater ELS. As discussed, based on the structure and activity information available for RPA 203328, BCS does not believe additional testing of RPA 203328 is necessary or warranted.”

EFED Response: If the registrant conducts an acceptable ELS study with a freshwater fish (of

most i nterest would be a test species for which acute toxicity data are available) exposed to RPA

202248 , EFED would be willing to consider applying an ACR based on RPA 202248 to estimate the chronic toxicity of RPA 203328 to freshwater fish. This same ACR could also be applied to estuarine/marine fish. Therefore, it would only be necessary for the registrant to submit one fish ELS study.



### For degradates RPA 202248 & RPA 203328, Guideline No. 850.5400

- Aquatic

non

- vascular plant growth Tier II

#19 Bayer Comm ent: “ The Agency appears to have requested a total of six (6) additional algal

studies with RPA 202248 and RPA 203328 that include Navicula pelliculosa

, Anabaena flos

aquae , and Skeletonema costatum for each metabolite. BCS targets metabolite testing to determine the relative toxicity of the metabolite to parent. In the case of isoxaflutole, RPA 202248 and RPA 203328, and this specific data request, both metabolites are orders magnitude

less toxic to Selenastrum capricor nutum

. In fact, for all aquatic taxa tested isoxaflutole metabolites are at least an order less toxic than parent. BCS b e lieves that the additional algal testing with the metabolites is excessive and highly unlikely that and requests that the Agency

reco nsider the need for these additional studies.”

EFED Response: EFED agrees that the available green algae ( S. capricornutum ) toxicity data are sufficient to allow for characterization of the relative toxicities of isoxaflutole, RPA 202248 and 203328 to alg ae. EFED no longer recommends that PRD request additional toxicity data involving exposures of the other 3 species of algae to RPA 202248 and 203328.

References:

Allen, R., P. Cain, P. Freesman, I. Hardy, R. Jones, I. Kelly, R. Lee, B. Narasimhan , T. S. Ramanarayanan, G. Sabbagh, L. Somerville, and R. Srinivasan. 2004. The Environmental Fate of Isoxaflutole Following Use on Corn in the U.S. Bayer CropScience Report No. B004653. Bayer Document No. M

- 251278

- 01

- 1. 374 pages. MRID No. 4633020111

Allen, R., M. Dobbs, R. Jones, G. Sabbagh. 2010. Environmental Fate and Ecological Risk Assessment for Isoxaflutole Use in Corn and Soybean. Bayer CropScience Report No. US0061,

Document No. M

- 372827

- 01

- 1, 28 p.

USEPA, 2010. Ecological Risk Assessment A ddressing the “Crop Destruct” Experimental Use Permit (EUP) for Isoxaflutole and its End

- product Balance® PRO Herbicide for use on Select Soybean varieties. Memorandum from M. Davy and W. Shaughnessy (OPP/EFED) to Kathryn Montague and James Stone (RD). DP Barcode 370959. April 16, 2010