2 T w o major degradates (unknown A and unknown D) were thought to be unidentified at the time of the problem formulation. BCS indicated that structures ( coded BCS

- CV14885 and BCS

CO60720) were proposed in the aerobic aquatic metabolism study (MRID 45386430)

. EFED acknowledges these structures.

Data needs were reassessed given this new information and EFED has revised its recommendations on the value of data on toxicity to certain aquatic organ isms (see below)

. EFED does not have any toxicity data for BCS

- CV14885 or BCS

- CO60720 (BCS incorrectly indicates that MRID 45386331 contains information about herbicidal activity of these degradates ). BCS

- CV14885 and BCS

- CO60720 are SU bridge

- intact degradates; therefore, toxicity to terrestrial and aquatic plants will be assumed the same as that of mesosulfuron

- methyl in the absence of data and a TTR approach will be used to estimate EECs. Following the same assessment procedures in the problem form ulation, it was determined that BCS

- CV14885 and BCS

- CO60720 toxicity studies with fish, aquatic invertebrates, aquatic non

- vascular plants, birds, and mammals are unlikely to change risk conclusions. However, the lack of BCS

CV14885 and BCS

- CO60720 toxicit y information for aquatic vascular plants could impact risk conclusions (see pg 22 of problem formulation).

In addition, a recent DER review found that the available ECM/ILV water stud ies ( MRID 46451 701 and 46451702) did not include the major degradat es of mesosulfuron

- methyl in aquatic environments (USEPA, 2013).

The following studies are recommended in addition to those indicated in the problem formulation:

• Aquatic plant growth (850.4400)

- vascular plant (BCS

- CV14885 and BCS

- CO60720)

• ECM/ILV ( water) (850.6100)

- to include the major degradates observed in aquatic environment s ( AE F160459, AE F160460, AE F140584, AE F147447, AE F092944, BCS

- CV14885 (benzoic acid with guanidine), and BCS

- CO60720 (methyl ester of benzoic acid with guanidine) )

The following study is no longer recommended:

• Aerobic Aquatic Metabolism (8 35.4300)

Modifications are made for the following study recommended in the problem formulation :

• ECM/ILV ( soil ) (850.6100)

- to include the major degradates observed in soil environments (AE F154851, AE F099095, and AE F092944) . Minor degradate observed in the soil environment are not recommended.3 Ecological Effects

BCS Comment:

Bayer CropScience provided comments on ecological effects data gaps identified in the prob lem formul ation regarding their intent to submit studies that address data gaps and refine uncertainties

.

EFED Response :

EFED will review submitted studies to the extent that they reduce uncertainty in the risk conclusions

. Specific comment on 850. 45 00 :

”

........ Bayer CropScience believes the existing study is sufficient to properly characterize the risk to green alga and would appreciate clarification from the Agency on the request for additional data ”

. After review, some studies were reclassified and no longer meet a given data requirement. The existing study (MRID 45386306) was downgraded to Invalid because the control was contaminated with test substance (see DP 412289 and accompanying DER amendment). Therefore, submission of a new study is sti ll recommended.

Specific comment on 850.1400 (mesosulfuron

- methyl) and 850.4500 (AE F092944, AE F099095, and AE F154851):
“BCS will submit these reports if requested under the DCI”.

Although data gaps, EFED did not recommend these studies given that they would unlikely change the risk conclusions based on information available at the time of the problem formulation. However, if submitted EFED will consider the studies to the extent t hat they reduce uncertainty in the risk conclusions

. Specific comment on t errestrial plant toxicity:

“....EPA noted that in the lack of additional data on terrestrial nontarget plant toxicity SU bridge

- intact degradates will be assumed equal in toxicity t o TGAI (mesosulfuron

- methyl) . BCS requests that the Agency review Rosinger, C. 1999 (MRID 45386331) which demonstrates > 10 fold decrease in pre

- and/or post

- emergent herbicidal activity of major plant and soil degradates of mesosulfuron

- methyl against a w ide range of grass and broad

- leaf plant species”.

EFED will consider all lines of evidence including MRID 45386331 in determining if SU bridge

intact degradates will be assumed equal in toxicity to mesos ulfuron

- methyl. A preliminary review of MRID 453863 31 suggests that three of the bridge

- intact degradates (AE F154851, AE F160459, and AE F160460) are less toxic than mesosulfuron

- methyl to the tested plant species. Shortcomings of the report include a lack of information on experimental design (was it th e same4 for mesosulfuron

- methyl and the degradates) and the measure of herbicidal activity (what endpoints were considered). EFED is unaware of any toxicity data (terrestrial plants) for the other two bridge

- intact degradates ( BCS

- CV14885 and BCS

- CO60720). Data are not requested at this time; however, SU bridge

- intact degradates will be assumed equal in toxicity to mesosulfuron

- methyl in the absence of data

.
Environmental Fate

BCS C omment ( Aerobic Aquatic Metabolism ):

“There are no unknown major metabolites in the submitted study. All metabolites were identified and described in the reports.” “....Therefore, based on the structural elucidation of these metabolites, the submitted report (Steinfuhrer and Zumdick, 2000; MRID 45386430) should fulfill t he requirements and repeat of the study is not warranted.”

“Metabolite Unknown A (coded as BCS

- CV14885) was synthesized and shown not to have any herbicidal activity (Rosinger, C., 1999; MRID 45386331).”

EFED Response :
EFED acknowledges the degradate identification data from “ LC/MS

- investigations ” (page 55

- 57, MRID 45386430) and concurs all major metabolites were identified. EFED will revise the data evaluation record (DER) for MRID 45386430 to reflect the changes. An aerobic aquatic metabolism study is no longer recommended.

There is no toxicity information regarding Unknown A (BCS

- CV14885) in MRID 45386331.

BCS Comment ( Aquatic F ield D issipation ):

“Bayer believes that the currently available information is adequate to characterize mesosulfuron

- methyl's fate in aquatic systems, and in conjunction with the available aquatic toxicity studies, assess the potential risk to aquatic organisms. Mesosulfuron

- methyl is applied at a very low maximum rate of 15 g a.i./ ha (0.0134 l b a.i./acre) with only one application per year, and is not registered for direct application to water, so it is unlikely to reach aquatic habitat at high concentrations. .... While mesosulfuron does exhibit some toxicity to aquatic plants, the potential eff ects on aquatic plants are well characterized (Teixeira, 2003, C036256; Hoberg, 2009, M

- 329474

- 01

- 1; etc.). Although not designed as an aquatic dissipation study, the artificial pond study of Hoberg, 2009 did demonstrate dissipation of mesosulfuron from th e water phase at a half

- life of 39 d based on the kinetic evaluation of 7 separate outdoor ponds. .... BCS will submit the Hoberg (2009) study if requested under the DCI.”

“Conducting an aquatic field dissipation study is unlikely to generate information th at will significantly change our understanding of the behavior of the molecule in the environment or its potential risk to aquatic organisms.”5 EFED Response :

EFED will review the a rtificial pond study by Hoberg ( 2009 ) if submitted; however, EFED reitera tes that a n aquatic field dissipation study is recommended to better characterize t he aquatic fate and risk of mesosulfuron

- methyl given that it is likely to enter water bodies through soil run

off, erosion
, and leaching because of its persistence and mobility

.

BCS Comment ( Environmental Chemistry Methods for Soil and Plant Material ):

“The metabolic fate of mesosulfuron

- methyl has been thoroughly investigated in numerous soils and sediment under aerobic and anaerobi c conditions, covering a wide range of textures and organic carbon contents....”

. “As shown above, only three metabolites (AE F154851, AE F099095 and AE F092944) exceeded 10% of applied radioactivity in soil and are considered major metabolites.”

. “Therefore , Bayer proposes to develop and validate an analytical method containing parent and the major metabolites AE F154851, AE F099095, and AE F092944. These analytes will adequately define the behavior of mesosulfuron

- methyl in the soil environment.”

EFED Resp onse :

EFED recommends submission of the proposed soil analytical method containing mesosulfuron

methyl and the major soil metabolites ( AE F154851, AE F099095, and AE F092944 )

. The method should follow the 850.6100 guideline. EFED concurs that minor soil degradates (AE F160459, AE F160460, AE F140458, and AE F147447) are not necessary for the recommended soil study (these degradates were previously recommended in the problem formulation).

In addition
, EFED recommends an aquatic analytical method (guideline 850.6100 ) that include s the major degradates observed in the available aquatic studies (listed below) : AE F160459, AE F160460, AE F140584, AE F147447, AE F092944, BCS

- CV14885 (Unknown A, benzoic acid with guanidine ), and BCS

- CO60720 (Unknown D, methyl ester benzoic acid with guanidine )

. This study is recommended because a recent DER review found that the submitted ECM/ ILV (water) studies (MRID 46451 701 and 46451702) did not include the major degradates of mesosulfuron

- methyl in aquatic environm ents (USEPA, 2013).

Hydrolysis ( MRID 45386418) : AE F092944 (38.4%, pH 4) and AE F140584 (50.3%, pH 4)

Anaerobic Aquatic Metabolism ( MRID 45386427 and MRID 45386429) : AE F160459 (25.9%,) and AE F160460 (12.6%)

Aerobic aquatic Metabolism ( MRID 453864 30 and MRID 45386431) : AE F160459 (21.6%)
, AE F147447 (16.1%)
, Unknown A (U1) (6.9

- 22%)

-- r evised as: benzoic acid with guanidine
, and Unknown D (U3) (6.2

- 13.1%)

-- r evised as methyl ester of benzoic acid with guanidine

.6 BCS Comment (P otential for B ioaccumulation of M esosulfuron

- methyl in F ish ):

“In Table 16 of the Preliminary Problem Formulation EPA noted a waiver was granted in December 2003 (DP Barcode 297232) for a fish bioaccumulation study.....this study should not be listed as a data gap.”

EF ED Response :
A data gap means there are no data available. However, EFED acknowledges the previously granted data waiver request

. A fish bioaccumulation study is not recommended

.

R EFERENCES

Hoberg, J. (2009). Outdoor Growth Inhibition of Aquatic Plants Exposed to Mesosulfuron

methyl. Report Number EBMML001. Document Number: M

- 329474

- 01

- 1. Unpublished study performed by Bayer CropScience. 238 p.

Rosinger, C. (1999). Evaluation of Herbicidal Potential of Metabolites of AE F130060. Report Nu mber: C002929. Document Number: M

- 185253

- 01

- 1. Unpublished study performed by Bayer CropScience. 10p. MRID: 45386331.

USEPA 2013. Review of Environmental Chemistry Methods (MRID 46451701) and Independent Lab Validation (MRID 46451702) for Mesosulfuron

- m ethyl. DP410701. 6pp.