Document ID: EPA-HQ-OPP-2012-0586-0008
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2013-08-28T04:00Z

OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460
                                       
                                       
                                       
  

MEMORANDUM

DATE:	March 26, 2013

SUBJECT:	Halosulfuron methyl Drinking Water Assessment for Additional Food/Feed Uses on Artichokes and Caneberry Subgroup 13-07A (DP Barcode D404096; PC Code 128721)

TO:	Barbara Madden, Risk Manager
		Sidney Jackson, Risk Manager Reviewer
		Luis Suguiyama, Acting Chief
		Risk Integration Minor Use, and Emergency Response Branch
		Registration Division (7505P)

&		Sheila Healy, Risk Assessor
		Christine Olinger, Chief
		Risk Assessment Branch III
		Health Effects Division (7509P)

FROM: 	Michael R. Barrett, Senior Chemist
		Environmental Risk Branch V
		Environmental Fate and Effects Division (7507P)

THROUGH:	Mah T. Shamim, Ph.D., Chief
		Environmental Risk Branch V
		Environmental Fate and Effects Division (7507P)

Tier I Estimated Surface and Ground Drinking Water Concentrations (EDWCs) for halosulfuron methyl, a sulfonylurea herbicide, were evaluated for the proposed new uses.  This drinking water exposure assessment incorporates proposed use patterns for artichokes and Caneberry crop Subgroup 13-07A (includes "Blackberry; loganberry; raspberry, black and red; wild raspberry; cultivars, varieties, and/or hybrids of these").  Conclusions from our evaluation about the potential level of acute and chronic exposure to halosulfuron methyl in drinking water remain the same as in the Environmental Fate and Effects Divison's (EFED's) previous assessment (see DP Barcode D394244, review dated 5/15/2012).  The current acute and chronic drinking water exposure estimates are summarized in Table 1.

Table 1. Tier I Estimated Drinking Water Concentrations (EDWCs) for human health drinking water risk assessment.

DRINKING WATER SOURCE
(MODEL USED) 
USE
(rate modeled)
MAXIMUM ESTIMATED DRINKING WATER CONCENTRATION  (EDWC)[c]  ( ppb) 
Groundwater
(SCI-GROW)
Fallow ground
(0.125 lb a.i./A/season) [a]
Acute
                                     0.065

Chronic
                                   <0.065
Surface Water
(Tier 1 Rice Model v.1.0)
Paddy Water/Tail Water; Rice
(0.0625 lb a.i./A/season) [b]
Acute
                                     59.2

                                       
Chronic
                                   <59.2
a Covers ground water exposure all uses other than rice; for the corn, fallow ground, and sugarcane use patterns of halosulfuron-methyl, based on a seasonal application 0.125 lb a.i./A.  Tier 1 estimates for exposure to parent halosulfuron methyl with the PFAM model may be higher but are not expected to be as high as with the Tier 1 Rice model. 
b Seasonal rate is 0.0625 lb a.i. /A, which is half of the rate of fallow ground.
c Surface water concentrations calculated by the Tier I Rice Model v1.0 and ground water concentrations calculated by SCI-GROW do not distinguish between peak and chronic concentration.

Background:

The proposed use rates for the specialty crop groups artichokes and caneberries are similar to other registered crops with the maximum season / annual rates equal to the highest such rates allowed on other crops (the proposed uses are summarized in Table 2; a summary of current uses is found in the previous Drinking Water Assessment attached at the end of this document.) However, the highest drinking water exposures are still expected from the use on rice which can involve direct application to fields which are flooded and from which water may be released into surface waters which are used as drinking water supplies.

Table 2. Proposed uses of halosulfuron-methyl.    Use information was obtained from the current and proposed labels for GWN-3061 [EPA Reg. No. 81880-2] and SANDEA Herbicide [EPA Reg. No. 81880-18].

Crop(s)
                            Single Application rate
                                  (lb a.i./A)
                       Max. # applications per Season[2]
                             Minimum Interval [2]
                                      PHI
                                    (days)
                              Maximum Annual Rate
                                  (1b a.i./A)
Artichoke
(ground application)
                                0.0469 - 0.0938
                                       2
                                      NS
                                      NS
                                    0.0938
Caneberry subgroup 13-07A; East of Rockies (ground application)
                                0.0234 - 0.0469
                                       2
                                      45
                                      14
                                    0.0938
Caneberry subgroup 13-07A; West of Rockies (ground application)
                                0.0352 - 0.0938
                                       2
                                      45
                                      14
                                    0.0938

Since the previous assessment there have been new developments in Terms of EFED models which provide the ability to conduct refined exposure assessments for drinking water from both surface water and groundwater sources, as follows:

For groundwater, the Pesticide Root Zone Model for GroundWater (PRZM-GW) provides Tier 1 and higher Tier site and region-specific exposure estimates for vulnerable groundwaters used as drinking water sources. More details can be found at:
http://www.epa.gov/oppefed1/models/water/index.htm#przm_gw

For surface water based drinking water supplies impacted by uses at sites where flooding is expected during part of the crop production cycle, the Pesticide Flooded Application Model. (PFAM) has been approved by EFED to provide more refined exposure estimates for acute and especially chronic drinking water exposure. This model is not yet posted on the EPA website, but currently, additional details can be found here:
https://sites.google.com/site/pfamodel/home

Conclusions

Although it is expected that the exposure levels estimated with PRZM-GW might be higher at the Tier 1 level than previously estimated we did not update the groundwater modeling for this review because even the most vulnerable drinking water wells are not expected to have as high an exposure potential as surface drinking water sources directly impacted by effluent / discharge from rice fields. EFED will therefore continue to rely upon the Tier 1 rice model estimates for a conservative estimate of drinking water exposure; but we do note that more refined estimates are possible with the newly implemented PFAM model, should such refinements become necessary in the future (the Health Effects Division is not requesting such refinements at this time.) 

              OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460
                                       
                                       
                                       

ATTACHMENT A: Copy of DWA dated 5/15/2012.
MEMORANDUM

DATE:	May 15, 2012

SUBJECT:	Halosulfuron methyl Drinking Water Assessment for Additional Food/Feed Uses on Proso Millet, Pasture and Rangeland Grass Forage, Fodder and Hay (Crop Group 17) (DP Barcode D394244; PC Code 128721)

TO:		Maggie Rudick, Risk Manager
		Kable Davis, Product Manager #25
		Dan Kenny, Chief
		Herbicide Branch
		Registration Division (7505P)

&		Whang Phang, Risk Assessor
		Nancy Dodd, Chemist
		Paula Deschamp, Chief
		Risk Assessment Branch III
		Health Effects Division (7509P)

FROM: 	José L. Meléndez, Chemist
		Environmental Risk Branch V
		Environmental Fate and Effects Division (7507P)

THROUGH:	Mah T. Shamim, Ph.D., Chief
		Environmental Risk Branch V
		Environmental Fate and Effects Division (7507P)

Tier I Estimated Surface and Ground Drinking Water Concentrations (EDWCs) for halosulfuron methyl, a sulfonylurea herbicide, were evaluated for the proposed new uses.  This drinking water exposure assessment incorporates proposed use patterns for proso millet, pasture and rangeland grass forage, fodder and hay (Crop Group 17).  Conclusions about the potential level of acute and chronic exposure to halosulfuron methyl in ground drinking water remain the same as in EFED's previous assessment; furthermore, exposure due to the use on rice was calculated.  See the Attachment B for a copy of the previous review (includes DP Barcode D358032 dated 6/4/2009, and subsequently DP Barcode D366411 dated 8/5/2010).

This drinking waters assessment (DWA) relies heavily on the previous assessment in that the groundwater values, a summary of the environmental fate characteristics, uncertainties, chemical structures, and several other details about halosulfuron methyl were previously provided.  Although it has been found that some degradates of halosulfuron methyl are present in the environment and could occur in drinking water, the residues of concern for the drinking water assessment (DWA) include parent halosulfuron methyl only (e.g., refer to HEDs Scoping Document, DP Barcode D394808).  A summary of the modeling results is provided in Table 1-1.  These estimates are, as in previous assessments, for exposure to parent halosulfuron methyl only.  In previous assessments, the uses on rice were not included.  Therefore, besides the EDWCs for several crop uses, the EDWCs for the uses on rice were calculated.  The results for the use on rice are significantly higher than for previous crops.  For modeling approach, assumptions, and uncertainties, see below.  A more definitive assessment and refinements are possible if needed by HED.  Should any questions arise, contact EFED.

Table 1-1.  Tier I Estimated Drinking Water Concentrations (EDWCs) for human health drinking water risk assessment
DRINKING WATER SOURCE
(MODEL USED) 
USE
(rate modeled)
MAXIMUM ESTIMATED DRINKING WATER CONCENTRATION  (EDWC)[c]  ( ppb) 
Groundwater
(SCI-GROW)
Fallow ground
(0.125 lb a.i./A/season) [a]
Acute
                                     0.065

Chronic
                                   <0.065
Surface Water
(Tier 1 Rice Model v.1.0)
Paddy Water/Tail Water; Rice
(0.0625 lb a.i./A/season) [b]
Acute
                                     59.2

                                       
Chronic
                                   <59.2
a Covers all uses other than rice; for the corn, fallow ground, and sugarcane use patterns of halosulfuron-methyl, based on a seasonal application 0.125 lb a.i./A.
b Seasonal rate is 0.0625 lb a.i./A, which is half of the rate of fallow ground.
c Surface water concentrations calculated by the Tier I Rice Model v1.0 and ground water concentrations calculated by SCI-GROW do not distinguish between peak and chronic concentration.

Modeling was previously performed with the Tier 1 Screening Concentration In GROund Water (SCI-GROW) model for ground water (these results were previously obtained and are described in the Attachment B).  Besides, in this assessment the Tier 1 Rice Model v.1.0 was used to estimate drinking water concentrations from the rice use (it is noted, however, that EFED's Tier 1 Rice Model v.1.0 is likely to provide conservative concentrations as described below). 

The Tier 1 Rice Model v.1.0, Modeling Approach and Uncertainties
The Tier I Rice Model v1.0 relies on an equilibrium partitioning concept to provide conservative estimates of environmental concentrations resulting from application of pesticides to rice paddies.  When a pesticide is applied to a rice paddy, the model assumes that it will instantaneously partition between a water phase and a sediment phase.  The simplified equation for the Tier 1 Rice Model v.1.0 (USEPA 2007) is as follows:
   
   Cw= mai    '0.00105+0.00013Kd  

  
Where:    Cw = water concentration or the EDWC [ug/L or ppb]
      mai' = mass applied per unit area [kg/ha] (i.e., the seasonal application rate)
      Kd = water-sediment partitioning coefficient [L/kg]

Note that neither the degradation of the pesticide nor the mass transfer from the aqueous phase to the sediment is considered in this conceptualization, which greatly simplifies the model.  The absence of degradation adds conservatism to the model (i.e., estimated concentrations should be higher than those usually found in rice paddies).  The absence of mass transfer processes can either add or reduce conservatism depending on numerous conditions such as whether the pesticide is soil or water applied and whether actual degradation occurs preferentially in the sediment or the water compartment; however, consideration of this parameter is a refinement beyond a Tier I conceptualization.  Table 1-2 provides a summary of the input parameters and results of the rice model.

Table 1-2. Tier I Rice Model v1.0 input parameters for halosulfuron-methyl use on rice
                                   Parameter
                                     Value
                                Justification[1]
                                     Source
                      Application Rate (mai') (kg a.i./ha)
                                    0.07005
 0.0625 lb a.i./A/application x 1 application = 0.0625 lb a.i./A x 1.1208 kg·A/ha·lb = 0.07005 kg a.i./ha
                                 Product label
                Soil-to-Water Partition Coefficient (Kd) (L/kg)
                                      1.03
 Kd = Mean KOC (103 L/kgOC) x 1% organic carbon = 1.03 L/kg
                                 MRID 42139411
                                     EDWCs
                              (acute and chronic)
                                     (ppb)
                                      59.2
                          Cw= mai    '0.00105+0.00013Kd
                                       
                       Cw= 0.070050.00105+0.00013(1.03)
                                       
                                 CW = 59.2 ppb
                                  USEPA 2007
[1] Refer to the Appendix III of the Tier 1 Rice Model v.1.0 Documentation (USEPA 2007).

Most of the assumptions used in this model help ensure that the outputs are protective of most environments associated with rice agriculture.  The model assumptions include the following:

      1.  Movement of pesticide on suspended sediment is not considered.
      2.  Degradation does not occur.
      3.  Volatilization and other dissipation processes are not considered.
      4.  Partitioning to sediment is instantaneous.
      5.  Water is available for human or wildlife exposure instantaneously.
      6.  Water column depth is 10 cm.
      7.  Sediment depth is 1 cm.
      8.  All pore space is saturated with water.
      9.  Organic carbon fraction is 0.01.
      10.  Bulk density is 1300 kg/m[3].
      11.  Grain density is 2650 kg/m[3].

The Tier 1 Rice Model v.1.0 provides screening-level estimates and as such, are expected to exceed peak values found in the environment in most cases.  This expectation is due to the protective assumptions of the model listed above, such as exclusion of degradation as well as dilution with uncontaminated water outside the paddy.  They represent paddy discharge water that has not degraded, and has not diluted with uncontaminated water outside the paddy.

Estimates from the Tier I model generally do not represent typical concentrations found in human drinking water, as they represent paddy discharge water.  The chronic concentrations as well as offsite concentrations are expected to be conservative.  
If Tier I estimates calculated by this screening method do not exceed the HED's concern level in a risk assessment, there is high confidence that there will be little or no risk above the level of concern from exposure through water resources.  However, because of the uncertainties associated with a screening method, when a level of concern is exceeded it cannot be determined whether the exceedance will in fact occur or whether this method has overestimated the exposure.

For DWA, evaluation of the Tier I Rice Model v.1.0 indicated that modeled within-paddy estimates are conservative, exceeding peak measured concentrations of pesticides in water bodies well downstream of rice paddies in five evaluated studies by less than one order of magnitude to multiple orders of magnitude.  The five studies assessed were conducted in Louisiana and California using four different pesticides (USEPA 2007).  It appears that the range of modeled estimate exceedances over measured concentrations is most likely in response to chemical, environmental, and study-specific factors.  Estimates from the Tier I model generally do not represent typical concentrations found in human drinking water, as they represent direct paddy discharge water.

Updated Use Information
The current and proposed use sites for halosulfuron methyl are summarized in Table 1-3 (the proposed uses are shaded blue).  Halosulfuron methyl is a selective preemergence or post-emergence sulfonylurea herbicide.  It is currently registered for a number of food crops and fallow ground by Canyon Group, LLC for the products GWN-3061 [contains 75% A.I., EPA Reg. No. 81880-2], YUKON Herbicide [contains 12.5% A.I. plus 55% of the sodium salt of dicamba, EPA Reg. No. 81880-6] and SANDEA Herbicide [contains 75% A.I., EPA Reg. No. 81880-18].  Halosulfuron was originally registered in the United States in 1994 by Nissan Chemical Industries, Inc. (NCI) and Monsanto Company.  Gowan Company and Nissan Chemical Industries, Inc. have formed a joint venture named Canyon Group LLC in 1994.  The current petition for registration for proso millet, and pasture and rangeland (Crop Group 17) was submitted on behalf of Canyon Group LLC. 

Table 1-3.  Registered and proposed uses of halosulfuron-methyl.  New uses shaded blue.  Use information was obtained from the current and proposed labels for GWN-3061 [EPA Reg. No. 81880-2], YUKON Herbicide [EPA Reg. No. 81880-6] and SANDEA Herbicide [EPA Reg. No. 81880-18]
Crop(s)
                               Application rate
                                  (lb a.i./A)
                       Max. # applications per Season[2]
                             Minimum Interval [2]
                                      PHI
                                    (days)
                              Maximum Annual Rate
                                  (1b a.i./A)
Proso Millet
(ground application)
                                0.0234 - 0.0313
                                       1
                                      NS
                                      37
                                    0.0313
Pasture & Rangeland
(ground application)
                                0.0313 - 0.0625
                                       2
                                      NS
                                      N/A
                                    0.0625
Field corn (including grown for seed)
                                0.031 - 0.0625
                                       2
                                      NS
                                      30
                                     0.125
Sweet corn and popcorn
                                    0.0313
                                       2
                                      NS
               30 day pre-grazing or forage harvesting interval
                                  0.0625 [3]
Grain sorghum (milo)

                                 0.031 - 0.047
                                       1
                                      N/A
               30 day pre-grazing or forage harvesting interval
                                     0.047
Rice[1]

                                0.0313 - 0.0625
                                     2 (?)
Preplant, postplant, and post flood; preplant and at plant burndown applications allowed.
                                      NS
                                      48
                                    0.0625
Sugarcane

                                0.031 - 0.0625
                                       3
                                      NS
           30 day pre-grazing or forage / silage harvesting interval
                                     0.125
Cotton

                                0.031 - 0.0625
                                      NS
                        Poe up to row closure permitted
                                      NS
                                      28
                                    0.0625
Fallow ground

                                0.031 - 0.0625
                                       2
                                      NS
                                      N/A
                                     0.125
Dry shelled beans
                                 0.023 - 0.031
                                      NS
                                      NS
                                      30
                                   0.094 [4]
                          (0.047/cc, 0.094/12 months)
Pea and bean, succulent shelled, subgroup 6B
                                     0.023
                                      NS
                                      NS
                                      NS
                               (0.023 per year)
Pea and bean, succulent shelled, subgroup 6B (west of the Rockies)
                                 0.023 - 0.047
                                      NS
                                      NS
                                      30
                               (0.047 per year)
Vegetable, tuberous and corm, subgroup 1C
                                 0.023 - 0.047
                                       1
                                      N/A
                                      45
                                     0.047
Rhubarb
                                 0.023 - 0.047
                                       2
                                      N/A
                                      60
                                     0.047
Bushberry subgroup 13-07B
                                 0.023 - 0.047
                                      NS
                                      45
                                      14
                                     0.094
Apples (east of the Rockies)
                                 0.023 - 0.047
                                      NS
                                      NS
                                      14
                                     0.094
                                       
Apples (west of the Rockies)
                                 0.035 - 0.094
                                      NS
                                      NS
                                      14
                                     0.094
                                       
Soybeans

                                0.031 - 0.0625
                                     2 (?)
   Preemergence or Preplant Spring  -  21 days before planting to emergence,
                                 Fall burndown
                                      NS
                             (probably ~150 days)
                                      NS
                                   0.125 (?)
Okra
                                 0.023 - 0.047
                                      NS
                                     0.094
                                      30
                                     0.094
[1] Do not reintroduce water into rice fields or checks for at least five days following dry broadcast applications of product.  Do not make more than one pre-plant or at planting application of product to rice per growing season.
[2] N/A = not applicable.  NS = not specified.
[3] Some labels are unclear and imply that the second application to sweet corn/popcorn may not exceed 0.047 lb a.i./A.
[4]Although these are the limits stated on the label, it also states "Make only one Sandea application per crop cycle". Since it does not appear to be possible to have more than 2 crops per year, EFED modeled this use in that way. 

References
U.S. Environmental Protection Agency 2007.  Guidance for Tier I Estimation of Aqueous Pesticide Concentrations in Rice Paddies (dated 05/08/2007).  Available at http://www.epa.gov/oppefed1/models/water/rice_tier_i.htm (accessed 05/02/2012).

Attachment B. COPY OF DWA DATED 8/5/10
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460

                                                                               
                                      OFFICE OF
                             PREVENTION, PESTICIDES AND
                                  TOXIC SUBSTANCES
                                                                               

                                                
      	
PC Code: 128721
DP Barcode: D366411

MEMORANDUM                                                                         August 5, 2010

SUBJECT:	Halosulfuron methyl Drinking Water Assessment for Additional food uses on Dried Shelled Peas & Beans (Except Soybean), Succulent Shelled Peas & Beans, Apples, Rhubarb, Bushberry, Fruiting Vegetables and Tuberous & Corm Vegetables 

            (DP Barcode: D366411; PC Code 128721)

TO:		Whang Phang, Risk Assessor
		Nancy Dodd, Chemist
		Health Effects Division (7509P)

FROM: 	Michael R. Barrett, Ph.D. Senior Chemist
		Environmental Fate and Effects Division (7507P)

THROUGH:	Mah T. Shamim, Ph.D., Chief
		Environmental Risk Branch V
		Environmental Fate and Effects Division (7507P)

Previously calculated (DP Barcode D358032  -  6/4/2009 assessment) Tier I Estimated Surface Drinking Water Concentrations (EDWCs) for halosulfuron methyl (the residues of concern include parent compound only) were reevaluated for the proposed new uses. This drinking water exposure assessment incorporates proposed use patterns for several new crops. Conclusions about the potential level of acute and chronic exposure to halosulfuron methyl in drinking water remain the same as in our previous assessment (see Appendix 2 for a copy of the previous review):

For parent alone:
   * 8.3  ug/l or ppb for acute exposure (1 in 10 year annual peak daily concentration) 
   * 1.7 ug/l for (non-cancer) chronic exposure (1 in 10 year annual mean concentration)
      
These EDWCs were calculated using the FIRST mode run for the corn, fallow ground, and sugarcane use patterns (further details are provided in our previous review cited above.) EDWCs were also previously estimated for ground-water source drinking water and remain unchanged (0.065 ug/l for acute and chronic exposure.)

Discussion

Although some degradates of halosulfuron-methyl have been found to be present in the environment and could occur in drinking water, the residues of concern for the drinking water assessment consist of parent halosulfuron-methyl only and these estimates are, as in previous assessments, for exposure to parent halosulfuron methyl only.

Modeling was with the Tier 1 PRZM-EXAMS metamodel "FIRST" (FQPA Index Reservoir Screening Tool) for surface water and the SCI-GROW (Screening Concentration In GROund Water) model for ground water (see Appendix 1 for details). A suitable model for estimation of drinking water concentrations from the rice use is not currently available (EFED's tier 1 rice model does not provide concentration estimates that can be associated with levels expected in drinking water.)

Updated Use Profile

The current and proposed use sites for halosulfuron methyl are summarized in Table (the proposed uses are marked by an asterisk). Halosulfuron-methyl is a selective preemergence or post-emergence sulfonylurea herbicide.  Halosulfuron is currently registered for a number of food crops and fallow ground under Section 3 by Nissan Chemical Industries, Inc. product GWN-3061 [EPA Reg. No. 81880-2] and other products and the Gowan Company product Permit Herbicide [81880-2-10163]. Halosulfuron was originally registered in the United States in 1994 by Nissan Chemical Industries, Inc. (NCI) and Monsanto Company. Gowan Company and NCI have formed a joint venture named Canyon Group LLC. The current petition for registration for several minor use crops being reviewed here has been submitted by Interregional Research Project No.4. 

Table 1.  Registered and proposed uses of halosulfuron-methyl.
Crop(s)[1] a
Max. Application rate (min.)
Max. # applications / Season[3]
Minimum Interval [2, 3]
PHI
(days)

Maximum Annual Rate
(1b ai/A)
Field corn

0.0625
(0.031)
2
NS
30
0.125
Sweet corn and popcorn

0.0313
2
NS
30 day pre-grazing or forage harvesting interval
0.0625 a 
Grain sorghum

0.047
1
NA
30 day pre-grazing or forage harvesting interval
0.047
Rice

0.0625
2 (?)
Preplant, postplant, and post flood applications allowed.
NS
48
0.0625
Sugarcane

0.0625
(Range 0.031-0.62)
3
NS
30 day pre-grazing or forage / silage harvesting interval
0.125
Cotton

0.0625
(Range 0.031-0.62)
NS
Poe up to row closure permitted
NS
28
0.0625
Fallow ground

0.0625
(Range 0.031-0.62)
2
NS
NA
0.125
* Dry shelled beans and pea (east of the Rockies)
(Ground app.)
0.031
(Range 0.023-0.031)
NS
NS
30
0.094 [4] 
(0.047 per crop cycle, 0.094 per 12 months)
* Dry shelled beans and pea (west of the Rockies)
(Ground app.)
0.047
(Range 0.023-0.047)
NS
NS
30
0.094
(0.047 per crop cycle, 0.094 per 12 months)
* Pea and bean, succulent shelled, subgroup 6B
0.023
(0.023)
NS
NS
NS
0.023
* Succulent snap beans (incl. lima beans)
0.0625
(0.031)
NS
NS
30
(0.0625 per crop cycle, 0.125 per 12 months)
Vegetable, tuberous and corm, subgroup l C
07.047
(0.023)
1
NA
45
0.047
Rhubarb
0.047
(0.023)
2
NA
60
0.047
* Bushberry
0.047
(0.023)
NS
45
60
0.094
* Apples (east of the Rockies)
0.047
(0.023)
NS
NS
14
0.094

* Apples (west of the Rockies)
0.094
(0.035)
NS
NS
14
0.094

Soybeans

0.0625 
(Range 0.031-0.62)
2 (?)
Preemg or Preplt  -  21 days bef. Planting to emg. 
Fall burndown  -  anytime after harvest until ground freezes

NS 
(probably about 150 days)
NS
0.125 (?)
[1] Crop uses currently being proposed are marked with an "*"
[2] NA = not applicable.
[3] NS = not specified.
[4] Although these are the limits stated on the proposed label, the label also states "Make only one Sandea application per crop cycle". Since it does not appear to be possible to have more than 2 crops per year, we modeled this use in that way. 
[a]  Some labels are unclear and imply that the second application to sweet corn / popcorn may not exceed 0.047 lb ai / acre.

Note that there are rotational crop intervals of up to 36 months for many crops (including 36 months for sugar beets in ND, MN, and the Red River Valley and 24 months for spinach, red beet, and sugar beets (in other use areas).

APPENDIX 1: Aquatic Exposure:  SCI-GROW and FIRST Water Quality Modeling Inputs and Results 

Model inputs and results (updates the previous review are summarized in Table 2, Table 3, and Table 4.  No acceptable scenario for estimation of drinking water concentrations from the rice use exists at this time so no estimates are provided (results of the tier 1 rice model have been presented previously, see DP Barcode D278449.)  Note that the current EFED rice model for ecological aquatic exposure from a rice use overestimates levels that would occur in drinking water because it does not consider the degradation of the pesticide or the dilution of the pesticide as it is transported away from the rice field into the drinking water source. In the absence of an acceptable EFED and OPP approved model the rice use was therefore not directly evaluated.

Table 2.  Environmental Fate model input values used with FIRST drinking water exposure assessment model (field corn and sugarcane uses). 

Parameter
Input
Source
Solubility (ppm)
1630
Product chemistry submissions. Solubility decreases to 15 ppm at pH 5 and increases to 7470 ppm at pH 9.
Aerobic soil t1/2 (days) 1
48
90% Upper-bound confidence limit on mean[2] (MRID 42139410; additional data considered from MRIDs 42661413, 42661413, 42976302, 42976303, and 42976304.) 
Aerobic aquatic t1/2 (days) 
96
EFED Input Guidance for compound with no aerobic aquatic study (2x the aerobic soil half-life.
Photolysis t1/2 in water (days)
30
MRID 42661409.

Organic carbon partition coefficient  -  KOC (mL/g)
103
Average or median value from batch -equilibrium adsorption studies (MRID 42139411)
Application rate (lb a.i./Acre) 2
0.0625
Label -maximum single rate for applications to field corn or sugarcane. Lower rates for other crops (refer to the usage summary table for details.)
# applications/year
2, or...
Label maximum for field corn or sugarcane. One application at the maximum rate for other crops.
Application interval, days
21
Estimated from label directions allowing a split application in the period from spike to layby for corn; a 45-day interval between applications was also modeled.
Application Method
Aerial or...
Allowed on label for corn, sorghum, and rice. Ground application assumed for other crops.
1 For halosulfuron, field dissipation half-lives and monolith lysimeter dissipation half-lives were on average much longer than for the aerobic metabolism studies.  An overall mean of these studies was calculated after first assuming the degradation half-lives in the field studies were equal to 1.2 times the dissipation half-lives for the top soil layer.  Additional indication of the potentially high persistence of halosulfuron is provided by the halosulfuron registration label which strongly implicates that halosulfuron may persist in soil at phytotoxic levels for up to three years after application.  After application of halosulfuron, rotational restrictions of one year to three years exist on various crops.  These label restrictions are consistent with an active ingredient that persists in the environment for years (in this case, at phytotoxic levels).

[2] Values given in this table are for halosulfuron methyl corn/ sugarcane uses, which were the crops which yielded the highest EECs with both models.  Model input and output files are provided in Appendix B.

Results of surface water source modeling are summarized in Table 3 and ground-water modeling in Table 5.  The acute exposure concentrations for an index reservoir with FIRST range from 3.8 to 8.3 ppb or ug/L for the various use patterns modeled.  The chronic exposure estimates (annual average EDWC) with FIRST ranged from 0.8 to 1.7 ppb. The highest acute and chronic exposure EDWC were both associated with a corn and sugarcane use pattern.  The Tier 1 EDWC for ground-water (using the SCI-GROW model) was significantly lower (0.065 ppb for both acute and chronic exposure). 

Table 3.  Summary of halosulfuron methyl scenarios modeled with FIRST. 

Represent-ative Crop

Single Rate, lb ai/A

# of applica-tions

Interval between appl., days

Total seasonal rate, ai/a

Acute EDWC, ug/L

Annual EDWC, ug/L

Tomato

0.047

2

21

0.094

6.2

1.3

Asparagus[1] 

0.047

2

45

0.094

5.5

1.2

Sugarcane

0.042

3

21

0.125

7.3

1.5

Corn, Sugarcane
(ground)

0.063

2

21

0.125

8.3

1.7

Corn, Sugarcane,
Fallow ground

0.063

2

45

0.125

7.3

1.5

Pioneer IR corn,
Apples - west of Rockies

0.094

1

NA

0.094

3.8

0.80
Soybean

0.063
2
150
0.125
5.4
1.1
Cotton
0.063
1
NA
0.063
4.7
1.0
[Note:  The EFED  default 87% crop area assumption was used except for corn (46% crop area).]
[1] And flowering vegetables. This model run is also representative of dried shell beans east of the Rockies (only lower rates permitted for dry beans west of the Rockies) and apples east of the Rockies.

Table 4.  Environmental Fate Input Parameters for halosulfuron methyl in SCI-GROW.

                                   Parameter
                                 Halosulfuron
                                    Source
Organic Carbon Partition Coefficient (KOC)
103 (Avg.)
                                 Median value.
Aerobic Soil Metabolism Half-Life (days)
48
                                Average value.

Table 5.  Summary of halosulfuron methyl ground-water scenario modeled with SCI-GROW.
                              Representative Crop
                             Single Rate, lb ai/A
                               # of applications
                           Total seasonal rate, ai/a
                                Acute EEC, ug/L
                               Chronic EEC, ug/L
Field corn, sugarcane
                                    0.0625
                                       2
                                     0.125
                                     0.065
                                     0.065

New and updated model runs

A. SCI-GROW
                          VERSION 2.3
            ENVIRONMENTAL FATE AND EFFECTS DIVISION
                 OFFICE OF PESTICIDE PROGRAMS
             U.S. ENVIRONMENTAL PROTECTION AGENCY
                        SCREENING MODEL
                FOR AQUATIC PESTICIDE EXPOSURE
 
 SciGrow version 2.3
 chemical:Halosulfuron-methyl
 time is  5/22/2009  17:29:40
 ------------------------------------------------------------------------
  Application      Number of       Total Use    Koc      Soil Aerobic
  rate (lb/acre)  applications   (lb/acre/yr)  (ml/g)   metabolism (days)
 ------------------------------------------------------------------------
      0.063           2.0           0.125      1.03E+02       48.0
 ------------------------------------------------------------------------
 groundwater screening cond (ppb) =   6.54E-02 
 ************************************************************************

B. FIRST

   RUN No.   1 FOR Halosulfuron met ON   Corn, Suga    * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .063(   .110)   2  21     103.0 1630.0   AERIAL(16.0)  87.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0  JAN 1, 2007
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              8.385                      1.773

   RUN No.   2 FOR Halosulfuron Met ON   corn  -  special** * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .063(   .110)   2  21     103.0 1630.0   AERIAL(16.0)  46.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0  JAN 1, 2007
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              4.434                       .937
** this run utilizes a corn-specific PCA.

   RUN No.   3 FOR Halosulfuron met ON   Soybeans      * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .063(   .070)   2 150     103.0 1630.0   AERIAL(16.0)  87.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0  JAN 1, 2007
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              5.381                      1.138

APPENDIX 2: Previous Drinking Water Exposure Assessment

                          [Begins on following page]

                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460

                                                                               
                                      OFFICE OF
                             PREVENTION, PESTICIDES AND
                                  TOXIC SUBSTANCES
                                                                               

                                                
      	
PC Code: 128721
DP Barcode: D358032

MEMORANDUM                                                                         June 4, 2009

SUBJECT:	Halosulfuron methyl Drinking Water Assessment for Additional food uses (including proposed use on soybean)
            (DP Barcode: D358032; PC Code 128721)

TO:		Whang Phang, Risk Assessor
		Nancy Dodd, Chemist
		Health Effects Division (7509P)

FROM: 	Michael R. Barrett, Ph.D. Senior Chemist
		Environmental Fate and Effects Division (7507P)

THROUGH:	Mah T. Shamim, Ph.D., Chief
		Environmental Risk Branch V
		Environmental Fate and Effects Division (7507P)

I. Summary and Conclusions

A drinking water exposure assessment was performed for halosulfuron-methyl (methyl 5-{[(dimethoxy-2-pyrimidinyl) amino] carbonylaminosulfonyl -3-chloro -1-methyl-1-H- pyrazole-4-carboxylate) that incorporates a proposed use pattern for soybeans and updates a previous Drinking Water Assessment (see 1/22/02 "Expanded Section 3 and IR-4 Uses to add Asparagus and Flowering Vegetables to Halosulfuron-methyl Label" (Pages 19-24 and 58-62, see also DP Barcode D278449, reviews dated 8/13/2002). The current and proposed use sites for halosulfuron methyl are summarized in 

Table 1-3.  Registered and proposed uses of halosulfuron-methyl.  New uses shaded blue.  Use information was obtained from the current and proposed labels for GWN-3061 [EPA Reg. No. 81880-2], YUKON Herbicide [EPA Reg. No. 81880-6] and SANDEA Herbicide [EPA Reg. No. 81880-18]
Crop(s)
                               Application rate
                                  (lb a.i./A)
                       Max. # applications per Season[2]
                             Minimum Interval [2]
                                      PHI
                                    (days)
                              Maximum Annual Rate
                                  (1b a.i./A)
Proso Millet
(ground application)
                                0.0234 - 0.0313
                                       1
                                      NS
                                      37
                                    0.0313
Pasture & Rangeland
(ground application)
                                0.0313 - 0.0625
                                       2
                                      NS
                                      N/A
                                    0.0625
Field corn (including grown for seed)
                                0.031 - 0.0625
                                       2
                                      NS
                                      30
                                     0.125
Sweet corn and popcorn
                                    0.0313
                                       2
                                      NS
               30 day pre-grazing or forage harvesting interval
                                  0.0625 [3]
Grain sorghum (milo)

                                 0.031 - 0.047
                                       1
                                      N/A
               30 day pre-grazing or forage harvesting interval
                                     0.047
Rice[1]

                                0.0313 - 0.0625
                                     2 (?)
Preplant, postplant, and post flood; preplant and at plant burndown applications allowed.
                                      NS
                                      48
                                    0.0625
Sugarcane

                                0.031 - 0.0625
                                       3
                                      NS
           30 day pre-grazing or forage / silage harvesting interval
                                     0.125
Cotton

                                0.031 - 0.0625
                                      NS
                        Poe up to row closure permitted
                                      NS
                                      28
                                    0.0625
Fallow ground

                                0.031 - 0.0625
                                       2
                                      NS
                                      N/A
                                     0.125
Dry shelled beans
                                 0.023 - 0.031
                                      NS
                                      NS
                                      30
                                   0.094 [4]
                          (0.047/cc, 0.094/12 months)
Pea and bean, succulent shelled, subgroup 6B
                                     0.023
                                      NS
                                      NS
                                      NS
                               (0.023 per year)
Pea and bean, succulent shelled, subgroup 6B (west of the Rockies)
                                 0.023 - 0.047
                                      NS
                                      NS
                                      30
                               (0.047 per year)
Vegetable, tuberous and corm, subgroup 1C
                                 0.023 - 0.047
                                       1
                                      N/A
                                      45
                                     0.047
Rhubarb
                                 0.023 - 0.047
                                       2
                                      N/A
                                      60
                                     0.047
Bushberry subgroup 13-07B
                                 0.023 - 0.047
                                      NS
                                      45
                                      14
                                     0.094
Apples (east of the Rockies)
                                 0.023 - 0.047
                                      NS
                                      NS
                                      14
                                     0.094
                                       
Apples (west of the Rockies)
                                 0.035 - 0.094
                                      NS
                                      NS
                                      14
                                     0.094
                                       
Soybeans

                                0.031 - 0.0625
                                     2 (?)
   Preemergence or Preplant Spring  -  21 days before planting to emergence,
                                 Fall burndown
                                      NS
                             (probably ~150 days)
                                      NS
                                   0.125 (?)
Okra
                                 0.023 - 0.047
                                      NS
                                     0.094
                                      30
                                     0.094
[1] Do not reintroduce water into rice fields or checks for at least five days following dry broadcast applications of product.  Do not make more than one pre-plant or at planting application of product to rice per growing season.
[2] N/A = not applicable.  NS = not specified.
[3] Some labels are unclear and imply that the second application to sweet corn/popcorn may not exceed 0.047 lb a.i./A.
[4]Although these are the limits stated on the label, it also states "Make only one Sandea application per crop cycle". Since it does not appear to be possible to have more than 2 crops per year, EFED modeled this use in that way. 

.

Modeling was with the Tier 1 PRZM-EXAMS metamodel "FIRST" (FQPA Index Reservoir Screening Tool) for surface water and the SCI-GROW (Screening Concentration In GROund Water) model for ground water. The acute exposure concentrations with FIRST ranged up to 8.3 ppb or ug/L as estimated for the use pattern for corn and sugarcane.  Chronic exposure (annual average EDWC) estimates ranged up to 1.7 ppb, also calculated for the corn and sugarcane use pattern.  Tier 1 EDWC for ground-water (using the SCI-GROW model) were significantly lower. A suitable model for estimation of drinking water concentrations from the rice use is not currently available (EFED's tier 1 rice model does not provide concentration estimates that can be associated with levels expected in drinking water.)

II. Discussion

      A.  USE PROFILE

Halosulfuron-methyl is a selective preemergence or post-emergence sulfonylurea herbicide.  Halosulfuron is currently registered under Section 3 by Nissan Chemical Industries, Inc. product GWN-3061 [EPA Reg. No. 81880-2] and other products and the Gowan Company product Permit Herbicide [81880-2-10163]. Halosulfuron was originally registered in the United States in 1994 by Nissan Chemical Industries, Inc. (NCI) and Monsanto Company. Gowan Company and NCI have formed a joint venture named Canyon Group LLC. Canyon Group LLC has submitted a request for a new use on soybeans.  Halosulfuron-methyl is currently registered for use on some fruiting vegetables, field corn, sweet corn, grain sorghum, rice, sugarcane, tree nuts, and turfgrass. This drinking water assessment also considers the impact of a proposed use on soybeans. Registered uses are summarized in 

Table 1-3.  Registered and proposed uses of halosulfuron-methyl.  New uses shaded blue.  Use information was obtained from the current and proposed labels for GWN-3061 [EPA Reg. No. 81880-2], YUKON Herbicide [EPA Reg. No. 81880-6] and SANDEA Herbicide [EPA Reg. No. 81880-18]
Crop(s)
                               Application rate
                                  (lb a.i./A)
                       Max. # applications per Season[2]
                             Minimum Interval [2]
                                      PHI
                                    (days)
                              Maximum Annual Rate
                                  (1b a.i./A)
Proso Millet
(ground application)
                                0.0234 - 0.0313
                                       1
                                      NS
                                      37
                                    0.0313
Pasture & Rangeland
(ground application)
                                0.0313 - 0.0625
                                       2
                                      NS
                                      N/A
                                    0.0625
Field corn (including grown for seed)
                                0.031 - 0.0625
                                       2
                                      NS
                                      30
                                     0.125
Sweet corn and popcorn
                                    0.0313
                                       2
                                      NS
               30 day pre-grazing or forage harvesting interval
                                  0.0625 [3]
Grain sorghum (milo)

                                 0.031 - 0.047
                                       1
                                      N/A
               30 day pre-grazing or forage harvesting interval
                                     0.047
Rice[1]

                                0.0313 - 0.0625
                                     2 (?)
Preplant, postplant, and post flood; preplant and at plant burndown applications allowed.
                                      NS
                                      48
                                    0.0625
Sugarcane

                                0.031 - 0.0625
                                       3
                                      NS
           30 day pre-grazing or forage / silage harvesting interval
                                     0.125
Cotton

                                0.031 - 0.0625
                                      NS
                        Poe up to row closure permitted
                                      NS
                                      28
                                    0.0625
Fallow ground

                                0.031 - 0.0625
                                       2
                                      NS
                                      N/A
                                     0.125
Dry shelled beans
                                 0.023 - 0.031
                                      NS
                                      NS
                                      30
                                   0.094 [4]
                          (0.047/cc, 0.094/12 months)
Pea and bean, succulent shelled, subgroup 6B
                                     0.023
                                      NS
                                      NS
                                      NS
                               (0.023 per year)
Pea and bean, succulent shelled, subgroup 6B (west of the Rockies)
                                 0.023 - 0.047
                                      NS
                                      NS
                                      30
                               (0.047 per year)
Vegetable, tuberous and corm, subgroup 1C
                                 0.023 - 0.047
                                       1
                                      N/A
                                      45
                                     0.047
Rhubarb
                                 0.023 - 0.047
                                       2
                                      N/A
                                      60
                                     0.047
Bushberry subgroup 13-07B
                                 0.023 - 0.047
                                      NS
                                      45
                                      14
                                     0.094
Apples (east of the Rockies)
                                 0.023 - 0.047
                                      NS
                                      NS
                                      14
                                     0.094
                                       
Apples (west of the Rockies)
                                 0.035 - 0.094
                                      NS
                                      NS
                                      14
                                     0.094
                                       
Soybeans

                                0.031 - 0.0625
                                     2 (?)
   Preemergence or Preplant Spring  -  21 days before planting to emergence,
                                 Fall burndown
                                      NS
                             (probably ~150 days)
                                      NS
                                   0.125 (?)
Okra
                                 0.023 - 0.047
                                      NS
                                     0.094
                                      30
                                     0.094
[1] Do not reintroduce water into rice fields or checks for at least five days following dry broadcast applications of product.  Do not make more than one pre-plant or at planting application of product to rice per growing season.
[2] N/A = not applicable.  NS = not specified.
[3] Some labels are unclear and imply that the second application to sweet corn/popcorn may not exceed 0.047 lb a.i./A.
[4]Although these are the limits stated on the label, it also states "Make only one Sandea application per crop cycle". Since it does not appear to be possible to have more than 2 crops per year, EFED modeled this use in that way. 

.

Table 6.  General usage information for halosulfuron-methyl.
Crop(s)
Max. Application rate (range)
Max. # applications / Season
Interval
PHI
(days)

Maximum Annual Rate
(1b ai/A)
Field corn

0.062
(Range 0.031-0.62)
2
NS
30
0.125
Sweet corn and popcorn

0.0313
2
NS
30 day pre-grazing or forage harvesting interval
0.0625
Grain sorghum

0.047
1
NA
30 day pre-grazing or forage harvesting interval
0.047
Rice

0.0625
2 (?)
Preplant, postplant, and post flood applications allowed.
NS
48
0.0625
Sugarcane

0.0625
(Range 0.031-0.62)
3
NS
30 day pre-grazing or forage / silage harvesting interval
0.125
Cotton

0.0625
(Range 0.031-0.62)
NS
Poe up to row closure permitted
NS
28
0.0625
Fallow ground

0.0625
(Range 0.031-0.62)
2
NS
NA
0.125
Dry beans

0.047
(Range 0.023-0.47)
NS
NS
NS
0.094
(0.047 per crop cycle, 0.094 per 12 months)
Soybeans

0.0625 
(Range 0.031-0.62)
2 (?)
Preemg or Preplt  -  21 days bef. Planting to emg. 
Fall burndown  -  anytime after harvest until ground freezes

NS 
(probably about 150 days)
NS
0.125 (?)
NA = not applicable.
NS = not specified.

Note that there are rotational crop intervals of up to 36 months for many crops (including 36 months for sugar beets in ND, MN, and the Red River Valley and 24 months for spinach, red beet, and sugar beets (in other use areas).

      B.  ENVIRONMENTAL FATE AND TRANSPORT CHARACTERIZATION

Halosulfuron-methyl has properties with regards to persistence and sorptivity that allow for a potential for residues to occur in ground and surface waters from its use as a herbicide. A summary of halosulfuron-methyl properties as included in the modeling of exposure from drinking water is provided in the "Estimation of Drinking Water Exposure" section of this document.

Although some degradates of halosulfuron-methyl have been found to be present in the environment and could occur in drinking water, the residues of concern for the drinking water assessment consist of parent halosulfuron-methyl only (see Appendix A for chemical structures).  

The environmental fate profile for halosulfuron methyl is complex indicating highly variable persistence, significant mobility in many soils, and / or the presence of a number of degradation products in the environment. Laboratory studies have demonstrated that halosulfuron degradation products can also be quite persistent and mobile.   

Some of the data would indicate relatively rapid degradation of halosulfuron under some conditions: aerobic soil metabolism half-lives and hydrolysis rates of only a few weeks in pure water (Table 7).  However, there are also clear indications of very long (i.e., up to two or three years) persistence of halosulfuron residues: Firstly, in some of the field studies a significant portion of the applied halosulfuron methyl persisted for several months or longer (see the 90% disappearance times in Table 7) and a first-order kinetic model poorly described the data and severely under predicted the residue levels remaining several months to a year or more after application. Secondly, recognition of the danger of residues persisting at phytotoxic levels for an extended period is captured in label restrictions that prohibit rotation into many crops for 1, 2, or even three years after the last application of halosulfuron methyl. 

Of several environmental degradates all are fragments of the parent molecule (i.e., containing either the pyrimidine or pyrazole moieties, but not both due to cleavage of the sulfonylurea bridge) with the exception of the "halosulfuron-methyl rearrangement ester", sometimes referred to as "RRE" or "MON 5781." This product results from the abstraction of the S02NHCO moiety between the rings, such that the pyrimidine and pyrazole rings are then joined together only by an NH group. Since these degradates are not included in the drinking water residues of concern, they are not discussed further in this assessment. 

Additional details on the environmental fate of halosulfuron are provided in an August 13, 2002 Risk Assessment (including drinking water) by EFED (DP Barcode D278449).

Table 7.  Summary of information on halosulfuron-methyl persistence in soil and water.

                             Study or Data Source
                                      pH
                                Half-life, days
                                  DT50, days
                                  DT90, days
Hydrolysis, pH 5
5.0
27
~27
                                                                             NC
Hydrolysis, pH 7
7.0
15
~15
                                                                             NC
Hydrolysis, pH 9
9.0
<1
<1
                                                                             NC
Anaerobic aquatic degradation - clay loam with pond water
7.0
19 to 27
28 to 30
                                                                      ~60 to 90
Aerobic soil degradation, Sarpy sandy loam
8.0
11
NC
                                                                             63
Aerobic soil degradation, Sable silty clay loam
5.8
16
NC
                                                                            110
Lysimeter and field dissipation studies*
Lysimeter field soil, NC Norfolk sandy loam*[1]
6.0
15 to 22
4 to 12
                                                                       45 to 95
Lysimeter field soil, IA Black Hawk loam*
5.9
44 to 81
38 (7 to 86)
                                                                        >370
CA San Ysidoro sandy clay loam*
6.0
61
35
                                                                            455
GA Dothan loamy sand*[2]
6.0
4
NC	
                                                                             NC
IA Harp loam*
6.5
18
30
                                                                            365
CA Hanford sandy loam*[2]	
6.8
64
NC
                                                                             NC
MO Mexico silt loam*
7.2
25
12
                                                                         <60
IL Harpster loam*
7.7
34
36
                                                                            181
TX Uvalde clay loam*
8.3
6
17
                                                                             65
*For these field dissipation and lysimeter studies, half-lives and disappearance times were calculated from the dissipation data from the top six-inch layer of soil.  Note that the analytical methods were insufficiently sensitive to accurately measure halosulfuron-methyl concentration in most of the soil samples below six inches.  This could have resulted in a substantial fraction of the halosulfuron-methyl remaining being unaccounted for, especially in studies where rainfall was high early after application and the soils sufficiently permeable.		
NC = Value not calculated due to data limitations.
 [1] Rainfall was extremely high early in this study (about 14 inches in the first 35 days after application), 
promoting substantial leaching of the pesticide. Therefore, the actual disposition of halosulfuron-methyl could have been affected (degradation rate could have been lower in dry soil).
[2] The CA Hanford sandy loam and GA loamy sand sites were turf plots leading to difficulty in accounting of the applied residues and soil residue levels were often too low to accurately analyze for even right after application.

      C.  ESTIMATION OF DRINKING WATER EXPOSURE

Previous modeling (DP Barcode D278449) was done with the metamodel "FIRST" (FQPA Index Reservoir Screening Tool). The modeling results provided in this drinking water assessment update and supplement the previous modeling.

FIRST utilizes a fixed high-end reservoir exposure scenario simulated with the USEPA Pesticide Root Zone Model (PRZM) and Exposure Analysis Modeling System (EXAMS). FIRST provides a measure of drinking water exposure that is designed to be protective for all crops by using a standard reservoir scenario designed to be conservative for the entire US.  SCI-GROW similarly  provides a measure of drinking water exposure from ground-water sources that is designed to be protective in that it is based on residues measured following  application of pesticides at maximum allowed rates at vulnerable sites under vulnerable conditions (i.e., shallow aquifers, sandy, permeable soils, and substantial rainfall and/or irrigation to maximize leaching). Model inputs and results are summarized in Table 2, Table 3, and Table 4.  No acceptable scenario for estimation of drinking water concentrations from the rice use exists at this time so no estimates are provided (results of the tier 1 rice model have been presented previously, see DP Barcode D278449.)  Note that the rice model overestimates levels that would occur in drinking water because it does not consider the degradation of the pesticide or the dilution of the pesticide as it is transported away from the rice field into the drinking water source.

Table 8.  Environmental Fate model input values used with FIRST drinking water exposure assessment model (field corn and sugarcane uses). 

Parameter
Input
Source
Solubility (ppm)
1630
Product chemistry submissions. Solubility decreases to 15 ppm at pH 5 and increases to 7470 ppm at pH 9.
Aerobic soil t1/2 (days) 1
48
90% Upper-bound confidence limit on mean[2] (MRID 42139410; additional data considered from MRIDs 42661413, 42661413, 42976302, 42976303, and 42976304.) 
Aerobic aquatic t1/2 (days) 
96
EFED Input Guidance for compound with no aerobic aquatic study (2x the aerobic soil half-life.
Photolysis t1/2 in water (days)
30
MRID 42661409.

Organic carbon partition coefficient - Koc (mL/g)
103
Average or median  value from batch -equilibrium adsorption studies (MRID 42139411)
Application rate (lb a.i./Acre) 2
0.0625
Label -maximum single rate for applications to field corn or sugarcane.
# applications/year
2
Label maximum for field corn or sugarcane.
Application interval, days
21
Estimated from label directions allowing a split application in the period from spike to layby for corn; a 45-day interval between applications was also modeled.
[1] For halosulfuron, field dissipation half-lives and monolith lysimeter dissipation half-lives were on average much longer than for the aerobic metabolism studies.  An overall mean of these studies was calculated after first assuming the degradation half-lives in the field studies were equal to 1.2 times the dissipation half-lives for the top soil layer.  Additional indication of the potentially high persistence of halosulfuron is provided by the halosulfuron registration label which strongly implicates that halosulfuron may persist in soil at phytotoxic levels for up to three years after application.  After application of halosulfuron, rotational restrictions of one year to three years exist on various crops.  These label restrictions are consistent with an active ingredient that persists in the environment for years (in this case, at phytotoxic levels).

[2] Values given in this table are for halosulfuron methyl corn/ sugarcane uses, which were the crops which yielded the highest EECs with both models.  Model input and output files are provided in Appendix B.

Results of surface water source modeling are summarized in Table 3 and ground-water modeling in Table 5.  The acute exposure concentrations for an index reservoir with FIRST range from 3.8 to 8.3 ppb or ug/L for the various use patterns modeled.  The chronic exposure estimates (annual average EDWC) with FIRST ranged from 0.8 to 1.7 ppb. The highest acute and chronic exposure EDWC were both associated with a corn and sugarcane use pattern.  The Tier 1 EDWC for ground-water (using the SCI-GROW model) was significantly lower (0.065 ppb for both acute and chronic exposure). 

Table 9.  Summary of halosulfuron methyl scenarios modeled with FIRST. 

Represent-ative Crop

Single Rate, lb ai/A

# of applica-tions

Interval between appl., days

Total seasonal rate, ai/a

Acute EDWC, ug/L

Annual EDWC, ug/L

Tomato

0.047

2

21

0.094

6.2

1.3

Asparagus[1] 

0.047

2

45

0.094

5.5

1.2

Sugarcane

0.042

3

21

0.125

7.3

1.5

Corn, sugarcane

0.063

2

21

0.125

8.3

1.7

Corn, sugarcane

0.063

2

45

0.125

7.3

1.5

Pioneer IR corn

0.094

1

NA

0.094

3.8

0.80
Soybean

0.063
2
150
0.125
5.4
1.1
[Note:  The EFED  default 87% crop area assumption was used except for corn (46% crop area).]
[1] And flowering vegetables.

Table 10.  Environmental Fate Input Parameters for halosulfuron methyl in SCI-GROW.

                                   Parameter
                                 Halosulfuron
                                    Source
Organic Carbon Partition Coefficient (KOC)
103 (Avg.)
                                 Median value.
Aerobic Soil Metabolism Half-Life (days)
48
                                Average value.

Table 11.  Summary of halosulfuron methyl ground-water scenario modeled with SCI-GROW.
                              Representative Crop
                             Single Rate, lb ai/A
                               # of applications
                           Total seasonal rate, ai/a
                                Acute EEC, ug/L
                               Chronic EEC, ug/L
Field corn, sugarcane
                                    0.0625
                                       2
                                     0.125
                                     0.065
                                     0.065

      D.  COMPARISON OF MODELED AND MEASURED DRINKING WATER CONCENTRATIONS

Since the last major drinking water assessment for halosulfuron-methyl no new major drinking water source monitoring studies for halosulfuron-methyl were identified from the literature.  However, the monitoring data that do exist would suggest that concentrations in ground and surface waters are generally low (well below 1 ug/L even in waters in or very near treated areas). 

Limited monitoring data exist for halosulfuron from Battaglin et al. (1999, 2000) who screened reservoir, river, and ground water samples for a variety of low-rate herbicides, including halosulfuron.  Out of 129 water samples from Midwestern streams and rivers, halosulfuron was detected in 7 samples at concentrations above 0.01 ug/L (ppb), with a maximum concentration of 0.067 ppb.  No sampling for halosulfuron was reported in the 1992 Pesticides in Ground Water Database (Jacoby et al., 1992).  Previously, a prospective Ground-Water Monitoring Study (see EFED Review of DP Barcode D226451 dated 2/14/97) was requested, but that requirement has been deferred by the Agency. 

Although the monitoring data demonstrate lower concentrations than those modeled, they are insufficiently targeted towards vulnerable waters associated with halosulfuron-methyl use to be used to calculate drinking water exposure.	

APPENDIX A: Chemical structures of halosulfuron-methyl and selected environmental degradates.

Halosulfuron-methyl
methyl 5-{[(dimethoxy-2-pyrimidinyl) amino] carbonylaminosulfonyl -3-chloro -1-methyl-1-H- pyrazole-4-carboxylate

Halosulfuron rearrangement ester
1 H-Pyrazole-4-carboxylic acid, 3-chloro-5-. [(4,6-dimethoxy-2-pyrimidinyl)amino]-1-methyl, methyl ester
OR
Methyl 3-Chloro-5-(4,6-dimethoxypyrimidin-2-ylamino)-
1-methylpyrazole-4-carboxylate

Halosulfuron aminopyridine

Halosulfuron guanidine

APPENDIX B: Aquatic Exposure:  SCI-GROW and FIRST Water Quality Modeling Inputs and Results 

New and updated model runs

A. SCI-GROW
                          VERSION 2.3
            ENVIRONMENTAL FATE AND EFFECTS DIVISION
                 OFFICE OF PESTICIDE PROGRAMS
             U.S. ENVIRONMENTAL PROTECTION AGENCY
                        SCREENING MODEL
                FOR AQUATIC PESTICIDE EXPOSURE
 
 SciGrow version 2.3
 chemical:Halosulfuron-methyl
 time is  5/22/2009  17:29:40
 ------------------------------------------------------------------------
  Application      Number of       Total Use    Koc      Soil Aerobic
  rate (lb/acre)  applications   (lb/acre/yr)  (ml/g)   metabolism (days)
 ------------------------------------------------------------------------
      0.063           2.0           0.125      1.03E+02       48.0
 ------------------------------------------------------------------------
 groundwater screening cond (ppb) =   6.54E-02 
 ************************************************************************

B. FIRST

   RUN No.   1 FOR Halosulfuron met ON   Corn, Suga    * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .063(   .110)   2  21     103.0 1630.0   AERIAL(16.0)  87.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0  JAN 1, 2007
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              8.385                      1.773

   RUN No.   2 FOR Halosulfuron Met ON   corn  -  special** * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .063(   .110)   2  21     103.0 1630.0   AERIAL(16.0)  46.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0  JAN 1, 2007
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              4.434                       .937
** this run utilizes a corn-specific PCA.

   RUN No.   3 FOR Halosulfuron met ON   Soybeans      * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .063(   .070)   2 150     103.0 1630.0   AERIAL(16.0)  87.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0  JAN 1, 2007
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              5.381                      1.138

Previous model runs (see DP Barcode D278449)

A. Ground Water - SCI-GROW
              

   RUN No.   1 FOR Halosulfuron methyl ** INPUT VALUES **     
   --------------------------------------------------------  
    APP RATE   APPS/   TOTAL/     SOIL   AEROBIC SOIL METAB  
    (LBS/AC)   YEAR    SEASON     KOC     HALFLIFE (DAYS)    
   --------------------------------------------------------   
       .063      2       .125      103.0        48.00

   GROUND-WATER SCREENING CONCENTRATION (IN PPB)
   --------------------------------------------------------  
                     .0652
   --------------------------------------------------------  

B. Surface Water - FIRST
	
   RUN No.   1 FOR Halosulfuron met ON   Tomatoes e    * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .047(   .082)   2  21     103.0 1630.0   GROUND( 6.4)  87.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB))    Ver 1.0 AUG 1, 2001
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              6.231                      1.311

   RUN No.   2 FOR Halosulfuron met ON   Asparagus     * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .047(   .072)   2  45     103.0 1630.0   GROUND( 6.4)  87.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB))    Ver 1.0 AUG 1, 2001
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              5.465                      1.150

   RUN No.   3 FOR Halosulfuron met ON   Sugarcane     * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .042(   .095)   3  21     103.0 1630.0   GROUND( 6.4)  87.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB))    Ver 1.0 AUG 1, 2001
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              7.276                      1.531

   RUN No.   4 FOR Halosulfuron met ON   Corn, suga    * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .063(   .109)   2  21     103.0 1630.0   GROUND( 6.4)  87.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB))    Ver 1.0 AUG 1, 2001
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              8.286                      1.744

   RUN No.   5 FOR Halosulfuron met ON   SCane, FCo    * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .063(   .095)   2  45     103.0 1630.0   GROUND( 6.4)  87.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB))    Ver 1.0 AUG 1, 2001
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              7.267                      1.530

   RUN No.   6 FOR Halosulfuron met ON   Pioneer IR    * INPUT VALUES * 
   --------------------------------------------------------------------
    RATE (#/AC)   No.APPS &   SOIL  SOLUBIL  APPL TYPE  %CROPPED INCORP
     ONE(MULT)    INTERVAL    Koc   (PPM )   (%DRIFT)     AREA    (IN)
   --------------------------------------------------------------------
   .094(   .094)   1   1     103.0 1630.0   GROUND( 6.4)  46.0    .0

   FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 
   --------------------------------------------------------------------
   METABOLIC  DAYS UNTIL  HYDROLYSIS   PHOTOLYSIS   METABOLIC  COMBINED
    (FIELD)  RAIN/RUNOFF  (RESERVOIR)  (RES.-EFF)   (RESER.)   (RESER.) 
   --------------------------------------------------------------------
     48.00        2          N/A     30.00- 3720.00    96.00     93.58

   UNTREATED WATER CONC (MICROGRAMS/LITER (PPB))    Ver 1.0 AUG 1, 2001
   --------------------------------------------------------------------
        PEAK DAY  (ACUTE)      ANNUAL AVERAGE (CHRONIC)      
          CONCENTRATION             CONCENTRATION            
   --------------------------------------------------------------------
              3.783                       .796