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 
2

same as in the Environmental Fate and Effects Divison’s (EFED’s) previous assessment (see DP 

Barcode D394244, review dated 5/15/20121). 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.

 

1

The most recent review (D394244) is designated as Attachment A, this review further cites the previous reviews 

(includes DP Barcode D358032 dated 6/4/2009, and subsequently DP Barcode D366411 dated 8/5/2010), designated 

here as Attachment B).
3

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 Season2

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.)
1

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 
2

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).

2

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:

 

2

http://www.epa.gov/oppefed1/models/water/index.htm (accessed 5/7/12).
3

 =





0.00105 + 0.00013

 

Where: Cw = water concentration or the EDWC [μg/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 Justification1Source

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

 =





0.00105 +0.00013

 =

0.07005

0.00105 +(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.
4

9. Organic carbon fraction is 0.01.

10. Bulk density is 1300 kg/m3.

11. Grain density is 2650 kg/m3.

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

3

are summarized in Table 1-3 (the 

proposed uses are shaded blue). Halosulfuron methyl is a selective preemergence or postemergence 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.

 

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

carboxylate
5

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 Season2

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 pregrazing or 

forage 

harvesting 

interval

0.0625 3

Grain sorghum (milo) 0.031 - 0.047 1 N/A 30 day pregrazing or 

forage 

harvesting 

interval

0.047

Rice1

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 pregrazing 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)
6

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 Season2

Minimum 

Interval 2

PHI

(days)

Maximum 

Annual Rate

(1b a.i./A)

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.

4Although 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).
1
2

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

4

(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.5 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):

 

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

5

Including dried shelled peas & beans (except soybean), succulent shelled peas & beans, apples, rhubarb, bushberry, fruiting 

vegetables and tuberous & corm vegetables; proposed and current uses are summarized in Table 1.
3

For parent alone:

 8.3 μg/l or ppb for acute exposure (1 in 10 year annual peak daily concentration)

 1.7 μg/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 μg/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.
4

Table 1. Registered and proposed uses of halosulfuron-methyl.

Crop(s)1a Max. 

Application 

rate (min.)

Max. # 

applications / 

Season3

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 pregrazing or 

forage 

harvesting 

interval

0.0625 a

Grain sorghum 0.047 1 NA 30 day pregrazing 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 pregrazing 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
5

Crop(s)1a Max. 

Application 

rate (min.)

Max. # 

applications / 

Season3

Minimum 

Interval 2, 3

PHI

(days) Maximum 

Annual Rate

(1b ai/A)

* 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).
6

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) 148 90% Upper-bound confidence limit on mean2

(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 halflife.

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) 20.0625 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.
7

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. 

Representative CropSingle 

Rate, lb 

ai/A

# of 

applications

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

Asparagus10.047 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
8

Representative CropSingle 

Rate, lb 

ai/A

# of 

applications

Interval 

between 

appl., days

Total 

seasonal 

rate, ai/a

Acute 

EDWC, 

ug/L

Annual 

EDWC, 

ug/L

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 

************************************************************************
9

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.
10

 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
11

APPENDIX 2: Previous Drinking Water Exposure Assessment

[Begins on following page]
12

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- pyrazole4-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 
13

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 Season2

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 pregrazing or 

forage 

harvesting 

interval

0.0625 3

Grain sorghum (milo) 0.031 - 0.047 1 N/A 30 day pregrazing or 

forage 

harvesting 

interval

0.047

Rice1

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 pregrazing 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)
14

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 Season2

Minimum 

Interval 2

PHI

(days)

Maximum 

Annual Rate

(1b a.i./A)

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.

4Although 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.)
15

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 
16

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 Season2

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 pregrazing or 

forage 

harvesting 

interval

0.0625 3

Grain sorghum (milo) 0.031 - 0.047 1 N/A 30 day pregrazing or 

forage 

harvesting 

interval

0.047

Rice1

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 pregrazing 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)
17

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 Season2

Minimum 

Interval 2

PHI

(days)

Maximum 

Annual Rate

(1b a.i./A)

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.

4Although 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
18

Crop(s) Max. 

Application 

rate (range)

Max. # 

applications / 

Season

Interval PHI

(days) Maximum 

Annual Rate

(1b ai/A)

Sweet corn 

and popcorn

0.0313 2 NS 30 day pregrazing or 

forage 

harvesting 

interval

0.0625

Grain 

sorghum

0.047 1 NA 30 day pregrazing 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 pregrazing 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
19

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
20

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 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*26.0 4 NC NC

IA Harp loam* 6.5 18 30 365

CA Hanford sandy loam*26.8 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
21

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

*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
22

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) 148 90% Upper-bound confidence limit on mean2

(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 halflife.

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) 20.0625 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. 
23

Representative CropSingle 

Rate, lb 

ai/A

# of 

applications

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

Asparagus10.047 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
24

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)6 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)7. 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.

 

6

Battaglin, W.A., Furlong, E.T., Burkhardt, M.R., and Peter, J.C. 1999. Occurrence of Sulfonylurea, Sulfonamide, 

Imidazolinone, and other herbicides in Midwestern rivers, reservoirs, and ground water, 1998 in U.S. Geological 

Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Charleston, South Carolina, 

March 8-12, 1999: U.S. Geological Survey Water-Resources Investigations Report 99-4018B, Volume 2, pp. 215-

225. 

Battaglin, W.A., Furlong, E.T., Burkhardt, M.R., and Peter, J.C. 2000. Occurrence of Sulfonylurea, 

Sulfonamide, Imidazolinone, and other herbicides in rivers, reservoirs, and ground water in the Midwestern United 

States, 1998. Science Total Environ. Vol. 248, Issues 2-3, 5 April 2000, Pages 123-133.

7

Jacoby, H.J. et al. U.S. EPA. 1992. Pesticides in Ground Water Database -A Compilation of Monitoring 

Studies: 1971-199, EPA 734-12-92-001.
25

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-Hpyrazole-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
26

Halosulfuron guanidine
27

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 * 
28

 --------------------------------------------------------------------

 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

 
29

 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 * 
30

 --------------------------------------------------------------------

 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
31

 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) 
32

 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