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

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

PC Code: 118602 DP Barcodes: 362654

Date : May 13, 2010 MEMORANDUM

SUBJECT: Tier I Drinking Water Assessment for the Section 3 Proposed Registration of Imazosulfuron on Turf, Tomato, Peppe rs (Bell and Non-bell) and Rice

TO: James Tompkins, Risk Manager Bethany Benbow, Risk Manager Reviewer Herbicide Branch Registration Division

FROM: Faruque Khan, Senior Scientist Environmental Risk Branch I Environmental Fate and Effects Division

THROUGH: Anita Pease, Acting Branch Chief Environmental Risk Branch I Environmental Fate and Effects Division

A Tier I screening-level drinking water assessm ent was conducted to su pport the human health risk assessment for the Section 3 proposed new chemical registration for imazosulfuron. Modeled application rates repres ent the maximum application rate s on the proposed label for use on turf grass, tomato, peppers (bell and non-bell) and rice (EPA Reg. No. pending). Foliar spray applications (ground spray) are proposed for turf grass, tomato, peppers (bell and non-bell) and aerial application is proposed for rice. Tier 1 surface water and groundwater modeling was conducted for two ground spray applications with 21 da ys interval for turf at a rate of 0.67 lbs. a.i./A. In addition, Tier 1 surface water m odeling was also conducted for one ground spray application for food (tomato and peppers) uses and one aerial application for rice at a rate of 0.3 lbs. a.i./A per year.

Imazosulfuron is a selective su lfonylurea herbicide with major routes of degradation being aerobic and anaerobic biodegradation and aque ous photolysis. There are several major degradates identified in the environmental fa te studies. Residues of Concern Knowledgebase Subcommittee (ROCKS) of the Hea lth Effects Division (HED) reviewed the structures of these degradates to determine residues of c oncern (DP Barcode: 359190). As 2-chloro- N-[[(4-hydroxy6-methoxy-2-pyrimidinyl)amino]carbonyl]imidazo[1,2- α ]pyridine-3-sulfonami de (HMS) retains

1both imidazolyl (IM) and pyrimidinyl (PM) ring stru ctures, its toxicity is likely comparable to the parent. Structure-activity relationship (SAR) and Deductive Estimation of Risk based on Existing Knowledge (DEREK) analys es revealed the same structural alerts as the parent compound; therefore, HMS is considered a residue of concern. DEREK analysis of [2

- chloroimidazo[1,2-alpha]pyridin -3-sulfonamide (IPSN), 2 -(2-imino-1,2-dihydropyridin-1- yl)oxalic acid (IHOA), 2-amino-4,6-dimet hoxypyrimidine (ADPM), (4,6-dimethoxypyrimidine2-yl) aminocarbonylsulfamic acid (SDPM), and 4,6-dimethoxy-2-ureidopyrimidine (UDPM) showed that all of these cleavag e products except IHOA (a low mo lecular weight acid) retained at least one of the same structural alerts as the parent. Therefore drinking water exposure of total toxic residue (parent plus five degradates listed in Table 1 ) is considered in this assessment based on the memorandum provide d by ROCKS (DP Barcode: 359190).

Table 1. Summary of Metabolites and Degrad ates to be included in the Risk Assessment.

Matrix Residues included in Risk Assessment Residues included in Tolerance Expression Drinking Water Imazosulfuron, HMS, IPSN, ADPM, UDPM, and SDPM Not Applicable

Imazosulfuron = 2-chloro- N -[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]imidazo[1,2- α ]pyridine-3- sulfonamide HMS = 2-chloro- N -[[(4-hydroxy-6-methoxy-2-pyrimidinyl)amino]carbonyl]imidazo[1,2- α ]pyridine-3- sulfonamide IPSN = 2

- chloroimidazo[1,2-alpha]pyridin-3-sulfonamide ADPM = 2-amino-4,6-dimethoxypyrimidine UDPM = 4,6-dimethoxy-2-ureidopyrimidine SDPM = (4,6-dimethoxypyrimidine-2-yl)aminocarbonylsulfamic acid

The recommended estimated drinking water concentrations (EDWCs) for the human health risk assessment are based on highest predicted value for surface wa ter and groundwater ( Table 2)

. The recommended EDWCs in surface water are ba sed on aerial spray application of 0.3 lbs. a.i./A per year for rice. The concentrations in ground water are based on ground spray on turf at 1.34 lbs. a.i./A per year. Additional EDWCs for various scenarios can be found in Appendix A. If additional refinements are necessary, please contact Faruque Khan at 703-305-6127 or khan.faruque@epa.gov.

Table 2. Tier I EDWCs for Imazosulfuron for ground spray applications to Turf
Drinking Water Source Model Use rate (lbs ai/A/year) Acute ( μ g/L) Chronic ( μ g/L)

Surface water RICE 0.3 278.9 278.9

Groundwater SCI-GROW 1.34 4.8 4.8

1.1 Drinking Water Exposure Modeling

Tier 1 modeling was used to estimate the drin king water exposure for use in the dietary risk assessment of imazosulfuron. The following is a desc ription of the models used, the selection of the model input parameters, and a characteri zation of the output from these simulations.

21.1.1 Models Tier 1 EDWCs for surface water were generated using FIRST, dated August 5, 2001. FIRST is a screening model designed by the Environmental Fate and Effects Division (EFED, 2001a) of the Office of Pesticide Programs (OPP) to estimate the concentrations found in drinking water from surface water sources for use in hum an health risk assessment. As such, it provides upper bound values on the concentrations that might be found in drinking water due to the use of a pesticide. FIRST is a single-event model (one runoff event) , but can account for spray drift from multiple applications. FIRST is hardwired to represent the Index Reservoir, a standard water body used by OPP to assess drinking water exposure (Office of Pesticide Programs, 2002). It is based on a real reservoir, Shipman City Lake in Illinois, which is known to be vulnerable to pesticide contamination. The single runoff event moves a maxi mum of 8% of the applied pesticide into the reservoir. This amount can be reduced due to degradation on the field and the effects of binding to soil in the field. FIRST also uses a Percent Cropped Area (PCA) factor to adjust for the area within the watershed that is planted to the modeled crop. The national default PCA of 0.87 was applied in this assessment.

The EFED Rice Model (USEPA, 2007) was used to estimate the concentration of imazosulfuron expected in surface water potentially used for drinking water following application to rice. The model calculates exposure as a function of the am ount of pesticide applied and the pesticide’s soil-to-water partition coefficien t. Concentrations are assumed to immediately and evenly distribute throughout the rice paddy water. Dissipation processes, such as degradation, volatilization, and potentia l dilution with uncontaminated water outside the paddy are not accounted for by the model. The single exposure estimate produced with th e Rice Model is used as both an acute and a chronic screening exposure es timate that is expected to represent high-end exposure in released flood wate r (tailwater). The EDWC produ ced by the Rice Model was not adjusted by an agricultural Pe rcent Cropped Area (PCA) value because these values may not apply to semi-aquatic agriculture. PCA values were designed for exposure estimates in runoff from terrestrial crops, not for exposure es timates in tailwater from flooded crops.

Tier 1 EDWCs for groundwater were genera ted with SCIGROW 2.3, dated July 29, 2003 (EFED, 2001b). SCIGROW is a regression mode l used as a screening tool for ground water used as drinking water. SCIG ROW was developed by regressi ng the results of Prospective Ground Water studies against the Relative Index of Leaching Potential (RILP). The RILP is a function of aerobic soil metabo lism and the soil-water partition coefficient. The output of SCIGROW represents the concentrations that might be expected in shallow unconfined aquifers under sandy soils.

1.1.2 Modeling Approach and Input Parameters Tables 3 and 4 summarize the model input parameter values used in FIRST and SCIGROW, respectively. These parameters were selected in accordance with EFED’s input parameter guidance (Environmental Fate and Effects Di vision, 2009). An aerobic soil metabolism first order half-life based on total toxi c residue (imazosulfuron and liste d degradates in Table 1) was used for surface water modeling with FIRST an d groundwater modeling with SCIGROW. First order degradation half-lives for aerobic aquatic and aquatic photolysis for total toxic residue were also used for surface water modeling. Sin ce the experimental phototransformation halflives of IM and PM labels are based on the continuous irradiation used in the laboratory study,

3estimated half-lives were adjusted by multiply ing with 0.5 based on a 12-hour light/12-hour dark cycle. Also, the intensity of the xenon la mp over the wavelengt hs 290-800 nm was 558 W/m 2

, compared to 380 W/m 2 for natural sunlight over a 12-hour (solar) day at 40 ° N latitude during June through August. Therefore, 1 hour of artif icial light was equivalent to 1.47 hours of natural sunlight. Calculations of first- order degradation rates for tota l toxic residue can be found in Appendix B. The soil-water partitioning coe fficient used in FIRST and SCIGROW was 98 ml/g oc , the lowest non-sand K oc .

Table 3. FIRST (v 1.1) input pa rameter values for total residue a of imazosulfuron applied by ground spray

Parameter Value Source Comments

Application Rate (lb a.i./A) 0.67 (turf) 0.3 (food uses) As per V-10142 label Direction ---

Number of Applications 2 (turf) 1 (food uses) As per V-10142 label Direction ---

Minimum Application Intervals (days) 21 (turf only) As per V-10142 label Direction For Ground Application

Soil Partitioning Coefficient (K foc ; ml/g oc ) 98 MRID 47305122 lowest non-sand value b

Aerobic Soil Metabolism t 1/2 (d) 207.15 MRID 473051-17
MRID 477668-01 90 th percentile upper confidence bound on the mean half-life of total toxic residue of imazosulfuron

Wetted in? No foliar applied As per V-10142 label Direction

Depth of Incorporation (inches) 0 foliar applied As per V-10142 label Direction

Methods of Application Ground spray As per V-10142 label Direction As per V-10142 label Direction

Percent Cropped Area 0.87 National default Input parameter guidance (USEPA, 2002)

Solubility in Water (mg/L) 419 Product chemistry data Input parameter guidance (USEPA, 2009)

Aerobic Aquatic Metabolism
t 1/2 (d) 192.03 MRID 476397-02

MRID 476791-05 90 th percentile upper confidence bound on the mean half-life of total toxic residue of imazosulfuron

Hydrolysis t 1/2 at pH 7.0 (days) 0 MRID 473051-19 Stable to hydrolysis @ pH 7.0

4Table 3. FIRST (v 1.1) input pa rameter values for total residue a of imazosulfuron applied by ground spray

Parameter Value Source Comments

Aquatic Photolysis t 1/2 (d) 61.69 MRID 473051-20 90 th percentile upper confidence bound on the mean of IM and PM rings of imazosulfuron

a = Residues of concern (Parent plus degradates, i.e., HMS, IPSN, UDPM, ADPM and SDPM) recommended by Residues of Concern Knowledg ebase Subcommittee (ROCKS)

b = According to Guidance for selecting input parameters in modeling for environmental fate and transport of pesticides. Version II. October, 2009.

Table 4. SCIGROW 2.3 input paramete r values for total residue of Imazosulfuron applied by ground spray.

Parameter Value Source Comments
Maximum Application Rate (lb a.i./A/application) 0.67 Ground Application As per V-10142 label Direction

Maximum Number of Applications per Year 2 Ground Application As per V-10142 label Direction

Aerobic Soil Metabolism Half-life (d) 207.15 MRID 473051-22 90 th percentile upper confidence bound on the mean half-life of total toxic residue of imazosulfuron
Organic Carbon Partition Coefficient (Kf oc , ml/g oc ) 98 MRID 473051-17 Lowest non-sand value a

a = According to Guidance for selecting input parameters in modeling for environmental fate and transport of

pesticides. Version II. October, 2009.

Input parameters for the Rice Model are listed in Table 5 ; data source and justification descriptors accompany values for each paramete r. The mean Freundlich soil-to-water partition coefficient (K f ) from four soils (1.19) wa s used to model partitioni ng to rice paddy sediment. The organic carbon partition coefficient (K OC ) was not used, as it is a less precise descriptor of imazosulfuron’s mobility.

Table 5. Rice Model input pa rameters for imazosulfuron.

Input Parameter Value Justification Source Application Rate (kg a.i./ha) 0.3 0.3 lbs a.i./A x 1.121 kg·A/ha·lbs = 0.336 kg a.i./ha Proposed label

Soil-to-Water Partition Coefficient (K f ) (L/kg) 1.19 Mean K f is used when mean K OC use is not appropriate. MRID 46219074 MRID 46578971

1.1.3 Modeling Results The FIRST, RICE and SCI-GROW out put files are located in Appendi x A. Based on the results of these simulations, EFED recommends acu te and chronic surface water EDWC of 278.9 μg/L

5for use in the human health risk assessment. These recommendations are based on the use of imazosulfuron on rice at an annua l application rate of 0.3 lb a.i./A/year. The recommended EWDC for groundwater is 4.8 μg/L and is based on maximum appli cations at 0.67 lb a.i./A of two application per year for the use of imazosulfuron on turf. The estimated drinking water concentrations (EDWCs) for va rious scenarios are listed in Table 5

.

Table 5. Tier I EDWCs for Imazosul furon for Turf, food uses and rice
Drinking Water Source Models Use rate (lbs ai/A/year) Acute ( μ g/L) Chronic ( μ g/L)

RICE 0.3 278.9.0 278.9.0

1.34* 101.25 33.27 Surface water

FRIST 0.3** 23.47 7.71

Groundwater SCI-GROW 1.34* 4.8 4.8
* Application rate for turf ** Application rate for tomato and pepper

1.2 Monitoring Data

There were no national-scale mon itoring data available for this new chemical assessment.

1.3 Drinking Water Treatment

There is no available information on the dri nking water treatment effects on imazosulfuron.

2 CONCLUSIONS

The estimated concentrations provided in this assessment are conservative estimates of imzosulfuron concentrations in untreated drinking water. A major source of uncertainty is the nature of the non-extract able residues formed during degrad ation in soils. Non-extractable residues were identified at maximums of 33-88% of applied radioactivity in aerobic soil, aerobic and ananerobic aquatic metabolism studies. The non-extractable residues ar e uncharacterized and it is uncertain whether th ey consist of degradates of risk c oncern. Under sterile conditions these non-extractables were not formed su ggesting that the formation of th em is microbially mediated.

If dietary risks require refineme nt, higher tiered models and m odeling scenarios can be utilized to characterize EDWCs upon request.

6References

Environmental Fate and Eff ects Division. 2001a. FIRST (F)IFRA (I)ndex (R)eservoir (S)creening (T)ool. Tier 1 Model for Dr inking Water Exposure: User's Manual. http://www.epa.gov/oppefed1/models /water/first_users_manual.htm

Environmental Fate and Effect s Division. 2001b. SCI-GROW - (S)creening (C)oncentration (I)n (GRO)und (W)ater: User's Manual. http://www.epa.gov/oppefed1/models /water/scigrow_users_manual.htm

Environmental Fate and Effect s Division. 2009. Guidance for Se lecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides, Ve rsion II. U. S. Environmental Protection Agency. Washington, D.C. http://www.epa.gov/oppefed1/models/water/

USEPA. 2007. Policy for Estimating Aqueous Concentrations from Pesticides Labeled for Use on Rice. EFED Policy Memorandum. U.S. En vironmental Protection Agency, Office of Pesticide Programs, Washington, DC. http://www.epa.gov/oppefed1/models /water/rice_tier_i.htm#model

Office of Pesticide Programs. 2000. Part A. Guidance for Use of the Index Reservoir in Drinking Water Assessments. http://www.epa.gov/oppfead1/tr ac/science/reservoir.pdf

7Appendix A

Surface water (FRIST)

**Ground Application**

RUN No. 1 FOR Imazosulfuron ON Turf * INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- .670( 1.295) 2 21 98.0 419.0 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.)

-------------------------------------------------------------------- 207.15 2 N/A 61.69- 7649.56 192.03 187.33

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 JAN 1, 2007

-------------------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

-------------------------------------------------------------------- **101.248 33.268**

RUN No. 2 FOR Imazosulfuron ON Food Uses * INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- .300( .300) 1 1 98.0 419.0 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.)

-------------------------------------------------------------------- 207.15 2 N/A 61.69- 7649.56 192.03 187.33

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 JAN 1, 2007

-------------------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

-------------------------------------------------------------------- **23.466 7.710**

8Rice Model (USEPA, 2007).

The formula of the Tier I Rice Model v1.0 is as follows:

d ai
w K m C 00013.0 00105.0 '

+ =

and, if appropriate:

oc d KK 01.0 =

where: C w = water concentration [μg/L]

m ai ' = mass applied per unit area [kg/ha] K d = water-sediment partitioning coefficient [L/kg] K oc = organic carbon partiti oning coefficient [L/kg]

Example calculation:

EEC = (0.336 kg a.i./ha) / [0.00105 + (0.00013 x 1.19 L/kg)]

= 278.9 μg/L (ppb)

Ground water

SCIGROW 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:Imazosulfuron time is 5/ 5/2010 15: 3:43

------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------ 0.670 2.0 1.340 9.80E+01 207.1

------------------------------------------------------------------------ groundwater screening cond (ppb) = 4.80E+00 ************************************************************************

9Appendix B

Calculations of Half-life for total toxic residue

Aerobic Soil Metabolism (MRID 473051-17

10Aerobic Soil Metabolism (MRID 477668-01

-

11Aerobic Aquatic Metabolism (MRID 476397-02)

1

12Aerobic aquatic Metabolism (MRID 476791-05

13Aquatic Photolysis (IM Ring)

14Aquatic Photolysis (PM Ring)

Half life calculation for total system:

PM ring 32.66 Days IM Ring 4.72 Days 90th %ile 61.69 Days

15