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

May 8,2012

MEMORANDUM OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

SUBJECT: Revised Drinking Water Assessment for Fluoxastrobin Use on Rice PC Code: 028869; DP Barcode: 401613

TO: Heather Garvie, Risk Manager Reviewer Fungicide Branch Registration Division (7505P)

THROUGH:

# DanaSpatz,BranchChief~~ 51'6\.L.. 

# D

Rosanna Louie-Juzwiak, Risk Assessment Process Leader 

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Environmental Risk Branch 3 Environmental Fate and Effects Division (7507P)

FROM: Rochelle F. H. Bohaty Ph.D., Chemist

## ~_v __ Environmental Risk Branch 3 - Environmental Fate and Effects Division (7507P)

REVIEWED BY: Ronald Parker, Senior Environmental Engineer Environmental Risk Branch 3 Environmental Fate and Effects Division (7507P)

EXECUTIVE SUMMARY

This memorandum provides an updated drinking water assessment (DW A) for the proposed use offluoxastrobin**[(E)-{2-[6-(2-chlorophenoxy)-5~fluoropyrimidin-4-yloxy]phenyl}**(5,6-dihydro1 ,4,2-dioxazin-3-y1)methanone O-methyloxime; CAS 361377-29-9] on rice. This updated DWA reflects an increase in the amount of fluoxastrobin to be applied in both the maximum single and seasonal application rates, and the resulting slightly higher estirTIated drinking water concentration (EDWC) than was previously modeled (refer to DP392990). Fluoxastrobin is a strobilurin fungicide that inhibits respiration in fungi by blocking electron transport through mitochondrial systems. The proposed fluoxastrobin use on rice will be included on three different end-use products: Evito® 480 SC Fungicide, DISARMTh{ 480 SC Fungicide (alternative brand name: Armor Tech TM DISARMTM 480 SC Fungicide), and Fluoxastrobin 480 SC Fungicide Seed Treatment.2 The proposed Evito ® 480 SC Fungicide SL label (updated label received May 2, 2012) allows for a maximum of 5.7 fluid ounces (fl oz) product/acre (0.18 lb a.i./acre) and a maximum of 11.4 fl oz (0.36 lb a.i./acre) on rice. The proposed label does not specify a water holding period for paddy discharge following fluoxastrobin applicati ons on rice. The maximum number of proposed applications is two per season with a mi nimum application interval of 27 days. 1 Application methods include aerial, ground, and chemigation sprays.

EDWCs are based on the Tier I ri ce model for surface water and the Tier I groundwater model. Table 1 highlights fluoxastrobin EDWCs in surface water and groundwater for fluoxastrobin use on rice. The only residue of concern identif ied by Health Effects Division is parent fluoxastrobin. 2 Therefore, this DWA considers only fluoxastrobin (no transformation products are included).

Table 1. Estimated Drinking Water Concentrat ions Resulting From the Proposed Use of Fluoxastrobin on Rice Compared to Previously Reported EDWCs as a Result of Use on Turf

Parameter Surface Water Groundwater Tier I Rice Model

EDWCs

μ g/L Tier II PRZM-EXAMS EDWCs for Turf*
μ g/L Tier I SCI-GROW EDWCs for Rice
μ g/L Tier I SCI-GROW EDWCs for Turf*
μ g/L

Acute 1-in-10 Year Peak

93 60.7

0.038 0.23

Chronic 1-in-10 Year Annual

Average 52.9

Cancer 30 Year Annual Average 23.5

*Previously reported values 3

The proposed use of fluoxastrobin on rice may re sult in a peak concentration of 93 μg/L in surface water based on the Tier I rice model esti mate. This is higher than previously reported EDWCs for other fluoxastrobin us es. The most conservative ED WCs reported for fluoxastrobin prior to this assessment was for turf. 3 Error! Bookmark not defined. These results were based on Tier II surface water modeling and were reported to be 60.7 μg/L for the 1-in-10 year peak concentration, 52.9 μg/L for the 1-in-10 year annu al average concentration, and 23.5 μg/L for the 30 year annual average concentration. For comp arison, EDWCs for turf are also presented in Table 1 . Based on further analysis of the propos ed fluoxastrobin use on rice, EDWCs in

1 Email from Heather Garvie (EPA/RD) to Rosanna Louie-Juzwiak (EPA/EFED), March 15, 2012. 2 DP 289104 Drinking Water and Aquatic Exposure Assessment-Addendum 1 , November 23, 2004; All DWAs have considered parent fluoxastrobin as the only residue of concern. HED has not indicated to EFED that this approach should be revised.3 groundwater are not expected to exceed 0.23 μg/L as previously reported for turf uses. 3 Table 1 also highlights fluoxastrobin ground water EDWCs for fluoxastrobin use on rice as well as turf for comparison.

PROBLEM FORMULATION

Fluoxastrobin [ ( E )-{2-[6-(2-chlorophenoxy)-5-fluoropyrim idin-4-yloxy]phenyl}(5,6-dihydro1,4,2-dioxazin-3-yl)methanone O -methyloxime; CAS 361377-29-9] is a strobilurin fungicide used to control fungal diseases such as blight and leaf spot. The mode of action for strobilurin fungicides is to inhib it respiration in fungi by blocking electron transport through mitochondrial systems. The chemical identification as well as physical-chemical propertie s of fluoxastrobin are provided in Table 2

. Table 2. Physical-Chemical Char acteristics of Fluoxastrobin

Chemical Name ( E)-{2-[6-(2-chlorophenoxy)-5-fluoropyrimidin-4-yloxy]phenyl}(5,6-dihydro1,4,2-dioxazin-3-yl)methanone O -methyloxime

Chemical Structure O

N N O N O O N

Cl F

O CH 3

Chemical Abstracts Service (CAS) Registry Number 361377-29-9 Empirical Formula C 21 H 16 ClFN 4 O 5 USEPA Pesticide Code (PC #) 028869 Smiles Notation Clc4ccccc4Oc3ncnc(Oc2 ccccc2C(=N\OC)/C=1OCCON=1)c3F Molecular Weight 458.8 g/mol Vapor Pressure (25 °C) 4.23 x 10 -12 torr Water Solubility (20 °C) 2.3 mg/L
Henry’s Law Constant 1.01 x 10 -7 Pa m 3 / mole (9.98 atm - m 3 /mol) Log K ow 2.86

Previous Drinking Water Assessments

Several drinking water assessments (DWAs) have been completed for fluoxastrobin including for use on: peanut, potato, tuber vegetables, leaf petioles subgroup, fruiting vegetables, turf and seed treatments for potato, peanut, and turf (DP 289104); field and seed corn, low-growing berries, and soybean 4 ; corn and wheat, 5 and; squash/cucumber, and in-furrow and banded uses

3 R. Bohaty, Drinking Water Assessment for Fluoxastrobin Use on Squash/Cucumber (crop subgroup 9B) and New In-Furrow and Banded Uses on Tuberous and Corm Vegetables (crop subgroup 1C) as well as Peanut PC Code: 028869; DP Barcode: 379114, 384377 (revised turf EDWCs are pr esented in this document) 4 J. Hetrick, Drinking Water Assessment to Support Fluoxastrobin Use on Low-Growing Berries, Soybean, and Corn PC Code: 028869; DP Barcode: D356984, D3576994 on tuberous and corm vegeta bles, as well as peanut. 3 Past assessments have been completed using PRZM-EXAMs (P esticide R oot Z one M odel, version 3.12.3, June 2006; EXAMS (EX posure A nalysis M odeling S ystem, version 2.98.04.06, April 2005) and SCI-GROW (S creening C oncentration i n Gro undw ater, version 2.3, August 8, 2003) modeling. Turf uses provided the most conservative estimated dr inking water concentrations (EDWCs).

Use Characterization

Fluoxastrobin is currently registered for use on peanut, tuberous and corm vegetables, leaf petioles vegetables, fruiting, tuberous, and corm vegetables, ornamentals, turf and as a seed treatment on potato, peanut and turf. Maximum si ngle application rates range from 0.12 to 0.55 lb a.i./a and maximum yearly applicati on rates range from 0.24 to 2.2 lb a.i./a. 6 Application methods currently registered include aerial, chemigation, and ground sprays. While the geographic extent of fluoxastro bin use is unknown it is likely widespread based on the wide variety of approved uses.

The proposed use on rice is for a foliar application that can be applied with aerial, chemigation, and ground application equipment. The ma ximum number of proposed fluoxastrobin applications on rice is two per s eason with a maximum single app lication rate of 0.18 lb a.i./a and a minimum application interval of 27 days 7 (as shown in Table 3 ). The maximum yearly application rate is 0.36 lb a.i./a. The label limits applications to 28 days prior to harvest. The label does not limit direct applic ations to flooded fields nor does it require a water holding period prior to discharging paddy wate r after fluoxastrobin applications . The geographic extent of the use is not specifically limited by the label; however, majority of the rice production in the United States occurs in Arkansas, Calif ornia, Mississippi, Missouri, Loui siana, and Texas. Survey data from the National Agricultural Statistics Serv ice (NASS) on rice acres planted in the United States for the year 2010 is provided in Table 4

. 8 Rice has also been grow n in Florida, Missouri, Oklahoma, and Tennessee. 9

Table 3. Fluoxastrobin Application Rates: Turf and Proposed Use on Rice

Crop Single Application Rate Range lb a.i./acre No. of Applications Minimum Interval

days Max Annual Application Rate lb a.i./acre/yr Application Technique

Rice 0.18 2 27 0.36 Air, Ground, and Chemigation

5 R. Bohaty, Drinking Water Assessment to Support Fluoxastrobin Use on Sweet Corn and Wheat PC Code: 028869; DP Barcode: 366189 6 For turf, the label permits four applications at a rate of 0.50 lb ai/A; however, the maximum yearly application rate is 2.2 lb a.i./a; therefore, the maximum single application ra te is assumed to be 0.55 lb a.i./a. The discrepancy is the result of the number of significant figures assumed in application rate conversion calculations. 7 Email from Heather Garvie (EPA/RD) to Rosanna Louie-Juzwiak (EPA/EFED), March 15, 2012. 8 Survey data from the from the Quick Stats Database of the National Agricultural Statistics Service available at http://quickstats.nass.usda.gov/results/6432EC45-FA6F-3DE6-A48F-98F1917AAEA8 9 2007 census data from the Quick Stats Database of the National Agricultural Statistics Service available at http://quickstats.nass.usda.gov.5 Turf 6 0.55 4 7 2.2 Ground See document footnote number 6 at the bottom of the page.

Table 4. Summary of acres planted with rice in 2010 8

State Acreage Planted (x 1000) Percent Production (cwt) Percent

Arkansas 1,791 49% 115,675,000 48% California 558 15% 44,326,000 18% Louisiana 540 15% 32,625,000 13% Mississippi 305 8% 20,756,000 9%

Missouri 253 7% 16,254,000 7%

Texas 189 5% 13,468,000 6% United States 3,636 243,014,000

Environmental Fate Assessment

Based on laboratory studies, fluoxast robin persists in soils for se veral months to more than a year, and is slightly to moderately mobile in soils. As for aquatic e nvironments, fluoxastrobin has been shown to be stable to hydrolysis. Fl uoxastrobin is slightly su sceptible to microbial degradation in aquatic environments. Aqueous phot olysis of fluoxastrobin has been shown to be a major route of fluoxastrobin transformation in st erile water. However, an additional photolysis study performed in natural water/sediment syst ems indicates that the majority of applied fluoxastrobin adsorbs to sediment and no tran sformation occurs under pseudo environmental conditions. Thus, the dissipation of fluoxastrobin in water is expected to depend on physical characteristics of the water ( e.g. , sediment loading, depth, etc.) which have an effect on sunlight penetration as well as the rate of fluoxast robin sediment partitioning. Partitioning of fluoxastrobin between water and sediment was va riable between submitted studies. Based on the log K ow fluoxastrobin is not expect ed to bio concentrate. This is supported by the fish bioaccumulation study. Environmental fate prope rties of fluoxastrobin are summarized in Table 5

. Table 5. Environmental Fate and Transp ort Characteristics of Fluoxastrobin

Parameter Data Study ID Study Status Hydrolysis Half-life (t 1/2 ) pH 7: Stable 45865304 Acceptable
Aquatic Photolysis Half-life (t 1/2 ) pH 7: 4.1, 20.1, and 28.3 days 45865306 & 45865403 Acceptable
Soil Photolysis Half-life (t 1/2 ) Stable 4586530 8 Acceptable

Aerobic Soil Metabolism Half-life (t 1/2 ) 29.4, 26.2, 30.1, 46.6, 323 and 393 days 1 45865309 & 45865310 Acceptable

Aerobic Aquatic Metabolism Half-life (t 1/2 ) 29 and 51 days (water) 363 and 271 (sediment) 190 and 150 days (total system) 45865313 46925806 2 Acceptable6 Parameter Data Study ID Study Status
Anaerobic Soil Metabolism half-life (t 1/2 ) No data

Anaerobic Aquatic Metabolism half-life (t 1/2 ) 147 days (water) 211 days (sediment)

187 (total system) 45865312 46925806 2 Acceptable

Adsorption Coefficient (K d ) 26.26, 12.70, 16.21, and 3.35 mL/g 45865315 Supplemental Soil Partition Coefficient (K oc ) 1580, 629, 758, and 424 mL/g

Terrestrial Field

Dissipation 578, 533, 347, and 239 days 45865318, 45865320, 45865323, &

45865324 Acceptable

Aquatic Field

Dissipation Application 1: 6 days (water) 3 and 20 days 3 (total system) Application 2: 10 days (water) 3 and 135 days 4 (total system) 48532004 Upgradable 5

Fish BCF 18 45865421 Supplemental
1. There is a direct correlation with the level of soil microbial viability and the rate of degradation observed in the aerobic soil metabolism studies for fluoxastrobin. 2. On February 1, 2006, the registrant responded (MRID 46925806) to the deficiencies in the data evaluation report and the acceptability of the aerobic and anaerobic aquatic studies submitted in support of the fluoxastrobin registration (MRIDs 45865313 and 45865312, respectively). These studies were reevaluated and determined to be acceptable as EFED does not expect fluoxastrobin to sorb to the glass test apparatus to a sufficient degree to affect the study results, as dem onstrated by the material balance. 3. Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media (final draft document December 21, 2011); Nth-Order Rate Model or Indeterminate Order Rate Equation Model (IORE) Representative half-life (T R IORE ) 4. Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media (final draft document December 21, 2011); Double First-Order in Parallel (DFOP) second (“slow”) half-life (t 1/2 ) 5. Data can only be used qualitatively for risk assessment purposes and should not be used as a rational for additional refinements.

The two major soil metabolites of fluoxastro bin identified are HEC5725-E-des-chlorophenyl (HEC 7155) and HEC5725-carboxylic acid (HEC 7180). The only major degradate found in aqueous studies is HEC5725-oxazepine, which forms through direct photolysis in sterile water. An additional photolysis study performed in natura l water/sediment systems indicates that the majority of applied fluoxastrobin adsorbs to sediment and no oxazepine forms under pseudo environmental conditions. This indicates aquatic photolysis of fluoxastrobin in the environment may be minimal as sediment partitioning reduces the available fluoxastrobin that may undergo photolysis. An aquatic field di ssipation study (discussed in more detail below) does not report transformation products, a study deficiency; th erefore, the formation of fluoxastrobin transformation products in the environment cannot be corroborated. Transformation is likely to be minimal based on the half-life of fluoxastrobi n in the total system (water and sediment).

Terrestrial field dissipation studi es indicate that fluoxastrobin pers ists for over a year. However, it was not observed to leach through soil. Out of the three major metabolites mentioned above, only HEC5725-E-des-chlorophenyl wa s detected in the terrestria l field studies. The observed7 concentration of HEC5725-E-de s-chlorophenyl is below 10% of the total applied. This metabolite is also observed in the deeper soil layers, but at less than 1% of the total applied. A recently submitted aquatic field dissipation study c onducted on rice has several deficiencies that limit its use for risk assessment purposes at this time; however, the study suggests fluoxastrobin readily dissipates from the wate r column but may persist in sedi ment. The rapid dissipation of fluoxastrobin from the water column is due to partitioning to sediment; however, the role of transformation was not investigated. The route of fluoxastrobin dissipation under aquatic field conditions could not be determined as soil and water samples were not analyzed for transformation products. The total sy stem (water and soil/sediment) half-life as well as residual residues indicate fluoxastrobin persists be yond the study duration. This suggests that accumulation (carry over) of fluoxastrobin in ri ce paddies is possible. The mobility of fluoxastrobin in the soil profile could not be as sessed based on the data included in this study.

Relevant Rice Growing Practices

In general, rice fields are prepared (disking and harrowing) prior to seedin g in order to destroy winter vegetation and reduce the ch ance of seedling drift. The fields are then leveled in order to maintain a flood and reduce runoff. After land preparation, rice seeds are planted via waterseeding or dry-seeding on well prepared seed beds. If dry-seeded, the fields are then flushed with irrigation water to obtain a uniform seed germ ination and seedling emergence. In between planting and establishment of permanent flood (three to four weeks after the seeding), fields may be flushed several times to maintain moistu re in the soil. Once the permanent flood is established, it is maintained until 2 to 3 weeks before harvesting. Flooded water (also referred to as paddy water in this assessment) is released an d fields are drained two to three weeks before harvesting to facilitate harvesti ng operations that use machines.

In California, rice is grown primarily in cont inuously flooded, flow-through systems, where the rice is seeded by airplane into the water. 10 However, the practice of dry seeding of rice in California has increased due to weed resistance issues. 11 Flooded paddies are normally drained two to three weeks prior to harves t. Information from the University of California Rice Research and Information Program states that paddy water dept hs typically range from four to greater than eight inches. 12

In the southeastern United States, rice can be planted via water-seed ing, drill-seeded, or broadcast dry; however, most of the planting is vi a water-seeding to control red rice. In dry seed planting, four to six weeks may elapse between planting and permanent flood establishment, although flooding fields immediat ely after seeding can improve weed control. A uniform flood depth of less than four inches ( one to two inches is preferred) is usually maintained prior to rice emergence, and then the flood dept h is increased to four inches. 13

10 Hill, J.E., Dickey, D. 1998. Crop Profile for Rice in California. http://www.ipmcenters.org/Cro pProfiles/docs/carice.pdf 11 Hill, J. E., Williams, J. F., Mutters , R. G., & Greer, C. A. 2006. The California rice cropping system: agronomic and natural resource issues for long-term sustainability. Paddy Water Environ, 4, 13-19. 12 http://www.plantsciences.ucdavis.edu/ucce rice/rice_production/planting_water_mgmt.htm 13 Shipp, M. 2002. Crop Profile for Rice in Louisiana. http://www.ipmcenters.org/Cro pProfiles/docs/LArice.pdf8 Conceptual Model

An illustration highlighting possible pesticide dissip ation routes in the environment are shown in Figure 1 . Although foliar interception may reduce the amount of fluoxastrobin available for runoff, it is believed that fluoxastrobin coul d reach surface waters through spray drift, penetration of the canopy to the soil surface or standing wate r during application, and foliar wash-off followed by runoff. The soil/water partitioning of fluoxastro bin indicates that fluoxastrobin runoff is primarily going to occur vi a soil or sediment transport; however, some dissolution in runoff water is possi ble as water:sediment partitioni ng is an equilibrium process.

Figure 1. Probable Routes of Pestic ide Dissipation in the Environment

For fluoxastrobin use on rice, appl ications may lead to direct surface water contamination as a result of spray drift or indi rect contamination through discha rge of the paddy water containing soil sorb fluoxastrobin and dissolved fluoxastrobin. Based on the fate properties of fluoxastrobin it may be persistent in the environment for severa l months to more than a year post-application and may accumulate in soil and sediment. Fluoxastrobin is stable to hydrolysis and microbial mediated degradation in aquatic environments; however, aqueous photolysis is a major route of degradation. The phototransformation of fl uoxastrobin in water depends on physical characteristics of the water ( e.g. , sediment loading, depth, etc.) which have an effect on sunlight penetration. In general, paddy water is shallo w; therefore, aquatic photolysis may be a dissipation route for fluoxastrobin. The relatively short half-life va lues in both the aquatic field dissipation study (column water) and the aqueous photolysis st udy indicate fluoxastrobin may dissipate rapidly from shallow paddy water after the permanent flood is established; however, aquatic laboratory studies indica te fluoxastrobin water:sediment partitioning is variable. Both laboratory as well as field studies indicate that fluoxastrobin ma y remain in the sediment for more than a year and has the potential to accumulate.

Sorption studies indicate fluoxastrobin is moderately mobile in soil; however, field dissipation studies do not indicate that it is likely to impact groundwat er. In addition, rice production generally occurs on fine-textured, poorly drained soils, soils with impervious hardpans, clay pans9 or soils that generally retain water which re duces the likelihood of groundwater contamination for fluoxastrobin use on rice.

Analysis Plan

The EFED Tier 1 Rice Model (v1.0, May 8, 2007) 14 was used to estimate aquatic exposures for applications directly to wate r (flooded field). The model es timates exposure in a water body holding a 10 cm water depth. When a pesticide is applied to a water body, the model assumes that it will instantaneously pa rtition between a water phase a nd a sediment phase based on the partition coefficient of the chemical. The formul a of the Tier I Rice Model v1.0 is as follows:

d ai

w 

### K m C 00013

. 0 00105

. 0 '



###  

and, if appropriate: K d = 0.01K oc 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 partitioning coefficient (L/kg)

The Tier I Rice Model was calibrated to generate estimates that are similar to or greater than dissolved concentrations measured within rice paddies and in discha rged paddy water. The calibration involved determination of the sediment interaction depth by calibrating the model to maximum residues measured in paddy water in dissipation studies. The model does not account for pesticide degradation, volatilization, dilu tion, foliar interception, or other dissipation processes. The model was not evaluated or calibra ted for concentrations measured in sediment. Tier I groundwater EDWCs from the proposed us e of fluoxastrobin on rice were estimated using SCI-GROW (S creening C oncentration i n Gro undw ater, version 2.3, August 8, 2003). SCIGROW is an empirical model based on a linear best fit through 13 pr ospective groundwater studies (one year of applicatio n). SCI-GROW was designed solely for use as a Tier I screening tool and does not have the capability to consid er mitigating circumstances like variability in leaching potential of different so ils, weather (including rainfa ll), or depth to aquifer.

Detailed descriptions and documentation for the aforementioned models can be found on the Office of Pesticide Program’s models website. 15

14 USEPA 2007. Guidance for Tier I Estimation of Aqueous Pesticide Concentrations in Rice Paddies . Memo from S. Bradbury to Environmental Fate and Effects Division; May 8, 2007

. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Subs tances, Office of Pesticide Programs, Environmental Fate and Effects Division, Washington, DC. Available at http://www.epa.gov/oppefed1/models/water/index.htm#rice (accessed September 27, 2010). 15 http://www.epa.gov/oppefed1/models/water/index.htm10 Selecting Input Parameters

The input parameters used in this DWA were selected from the environmental fate data submitted to support fluoxastrobin registration in accordance with US EPA-OPP EFED water model parameter guidance. 16 The input values used in the model runs are provided in Table 6

.

Table 6

. Input Parameters Used in the Rice Mode l and SCI-GROW Modeling to Estimate Fluoxastrobin Drinking Water Concentrations

Parameter Values Source

Aerobic Soil Metabolism (t 1/2 ) SCI-GROW: 38 days (median half-life value) MRID 45865309 & 45865310
Soil Adsorption Coefficient K oc SCI-GROW: 424 lowest K oc value Rice Model: 848 mL/g mean K oc value MRID 45865315

Surface Water

The proposed use of fluoxastrobin on rice may resu lt in a surface water peak concentration of 93 μg/L. 17 The Tier I Rice Model only provides a single output value; therefor e, this value should be used for all exposure durations ( i.e. , 1 in 10 year peak concen tration, 1 in 10 year annual average concentration, and 30 year annual average). The EDWC of 93 μg/L for rice is higher than previously reported EDWCs for other fl uoxastrobin uses. The most conservative EDWCs reported for fluoxastrobin prior to this assessment was for turf. 3 These results were based on Tier II surface water modeling (PRZM-EXAMS) and were reported to be 60.7 μg/L for the 1-in-10 year peak concentration, 52.9 μg /L for the 1-in-10 year annua l average concentration, and 23.5 μg/L for the 30 year annual average concentratio n. The results for rice and turf are compared in Table 7

. Table 7. Estimated Drinking Water Concentrat ions Resulting From the Proposed Use of Fluoxastrobin on Rice Compared to Previously Reported Turf Values

Parameter Surface Water
Tier I Rice Model EDWCs
μ g/L Tier II PRZM-EXAMS EDWCs for Turf*
μ g/L
Acute 1-in-10 Year Peak

93 60.7

Chronic 1-in-10 Year Annual Average 52.9

Cancer 30 Year Annual Average 23.5

16 Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides
, Version 2.1, October 22, 2009. 17 Calculation: 93 μg/L = 0.20 kg a.i./h/[0.00105+0.00013(0.01 x 848)]11 *Previously reported values 3

Estimates from the Tier I rice model generally do not represent concen trations found in human drinking water as the estimates represent paddy water and, in gene ral, drinking water intakes are not located within a paddy or near discharge si tes. Nevertheless, the es timate provides an upper bound concentration for the potential exposure to fluoxastrobin in surface water used to supply drinking water following fluoxastrobi n applications to rice. While th e Tier I rice model also does not consider transformation ( i.e. , anaerobic and aerobic aqua tic metabolism and aquatic photolysis) fluoxastrobin is only slightly suscep tible to metabolism (aquatic metabolism total system half-life values 150-190 days) and photol ysis in the environment is assumed to be minimal. Aquatic photolysis may be a major route of fluoxastrobin dissipation in the environment; however, aquatic photo lysis is assumed to only occur in a small fraction of the water column (top few centimeters) and is heavil y affected by physical characteristics of the water ( e.g. , sediment loading, depth, etc.) as well as the canopy coverage and water:sediment partitioning. A laboratory aquatic photolysis study conducted with natural water indicates fluoxastrobin partitions to sediment, limiting photolysis. Aerobic and anaerobic aquatic metabolism studies submitted show that fluoxastr obin readily sorbs to sediment in aquatic environments, reducing the water concentration ra pidly; however, sorption is considered in the Tier I rice model; therefore, so rption of fluoxastrobin to sediment is reflected in the reported concentration.

The recent aquatic field dissipati on study does not permit the identifi cation of the mechanisms of fluoxastrobin dissipation in the environment; howeve r, fluoxastrobin is exp ected to be relatively stable based on the total system half-life value of 135 days. Therefore, consideration of fluoxastrobin transformation not co nsidered in the Tier I rice m odel are not expected to reduce the EDWC, as the chemical is fairly persistent.

Groundwater

Tier I fluoxastrobin EDWCs in groundwater resu lting from the proposed use on rice are shown in Table 8 . Fluoxastrobin EDWCs in groundwater are not expected to exceed 0.038 μ g/L for the proposed use on rice. This is lower than the EDWCs previously determined for turf (0.23 μ g/L).

Table 8. Tier I Fluoxastrobin Estimated Dri nking Water Concentrations for Groundwater Resulting from Its Proposed Use of on Rice Co mpared to Previously Reported Turf Values

Parameter Groundwater Tier I SCI-GROW Rice
μ g/L Tier I SCI-GROW Turf*
μ g/L EDWC 0.038 0.23

Monitoring Data

Fluoxastrobin is a fairly new chemical so monito ring data is limited. The National Water-Quality Assessment Program (NAWQA) database indicates that surface water and bed sediment samples were analyzed for fluoxastrobin at two Georgia sites. The fluoxa strobin concentrations were12 below the limits of detections (4.2 ng/L for water and 1.8 μg/kg for sediment). There is no evidence that other monitoring sites or programs are looking for or detecting fluoxastrobin in surface water or sediment.

No groundwater monitoring data could be locate d as of the date of this assessment.

Uncertainties

1. An aquatic field dissipation study has been submitted and reviewed; however, the study has been classified as upgradeable and without additional data its use in risk assessment is limited. Aquatic field dissipation data is used to confirm the conceptual environmental fate model derived from laboratory studies to insure that all appropriate dissipation pathways are identified and that all environmentally relevant transformation products are identified. This cannot be completed without the submission of additional information on the potential role of aquatic photolysis on the dissipation of fluoxastrobin, which may help refine aquatic exposure estimates; however, the estimated half-life is relatively long (135 days).

Assessment Conclusions

The EDWCs for the proposed use of fluoxastrobin on rice in surface water were estimated using the Tier I rice model. Estimates from the Tier I model generally do not represent concentrations found in human drinking water as the estimates re present paddy water and, in general, drinking water intakes are not located with in a paddy or near discharge site s. This estimate provides an upper bound concentration that may result from the use of fluoxastrobin on rice. The Tier I surface water EDWCs are expected to be hi gher than those for groundwater so EFED recommends that the Health Effects Division use the surface water EDWCs resulting from rice use in future assessments.