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 d--

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 (DWA) 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 TechTM 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 applications on rice. The maximum number of proposed 

applications is two per season with a minimum application interval of 27 days.1 Application 

methods include aerial, ground, and chemigation sprays. 

EDWCs are based on the Tier I rice 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 identified by Health Effects Division is parent 

fluoxastrobin.2 Therefore, this DWA considers only fluoxastrobin (no transformation products 

are included). 

Table 1. Estimated Drinking Water Concentrations 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 

μg/L

Tier II 

PRZM-EXAMS 

EDWCs for Turf*

μg/L

Tier I SCI-GROW 

EDWCs for Rice 

μg/L

Tier I SCI-GROW 

EDWCs for Turf*

μg/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 values3 

The proposed use of fluoxastrobin on rice may result in a peak concentration of 93 μg/L in 

surface water based on the Tier I rice model estimate. This is higher than previously reported 

EDWCs for other fluoxastrobin uses. The most conservative EDWCs reported for fluoxastrobin 

prior to this assessment was for turf.3Error! 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 annual average concentration, and 23.5 μg/L for the 

30 year annual average concentration. For comparison, EDWCs for turf are also presented in 

Table 1. Based on further analysis of the proposed 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 groundwater EDWCs for fluoxastrobin use on rice as well as turf 

for comparison. 

PROBLEM FORMULATION 

Fluoxastrobin [(E)-{2-[6-(2-chlorophenoxy)-5-fluoropyrimidin-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 inhibit respiration in fungi by blocking electron transport through mitochondrial 

systems. The chemical identification as well as physical-chemical properties of fluoxastrobin are 

provided in Table 2. 

Table 2. Physical-Chemical Characteristics 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

CH3

Chemical Abstracts Service 

(CAS) Registry Number 361377-29-9 

Empirical Formula C21H16ClFN4O5

USEPA Pesticide Code (PC #) 028869 

Smiles Notation Clc4ccccc4Oc3ncnc(Oc2ccccc2C(=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 m3 / mole (9.98 atm - m3/mol) 

Log Kow 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 soybean4

; 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 presented 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, D357699
4

on tuberous and corm vegetables, as well as peanut.3

 Past assessments have been completed 

using PRZM-EXAMs (Pesticide Root Zone Model, version 3.12.3, June 2006; EXAMS 

(EXposure Analysis Modeling System, version 2.98.04.06, April 2005) and SCI-GROW 

(Screening Concentration in Groundwater, version 2.3, August 8, 2003) modeling. Turf uses 

provided the most conservative estimated drinking 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 single application rates range from 0.12 to 0.55 

lb a.i./a and maximum yearly application 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 fluoxastrobin 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 maximum number of proposed fluoxastrobin 

applications on rice is two per season with a maximum single application rate of 0.18 lb a.i./a 

and a minimum application interval of 27 days7

 (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 applications to flooded fields nor does it require a water holding period 

prior to discharging paddy water 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, California, Mississippi, Missouri, Louisiana, and Texas. Survey data 

from the National Agricultural Statistics Service (NASS) on rice acres planted in the United 

States for the year 2010 is provided in Table 4.

8

 Rice has also been grown 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 rate 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

Turf6 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 20108 

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, fluoxastrobin persists in soils for several months to more than a 

year, and is slightly to moderately mobile in soils. As for aquatic environments, fluoxastrobin 

has been shown to be stable to hydrolysis. Fluoxastrobin is slightly susceptible to microbial 

degradation in aquatic environments. Aqueous photolysis of fluoxastrobin has been shown to be 

a major route of fluoxastrobin transformation in sterile water. However, an additional photolysis 

study performed in natural water/sediment systems indicates that the majority of applied 

fluoxastrobin adsorbs to sediment and no transformation 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 fluoxastrobin sediment partitioning. Partitioning of 

fluoxastrobin between water and sediment was variable between submitted studies. Based on the 

log Kow fluoxastrobin is not expected to bio concentrate. This is supported by the fish 

bioaccumulation study. Environmental fate properties of fluoxastrobin are summarized in Table 

5. 

Table 5. Environmental Fate and Transport Characteristics of Fluoxastrobin

Parameter Data Study ID Study Status 

Hydrolysis Half-life 

(t1/2) pH 7: Stable 45865304 Acceptable 

Aquatic Photolysis 

Half-life (t1/2) pH 7: 4.1, 20.1, and 28.3 days 45865306 & 

45865403 Acceptable 

Soil Photolysis 

Half-life (t1/2) Stable 45865308 Acceptable 

Aerobic Soil 

Metabolism 

Half-life (t1/2) 

29.4, 26.2, 30.1, 46.6, 323 and 393 

days1

 

45865309 & 

45865310 Acceptable 

Aerobic Aquatic 

Metabolism Half-life 

(t1/2) 

29 and 51 days (water) 

363 and 271 (sediment) 

190 and 150 days (total system)

45865313 

469258062 Acceptable 
6

Parameter Data Study ID Study Status 

Anaerobic Soil 

Metabolism half-life 

(t1/2) 

No data 

Anaerobic Aquatic 

Metabolism half-life 

(t1/2) 

147 days (water) 

211 days (sediment) 

187 (total system) 

45865312 

469258062 Acceptable 

Adsorption Coefficient 

(Kd) 26.26, 12.70, 16.21, and 3.35 mL/g 

45865315 Supplemental 

Soil Partition 

Coefficient (Koc) 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 

days3 (total system) 

Application 2: 10 days (water)3

 and 135 

days4 (total system) 

48532004 Upgradable5 

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 demonstrated 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 (TR 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 (t1/2) 

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 fluoxastrobin 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 natural 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 dissipation study (discussed in more detail below) does not report 

transformation products, a study deficiency; therefore, the formation of fluoxastrobin 

transformation products in the environment cannot be corroborated. Transformation is likely to 

be minimal based on the half-life of fluoxastrobin in the total system (water and sediment). 

Terrestrial field dissipation studies indicate that fluoxastrobin persists 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 was detected in the terrestrial field studies. The observed 
7

concentration of HEC5725-E-des-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 conducted 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 water column but may persist in sediment. 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 system (water and soil/sediment) half-life as well as residual 

residues indicate fluoxastrobin persists beyond the study duration. This suggests that 

accumulation (carry over) of fluoxastrobin in rice paddies is possible. The mobility of 

fluoxastrobin in the soil profile could not be assessed based on the data included in this study. 

Relevant Rice Growing Practices

In general, rice fields are prepared (disking and harrowing) prior to seeding in order to destroy 

winter vegetation and reduce the chance 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 germination 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 moisture 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 and fields are drained two to three weeks before 

harvesting to facilitate harvesting operations that use machines. 

In California, rice is grown primarily in continuously 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 harvest. Information from the University of California Rice Research 

and Information Program states that paddy water depths typically range from four to greater than 

eight inches.12 

In the southeastern United States, rice can be planted via water-seeding, drill-seeded, or 

broadcast dry; however, most of the planting is via 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 immediately 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 depth is increased to four inches.13

 

10 Hill, J.E., Dickey, D. 1998. Crop Profile for Rice in California. 

http://www.ipmcenters.org/CropProfiles/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/uccerice/rice_production/planting_water_mgmt.htm 

13 Shipp, M. 2002. Crop Profile for Rice in Louisiana. http://www.ipmcenters.org/CropProfiles/docs/LArice.pdf
8

Conceptual Model 

An illustration highlighting possible pesticide dissipation 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 could reach surface waters through spray drift, 

penetration of the canopy to the soil surface or standing water during application, and foliar 

wash-off followed by runoff. The soil/water partitioning of fluoxastrobin indicates that 

fluoxastrobin runoff is primarily going to occur via soil or sediment transport; however, some 

dissolution in runoff water is possible as water:sediment partitioning is an equilibrium process. 

Figure 1. Probable Routes of Pesticide Dissipation in the Environment 

For fluoxastrobin use on rice, applications may lead to direct surface water contamination as a 

result of spray drift or indirect contamination through discharge 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 several 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 fluoxastrobin 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 shallow; therefore, aquatic photolysis may be a 

dissipation route for fluoxastrobin. The relatively short half-life values in both the aquatic field 

dissipation study (column water) and the aqueous photolysis study indicate fluoxastrobin may 

dissipate rapidly from shallow paddy water after the permanent flood is established; however, 

aquatic laboratory studies indicate fluoxastrobin water:sediment partitioning is variable. Both 

laboratory as well as field studies indicate that fluoxastrobin may 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 groundwater. In addition, rice production 

generally occurs on fine-textured, poorly drained soils, soils with impervious hardpans, clay pans 
9

or soils that generally retain water which reduces 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 water (flooded field). The model estimates 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 partition between a water phase and a sediment phase based on the 

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

d

ai

w K

m C

0.00105 0.00013

'

 

and, if appropriate: 

Kd = 0.01Koc

 where 

Cw water concentration (μg/L) 

mai’ mass applied per unit area (kg/ha) 

Kd water-sediment partitioning coefficient (L/kg) 

Koc 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 discharged 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, dilution, foliar interception, or other dissipation 

processes. The model was not evaluated or calibrated for concentrations measured in sediment. 

Tier I groundwater EDWCs from the proposed use of fluoxastrobin on rice were estimated using 

SCI-GROW (Screening Concentration in Groundwater, version 2.3, August 8, 2003). SCIGROW is an empirical model based on a linear best fit through 13 prospective groundwater 

studies (one year of application). SCI-GROW was designed solely for use as a Tier I screening 

tool and does not have the capability to consider mitigating circumstances like variability in 

leaching potential of different soils, weather (including rainfall), 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 Substances, 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.htm
10

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 Model and SCI-GROW Modeling to Estimate 

Fluoxastrobin Drinking Water Concentrations

Parameter Values Source 

Aerobic Soil Metabolism 

(t1/2)

SCI-GROW: 38 days (median half-life 

value) MRID 45865309 & 45865310

Soil Adsorption 

Coefficient Koc

SCI-GROW: 424 lowest Koc value 

Rice Model: 848 mL/g mean Koc value MRID 45865315

Surface Water 

The proposed use of fluoxastrobin on rice may result in a surface water peak concentration of 93 

μg/L.17 The Tier I Rice Model only provides a single output value; therefore, this value should 

be used for all exposure durations (i.e., 1 in 10 year peak concentration, 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 fluoxastrobin 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 annual average concentration, and 23.5 

μg/L for the 30 year annual average concentration. The results for rice and turf are compared in 

Table 7. 

Table 7. Estimated Drinking Water Concentrations Resulting From the Proposed Use of 

Fluoxastrobin on Rice Compared to Previously Reported Turf Values

Parameter

Surface Water

Tier I 

Rice Model EDWCs 

μg/L

Tier II PRZM-EXAMS 

EDWCs for Turf*

μg/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 values3

Estimates from the Tier I rice model generally do not represent concentrations found in human 

drinking water as the estimates represent paddy water and, in general, drinking water intakes are 

not located within a paddy or near discharge sites. Nevertheless, the estimate provides an upper 

bound concentration for the potential exposure to fluoxastrobin in surface water used to supply 

drinking water following fluoxastrobin applications to rice. While the Tier I rice model also does 

not consider transformation (i.e., anaerobic and aerobic aquatic metabolism and aquatic 

photolysis) fluoxastrobin is only slightly susceptible to metabolism (aquatic metabolism total 

system half-life values 150-190 days) and photolysis in the environment is assumed to be 

minimal. Aquatic photolysis may be a major route of fluoxastrobin dissipation in the 

environment; however, aquatic photolysis is assumed to only occur in a small fraction of the 

water column (top few centimeters) and is heavily 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 fluoxastrobin readily sorbs to sediment in aquatic 

environments, reducing the water concentration rapidly; however, sorption is considered in the 

Tier I rice model; therefore, sorption of fluoxastrobin to sediment is reflected in the reported 

concentration. 

The recent aquatic field dissipation study does not permit the identification of the mechanisms of 

fluoxastrobin dissipation in the environment; however, fluoxastrobin is expected to be relatively 

stable based on the total system half-life value of 135 days. Therefore, consideration of 

fluoxastrobin transformation not considered in the Tier I rice model are not expected to reduce 

the EDWC, as the chemical is fairly persistent. 

Groundwater 

Tier I fluoxastrobin EDWCs in groundwater resulting from the proposed use on rice are shown 

in Table 8. Fluoxastrobin EDWCs in groundwater are not expected to exceed 0.038 μg/L for the 

proposed use on rice. This is lower than the EDWCs previously determined for turf (0.23 μg/L). 

Table 8. Tier I Fluoxastrobin Estimated Drinking Water Concentrations for Groundwater 

Resulting from Its Proposed Use of on Rice Compared to Previously Reported Turf Values

Parameter

Groundwater

Tier I SCI-GROW 

Rice 

μg/L

Tier I SCI-GROW 

Turf*

μg/L 

EDWC 0.038 0.23 

Monitoring Data 

Fluoxastrobin is a fairly new chemical so monitoring 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 fluoxastrobin concentrations were 
12

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 located 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 represent paddy water and, in general, drinking 

water intakes are not located within a paddy or near discharge sites. 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 higher than those for groundwater so EFED 

recommends that the Health Effects Division use the surface water EDWCs resulting from rice 

use in future assessments.