UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WAS H I NG TO N D

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OFFICE OF CH E MICAL SAFETY AND POLLUTION PREVENTION PC Code: 125851 DP Barcode: 420998 DATE: August 11, 2014 MEMORANDUM



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TO: Isoxaben: Drinking Water Assessment for Registration Review Andrew Shelby, Physical Scientist

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nvironmental Fate and Effects Divison/ERB6 (7507P) {/ MarkCorbin,BranchChief**~~ e~** **·** k <- Environmenta l Fate and Effects Divison!ERB6 (7507P)**/'\I \**  

### YDennis McNeilly, Risk Assessor, Christina Swartz, Branch Chief Health Effects Division/RAB2 (7509P) Christina Scheltema, Chemical Review Manager Pesticide Re-Evaluation Division (7508P)
The Environmental Fate and Effects Division (EFED) ofthe Office of Pesticide Programs (OPP) has completed a Drinking Water Assessment for the registration review of isoxaben. The chemical is registered for use on turf grass, ornamentals, groundcover/perennials, non-cropland, Christmas tree/conifer plantations, hardwood nurseries, fruit trees, nut trees, vineyards, and Eucalyptus. The maximum single application rate for the broadcast use is 1.02 lbs a.i./A and the maximum annual application rate is 4.03 lbs a.i./ A. The assessment considers a parent only approach but also provides for characterization the major degradates as parent in a total toxic residue (TTR) screening level approach assuming stability oftoxic residues to biotic and abiotic degradation. Major degradates include hydroxy isoxaben, dimethoxy benzamide, methoxyphenyl pyrimidinol, and AEM hexenoyl. Degradates are characterized in detail in the drinking water degradates identification memo (D374526). Hydroxy isoxaben, methoxyphenyl 1pyrimid inol , AEM hexenoyl isoxaben, and dimethoxy benzamide are included with paren t isoxaben as residue s of concern as identified b y HED (03752 4 5; see attac h e d). Unidentified degradates from th e a qu eo us photolysis stu d y were no t noted a s residu es of conce rn bu t their

inclusion as residu es of conce rn is characteri ze d . Due to the p ersistence and moderate mo bility of i soxaben, groundwater esti m a t e d drinking water concentrations (EDWCs ) were higher than surface water E DW Cs. Based on modeling results , the m aximum estimated groun d water exposure co n centrat ions for total toxic res idu es of isoxaben and t he recommended conce n t r ations f or use i n HE D ' s dietary assessment are: 1,010 Jlg/L for the peak concentrat i o n

909 Jl g/L for t h e post-breakthrough average The maximum estimated 1-in - 1 0 year peak s ur face water ex po sure concen t r at ion fo r TTR of i soxabe n is 89.6 J..Lg/L derived fr om the Surface Water Co n ce n tration Calcu l a t or (SWCC v1.106). Fate and Transport Cha rac t erization

Th e most significant degradation pathway for isoxaben differs depending on surface water or grou nd water exposure. Due to isoxaben's m oderate mobility (average K o c = 354 Llmg o.c.), both surface water and g roun d water e x po s ure are possible depending on so i l permeability. In th e case of groundwater exposu re , anaerobic metabolism is t he dominant form of dissipation with an anaerobic so il m e t abolism hal f -life of thr ee d ays. I n t he case o f surface wa t e r exposure, aqu eous photolysis i s the dominant form of dissipation wi th a half-life o f s ix days. Isoxaben i s stab l e to h y dr olys i s and persistent to aerobic m etabo l ism with aerobic so il metabolism half-lives ranging from 150 to 891 days and aerobic aquatic half-lives ranging from 435 days to stab l e. I soxaben i s non-volatile w i th a Henr y' s L aw Constant of 1.26* 1 o- 9 atm-m 3 / mol. Mo ni t oring Data Neither U SGS Na t i onal Wate r-Quality Assessme nt Program (NA WQA ) or t h e Water Quality

Portal (W QP ) i ncl ud e any m oni toring data for i soxa b e n as of June 2, 201 4 . Drinking Water Ex po s ure Modeling T h ough uses in orc h a r d s, v in eyar d s and on E u calyptus allow f ewer applicat i ons and/or have a lower maximum applicatio n rate, scenarios r epresen tin g these uses also rep r esent uses with maximum annual applicatio n s and the m aximum ap plica t ion rat e . Therefore , a ll s urfac e water sce nari o s were mo de l ed u s in g maxim u m application rate (1.02 l b s a.i./A) a nd maximum numb e r of reap p lication s ( 4 per year). Scenarios se l ecte d that represent orchard s , v i ne ya rds and

E ucal ypt us are also representative of Christmas tree/conifer plantation s , h ardwoo d nursery , orname ntals , and non-crop l and which have uses at the maximum app li cation rate and numb er of r eap pli ca tion s . A ll availab l e SWCC scenarios that are r ep r esentative of orc h ards, vineya rd s , nurseries, or turf were modeled. Thi s cr it erion i ncludes 18 scenarios that are geogra phica lly distributed across the coterminous U.S . A ll six curren tl y available groundwater sce nari os were modeled with maximum applicat ion rate and number of reapplications. The c urrentl y available 2groundwater scenarios are representative ofvulnerable groundwater conditions which have the potential to be present for all isoxaben uses. 

### Table 1 : Isoxaben Summary Use

Use Application Max. Max Max Min

. Comment method Single # App App app rate app s rate per interval (lb pe r year ( lb (day s) a.i ./ A) year a .i/ A) Turfgrass Ground 1.02 4* 4
. 03 56-60 Incons istent restrictions on use in AZ, NY , and on chemigation Lawns Ground 1.0 4* 3.2 60* Ornamentals (landscape , Ground 1.02 4* 4
.03 56-60* AZ restrictions for container, field) commercial use Groundcovers /perennials Ground 1.02 4* 4
.03 60 AZ re striction

. • Not for commercial use . Non-cropland Ground 1.02 4* 4 .03 60 AZ restriction

. • Not for commercial use. Non-bearing fruit & nut Ground 1.0 3* 3
.0 60* AZ restriction trees & non-bearing vineyards Christmas tree/conifer Ground 1.02 4* 4.03 60 Not for commerc ial use in plantations, hardwood AZ nursery Fruit and nut trees and Ground 1.02 2 2.0 30* Not for use in NY vineyards Eucalyptus Ground 0.75 2 1.0 30 62 719-612 only : Not for use in NY ; do not apply w ithin 200 ft of susceptible nontarget plants *Not specified or inconsi stent across all product labels Parameters for the derivation of surface water concentrations and the groundwater concentration for all uses are as follows: 

### T bl 2 SWCC

a e 

# . an 

## - apu d PRZM GW In t 

### Parame er va ues t I 

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### or soxa b

### en PARAMETER (units) VALUE (S) SOURCE COMMENT Application Rate (kg a.i

. /ha) 1.14 Product 1.02 lbs a .i./ A ; Maximum application rate for labels turfgrass, ornamentals, groundcover /perenials, noncropland, Christmas tree/conifer plantations , hardwood nursery , fruit and nut trees and vineyards. Number ofApplication s 4 Maximum number of app li cations for turfgrass, ornamentals , groundcover /perenials, non-cropland, Christmas tree/conifer plantations , and hardwood nursery

3PARAMETER (units) VALUE(S) SOURCE COMMENT I nterval between App l ications 56 Minimum application interval for use patterns with 4 (days) appl i cations pe r year (turfgrass and ornamental s) Molecular weight (g/mol) 332.39

Henry's La w Constant (atm- 1.26* to· 9 Calculated (V APR/760 )/ (SOL/MWT), m 3 / mol) where V APR is vapor pressure in torrs , MWT is the molecular weight in g moi· 1 , and SOL is the solubility in water in mg L" 1 • Vapor Pressure (torr) 4.1 * 10 · 9 I UPAC MRID 153106 r eports a valuce of <3. 9* to · 7 torr Footprint Solub ili ty in Water @ 20 ° C , 1.42 MRID (mg/L or ppm) 47140001

Soil Partition Coeffic i ent 354 MRID Average of280 , 190 , 310 , 420 , and 570 mLig o.c. 1 (Koc)(mUg) 41106303 CAM (Chemica l Application l Broadcast, applied to bareground and unincorpora ted. Method) Depth of In corporat i on 0 (inches) Application efficiency 0.99 Ground Application (decimal) Spray drift fraction (decimal) 0.061 G r ound Application Percen t Cropped Area 1.0 l 00% cropped area con s ervatively assumed due to (decimal) non-agri c ultu r al use patterns. App l icat i o n date (day/month) Product 4 application s with 56 day retreatment in tervals. March 1 Labels April26 June 23 August 20 Hydrolysis Half-life (days) Stable MRID 250449

Aqueous P hotolysis H alf- life Parent 6.0 MRIO Parent input used in the calculati on ofEDWC s as @p H 7 (days) TTR 93.5 47140003 request ed by HED (0375245). TTR t 112 includes unidentified degrad a te and is provided for charact e rization. 4PARAMETER (units) VALOB(S) SOURCE COMMENT Aerobic Aquatic Metabolism Par ent 22.0 MRIO 63 (TTR) and21.5 (parent) days in Water

- sand; SFO Half-life (days) TTR282 46393202 171 (TTR ) and 21 (parent)Stable in Water-sandy loam; N/A 90th percenti le mean of values used as input 1 Anaerobic Aquatic Parent 17.4 Anaerobic soi l input = single t 112 x 3 1 Metabolism Half-life (days) TTR 1608 Anaerobic aquatic input = anaerobic soil input x 2 1 Aerobic Soil Metabolism Par ent 443 MRID 274 (TTR) and 150 (parent)days in Sandy Loam; Half-lif e (days) TTR 723 47 140004 DFOP ; isoxazole label 264 (TTR ) and 199(parent) days in Sandy Loam; SFO; phenyl label 340 (TTR) and 207 (pa rent)days in Silt Loam; S FO ; phenyl label MRID 360(TTR) and 280 (parent)days in Silt Loam ; SFO ; 49090101 phenyl label l123(TTR) and 891 (parent) days in Sand; SFO ; phenyl label 1 85 days in Sandy clay loam; DFOP; combined label 90th percent ile mean of values used as input 1 Anaerobic Soil Metabo lism Parent 2
.9 MRID Sandy clay loam ; SFO; total system Half

- life (days) TTR268 46393201

1 " Input Parameter Guidance " refers to Guidance for Selectmg Input Parameters m Mo dehng the Envtronmental Fate and Transport ofPestici<les ; Version 2.1 , October 22 , 2009. Surface water and groundwater EDWCs are presented below wit h hi ghest representative EDWCs hi ghlighted in bold . All relevant surface water scenarios tha t are relatable to isoxa ben uses were se lected and paramet erized at maximum application rates and with the maximum number of reapplications

. Inclusion of aqueous photo lysis degradates in the total toxic re sidue approach results in surface water EDWCs 1% to 17% higher than those reported below.

5Table 3: EDWCs for Total Toxic Residues of Isoxaben in Surface Water. Crop Scenario 1-in- 1 0 year 1-in- 1 0 year 30-year annual (application date) Acute annual average (ppb) concentration average (ppb) (ppb) CA Almond 24.1 16.2 14.6 CA Citrus 13.9 10.7 9.7 CA Frui t 20.4 16.2 1 2.6 CA Grapes 18.8 13.9 10.9 CA Nursery 28.3 19.9 11 FL Citrus 89.6 32.2 21.6 FL Nursery 60.4 19.3 13.5 FL Turf 24.1 15 11.3 MI Nursery 54.3 30.7 24.7 NC Apple 69.5 28.1 17 NJ N u rsery 59.2 28 20 .1 NY G r a p e 77.1 43.6 33.6 OR App l e 35.8 21.5 16.3 OR Nursery 26.5 18.6 16.1 OR Xmas Tree 21.7 14.7 1 2.8 PA Aj:>ple 59.7 31.7 21.9 PA Turf 39.8 24.1 16.9 TN Nursery 60.6 22.4 15.3 A ll current l y avai l able groundwate r scenarios were run i n a sc r eening l eve l approach to assess for vulnerable groundwater conditions. Groundwater EDWCs are substantially higher than surface water EDWCs due to is oxaben's moderate mobility and high persi ste nce.

Table 4: EDWCs for Total Toxic Residues of Isoxaben in Groundwater Scenario P eak (ppb) Post Breakthrough Average (ppb) Delmarva 739 673 F l orida Citrus 805 721 F l orida Potato 126 125 Georgia Coastal 301 259 No rth Carolina Coastal 971 867 Wisconsin Sands 1010 909 6