Document ID: EPA-HQ-OPP-2012-0980-0011
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2013-12-20T05:00Z

OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460
                                       
                                       
                                       
                                       
                                       
                                 July 9, 2013

                                                                PC Code: 036602
MEMORANDUM	DP Barcode: 409108 & 409109

SUBJECT:	Mandipropamid: Drinking Water Exposure Assessment for Proposed Section 3 New Uses on: Basil, Ginseng and Succulent Beans; and Expanded Uses on Bulb Vegetables, Cucurbits, Grapes, and Fruiting Vegetables including Tomatoes.

FROM:	Richard Shamblen, Biologist
	ERB2/EFED (7507P)

THROUGH:  Greg Orrick, Environmental Scientist	
            Brian Anderson, Branch Chief
	ERB2/EFED (7507P)

TO:	Dennis McNeilly, Risk Assessor
	Christina Swartz, Branch Chief
	RAB2/HED (7509P)

	Tony Kish, Risk Manager, RM Team 20
            Rosemary Kearns, Risk Manager Reviewer
            Laura Nollen, Biologist, RIMU ERB/RD	
            FB/RD (7505P)

      The Environmental Fate and Effects Division (EFED) conducted a Tier 1 drinking water exposure assessment for the fungicide mandipropamid. The registrant seeks a Section 3 new use registration for basil, ginseng and succulent beans; and expansion of currently registered use groups including bulb vegetables, cucurbits, grapes, and fruiting vegetables including tomatoes. Previous exposure assessments evaluated maximum single application rates of 0.13 lbs a.i./A, four times per season. The registrant seeks to increase the total annual application rate to 2.08 lbs a.i./ A for tomato and basil by allowing for up to four crop production seasons per year. This proposed multi-season total annual application rate exceeds those assessed in previous drinking water exposure assessments.  
      
      Tier 1 exposure model results are summarized in Table 1. PRZM-GW was used to estimate mandipropamid exposure in ground water. Maximum estimated drinking water concentrations (EDWC) in ground water are 87 and 79 ug/L for acute and chronic exposures, respectively. These values are as much as 480 times higher than SCI-GROW model results. Maximum acute and chronic EDWCs in surface waters are 79 and 9.0 ug/L, respectively.
Table 1. Tier 1 Estimated Drinking Water Concentrations (EDWC) for Maximum Mandipropamid Use Patterns.
                             Drinking Water Source
                               (Model, Version)
                                      PCA
                                      (%)
                               Crop Use Pattern
                             (Maximum Annual Rate)
                                     Acute
                                    (μg/L)
                                Chronic (μg/L)
Surface Water (FIRST, 1.1.1)
                                      91
                              Tomato & Basil 
                               (2.08 lbs a.i./A)
                                      79
                                      9.0
Ground Water (PRZM-GW, 1.01)
                                      N/A
                              Tomato & Basil 
                               (2.08 lbs a.i./A)
                                      87
                                      79
Ground Water (SCI-GROW, 2.3)
                                      N/A
                              Tomato & Basil 
                               (2.08 lbs a.i./A)
                                     0.18
Abbreviations: A= acre; a.i. = active ingredient; ha = hectare; kg = kilograms; μg = micrograms; lbs = pounds (US); N/A = not applicable
      
      Two previous Tier 1 drinking water assessments of mandipropamid produced nearly identical exposure estimates (USEPA, 2007; and, 2011). Results of multiple FIRST (v.1.1.0) model scenarios indicated EDWCs in surface waters ranging from 7 to 36 ug/L for chronic and acute exposures. Ground water exposure estimates in both assessments were about 2.4 ug/L when calculated by SCI-GROW (v. 2.3). PRZM-GW (v. 1.01) was not used. 
      
      Differences between the previous two and current drinking water exposure assessments reveal that ground water exposure concentrations decreased by more than a factor of 13, whereas acute surface water exposure concentrations nearly doubled. These differences are likely attributed to a variety of recent changes incorporated into the drinking water assessment. In particular, the following factors adopted for this risk assessment may account for the differences: 
         1)       Four seasons per year are assumed for tomato and basil, whereas only one season per year was assumed for previously assessed use sites; 
         2)       Changes to EFED model input parameter guidance, version 2.1 (USEPA, 2009);
         3)       Higher KOC model input adjustments: mean (575 L/kg) used instead of lowest (405 L/kg); 
         4)       Lower aerobic soil metabolism model input values: 133 d instead of 81.3 d; 
         5)       Total Residue modeling approach (USEPA, 2013) was used to calculate aerobic aquatic metabolism input of 108 days instead of separately modeling a range of half-lives of 19 to 1323 days for parent and degradates;
         6)       Percent Cropped Area (PCA) factor of 0.91 used instead of 0.87 (USEPA, 2012a); and, 
         7)       Revisions to the PestDF kinetics software used to calculate half-lives. 
      
      The Total Residue (TR) modeling approach (USEPA, 2013) was used to estimate aerobic aquatic half-lives, and estimate drinking water concentrations in surface waters. Previous drinking water assessments calculated separate half-lives for the parent compound and two degradates of concern, for which exposure was estimated with separate model runs. Simple addition of the exposure estimates for mandipropamid and it's degradates of concern was used to generate estimated drinking water concentrations. Previous authors acknowledge this approach is conservative because the exposure estimates may not be temporally coincident. The TR method, however, tallies the parent compound and it's degradates of concern prior to calculating a Total Residue half-life using PestDF.
      
1. Use Characterization
      
      Mandipropamid is a fungicide used to control downy mildew, phytophthora blight and root rot, blue mold, and late blight in vegetable production. The fungicide can be applied as a post-emergent, foliar spray using ground, aerial, or chemigation equipment. The proposed label specifies a maximum seasonal application rate of 0.52 lbs. active ingredient per acre (a.i./A), and is divided into four separate applications of 0.13 lbs. a.i./A with a 7-day minimum interval.
      
      The proposed expanded and new use patterns are summarized in Table 2. For six (6) of the eight (8) proposed new and expanded crop uses, the maximum application rate per event and season remain consistent with previously assessed application rates (USEPA, 2007; and, USEPA, 2011). The registrant proposes, however, to expand the product application to tomato and basil with up to four (4) crop production seasons per calendar year. Thus, the registrant proposes a total of sixteen (16) application events for a cumulative annual application rate of 2.08 lbs a.i./A. 
      
Table 2. Proposed Use Patterns for Mandipropamid
                                 Registration
                                    Status
                                   Use Site
                                    Maximum
                                  Application
                                   Rate[1)]
                                 (lbs a.i./A)
                                    Maximum
                            Number of Applications
                                  per Season
                       Minimum Application Interval[2)]
                                    (days)
                                    Maximum
                              Annual Application
                                   Rate[3)]
                                 (lbs a.i./A)
                               Maximum Number of
                           Applications per Year[3)]
                                   Proposed
                                      New
                                      Use
Bean (succulent);
Ginseng
                                     0.13
                                       4
                                       7
                                     0.52
                                       4
                                       
Basil (fresh and dried)
                                     0.13
                                       4
                                       7
                                     2.08
                                      16
                               Proposed Expanded
                                      Use
Bulb Vegetables;
Cucurbits;
Fruiting Vegetable (except tomato);
Grapes
                                     0.13
                                       4
                                       7
                                     0.52
                                       4
                                       
Tomato
                                     0.13
                                       4
                                       7
                                     2.08
                                      16
Abbreviations: A= acre; a.i. = active ingredient; lbs = pounds

Note(s):
   1) Single application event.
   2) Minimum number of days between application events.
   3) Year is defined as a calendar year; January 1 through December 31.

      The proposed label covers thirteen (13) use sites. There are no requested use changes for five (5) crops or crop groups: brassica; hops; leafy vegetables; potatoes and other tuberous and corm vegetables; and tobacco. The registrant seeks new use registrations for mandipropamid on the three (3) following crops and crop groups, including hybrids and varieties thereof:
      1. Basil: (fresh and dried); 
      2. Bean (succulent subgroup): Cicer arietinum (chickpea, garbanzo bean); Lupinus spp. (inkling sweet lupine, white sweet lupine, white lupine, and grain lupine). Phaseoulus spp. (including kidney bean, lima bean, mung bean, navy bean, pinto bean, snap bean, and waxbean); Vicia faba (broad bean, fava bean); Vigna spp. (including asparagus bean, black-eyed pea and cowpea); in succulent form only; and, 
      3. Ginseng.
      
      The registrant seeks to expand the current registration of mandipropamid on the following five (5) crops and crop groups, including hybrids and varieties thereof:
      1. Bulb vegetables including cultivars, varieties, and/or hybrids of these and others in
         * the onion (dry) subgroup 3-07A: daylily; fritillaria; garlic; garlic (great-headed); garlic (serpent); lily onion; onion (Chinese); onion (pearl); onion (potato); shallot; and,
         * the green onion (subgroup 3-07B): chive; chive (Chinese); elegans hosta; fritillaria; kurrat; lady's leek; leek; leek (wild); onion Beltsville bunching); onion (fresh); onion (green); onion (macrostem); onion (tree tops); onion (Welsh); and shallot; 
      2. Cucurbit vegetables: Chayote (fruit); Chinese wax gourd (Chinese preserving melon); citron melon; cucumber; gherkin; gourds, edible (includes hyotan, cucuzza, hechima, Chinese okra); Momordica spp. (includes balsam apple, balsam pear, bitter melon, Chinese cucumber); muskmelon (includes true cantaloupe, cantaloupe, casaba, crenshaw melon, golden pershaw, melon, honeydew melon, honey balls, mango melon, Persian melon, pineapple melon, Santa Claus melon, and snake melon); pumpkin; squash, summer (includes crookneck squash, scallop squash, straintneck squash, vegetable marrow, zucchini); squash, winter (includes butternut squash, calabaza, hubbard squash, acorn squash, spaghetti squash); watermelon.  
      3. Grapes including cultivars, varieties, and/or hybrids of subgroup 13-07F (except fuzzy kiwifruit): Amur river grape, gooseberry, grape, kiwifruit (hardy); maypop; schisandra berry; 
      4. Fruiting Vegetable Group (except tomatoes) including cultivars, varieties, and/or hybrids of these and others in this group: African eggplant, bell pepper; cocona; eggplant, garden huckleberry; goji berry; groundcherry; martynia; naranjilla; okra; pea eggplant; pepino; nonbell pepper; roselle; scarlet eggplant; sunberry; and,
      5. Tomato (includes tomato, bush; tomato, currant; tomatillo; tomato tree).

2. Environmental Fate Characterization
      
      When Mandipropamid is released into the environment, it is expected to be somewhat persistent and has low to moderate mobility.  The primary degradation route is typically expected to be metabolism with half-lives ranging from approximately 40 to 90 days in aerobic conditions in water and soil laboratory studies. Half-lives from field studies were similar and ranged from 75 to 100 days.  The fungicide degrades relatively quickly via photolysis with a half-life of approximately 2 days.  However, photolysis is only relevant under some environmental conditions and field studies suggest that it is not a major degradation route under conditions of those studies.  Mandipropamid degrades very slowly via hydrolysis, and volatilization from soil and water is expected to be minimal.  Bioconcentration is also not a primary concern. 
      
      For general characterization and pesticide exposure modeling purposes, Table 3 contains selected physical and chemical properties and environmental fate data, and corresponding sources of data for mandipropamid.
      
      There are several data uncertainties from pesticide metabolism and mobility studies used in this drinking water assessment, including:
      
         1.          There is no statistically significant degradation of mandipropamid by hydrolysis at the p = 0.05 confidence level. Based on the level of uncertainty in the hydrolysis study due to background variability, the degradation might be as fast as 1900 day at pH 7 and not be detected in the current 30 day study. In order to bound the effects of hydrolytic degradation in the PRZM-GW simulations, estimates were made using the 1900 day hydrolysis half-life rather than assuming no hydrolytic degradation and the EDWC decreased from 90 to 79 day (12%).
         
         2.          Of the three aerobic aquatic metabolism studies, only one study (MRID 46800031) is currently classified as "supplemental and upgradeable." Additional information is needed related to identification of all major transformation products for both systems. The remaining two studies are classified "unacceptable."

         3.          There are two batch equilibrium studies that are classified as "supplemental and upgradeable." One study (MRID 46800038) includes four foreign soils, for which taxonomic classifications are needed to clarify if they represent domestic agricultural use areas where the pesticide is anticipated to be applied. For this assessment, it is assumed that three U.S. soils from one study (MRID 46800040) are representative of agricultural use areas. Although the USEPA guideline requires five soil types (USEPA, 2008b), data from the three domestic soils were used for modeling purposes, pursuant to model input parameter guidelines, in the absence of additional acceptable data.

         4.          There are five aerobic soil metabolism studies representing seven soils, yet only one study (MRID 46800020) with one soil type is currently acceptable. This is because the acceptable soil is domestic and the other six are foreign soils without taxonomic classifications with which to assess their representativeness of agricultural areas where the pesticide will be applied. Although the USEPA guideline requires four soil types for determination of transformation rates (USEPA, 2008c), the one soil type was used for modeling purposes, pursuant to model input parameter guidelines, in the absence of additional acceptable data.
      
      Reported half-life values for aerobic soil and aquatic metabolism studies were calculated using the PestDF (version 2.14.1) software from referenced study data (PestDF model results and metabolism calculations are attached in Appendix B).
      
Table 3. Chemical Properties and Environmental Fate Parameters of Mandipropamid
                                   Parameter
                                    (units)
                                     Value
                                  Reference 
                                    (MRID)
                     Selected Physical/Chemical Parameters
Molecular Mass 
(Empirical Formula)
                                  411.9 g/mol
                                 (C23H22ClNO4)
                                   46800004
Vapor pressure  (25 °C)[1][)]
(mmHg)
                               <7.1x10[-][9]
                                   46800006
Aqueous solubility (25C)
(mg/L)
                                      4.2
                                   46800006
Henry's Law Constant: calculated (25 °C)
(atm-m[3]/mol) 
                               <9.1x10[-12] 
                                   46800006
Log octanol-to-water partition 
coefficient (25 C)
(log KOW)
                                      3.2
                                   46800006
Dissociation constants 
(pKa, pKb)
 No pKa was found in the range of 1.0 to 12.0 by spectrophotometric titration.
                                   46800006
                                  Persistence
Hydrolysis 
half-life  (25C)
(days)  (pH 4, 7 and 9)
                       no significant degradation (pH 5)
                                  1900 (pH 7)
                                  1000 (pH 9)
                                   46800007
Aqueous photolysis
half-life  (25C)
(days)
                                      1.9
                                   46800009
Aerobic soil metabolism
half-life (25°C)
(days) (Soil Texture)
                               44   (Sandy loam)
                                   46800020
Aerobic aquatic metabolism 
half-life (25°C)
(days) (Aquatic sample system: Sediment)
                       79       (Swiss Lake: Loamy Sand)
                       94     (Calwich Abbey: Silt Loam)
                                   46800031
                                   Mobility
Freundlich organic carbon-normalized coefficient (KFOC)[2][)]
(mL/goc) (Soil Texture)
                              694   (Sandy loam)
                                   46900040

                              406   (Loamy Sand)
                                       

                              625   (Loamy Sand)
                                       
                               Field Dissipation
Terrestrial field dissipation
half-life[3)]
(days) (Soil Texture)
                               75   (Sandy loam)
                                   46800045

                              100   (Loamy sand)
                                   46800046

                               82   (Loamy sand)
                                   46800047
                             Fish Bioconcentration
Fish bioconcentration factors (steady-state, total residues)
(L/kg)
Depuration Rate:
                                Edible: 8.8-10
                               Inedible: 160-190
                              Whole body: 35-48x
                        Depuration: >82% in 25 hours
                                   46800109
Abbreviations: atm = atmosphere; °C = degree Celsius; g= gram; Hg = mercury; L = liter; log = logarithm, base 10; m[3] = cubic meter; mg = milligram; mL = milliliter; mm = millimeter; mol = mole; NA = Not applicable; MRID = master record identification

Note(s):
   1) Converted to torr (mmHg) from Pascal units (Pa).
   2) The coefficient of variation (CV) for KFOC (0.3) is less than the CV of Kd (0.5), thus sorption was correlated with organic carbon content. KFOC was calculated with the following equation: (KF/ % organic matter)*100 (USEPA, 2008b). Calculations are provided in the Adsorption/ Desorption spreadsheet attached in Appendix B. 
   3) Field dissipation data are not used for modeling purposes in the Tier 1 drinking water assessment.  Thus, half-lives were not re-calculated.
   
3. Drinking Water Exposure Modeling

   2.1 Model Parameterization
   
      2.1.1 FIRST (Version 1.1.1)
   
      EFED used the FQPA Index Reservoir Screening Tool (FIRST) Version 1.1.1 (USEPA, 2008a) to calculate Tier 1 estimated drinking water concentrations (EDWC) for surface water systems. The model is used to estimate both acute and chronic potential concentrations in untreated drinking water (USEPA, 2001a). Model input parameters (USEPA, 2001a), values selected, brief justification statements for values selected (USEPA, 2009), and data sources are summarized below in Table 4. 
      
      Total Residue (TR) kinetics calculations were used to estimate the aerobic aquatic metabolism half-life model input value (USEPA, 2013). TR kinetics calculations are presented in Appendix B. Total residues include the mandipropamid parent compound and its major degradates of concern, SYN500003 and SYN 504851. Other model inputs did not require TR calculations because the degradates of concern were not present in the supporting studies at concentrations greater than 10% of the applied.
      
Table 4. FIRST (v1.1.1) Input Parameters
                                   Parameter
                                     Value
                                 Justification
                                   Reference
                                    (MRID)
Application Rate
(lbs a.i./ A)
                                     0.13
                           Maximum application rate
                                Proposed label
Application Events 
(per year)
                                      16
                    Maximum number of applications per year
                                Proposed label
                                Meeting Minutes
Minimum Application Interval
(days)
                                       7
                         Minimum application interval
                                Proposed label
Application Method
                                    Aerial
                   Application equipment of maximum exposure
                                Proposed label
Incorporation Depth 
(cm)
                                       0
             Product is foliar applied via ground or aerial spray
                                Proposed label
Wetted-in
                                      No
                                Not applicable
                                 US EPA, 2009
Solubility (25C)
(mg/L)
                                      4.2
                               Maximum value at
                                   20 - 25C
                                    46800006
Hydrolysis
Half-life
(days)
                                     1900
                      Represents the study value at pH 7.
                                   4680007; 
                                   46800008
Aquatic Photolysis
Half-life
(days)
                                      1.9
                      Represents the maximum study value.
                                   46800009
Aerobic Aquatic Metabolism
Half-life
(days)
                                      108
           Total Residue approach was used to calculate half-lives.
                                       
Represents the upper 90[th] percentile confidence bound on the mean of two total residue half-lives.
                                   46800031
Organic Carbon Partition Coefficient (KOC)
(mL/kgOC)
                                      575
                     Represents the mean of three values.
                                   46800040
Aerobic Soil Metabolism
Half-life
(days)
                                      133
                  Represents 3x the single acceptable value.
                                   46800020
Percent Cropped Area (PCA) Adjustment Factor
(decimal)
                                     0.91
                 National-level PCA for all agricultural land
                                 US EPA, 2012a
Abbreviations: A= acre; a.i. = active ingredient; cm = centimeter; kg = kilogram; L = liter; lbs. = pounds; mg = milligram; mL = milliliter; MRID = master record identification

      2.1.2 SCI-GROW (Version 2.3)
      
      The Screening Concentration in Ground Water (SCI-GROW version 2.3) model was used to estimate drinking water pesticide concentrations in ground water.  Results of the Tier 1 model determine if mandipropamid potentially poses sufficient risk to warrant higher level assessment (USEPA, 2001b).  Table 5 summarizes the SCI-GROW input parameters (USEPA, 2001b), justification for values selected (USEPA, 2009), and appropriate references and data sources (USEPA, 2001b; and, USEPA, 2009).
      
Table 5. SCI-GROW (Version 2.3) Input Parameters
                                   Parameter
                                     Value
                                 Justification
                                   Reference
                                    (MRID)
Application Rate
(lbs a.i./ A)
                                     0.13
                           Maximum application rate
                                Proposed label
Application Events 
(per year)
                                       16
                    Maximum number of applications per year
                                Proposed label
                                Meeting Minutes
Organic Carbon Partition Coefficient (KOC)
(mL/kgOC)
                                      625
                          Median of three KOC values;
                        less than three-fold variation
                                   46800040
Aerobic Soil Metabolism
Half-life
(days)
                                      44
                Single acceptable aerobic soil metabolism value
                                   46800020
Abbreviations: A= acre; a.i. = active ingredient; cm = centimeters; kg = kilogram; L = liter; mg = milligrams; mL = milliliter; MRID = master record identification

      2.1.3  PRZM-GW (Version 1.01)
      
      As part of a one-year evaluation period, EFED scientists are using the Pesticide Root Zone Model for Ground Water (PRZM-GW v. 1.01) model in conjunction with SCI-GROW to estimate Tier 1 pesticide concentrations in ground water used as drinking water (USEPA, 2012d). PRZM-GW input parameters are summarized below in Table 6. 
      
      A cumulative annual application rate of 2.33 kg a.i./ ha (2.08 lbs a.i./ A) was used in PRZM-GW. This rate represents the registrant's proposed most conservative use pattern (i.e. four (4) crop production seasons per calendar year for use on both tomatoes and basil).
      
      PRZM-GW v.1.01 is limited to eleven (11) pesticide application events per year. In order to model 16 application events using 11 input events, values for the following input parameters were adjusted: 1) single-event maximum application rate; 2) number of application events per year; and, 3) application interval, 4) number of years to simulate. 
      
      The single-event maximum application rate was increased from 0.147 kg a.i./ ha (0.13 lbs a.i./A) to 0.212 kg a.i./ ha (0.19 lbs a.i./ A). Correspondingly, the number of annual application events decreased from sixteen (16) to eleven (11). Moreover, the application interval was equally distributed across the calendar year.  This increased the proposed label's minimum application interval from 7 to 33 days. The cumulative annual application rate of 2.33 kg a.i./ ha (2.08 lbs a.i./A), however, remains consistent with the registrant's proposed label product application scenario. Because PRZM-GW is limited to 800 total application events, the extended simulation was conducted every year through year 72.
      
      An analysis was performed on the effects of adjusting PRZM-GW input parameters. Results indicate no difference as a result of using higher single-event application rates, reduced numbers of applications per year, and increased application intervals with respect to those of the proposed product label.
      
Table 6. PRZM-GW (Version 1.01) Input Parameters
                                   Parameter
                                     Value
                                 Justification
                                    Source
Application Rate[1][)]
(kg  a.i./ ha)
                                     0.212
See text above table. Maximum annual application rate is divided into 11 application events spread across the year.
                                Proposed Label
Application Events 
(per year)
                                      11
                                       
                                Proposed Label
Application interval 
(days)
                                      33
                                       
                                Proposed Label
Application Method
                                       2
   1)    Proposed use pattern.
   2)    Above canopy selected: product is applied to target foliage.
                                Proposed Label
                                 USEPA, 2012c
Initial Application
Date[2&3][)]
                                  February 2
1) Proposed four crop production seasons during the calendar year.
2) Eleven (11) application events evenly distributed.
3) Sensitivity analysis (see text above table)
                                 USEPA, 2012c
Hydrolysis 
Half-life
(days)
                                     1900
                      Represents the study value at pH 7.
                                   46800007
Aerobic Soil Metabolism
Half-life (25C)
(days)
                                      133
            Represents 3x the single acceptable half-life at 25°C.
                                   46800020
Organic Carbon Partition Coefficient (KOC)
(ml/gOC)
                                     575 
                         Represents the mean of three
                                  KOC values
                                   46800040
Abbreviations: A= acre; a.i. = active ingredient; cm = centimeters; ha = hectare; kg = kilograms; ml = milliliter; C = degree Celsius

Note(s):
   1) Unlike the other two models used in this drinking water assessment, the pesticide application rate for PRZM-GW requires metric units.  
   2) The initial application date selected represents eleven (11) evenly distributed application dates (i.e. approximately every 33 days) during the calendar year, beginning February 2. 
   3) Calendar dates are set to "Absolute."
   
   3.1 Model Results
      
      Results of the three models used in this drinking water assessment are summarized in Table 1.  FIRST model estimated drinking water concentrations (EDWCs) were 79 ug/L for acute exposure and 9.0 ug/L for chronic exposure.  The SCI-GROW EDWC was 0.18 ug/L.  PRZM-GW EDWCs are tabulated in Table 7.
      
      For the PROZM-GW model, all six geographic scenarios were modeled as surrogates for tomato and basil crops. The Wisconsin corn scenario provided the most conservative estimates for acute and chronic drinking water exposure concentrations, at 87 and 79 ug/L, respectively.

Table 7. PRZM-GW Estimated Drinking Water Concentrations and Average Breakthrough Time for Mandipropamid Use Scenarios[1)].
                                     Crop
                                   Scenario
                                    Maximum
                                     Daily
                                 Concentration
                                    -Acute-
                                    (ug/L)
                                    Average
                               Breakthrough Time
                                    (years)
                           Post-breakthrough Average
                                   -Chronic-
                                    (ug/L)
                                    Tomato
                                   DMV corn
                                      47
                                      14
                                      40
                                    Tomato
                                   FL citrus
                                      57
                                      14
                                      52
                                    Tomato
                                 FL potato[2)]
                                     0.14
                                      34
                                     0.08
                                    Tomato
                                 GA peanut[2)]
                                      11
                                      28
                                      10
                                    Tomato
                                   NC cotton
                                      31
                                      16
                                      26
                                    Tomato
                                  WI corn[2)]
                                      87
                                      28
                                      79
Abbreviations: ug = micrograms; L = liter

Note(s):
   1) PRZM-GW model results are reported to two (2) significant figures.
   2) The PRZM-GW extended weather files were created and used for these scenarios. 

                                       
                                       
   Figure 1: PRZM-GW WI Corn Extended Weather Scenario
                                       

      
       Uncertainty regarding PRZM-GW outputs results from the extended time period of ground water flow and the model's underlying assumptions, including that soils are sterile below a 1-meter depth.  Bacteria in soils greater than one meter below the surface may degrade the residues of concern (ROC), however potentially at a slower rate than in the surface layer, and may potentiate over years or decades in order to degrade the ROC at a faster rate. Mandipropamid residues of concern have an average breakthrough time of 28 years with the Wisconsin scenario. Breakthrough times for PRZM-GW have been up to one order of magnitude shorter than observed for bromide (USEPA, 2012e) and up to one order of magnitude longer than observed for oxamyl (MRID 45591605).
      
      Also, the model represents a drinking water well that is surrounded by a large pesticide-treated area. Most drinking water wells are not surrounded by large pesticide-treated areas. Therefore, horizontal convection and dispersion may attenuate persistent, dissolved residues such as these over time.

References

MRID 45591605. Hiscock, A., R. Warren, and B. Patterson. A Small-Scale Prospective Groundwater Monitoring Study for Oxamyl. DuPont Report No. AMR 4318-97. Unpublished study conducted by Stone Environmental, Inc., Ecologic, Inc., Agricultural Systems Associates, AGVISE Laboratories, Centre Analytical Laboratories, Inc., and E.I. du Pont de Nemours and Company; submitted by E.I. du Pont de Nemours and Company, Wilmington, DE. Jan. 14, 2002.

USEPA, 2001a.  FIRST User's Manual: FQPA Index Reserovir Screening Tool. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. August 1, 2001.

USEPA, 2001b.  SCI-GROW Screening Concentration In Ground Water: User Manual. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. November 1, 2001.

USEPA. 2006.  Guidance for Developing a Tier 1 Drinking Water Exposure Assessment. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Jan. 27, 2006.

USEPA. 2007.  Drinking water assessment for mandipropamid and its two degradates (SYN500003, SYN504851) use on brassica vegetables, bulb vegetables, cucurbits, fruiting vegetables, grapes, leafy vegetables, potatoes, tomatoes, tuberous and corn vegetables. DP barcode D339258. U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic Substances, Environmental Fate and Effects Division. Memorandum to the Health Effects Division. April 23, 2007.

USEPA, 2008a.  FIRST FQPA Index Reservoir Screening Tool, Version 1.1.1. U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic Substances, Environmental Fate and Effects Division. March 25, 2008.

USEPA. 2008b.  Fate, Transport and Transformation Test Guidelines: OPPTS 835.1230 Adsorption/ Desorption (Batch Equilibrium), U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic Substances (7101), Environmental Fate and Effects Division. EPA 712-C-08-009, October, 2008.

USEPA. 2008c.  Fate, Transport and Transformation Test Guidelines: OPPTS 835.4100 Aerobic Soil Metabolism; and, OPPTS 835.4200 Anaerobic Soil Metabolism, U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic Substances (7101), Environmental Fate and Effects Division. EPA 712-C-08-016, EPA 712-C-08-017, October, 2008.

USEPA. 2009.  Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides; version 2.1. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Oct. 22, 2009.

USEPA. 2011.  Mandipropamid: Drinking Water Exposure Assessmnt of Section 3 new Use for Outdoor; Non-food Crops.  DP barcode D383758. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Memorandum to the Registration. Division. March 2, 2011.

USEPA. 2012a.  Guidance on Development and Use of Percent Cropped Area and Percent Turf Area Adjustment Factors in Drinking Water Exposure Assessments: 2012 Update. Internal Environmental Fate and Effects Division memorandum. U.S. Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention. Mar. 16, 2012.

USEPA. 2012b.  Guidance for Using PRZM-GW in Drinking Water Exposure Assessments. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Oct. 15, 2012.

USEPA. 2012c.  Guidance for Selecting Input Parameters for Modeling Pesticide Concentrations in Groundwater Using the Pesticide Root Zone Model. Version 1.0. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division; and, Health Canada, Pesticide Management Regulatory Agency, Environmental Assessment Directorate. Oct. 15, 2012.

USEPA. 2012d.  Approval of PRZM-GW for Use in Drinking Water Exposure Assessments. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division, Memorandum to the Environmental Fate and Effects Division. Dec. 11, 2012.

USEPA. 2012e. Identification and Evaluation of Existing Models for Estimating Environmental Pesticide Transport to Groundwater. Final Report (Draft). U.S. Environmental Protection Agency; Health Canada. Jan. 27, 2012.

USEPA. 2013.  Guidance for Modeling Pesticides Total Toxic Residues (TTR) - DRAFT: v.01. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. January 3, 2013.

Appendix A. Exposure Model Input/Output Files

FIRST and SCI-GROW Output Files, with input values embedded in the Output Files.

PRZM-GW Input Files

Appendix B. Calculations

Aerobic Aquatic Metabolism Total Residue:

Aerobic Soil Metabolism with R model degradation kinetics:

Soil Adsorption/ Desorption: