Document ID: EPA-HQ-OPP-2015-0735-0008
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2016-07-27T04:00Z

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

                                       
MEMORANDUM

DATE:	March 31, 2015

SUBJECT:	Tier I Estimated Drinking Waters Concentrations of Etoxazole, and Its Transformation Products R-8 and R-13, for the Use in the Human Health Risk Assessment: Petition to Establish Import Tolerances for Etoxazole in or on the Raw Agricultural Commodity Orange and in or on Orange, Oil
		(PC Code 107091; DP Barcode 426353)

TO:		Rita Kumar, Risk Manager Reviewer
		Mark Suarez, Review Manager #7
		Meredith Laws, Branch Chief
		Invertebrate-Vertebrate Branch 3
		Registration Division (7505P)

AND:		Thomas Bloem, Risk Assessor
      Charles Smith, Branch Chief
		Registration Action Branch 1
		Health Effects Division (7509P)

FROM:	José Meléndez, Chemist
		Environmental Risk Branch 5
		Environmental Fate and Effects Division (7507P)

THROUGH:	Mah T. Shamim, Ph.D., Branch Chief
            Environmental Risk Branch 5
		Environmental Fate and Effects Division (7507P)

This memo presents the Tier I Estimated Surface Drinking Water Concentrations and Estimated Ground Water Concentrations (EDWCs) for etoxazole and its transformation products R-8 and R-13 [as per the request of the Metabolism Assessment Review Committee (or MARC), DP Barcode D288817, 04/23/2003], calculated using the Tier I surface water aquatic model FIRST and the Tier I/II groundwater model PRZM-GW (in the tier I mode), for use in the human health risk assessment.  Valent U.S.A. Corporation submitted on behalf of Sumitomo Chemical Latin America, a petition to establish import tolerances for etoxazole in or on the raw agricultural commodity orange and in or on orange, oil.

Based on an inspection of the uses of etoxazole, it has been found that the previously modeled crop mint represents a scenario with the highest exposure and consequently the highest surface water EDWCs (with single application rates of 0.18 lb a.i./A and seasonal rates of 0.36 lb a.i./A, i.e., two applications at the maximum rate are allowed).  Therefore, the estimated drinking water concentrations in surface waters do not change from the previous ones.  However, the estimated drinking waters concentrations in groundwater have not been previously calculated using the new model PRZM-GW.

The purpose of this drinking water assessment (DWA) is to update previous results by adding the PRZM-GW modeling results (for details refer to the Appendix A).  For an electronic copy of the previous drinking water assessment (DWA, DP Barcode D386080, dated 01/31/2011) see Attachment I.  The attachment has a summary of environmental fate for etoxazole, the nomenclature, and structures of R-8 and R-13.  Since the previous DWA, for the crop mint a single application at 0.18 lb a.i./A was approved (instead of the previously modeled two applications); therefore, the highest exposure scenario is currently corn, with two applications at 0.135 lb a.i./A and an interval between applications of 14 days.  For that reason, for the groundwater assessment corn was modeled instead of mint.  For additional details about the modeling approach, refer to the Appendix A.

The Tier I EDWCs for etoxazole and for its major transformation products R-8 and R-13 (as per the request of the MARC in 2003), calculated using FIRST (surface water) and PRZM-GW (groundwater) for use in the human health risk assessment were as shown in Table 1.  A more definitive assessment could be performed, using Tier II aquatic models SWCC and possible additional refinements to PRZM-GW.  Should any questions arise, please, contact Jose Melendez at Melendez.Jose@epa.gov.

Table 1.  Tier I Estimated Drinking Water Concentrations (EDWCs) for human health drinking water risk assessment application of etoxazole, based on a seasonal application on mint at 0.36 lb a.i./A/season[1] (surface waters) or corn at 0.27 lb a.i./A/season (groundwater).
Chemical
                           Acute EDWC Surface Water
                                FIRST (ppb)[2]
                                 Chronic EDWC
                                 Surface Water
                                FIRST (ppb)[2]
                          Max. Acute EDWC Groundwater
                               PRZM-GW (ppb)[3]
                Max. Chronic EDWC Groundwater  PRZM-GW (ppb)[3]
Etoxazole
                                     6.07
                                     0.618
                                    <0.1
                                    <0.1
R-8
                                     8.03
                                     4.08
                                       
                                       
R-13
                                     1.63
                                     0.063
                                       
                                       
[1] For the use on mint, the current maximum seasonal rate is 0.18 lb a.i./A.  Presented results are from the previous DWA (DP Barcode D386080, dated 01/31/2011).
[2] Results presented in ppb of each of the chemicals, as opposed to ppb of parent equivalent.
[3] Groundwater results are for the total toxic residues (parent + R-8 + R-13), expressed in ppb parent equivalent.  For all six standard scenarios, breakthrough was incomplete.  EDWCs are low compared to surface water EDWCs.

Identification of specific data gaps:
The environmental fate data base for etoxazole was found to be adequate for a Tier 1 drinking water assessment.  In the Problem Formulation for Registration Review (DP Barcode D418231, dated 07/01/2014), aerobic and anaerobic aquatic metabolism studies were required.

Appendix A. Tier 1 Groundwater PRZM-GW EDWCs

The PRZM-GW generated EDWCs for the total toxic residues of human health concern (TTRs included etoxazole, R-8 and R-13), for the use on corn, are summarized in Table A-2.

Conceptual Model

Figure A-1 depicts the general groundwater scenario concept for estimating pesticide concentrations in drinking water as implemented in PRZM-GW. This conceptual model is based on a rural drinking water well beneath an agricultural field (a high pesticide use area) drawing from an unconfined, high water-table aquifer. 

                                       
 
Figure A-1. General Groundwater Scenario Concept for Estimating Pesticide Concentrations in Drinking Water as Implemented in PRZM-GW; The black line through the soil profile represents the decline in degradation with respect to the depth.

The depth of the well is site specific (i.e., scenario specific). The well extends into a shallow unconfined aquifer and has a well-screen that starts at the top and extends down into the aquifer. The length of the well-screen represents the region of the aquifer where drinking water is collected. The well-screen length is well-specific and can be adjusted.  Processes included in the conceptual model that influence pesticide transport through the soil profile include water flow, chemical specific dissipation and transportation parameters (i.e., degradation and sorption), and crop specific factors, including transpiration, pesticide interception and management practices.

The following is a brief description of the PRZM-GW model.  More information is available at http://www.epa.gov/oppefed1/models/water/index.htm#przm_gw (accessed 03/20/2015).

      Tier 1 groundwater estimated drinking water concentrations (EDWCs) for a chemical, resulting from its use for bare ground pre-plant applications were derived with PRZM-GW (Pesticide Root Zone Model for Groundwater, version 1.07, March 6, 2014), using the GW-GUI (Graphical User Interface, version 1.07, March 6, 2014).  PRZM-GW is a one-dimensional, finite-difference model that estimates the concentrations of pesticides in groundwater.  It accounts for pesticide fate in the crop root zone by simulating pesticide transport and degradation through the soil profile after a pesticide is applied to an agricultural field. PRZM-GW permits the assessment of multiple years of pesticide application (up to 100 years) on a single site.  Six standard scenarios, each representing a different region known to be vulnerable to groundwater contaminations, are available for use with PRZM-GW for risk assessment purposes.  In PRZM-GW simulations, each of these standard scenarios was used.  PRZM-GW output values represent pesticide concentrations in a vulnerable groundwater supply that is located directly beneath a rural agricultural field.

Input Parameters for PRZM-GW and Results

For input parameters used in this model, refer to Table A-1.  In the previous DWA, each of the degradates was modeled separately, using the residue summation approach; however, in the Problem Formulation for Registration Review (refer to Appendix E of DP Barcode D418231, dated 07/01/2014), the half-lives for the total toxic residues (TTRs) that included the parent compound plus R-8 plus R-13 were calculated and used in this assessment (total residue approach).

Table A-1. Etoxazole total toxic residues (TTRs) PRZM-GW Input Parameters for modeling applications of the chemical on corn
                               PARAMETER (units)
                                   VALUE[1]
                                    SOURCE
                                    COMMENT
App date (day/month)
                                     15-04
Apps are set to occur between emergence and harvest with PHI for corn of 21 days.
Delmarva emergence 10-04, crop maturation 30-05, harvest 15-06

                                     01-06
                                       
FL citrus crop emergence 01-01, crop maturation 01-02, harvest 31-12

                                     01-04
                                       
FL potatoes emergence 15-02, crop maturation 01-05, harvest 01-06

                                     01-08
                                       
GA coast emergence 01-05, crop maturation 01-08, harvest 01-10

                                     01-09
                                       
NC coast emergence 15-05, crop maturation 01-08, harvest 01-11

                                     15-08
                                       
WI sand emergence 01-05, crop maturation 21-07, harvest 20-10
Maximum Application Rate (kg a.i./ha)
                                     0.151
Max in the label for sample product ZEAL[(R)] WDG Miticide, EPA Reg. No. 59639-123.
Maximum application rate is 0.135 lb a.i./A x 2 applications at 21day intervals.  See Table A-1.
Number of Applications per Year
                                       2
                                       

Retreatment Intervals (days)
                                      14
                                       

Chemical Application Method (CAM)
                                       2
                                     Label
Foliar
Incorporation Depth (cm)
                                      0.0
                                       
---
Air diffusion coefficient (cm[2]/day)
                                      0.0
                                      N/A
Assuming no volatilization.
Vaporization enthalpy (kcal/mol)
                                      0.0
                                      N/A
Assuming no volatilization.
Henry's Law Constant (atm-m[3]/mol)
                                      0.0
                                      N/A
Assuming no volatilization.
Partition Coefficient
(Kd; mL/g)
                                      151
                    45090024, 45090026, 46299905, 46299906
Represents the average Kd value among eight values ranging from 66 to 335 ml/g; the Kd model was utilized because it represents the mobility of etoxazole better than KOC (i.e., binding is not correlated with OC.
Aerobic Soil Metabolism Half-life at 25°C (days)

                                      370
                         45090019, 45090021, 45090022
90[th] percentile confidence bound on the mean half-life value: three values are available: 234 days and 525 days at 20°C, and 66.3 days at 25°C; respective half-lives corrected to 25°C are 165 days, 371 days and 66.3 days; mean = 200.77 days, std. dev. = 155.47 days, n = 3, t90,n-1 = 1.886
Hydrolysis Half-life (days)
                                      99
                                   45090017
Etoxazole shows relatively high stability in pH 7 solution.
1 Parameters are selected as per "Guidance for Selecting Input Parameters for Modeling Pesticide Concentrations in Groundwater Using the Pesticide Root Zone Model" v.1.0, dated October 15, 2012.

Modeling results are provided in Table A-2.

Table A-2. Etoxazole total toxic residues (TTRs) Estimated Drinking Water Concentrations (EDWCs) resulting from the use of the chemical on corn
                                 Crop/Scenario
                              Highest Daily Value
                                    (ug/L)
                           Post Breakthrough Average
                                    (ug/L)
                     Average Simulation Breakthrough Time
                                    (days)
                            Corn/Tier I Delmarva[1]
                                       0
                                 Incomplete[2]
                                 Incomplete[2]
                           Corn/Tier I FL citrus[1]
                                1.43 x 10[-12]
                                 Incomplete[2]
                                 Incomplete[2]
                          Corn/Tier I FL potatoes[1]
                               1.76 x 10[-1][4]
                                 Incomplete[2]
                                 Incomplete[2]
                            Corn/Tier I GA coast[1]
                                       0
                                 Incomplete[2]
                                 Incomplete[2]
                            Corn/Tier I NC coast[1]
                                       0
                                 Incomplete[2]
                                 Incomplete[2]
                            Corn/Tier I WI sand[1]
                                       0
                                 Incomplete[2]
                                 Incomplete[2]
1 This scenario was run with an extended weather file.
2 Incomplete despite running an extended weather file.
Attachment I. Electronic Copy of the Previous Drinking Water Assessment (DP Barcode D386080, dated 01/31/2011)