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







                                                                PC Code: 128847
                                                             DP Barcode: 398836
                                                                               
                                                        Date: February 23, 2012
                                                                               
                                                                               
                                                                    MEMORANDUM	

SUBJECT:	Revised drinking water exposure assessment of parent difenoconazole and its major metabolite, CGA-205375 (M1) for grape.  

TO:	Sidney Jackson, Risk Manager Reviewer
               Barbara Madden, Risk Manager
	Registration Division (7505P)	
	
FROM:	Faruque Khan, Ph.D., Senior Fate Scientist
	Environmental Risk Branch I
	Environmental Fate and Effects Division (7507P)

APPROVED
 BY:	Nancy Andrews, Ph.D., Branch Chief, 
	Sujatha Sankula, Ph.D. Lead Biologist
               Environmental Risk Branch I	
	Environmental Fate and Effects Division (7507P)

      This memorandum provides a revised drinking water assessment based on a recent recommendation from the Health Effects Division's Residues of Concern Knowledgebase Sub-committee (ROCKS). The ROCKS recommended to include parent difenoconazole and its major metabolite, CGA-205375 (M1) for drinking water assessment to establish tolerances for difenoconazole in support of human health risk assessment (US EPA, 2011a, D391350). Previously recommended Estimated Drinking Water Concentrations (EDWCs) were based on aerial application of difenoconazole (parent only) for grape scenario (USEPA 2009, D361398).  This drinking water assessment was performed using total residue method (i.e. parent plus CGA 205375) for grape following the approach used in a recent drinking water assessment for various crops (US EPA 2011b, DP395784). The EDWCs values for acute (peak), annual mean (chronic) and the highest 30 year annual average (cancer chronic) concentrations were 17.4 ug/L, 11.8 ug/L, and 8.6 ug/L respectively. Since the revised EDWCs for surface water are higher than the previously recommended EDWCs for this chemical, the current EDWCs for surface water supersede the EDWCs previously recommended for this chemical.
      Estimated ground water concentration of 1.12x 10[-2] ug/L for grape is lower than the previously recommended concentration of 1.30x 10[-2] ug/L for citrus (US EPA, 2011b; D395784). Therefore, recommended EDWC for ground water is 1.30x 10[-2] ug/L and this concentration can be considered as both the acute and chronic values.
      . Drinking Water Exposure Modeling

      The EDWCs were generated using EFED's standard suite of models.  Since there is no modification of input parameters for PRZM/EXAMS and SCIGROW models, detailed description of models and inputs parameters can be obtained from the previous assessment (USEPA, 2011b, D395784). However, inputs for PRZM/EXAMS in Table A-1 and for SCIGROW in Table A-2 as well as outputs of PRZM/EXAMS and SCIGROW models for grape scenario were provided in the Appendix A.
	Standard percent cropped areas (PCA) were used for grape as estimates of the extent of watershed on which crops is grown (Effland et al., 1999).  The default agricultural PCA of 0.87 was used for the proposed uses because they are not confined to specific regions of the U.S 


                                  References

Effland, W. R., N. C. Thurman, I. Kennedy.  1999.  Proposed Methods for Determining Watershed-derived Percent Crop Areas and Considerations for Applying Crop Area Adjustments to Surface Water Screening Models.  Presentation to the FIFRA Science Advisory Panel, May 27, 1999.  Online at: http://www.epa.gov/scipoly/sap/1999/index.htm

US EPA, 2009a.  Difenoconazole (Parent Only) Drinking Water Assessment in Support of New Use Registration Action for Bulb Vegetables, Brassica (Cole) Leafy Vegetables, Cucurbit Vegetables, Citrus Fruit, Grapes, and Tree Nuts.  May 28, 2009. (D361398) 

USEPA.  2009b. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides, Version 2.1.  U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Environmental Fate and Effects Division, October 22, 2009. 

USEPA.  2010.  Water Models.  U.S. Environmental Protection Agency, Pesticides: Science and Policy.  Online at: http://www.epa.gov/oppefed1/models/water/

US EPA, 2011a. Difenoconazole:  Report of the Residues of Concern Knowledgebase Sub-committee (ROCKS). DP Code: D391350.  

US EPA, 2011b.  Revised drinking water exposure assessment to establish a tolerance of parent difenoconazole and its major CGA-205375 (M1) metabolite on fruiting vegetables group 8-10, low growing berry subgroup, 13-07G except cranberry, citrus fruit group 10-10, pome fruit group, (subgroup 11), and tuberous and corm vegetable (subgroup 1C).  December 20, 2011. (D395784) 


                                  APPENDIX A
                                       
                                       

The input parameters used for PRZM/EXAMS modeling.
      
Table A-1.  PRZM/EXAMS Chemical Specific Input Parameters for Difenoconazole
Parameter
Input Value and Unit
Source/Comments
Maximum application rate
Grape: 0.46 lbs ai/A 
 
Product Inspire[TM] 
(EPA Reg. No.) 100-1262
Maximum number of applications
4 
Product Label as above
Method of application (CAM = 2)
Foliar spray -Aerial
Product Label as above
Application date
NY Gape: August 18

Application date was assumed 7-14 days before harvest based on crop profile and label instructions:  
Minimum interval between applications 
10 days
Product Label as above
Application efficiency 
0.95 (aerial Application)
EFED Model Input Guidance, Version 2.1 (2009b) a
Spray drift
0.16 (Aerial Application)
EFED Model Input Guidance, Version 2.1 (2009b)
Partition coefficient Koc[b]
5381 mL/g
MRIDs: 42245135 and 46950121
Henry's Law constant
8.9 x 10-12  atm x m[3]/mol
MRID 46515901
Hydrolysis
Stable
MRID 42245127
Aerobic soil metabolism (t1/2)[c]
489.6 days
MRIDs.: 46950109-12 and 46950114
Aerobic aquatic metabolism (t1/2) d
632.9 days
MRIDs.: 46950116 & 46950117
Anaerobic aquatic metabolism (t1/2) [e]
1485.3 days
MRID 46950119
Aquatic photolysis t1/2 (days) 
Stable
MRID 46950105
Vapor pressure
2.5 x 10-10 mm Hg (25 [o]C)
MRID 46515901
Solubility in water 
15 mg/L (25 [o]C)
MRID 46515901
Molecular Weight
406.27 
MRID 46950104
Percent cropped area 
0.87 
U.S. EPA 2003
[a] Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides (Version 2.1; Oct. 22, 2009b)
[b] There was a positive correlation between the KF values vs. organic matter content; therefore, the average Koc was used as an parameter.  
[c] The 90% of the upper confidence limit (UCL) of the mean metabolism half-life.
[d] The 90% of the UCL of the mean metabolism half-life of all available half-lives but those obtained for high test rate.
[e] At proposed application rate only one half-life was available, the half-life was multiplied by three (i.e., 3 x 495.1 days).











An example (PA Tomato STD) input and output of  PRZM/EXAMS modeling.

stored as NYgrapeA.out						
Chemical: Difenconazole						
PRZM environment: NYGrapesSTD.txt	modified Tueday, 29 May 2007 at 12:59:44			
EXAMS environment: ir298.exv	modified Tueday, 26 August 2008 at 05:14:08			
Metfile: w14860.dvf	modified Tueday, 26 August 2008 at 05:15:12					
Water segment concentrations (ppb)						
						
Year	Peak	96 hr	21 Day	60 Day	90 Day	Yearly
1961	1.7	1.7	1.4	1.2	1.2	0.5
1962	9.8	9.1	7.3	5.7	5.4	2.7
1963	6.3	6.2	5.7	5.1	4.9	4.4
1964	10.3	9.8	8.9	7.5	7.0	5.5
1965	8.8	8.6	7.9	7.4	7.3	6.4
1966	11.7	11.2	10.1	8.8	8.4	7.3
1967	10.6	10.2	9.3	8.9	8.9	8.0
1968	9.2	9.0	8.7	8.4	8.2	7.8
1969	8.6	8.4	8.1	7.9	7.7	7.5
1970	13.5	13.0	12.2	10.7	10.2	8.1
1971	10.3	10.1	9.6	9.4	9.3	8.7
1972	10.0	9.9	9.4	9.1	9.0	8.6
1973	12.5	12.0	10.8	9.7	9.3	8.5
1974	13.0	12.5	11.1	10.0	9.6	8.6
1975	19.4	18.8	16.3	13.7	12.9	10.0
1976	11.9	11.6	11.3	11.0	10.9	10.5
1977	18.2	17.5	16.4	15.3	14.6	11.4
1978	16.4	16.0	14.9	14.2	13.9	12.4
1979	19.5	18.9	17.2	16.4	15.8	13.2
1980	20.6	20.0	18.3	17.0	16.5	14.3
1981	16.8	16.5	15.7	14.9	14.8	14.1
1982	15.7	15.4	14.7	14.2	14.0	13.3
1983	16.4	16.1	15.8	14.9	14.8	13.0
1984	18.9	18.2	16.4	14.7	14.2	12.9
1985	16.5	16.0	14.9	13.9	13.3	12.4
1986	20.0	19.2	17.5	15.3	14.6	12.6
1987	19.9	19.3	17.7	16.1	15.7	13.4
1988	17.0	16.6	15.7	14.9	14.8	13.6
1989	16.9	16.5	15.1	14.4	14.1	13.2
1990	21.3	20.5	18.9	16.7	16.1	13.4
						
Sorted results						
Prob.	Peak	96 hr	21 Day	60 Day	90 Day	Yearly
0.0	21.3	20.5	18.9	17.0	16.5	14.3
0.1	20.6	20.0	18.3	16.7	16.1	14.1
0.1	20.0	19.3	17.7	16.4	15.8	13.6
0.1	19.9	19.2	17.5	16.1	15.7	13.4
0.2	19.5	18.9	17.2	15.3	14.8	13.4
0.2	19.4	18.8	16.4	15.3	14.8	13.3
0.2	18.9	18.2	16.4	14.9	14.8	13.2
0.3	18.2	17.5	16.3	14.9	14.6	13.2
0.3	17.0	16.6	15.8	14.9	14.6	13.0
0.3	16.9	16.5	15.7	14.7	14.2	12.9
0.4	16.8	16.5	15.7	14.4	14.1	12.6
0.4	16.5	16.1	15.1	14.2	14.0	12.4
0.4	16.4	16.0	14.9	14.2	13.9	12.4
0.5	16.4	16.0	14.9	13.9	13.3	11.4
0.5	15.7	15.4	14.7	13.7	12.9	10.5
0.5	13.5	13.0	12.2	11.0	10.9	10.0
0.5	13.0	12.5	11.3	10.7	10.2	8.7
0.6	12.5	12.0	11.1	10.0	9.6	8.6
0.6	11.9	11.6	10.8	9.7	9.3	8.6
0.6	11.7	11.2	10.1	9.4	9.3	8.5
0.7	10.6	10.2	9.6	9.1	9.0	8.1
0.7	10.3	10.1	9.4	8.9	8.9	8.0
0.7	10.3	9.9	9.3	8.8	8.4	7.8
0.8	10.0	9.8	8.9	8.4	8.2	7.5
0.8	9.8	9.1	8.7	7.9	7.7	7.3
0.8	9.2	9.0	8.1	7.5	7.3	6.4
0.9	8.8	8.6	7.9	7.4	7.0	5.5
0.9	8.6	8.4	7.3	5.7	5.4	4.4
0.9	6.3	6.2	5.7	5.1	4.9	2.7
1.0	1.7	1.7	1.4	1.2	1.2	0.5
						
0.1	20.0	19.3	17.6	16.3	15.8	13.6
					Average of yearly averages:	9.9
						
Inputs generated by pe5.pl - Novemeber 2006						
						
Data used for this run:						
Output File: NYgrapeA						
Metfile:	w14860.dvf					
PRZM scenario:	NYGrapesSTD.txt					
EXAMS environment file:	ir298.exv					
Chemical Name:	Difenconazole					
Description	Variable Name	Value	Units	Comments		
Molecular weight	mwt	406.27	g/mol			
Henry's Law Const.	henry	8.90E-12	atm-m^3/mol			
Vapor Pressure	vapr	2.50E-10	torr			
Solubility	sol	15	mg/L			
Kd	Kd		mg/L			
Koc	Koc	5381	mg/L			
Photolysis half-life	kdp	0	days	Half-life		
Aerobic Aquatic Metabolism	kbacw	632.9	days	Halfife		
Anaerobic Aquatic Metabolism	kbacs	1485.3	days	Halfife		
Aerobic Soil Metabolism	asm	489.6	days	Halfife		
Hydrolysis:	pH 7	0	days	Half-life		
Method:	CAM	2	integer	See PRZM manual		
Incorporation Depth:	DEPI		cm			
Application Rate:	TAPP	0.128	kg/ha			
Application Efficiency:	APPEFF	0.95	fraction			
Spray Drift	DRFT	0.16	fraction of application rate applied to pond			
Application Date	Date	18-07	dd/mm or dd/mmm or dd-mm or dd-mmm			
Interval 1	interval	10	days	Set to 0 or delete line for single app.		
app. rate 1	apprate		kg/ha			
Interval 2	interval	10	days	Set to 0 or delete line for single app.		
app. rate 2	apprate		kg/ha			
Interval 3	interval	10	days	Set to 0 or delete line for single app.		
app. rate 3	apprate		kg/ha			
Record 17:	FILTRA					
	IPSCND	1				
	UPTKF					
Record 18:	PLVKRT					
	PLDKRT					
	FEXTRC	0.5				
Flag for Index Res. Run	IR	Reservoir				
Flag for runoff calc.	RUNOFF	total	none, monthly or total(average of entire run)			

PCA Adjusted EDWCS

                                       
                                     Peak
                                     96 hr
                                    21 Day
                                    60 Day
                                    90 Day
                                    Yearly
Average of yearly averages

                                       
                                     20.0
                                     19.3
                                     17.6
                                     16.3
                                     15.8
                                     13.6
                                      9.9
PCA Adjusted (0.87)
                                     17.4
                                     16.8
                                     15.4
                                     14.2
                                     13.7
                                     11.8
                                      8.6

The input parameters used for SCI-GROW modeling.

Table A-2. SCI-GROW Input Parameters for Difenoconazole Applied on Multiple Crops at the Maximum Label Application Rate.
Model Input Variable
Input Values
Koc (the lowest value of all available Kocs, MRIDs: 42245135 and 46950121)[1]
3471 ml/g
Application Rate
 0.114 lb. a.i./acre 
Number of Applications 
4
Aerobic Soil Metabolism half-life[2]
223.6 days
Hydrolysis
Stable
[1] The Koc shows greater than three-folds variation, thus, the lowest value was uses per guidance as of Oct. 22, 2009 (USEPA 2009b).
[2] Median of seven values.
                                       
                    Input and output of  SCIGROW modeling.
                                       
                             SCIGROW (VERSION 2.3)
                    ENVIRONMENTAL FATE AND EFFECTS DIVISION
                         OFFICE OF PESTICIDE PROGRAMS
                     U.S. ENVIRONMENTAL PROTECTION AGENCY
                                SCREENING MODEL
FOR AQUATIC PESTICIDE EXPOSURE
SciGrow version 2.3
chemical:Difenconazole
time is  9/20/2010  10:27:23
    ------------------------------------------------------------------------
       Application      Number of       Total Use    Koc      Soil Aerobic
     rate (lb/acre)  applications   (lb/acre/yr)  (ml/g)   metabolism (days)
    ------------------------------------------------------------------------
            0.114           4.0           0.456      3.47E+03      185.0
    ------------------------------------------------------------------------
                 groundwater screening cond (ppb) =   1.12E-02 
    ************************************************************************

