 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

                              WASHINGTON, D.C. 20460

  SEQ CHAPTER \h \r 1 OFFICE OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES

  SEQ CHAPTER \h \r 1 								Chemical: MCPB (and Salt)

								PC Code: 019201

								DP barcode:  343745

February 27, 2008								

MEMORANDUM

Subject:	Drinking Water Assessment for MCPB Use on Mint

To:		Susan Stanton

		Risk Manager Reviewer 

Registration Division (7508P)

From:		James Lin, Environmental Engineer

		Nancy Andrews, Branch Chief

		Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

A previous drinking water assessment for MCPB was completed August 3,
2005 (DP 314053).  The assessment was targeted for uses on peas with a
single maximum application rate of 1.5 lb. ae/A).  Both monitoring
analysis and modeling approach were applied in the assessment.  The
complete drinking water assessment is attached (pages 7 – 16).  

This new IR-4 tolerance petition for EFED is to assess drinking water
impacts associated with use on Mint.  The standard EFED Oregon Mint
scenario is used for this assessment.  The scenario describes the mint
growing in Marion County, Oregon within the Major Land Resource Area
(MLRA) – A2.  The timings of mint growing are April 15, July 25, and
August 1, respectively for the emergence date, maturation date, and
harvest date.  The 30 years of weather records are from weather station
- 24232.   

All the modeling inputs of physical chemical parameters and
environmental fate study parameters are adopted from the previous
assessment (see pages 9 and 10).  The only exception is the use rate
which is based on the proposed label.  The recommended Thistrol®
herbicide label language for mint uses are as follows.  

For suppression of field bindweed and other broadleaf weeds listed on
this label: apply early post-emergence at the rate of 1 to 2 pints per
acre (0.25 to 0.5 lb. acid equivalent/acre (lb. ae/A)) in sufficient
water for coverage.  

Field bindweed suppression improves as the runners begin to exceed 6 to
8 inches in length.  Mint oil yield may be reduced if applications are
made when the crop is 6 inches or more tall.  Mint may be discolored or
twisted, but the production benefits gained from suppressing bindweed
typically far exceeds the risk of mint injury.

For control of winter annual weeds listed, a fall application at 1 to 2
pints per acre (0.25 to 0.5 lb. ae/A) may be applied.  A single spring
application works best for field bindweed suppression.

Based on two applications of 0.5 lb. ae/A, one for the spring
application and the other for fall application, the Oregon Mint modeling
scenario predicts the drinking water concentrations after PCA (0.87)
correction of 8.32 ug/L, 4.31 ug/L, and 3.22 ug/L, respectively for the
1-in-10 years acute (peak), chronic (annual average) and cancer (30-year
average).  The PE5 output is included in Appendix 1.  These values are
less than the previous estimates, therefore, for the drinking water
assessment purpose, the previous estimated drinking water concentrations
for use on peas should be used as the representative drinking water
concentrations. 

The recommended estimated drinking water concentrations (EDWCs) for the
human health risk assessment are as follows:

	Surface water (PRZM/EXAMS)

Acute (peak)				54.7 ug/L

Chronic (annual average)		13.5 ug/L

Cancer (30-year average)		7.3 ug/L

Groundwater (SCI-GROW)			2.1 ug/L

Appendix 1.  PE5 output of Oregon Mint Scenario.

stored as MCPORMT.out

stored as MCPORMT.out

Chemical: MCPB

PRZM environment: ORmintSTD.txt	modified Tueday, 29 May 2007 at 12:00:46

EXAMS environment: ir298.exv	modified Thuday, 29 August 2002 at 14:34:12

Metfile: w24232.dvf	modified Wedday, 3 July 2002 at 08:06:10

Water segment concentrations (ppb)

Year	Peak	96 hr	21 Day	60 Day	90 Day	Yearly

1961	5.928	5.878	5.677	5.311	4.948	2.459

1962	9.697	9.604	9.394	8.047	6.975	4.72

1963	8.394	8.274	7.796	6.916	6.629	4.728

1964	6.589	6.545	6.383	5.934	5.212	4.156

1965	6.027	5.987	5.857	5.459	4.808	2.942

1966	5.704	5.66	5.513	5.104	4.546	3.121

1967	5.977	5.917	5.668	5.038	4.623	3.247

1968	10.18	10.02	9.278	7.864	6.881	3.776

1969	6.744	6.696	6.447	5.755	5.082	3.595

1970	5.648	5.611	5.376	5.075	4.441	2.859

1971	6.86	6.737	6.423	6.155	5.645	3.252

1972	6.258	6.205	5.986	5.799	5.458	3.576

1973	6.313	6.265	6.195	5.293	4.796	3.689

1974	5.25	5.207	5.049	4.653	4.103	2.397

1975	5.94	5.893	5.609	5.037	4.533	3.305

1976	5.948	5.904	5.752	5.517	5.351	3.544

1977	7.075	7.021	6.757	6.349	6.053	4.981

1978	6.004	5.956	5.793	5.471	5.17	3.65

1979	12.81	12.6	11.82	10.58	9.264	5.314

1980	7.182	7.037	6.867	6.378	5.829	5.046

1981	7.975	7.887	7.387	6.165	5.251	3.259

1982	5.661	5.619	5.465	5.043	4.509	3.052

1983	5.354	5.315	5.175	4.825	4.299	2.825

1984	7.03	6.97	6.725	5.802	4.982	3.784

1985	7.133	7.069	6.829	6.306	6.01	4.021

1986	7.229	7.173	6.93	6.413	5.799	4.557

1987	6.091	6.046	5.879	5.721	5.224	3.878

1988	6.562	6.419	5.823	5.648	5.169	3.472

1989	7.259	7.185	6.843	6.431	5.908	4.333

1990	6.135	6.086	5.703	5.11	4.641	3.576









Sorted results







Prob.	Peak	96 hr	21 Day	60 Day	90 Day	Yearly

0.032258064516129	12.81	12.6	11.82	10.58	9.264	5.314

0.0645161290322581	10.18	10.02	9.394	8.047	6.975	5.046

0.0967741935483871	9.697	9.604	9.278	7.864	6.881	4.981

0.129032258064516	8.394	8.274	7.796	6.916	6.629	4.728

0.161290322580645	7.975	7.887	7.387	6.431	6.053	4.72

0.193548387096774	7.259	7.185	6.93	6.413	6.01	4.557

0.225806451612903	7.229	7.173	6.867	6.378	5.908	4.333

0.258064516129032	7.182	7.069	6.843	6.349	5.829	4.156

0.290322580645161	7.133	7.037	6.829	6.306	5.799	4.021

0.32258064516129	7.075	7.021	6.757	6.165	5.645	3.878

0.354838709677419	7.03	6.97	6.725	6.155	5.458	3.784

0.387096774193548	6.86	6.737	6.447	5.934	5.351	3.776

0.419354838709677	6.744	6.696	6.423	5.802	5.251	3.689

0.451612903225806	6.589	6.545	6.383	5.799	5.224	3.65

0.483870967741936	6.562	6.419	6.195	5.755	5.212	3.595

0.516129032258065	6.313	6.265	5.986	5.721	5.17	3.576

0.548387096774194	6.258	6.205	5.879	5.648	5.169	3.576

0.580645161290323	6.135	6.086	5.857	5.517	5.082	3.544

0.612903225806452	6.091	6.046	5.823	5.471	4.982	3.472

0.645161290322581	6.027	5.987	5.793	5.459	4.948	3.305

0.67741935483871	6.004	5.956	5.752	5.311	4.808	3.259

0.709677419354839	5.977	5.917	5.703	5.293	4.796	3.252

0.741935483870968	5.948	5.904	5.677	5.11	4.641	3.247

0.774193548387097	5.94	5.893	5.668	5.104	4.623	3.121

0.806451612903226	5.928	5.878	5.609	5.075	4.546	3.052

0.838709677419355	5.704	5.66	5.513	5.043	4.533	2.942

0.870967741935484	5.661	5.619	5.465	5.038	4.509	2.859

0.903225806451613	5.648	5.611	5.376	5.037	4.441	2.825

0.935483870967742	5.354	5.315	5.175	4.825	4.299	2.459

0.967741935483871	5.25	5.207	5.049	4.653	4.103	2.397









0.1	9.5667	9.471	9.1298	7.7692	6.8558	4.9557

					Average of yearly averages:	3.7038

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: MCPORMT

Metfile:	w24232.dvf

PRZM scenario:	ORmintSTD.txt

EXAMS environment file:	ir298.exv

Chemical Name:	MCPB

Description	Variable Name	Value	Units	Comments

Molecular weight	mwt	228.6	g/mol

Henry's Law Const.	henry	3.42e-9	atm-m^3/mol

Vapor Pressure	vapr	4e-7	torr

Solubility	sol	600	mg/L

Kd	Kd	0.85	mg/L

Koc	Koc		mg/L

Photolysis half-life	kdp	2.6	days	Half-life

Aerobic Aquatic Metabolism	kbacw	156	days	Halfife

Anaerobic Aquatic Metabolism	kbacs	68	days	Halfife

Aerobic Soil Metabolism	asm	78	days	Halfife

Hydrolysis:	pH 7	0	days	Half-life

Method:	CAM	1	integer	See PRZM manual

Incorporation Depth:	DEPI	0	cm

Application Rate:	TAPP	0.56	kg/ha

Application Efficiency:	APPEFF	0.95	fraction

Spray Drift	DRFT	0.16	fraction of application rate applied to pond

Application Date	Date	20-04	dd/mm or dd/mmm or dd-mm or dd-mmm

Interval 1	interval	160	days	Set to 0 or delete line for single app.

app. rate 1	apprate	0.56	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	monthly	none, monthly or total(average of
entire run)



Appendix 2.  Drinking Water Assessment for MCPB (DP 314053) 









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