	

  SEQ CHAPTER \h \r 1 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE  OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES





  SEQ CHAPTER \h \r 1 	December 18, 2007

	PC Code: 041101

	DP Barcodes 323344; 335734; 295045; 295035

MEMORANDUM

Subject: 	Ethoprophos Drinking Water Assessment; Including Evaluation of
Submitted Ground and Surface Water Monitoring Studies (Revised from
6/28/07 assessment)

To:		Jacqueline Guerry, Chemical Review Manager

		Kevin Costello, Team Leader…  

		Special Review and Reregistration Division, RB3 (7508P)

From:		Michael R. Barrett, Ph.D., Senior Chemist					

		Environmental Risk Branch V

Environmental Fate and Effects Division (7507P)		

Thru:		Mah Shamim, Ph.D., Chief					

		Environmental Risk Branch V

Environmental Fate and Effects Division (7507P)		

Concerns about the potential for ethoprophos residues of concern (parent
ethoprophos and 4 metabolites are included) to reach surface water or
ground water used for drinking water at levels of concern were
identified in the “Interim Reregistration Eligibility Decision for
Ethoprop” published September 2001.  As a result of these concerns,
the registrant was required by the Agency to conduct monitoring surveys
to determine concentrations of ethoprophos residues of concern that may
occur in ground water.

Attached is a review of the registrant’s studies along with an updated
Drinking Water Assessment for ethoprophos.

TABLE OF CONTENTS

  TOC \o "1-3" \h \z \u    HYPERLINK \l "_Toc170710174"  Ethoprophos
Drinking Water Assessment: Including Evaluation of Submitted Ground and
Surface Water Monitoring Studies	  PAGEREF _Toc170710174 \h  3  

  HYPERLINK \l "_Toc170710175"  EXECUTIVE SUMMARY	  PAGEREF
_Toc170710175 \h  3  

  HYPERLINK \l "_Toc170710176"  Recommendations	  PAGEREF _Toc170710176
\h  4  

  HYPERLINK \l "_Toc170710177"  Surface Water Exposure Characterization	
 PAGEREF _Toc170710177 \h  4  

  HYPERLINK \l "_Toc170710178"  Ground-Water Exposure Characterization	 
PAGEREF _Toc170710178 \h  4  

  HYPERLINK \l "_Toc170710179"  Mitigation Measures	  PAGEREF
_Toc170710179 \h  5  

  HYPERLINK \l "_Toc170710180"  PROBLEM FORMULATION	  PAGEREF
_Toc170710180 \h  6  

  HYPERLINK \l "_Toc170710181"  Background	  PAGEREF _Toc170710181 \h  6
 

  HYPERLINK \l "_Toc170710182"  Product Chemistry for Ethoprophos	 
PAGEREF _Toc170710182 \h  7  

  HYPERLINK \l "_Toc170710183"  Use Characterization	  PAGEREF
_Toc170710183 \h  8  

  HYPERLINK \l "_Toc170710184"  Use Profile	  PAGEREF _Toc170710184 \h 
8  

  HYPERLINK \l "_Toc170710185"  Method and Rates of Application:	 
PAGEREF _Toc170710185 \h  8  

  HYPERLINK \l "_Toc170710186"  Analysis Plan / Basis for the Monitoring
Study Requirements	  PAGEREF _Toc170710186 \h  11  

  HYPERLINK \l "_Toc170710187"  Risk Issues for the Degradates	  PAGEREF
_Toc170710187 \h  11  

  HYPERLINK \l "_Toc170710188"  ANALYSIS	  PAGEREF _Toc170710188 \h  12 


  HYPERLINK \l "_Toc170710189"  Fate and Transport Characterization	 
PAGEREF _Toc170710189 \h  12  

  HYPERLINK \l "_Toc170710190"  Summary of Previous Drinking Water
Exposure Modeling	  PAGEREF _Toc170710190 \h  13  

  HYPERLINK \l "_Toc170710191"  Surface Water Monitoring Study for
Ethoprophos Residues in US High Use Areas	  PAGEREF _Toc170710191 \h  16
 

  HYPERLINK \l "_Toc170710192"  Surface Water Monitoring Study Design	 
PAGEREF _Toc170710192 \h  16  

  HYPERLINK \l "_Toc170710193"  Analytical methods	  PAGEREF
_Toc170710193 \h  17  

  HYPERLINK \l "_Toc170710194"  Site Selection Criteria for Surface
Water CWS	  PAGEREF _Toc170710194 \h  17  

  HYPERLINK \l "_Toc170710195"  Surface Water Monitoring Results	 
PAGEREF _Toc170710195 \h  20  

  HYPERLINK \l "_Toc170710196"  Other Surface-Water Monitoring Data	 
PAGEREF _Toc170710196 \h  21  

  HYPERLINK \l "_Toc170710197"  Surface Water Exposure Summary and
Conclusions	  PAGEREF _Toc170710197 \h  24  

  HYPERLINK \l "_Toc170710198"  Ground Water Monitoring Study for
Ethoprophos Residues in US High Use Areas	  PAGEREF _Toc170710198 \h  27
 

  HYPERLINK \l "_Toc170710199"  Ground Water Monitoring Study Design	 
PAGEREF _Toc170710199 \h  27  

  HYPERLINK \l "_Toc170710200"  Site Selection Criteria for Domestic
Well Study	  PAGEREF _Toc170710200 \h  27  

  HYPERLINK \l "_Toc170710201"  Ground Water Monitoring Results	 
PAGEREF _Toc170710201 \h  29  

  HYPERLINK \l "_Toc170710202"  Ground Water Exposure Summary and
Conclusions	  PAGEREF _Toc170710202 \h  29  

 

Ethoprophos Drinking Water Assessment: Including Evaluation of
Submitted Ground and Surface Water Monitoring Studies

EXECUTIVE SUMMARY

Ethoprophos (also commonly referred to as ethoprop in many historical
regulatory documents) is an organophosphate insecticide which has been
most recently comprehensively reviewed in the “Interim Reregistration
Eligibility Decision for Ethoprop” published September 2001 and in a
subsequent “Addendum to the 2001 Ethoprop Interim Reregistration
Eligibility Decision (IRED)” published February 2006.  Concerns were
identified in the IRED regarding drinking water exposure at
toxicologically significant levels (based upon Tier 2 modeling) and
surface and ground water monitoring studies were requested to facilitate
more refined drinking water exposure estimates reflecting actual use
patterns and conditions.  

Ethoprophos is applied once either at pre-plant, at-plant, or
pre-emergence for most field crops.  Annual maximum application rates
for registered crops are up to 12 lb ai per acre.  The most recent
national usage estimate is about 1,000,000 pounds applied annually (for
the years 1998 to 2000).  White potatoes, sugarcane, and tobacco are the
crops with the highest number of pounds of ethoprophos applied annually.

The submitted surface water monitoring study provides useful information
on the actual exposures to ethoprophos residues of concern or potential
exposures from drinking water (typically only raw and not finished water
was sampled in the surface water monitoring study).  Monitoring results
indicate that exposure to residues of one or more degradate of concern
at previously identified drinking water levels of concern appears
possible for surface waters used for drinking water (see particularly
the “  REF _Ref181073517 \h  Surface Water Exposure Summary and
Conclusions ” section of this assessment for details).  

 

Given the limited scope of the monitoring program and comparisons to
other available monitoring data, there still remains a potential for
exposure to ethoprophos residues of concern at some sites under some
conditions at levels approaching or exceeding previously identified
drinking water levels of concern.  In particular, acute exposure levels
from surface waters may in some cases exceed these previously calculated
drinking water levels of concern.  An updated human health risk
assessment may be required (see the “Recommendations” section). 
Also, additional ancillary data (on pesticide usage) are requested from
the registrant to reduce the uncertainties (see the
“Recommendations” section) about  exposure levels.

The ground-water monitoring study does not confirm significant exposure
in existing domestic wells located in some proximity of
ethoprophos-treated fields.  To confirm these results as being
representative of high-end ground water exposure, additional
characterization data are requested for the monitored sites most likely
to be vulnerable to ethoprophos leaching to well water, refer to the
“Recommendations” section for details. 

Recommendations

Surface Water Exposure Characterization

The registrant should, in order to permit a more complete evaluation of
the representativeness of the surface-water based CWS monitoring
results, submit county level sales data for a minimum of the three years
the monitoring program was conducted (2002, 2003, and 2004) and for 2006
(2005 sales data would also be useful).  Watershed wide usage levels
should be separately calculated for each monitored watershed for the
years 2002, 2003, and 2004.  Watershed-wide usage levels for 2006 should
be calculated not only for the watersheds selected for monitoring but
also for all of the original candidate watersheds and compared with the
1999 sales data which serve as a basis for the registrant’s original
watershed usage level calculations.

Ground-Water Exposure Characterization

For the ground-water monitoring study, the process for narrowing the
site selection efforts from the original list of candidate counties and
for identifying the domestic wells within the study target regions that
were located closer to ethoprophos-treated fields and most likely to be
hydraulically connected with those fields is not adequately described,
more details on this process should be submitted.  

The registrant should, in order to permit a more complete evaluation of
the representativeness of the domestic well monitoring results complete
the following data collection efforts and submit the results: 

Conduct a historical survey of ethoprophos usage for the ten years prior
to the ground-water monitoring period (i.e., for 1994 to 2003) and 2004
for each of the owners / farmers / commercial applicators associated
with possible pesticide usage on agricultural fields within 300 feet of
the monitored sites.  This survey may be restricted to only the 100
wells with evidence of a treated field within 300 feet of the wellhead
from the previous survey (that is, no further historical usage
investigation is required for the remaining 53 wells were the closest
treated field during the 2001 to 2004 period was > 300 feet from the
wellhead). These data should be collected at the level of detail that
appears to be generally reliable based upon the level of detail of
pesticide application records (if even available) or the level of
clarity of recollection of the interviewee. For example, if the years
and rates of ethoprophos usage have not generally be recorded, then it
may be more reliable to just record the best estimate of the number of
years between 1994 and 2000 (along with the annual records of
ethoprophos applications that have apparently already been recorded for
the previous review).  

Secondly, if available, historical sales records, at a county level (or
the highest level of geographic detail available) should be collected
for 1994 to 2004 and compared on a county to county basis with each of
the 153 monitored wells. The counties included in this survey for which
these historical sales data should be collected are: 

.

Coastal Georgia: 	Coffee, Cook, Tift, Lowndes, Colquitt, Berrien, and
Lanier Counties 

Maine: 		Androscoggin and Aroostook Counties

NE North Carolina: 	Edgecomb, Wilson, Nash, and Halifax Counties

Western Oregon: 	Benton, Polk, Marion, Multnomah, Washington, Linn,
Yamhill, and

Clackamas Counties

S Central WA:		Grant, Franklin, Walla Walla, Adams, and Yakima Counties

Also being required is submission of annual updates on ethoprophos sales
and / or usage resolved by US county (or another similar reporting unit,
if approved by the Agency).  If total ethoprophos sales increase in any
year by substantially more than the average 2004 to 2006 level, then
additional monitoring data may be required by the Agency to update the
drinking water exposure and risk assessment.  

After the above efforts are completed to the extent feasible, the
registrant should evaluate each site with a treated field within 300
feet of one or more sampled wells and estimate (or make a determination
that an estimate is not possible given readily available information)
the following:

The total distance (vertical and horizontal) between the closest edge of
the treated field and the well screen.

Whether the treated field(s) are within the recharge area of the sampled
well

Given the available soil profile characteristic information, the use of
tile drains, local weather history, and any other available information
make a determination as to a reasonable range of travel times of
ethoprophos (parent or degradates) -bearing water (that is, if in fact
ethoprophos residues do persist in the vadose zone and leach) to the
source ground water of the sampled well.  

Determine how may of the sampled wells can plausibly be expected to have
been impacted from the known ethoprophos applications given all of the
above information (or if this still cannot be determined, so state).

Mitigation Measures

Results of this assessment indicate that, with the information submitted
to date, there is uncertainty remaining about the need for mitigation
measures to reduce ethoprophos exposure. Any decision on label changes
that may be needed may be deferred until the Health Effects Division of
the Office of Pesticide Programs updates the Risk Assessment using
current methods and current information on drinking water exposure.

PROBLEM FORMULATION

Background

Ethoprophos (also commonly referred to as ethoprop in many historical
regulatory documents) is an organophosphate insecticide which has been
most recently comprehensively reviewed in the “Interim Reregistration
Eligibility Decision for Ethoprop” published September 2001 and in a
subsequent “Addendum to the 2001 Ethoprop Interim Reregistration
Eligibility Decision (IRED)” published February 2006.  There also was
a stand-alone drinking water assessment completed in April 2000 (DP
Barcode:  D261891).   Ethoprophos was also included in the
Organophosphorus

Cumulative Risk Assessment – 2006 Update (this version was published
August 2006) which evaluates cumulative risk due to the organophosphorus
pesticides from exposures in food, drinking water, and residential uses.

This document provides a review of monitoring studies that were an
outgrowth of these recent reviews:

QUOTE:

To address both surface and ground water risk concerns, the technical
registrant is to conduct monitoring programs in high usage areas with
vulnerable soil conditions.  

-- Page 2 in the 2001 IRED for Ethoprop.

Risk concerns which served as impetus for the monitoring data
requirements are discussed in the “Analysis Plan” section.

Both a survey of domestic wells of and of public drinking water supplies
utilizing surface water sources in areas determined to represent
relatively high use areas for ethoprophos have been completed by the
registrant and the final reports for these studies are reviewed herein.
The drinking water exposure assessment is updated here based upon a
critical analysis of the study design and results for both the ground
water and surface water surveys in the context of historical and current
use patterns.

Four metabolites were identified as residues of concern and have been
included in both monitoring programs (  REF _Ref169335734 \h  Table 1 ).

Table   SEQ Table \* ARABIC  1 .  Common names, residue designations,
chemical names, formulas, and structures of ethoprophos and its major
degradates.

Common Names1 

Chemical Name 

[formula]	Molecular wt.	Structure

Ethoprophos or 

Ethoprop

O-ethyl-S,S-dipropylphosphorodithioate 

[C8H19O2PS2]	



SME or

Metabolite II or

S-methyl degradate

O-ethyl-S-methyl-S-propylphosphorodithioate 



OME or 

Metabolite III or

O-methyl degradate

O-ethyl-O-methyl-S-propylphosphorothioate



M1 or

OHE or 

Metabolite IV

O-ethyl-S-propylphosphorothioate



M2 or

SSDP or

S,S-dipropyl degradate

S,S-dipropylphosphorodithioate 

 

1 Includes the trivial names used in the IRED documents and the
registrant’s monitoring study reports.  Note that the IRED had
assigned metabolite numbers II, III, and IV to SME, OME and M1,
respectively; no metabolites was designated Metabolite I.  M2 was not
assigned a metabolite number in the IRED.



Product Chemistry for Ethoprophos

Common Name: 		Ethoprophos

Chemical Name:		O-ethyl-S,S-dipropylphosphorodithioate

Chemical Family:		Organophosphate

CAS Registry Number:	13194-48-4 

OPP Chemical Code: 		041101 

Empirical Formula:		C8H19O2PS2 

Molecular Weight:		242.3

Trade and Other Names: 	MOCAP®

Basic Manufacturer:		Bayer CropScience

Use Characterization

Ethoprophos is an organophosphorus insecticide and nematicide, first
registered in 1967, used on several agricultural crops and field-grown
ornamentals. Ethoprophos is applied once either at pre-plant, at-plant,
or pre-emergence for most field crops. Most of ethoprophos is formulated
as either a granular product or an emulsifiable concentrate (liquid)
product. Usage data from 1987 to 1996 indicated an average domestic use
of approximately 700,000 lb active ingredient (ai) per year, while more
recent data provided by the technical registrant indicated that domestic
use in 1998 to 2000 was about 1 million lb ai per year.  Although the
registrant based site selection for their monitoring studies on  1999
sales (Surface Water Study) or 2002 sales data (Ground Water Study),
neither these or any more recent sales / usage data were included with
their final reports on the ground-water and surface water monitoring
programs.

Use Profile

The following information is based on the currently registered uses of
ethoprophos.

Type of Pesticide: Insecticide/nematicide

Summary of Use Sites:

Food:	Bananas/plantains, beans (dry, snap, and lima), cabbage, corn
(sweet and field), cucumber, pineapple, sugarcane, sweet potato, and
white potato.

Residential:		No residential uses.

Public Health:		No public health uses.

Other Nonfood:	Tobacco, as well as field-grown ornamentals.

Target Pests:		Ethoprophos is used for the control of wireworms and
nematodes, which live below the soil surface.

Method and Rates of Application:

Equipment –

The current labels for ethoprophos indicate that the products may be
applied by chemigation (i.e., drip irrigation and sprinkler irrigation),
granule applicator (i.e., tractor-drawn mechanical spreader and
push-type spreader), and ground sprayer equipment.

Method –

The insecticidal/nematicidal activity of ethoprophos is highly dependent
upon incorporating the product into the soil (mechanically or with
water) soon after application to be effective, especially for those
nematodes and insects which live deep in the soil.  All labels specify
immediate soil incorporation by mechanical equipment for all products as
they are being applied by ground equipment, or that watering-in is to be
conducted immediately following applications (for chemigation methods
which are permitted on bananas, plantains, and pineapples only).  No
aerial applications of any type or hand-held application methods are
permitted.  For some crops only banded (not broadcast) applications are
permitted (this restriction applies to the EC label for cabbage and the
EC and granular formulations for sweet potatoes).

Ethoprophos is applied to most crops pre-plant or pre-emergent, but it
can also be applied as follows: pineapple plants as a chemigation
treatment; pineapple plants as a soil treatment (only granular
formulations); banana and plantain plants as soil-directed liquid spray
or granular broadcast (backpack spreader or by hand) around the stems of
the plants up to 2 times per year; and corn at cultivation after plant
emergence until layby (i.e., the last time the corn plants are
cultivated). In addition, potatoes may be treated prior to crop
emergence.

Rate –

For soil treatments of field crops, the maximum label rates range from 2
lb active ingredient per acre (ai/acre) on cucumbers to 12 lb ai/A on
potatoes for agricultural crops. The majority of ethoprophos
applications are to potatoes in the Pacific Northwest (PNW), where
growers apply either granular or EC formulation at two application
rates: 12 lb ai/A for control of nematodes, and 6 lb ai/A for control of
wireworms. For bananas, the EC label states “apply 8 mL of MOCAP EC in
a radius of 3/4 meter around each producing stem,” and the 10G and 15G
granular labels similarly list rates to be applied per producing stem
(at product rates which are equivalent to 6 grams or 0.2 ounces of and
gel labels specify that multiple applications are permitted, but not
more than 8 gallons of MOCAP® per acre per year for plant crops, or not
more than 5 gallons of MOCAP® per acre per year for ratoon crops.

Timing –

For field crops, applications must be pre-plant or at-plant and usually
occur in the spring, before the growing season, with only one
application per crop; only the banana, plantain, and pineapple labels
permit more than one application per year. For some ratoon row crops,
such as sugar cane, applications may occur only at the time of planting,
and the crop grows for 3 to 5 years before a new crop is replanted.
Applications to banana plants may be up to two times per year.
Concerning applications to pineapples (a crop not on any granular
labels), both the current EC and gel labels specify not more than 8
applications per year for plant crops, or not more than 5 applications
per year for ratoon crops, with the timing of these multiple
applications to pineapples specified as “about every two months.”
The timing of applications to pineapples relative to the pre-harvest
interval (PHI) on the current EC and gel labels state “Do not treat
within 120 days of harvest of either plant crop or ratoon crop.”

Use Classification: 

Ethoprophos is a restricted use chemical for most products containing
10% or more of the active ingredient, due to acute dermal toxicity.

Estimated Usage Analysis

  REF _Ref169337875 \h  Table 2  provides a somewhat dated estimated
usage of ethoprophos on representative crops.  The top crops by lbs ai
applied nationally per year are white potatoes, sugarcane, and tobacco
in decreasing order.  The top crops by percent acres treated annually
are bananas, sugarcane, sweet corn, and sweet potatoes in decreasing
order. This analysis covers primarily data sources from 1987 to 1996 and
does not therefore reflect any changes in use patterns since 1996 (data
sources and calculation methods are detailed in the 2001 IRED document).
  In comparing these usage data to the monitoring results, it should be
noted that the surface monitoring study by the registrant included
sampling from 2002 to 2004 and the ground-water monitoring study
sampling occurred from May to July of 2004.   The registrant states in
their monitoring study reports that the major crops are potatoes, sweet
potatoes, tobacco, sugarcane, beans (lima and snap), cabbage, and
cucumbers (no specific estimates on usage are given.)  In documents
supplied to the Agency (but apparently not formally submitted) prior to
the initiation of this study the registrant estimated ethoprophos total
US sales were around 600,000 pounds in 2002, this is reasonably close to
the estimates we made (  REF _Ref169337875 \h  Table 2 ). These sales
data were broken down by county (more information on ethoprophos usage
or sales data may need to be formally submitted, refer to the technical
analysis of the registrant’s monitoring studies in this document.)

Table   SEQ Table \* ARABIC  2 .  Estimated Quantitative Usage Analysis
of Ethoprophos for Representative Sites

  SEQ CHAPTER \h \r 1 Site	%  of  Crop Treated	Pounds of Active
Ingredient Applied

	Weighted Average 1	Estimated Maximum	Weighted Average

Field Crops:



	Beans, Dry	< 0.05%	0.1%	1,000

Beans, Green	1.4%	2.8%	15,000

Corn (field)	< 0.05%	0.1%	20,000

Peanuts	0.4%	1.6%	10,000

Sugarcane	7.0%	15.3%	200,000

Tobacco	3.2%	4.3%	100,000

Total Field Crops:

	346,000

Fruits:



	Bananas 2	6.4%	16.0%	- 3

Citrus seedlings	-	-	-

Pineapples 4	1.0%	5.0%	-

Plantains	-	-	-

Vegetables:



	Cabbage	0.7%	2.9%	1,000

Cucumbers	1.0%	2.1%	3,000

Potatoes, white	2.8%	5.3%	250,000

Sweet Potatoes	4.1%	8.2%	40,000

Sweet Corn	3.8%	8.9%	30,000

Total Vegetables:

	324,000

Turf & Ornamentals (all)	-

21,000

TOTAL

	691,000

1  Based on data for 1987-1996, with the most recent years and the more
reliable data weighted more heavily. 

2  The estimates of the percent crop treated for bananas are based on an
average of the percent of the banana crop treated in six Latin American
countries, and weighted based on the quantity imported into the U.S. for
each producing country.

3  A dash (-) indicates information is not available in Agency sources
or is insufficient for purposes of making estimates. 

4  The estimates for the percent crop treated for pineapples are based
on an average of the percent of crop treated for pineapples in two
foreign countries, and weighted based on the quantity of U.S. imports,
as well as the estimate of the minimal historical United States
production in Hawaii.



Analysis Plan / Basis for the Monitoring Study Requirements

For the 2001 IRED, the acute drinking water level of comparison (DWLOC)
calculated was 0.6 ppb, and the DWLOCs for chronic and cancer exposures
were 1.0 ppb, which were much lower than the drinking water estimated
concentrations (DWECs) – see   REF _Ref170708386 \h  Table 6 ,   REF
_Ref170708338 \h  Table 7 , and   REF _Ref170708340 \h  Table 8 . Based
on screening level models, the highest DWEC for acute surface water
concentrations was 127 ppb, and the highest chronic and cancer DWECs for
surface water concentrations were 25 ppb and 13 ppb, respectively. For
ground water, the highest estimated concentration was 10.1 ppb. Thus,
the DWECs for surface and ground water exceed the Agency’s respective
DWLOCs. To address both surface and ground water risk concerns, the
technical registrant was required to conduct monitoring programs in high
usage areas with vulnerable soil conditions. The actual measured surface
and ground water concentrations were expected to be less than the DWLOCs
(largely because actual usage intensity is expected to be significantly
lower than the allowable level and the exposure modeling assumes a worst
case situation for usage intensity and application rate). However, the
IRED states that if the results of either monitoring program indicate a
potential unacceptable drinking water risk level, the technical
registrant has agreed to drop select uses from the technical and product
labels until risk concerns are fully addressed.  In subsequent sections
of this document, the ground water and surface water monitoring programs
that have now been submitted are reviewed in the context of these risk
concerns, as well as the degree to  the monitoring data represent truly
represent worst-case exposure scenarios and the level of uncertainty
associated with such a determination.

This review analyzes exposure based upon the now completed surface and
ground-water monitoring studies for ethoprophos.  While the nominal
concentrations reported are indeed below the DWLOCs calculated for the
IRED, a full exposure evaluation requires that these data be evaluated
in terms of the representativeness of the range of uses and use
scenarios that are most likely to result in the highest possible
ethoprophos drinking water exposures.  A careful analysis is needed to
determine whether it is plausible to expect higher exposure levels than
reported under any current future usage conditions. Separate evaluations
are provided for both the Surface Water and Ground Water monitoring
surveys.

Risk Issues for the Degradates

The Agency has determined that four ethoprophos
metabolites/environmental degradates are of toxicological concern for
water (see   REF _Ref170275246 \h  Table 3  for acute and chronic
endpoints of concern for each compound as most recently evaluated by the
Health Effects Division), each of these compounds was included in the
suite of analytes for both the ground- and surface-water monitoring
surveys. This review assesses both parent only exposure and total
exposure as parent equivalents.  Unlike many other organophosphorus
pesticides, ethoprophos does not form potential more highly toxic oxon
metabolites (Organophosphorus Cumulative Risk Assessment – 2006
Update).

Table   SEQ Table \* ARABIC  3 .  Residues of Toxicological Concern
(Parent Ethoprophos and its Important Metabolites) in Various Risk
Assessments Conducted.



Common Name; Residue Designation (Chemical Name) 	Non-Cancer (acute and
chronic) Food and Water 	Cancer Food 	Cancer Water 

Parent Ethoprophos 	X 	X 	X 

SME 	X 	X 	X 

OME 	X 	X 	X 

OHE (M1) 	X 	X 

	SSDP (M2)	X 







Although the Agency has determined that four ethoprophos
metabolites/environmental degradates are of toxicological concern for
water (cancer risk) (Table 2), the PRZM-EXAMS with the Standard Index
Reservoir modeling did not include any of the environmental degradates
of ethoprophos due to a lack of fate information.  Results from various
aquatic and soil metabolism studies indicated that none of the
individual environmental degradates were ever present at greater than
about 4% of the applied ethoprophos concentration.  However, the results
of the submitted studies, as discussed below, do indicate that at least
the SME exposure may be significant in some drinking water. 
Nonetheless, given the fate parameters used for parent ethoprophos
(e.g., degradation half-lives of at least several months by most
pathways), it is highly unlikely that even if the data existed to model
the degradates separately that SME residues alone or even total residues
would be estimated to be significantly higher than estimated with the
current modeling.  Furthermore, the monitoring studies that were
requested of the registrant and that are being reviewed here provide a
basis to evaluate more closely exposure levels under actual use patterns
rather than the much heavier usage rates that must be assumed for
conservative modeling assessments.

ANALYSIS

Fate and Transport Characterization

The environmental fate of parent ethoprophos is much more fully
characterized than the fate of certain degradates that constitute
residues of concern for drinking water assessments.  There is no reason
to believe that any of the degradates of concern, if stable in the
environment, will have significantly less potential to reach surface
waters or ground waters that may serve as drinking water sources.

Ethoprophos is a soluble (aqueous solubility: 843 ppm), somewhat
volatile (vapor pressure: 3.5 x 10-4 mm Hg at 26 C)
insecticide/nematicide.  Based on laboratory data, ethoprophos is fairly
persistent (most degradation pathways with first order kinetic
half-lives of a few months or longer); however, in field studies,
dissipation was more rapid than would be predicted on the basis of
degradation alone (from rates measured in the laboratory studies),
especially under warm, moist conditions.  The difference in half-lives
between laboratory and field studies may be partially due to
leaching/runoff, as well as to the increased soil moisture and
temperature in the field soils, which might result in increased
microbial degradation and volatilization.

Because of its high solubility and moderately low soil sorption
potential (Kd: 2.1 L/kg in silt loam soil; Kads: 1.08-3.78), ethoprophos
has the potential to contaminate surface water through dissolved runoff.
 Ethoprophos is, however, either mechanically incorporated or watered
into the soil, which will reduce the runoff potential.  Its persistence
and mobility in laboratory studies suggest that ethoprophos and its
degradates could also pose a threat to ground water resources. 

Ethoprophos is stable to hydrolysis, and does not readily undergo
photodegradation in water or on soil.  The results from the available
aerobic soil metabolism study established a half-life of 100 days.  At
252 days post-treatment, 24.8% of the applied radioactivity was
undegraded ethoprophos.  The major degradate was CO2 (accounting for
53.9% of the applied radioactivity by the end of the study); the major
nonvolatile degradates were identified as
O-ethyl-S-methyl-S-propylphosphorodithioate (SME),
O-ethyl-O-methyl-S-propylphosphorodithioate (OME), and
O-ethyl-S-propylphosphorothioate (OHE or M1), with the measured amount
of each accounting for less than 4% of the applied, at every sampling
interval.  In addition, an anaerobic soil metabolism study showed a
similar rate of degradation, with the half-life of approximately 100
days.  During the 56-day anaerobic incubation test, a total of 2.25% of
the radioactivity had been volatilized, and 10.5% was remaining in the
soil in an unextractable form.  The degradates OME and OHE (M1) each
accounted for less than 1% of the applied radiolabeled parent
ethoprophos.

Ethoprophos is considered to be mobile in soil.  The Freundlich Kd
values determined from a batch equilibrium study were found to be
moderately low, suggesting a limited potential for sorption to soil. 
The reported ethoprophos Kd values increase with an increase in the
amount of organic carbon in the soils.  Mobility information on OHE (M1)
indicates that it also is highly mobile; however, the mobility of the
other degradates (OME, SME, and S,Sdipropylphosphorodithioate [SSDP or
M2]) is not known; however, the similarities in structure of these
compared with parent ethoprophos and OHE (M1) suggest that these other
three degradates will all have similar, moderately low soil sorption
values.

An aerobic aquatic metabolism laboratory study was conducted with
sediment/water systems.  The reported data indicated a half-life value
75 days in the sand sediment/water system and a half-life of 90 days in
the silt loam sediment/water system.  Nonextractable residue amounts
were reported, and in addition, specific degradates were analyzed.  Of
the degradates, OHE (M1) was identified as the degradate reported to be
present at the greatest concentration, but it was never reported at
greater than about 1% at any of the time intervals of analysis. 

In a laboratory volatility study, the resulting volatiles comprised only
a small amount of the applied dose, with parent ethoprophos being about
one quarter to one-half of the volatile components on day 7, the last
day of sampling.  The vapor pressure of ethoprophos is moderate to high,
depending on the classification scheme used (the vapor pressure is 3.5 x
10-4 mm Hg; between 1 x 10-8 and 1 x 10-3 mm Hg is generally considered
to be in the moderate range for pesticides), and it has a Henry’s Law
Constant which is moderately low (1.5 x 10-7 atm m3/mol), suggesting
that ethoprophos would not be expected to volatilize from water to a
great extent.

Summary of Previous Drinking Water Exposure Modeling

For surface water, the Drinking Water Estimated Concentrations (DWECs)
of ethoprophos were calculated by Tier II modeling procedures, which
included PRZM-EXAMS, with the Agency Standard Index Reservoir and the
percent cropped area factor (PCA).  For the IRED, the scenarios modeled
included:

Louisiana sweet potatoes

North Carolina tobacco

Louisiana sugar cane

Maine potatoes

Ohio corn

Specific input values for this modeling are summarized in   REF
_Ref170109528 \h  Table 4 . DWECs, which have been adjusted from the
previously modeling to reflect the current label maximum rates, are
summarized in   REF _Ref170114850 \h  Table 5 .

Table   SEQ Table \* ARABIC  4 .  Key input values for PRZM-EXAMS
modeling. 

Chemical name	Ethoprophos

Molecular Weight	242.3

Solubility	  843 mg L-1

Vapor Pressure	3.5 x 10-5 torr

pH 5 Hydrolysis half life	Stable

pH 7 Hydrolysis half life	Stable

pH 9 Hydrolysis half life	Stable

Soil Photolysis half life 	Stable

Aquatic photolysis half life	stable 

Aerobic soil metabolism half life	 300 days (3 x single study value)

Aerobic aquatic metabolism  half life	162 days (upper 90% c.i. of
registrant' study, MRID 44989502)

Anaerobic soil metabolism half life	 300 days (3 x single study value)

Anaerobic aquatic metabolism half life	600 days (no study conducted; 2 x
Anaerobic soil metabolism)

Kd	2.1  L kg-1 (value for silt loam)

Application Rates	corn: 6 lb a.i. acre-1

potato: 6 lb a.i. acre-1 **

tobacco: 6 lb a.i. acre-1

sugar cane: 6 lb a.i. acre-1

sweet potato: 3.9 lb a.i. acre-1

** Reflects maximum rate for usage E. of the Mississippi River only (12
lb ai/A rate permitted West of the Mississippi River.)

Application Efficiency	100%

Spray drift  mass input to pond	0

Number of Applications	1

Application Method	Broadcast

percent crop area	0.87 (default value; all crops except corn), 0.46
(corn)



Table   SEQ Table \* ARABIC  5 .  Surface Water Source Drinking Water
DWECs for ethoprophos based upon currently registered uses.





crop	

Acute Concentration

(upper 1-in-10 year peak concentration)	Chronic Concentration

(upper 1-in-10 year annual mean concentration)	

Overall Mean

(mean of means for all years simulated)

LA sugarcane	138	18	5.9

LA sweet potato	83	14	8.5

NC tobacco	46	13	4.2

OH corn	15	5.0	2.6

Maine potato	21	8.0	3.7

Values in bold text were used for acute, non-cancer chronic, and cancer
risk estimates (138, 14, and 8.5 ug/L, respectively.) 

Exposure estimates are based upon currently registered rates, which have
changed since these usage scenarios were previously modeled (See:
“Review of Aerobic Aquatic Metabolism study (162-4) and updated tier
II drinking water EECs for Ethoprop for use in the human health risk
assessment”, EFED review dated April 24, 2000).



The original modeling for the IRED utilized for all surface water model
scenarios, except for ethoprophos use on corn, the default PCA value of
87% was used to predict surface water DWECs. The model results indicated
that the surface water source DWECs exhibited the highest acute risk
concentration for use on sugarcane in Louisiana (138 ppb; see   REF
_Ref170114850 \h  Table 5 ). The chronic non-cancer DWECs were the
highest for use on sweet potatoes in Louisiana (14 ppb). The chronic
cancer DWECs were the highest for use on sweet potatoes in Louisiana,
(8.5 ppb).

Table   SEQ Table \* ARABIC  6 .  Summary of DWEC and DWLOC Calculations
for Acute Risk (modified for current maximum use rate from 2001 IRED).

Population Subgroup 1 	Acute PAD (mg/kg/day) 	Food Exposure (mg/kg/day) 
Allowable Water Exposure (mg/kg/day) 	Ground Water: SCI-GROW (ppb) 2 
Surface Water: PRZM-EXAMS (ppb) 1 	DWLOC (ppb) 

U.S. Population 	0.00025 	0.000096 	0.000154 	10.1 	138 	5 

Infants <1 yr 	0.00025 	0.000188 	0.000062 	10.1 	138 	0.6 

1 Based on the highest acute exposure levels modeled (using the Standard
Index Reservoir with the Louisiana sweet potatoes scenario at an
application rate of 6 lb ai/A).



Table   SEQ Table \* ARABIC  7 .  Summary of DWEC and DWLOC Calculations
for Chronic Non-Cancer Risk.



Population Subgroup 1 	Chronic PAD (mg/kg/day) 	Food Exposure
(mg/kg/day) 	Allowable Water Exposure (mg/kg/day) 	Ground Water:
SCI-GROW (ppb) 2 	Surface Water: PRZM-EXAMS (ppb) 4 	DWLOC (ppb) 

U.S. Population 	0.0001 	<0.000001 	0.000100 	10.1 	14 	4 

Children (1-6 yrs) 	0.0001 	0.000001 	0.000099 	10.1 	14 	1 

1 Based on the highest chronic exposure levels modeled (using the
Standard Index Reservoir with the Louisiana sweet potatoes scenario at
an application rate of 6 lb ai/A). The highest estimated chronic
(non-cancer) risk surface water exposure from PRZM-EXAMS with Standard
Index Reservoir is based on the North Carolina tobacco scenario at an
application rate of 12 lb ai/A.



Table   SEQ Table \* ARABIC  8 .  Summary of DWEC and DWLOC Calculations
for Chronic Cancer Risk.



Population Subgroup 1 	Q1 * (mg/kg/day)-1 	Food Exposure (mg/kg/day) 
Allowable Water Exposure (mg/kg/day) 	Ground Water: SCI-GROW (ppb) 2 
Surface Water: PRZM-EXAMS (ppb) 3 	DWLOC (ppb) 

U.S. Population 	2.81x10-2 	0.000004 	0.000035 	10.1 	8.5 	1 



Surface Water Monitoring Study for Ethoprophos Residues in US High Use
Areas

As already noted, this study was submitted in response to a data
submission requirement of the IRED, since the Tier 2 modeling indicated
that ethoprophos residues in water might exceed levels of concern.  The
purpose of this study was to determine whether ethoprophos use may in
fact result in drinking water exposure at levels of concern by targeting
for monitoring of ethoprophos residues select community water systems
across the United States where conditions are likely to result in the
highest levels in surface waters serving as drinking water sources.

Surface Water Monitoring Study Design

The surface water monitoring program included 5 Community Water Systems
– 2 in Oregon and 1 each in Ca, LA, and NC. A separate site selection
report was prepared before initiating the monitoring program (originally
submitted as MRID 454708-01, but resubmitted with the final monitoring
study report being reviewed here).  

Sampling was weekly for the most relevant 3 months (during and following
the application season) and monthly for the rest of the year.  However,
at the Louisiana site (where the S-methyl or M degradate was
consistently detected in the spring and summer) sampling was increased
to a weekly basis throughout most of 2003 and 2004.  

•	Paired raw and finished water

•	3 year duration, 2002 to 2004

The analytical plan, however, was not the same as the sampling design. 
The registrant chose not to analyze most of the finished water samples.
Not a single finished water sample was ever analyzed from the entire
three-years worth of monthly or weekly sampling events at the Jefferson
(OR); Ontario (OR), or Lodi (CA) CWSs.  This is discussed in further
detail in the Monitoring Results section below.

Analytical methods

Residues of ethoprophos and its four metabolites in water were analyzed
using liquid chromatography with mass spectrometry detection (LCIMSIMS).
This method employs direct

injection of the unfiltered water sample onto the analytical column. The
method detection limits

(MDL) for ethoprophos and its metabolites in water are as follows: 

3 ppt (parts per trillion) or ng/L for ethoprophos 

4 ppt for S-methyl ethoprophos (SME)

6 ppt for O-methyl ethoprophos (OME)

7 ppt for des-S-isopropyl- ethoprophos (OHE or M1) 

2 ppt for des-O-ethyl-ethoprophos (SSDP or M2) 

.

The method limits of quantitation (LOQ) set by the registrant for each
analyte are as follows: 

9 ppt for ethoprophos

12 ppt for SME

18 ppt for OME

21 ppt for OHE or M1 

6 ppt for SSDP or M2 

Quality Assurance procedures, including procedural recoveries, storage
stability test results, and control sample analysis procedures and
results are described in the registrant’s final report.  No problems
have been identified that would affect the validity of the test results.

Site Selection Criteria for Surface Water CWS

The registrant developed a selection process for Community Water Systems
(CWS) drawing predominantly from surface water sources based upon
estimated usage level of ethoprophos in the watershed.  Measures of
intrinsic vulnerability to runoff for the watershed were not
incorporated into the selection system (however, once the systems were
selected the watershed boundaries of the selected systems were more
precisely delineated and several measures of vulnerability based upon
soil hydrogeologic group, soil texture, precipitation “depth”, etc.
were calculated for each watershed). The registrant summarizes the
process for characterizing usage in each of the candidate CWS watersheds
as follows: 

The process consisted of identifying candidate community water systems
in high ethoprophos use areas of the five regions and determining the
watershed boundaries for each of these community water systems. The
potential use of ethoprophos in each of these watersheds was then
evaluated in three different ways. First, the total agriculture area and
row crop area in each watershed was determined using the National Land
Cover Data (NLCD). Second, county level data from the 1997 Census of
Agriculture (AgCensus) were used to provide an estimate of crops that
can potentially be heated with ethoprophos in a watershed, assuming
uniform use throughout a county. Third, ethoprophos use in the watershed
was also estimated with county sales data by assuming that ethoprophos
use within a county was proportional to row crop distribution. The
results of these three evaluations were considered together to make a
final selection.

A more complete description of the process of apportioning usage to
watersheds using these data layers and Geographic Information System
software is provided on pages 19 and 20 of their report (MRID 46983601).

The underlying usage data were not submitted although the final
calculated watershed-wide usage intensity values for all candidate CWS
were included in the report.  The key data underlying these watershed
usage calculations were the county sales data for 1999; these data were
assumed to represent county-wide annual usage levels (and further
apportioned using GIS techniques to the portions of the county with
cropland that might include crops on ethoprophos labels).  Since the
sales data for site selection were not submitted, the quality of the
registrant’s calculations of watershed usage levels cannot be
critically evaluated. 

Overall, the registrant identified the following candidate CWS
watersheds meeting their eligibility criteria (listed by region in order
of the estimated watershed-wide usage intensity of ethoprophos (primary
data source was 1999 ethoprophos county sales data) :

Eastern North Carolina

Wilson

Greenville

Lumberton

Tarboro

Goldsboro

Rocky Mount # 1

Rocky Mount # 2

Enfield

Bolivia

Smithfield # 1

Smithfield # 2



Willamette River Basin (OR)

Jefferson

Adair

Corvallis

Amity

Philomath

Stayton

Sheridan

Salem

Silverton



Columbia River Basin (OR – WA)

Ontario, OR

Hermiston, OR

Pasco, WA

Kennewick, WA

Richland, WA

Yakima, WA



Skagit River Basin (WA)

Anacortes

Mt. Vernon # 1

Mt. Vernon # 2

Mt. Vernon # 3

Mt. Vernon # 4



North and Central California

Lodi

Riverside

Antioch # 1

Stockton # 1

Santa Ynez

Santa Barbara # 1

Goleta

Santa Barbara #2

Yreka

Antioch # 2

Stockton # 2

Louisiana and the Mississippi River Basin

Franklin

Berwick

Logansport

Franklin # 2

Monroe

Several systems directly on the Mississippi River (usage not calculated)

The five originally selected systems were:

City of Jefferson Water Treatment Plant Jefferson. OR

City of Ontario Water Treatment Plant Ontario. OR

Little Potato Slough Mutual Water Company Lodi. CA

Berwick-Bayou Vista Joint Waterworks Berwick. LA

City of Wilson-Wiggins Mill Water Treatment Plant Wilson. NC



The Berwick system was subsequently changed to Franklin, LA because in
follow-up site investigation the complicated intake system of Berwick
was found to not result in a water source very representative of the
targeted Bayou Teche watershed, but the Franklin intakes did fully
represent water from the Bayou Teche watershed.

No sites were selected in the Skagit River basin because land use
analysis revealed that the potential ethoprophos use areas (planted to
crops with registered uses) were all outside the CWS watersheds.
Analysis of usage in California revealed that both California
Environmental Protection Agency usage data and ethoprophos usage data
resulted in essentially identical rankings of systems by estimated
watershed usage intensity.

The systems selected for monitoring were generally the ones with the
greatest estimated watershed-wide ethoprophos usage intensity in each
region.

Surface Water Monitoring Results

Ethoprophos detections were relatively rare, with the only confirmed
detections occurring in the Franklin and Wilson systems (  REF
_Ref170281645 \h  Table 9 ).  The SME metabolite was detected much more
frequently overall, but by far most consistently in raw water samples of
the Franklin, LA watershed (  REF _Ref170281858 \h  Table 10 ). In fact,
ethoprophos was consistently detected from spring to early fall each of
the three years of monitoring at Franklin (roughly from March or April
to September or October or November).

Table   SEQ Table \* ARABIC  9 .  Representative hydrologic
characteristics, estimated ethoprophos usage intensity, and ethoprophos
detection rates in monitored CWS.



Watershed ID	Watershed Area (acres)	% C & D hydrologic	Runoff Depth, in.
% Ethp.-Crops	Ethoprophos lb / ws* Acre	% Parent > 3 ppt	% SME Detects >
4 ppt

Jefferson, OR	1,141,478	49.3	0.10	0.5	0.0059	0.00	 2.90

Ontario, OR	37,686,339	59.4	0.05	1.3	0.0032	0.00	 1.45

Lodi, CA	1,320,278	59.8	0.33	0.3	0.0009	0.00	 0.00

Franklin, LA	1,304,097	66.3	2.18	3.1	0.0097	0.81	57.26

Wilson, NC	150,166	27.1	0.54	5.8	0.0077	2.90	 5.80

* ws = watershed



Table   SEQ Table \* ARABIC  10 .   Raw water ethoprophos and SME
detection rates and maximum observed concentrations for the five
monitored CWS.



Watershed	Ethoprophos detection rate	SME Degradate Detection Rate
Ethoprophos Maximum , ppt	SME Maximum, ppt

Jefferson, OR	0.00%	0.00%	0.0	2.9

Ontario, OR	0.00%	1.45%	0.0	6.7

Lodi, CA	0.00%	0.00%	0.0	0.0

Franklin, LA	0.81%	57.26%	14.4	202.0

Wilson, NC	2.90%	5.80%	12.4	11.8



Ethoprophos parent was never detected in the finished water samples;
however, this is somewhat misleading because most finished water samples
were never analyzed for the parent compound.  Analyses for parent
ethoprophos (as well as degradates) were performed for only in 7 out of
the collective total of approximately 280 sampling events for 4 of the 5
CWS included in the study. Not a single sample of finished water was
analyzed for any ethoprophos residues at the Jefferson, Ontario, or Lodi
sites. Finished water was almost always not analyzed from a particular
sampling event unless quantifiable residue (>LOQ) were first detected in
a corresponding raw water sample. Even when detections of one or more of
the analytes occurred in the raw water samples, the corresponding
finished water samples were still often never analyzed.

SME patterns of detection were similar in finished water and raw water,
but on average the concentrations in finished water were lower than the
companion raw water samples taken from the CWS source water on the same
day.  There were a number of cases where the raw water had detectable
levels of SME but SME was not detectable in the corresponding finished
water sample).  At the Franklin, LA site finished water samples
generally had significantly lower concentrations than the raw water
samples taken on the same day.  However, a common problem in CWS surveys
is the difficulty in matching exactly the water source for pretreatment
samples with the water source represented by the posttreatment sample
collected.  Previous studies have demonstrated that finished water
sample pesticide concentrations do not necessarily have any one-to-one
correspondence with the pesticide concentrations in raw water samples
collected on the same day.   Furthermore, general conclusions about
treatment effects on ethoprophos residues cannot be made with three
years of data from a single CWS.  We are unable to assume that all of
the unanalyzed finished water samples did not contain ethoprophos
residues, especially with essentially no finished water samples analyzed
for comparison at 4 of the 5 CWS. 

Other Surface-Water Monitoring Data

The IRED summarizes the available data as follows:

Although the levels of ethoprophos found in the various studies suggest
that ethoprophos does not appear to exceed the DWLOCs, the reported
samples were not correlated with use patterns, were collected randomly
throughout the year, and were of insufficient numbers to make definitive
statements as to extent of concentrations of ethoprophos in surface
waters. Additionally, information on the site characteristics within the
monitored basins would be necessary to understand the relative
vulnerability of the recipient surface waters. Thus, the DWECs are based
on modeling estimates.

Discussed below are some key recent monitoring results for ethoprophos
parent, which include some detections above the previously calculated
DWLOC.  These data are provided for context on the levels that can occur
in certain relatively-well characterized watersheds / circumstances;
they are not directly representative of the levels occurring in drinking
water sources (as none of these sites have confirmed drinking water
intakes in the immediate downstream area of the sampled watershed).

Probably the largest monitoring program for pesticides that is
well-characterized in terms of watershed land use and hydrogeology is
the United States Geological Survey National Water Quality Assessment
(NAWQA) program.  A number of detections of parent ethoprophos were
reported from NAWQA studies. The NAWQA sampling program is not limited
to waters used as drinking water sources and extrapolation of the
results to drinking water exposure assessments is not straightforward.

The latest published pesticide data summary by USGS from this program
includes the following (all results are for parent ethoprophos only):

In streams located in watersheds with agricultural land use predominant:

Maximum 455 ppt, 1.82% of samples with detections > 10 ppt.

In streams in watersheds with mixed land use:

Maximum 140 ppt, 0.59% of samples with detections > 10 ppt.

In streams located in watersheds with urban land use predominant:

Maximum 124 ppt, 0.32% of samples with detections > 10 ppt.

(Source:   HYPERLINK
"http://ca.water.usgs.gov/pnsp/pestsw/Pest-SW_2001_Text.html" 
http://ca.water.usgs.gov/pnsp/pestsw/Pest-SW_2001_Text.html   - only
includes NAWQA samples taken from 1992 to 2001).

A data retrieval was also performed from the “USGS National Water
Quality Assessment Data Warehouse” which showed some higher detections
(up to 5,750 ppt); all but one of the detections above 400 ppt were from
Zollner Creek in the Willamette Basin of Oregon; this is a small creek
with a drainage area of 15 square miles at the sampling location.  The
overall rate of ethoprophos detections from the NAWQA data download was:

0.02% of samples with detections  > 1000 ppt

0.20% of samples with detections  > 100 ppt

0.74 % of samples with detections  > 20 ppt

(the percentage > 10 ppt could not be accurately determined because too
many samples could not be quantified for ethoprophos at this level)

These NAWQA results can not be directly taken to be representative of
the frequency and level of ethoprophos occurrence in watersheds with
relatively high-level usage of this pesticide nor of the subset of these
watersheds with currently functioning community water intakes utilizing
surface water sources.  They are from study sites that were not targeted
to ethoprophos-specific use areas, although the data from streams with
agricultural land use predominant are presumably more likely to be in
watersheds with a significant level of ethoprophos usage (and, e.g., one
of the study units included the Yakima River basin, which is a know use
area for ethoprophos).

USGS staff for the NAWQA study project provided additional details on
the Zollner Creek study site (which had the majority of the high-level
ethoprophos detections) and monitoring results in a personal
communication to EFED staff (e-mail on 11/15/2007 from Hank Johnson,
Hydrologist, Columbia Basin Studies Team, Oregon Water Science Center,
Portland, OR). The watershed, as noted above, is much smaller than would
be typical of a surface-water based community drinking water source. 
The watershed is nearly 100% agricultural land, although direct
information on any ethoprophos usage in the basin was not available. Of
the crops observed or presumed to occur in the watershed, only
ornamentals and hops [24(c) labels for Oregon] have had legal
registrations for ethoprophos applications. Both crops are common in the
area, but only ornamental acreages were observed by the study authors,
including a large area near the stream gage (where monitoring samples
were collected) and a pond / reservoir near the downstream end of the
watershed with ornamental fields adjacent. An exact acreage for crops
with ethoprophos registered uses could not be calculated for this
watershed.

More recently, the Washington State Department of Agriculture and
Washington State University have conducted surveys of pesticide
concentrations (including parent ethoprophos) in three streams located
in predominantly agricultural land use watersheds in the Lower Yakima
River basin (part of the Columbia River basin that was one of the study
areas in the registrant’s study) over 2003 to 2006, with additional
streams including some in the Lower Skagit-Samish Watersheds sampled in
2006. These sites include some of the potential use areas examined for
the registrant’s ethoprophos CWS study being reviewed here. 
Ethoprophos was most frequently detected in the Marion Drain with a
frequency of 5, 20, 15, and 6%, respectively, for each successive year
of monitoring (the minimum reporting limit for a detection was generally
around 10-12 ppt).  These data are from watersheds that are included in
some of the registrant study areas and provide some interesting insights
into their study.  The Marion Drain watershed at the sampling location
totals 85,786 acres (134 square miles) and is about 20 to 25 miles long
and 10 or 15 miles wide at most points. About 55% of the land area is
agricultural.  Percent watershed land cover for crops with ethoprophos
registrations during part or all of the monitoring time frame were as
follows:

Corn			7.48%

Potatoes		1.03%

Beans 			0.22%

Cabbage		0.15%

Turfgrass		0.09%

The total estimated coverage for crops with ethoprophos registrations
was 9% of the watershed.  This compares to about 1.3% for the Ontario,
OR watershed study from the Columbia River basin and included in the
registrant’s study and to about 5.8% for the Wilson, NC CWS watershed
(the one with the highest ethoprophos crop density of all of the
watersheds surveyed). With the very low rates of use on corn (about 0.1%
of field corn acres treated annually, e.g.) and potatoes (well under 5%
treated), the total percentage of the Marion Drain watershed treated in
any particular year was likely <<1% and within the range or possibly
slightly over the range of treatment percentages for the five CWS raw
intake water monitored by the registrant.  



Year	# of Samples	% Detections **	Maximum Detect, ppt

2003	18	5	46

2004	31	20	180

2005	29	15	270

2006	31	6	22

** The method minimum quantitative detection limit varied from 25 to 30
ppt.  The minimum reporting limit appeared to be around 10 ppt (lowest
reported value for ethoprophos for the four years of monitoring was 12
ppt.)



It is not known why water samples from the Marion Ditch watershed
contained ethoprophos parent concentrations at significantly higher
levels and detected at significantly greater frequency (in spite of the
reduced sensitivity of their analytical method compared to the
registrant’s method).   The WSU sampling program does provide evidence
(even though the sampling sites were not particularly matched with
drinking water intake locations) that parent ethoprophos may under some
circumstances occur at higher concentrations in surface waters that may
be used for drinking water than determined in the registrant’s study. 
Unfortunately, no significant outside monitoring data are available for
ethoprophos degradates.

Surface Water Exposure Summary and Conclusions

A summary of the levels of exposure to ethoprophos parent and degradates
estimated or measured via modeling and monitoring of surface waters is
provided in   REF _Ref181075732 \h  Table 11 .  

Although the submitted data appear to represent some of the highest
ethoprophos usage rates where CWS already exist, there are some
deficiencies in the characterization, particularly the reliance on 1999
sales data as the primary source of information on the spatial
distribution of current and future use of ethoprophos (future because
these data are being used to assess future potential drinking water
exposure.)

Both the Agency’s and the registrant’s usage data and their GIS
analysis of usage point to low usage rates on a watershed wide basis. 
Calculated usage rate averaged across the watershed was below one
thousandth of a pound active ingredient per watershed acre at all five
watersheds associated with the sampled CWS.  This is a rate that is
about 20x to 100x below some of the highest watershed usage rates for
herbicides used on a variety of the major acreage row crops in the
United States. The difference between the actual usage rates for
ethoprophos and the modeled rates (which have to be based upon potential
rates allowable under the label rather than on actual measured rates)
for a range of standard scenarios (representing different crop use
sites) is even greater (300 to 5000-fold for the registrant’s study
sites and 30 to 250-fold for the Marion Ditch watershed in the WSU
study.)

Table   SEQ Table \* ARABIC  11 .  Surface Water Source Drinking Water:
comparison of modeled and measured watershed use rates and ethoprophos
acute and chronic (annual mean) concentrations.





Crop	Modeled

(ppb)

	Measured, registrant study**

(ppb)

	Measured, WSU study Marion Ditch site

(ppb)



Watershed usage intensity (lb ai/A)	2.8 to 5.2	0.0009 to 0.0097	0.0220
to 0.1100*

Acute Conc. Ppb	21 to 138	0.014

(0.202 for SME degradate)	0.270

Chronic Conc. Ppb

(highest annual mean)	5 to 18	<0.003

(0.015 for SME degradate)	

0.014

* Calculated using the study author’s GIS determinations of percent
ethoprophos-labeled crop area in the Marion Ditch watershed and the
ethoprophos application rate / A of ethoprophos labeled crop estimates
by the registrant for the nearby Ontario, OR and Jefferson, OR
watersheds.   

** Only the registrant studies are confirmed to represent sources for
drinking water.

Annual mean concentrations were calculated assuming that for samples
with no reported detection, residue levels were at ½ the minimum
reporting limit.

NC = Not calculated



This analysis shows that ethoprophos parent exposure may be
significantly higher in some watersheds that were not monitored (such as
the Marion Ditch) but are of sufficient size to be used for drinking
water sources (Marion Ditch, however, to our knowledge, is not close to
any drinking water facilities).  Whether this translates into higher
ethoprophos exposure through drinking water from some CWS not
investigated in the registrant’s study is not known.  Unfortunately
there are no similar outside monitoring data on ethoprophos degradate
residues in surface waters, but it is at least plausible that degradate
concentrations could be similarly higher in some watersheds.  The USGS
NAWQA data show that higher residues may occur in some apparently
smaller streams (which are less likely to represent a significant
portion of a public drinking water supply).

The only known drinking water facilities downstream of the Marion Ditch
sampling point are further downstream below the confluence of Marion
Drain with the Yakima River and the confluence of the Yakima with the
Columbia River.  The PRZM-EXAMS modeling seems to give reasonable acute
and chronic exposure predictions when the differences in usage rates and
the actual usage rates at monitored sites are accounted for.

Definitive conclusions cannot be made about how much ethoprophos was in
the actual finished water since such a small percentage of the finished
water samples were actually analyzed for ethoprophos in the
registrant’s study (although the presumption is that, on average,
residues would be significantly lower, individual samples could have had
higher residues).  It is also problematic that the ethoprophos detection
rates in an independent monitoring program in Washington state seem to
be significantly higher than would be expected from examination of the
registrant’s results for parent compound (including a maximum detected
concentration 20x greater than in the registrant’s study).
Nonetheless, both studies do confirm that ethoprophos concentrations, if
usage patterns remain fairly stable, are unlikely to reach the modeled
levels.  

Significant uncertainty remains about whether acute and chronic exposure
might be up to several times greater than that observed in 3 years of
monitoring at 5 sites by the registrant and about why outside monitoring
showed much higher residues of parent ethoprophos than the
registrant’s study showed (however, most of these parent
concentrations were in a similar range to the levels of the SME
degradate observed in the registrant’s studies).   This uncertainty
leads to a concern that acute exposure may lead to exposure above the
previously calculated DWLOC:  For example the single highest weekly
value for SME (which could still underestimate the highest daily acute
exposure in a high runoff year) was 0.20 ppb (average value for 2
samples analyzed on the same day) and the lowest acute  DWLOC ( for
infants) is 0.60 ppb; we judge that occurrences of up to 0.6 ppb in
drinking water are quite plausible given the aforementioned
uncertainties.  This judgment is supported by simple statistics:  for
example, if the acute exposure period needed for an adverse effect is 24
hours, then the chances of the sample with the highest concentration
from three years of weekly monitoring representing the true maximum
daily concentration is about 1 in 23 (assuming 30 years of daily
monitoring, similar to what is simulated in the PRZM/EXAMS modeling). 
Even the chance of the highest monitored value exceeding the 90th
percentile of the distribution of the maximum daily values in a year is
less than 50%.  And this does not even take into account the possibility
that exposure levels would not necessarily be found to be higher at the
five monitored CWS than at any other CWSs in the country, if those
exposure levels were known.  Again, comparison of SME to the DWLOC is
appropriate since SME is included in the residues of toxicological
concern.

The margin between the highest annual mean concentration of SME (or
parent ethoprophos) measured and the previously calculated DWLOCs for
chronic (non-cancer) exposure is significantly greater: For example, the
highest time-weighted annual mean concentration for SME in the
registrant’s study was 0.015 ppb, this is more than 60x less than the
lowest DWLOC of 1 ppb (for children 1 to 6 years old).  While the
plausibility (assuming usage patterns do not dramatically change) that
annual mean concentrations would be 60x at any other site is in
question, it certainly is possible that residue levels could be
significantly above 0.015 ppb.  Statistically the chance of getting a
30-year maximum annual mean from 3 years of monitoring is 1 in 10. 
Additional uncertainty is introduced by the possibility that exposure
levels could be higher at CWSs that were not monitored.

In conclusion, the registrant’s studies demonstrate that ethoprophos
residues of concern under current use patterns are substantially lower
than previously estimated (with modeling).  These studies fail to
conclusively demonstrate that ethoprophos will never exceed previously
calculated DWLOCs, especially for acute endpoints.  An updated drinking
water risk assessment is recommended. 

Ground Water Monitoring Study for Ethoprophos Residues in US High Use
Areas

The purpose of this study was to determine whether ethoprophos use may
in fact result in drinking water exposure at levels of concern by
targeting for monitoring of ethoprophos residues select domestic
drinking water wells across the United States where conditions are
thought to likely to result in the highest potential for ethoprophos
leaching to ground water that may be used for drinking water.

Ground Water Monitoring Study Design

A total of 153 wells were sampled (usually only one time) from 93
separate fields in 5 regions.  The fields were located across 18
counties in NC, GA, ME, OR, and WA. In general, out of 172 samples there
were only 2 “confirmed” detections of parent ethoprophos at <0.01
ug/L and no detections of the 4 metabolites analyzed.  However, the
hydrogeologic association….

Site visits and well water collection for analysis of ethoprophos
residues were made between May and July of 2004.  Wells were selected
only from farmers or landowners that confirmed at least one field on
their property had been treated with ethoprophos and that they had at
least one well which met the study criteria.  After interviews with the
owners / farmers 93 ethoprophos-treated fields were selected for
characterization.  Of these fields, 75% were irrigated, 29% were tiled,
and 24% had no irrigation or tiles.  

Table   SEQ Table \* ARABIC  12 .  Most recent applications of
ethoprophos on fields in the vicinity of sampled domestic wells.  

  

# of Fields	Year of Last Application

7	2004

82	2002 or 2003

4	2001



Of 153 well sampled, 1 was inside the treated field, 10 wells were
within 50 feet of the edge of the treated field, and 100 wells (65%)
were within 300 feet.  The maximum allowable distance from the treated
field for any well was 1000 feet.  Samples were usually collected from a
kitchen tap and not directly from the well.

Site Selection Criteria for Domestic Well Study

The registrant made a determination of the regions in the US likely to
be the most vulnerable to ethoprophos movement to groundwater. Using
MOCAP brand nematicide and insecticide sales data for 2002, a total of
58 counties in 13 major use areas of the US were identified for
evaluation. Soil properties (surface texture, hydrologic group and
slope) and historical precipitation in each of the 58 counties were
combined with the sales data to provide an overall score as a measure of
vulnerability in each county. Based on these results (which are not
provided in their report), and following meetings of registrant
representatives with EPA, five regions in the US were selected for the
monitoring program.

The following use areas were selected for screening of appropriate wells
to be sampled:

1. South-central Washington

Grant, Franklin, Walla Walla, Adams, and Yakima Counties

2. Western Oregon

Benton, Polk, Marion, Multnomah, Washington, Linn, Yamhill, and
Clackamas Counties

3. Coastal Georgia

Coffee, Cook, Tift, Lowndes, Colquitt, Berrien, and Lanier Counties

4. Northeastern North Carolina

Edgecomb, Wilson, Nash, and Halifax Counties

5. Maine

Androscoggin and Aroostook Counties

Ethoprophos usage and domestic well locations were investigated by
interviews with farmers who had purchased any ethoprophos over the 2001
to 2004 period. Not all farmers who had purchased ethoprophos in recent
years were interviewed: interviews were only performed until a
sufficient number of farmers were contacted in each respective area to
ensure approximately 30 private wells in each area. Each farmer
interviewed was asked to identify all potable wells within 1000 feet of
any ethoprophos-treated field. An inquiry was also made regarding the
proximity of a well from an ethoprophos tank mixing - loading area. Well
suitability was assessed prior to selection for further evaluation based
on the following criteria:

- Verification of farmer / grower contact information

- Size and location of field(s) treated with ethoprophos

- Location of wells and distance from treated field

- Names, contact information and location of landowners with potable
wells within 1000 feet of the ethoprophos-treated field, prioritizing
those within 300 feet of the ethoprophos-treated field.

Following initial site contact, the interview was continued during a
site visit to complete the documentation and / or confirm the data
collected in the initial conversation. Publications such as soil
surveys, plat books, county road maps, etc. were used, when available,
to assist in the preliminary documentation of well and field location.
After the initial contact with a farmer, it was necessary for the
interview to continue during a site visit to complete the documentation
and / or confirm the data collected in the initial conversation. All
pertinent site and well information were documented in the study
records.

General soil characterization information of the ethoprophos-treated
field was obtained and recorded from farmer / owner interviews, county
soil surveys if available, and / or the local

Natural Resources Conservation Service (NRCS) office.

The details of the criteria for the selection of counties to choose the
wells to be monitored from and then the wells to be monitored are
unclear at this point.  Ninety three fields were selected with a total
of 153 wells associated with these fields sampled as previously
described.  These wells were all located within 18 of the original list
of 58 target counties. Site selection efforts did not take place in the
other 40 target counties; the process and criteria for narrowing the
search to these 18 counties is not described. Presumably, detailed
investigation of additional candidate sites may have facilitated
selection of a larger percentage of sites with domestic wells closer to
fields with a long-term history of ethoprophos application and that had
wells with evidence of a hydraulic connection between the ethoprophos
treatment areas and the well source water.

Ground Water Monitoring Results

Ethoprophos detections were relatively rare (methods and reporting and
quantification limits were the same as for the surface water monitoring
study and are listed in the “  REF _Ref170626460 \h  Analytical
methods ” earlier in this document. Of the 172 samples analyzed (a few
wells were sampled more than once), there were two confirmed detections
of parent ethoprophos in wells located in Maine at concentrations under
10 ppt (ng/L). None of the metabolites were detected in any sample.

Ground Water Exposure Summary and Conclusions

The lack of detections of ethoprophos in this study appears to
demonstrate that the probability of occurrence of ethoprophos at levels
of concern is low at any given time in any existing well located within
1000 feet of a field with a known history of at least one ethoprophos
application.  However, more general conclusions cannot be made about the
potential for ethoprophos to leach under field conditions without
further supporting information for this study.  It is not known, for
example, how many of the treated fields actually constituted a recharge
area for the sampled ground water nor is it known for how many sites is
it physically possible for leaching to the sampled ground water to occur
over the time frame between the surface application of ethoprophos and
the well water sampling that was performed.  

Additional long-term characterization of usage would permit a more
complete evaluation of the representativeness of the domestic well
monitoring results of the highest likely ground water exposure scenarios
for ethoprophos.  We recommend:

Conducting a historical survey of ethoprophos usage for the ten years
prior to the ground-water monitoring period (i.e., for 1994 to 2003) and
2004 for each of the owners / farmers / commercial applicators
associated with possible pesticide usage on agricultural fields within
300 feet of the monitored sites.  This survey may be restricted to only
the 100 wells with evidence of a treated field within 300 feet of the
wellhead from the previous survey (that is, no further historical usage
investigation is required for the remaining 53 wells were the closest
treated field during the 2001 to 2004 period was > 300 feet from the
wellhead). These data should be collected at the level of detail that
appears to be generally reliable based upon the level of detail of
pesticide application records (if even available) or the level of
clarity of recollection of the interviewee. For example, if the years
and rates of ethoprophos usage have not generally be recorded, then it
may be more reliable to just record the best estimate of the number of
years between 1994 and 2000 (along with the annual records of
ethoprophos applications that have apparently already been recorded for
the previous review).  

Secondly, if available, historical sales records, at a county level (or
the highest level of geographic detail available) should be collected
for 1994 to 2004 and compared on a county to county basis with each of
the 153 monitored wells.

Further details on our recommendations are provided in the   REF
_Ref170633042 \h  EXECUTIVE SUMMARY  section of this document.



Appendix A.  		Table of Current Use Patterns for Ethoprophos (reflects
all changes implemented from the IRED Addendum recommendations)

Site:

Application Type

Application Timing

Application Equipment	Formulation

[EPA Reg. No./ SLN No.]

	Maximum Single

Application Ratea	Maximum Number of Appls.b	Minimum Retreatment Interval
Use Limitation

Food/Feed Crops Uses

Bananas/Plantains

Application to soil adjacent to stem

Growing plants

Ground Equipment	G

[264-457]	10.6 lb ai/A;

rate on a per plant basis:

0.2 oz (6 grams) of ai	2 per year	6 months	Treat only the soil within a
radius of 30 inches (3/4 meters) of plant stern.

The registrant submitted a request to voluntarily terminate use on
bananas from the EC formulation product labels.  

Beans (Lima/Snap)

Broadcast

Preplant or at planting

Ground equipment	G

[264-457]	8.1 lb ai/A	1	NA	The registrant submitted a request to
voluntarily terminate use on snap/lima beans from the granular and EC
formulation product labels.  The requests were published in the Federal
Register on October 24, 2001 and November 4, 2005 for snap and lima
beans respectively.  The Final Cancellation Letter was issued to the
registrant on February 3, 2006.  



3 lb ai/A;

0.21 lb ai/1000 ft of row (minimum of 12″ band, 36″ row spacing)



	Cabbage

Broadcast

Preplant or at planting

Ground equipment	G

[264-457]	5.1 lb ai/A	1	NA

	Banded

At planting

Ground equipment	G

[264-457]	1.95 lb ai/A;

0.135 lb ai/1000 ft of row

(15″ band, 36″ row spacing)



	Banded 

At planting

Ground equipment	6 lb/gal EC

[264-458]	1.65 lb ai/A;

2.4 fl oz of EC/1000 ft of row (minimum of 12″ band, 36″ row
spacing)	1	NA	CA Only

Only banded applications to cabbage are allowed for the EC because
broadcast applications of EC to cabbage have been voluntarily deleted.  

Site:

Application Type

Application Timing

Application Equipment	Formulation

[EPA Reg. No./ SLN No.]

	Maximum Single

Application Ratea	Maximum Number of Appls.b	Minimum Retreatment Interval
Use Limitation

Corn (Field and Sweet)

Broadcast

Preplant or at planting

Ground equipment	G

[264-457]	6 lb ai/A	1	NA	The registrant submitted a request to
voluntarily terminate use on field and sweet corn and application by
layby from the granular product labels.  The request was published in
the Federal Register on October 24, 2001.  The Final Cancellation Letter
was issued to the registrant on February 3, 2006.  



Banded

At planting

Ground equipment	G

[264-457]	4 lb ai/A:

0.15 lb ai/1000 ft of row

 12″ band, 20-40″ row spacing)





	Cucumbers

Banded

At planting

Ground equipment	G

[264-457]	1.95 lb ai/A:

0.315 lb ai/1000 ft of row

(minimum of 12″ band, 7 ft row spacing)

	1	NA	The registrant submitted a request to voluntarily terminate use on
cucumbers from the EC formulation product labels.  

Pineapple

Post-plant

Apply at base of each plant 1-2 months after planting 

Ground equipment	G

[264-457]	6 lb ai/A	4 per year	3 months	Do not treat within 120 days of
harvest.

The registrant submitted a request to voluntarily terminate use on
pineapples from the EC formulation product labels.  

Potatoes

Broadcast

Preplant to preemergence

Ground equipment	G

[264-457]

6 lb/gal EC

[264-458]	12 lb ai/A

(see Use Limitation for additional information on geographical
restrictions)	1	NA	The maximum application rate for the treatment of
nematodes west of the Mississippi River is 12/ lb ai/A.  For nematodes
east of the Mississippi River, the maximum rate is 9 lb ai/A.  For
wireworms, the maximum application rate is 6 lb ai/A nationally.

Banded

At planting

Ground equipment	G

[264-457]

	3 lb ai/A;

″ band, 36″ row spacing)







6 lb/gal EC

[264-458]	3 lb ai/A;

4.4 fl oz of EC/1000 ft of row (12″ band, 36″ row spacing)



	Site:

Application Type

Application Timing

Application Equipment	Formulation

[EPA Reg. No./ SLN No.]

	Maximum Single

Application Ratea	Maximum Number of Appls.b	Minimum Retreatment Interval
Use Limitation

Sugarcane

Broadcast

At planting

Ground equipment	G

[264-457]	6 lb ai/A	1	NA

	Banded

At planting

Ground equipment	G 

[264-457]	4 lb ai/A;

″ band, 6 ft row spacing)



	Sweet Potatoes

Broadcast

Preplant

Ground equipment	G

[264-457]	3.9 lb ai/A;

0.315 lb ai/1000 ft of row

(minimum of 12″ band, 42″ row spacing)	1	NA	Only banded applications
to sweet potatoes are allowed, because broadcast applications to sweet
potatoes have been voluntarily deleted.  

	6 lb/gal EC

[264-458]	3.9 lb ai/A;

6.9 fl oz of EC/1000 ft of row

(minimum of 12″ band, 42″ row spacing)



	Non Food/Feed Uses

Ornamentals (Field nursery stock only)

Broadcast only to soil

Preplant

Ground equipment	6 lb/gal EC	3 lb ai/A	1	NS	CA, OR, and WA only.

Nursery stock may only be mechanically transplanted into the treated
area, and not until 72 hours after treatment.  

Tobacco

Broadcast

Preplant or at planting

Ground equipment	G

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a  For banded applications, the maximum rate is expressed both as the
maximum rate per acre as lb ai/A, as well as the maximum rate per linear
1000 ft row, as lb ai (for granular products) or fl. Oz. ai (for the EC)
per 1000 ft linear row, with the minimum band width and row spacing
listed in parentheses.  

b Maximum number of applications for the growing crop.  Note that for
tropical crops (bananas, plantains, and pineapples), the at planting and
the ratoon crops may take more than a year to mature.  In addition, for
some agricultural row crops, in some parts of the country, more than one
crop per year may be grown, but each growing crop may only be treated
one time (i.e., one treatment per crop season).  



  Downloaded from the USGS National Water Quality Assessment Data
Warehouse on October 15, 2007 in “cross-tab extended” format for the
analyte parameter “Ethoprop_ water_ filtered (0.7 micron glass fiber
filter)_ recoverable_ micrograms per liter (29205)”. Url:   HYPERLINK
"http://infotrek.er.usgs.gov/traverse/f?p=136:9:0::NO:::#" 
http://infotrek.er.usgs.gov/traverse/f?p=136:9:0::NO:::# 

  Anderson, P., C. Burke, and D. Dugger . 2007.  Surface Water
Monitoring Program for Pesticides in Salmonid-Bearing Streams, 2006
Monitoring Data Summary (Published March 2007). WSU Publication Number
07-03-016 

Burke, C., P. Anderson, D. Dugger, and J. Cowles. 2006.  Surface Water
Monitoring Program for Pesticides in Salmonid-Bearing Streams,
2003-2005: A Cooperative Study by the Washington State Departments of
Ecology and Agriculture (published October 2006). WSU Publication Number
06-03-036. 

  Anderson, P., R. Jack,  C. Burke, J. Cowles, and B. Moran . 2004. 
Surface Water Monitoring Program for Pesticides in Salmonid-Bearing
Streams,  April to December 2003. Published November 2004). WSU
Publication Number 04-03-048. 

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