	UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

	WASHINGTON D.C., 20460

	OFFICE  OF 

	PREVENTION, PESTICIDES AND 

	TOXIC SUBSTANCES

MEMORANDUM	PC Code No. 056801

	DP #: 334714

	Date: May 02, 2007

Subject: Revised carbaryl drinking water assessment including
time-series simulations

To: 		Chistina Scheltema, Chemical Review Manager, SRRD

		Michael Goodis, Chief, SRRD

		Felicia Fort, Risk Assesor, HED

		Michael Metzger, Chief, HED

From:		Dirk Young, Ph.D., Environmental Engineer, EFED

	  	Elizabeth Behl, Chief ERB 4, EFED

Introduction

This memo formalizes the drinking water assessment previously sent under
D337058.  The estimates here have considered newly submitted data
(aerobic aquatic metabolism), regional percent crop areas, and includes
time series for use in refined HED assessments.  A previously sent email
(see D337058) includes the electronic copies of refined time series of
PRZM/EXAMS simulations for carbaryl.  This memo also provides an updated
surface water monitoring summary.

Models and Scenarios 

The surface water simulations were performed with PRZM version 3.12 beta
(dated May 24, 2001) and EXAMS version 2.98.04 (dated July 18, 2002). 
These models were run with the EFED PRZM EXAMS shell, PE4.  

During problem formulations meetings, BEAD, EFED, and SRRD selected
scenarios of greatest importance (in terms of usage and vulnerability)
for simulation of surface water concentrations with PRZM and EXAMS.  The
selected scenarios are summarized in Table 1.  One other scenario that
was discussed in the problem formulation meeting but was later not
modeled was a Michigan blueberry scenario.  EFED discarded this
simulation because blueberries are grown in Michigan in Hydrological
Group B soils which are not conducive to runoff and therefore would not
be a vulnerable surface water scenario in terms of PRZM/EXAMS
simulations; thus the blueberry use would be covered by the other more
conservative scenarios already provided.  

During the problem formulation meetings, it was concluded that regional
percent crop areas should be applied to the scenarios. These PCA
adjustments have important implications regarding the spatial
representation of these simulations.  In this regard, Table 1 below
gives the names of the time series simulation files that were sent,
along with a description of the relevance of each simulation with
respect to its ability to represent particular areas.  Table 1 also
gives the mechanisms and dates of pesticide applications for each of the
simulation and the file name for the  time series of daily values that
have been previously sent. 

Table 1.  Decsription of the simulations that have been sent
electronically.

Description and Relevance	Regional PCA	Application type	App Dates	Time
Series File Name

Georgia Peaches with the optional Dormant Spray, protective of USA	0.38
Aerial application; 3 in season at 3 lb and 1 dormant at 3 lb (Note that
due to model limitations, the last application is 2 lb short of 
allowable)	7-1, 8, 15; 10-15	ga peach with dormant regional PCA.csv

Georgia Peaches without the optional dormant Spray,  protective of USA
0.38	Aerial application; 3 in season at 3 lb 	7-1, 8, 15	ga peach No
dormant regional PCA.csv

California Peaches with the optional dormant spray, protective of
California	0.56	ground spray; 3 in season at 3 lb and 1 dormant at 3 lb
(Note that due to model implementation difficulties, the last
application is 1 lb in excess of max seasonal)	7-1, 8, 15; Oct 15	CA
peach with dormant regional PCA.csv

California Peaches without the optional dormant spray, of California
0.56	3 in season at 3 lb, 7 day interval, aerial	7-1, 8, 15	CA peach NO
dormant regional PCA.csv

Florida Citrus, protective of FL citrus	0.38	three 5-lb applications, 14
day interval aerial	1- 4, 18, 2-1	FL citrus regional PCA.csv

California Citrus should be protective of California	0.56	three 5-lb
applications, 7 day interval, aerial	1-4, 18, 2-1	CA citrus regular
regional PCA.csv

CA citrus alternative 12 lb application, protective of California	0.56
single 12-lb application, aerial	Jan 4	CA citrus 12 lb regional PCA.csv

California Grapes, protective of California	0.56	five 2 lb applications,
aerial	6-1, 8, 17, 24, 7-1	CA grape regional PCA.csv

PA Apple, protective of Mid Atlantic apples	0.46	five 3-lb applications,
14 days interval, aerial	6-1, 15, 29, 7-12, 26	PA apple regional PCA.csv

Pennsylvania one thinning application, protective of Mid Atlantic apples
0.46	Single 3-lb application, aerial	April 15	PA apple thinning regional
PCA.csv

PA, one thinning application at 2 lb (BEAD value for ~90% use),
protective of Mid Atlantic apples	0.46	Single 2-lb application , aerial
April 15	PA apple thinning regional PCA 2lb less than label.csv

Apple Oregon, protective of Western apples	0.63	five 3-lb applications,
14 days interval	4-15, 29, 5-11, 25, 6-4	OR apple springtime regional
PCA.csv

OR, one thinning application; protective of Western apples	0.63	single
3-lb application , aerial	June 15	OR apple thinning regional PCA.csv

OR, one thinning application at 2lb (BEAD value for ~90% use),
protective of Western apples	0.63	single 2-lb application , aerial	June
15	OR apple thinning regional PCA 2 lb less than label.csv

FL Strawberry with the regional PCA, protective of entire USA	0.38	five
2-lb applications, ground spray	1-3, 10, 17, 24, 2-1	FL strawberry
regional PCA.csv

CA strawberry, representative of California 	0.56	five 2-lb
applications, ground spray	3-3, 10, 17, 24, 31	CA strawberry regional
PCA.csv (used CA lettuce scenario as surrogate)



Chemical Input Parameters for Model Simulations 

Table 2 summarizes the chemical input parameters which were selected in
accordance with guidance (EFED, 2002) for use in PRZM/EXAMS.  For the
most part, these parameters are the same as those in the previous
assessment (see D288455), with the most significant exceptions being the
estimate for aquatic metabolic degradation and the foliar washoff rate. 


In the previous assessment, the aerobic aquatic metabolism half life
input parameter was 29.6 days and was based on an indirect relationship
to soil degradation, which according to EFED guidance (EFED, 2002) is to
be used if data are lacking (as in the previous case).  In the period
since that assessment, the registrant has submitted new studies (MRID
46580701, 46580702) to directly address aquatic aerobic metabolism, and
those studies show that carbaryl is stable to metabolic degradation in
aqueous environments.  This newer information is reflected in Table 2.

	Also, in the previous assessment a foliar washoff rate was calculated
using data from open literature.  Those calculation procedures are
described in D288376.  However, a review of this procedure revealed that
the calculated values in D288376 are not the appropriate parameters for
use in PRZM, and thus the procedure described in D288376 should not be
used.  Therefore, in this assessment the default value for foliar
extraction were used, as specified by EFED guidance (EFED, 2002).

Table 2. Carbaryl Parmeter Inputs to PRZM/EXAMS	

Parameter	Value	Source	Comments

Molecular Wt	201.22 g/mol



Solubility	32 mg/L



Vapor Pressure	1.36 x 10-6 torr at 25 C	D26726, Ferrira and Seiber
(1981) as appears in D267276

	Henry’s law Constant	1.28 x 10 -8 atm/ m3/mol	Suntio, et al. (1988)
as appears in D288455 and  D267276

	Hydrolysis Half life 	12 days at pH = 7	MRID 00163847

44759301; D288455

	Koc	198 mL/g	D288455

	Aerobic Aquatic half life	Insignificant with respect to hydrolysis	MRID
46580701, 46580702	New submission. On the order of 100 days, but much
unextracted material, and hydrolysis likely source of degradation

Aqueous photolysis	21 days	D288455

	Aerobic Soil Metabolism	12 days	D288455	Single study. 3X the single
value

Foliar degradation	3.71 days (0.187 per day)	D288455

	Foliar extraction	0.5 per cm	EFED, 2002	default



Model Results 

Concentrations resulting from model simulations are given in Table 3. 
All concentrations were adjusted by a percent cropped area (PCA) factor
(in this case regional rather than nation PCAs), as based on OPP
guidance (OPP, 2000) and as described earlier in Table 1. In addition to
the point estimates for drinking water exposure described above.  The
daily time series of concentrations have also been provided to HED in a
previous email (D337058).  The time series of estimates are intended for
use in refined HED dietary assessments.

The quality of the analysis is directly related to the quality of the
input parameters.  In general, the fate data for carbaryl are good.  The
paucity of soil and aquatic metabolism data is the main limitation of
the data set.  Because metabolism values are set to the upper 90%
confidence limit of the mean, the simulated concentrations will be
conservative estimates.  Inputs regarding application dates and rates
add additional uncertainty.  To address application rate uncertainty,
EFED used the maximum allowable rate for most cases, but also supplied
results based on BEAD-estimated “typical” rates in some cases. 
Application dates are known to have significant impacts on results and
uncertainty regarding dates remains significant in this assessment.  The
dates used in this assessment were based on discussions with BEAD. 

Table 3.  1-in-10 year surface water concentrations from PRZM/EXAMS
estimated using regional PCAs

Simulation Description	Acute	Chronic	Cancer

Georgia peach, Aerial Foliar Application; 3 in season at 3 lb and 1
dormant at 3 lb (Note that last application is 2 lb short of allowable
21	1.8	1.5

Georgia Peach without the dormant spray.  Aerial Foliar Application; 3
in season at 3 lb	21	1.4	1.2

CA peach with dormant spray. ground Foliar Application; 3 in season at 3
lb and 1 dormant at 3 lb (Note that last application is 1 lb in excess
of max seasonal)	21	2.0	1.3

CA peach without dormant spray.  Aerial Foliar Application; 3 in season
at 3 lb	21	1.8	1.0

FL citrus. 5 lb, 3 times, Aerial	66	4.1	2.8

CA citrus. 5 lb, 3 times, Aerial	35	2.8	2.2

CA citrus 12 lb. single 12 lb application. Aerial	44	3.4	2.5

CA grape. 2 lb 5 applications, 7 day interval. Aerial	30	2.7	2.7

Pennsylvania apple thinning, Single 3 lb app	18	1.0	0.54

Pennsylvania apple, 5 applications of 3 lb, 14-day interval	108	8.1	4.8

OR apple springtime 3 lb 5 times, 14 day interval	27	3.6	3.0

Thinning only, Single 3 lb	13.6	0.81	0.61

FL strawberry, Ground spray 2 lb 5 times, 7 day interval	64	4.5	3.6

CA strawberry Ground spray 2 lb 5 times, 7 day interval	58	3.7	1.7



Effects of Drinking Water Treatment

Some evidence (Whittaker et al., 1982) that conventional drinking water
treatment—that is, coagulation, flocculation and settling—reduces
carbaryl concentration up to 43%.  This is based on a study of
wastewater containing carbaryl treated with alum at 100 mg L-1 and 1 mg
L-1 of anionic polymer.  In addition, ozone has been shown to be 99%
effective at removing carbaryl from water (Shevchenko et al.,1982) and
removes it from water at a rate too fast to measure (Mason et al.,
1990); however, ozonation is infrequently used in public drinking water
in the United States.  Evidence suggests that chlorine and hypochlorite
may be ineffective at degrading carbaryl (Mason et al., 1990).  Based on
the hydrolysis data, softening would be expected to substantially reduce
carbaryl concentrations (via alkaline hydrolysis), as softening raises
the pH of the water as high as 11.  Softening is used in areas where
hard water is problematic. The Office of Pesticide Programs currently
does not have sufficient information to account for locations where
water softening processes are used at public drinking water treatment
facilities, and thus cannot systematically use this information in to
refine drinking water concentrations.

Monitoring: Surface Water Update

	EFED finalized the Environmental Fate and Ecological Risk assessment
for carbaryl in 2003 (USEPA 2003).  That assessment contained an aquatic
exposure assessment (including drinking water) as well as an ecological
risk assessment.  The Carbaryl Interim Reregistration Eligibility
Decision (IRED) was published for comment in 2004, and EFED completed a
response to those comments in 2005 (USEPA 2005).   Since that time, EFED
has obtained additional carbaryl monitoring data and summarizes it
below. Because an assessment of monitoring data was the basis of
exposure estimates from urban uses of carbaryl, special focus has been
given to updating those data sources.  

NAWQA tc \l3 "NAWQA 

e mean concentration was 0.11 μg/L, with a standard deviation of   0.43
μg/L.  In a summary of pesticide occurrence and concentrations for 40
NAWQA stream sites with primarily agricultural basins, carbaryl was
detected in 11% of the samples (N = 1,001) with a maximum concentration
of 1.5 µg/L.  

In a report released in 2006 summarizing pesticide results from NAWQA
from 1992 – 2001 (USGS 2006), carbaryl is listed as one of the 14 most
frequently detected pesticide compounds in surface water and one of the
3 most frequently detected insecticides.  Carbaryl was detected in 50%
of urban samples over this time period.  The majority of carbaryl
concentrations detected were low with 35% of the urban samples (and 70%
of the detections) less than 0.1 µg/L.  Detection frequencies in
agricultural and mixed land use streams were lower (10% and 17%,
respectively), and concentrations associated with those land uses were
almost all less than 0.1 µg/L. 

ociated with agricultural uses (33.5 μg/L), is unusual but not outside
of the range predicted by modeling.

Pilot Reservoir Monitoring Study  tc \l3 "Pilot Reservoir Monitoring
Study 

In the 2003 assessment, EFED summarized this study, which was conducted
by the USGS and EPA to gain better understanding of pesticide behavior
in reservoirs.  Twelve reservoirs were sampled across the country with
an emphasis on watersheds that were expected to be vulnerable to
pesticide contamination, but with no particular emphasis on any
particular pesticide.  Samples were collected at the drinking water
intake (312 total samples), the reservoir outflow (73 samples) and
finished water from the water supply (225 samples). Not all sites had
samples collected at the reservoir outflow. Carbaryl was detected at 5
sites , 4 at the intake, 2 at the outflow, and two in finished.  In
addition, 3 samples, all from intakes, contained 1-naphthol.  The
highest carbaryl concentration detected was 0.043 μg L-1 at Blue Marsh
Reservoir in Pennsylvania while the carbaryl degradate, 1-naphthol, was
found at 0.228 μg L-1 at Higginsville, Missouri. It is worth noting
that 1-naphthol has other sources in the environment, including some
which are natural. It is also worth noting that, as with the NAWQA data
which uses similar analytical protocols, all detections of carbaryl were
qualified due to high background variability of the measurements.  These
data are consistent with other data which show widespread low-level
contamination of carbaryl in surface water. 

Registrant Drinking Water Monitoring Study tc \l3 "Registrant Drinking
Water Monitoring Study  

In 2003, EFED reviewed the final report from a study voluntarily
conducted by Aventis for carbaryl (USEPA 2003b).  A summary of this
study was included in the 2003 EFED assessment.  The study was designed
with the purpose of providing the Agency data useful in refining the
drinking water exposure estimates for carbaryl.  The study provides data
useful for characterizing the overall exposure to carbaryl, but it
cannot be used to estimate exposure quantitatively due to drawbacks
which include the following:

The study provided insufficient supporting data on non-agricultural
sales and national-scale non-agricultural carbaryl usage to determine
the relative vulnerability of the systems  representing "home and
garden" usage effects.  

The study design was insufficient to prove that sites sampled represent
the “the highest probable risk of human exposure to carbaryl in
surface water in each state”.  

The monitoring interval (one week to two weeks) is unlikely to capture
peak concentrations necessary for estimating acute dietary risk, given
the variable nature of the exposure. 

Concentrations measured at sites sampled were low (roughly 2 to 31 ppt)
in source drinking water (pre-treatment) and generally lower in treated
drinking water.  Interestingly, the highest concentrations were found in
finished drinking water not in source drinking water (181 ppt).

USGS-EPA Mini-pilot monitoring program

In September 2000, an Inter-governmental Steering Committee and two
workgroups were formed to advise and collaborate on further development
of regression models and other supporting activities.  The initial focus
of the Intergovernmental FQPA Drinking Water group was to design and
implement monitoring programs in support of the regression model
development efforts.  The purpose of the monitoring was to resolve
technical and logistical issues for development of a larger monitoring
program.

Phase I of the project sampled water-supply intakes for 5 community
water systems (CWS) that withdraw from free-flowing surface-water bodies
approximately 90 times over the course of a year with sampling occurring
most frequently during the primary pesticide application and pesticide
runoff periods.  The sites (in ND, GA, NC, OR, PA) were selected to
represent a variety of cropping regions and pesticide compounds in areas
dependent on precipitation-based agriculture.  Samples were shipped
overnight in iced coolers the USGS National Water-Quality Laboratory in
Denver Co. for analysis of residual pesticide concentrations. 
Importantly, monitoring locations were not selected to represent use of
any specific pesticide, thus the significance of detection frequencies
and levels of detection cannot be broadly interpreted.  Low levels of
carbaryl have been found (no sample greater than 1 μg/L) at several of
these locations.   

Surface Water Monitoring Program for Pesticides in Salmonid-Bearing
Streams tc \l3 "Registrant Drinking Water Monitoring Study  (Burke et
al., 2006)

The Washington State Department of Agriculture and the Washington State
Department of Ecology conducted a multi-year monitoring study to
characterize pesticide concentrations in selected salmonid-bearing
streams during the typical pesticide-use season.  Burke et al. (2006)
report results from the first three years of the study (2003-2005) in an
urban drainage represented by Thornton Creek in the Cedar-Sammamish
watershed, and in agricultural drainages represented by: Marion Drain,
Sulphur Creek Wasteway, and Spring Creek in the Lower Yakima watershed. 
From 2003 through 2005, 453 samples were collected from urban and
agricultural sites. A total of 51 pesticides and degradate compounds
were detected in the urban and agricultural drainages and ten of these,
including carbaryl, were above assessment criteria cited in the report
(Table 4). Ninety-six percent of carbaryl detections were below these
criteria. 

Table 4. Washington State Criteria for Carbaryl 

subject	species	Acute LC50 (ppb)	NOEC

(ppb)

Fish	Rainbow Trout	1200	600

Fish	Chinook	2400	120

invertebrate	Daphnia magna	5.6	1.5



Thornton Creek drains a 12.1-square-mile watershed before flowing into
Lake Washington and ultimately Puget Sound. The watershed has 75,000 to
100,000 residents, thousands of daily commuters, and encompasses
single-family units, multi-family apartment complexes, schools, parks,
Interstate 5, a shopping mall, and a golf course (Thornton Creek
Watershed Characterization Report, 2000; U.S. Census Bureau, 2000). 
Impervious surfaces cover approximately 50% of the watershed. 

The Lower Yakima watershed, an agricultural basin, is represented in
monitoring from the Marion Drain, Sulphur Creek Wasteway, and Spring
Creek encompassing a total area of 216,168 acres, 47% of which is
cropped.  The most common crops are grapes (18% of cropped area), apples
(14%), and wheat (13%).  Other crops include hops, mint, asparagus,
cherry, potatoes, pears, and nectarines.   The Yakima and Naches rivers
supply irrigation water to approximately 339,000 acres of cropland in
the Lower Yakima valley. Most of the water in the Yakima River system is
managed by the U.S. Bureau of Reclamation. Water distribution from
canals to farms is primarily managed by irrigation districts.  

μg/L.   Carbaryl was detected in samples collected in the agricultural
Lower Yakima watershed.  In 2003 carbaryl was detected in the Marion
drain at 0.14 ppb (in 1 of 18 samples); carbaryl was not detected in
2004 or 2005 at this location.  Carbaryl was detected in 2004 in the
Sulfur Creek Wasteway at 0.16 ppb (in 1 of 31 samples); carbaryl was not
detected in 2003 or 2005 at this location. On June 18, 2003, carbaryl
was detected at a concentration of 10 μg/L in the upper Spring Creek
station, and 1.7 μg/L at the mid-Spring Creek station.

This report also summarized “historical” data for these two areas,
collected largely by the USGS.  They observed that since monitoring of
Thornton Creek began in 1996, pesticides used have changed over the
years, including the phase out of diazinon in 2004.  They concluded that
carbaryl detection rates have risen slightly over the years, and that
the magnitude of detections has not approached endangered species or
invertebrate toxicological criteria used.  Reported detection
frequencies were substantially higher in the USGS studies (100% to 43%),
largely due to their more sensitive analytical methods. Peak
concentrations measured by the USGS in Thornton Creek were: 4.78 μg/L
(1999); 1.89 μg/L (2002); 0.212 μg/L (2003); 0.142 μg/L (2004).

Environmental Monitoring of Carbaryl Applied in Urban Areas to control
the Glassy-Winged Sharpshooter in California  tc \l3 "Registrant
Drinking Water Monitoring Study (Walters et al., 2003)

The Environmental Monitoring Branch of the Department of Pesticide
Regulation (DPR) 

Conducted monitoring of carbaryl and other selected insecticides to
provide information on concentrations in various environmental media,
including surface water, resulting from ground applications to control
glassy-winged sharpshooter (Homalodisca coagulata) infestations in
California.  Carbaryl insecticide was applied to plants in urban areas
to control a serious insect pest, the glassy-winged sharpshooter, newly
introduced in California. To assure there were no adverse impacts to
human health and the environment from the carbaryl applications,
carbaryl was monitored in tank mixtures, air, surface water, foliage and
backyard fruits and vegetables.  DPR reported:

 “There were three detections of carbaryl in surface water near
application sites: 0.125 ppb (parts per billion) from a water treatment
basin; 6.94 ppb from a gold fish pond; and 1737 ppb in a rain runoff
sample collected from a drain adjacent to a sprayed site.” 

DPR concluded that results from the five urban areas showed there were
no significant human exposures or impacts on the environment.

Trends in carbaryl concentrations in urban areas

OPP’s 2003 drinking water assessment relied upon monitoring data in
urban areas to characterize the impact of carbaryl use on water quality
in urban areas.  This section discusses trends that have been observed
in carbaryl concentrations in urban areas since the announcement of the
phase out of two other insecticides widely used in urban
areas—diazinon and chloryrifos.  There was speculation that with
diazinon and chlorpyrifos no longer available, homeowners would use more
carbaryl, and that carbaryl concentrations in streams in urban areas
would increase.  The residential use of liquid broadcast formulations of
carbaryl on turf was restricted in 2005 to areas less of than 1000 ft2. 
Risk managers concluded that this restriction may help reduce potential
runoff of carbaryl in urban environments; however the labels for
granular formulations were not modified.  How the carbaryl label changes
impact the extent of the area treated and how that would affect carbaryl
concentrations in urban streams is unclear.

The timing of the phase out decisions is important in understanding
trends in pesticide concentrations in the environment.  On one hand, the
date of the announcement of a phase out initiates a multi-year process
stipulating a “stop sale” date and some additional time for
pesticide applicators to use products they have purchased.  On the other
hand, the market and pesticide applicators may react quickly to such an
announcement.  EPA announced the agreement to phase out and eliminate
all residential uses of the insecticide diazinon on December 5, 2000. 
The terms of the four-year phase-out stipulated that technical
registrants reduce the amount of diazinon produced by 50% or more by
2003.  As of December 31, 2004, it was unlawful to sell diazinon
outdoor, non-agricultural products in the United States (the “stop
sale” date for all outdoor diazinon home, lawn, and garden products). 
According to existing stocks provisions, it remained legal for consumers
to use products bearing labeling that allowed these uses after that
date.  On June 8, 2000, EPA announced an agreement with pesticide
registrants to phase out and cancel nearly all indoor and outdoor
residential uses of chlorpyrifos within 18 months, effectively
eliminating use by homeowners.  Residential uses were restricted
certified, professional, or agricultural applicators.  Those uses that
posed the most immediate risks to children (home lawn, indoor crack and
crevice treatments, uses in schools, parks) were canceled first, ending
as of 12/31/2001.   The last remaining residential use, products used
for pre-construction termite control, was cancelled as of December 31,
2005.  

Based on the studies described below, the longer term impact of the
phase out on carbaryl concentrations in urban areas is not clear and may
vary by region due to differences in pest pressure and perhaps marketing
of different products.  Unlike the clear downward trend in
concentrations observed within a few years for the phased-out compounds
(diazinon and chlorpyrfos), the environmental outcome of this
registration decision may take longer to discern.  However, based on
these available data, there does not appear to be a steady upward trend
to carbaryl concentrations in urban areas following the phase-out of
diazinon and chlorpyrifos.

Quality of Stream water in the Puget Sound Basin—A Decade of Study and
Beyond (Embrey, S. and P. Moran, 2004) 

 μg /L.  The figure below (from the poster) shows a decrease in
diazinon detections and concentrations following the announcement of the
phase out in 2000.  There is also an increase in carbaryl detection
frequency and concentrations in the years following the announcement of
the phase out of diazinon.  The data also appear to show that carbaryl
concentrations began to decline toward the end of the study period in
2005, rarely exceeding 0.1 μg /L. 

Temporal Changes in Surface-water Insecticide Concentrations after the
phase out of diazinon and chlorpyrifos (Phillips et al., 2007)

A recently published paper by USGS scientists evaluated trends in
concentrations of carbaryl in the Northeast and Mid-West after the phase
out of diazinon and chlorpyrifos, insecticides in urban environments. 
They compared concentrations of these pesticides in samples collected
from 20 streams by the USGS between 1992 and 2004 and determined that 16
of these streams met criteria established for assessing trends of
carbaryl in urban streams.  Sample collection and analysis followed
standard NAWQA procedures for collection and analysis. Using seasonal
step trend analysis they evaluated the data to identify trends in
summer, fall/winter, and winter/spring.  Results showed a decrease in
diazinon and chlorpyrifos concentrations following the announcement of
the phase out in 2000.  In contrast, trends were not observed in
carbaryl concentrations in these regions during the same time period.

Summary

This memo provided the results from carbaryl surface water modeling as
well as an updated review of monitoring data was reviewed to
characterize the potential for carbaryl to contaminate surface drinking
water.  The modeling effort was initiated different than in the previous
assessment due to the availability of new data and the need of HED to
have a more refined drinking water assessment. The update of the
monitoring data was necessary due to the time that has elapsed since the
previous assessment.

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萑ː葠ː摧栱/ጀries of concentrations as well as point estimates of
concentration were generated from PRZM/EXAMS models and were provided to
HED.  These estimates incorporated regional PCA’s and therefore it is
important to consider the spatial relevance of each of the simulations,
as was given in Table 1.  The point estimates indicated acute
concentrations that ranged from 13 to 108 ppb.   In addition point
estimates, complete time series were also provided (also with regional
PCA) to HED to use in refined assessments.  

 Monitoring data reviewed for this update depict carbaryl as having
relatively high frequencies of detection.  This is consistent with the
2003 Environmental Fate and Ecological Risk assessment for carbaryl
which concluded that carbaryl is widely detected in non-targeted and
targeted monitoring studies.  Carbaryl is not very persistent in most
surface water conditions suggesting that the wide spread occurrence is a
result of its extensive use in a variety of applications.  Peak
concentrations from NAWQA data were as high as 33.5 μg/L in an
agricultural area .  In urban areas, detections are more frequent, and
the peak concentration was as high as 16.5 μg/L . For all areas,
detected concentrations were mostly low (less than 0.1 μg/L).  In
considering these data, it should be understood that nontargeted studies
such as NAWQA do not guarantee that  data are collected from areas of
the most benefit for exposure assessments such as those coinciding with
vulnerable application areas and times.  Additionally, these studies
typically do not include low-order streams or lentic (e.g. ponds and
wetlands) environments.  

References

Burke, C., Anderson P, Dugger, D., Cowles, J., 2006, Surface Water
Monitoring Program for Pesticides in Salmonid-Bearing Streams,
2003-2005.  A Cooperative Study by the Washington State Departments of
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Response to Phase 6 Comments on the Interim Reregistration Eligibility
Decision (IRED) Document for Carbaryl, D295072, 12/30/2005 

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