![](media/image1.png){width="1.3541666666666667in"
height="1.3541666666666667in"} **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 **Regional   **Application type**   **App     **Time Series
  Relevance**       PCA**                               Dates**   File Name**

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  CA strawberry,    0.56         five 2-lb              3-3, 10,  CA strawberry
  representative of              applications, ground   17, 24,   regional PCA.csv
  California                     spray                  31        (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     | 201.22      |                    |                |
| Wt**            | g/mol       |                    |                |
+-----------------+-------------+--------------------+----------------+
| **Solubility**  | 32 mg/L     |                    |                |
+-----------------+-------------+--------------------+----------------+
| **Vapor         | 1.36 x 10-6 | D26726, Ferrira    |                |
| Pressure**      | torr at 25  | and Seiber (1981)  |                |
|                 | C           | as appears in      |                |
|                 |             | D267276            |                |
+-----------------+-------------+--------------------+----------------+
| **Henry's law   | 1.28 x 10   | Suntio, *et al.*   |                |
| Constant**      | -8 atm/     | (1988) as appears  |                |
|                 | m3/mol      | in D288455 and     |                |
|                 |             | D267276            |                |
+-----------------+-------------+--------------------+----------------+
| **Hydrolysis    | 12 days at  | MRID 00163847      |                |
| Half life**     | pH = 7      |                    |                |
|                 |             | 44759301; D288455  |                |
+-----------------+-------------+--------------------+----------------+
| **Koc**         | 198 mL/g    | D288455            |                |
+-----------------+-------------+--------------------+----------------+
| **Aerobic       | In          | MRID 46580701,     | New            |
| Aquatic half    | significant | 46580702           | submission. On |
| life**          | with        |                    | the order of   |
|                 | respect to  |                    | 100 days, but  |
|                 | hydrolysis  |                    | much           |
|                 |             |                    | unextracted    |
|                 |             |                    | material, and  |
|                 |             |                    | hydrolysis     |
|                 |             |                    | likely source  |
|                 |             |                    | of degradation |
+-----------------+-------------+--------------------+----------------+
| **Aqueous       | 21 days     | D288455            |                |
| photolysis**    |             |                    |                |
+-----------------+-------------+--------------------+----------------+
| **Aerobic Soil  | 12 days     | D288455            | Single study.  |
| Metabolism**    |             |                    | 3X the single  |
|                 |             |                    | value          |
+-----------------+-------------+--------------------+----------------+
| **Foliar        | 3.71 days   | D288455            |                |
| degradation**   | (0.187 per  |                    |                |
|                 | day)        |                    |                |
+-----------------+-------------+--------------------+----------------+
| **Foliar        | 0.5 per cm  | EFED, 2002         | default        |
| extraction**    |             |                    |                |
+-----------------+-------------+--------------------+----------------+

## 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       21          1.8           1.5
  season at 3 lb and 1 dormant at 3 lb (Note that last                           
  application is 2 lb short of allowable                                         

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

  CA peach with dormant spray. ground Foliar           21          2.0           1.3
  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)                                                                  

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

  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.       30          2.7           2.7
  Aerial                                                                         

  Pennsylvania apple thinning, Single 3 lb app         18          1.0           0.54

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

  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      64          4.5           3.6
  interval                                                                       

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

## 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

In 2003, EFED reported that carbaryl was the second most widely detected
insecticide in surface water in the U. S. Geological Survey's (USGS)
National Water Quality Assessment (NAWQA) monitoring program
([http://water.usgs.gov/nawqa/nawqa_home.html)]{.underline}. Although
this monitoring does not target specific chemicals, carbaryl was
detected in 46% of 36 NAWQA study units from 1991 - 1998. Much of the
data in the NAWQA database are amended with an "E" qualifier to indicate
uncertainty found in the analysis. Typically this uncertainty is because
the concentration is beyond the limit of the calibration curve for the
analytical instrumentation; thus a high reported concentration is in
fact *high;* however, it is a less precise estimate than those
concentration that lie within the calibration curve. In the 2003
assessment of NAQWA data, 1,067 (21%) out of 5,198 surface water samples
had detections greater than the minimum detectable limit. The maximum
reported concentration was 5.5 µg/L across all sites. For samples with
positive detections the 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.

For this update, EFED searched NAWQA carbaryl data in the USGS data
warehouse from 1999 -- 2005. A total of 11,732 samples were collected in
that timeframe and analyzed for carbaryl with 29% of all samples
reporting a detection greater than the minimum detection limit. For
samples with detections, the mean concentration reported was 0.058 μg/L.
The maximum concentration reported was 33.5 μg/L at a location
associated with agricultural land (mean in agricultural areas: 0.094
μg/L). The detection frequency associated with agricultural uses was
lower (19%) than that associated with urban uses (50%). The highest
concentration reported in urban areas was 16 μg/L in Denver, CO
(concentration confirmed by Bret Bruce USGS South Platte). The higher
detection frequency in urban streams (versus agricultural or mixed land
uses) is consistent with data summarized in the 2003 assessment. The
concentrations detected in urban streams (mostly low concentrations, a
few detections in the multiple ppb range), is also consistent with
earlier data. The relatively high concentration reported associated with
agricultural uses (33.5 μg/L), is unusual but not outside of the range
predicted by modeling.

### 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 

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 (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*.*

From 2003-2005, 78 sampling events occurred in the urban Thornton Creek
watershed. Carbaryl was not detected in any sample above the practical
quantitation limit, or PQL, of 0.19 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 (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
ft^2^. 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) 

In a poster, Embrey and Moran (2004), summarized data collected by the
NAWQA program over a decade in the Puget Sound Basin and included data
on diazinon and carbaryl collected in Thornton Creek. During the first
cycle, the insecticide diazinon was often detected in samples from
Thornton Creek; some samples were at concentrations greater than 0.1 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.

![](media/image2.wmf){width="4.173611111111111in"
height="2.9118055555555555in"}

### 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.

In the modeling effort, complete time series 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
Ecology and Agriculture, <http://www.ecy.wa.gov/pubs/0603036.pdf>

D288376. Jones. R. David. 2003. *Review of "Estimation of the Foliar
Dissipation Half-life of Carbaryl" and Re-analysis of the Foliar
Degradation Rate*. EPA Internal Memorandum to Tony Britten.

EFED 2002. Pesticide Root Zone Model (PRZM) Field and Orchard Crop
Scenarios: Standard Procedures for Conducting Quality Control and
Quality Assurance, Environmental Fate and Effects Division/OPP/OPPTS, US
EPA.

Embrey, S. and P. Moran, 2006, *Quality of Stream water in the Puget
Sound Basin---A Decade of Study and Beyond,*
wa.**water**.usgs.gov/projects/pugt/data/4-2006-poster.pdf

Ferreira, G.A. and J.N. Seiber, 1981. *J. Agric. Food Chem*.,
**29**:93-99

Mason, Y, E. Chosen, and C. Rav-Acha. 1990. Carbamate Insecticides
Removal from Water by Chlorination and Ozonation. *Water Res*.
24(1):11-21

Suntio, L.R., et al., 1988. *Rev. Environ. Contam. Toxicol.*,
**103**:1-59

Shevchenko, M. A., P. N. Taran, and P. V. Marchenko., 1982. Modern
methods for purifying water from pesticides. *Soviet Journal of Water
Chemistry and Technology. 4(4):53-71*

Walters, J., Goh, K.S., Feng, H., Hernandez, J., and J. White, 2003,
*Environmental Monitoring of Carbaryl Applied in Urban Areas to control
the Glassy-Winged Sharpshooter, Environmental Monitoring and Assessment,
Vol. 82, No. 3, March 2003, pp. 265-280 (16)*

Whittaker, K. F., J. C. Nye, R. F. Wukasch, R. J. Squires, A. C. York,
H. A. Kazimier. 1982. *Collection and treatment of wastewater generated
by pesticide application*. EPA Report No. 600/2-82-028

USGS 2006, *Pesticides in the Nation's Streams and Ground Water, 1992 --
2001*, Circular 1291

USEPA, 2003a, *Environmental Fate and Ecological Risk assessment for the
Re-Registration of Carbaryl* , D285826, 3/31/2003

USEPA, 2003b, *Final Report of Carbaryl EEC's for Drinking Water,
additional simulations,* D288455, 6/30/2003

USEPA, 2005, *Response to Phase 6 Comments on the Interim Reregistration
Eligibility Decision (IRED) Document for Carbaryl,* D295072, 12/30/2005