Document ID: EPA-HQ-OPP-2005-0163-0202
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2007-10-12T04:00Z

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

	OFFICE OF

PREVENTION, PESTICIDES

AND TOXIC SUBSTANCES

									PC Code: 	098301

									DP Barcode:	299866

MEMORANDUM							DATE: July 24, 2007

SUBJECT: 	Review of “A Retrospective Groundwater Monitoring Study for
Aldicarb and Its Metabolites in the Southeastern United States (MRID
467937-06); Mississippi Delta (MRID 467937-05); Texas (MRID 467937-04);
California (MRID 467937-03);and Pacific Northwest (MRID 467937-02)

TO:		Sherrie Kinard, PM

Robert McNally, Branch Chief

		Special Review and Reregistration Division (7508P)

		

FROM: 	Nelson Thurman, Senior Environmental Scientist

Environmental Risk Branch 2

		Environmental Fate and Effects Division (7507P)	

		

THROUGH:	Dana Spatz, Acting Branch Chief	

		Environmental Risk Branch 2

		Environmental Fate and Effects Division (7507C)	

Bayer CropScience recently submitted retrospective groundwater
monitoring studies for aldicarb and its metabolites for the southeastern
US, Mississippi Delta, Pacific Northwest, California, and Texas.
Although this study was unsolicited by EPA, it provides valuable data in
support of the drinking water exposure assessments for both aldicarb and
the N-methyl carbamate cumulative assessments. Results have been
incorporated into those assessments.

In addition to reported detections of aldicarb residues (the parent plus
sulfone and sulfoxide degradates), the study included a substantial
amount of supporting information on aldicarb use and well, soil,
environmental, and hydrologic conditions that would influence the
transport of aldicarb to ground water.

The attached report summarizes EPA’s review of Bayer’s retrospective
ground water monitoring study. 

REVIEW OF 2005 RETROSPECTIVE GROUND WATER MONITORING STUDY FOR ALDICARB

Study References:

Jones, R.L., and T.S. Ramanarayanan. 2006. TEMIK® brand 15G Aldicarb
Pesticida: Summary of Five Retrospective Ground Water Monitoring Studies
conducted for Aldicarb and Its Metabolites in the Pacific Northwest,
California, Texas, Mississippi Delta and the Southeast Regions of the
United States in 2005. Bayer CropScience Study No. RAAVY010. MRID
487937-01.

Lee, R.E., R.L. Jones, D.R. Wyatt, and U.B. Handihalli. 2006. A
Retrospective Groundwater Monitoring Study for Aldicarb and Its
Metabolites in the Southeastern United States. Bayer CropScience Study
No. RAAVY009. MRID 467937-06.

Wyatt, D.R., R.L. Jones, U.B. Handihalli, and R.E. Lee. 2006. A
Retrospective Groundwater Monitoring Study for Aldicarb and Its
Metabolites in Mississippi Delta Region. Bayer CropScience Study No.
RAAVY008. MRID 467937-05.

Mosier, D.G., R.L. Jones, U.B. Handihalli, and R.E. Lee. 2006. A
Retrospective Groundwater Monitoring Study for Aldicarb and Its
Metabolites in Texas. Bayer CropScience Study No. RAAVY007. MRID
467937-04.

Lenz, M, R.L. Jones, D.R. Wyatt, U.B. Handihalli, and R.E. Lee. 2006. A
Retrospective Groundwater Monitoring Study for Aldicarb and Its
Metabolites in California. Bayer CropScience Study No. RAAVY006. MRID
467937-03.

Freeseman, P.I., R.L. Jones, R.E. Lee, U.B. Handihalli, and D.R. Wyatt.
2006. A Retrospective Groundwater Monitoring Study for Aldicarb and Its
Metabolites in the Pacific Northwest. Bayer CropScience Study No.
RAAVY005. MRID 467937-02.

Reviewed By:	Nelson Thurman, Senior Environmental Scientist

Environmental Risk Branch 2

			Environmental Fate and Effects Division (7507P)	

			USEPA Office of Pesticide Programs

Secondary 

Review By:		Dana Spatz, Acting Branch Chief, ERB2

Date:			July 5, 2007

SUMMARY

Bayer CropScience conducted a retrospective ground water monitoring
study to look for residues of aldicarb and its sulfoxide and sulfone
metabolites in potable water from private wells in aldicarb use areas.
This study monitored 1,673 drinking water wells and collected
information on ground-water depth, well depth, casing depth, well type
and age, soil types, recent aldicarb use history, crops, and distance of
the well from the treated field. The study provides useful information
on measured concentrations of aldicarb residues in drinking water wells
in selected areas of the United States with recent/current aldicarb use.
The study sampled 1,673 drinking water wells in five regions of the
country: the Southeastern US (800 wells), the Mississippi Delta (169
wells), the Pacific Northwest (303 wells), Texas (201 wells), and
California (200 wells).  

The study found that

Aldicarb residues – predominantly the sulfoxide and sulfone
metabolites – were detected in 10 percent of the wells sampled (160
out of 1,673), with the greatest frequencies of detections in the
Southeastern US (16%, with a maximum detect of 2.9 ug/L) and the
Mississippi Delta (9%, with a maximum detect of 2.6 ug/L) regions.
Because the single samples represent a snapshot in time, the Agency
assumed that the measured concentrations reflected a median
concentration for that particular well. 

Aldicarb detections showed a regional pattern, with this highest
frequency of detects in Alabama (22%) and South Carolina (21%) in the
Southeast region and southeastern Missouri/northeastern Arkansas (23%)
in the Mississippi Delta region. 

Frequency and magnitudes of detection for aldicarb residues were
generally greater for wells located within 300 feet of a field (~10% of
wells had detections); aldicarb residues were detected in 4-6% of wells
located >300 feet from the field, although detections were < 1ug/L.
Because the existing label has well setback requirements of 300 feet for
vulnerable soils, the Agency assumed that the monitoring data for those
wells that meet the setback criteria reflect aldicarb applications no
closer than 300 feet from the well.

Frequency and magnitudes of detection for aldicarb residues also were
generally greater where the reported ground water was closer to the
surface (23% detects for groundwater at <25 feet; 12% for groundwater at
25-50 feet), although residues were detected in 9% of wells where the
depth to groundwater was not known or not reported, with maximum detects
of up to 2.66 ug/L. Aldicarb residues were detected in 24-30% of wells
with reported well depths of <100 feet. However, detects of up to 2.66
ug/L were reported for deeper or unknown well depths.

A comparison of wells located near fields with restricted soils (as
identified in the TEMIK® 15G label) to those where the surrounding
fields contained no restricted soils showed that, while the frequency of
aldicarb detections was greater for wells near restricted soil types,
the magnitude of aldicarb residues was greater for wells with no
restricted soil types. 

The study pointed to some potential issues that pertain to the existing
label restrictions:

While depth to ground water is the key criteria for determining whether
well setbacks should be applied in certain states, that depth was
unknown or unreported for 42% of the wells sampled in the study. This
suggests that a substantial portion of aldicarb users do not know
whether the label restrictions even apply to their fields.

Although the Norfolk soil series is listed as a restricted soil type in
North Carolina, it is not listed in adjacent states. 

No restricted soil types are listed for Arkansas. However, aldicarb
detections in a number of wells in northeastern Arkansas (along with
southeastern Missouri) indicate that restricted soil types should be
considered for that state. A number of restricted soils in adjacent
states are also found in Arkansas.

BACKGROUND

Monitoring data provide a valuable check on exposures estimates from
models, which are intended to represent the upper end of potential
exposure. Comparison of model and monitoring results are most relevant
when monitoring sites are selected to be similarly representative of the
upper end of potential exposure, or where sufficient ancillary data are
provided to put the monitoring results in context to the relative
vulnerability within the use area. 

The registrant for aldicarb (Bayer CropScience) voluntarily conducted
this retrospective groundwater monitoring study in 2005 in response to
EPA’s preliminary risk assessment for aldicarb. Bayer provided no
protocol for review by the Agency prior to study initiation. In
preliminary assessments dating 2005 and earlier, EPA used available
ground-water monitoring data for its drinking water exposure assessment
while noting that current monitoring data is scarce. 

In 2005, EPA used the Pesticide Root Zone Model (PRZM) to estimate
concentrations of N-methyl carbamate residues (including aldicarb and
its sulfoxide and sulfone metabolites) in shallow, private drinking
water wells (USEPA OPP, 2005a, 2005b). The Agency subsequently used the
same methods to estimate drinking water exposures for a revised drinking
water exposure assessment for aldicarb (USEPA OPP, 2006).  

Median and maximum concentrations of total aldicarb residues (parent,
sulfoxide, sulfone) in shallow private wells estimated with PRZM were
1.7 and 3.0 ug/l, respectively, in the Florida central ridge, 3.1 and
6.5 ug/l in the southern Georgia coastal plain representing the southern
coastal plain from South Carolina westward to Alabama, and 0.6 and 1.3
ug/l in the North Carolina coastal plain, representing the coastal plain
regions of North Carolina and Virginia (USEPA OPP, 2006). The estimated
exposures for the FL central ridge were less than maximum reported
detects in private well monitoring data collected by the state of FL,
dating back to 1990. However, the high detections in that study
pre-dated recent label changes intended to reduce aldicarb residues in
drinking water wells. A comparison with recent in-field monitoring
(USGS, 2006) indicated that PRZM provided reasonable, protective
exposures compared to wells in the field. However, the Agency noted that
recent monitoring data that reflected label changes for aldicarb were
scarce or absent for most of the aldicarb use areas. Monitoring data
collected by the state of FL was of little use because of high method
detection limits (ranging from 2 to 4 ug/l) in wells sampled after the
label changes. 

This review evaluates the extent to which the registrant’s study
design and subsequent conduct were tailored to address the uncertainties
identified in the N-methyl carbamate cumulative risk assessment (NMC
CRA) and in the 2006 aldicarb drinking water exposure assessment. The
second part summarizes the monitoring results, with an emphasis on use
in support of the drinking water exposure assessment.

EVALUATION OF METHODS

Study Purpose 

The purpose of the study was to analyze for aldicarb residues (aldicarb,
aldicarb sulfoxide, aldicarb sulfone) in potable water samples from
private wells located within 1,000 feet of fields treated with aldicarb
between 2002 and 2005. The study focused on aldicarb use areas in five
regions of the country:

Site Selection and number of wells

Bayer first targeted specific aldicarb use regions of the country.
Within each region, they identified targets by county based on aldicarb
sales data (details not specified), setting target goals by county. The
original study goal was to sample 200 wells from each of 9 major use
areas in 5 regions:

Southeastern US (excluding FL)

Alabama

Georgia

South Carolina

North Carolina and Virginia

Mississippi delta

Texas

Pacific Northwest

Washington and northern Oregon

Idaho and southwestern Oregon

California

Bayer then contacted growers in these areas who had purchased TEMIK®
(aldicarb) products between 2002 and 2005. Bayer used calls to identify
drinking water wells located within 1,000 feet of fields treated with
aldicarb in 2002 or later. Other candidate wells were identified by
asking the growers and pesticide distributors/dealers whether they knew
of other growers who might be using aldicarb with nearby wells. Bayer
continued contacting growers until the sample target was reached. If the
target was not reached, Bayer would look for wells in other counties
within the use area.

The study ultimately analyzed samples from 1,673 drinking water wells in
the five regions: 

Southeastern US - 800 wells

Mississippi Delta  - 169 wells

Texas - 201 wells

Pacific Northwest - 303 wells

California - 200 wells

Site selection was based on sales data first, and then on history of
recent use and proximity of the well to the treated fields. The process
did not consider leaching vulnerability of the soils/vadose zone in site
selection. This might have left out other areas where, while overall
aldicarb sales are not as high, may have been vulnerable because of
soil/hydrologic/geologic conditions.

Because the samples do not represent a statistical sampling, but rely on
user/grower-identified and -volunteered wells, no inferences are
possible beyond the population of wells being sampled. Thus the results
of the study cannot be used to characterize the percentage of wells with
aldicarb detects within the larger use regions. Because this study
relied on the willingness of the grower to participate, the pool of
wells sampled in the study cannot be considered an unbiased sampling of
the larger population.

Sample collection and handling 

Samples were collected from an indoor or outdoor tap. Where a treatment
system existed, attempts were made to collect samples that bypassed the
treatment; otherwise, the presence of the treatment system was
documented. 

The taps were flushed for 30 seconds and then duplicate samples were
collected in 125-ml amber HDPE bottles. The samples were buffered with
0.5 ml of ammonium acetate to maintain the pH at 5. Samples were stored
on ice at the time of collection and shipping and were refrigerated or
frozen until analysis.

Analytical Method  

Aldicarb, aldiarb sulfone, and aldicarb sulfoxide were measured by
direct injection of the water sample onto an LC/MS/MS system. The Method
Detection Limit (MDL) was 0.007 ug/L for aldicarb and aldicarb sulfone
and 0.009 ug/L for aldicarb sulfoxide. The Limit of Quantification (LOQ)
was 0.021 ug/L for aldicarb and aldicarb sulfone and 0.027 ug/L for
aldicarb sulfoxide.

Bayer analyzed the first sample from each well and analyzed the second
replicate sample if aldicarb residues were detected (>MDL) in the first
sample. Confirmatory methods used alternate monitoring ions.

QA/QC procedures included 

Method verification on untreated controls and samples fortified at 0.025
ug/L and 0.25 ug/L (~LOD and 10X the LOD)

Analyte	% recovery: primary method	% recovery: confirmatory method

	0.025 ug/L	0.25 ug/L	0.025 ug/L	0.25 ug/L

Aldicarb	94.9	88.1	91.7	87.3

Ald. Sulfoxide	94.1	96.6	116	99.4

Ald. Sulfone	106	100	102	92.0

Procedural/ analytical recoveries for each set on samples fortified at
0.025 and 0.25 ug/L (see table below)

Analyte	Fortified at LOQ (0.025 ug/L)	Fortified at 10x LOQ (0.25 ug/L)

	% recovery	sd	n	% recovery	sd	n

Aldicarb	95.7	5.5	58	97.5	6.0	46

Ald. Sulfoxide	92.7	9.9	58	89.2	8.0	46

Ald. Sulfone	94.4	8.8	58	94.1	7.9	46

 

Field spike recoveries ranged from 93 to 106 percent.

 

Storage stability studies on aldicarb, aldicarb sulfone, and aldicarb
sulfoxide showed stability for up to 30 months in freezer storage and up
to 4 months in refrigerated storage. The longest time between sample and
analysis in the study was 38 days, well within the stability range. In
addition, for those samples that were stored at ambient temperatures for
a longer than expected time, triplicate samples fortified at 0.5 ug/L
were analyzed at daily intervals. 

Ancillary data collection  

The study provides a substantial amount of ancillary data that extend
the value of the study beyond the reported concentrations of aldicarb
residues in well water. Such information collected during the study and
compiled in the study reports include 

Aldicarb use history for 2002-2005

Latitude and longitude, valuable for spatial analyses

Soil maps showing the well locations in relation to soils and fields

Nature of the well (age, type, depth, construction, casing and screen
depths)

Distance from the well to the nearest field (NOTE: there is no
indication as to whether additional setback distances were followed
where conditions described in the label existed)

Depth to groundwater (presumably as reported by the owner)

This information allowed EPA to evaluate not just frequency and
magnitude of detections in the study areas, but also factors that may
have influenced the monitoring results. 

RESULTS AND DISCUSSION

Overall Study

Aldicarb residues were detected in just under 10 percent of the wells in
the monitoring study (Table 1). A single sample point from each well
provides no indication of temporal fluctuations in aldicarb residues.
While variations in pesticide residues over time are less drastic in
ground water than in surface water, such variations do occur (see, for
example, USGS, 2006). Thus, the samples provide a snapshot of aldicarb
residues and may not necessarily represent longer-term trends.
Additionally, travel time from the surface through the vadose zone to
ground water varies with factors such as depth, permeability of the
soil, amount of rainfall/irrigation, distance between the field of
application and the well, and hydraulic gradient between the well and
the field. While some wells may reflect the recent applications of
aldicarb reported in the study, other wells (especially deeper wells)
may reflect older aldicarb applications.

Table 1 – Summary of frequency and magnitude of detections of aldicarb
residues by state and region.

Region	State	Ttl Wells	Ttl Detects	% Detects	Max Detect	Min Detect

Southeast	AL	192	43	22.4%	1.77	0.008

	GA	202	11	5.4%	2.9	0.01

	SC	203	43	21.2%	2.66	0.008

	NC	177	29	16.4%	1.57	0.009

	VA	21	4	19.0%	0.024	0.007

	MS	3	0	0.0%	-	-

	TN	2	0	0.0%	-	-

	Total	800	130	16.3%	2.9	0.007

Mississippi Delta

	AR	55	6	10.9%	0.23	0.009

	LA	27	0	0.0%	-	-

	MO	35	8	22.9%	2.59	0.007

	MS	39	1	2.6%	0.22	-

	TN	13	0	0.0%	-	-

	Total	169	15	8.9%	2.59	0.007

Texas	TX	201	0	0.0%	-	-

California	CA	200	3	1.5%	0.33	0.13

Pacific Northwest

	ID	197	9	4.6%	0.68	0.009

	OR	11	0	0.0%	-	-

	WA	95	3	3.2%	0.025	0.011

	Total	303	12	4.0%	0.68	0.009

All Sites	Total	1673	160	9.6%	2.9	0.007

 

Figure   SEQ Figure \* ARABIC  1  – Well monitoring locations for
Bayer study, highlighting detections. Underlying aldicarb use data is
based on Thelin and Geonessi (2000).

Detections showed a regional distinction that reflected soil, geologic,
hydrologic, and climatic differences (Figure 1). In the southeast, 16%
of the wells had detections, with this highest frequency of detects in
Alabama (22%) and South Carolina (21%). The greatest detection was 2.9
ug/L from a well in Georgia. In the Mississippi Delta region, aldicarb
residues were detected in 9% of the wells. Almost all of the detections
in this region occurred in southeastern Missouri and northeastern
Arkansas, with the greatest detection of 2.59 ug/L from a well in
Missouri. No detections were reported in the Texas sites, where aldicarb
is predominantly used in western TX/ panhandle region where rainfall is
lower. In the Pacific Northwest, 4% of the wells had detections,
although the highest detection was 0.68 ug/L. While localized exceptions
may occur, the frequency and magnitude of aldicarb detections in the
western part of the United States is expected to be lower than in the
southeast because the rainfall is generally lower and the soils and
vadose zone are generally neutral to alkaline in pH, a condition which
favors more rapid hydrolysis of the sulfone and sulfoxide residues of
aldicarb.

Contributing Factors

The ancillary data collected for each well allowed EPA to evaluate the
influence of various factors on aldicarb concentrations found in the
wells. Table 2 focuses on the influence of well construction, depth, and
distance from the treated fields.

Table 2 – Influence of well location, depth, and distance from field
on aldicarb detections.

	Ttl Wells	% of Ttl Wells	Ttl Detect	% Detect	Max Detect	99.9th%ile	99th
%ile	95th %ile

All Monitoring Sites	1673

160	9.6%	2.9	2.61	0.69	0.06

	Well Type	Drilled	1584	94.7%	150	9.5%	2.9	2.62	0.68	0.05

	Dug	22	1.3%	6	27.3%	0.36	-	-	0.19

	Unknown	67	4.0%	4	6.0%	0.71	-	0.49	0.03

	GW Depth	0-24 ft	246	14.7%	56	22.8%	2.59	2.39	1.50	0.33

	25-49 ft	198	11.8%	24	12.1%	2.9	2.50	0.77	0.08

	50-99 ft	200	12.0%	12	6.0%	1.57	1.44	0.71	0.01

	100+ ft	331	19.8%	6	1.8%	0.71	0.52	0.05	<0.01

	Unknown	698	41.7%	62	8.9%	2.66	1.16	0.38	0.03

	Well Depth	0-24 ft	33	2.0%	9	27.3%	1.57	1.55	1.41	0.64

	25-49 ft	150	9.0%	45	30.0%	2.59	2.42	1.41	0.43

	50-99 ft	194	11.6%	47	24.2%	2.9	2.68	0.92	0.26

	100+ ft	1005	60.1%	36	3.6%	1.57	0.89	0.10	<0.01

	Unknown	291	17.4%	23	7.9%	2.66	2.03	0.19	0.01

	Dis-tance from field	0-100 ft	875	52.3%	91	10.4%	2.9	2.63	0.75	0.06

	101-300 ft	576	34.4%	58	10.1%	2.66	2.03	0.50	0.07

	301-500 ft	135	8.1%	6	4.4%	0.77	0.76	0.46	<0.01

	500+ ft	86	5.1%	5	5.8%	0.15	0.14	0.12	0.01

While dug wells, which tend to be shallower and uncased, had a much
higher frequency of detections than did drilled wells (27% to 10%), too
few dug wells were included in the study to draw meaningful conclusions.

The frequency of aldicarb detections shows a general trend with reported
depth to groundwater, decreasing from 23% for groundwater within 25 feet
of the surface to 2% for groundwater greater than 100 feet from the
surface (Table 2). However, the depth to groundwater was listed as
“unknown” for 42% of the wells sampled, increasing the uncertainty
of the data for evaluating the influence of depth to groundwater on
aldicarb detections in wells.

Well depths were reported for a larger fraction of wells (83% vs. 58%).
The frequency of detections for aldicarb residues ranged from 24 to 30
percent for wells less than 100 feet deep (Table 2). While the majority
of detections greater than 1 ug/L occurred in wells less than 400 feet
deep, detections greater than 2.5 ug/L occurred in wells with reported
well depths of over 750 feet (Figure 2).

Aldicarb detections occurred in 10% of sampled wells that were located
within 300 feet of the treated fields (Table 2). Detections occurred in
6% of wells located greater than 500 feet from treated fields. The study
does not indicate whether additional setback distances were applied
between the wells and the fields. While the summary data and figures do
not distinguish between wells located in restricted soil types, the
Agency assumed that aldicarb was applied according to label restrictions
(see the section below). Thus, while some of the wells are located less
than 300 feet from the field, the concentrations in those that meet the
label requirements reflect the effect of the 300-foot setback distance.
Total aldicarb residues tended to decrease with distance between the
well and the treated fields (Figure 3), with practically no detections
reported for wells located greater than 600 feet from treated fields.

Figure   SEQ Figure \* ARABIC  3  - Relationship between concentrations
of total aldicarb residues and distance between treated fields and the
well.

Comparing vulnerable areas identified on the label

The current aldicarb (TEMIK® 15G) label identifies soil restrictions in
a number of states as a precaution for ground water contamination. These
restrictions are triggered “if a vulnerable soil is present and the
water table is less than 25 feet below the ground surface” (from the
TEMIK® 15G label). Because the depth to groundwater was unknown or not
reported for a substantial portion of the sampled wells, the Agency
could not fully evaluate the effectiveness of the existing label
restrictions on the frequency and magnitude of aldicarb detections.
Further, the label is not clear as to whether presence of a listed
“vulnerable” soil refers to anywhere in the treated field or only in
the close proximity of the well. 

Restricted soil types are listed for those states included in the
Southeast and Mississippi Delta regions, except for Arkansas. No
restricted soil types are listed for California, Texas, or the Pacific
Northwest states.

In the absence of definitive information on groundwater depth, EPA
compared aldicarb residues in wells located near fields with restricted
soils to those where the surrounding fields contained no restricted
soils (Table 3). If a restricted field was identified in the
accompanying soil maps for the treated fields, the well was tagged as
having restricted soils for this analysis. While the frequency of
aldicarb detections was greater for wells near restricted soil types,
the magnitude of aldicarb residues was greater for wells with no
restricted soil types (Table 3). Wells located in the vicinity of soils
identified as vulnerable to leaching according to the Bayer made up 16%
of the total wells sampled in the Southeast region and 14% of the wells
sampled in the Mississippi Delta region (excluding Arkansas, which is
not included in the list of states containing restricted soils).

Table 3 – Magnitude and frequency of aldicarb detections for wells
located in relation to restricted soils (as identified on the TEMIK®
15G label).

Region	State	Wells w/ Restricted Soils	Wells w/ no restricted soils

Wells	Det.	% Det.	Max Det.	Wells	Det.	% Det.	Max Det.

South-east

	AL 	10	1	10.0%	0.03	182	42	23.1%	1.77

	GA 	16	3	18.8%	0.017	186	8	4.3%	2.9

	SC 	20	7	35.0%	1.4	183	36	19.7%	2.66

	NC	78	13	16.7%	1.57	99	16	16.2%	1.42

	VA	3	1	33.3%	0.007	18	3	16.7%	0.024

	MS	0	0	-	-	3	0	-	-

	TN	0	0	-	-	2	0	-	-

	Total 	127	25	19.7%	1.57	673	105	15.6%	2.9

Missi-ssippi Delta	AR (1)	20	4	20.0%	0.23	35	2	5.7%	0.042

	LA	0	0	-	-	27	0	-	-

	MO	22	4	18.2%	2.59	13	4	30.8%	0.074

	MS	1	0	0.0%	-	38	1	2.6%	0.22

	TN	0	0	-	-	13	0	-	-

	Total 	43	8	18.6%	2.59	126	7	5.6%	0.22

(1) The TEMIK® label lists no restricted soil types listed for Arkansas
(soils identified in adjacent states are listed here).

Of the wells located adjacent to fields with restricted soils identified
on the TEMIK® label, 37% of the wells in the Southeast and 67% of the
soils in the Mississippi Delta region were also located in areas where
the reported depth to ground water was less than 25 feet below the
surface. However, depth to ground water was not known for 34% of these
wells in the Southeast and 33% of these wells in the Mississippi Delta
region. 

The Norfolk soil is included on the restricted soil list for North
Carolina, but not in Alabama, Georgia, and South Carolina. Table 4
summarizes the frequency and magnitude of detections of wells located
near fields with Norfolk soils in those states. Wells located near
Norfolk soils are not included in the “wells with restricted soils”
column for AL, GA, and SC in Table 3. It is not clear from the label why
this soil was included as a vulnerable soil for North Carolina but not
for the other states in the southern Coastal Plain.

Table 4 – Magnitude and frequency of aldicarb detections in wells
located near Norfolk soils.

State	Wells near Norfolk Soils

	No. Wells	No. Detects	% Detects	Max Detect

AL	17	4	23.5%	0.5

GA	16	1	6.3%	0.04

SC	40	8	20.0%	1.57

NC	63	9	14.3%	1.06

Total 	136	22	16.2%	1.57

Bayer’s criteria for including a soil on the restricted soil type list
for a state is based on soil texture and organic matter content of the
soil. For states in the southeast and Mississippi delta regions, the
criteria are:

“Loamy sand or sand surface soils and subsoils with an average organic
matter in the upper 12 inches of less than 2% by weight.”

For states in the Midwest, the criteria vary slightly:

“Sandy loam, loamy sand, or sand surface soils, and loamy sand or sand
subsoils, with an average organic matter in the upper 12 inches of less
than 2% by weight.”

Soil texture and organic matter content act as surrogates for
identifying those soils that have a high potential for leaching and a
low capacity for retaining the pesticide. While these properties are
relatively simple to describe and can be identified with a knowledge of
the soil series mapped for the treated fields, they do not fully
integrate those soil properties that affect leaching potential and are
imperfect indicators of the potential for aldicarb residues to move to
groundwater. 

An alternative approach that more accurately assesses the potential for
aldicarb to reach ground water is the USDA Natural Resource Conservation
Service (NRCS) classification for soil leaching potential for pesticides
(USDA NRCS. 2003). NRCS used the rating criteria (Table 5) to derive the
soil leaching potential for all soils in the SSURGO county surveys for
Florida (available for download from the USDA NRCS Soil Data Mart at  
HYPERLINK "http://soildatamart.nrcs.usda.gov/" 
http://soildatamart.nrcs.usda.gov/ ). The criteria could be used to
identify soils that are vulnerable to pesticide leaching throughout the
country, particularly in the aldicarb use states, to provide a more
definitive list of vulnerable soils (those rated as having a HIGH soil
leaching potential for pesticides) than the current list of soils based
solely on soil texture and organic matter content.

Table 5: USDA NRCS (2003) Criteria Used for Soil Leaching Potential for
Pesticides.

Rating	Criteria

High	Hydrologic Group = A and % Surface Horizon Organic Matter Content X
Depth of the First Soil Horizon <= 30 or

Hydrologic Group = B and % Surface Horizon Organic Matter Content X
Depth of the First Soil Horizon <= 9 and the K Factor is <= 0.48 or

Hydrologic Group = B and % Surface Horizon Organic Matter Content X
Depth of the First Soil Horizon <= 15 and the K Factor is <= 0.26

Low	Hydrologic Group = B and % Surface Horizon Organic Matter Content X
Depth of the First Soil Horizon >= 35 and the K Factor is >= 0.40 or

Hydrologic Group = B and % Surface Horizon Organic Matter Content X
Depth of the First Soil Horizon >= 45 and the K Factor is >= 0.20 or

Hydrologic Group = C and % Surface Horizon Organic Matter Content X
Depth of the First Soil Horizon <= 10 and the K Factor is >= 0.28 or

Hydrologic Group = C and % Surface Horizon Organic Matter Content X
Depth of the First Soil Horizon >= 10

Very Low	Hydrologic Group = D

Intermediate	All other conditions

REFERENCES

Thelin, G.P., and L.P. Gianessi. 2000. Method for Estimating Pesticide
Use for County Areas of the Conterminous United States. US Geological
Survey Open-File Report 00-250. Sacramento, California, 2000.  
HYPERLINK "http://ca.water.usgs.gov/pnsp/rep/ofr00250/" 
http://ca.water.usgs.gov/pnsp/rep/ofr00250/ 

USDA NRCS. 2003. Florida NRCS Field Office Technical Guide. Section II.
Water Quantity and Quality. Available from the electronic FOTG site at  
HYPERLINK "http://efotg.nrcs.usda.gov/treemenuFS.aspx" 
http://efotg.nrcs.usda.gov/treemenuFS.aspx 

USEPA OPP. 2005a. N-methyl Carbamate Cumulative Risk Assessment: Pilot
Cumulative Analysis. Presented to the FIFRA Scientific Advisory Panel,
February 15-18, 2005 (  HYPERLINK
"http://www.epa.gov/scipoly/sap/meetings/2005/index.htm#feb" 
http://www.epa.gov/scipoly/sap/meetings/2005/index.htm#feb ). 

USEPA OPP. 2005b. Estimation of Cumulative Risk From N-Methyl Carbamate
Pestidices: Preliminary Assessment. Presented to the FIFRA Scientific
Advisory Panel, August 23-26, 2005 (  HYPERLINK
"http://www.epa.gov/scipoly/sap/meetings/2005/index.htm#august" 
http://www.epa.gov/scipoly/sap/meetings/2005/index.htm#august ).
Preliminary document available at   HYPERLINK
"http://www.epa.gov/scipoly/sap/meetings/2005/august/preliminarynmc.pdf"
 http://www.epa.gov/scipoly/sap/meetings/2005/august/preliminarynmc.pdf
; SAP comments available at   HYPERLINK
"http://www.epa.gov/scipoly/sap/meetings/2005/august/minutes.pdf" 
http://www.epa.gov/scipoly/sap/meetings/2005/august/minutes.pdf . 

USEPA OPP. 2006. Drinking Water Exposure Assessment for Total Aldicarb
Residues (Parent, Aldicarb Sulfoxide, and Aldicarb Sulfone) Based on the
N-Methyl Carbamate Cumulative Risk Assessment. Memorandum dated October
23, 2006, from Thurman and Angier to Kinard and Fort. The OPP web site
for aldicarb (  HYPERLINK
"http://www.epa.gov/oppsrrd1/reregistration/aldicarb/" 
http://www.epa.gov/oppsrrd1/reregistration/aldicarb/ ) provides
information on how to access aldicarb documents on the public document.

U.S. Geological Survey. 2006. Lake Wales Ridge Ground-Water Monitoring
Study. USGS Water Resources Investigations Report in preparation.
Available:   HYPERLINK "http://fisc.er.usgs.gov/Lake_Wales_Ridge/" 
http://fisc.er.usgs.gov/Lake_Wales_Ridge/ . Page last modified April 11,
2006. 

 PAGE   

 PAGE   15 

Figure   SEQ Figure \* ARABIC  2  - Relationship between concentrations
of total aldicarb residues and well depth.