UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE  OF 

PREVENTION, PESTICIDES AND 

TOXIC SUBSTANCES

Chemical:  Lactofen

PC Code 128888

DP Barcode:  D319594

Chemical: Sodium Acifluorfen

PC Code 114402

	

MEMORANDUM							   DATE: October 13, 2006

SUBJECT: 	Drinking water and aquatic exposure water assessments for IR4
Tolerance petition for the new use (R17) of lactofen on the fruiting
vegetable group and okra.

FROM:	James K. Wolf, Environmental Scientist

		Environmental Risk Branch 3

		Environmental Fate and Effects Division (7507P)

THRU:	Mark Corbin, Senior Environmental Scientist

		Environmental Risk Branch 3

		Environmental Fate and Effects Division (7507P)

		

		Daniel Rieder, Branch Chief

		Environmental Risk Branch 3

		Environmental Fate and Effects Division (7507P)

TO:		Daniel Rosenblatt, RM #05

		Shaja Brothers, Risk Manager Reviewer 

		Risk Integration, Minor Use, and Emergency Response Branch (7505P) 

	The Registration Division (RD) has requested that EFED prepare a
drinking water assessment for a new lactofen (Lactofen technical, EPA
Reg. No. 56639-94 and Cobra Herbicide (EPA Reg. No. 59639-34) use on
vegetables (Crop Group 8 - fruiting vegetables, and Okra), as part of
the tolerance assessment process.  In this memo, EFED presents a Tier 2
surface water assessment for drinking water and aquatic exposure
assessments for the use of lactofen on these crops.   Tier 1 estimates
of ground-water concentrations are also provided.

	Lactofen (Cobra) is formulated as an emulsifiable concentrate. 
Lactofen is a selective, broad spectrum herbicide for preemergence and
postemergence control of susceptible broadleaf weeds.  Lactofen works
primarily through contact.  Good coverage of actively growing weeds is
necessary for maximum weed control.  Adjuvants and additives are
generally required.  When applied as a postemergence treatment a portion
of the spray may contact the soil surface.  If soil moisture conditions
are favorable for preemergence activity following application, the
suppression of germination of small-seed broadleaf weeds may occur for 2
to 3 weeks.  Excessive crop or weed foliage at the time of application
will reduce the amount of herbicide spray contacting the soil surface,
thus, reducing the level of soil activity.  Lactofen is currently
approved for use on cotton, snap bean, kenaf, peanut, soybean, and
strawberry crops, and conifers and forestry nursery plantings uses
(Label # 59639-34, 10/24/05).    

A.  PROPOSED USE

	The IR-4 proposes a new use of lactofen for weed control in fruiting
vegetables (Crop Group 8) and okra.  The use is to be limited to nine
South Eastern states; Alabama, Arkansas, Florida, Georgia, Mississippi,
North Carolina, South Carolina, Tennessee, and Virginia.

	The proposed lactofen use rates for the new uses are summarized in
Table 1.  The use is limited to two applications of lactofen per season,
with the maximum rate 0.5 lb ai/acre per application (1.0 lb
ai/acre/season).  This use cannot be applied by air or within 30 days of
harvest.  The application rate for the previous water assessment was
limited to two, 0.20 lb ai/acre, applications (0.40 lb ai/acre seasonal
rate) on soybeans.  Aerial application was also allowable for these
other uses. 

Table 1.  Proposed lactofen (Cobra) use rates, number of applications,
and period of application.



Pesticide Use:	Rate per Application to row middle	 Max. Number
Applications	Time of Application

	Fl oz/acre	(lb ai/ac)



Pre-transplant	19 to 32 fl oz	0.30 to 0.50	1	Minimum 10 days before
transplant to row middles

Post-transplant	19 to 32 fl oz	0.30 to 0.50	1	Minimum 16 inches high
before second application; 

Peppers must transplanted 45 days before post transplant application

Total for Growing Season	38 to 64 fl oz	0.60 to 1.00	2	Do not apply
within 30 days of harvest



	The Health Effects Division (HED) has concluded that lactofen has two
degradates of concern; acifluorfen and amino acifluorfen, which should
be include in the drinking water assessment.  Therefore this water
assessment considers both parent lactofen and acifluorfen.  To estimate
acifluorfen (derived from lactofen) concentrations in surface and ground
water, acifluorfen was simulated separately assuming acifluorfen was
applied at 58.2 percent of the lactofen rate.  The 58.2 percent is the
average of the maximum amount of acifluorfen observed (7 days after
lactofen application) from the degradation of lactofen in the two ASM
studies.  For surface water, the acifluorfen was “applied” seven
days after the lactofen was applied and spray drift contribution was
assumed to be zero.

B.  BACKGROUND

	The drinking water assessment for lactofen is complicated by the fact
that lactofen has several degradates in common with another herbicide,
sodium acifluorfen (PC 114402).  Lactofen and sodium acifluorfen also
have some common uses (e.g., soybeans).  The major degradates of
lactofen include acifluorfen, desethyl lactofen, and amino acifluorfen. 
Acifluorfen and amino acifluorfen are also primary degradates of the
herbicide sodium acifluorfen.  There are also at least two degradation
pathways: lactofen to desethyl lactofen then desethyl lactofen to
acifluorfen and/or lactofen to acifluorfen.  Although, lactofen degrades
rapidly into acifluorfen, it is not formed instantaneously from
lactofen, and would not be expected to move through the soil matrix as a
single “pulse”.  The Health Effects Division (HED) has concluded
that acifluorfen and amino acifluorfen are degradates of concern (FR
Vol. 68, No. 19, Wednesday, 01/29/03).   Because lactofen is expected to
degrade to acifluorfen in the environment, the EPA has considered the
contribution of acifluorfen as an environmental degradate of lactofen
and from the use of the herbicide sodium acifluorfen (USEPA, 2003b;
D291747) in the aggregate assessment.  Data are insufficient to estimate
the amino acifluorfen concentration in water, but it is likely to be
less than that of acifluorfen (less mobile and lower amounts present as
radioactivity).  The concern for a cancer risk has been removed by HED
(D292794).  

	The drinking water assessments for surface water have been fairly
straight forward for lactofen (USEPA, 2003b; D291747) and sodium
acifluorfen (D239269; D291747).  Considerable disagreement has
transpired over the estimates of acifluorfen residues in ground water,
from lactofen and sodium acifluorfen, using the Tier 1 ground-water
screening model SCI-GROW.  SCI-GROW assumes that sorption is only
related to organic carbon content (Koc).  Acifluorfen is anionic under
normal field pH values, thus, other factors other than organic carbon
also influence sorption – pH, minerals, clay content, surface area,
etc (D291747).  Therefore, depending upon soil conditions, acifluorfen
may have more or less of a potential to sorb than suggested by Koc. 
Literature also suggest that there is a kinetic (time dependant
component) aspect to the sorption of acifluorfen (longer contact time
the greater the sorption) (Gaston and Locke, 2000). 

C.  MODELS AND SCENARIOS

	The Tier 2 surface water EDWCs (estimated drinking water
concentrations) and EECs (estimated environmental concentrations) for
lactofen and acifluorfen (a degradate of lactofen) were generated with
standard Florida pepper and Florida tomato cropping scenarios (Leovey,
2002) using PRZM3 (Carsel, 1997) and EXAMS (Burns, 2002).  PRZM
simulates pesticide fate and transport as a result of leaching, direct
spray drift, runoff and erosion from an agricultural field and EXAMS
estimates environmental fate and transport of pesticides in surface
water body for a 30-year period (1961-1990) (Appendix 1).  PRZM and
EXAMS were linked by the program PE4-PL (version 01).  The EDWCs and
EECs assessment for surface water uses a single or multiple sites which
typically represent a high-end exposure scenario from pesticide use on a
particular cropped or non-cropped site.  Ground-water concentrations
were estimated using the Tier 1 screening model SCI-GROW (USEPA,
2003f.).

Scenarios

	The Florida tomato and Florida bell pepper standard scenarios were
chosen to represent Crop Group 8, Fruiting Vegetables for the Tier 2
surface water assessments.  The okra crop profile also indicated that
okra could be grown under similar conditions.  Table 2 lists the
application dates for lactofen for the Florida bell pepper and tomato
scenarios.  The acifluorfen is “applied” 7 days after the lactofen. 
For ground water, the SCI-GROW model is not scenario specific, although,
it represents a site vulnerable to ground-water contamination.

 

Table 2.  Crop stage dates and dates for preemergence and postemergence
applications of lactofen used in PRZM/EXAMS modeling.   

Date: (DAY/MONTH)

Crop Stage1 	Preemergence Application	Postemergence Application

Florida Peppers



Date of Crop Emergence: 01/09	22/08	17/10 (45 days after plant)

Date of Crop Maturity:     15/11

 

Date of Crop Harvest:      12/01

 

Florida Tomatoes



Date of Crop Emergence: 10/01 	01/01	15/02

Date of Crop Maturity:     30/03



Date of Crop Harvest:      05/04



	1 Defined in the scenario.

Pesticide Inputs (application rate, number, spray drift fraction, fate
properties)

	The maximum lactofen label seasonal rate of 1.0 lb ai/acre was split
between pre-emergence and post-emergence (both at 0.5 lb ai/acre) for
each crop (Table 1).  The proposed application method is by ground
spray.  The spray drift fraction for drinking water was 0.064 and for
aquatic exposure assessments 0.01.  The rates of formation and decline
all lactofen degradates are not been well defined.  However in the two
lactofen aerobic soil metabolism (ASM) study, acifluorfen accounted for
52.3 and 64.1 percent of the applied radio-labeled lactofen on day 7
(D291747).  For this assessment, acifluorfen was simulated separately
assuming acifluorfen was applied at 58.2 percent of the lactofen rate
(0.291 lb ai/acre = 0.582 x 0.5 lb ai/acre) seven days after the
lactofen application, and where the spray drift contribution assumed to
be zero. 

	The environmental fate values used in for modeling are summarized in
Tables 6 and 7 for lactofen and Table 8 for acifluorfen.

	Detailed description, documentation, and direct links for running these
models can be found in:   HYPERLINK
"http://www.epa.gov/oppefed1/models/water/index.htm" 
http://www.epa.gov/oppefed1/models/water/index.htm .  Model outputs are
given in Appendix 2.

D.  DRINKING WATER

Surface Water

	The Tier 2 surface water EDWCs were estimated for the fruiting
vegetables (tomatoes, peppers) with the proposed maximum application
rate.  Table 3 summarizes the estimated exposure concentrations
(corrected for Percent Crop Area (PCA)) of lactofen and acifluorfen in
surface water as a result of two ground spray applications at the
maximum proposed lactofen rate of 0.50 lb ai/acre (Table 1). 
Acifluorfen was “applied” twice at a rate of 0.291 lb ai/acre (0.58
lb ai/acre maximum season rate)” seven days after the lactofen
application, with no spray drift.  The lactofen and acifluorfen
concentrations represent, the 1-in-10-year annual exceedance probability
for peak, yearly mean, and the overall mean for the Florida pepper and
tomato scenarios (Table 3).  

	The estimated peak concentration for lactofen is 1.48 µg/L, the annual
mean is 0.044 µg/L, and the long term average is 0.039 µg/L as this
represents the most conservative concentrations for the peak
concentration.  The estimated peak concentration for acifluorfen derived
from lactofen is 22.5 µg/L, the annual mean is 3.9 µg/L, and the long
term average is 2.0 µg/L, for the most conservative concentrations for
the peak concentration.  The default PCA of 0.87 is used, rather than a
crop specific PCA.  It is likely that the PCA for the proposed crops
could be lower for these new uses.

Table 3.  Estimated drinking water concentrations (EDWC) (μg/L) in
surface water for acute, chronic, and cancer exposure from lactofen and
the acifluorfen derived from lactofen in μg/L for peppers and tomatoes
using linked PRZM/EXAMS1 and Index Reservoir (IR) and Percent Crop Area
(PCA) for surface water.  The bold values are estimates to be used in
the drinking water assessment. 

Crop	Chemical Species	1-in-10 year

 Maximum/mean 

(μg/L)	Long term average

Mean (30 yrs.)

(µg/L)



(acute/chronic)	(cancer)

 Pepper	Lactofen	1.48/0.040	0.033

	Acifluorfen	22.5/3.5	2.0

 Tomato	Lactofen	1.13/0.044	0.039

	Acifluorfen	20.9/3.9 	1.7



Ground Water 

	The EFED Tier 1 assessment process currently uses the SCI-GROW model to
estimate ground-water concentrations.  The SCI-GROW (Screening
Concentration In GROund Water) is an empirical screening model based on
actual ground-water monitoring data collected from small-scale
prospective ground-water monitoring studies for the registration of a
number of pesticides that serve as benchmarks for the model (USEPA,
2003f).  The ground-water concentrations generated by SCI-GROW are based
on the largest 90-day average concentration recorded during the sampling
period.  The model was developed so that only under exceptional
circumstances would concentrations of a pesticide exceed the SCI-GROW
estimates.  It was thought that this exception should be rare since the
SCI-GROW model is based exclusively on ground-water concentrations
resulting from studies conducted at sites (shallow ground water and
coarse soils) and under conditions most likely to result in ground-water
contamination.  

	The SCI-GROW model was found to under estimate acifluorfen
concentrations observed in the Wisconsin sodium acifluorfen PGW Study
(acifluorfen range 1 to 46 µg/L; mean 7.33 µg/L) (USEPA, 1989; USEPA,
2003b, 2003c, 2003e).  Therefore, EFED did not think that the SCI-GROW
estimates were conservative for acifluorfen.  Later SCI-GROW over
estimated the acifluorfen concentrations in ground water (compared to a
lactofen PGW) when the acifluorfen was a degradation product of lactofen
(USEPA, 2003b).  Thus, SCI-GROW model was not used previously to
estimate the drinking water concentrations acifluorfen derived from
lactofen in ground water (USEPA, 2003b).  Several limitations of
SCI-GROW were identified as reasons why the SCI-GROW under predicted the
acifluorfen concentrations observed in ground water for the Wisconsin
PGW (D291747, D278403).   

	More recently, the ground-water EDWCs for acifluorfen derived from
lactofen were based upon observations from a PGW study.  Low level
concentrations of acifluorfen (as degradate of lactofen) were detected
during the Michigan lactofen PGW (USEPA, 2003c) in soil-water at several
depths (3- and 6-feet) (acifluorfen LOD in soil water = 0.035 µg/L. 
There were no ground-water detections of acifluorfen in the Michigan
lactofen prospective ground-water (PGW) monitoring study, with a limit
of detection (LOD) for acifluorfen of 0.035 µg/L in ground water
(USEPA, 2003b, 2003c).  The EDWCs for acifluorfen ground water were set
at the lactofen PGW study’s LOD method limit of detection (0.035
µg/L) for acifluorfen (USEPA, 2003b).  

	The uncertainty of this estimate increases when extrapolating the
findings of the lactofen PGW where 0.40 lb ai/acre lactofen was applied,
to the proposed new use rate is 1.0 lb ai/acre (an increase of 2.5 times
the previous use rate).  The concentrations of acifluorfen derived from
lactofen measured in the Michigan lactofen PGW were much lower than in
the Wisconsin sodium acifluorfen PGW study.  However, the estimated
maximum acifluorfen concentration “applied” under the proposed new
rate is 0.58 lb ai/acre (from 1.0 lb ai/acre lactofen) more comparable
in magnitude to that of the 0.75 lb ai/acre sodium acifluorfen used in
the Wisconsin PGW than at the Michigan study. 

Due to multiple detections, an understanding of the site's hydrology
(USEPA, 1989), and known acifluorfen use, EFED is highly confident that
acifluorfen residues can contaminate shallow ground water.  Knowing that
the sorption of acifluorfen is dependent on factors in addition to
organic carbon (minerals, pH, type of organic matter, etc.), one could
obtain better estimates of the acifluorfen concentration by lowering the
‘Koc’ value.  However, it was necessary to lower the Koc values
below what could be justified (based upon available information).  

In addition the difference in sorption of acifluorfen based upon soil
conditions, other factors have since been identified (D278403) that also
could have contributed to the occurrence of the “high” levels of
acifluorfen observed in ground water at the Wisconsin PGW. One is that
the amount and frequency that the irrigation water applied during the
Wisconsin PGW was based upon consumptive use without including the
actual precipitation.  This resulted in a high relative amount of water
being added.  Also, no acifluorfen degradates were identified, thus,
acifluorfen appears to have been leached out of the soil before
significant degradation (no degradation products were identified) and/or
sorption had occurred.  

These factors are possible reasons why the ground-water concentrations
were under estimated by SCI-GROW.  The acifluorfen concentrations
observed at the Wisconsin PGW site, while valid, probably do not reflect
the acifluorfen concentration likely from the application of lactofen
(or sodium acifluorfen) under more typical conditions.

	The lactofen and acifluorfen application rates for this assessment use
the same rates as those used above for the surface water estimates.  The
SCI-GROW model to estimate ground-water concentrations for lactofen
(Table 4) and acifluorfen (Table 5).

Lactofen

 	The high Koc (median = 10500 mL/g) and short aerobic soil half-life (<
3 days) indicates that lactofen has a low potential to leach.  The
estimated lactofen concentration in ground water is 6.00E-03 µg/L, the
lower limit of SCI-GROW, as concentrations estimated with Koc values
greater than 9995 ml/g are beyond the scope of the regression data used
in SCI-GROW development.  The fate data (Tables 7 and 8), prospective
ground-water monitoring studies and monitoring data confirm that
lactofen is not persistent or mobile.  With the exception of the
lactofen PGW, the Agency is not aware of any ground-water monitoring
data for lactofen.   

The estimated concentrations of lactofen for acute and chronic exposures
in ground water using SCI-GROW are presented in Table 4.  The estimated
concentrations of lactofen in ground water for the new use rate (1.0 lb
ai/acre) is less than 0.006 µg/L, the lower limit (0.006 µg/L) of the
algorithm used to calculate pesticide concentrations.  Although, the
maximum application rate is higher than used in the previously
assessment (USEPA, 2003b), EFED believes that the likelihood of lactofen
contamination ground water would still be quite low.  

	

Table 4. SCI-GROW estimates of lactofen EDWCs in ground water from two
0.5 lb ai/acre per year application of lactofen. 

Water Type	Chemical	Acute and Chronic (µg/L)

Ground Water	Lactofen	  0.006

  

Acifluorfen

	SCI-GROW estimates of ground-water concentrations depend upon the input
values (Table 9) selected for Koc, the aerobic soil metabolism
half-life, and the numbers and rate of application (USEPA, 2003b). 
Acifluorfen is anionic under normal field pH values, thus, other factors
other than organic carbon also influence sorption – pH, minerals, clay
content, surface area, etc. (Gaston and Locke, 2000).  Thus, the
sorption of acifluorfen is dependent upon other soil properties in
addition to organic carbon (matter) content.  

	The SCI-GROW estimates for acifluorfen in ground water, as a lactofen
degradate, in ground water using the range of Kocs, lowest (50.02 mL/g)
and the highest (198.7 mL/g), are 3.17 µg/L and 0.57 µg/L,
respectively.  However, by assuming that the (median from Table 9) Koc
reflects all the sources of sorption, the estimated acifluorfen
concentration for the new use (1.0 lb ai/acre lactofen = 0.58 lb ai/acre
acifluorfen) in ground water with SCI-GROW is 2.00 µg/L.  The
recommended EDWC for acifluorfen acute and chronic drinking water, for
the proposed new lactofen use, is 2.00 µg/L (Table 5).  The acifluorfen
(from sodium acifluorfen) exposure concentration for drinking water
previously used by HED was 3.67 µg/L (D291747).  

Table 5. SCI-GROW estimate of acifluorfen (as a degradate of lactofen)
in ground water from a 0.58 lb1 ai/acre annual application of lactofen.

Water Body	Chemical	Acute and Chronic

Ground Water	Acifluorfen	2.00 µg/L

	      1 Conversion of lactofen to acifluorfen is 58 percent (average
value), thus, 1 lb ai/acre yields 0.58 lb 

		ai/acre.

Aquatic Exposure Estimates

	Lactofen and acifluorfen concentrations for surface water aquatic
exposure estimates are given in Table 6.  The environmental fate inputs
used are the same as in the drinking water assessments.  The Standard
Pond has a different field to water body ratio compared to the Index
Reservoir and does not use a PCA.  The (ground) spray drift, as a
fraction, is 0.01 for the pond (EECs) compared to 0.064 used for the
drinking water assessment (EDWCs).

Table 6.  The 1-in-10 year estimated environmental concentrations (EECs)
for lactofen and a primary degradate acifluorfen in a standard farm pond
for aquatic exposure assessments. The bold values are recommended to be
used in the aquatic exposure assessment.



Scenario	

y mean concentration (μg/L).



Peak	21-day	60-day

 Pepper	Lactofen1	0.48	0.095	0.047

	Acifluorfen2	18.0 	17.7	17.0

Tomato	Lactofen1	0.28	0.076	0.051

	Acifluorfen2	14.4 	14.2	13.8 

1 Lactofen application = 2 applications at 0.5 lb ai/acre.

2 Acifluorfen estimate assumes that the conversion from lactofen is
0.582 (58.2 percent) – thus 2 applications at 0.291 lbs ai/acre (0.291
= 0.50 * 0.58)

Environmental Fate Summary

Lactofen:

	The lactofen environmental fate data is discussed in greater detail in
Drinking Water Exposure Assessment for Lactofen, Updated for Prospective
Ground-Water (PGW) Monitoring Study (USEPA, 2003b; D263956, D283774).

Aerobic soil metabolism and hydrolysis are the major degradation routes
for lactofen. Lactofen is not persistent (half-life less than 3 days) in
the environment, has a high affinity for binding (high Koc values), and
low solubility (Table 7).  Lactofen is not expected to leach to ground
water because of its high binding potential and short half-life.  A
lactofen PGW study confirms this (D283774).  Lactofen degradates to
desethyl lactofen and acifluorfen; desethyl lactofen will also degrade
to acifluorfen.  Other degradates include amino acifluorfen.  Desethyl
lactofen appears relatively stable to photolysis and hydrolysis at least
for the duration of the available studies.  	 

Aquatic degradation information for lactofen is lacking.  This increases
the uncertainty of our understanding of the fate of these compounds in
surface water.  The fate of lactofen in an aquatic system (surface
water) is less clear, but it is not persistent in soil and would have an
affinity to bind to sediment rather than remain in solution.  Whether
soil-bound lactofen will degrade to acifluorfen is not known.

TABLE 7.  LACTOFEN ENVIRONMENTAL FATE PROPERTIES AND MODEL INPUT VALUES
USED IN PRZM, EXAMS, and SCI-GROW.



LACTOFEN

PROPERTY	

FATE DATA	

MODEL INPUT CALCULATIONS	

MODEL INPUT VALUE	

SOURCE



Solubility (ppm)	

0.945

0.10 	

	

0.945	

E. Tamichi, Valent

EFED One-liner



Molecular Weight	

461.77	

	

461.77 	

EFED One-liner

Hydrolysis (days)

Half-life	pH 5: 10.7 @ 40  oC

pH 7:   4.6 @ 40 oC

pH 9 < 1.0 @ 40 oC	all values multiple by 5 to reflect 20o C, 2.5 by
slower for each 10o C1	53.51    @ 20 oC 

23.01    @ 20 oC

  5.01    @ 20 oC

	EFED One-liner

Henry’s Constant (atm. M3/Mol)	2.43E-08 (calculated)	

	2.43E-08	EFED One-liner

Photolysis half-life (days)	water:   2.75

soil:    23	converted to rate in hours	 2.75 days	E. TAMICHI, Valent

EFED One-liner

Aerobic Soil Metabolism half-life (days)2

	1:   2.41 (DT50)

2:   1.496 (DT50)	90th percent upper bound of mean = 2.82

(PRZM & SCI-GROW)	2.82 days

	1:EFED One-liner

Acc. #s 071228;

            073854

2:

MRID # 45722201 (D284417)

Anaerobic Soil Metabolism half-life	est. 18.5	multiply max. value by 3
55.5 days

	EFED One-liner

Aerobic Aquatic Half-life 	no data	estimated - multiply aerobic soil
input half-life value by 2 (multiply max aerobic soil value by 2)	5.64
days	 Est. from Aerobic soil metabolism

Anaerobic Aquatic Half-life	no data	estimated -multiply anaerobic soil
input half-life value by 2 (multiply max anaerobic soil value by 6)	111
days	EFED One-liner

Soil Water Partition (Koc) mL/g	  6600

15000	mean value 

(PRZM/EXAMS)

(SCI-GROW)	

10800 mL/g

10800 mL/g	E. TAMICHI, Valent

DP Barcode D242256

1 J.C. Harris.  1981. Rate of Hydrolysis. Pages 7-1 to 7-48. in Lyman,
W.J. et al., Research and Development of Methods for Estimating
Physiochemical Properties of Organic Compounds of Environmental Concern.
 US Army Medical Research Development Command, Frederick, MD  The
hydrolysis rate decrease (longer half-life) as temperature decreases.
Harris suggest that the rate is 2.5 slower for each 10 (C decrease. 
Thus, hydrolysis at 20 (C would be five times slower than at 40 (C.

The rate constants in hours are for acid, neutral, and basic hydrolysis,
KAH, KNH, and KBH, are -6.71/hr, 1.21 E-03/hr, and 4.57 E+02/hr,
respectively. 

2 The decline pattern of lactofen did not follow first order kinetics. 
Non-linear estimate of first order equation fit the data better.
Lactofen decline was very rapid.

	Lactofen undergoes hydrolysis with an increasing rate with increasing
pH (Table 8).  As the pH increases the percent and persistence of
acifluorfen and desethyl lactofen increases.   The final percentages of
14C lactofen and degrades acifluorfen (PPG-847) and desethyl lactofen
(PPG-947) at the three pH values used in the study are given in Table 8.
 It should be noted that this study was determined to be invalid because
lactofen residues bound to the container walls. Although this study was
flawed, it indicates that lactofen can degrade via hydrolysis resulting
in persistent degradates at concentrations similar to parent lactofen. 
The study was not long enough to understand the long term persistence of
these degradates.  The current scenario only considers a water with a
neutral pH (pH=7), thus, only the hydrolysis rate at pH 7 is used.

Table 8.  Final 14C-lactofen and degradates acifluorfen and desethyl
lactofen remaining in hydrolysis study at three pH values.



pH	

Time of Final

Sample Interval (hr)	

Lactofen 	

Acifluorfen

PPG-847	

Desethyl Lactofen

PPG-947





% of recovered



5	

944	

81.5	

1.3	

17.3



7	

720	

11.9	

9.6	

76.8



9	

 48	

2.5	

27.9	

65.6



Acifluorfen:

	Limited environmental fate data are available for acifluorfen (Table 9)
and desethyl lactofen especially as degradates of lactofen.  Soil
samples from a prospective ground-water (PGW) monitoring study (D283774)
were collected to conduct an aerobic soil metabolism (162-1) study
(D284417). The decline pattern of lactofen residues did not appear to
follow first-order kinetics.  Lactofen is not persistent. The calculated
half-life and the DT50 values were essentially the same (about 1.4
days).  The formation and decline patterns of acifluorfen tended to
follow a first-order decline curve upon reaching its maximum
concentration (on day 7).  The half-life (40 days) and the DT50 (40
days) were essentially the same.  Using a degradation series (lactofen
to desethyl lactofen to acifluorfen), a DT50 was calculated to be about
63 days.  The “half-life” of the desethyl lactofen was calculated to
be less than a day (<1 day).  

	The environmental fate of sodium acifluorfen, acifluorfen, and amino
acifluorfen are discussed in greater detail in the reregistration
eligibility document (RED) of sodium acifluorfen (PC Code 114402) and
other uses (DP Barcode D252561, D280710, 239268).  The environmental
fate parameters for sodium acifluorfen used in this reassessment are
listed in Table 9.  The aerobic soil metabolism rate for acifluorfen
ranges from 100 to 200 days (D291747) for sodium acifluorfen. 

	 

Acifluorfen is highly mobile with Kads values ranging from 0.148 to 3.1
mL/g (Table 9, D232775) suggesting a potential to leach to ground water.
This is confirmed by monitoring data. The Koc values range from 50.22 to
198.7 mL/g (Table 9). 

	The Kads values for the degradate acifluorfen amine (amino acifluorfen)
were 47.01, 19.34, 12.11, and 1.25 for loamy sand, loam, clay, and sand
soils, respectively (1/n values ranged from 0.802 to 0.936) (DP
D253561).  Koc values were 7368, 741, 652, and 431 for loamy sand, loam,
clay, and sand soils, respectively.  Using the relative mobility
classification of McCall et al (1980), acifluorfen amine has a mobility
classification of “immobile” in loamy sand, “low mobility” in
loam and clay, and “medium mobility” in sand.  

Acifluorfen can be quite persistent, is highly soluble, and is highly
mobile. The environmental fate properties suggest that if acifluorfen
reaches ground water it is quite persistent.  Monitoring data from a
prospective ground-water study confirms the persistence of acifluorfen
in ground water (D173298). There is also evidence in that sorption of
acifluorfen to different soils can be highly variable depending upon
specific soil properties.  This variability may explain the difference
in leaching seen at different locations.



	Acifluorfen will tend to remain in solution rather than being bound to
sediment, therefore, acifluorfen in runoff will remain in solution.
Acifluorfen and desethyl lactofen appear relatively stable to photolysis
and hydrolysis at least for the duration of the available studies.
Acifluorfen reduces to amino acifluorfen under anaerobic conditions. 
The degradate amino acifluorfen appears to be persistent but less mobile
than acifluorfen in non-sandy soils. Photolysis in water may be one of
the possible ways for acifluorfen to degrade in surface water as the
aqueous photolysis half-life ranges from 0.9 to 15 days.  However, when
light penetration is restricted the rate of photolysis would be reduced.

TABLE 9.  SELECTED (SODIUM) ACIFLUORFEN ENVIRONMENTAL FATE PROPERTIES
AND MODEL INPUTS VALUES USED IN PRZM, EXAMS and SCI-GROW.



ACIFLUORFEN

PROPERTY	

FATE DATA	

MODEL INPUT CALCULATIONS	

MODEL INPUT VALUE	

SOURCE



Solubility (ppm)	

2.50E+05	

	

2.50E+051	

EFED 

One-liner



Molecular Weight	

383.70	

	

383.70	

EFED 

One-liner



Hydrolysis (days)	

stable at pH 5,7,9	

	

 considered stable 	

EFED 

One-liner



Henry’s Constant

(atm.m3 /mol)	

1.51E-13 (calculated)	

	

1.51E-13	

EFED 

One-liner



Photolysis half-life

(days)	

Water: 3.8

(0.9 to 14.7)2

Soil:   57 @pH4	

upper 90%=mean +

n; single tail student t, α=0.1 and n = number of samples	

 3.8 days

13.31 days	

EFED 

One-liner

MRID 41891208

D232775



Aerobic Soil Metabolism half-life

(days)	

30, 60 - 180, 170, 59, 6

(60 and 180 were used to cover the range 60 - 180)

(100,108,193,200  used)

40

Mean – 150.25 days	

-

upper 90%=mean +

t90 x std/(n; single tail student t, α=0.1 and n = number of samples	

121 days

172.84 days

150.25 days (SCI-GROW)	

EFED 

One-liner

(MRID 00143572)

MRID 45722201



Anaerobic Soil Metabolism half-life

(days)	

<28 days	

multiply value by 3	

84 days

	

EFED 

One-liner



Aerobic Aquatic half-life (days)	

98%-day 0, 82%-day 35: half-life estimated to be 117 days

[2 x 172.84 = 345,68 days]	

multiple value  by 3

2 times aerobic soil metabolism half-life	

351 days

345.68 days	

EFED 

One-liner



Anaerobic Aquatic half-life (days)	

no data	

estimate by multiplying anaerobic soil half-life by 6 

(28 x 3 x 2) 	

168 days	

EFED 

One-liner



Soil Water Partition 

(Kd)mL/g 

(Kads mL/g)	

1.0

0.148, 0.346, 1.51, 1.87, 3.1   	

Mean = 1.39

upper 90%=mean +

t90 x std/(n; single tail student t, α=0.1 and n = number of samples	

previous 1 (assume OC=1%); Koc = 100 

(50.22 to 198.7)

Mean = 1.39

Kads = 2.22

[for PRZM and EXAMS]	

EFED 

One-liner

(MRID  42703501)

Soil Water Partition 

(Koc)  mL/g 

(Koc)ads mL/g)	

50.22, 56.96, 73.52, 164.9, 198.7

	

Use median (m) value

m  = 73.52

	

m  = 73.52

[for SCI-GROW]	

(MRID  42703501)

[D278403]

1  Bold values used as inputs for modeling.

2  Additional information was considered in reassessment. 

OTHER CONSIDERATIONS

	The potential for acifluorfen to contaminate ground water has been
recognized by the Agency since the mid -1980s.  Since this time a number
of assessments have been made by EFED as additional information became
available.  With the advent of the FQPA (Food Quality Protection Act),
concentrations of pesticide residues in water needed to be estimated so
they could be included in the dietary exposure estimates.  Until
recently (2002), there was a concern for dietary exposure for
acifluorfen due to a potential cancer risk (D292794), with the (ground)
drinking water concentration of concern (cancer DWLOC) of 2.8 µg/L. 
Estimates of acifluorfen residues (from ground-water monitoring and
modeling) in water occasionally exceeded this value under some
conditions.  A sodium acifluorfen PGW study (USEPA, 1989) conducted in
Wisconsin had acifluorfen concentrations higher (max. = 46 µg/L; mean =
7.33 µg/L) than predicted by SCI-GROW or observed in other monitoring
studies (D291747). 

	Additional information submitted to the Agency has removed the cancer
concern (D292794), so the chronic exposure (non-cancer) is now the point
of comparison. The chronic exposure (non-cancer) level of concern has
been estimated to be about 455 µg/L (DWLOC).  This value far exceeds
the levels of acifluorfen found in the monitoring programs and those
estimated by EFED screening models.  Based on the modeled estimates and
the limited monitoring it seems unlikely that acifluorfen concentrations
from lactofen applied to the new uses would reach this level in either
ground water or surface water.  

	The environmental fate input values for acifluorfen which were used
with SCI-GROW are summarized in Table 9.  SCI-GROW estimates of
ground-water concentrations depend upon the input values selected for
Koc, the aerobic soil metabolism half-life, and the numbers and rate of
application (USEPA, 2003b).  Acifluorfen is anionic under normal field
pH values, thus, other factors other than organic carbon also influence
sorption – pH, minerals, clay content, surface area, etc. (Gaston and
Locke, 2000).  Thus, the sorption of acifluorfen is dependent upon other
soil properties in addition to organic carbon (matter) content.  The
“application rate” or concentration of acifluorfen derived from
lactofen depends upon the degradation pathway and the assumptions used
concerning the rates of formation of acifluorfen and lactofen decline.  
The fate data (Tables 9) and retrospective ground-water monitoring study
suggests that acifluorfen is mobile and persistent enough to contaminate
ground water, and the prospective ground-water study (PGW) and
monitoring data confirms that acifluorfen can contaminate ground water.

 7.33 μg/L.  Due to multiple detections, an understanding of the site's
hydrology, and known acifluorfen use, EFED is highly confident that
acifluorfen residues can contaminate shallow ground water.

	The SCI-GROW model was found to under estimated acifluorfen
concentrations observed in the Wisconsin sodium acifluorfen PGW Study
(USEPA, 1989; USEPA, 2003b, 2003c, 2003e).  Thus, EFED did not think
that the SCI-GROW estimates were conservative.  Therefore, the SCI-GROW
model was not used previously to estimate the drinking water
concentrations acifluorfen derived from lactofen in ground water (USEPA,
2003b).  SCI-GROW over estimated acifluorfen concentrations compared
observed in Michigan PGW (USEPA, 2003c).

\	Knowing that the sorption of acifluorfen (due to its anionic nature)
is dependent on factors in addition to organic carbon (minerals, pH,
type of organic matter, etc.), the ‘Koc’ value was adjusted as a
means to improve the estimated acifluorfen concentrations (to conform
with those seen in the Wisconsin PGW).  Better estimates could be
obtained by lowering the Koc, however, it was necessary to lower the Koc
values below what might be thought of as a reasonable value (based upon
available information).  Additional factors have since been noted
(D278403) that could have contributed to the occurrence of the
“high” levels of acifluorfen observed in ground water at the
Wisconsin PGW.  These factors include:

The soil at the Wisconsin site was highly vulnerable- - low organic
carbon content, low water holding capacity, and perhaps minerals with
low sorption potential, 

Irrigation was applied based upon consumptive use (from study site)
estimates without taking into account any actual precipitation (i.e.,
the plots were irrigated whether irrigation was need or not), so with
the low water holding capacity, leaching would be enhanced,

Sodium acifluorfen was applied in one 0.75 lb ai/acre application,

The primary degradates (amino acifluorfen and desnitro acifluorfen) of
acifluorfen were analyzed for and not found, suggesting no degradation
and that leaching was the only dissipation pathway,

The measured peak concentration in ground water was 46 μg/L; the
average measured concentration was 7.33 μg/L.  The SCI-GROW estimates
are based upon the highest average concentrations for a three month
period.  Using the acifluorfen fate inputs (Table 8) as currently
recommend by EFED guidance (USEPA, 2002a), SCI-GROW estimates an
acifluorfen concentration of 2.57 μg/L for an application of sodium
acifluorfen 0.75 lb ai/acre.

	The high concentrations of acifluorfen in ground water at the Wisconsin
site are at least partially the result of the amount and frequency that
the irrigation water applied during the PGW.  It appears that the
“mobile” acifluorfen was leached out of the surface soil layers (the
most active microbial populations) before degradation and sorption
occurred.  This resulted in ground-water concentrations estimated by
SCI-GROW.  The acifluorfen concentrations observed at the Wisconsin PGW
site, while valid, probably do not reflect the acifluorfen concentration
likely from the application of lactofen (or sodium acifluorfen) under
more typical conditions.

 

	Low level concentrations of acifluorfen (as degradate of lactofen) were
detected during the Michigan lactofen PGW (USEPA, 2003c) in soil-water
at several depths (3- and 6-feet) (acifluorfen LOD in soil water = 0.035
µg/L.  There were no ground-water detections of acifluorfen in the
Michigan lactofen prospective ground-water (PGW) monitoring study, with
a limit of detection (LOD) for acifluorfen of 0.035 µg/L in ground
water (USEPA, 2003b, 2003c).  The EDWCs for acifluorfen ground water
were set at the lactofen PGW study’s LOD method limit of detection
(0.035 µg/L) for acifluorfen (USEPA, 2003b).   The uncertainty of this
estimate increases when extrapolating the findings of the lactofen PGW
where 0.40 lb ai/acre was applied, the proposed new use rate is 1.0 lb
ai/acre (an increase of 2.5 times the previous use rate).  The
concentrations of acifluorfen derived from lactofen measured in the
lactofen PGW were much lower than in the Wisconsin sodium acifluorfen
PGW study.

	

	 

cc://Christine Olinger, HED, RRB1APPENDIX 1.  

	The surface water EDWCs (estimated drinking water concentrations) and
EECs (estimated environmental concentrations) for lactofen and
acifluorfen were generated with standard cropping [Table B-1, Florida
peppers and tomatoes] scenarios (Leovey, 2002) using PRZM3 (version 3.12
beta, Carsel, 1997) and EXAMS (version 2.98.04, Burns, 2002).  PRZM
simulates pesticide fate and transport as a result of leaching, direct
spray drift, runoff and erosion from an agricultural field and EXAMS
estimates environmental fate and transport of pesticides in surface
water body for a 30-year period (1961-1990).  The EECs and EDWCs
assessment for surface water uses a single or multiple sites which
typically represent a high-end exposure scenario from pesticide use on a
particular cropped or non-cropped site.  PRZM and EXAMS were linked by
the program (PE4-PL, version 01).  Ground-water concentrations were
estimated using the Tier I screening model SCI-GROW (version 2.3,
compile 08/08/03).  Detailed description, documentation, and direct
links for running these models can be found in:   HYPERLINK
"http://www.epa.gov/oppefed1/models/water/index.htm" 
http://www.epa.gov/oppefed1/models/water/index.htm .  Model outputs are
given in Appendix 2.

	The standard farm pond scenario is used to estimate EECs for
ecological exposure.  The farm pond scenario, represents a 10-ha corn
(all cropped) field that is adjacent to a 1-ha pond that is 2 meters
deep standard pond (10,000-m2 pond, that has neither hydraulic inlets
nor outlets (i.e., pesticide cannot leave by outflow).  The Index
Reservoir (IR) is intended as a drop-in replacement for the standard
pond for use in drinking water exposure assessment.  It is used in a
manner similar to the standard pond, except that flow rates have been
modified to reflect local weather conditions.  The index reservoir (IR)
is approximately 82 m wide and 640 m long, with an area of 5.3 ha
(USEPA, 2000).  The area of the entire watershed is 172.8 ha, thus, the
field to watershed ratio is different.  Weather and agricultural
practices are simulated for 30 years so that the 10-year exceedance
probability at the site can be estimated. The simulation was generated
using 30 years of meteorological data, encompassing the years from 1961
to 1990. Guidance for using the IR is located at:   HYPERLINK
"http://www.epa.gov/pesticides/trac/science/html" 
http://www.epa.gov/pesticides/trac/science/html .  Model outputs are
given in Appendix 3.

The Percent Crop Area (PCA) is a generic watershed-based adjustment
factor that will be applied to pesticide concentrations estimated for
the surface water component of the drinking water exposure assessment
using PRZM/EXAMS with the index reservoir (IR).  The output generated by
the linked PRZM/EXAMS models is multiplied by the maximum percent of
crop area (PCA) in any watershed (expressed as a decimal) generated for
the crop or crops of interest.  Currently, OPP will apply PCA
adjustments for four major crops. Guidance for using PCAs and a thorough
discussion of this method and comparisons of monitoring and modeling
results for selected crop/site combinations is located at:
http://www.epa.gov/pesticides/trac/science/.  No PCA adjustment is
required for SCI-GROW.  Model outputs are given in Appendix 4.

Ground-Water Monitoring:

Lactofen Prospective Ground-Water (PGW) Monitoring Studies

The registrant previously conducted a small-scale PGW monitoring study,
where lactofen (Cobra) was applied at the rate of 0.45 lb ai/acre, at a
"hydro-geologically vulnerable" site in Ohio.  Site instrumentation was
standard and met minimum guideline requirements at the time or the
study.  Lactofen was not detected in ground water at or above the study
limit of quantification (1.0 µg/L).  Several detections were suspected,
but not verified, and were assumed by the registrant to be the result of
analytical interference.  Evidence of the metabolite acifluorfen
leaching was also not observed in this prospective study.  The Agency
concluded that there was no evidence to suggest the leaching of lactofen
or formation acifluorfen.  Since no tracer was used, there is no
collaborative evidence to demonstrate that any leaching actually took
place during the study (D203252).   

	A second small-scale PGW conducted for lactofen in Michigan (USEPA,
2003c).  Lactofen concentrations in soil declined with no evidence of
leaching. The soil and soil water concentrations of acifluorfen at the
Michigan lactofen PGW were typically lower than those observed at the
Wisconsin sodium acifluorfen PGW study.  This most likely is due to the
fact that the 0.40 lb ai/acre lactofen (Michigan site) yields about 0.23
lb ai/acre (58% conversion) compared to higher rate of sodium
acifluorfen used (0.75 lb ai/acre) in the Wisconsin study (D915031). 
The formation of acifluorfen from lactofen is not instantaneous, and
therefore will not move through the soil matrix a single “pulse”.   

	Low level concentrations of acifluorfen (degradate) were detected
during the Michigan lactofen PGW (USEPA, 2003c) in soil-water at several
depths (3- and 6-feet) (acifluorfen LOD in soil water = 0.035 µg/L),
but there were no detections in the ground water (acifluorfen LOD in
ground water = 0.035 µg/L).  The leaching of acifluorfen is not
unexpected based upon the fate 

data (low sorption and persistent).  Leaching of acifluorfen below six
feet is possible and also likely.  

Sodium Acifluorfen Prospective Ground-Water (PGW) Monitoring Studies

	The Wisconsin sodium acifluorfen PGW study (USEPA, 1989) reported
acifluorfen concentrations ranging from > 1 µg/L to 46 µg/L.  The long
term average acifluorfen concentration at the prospective study site was
7.33 µg/L.  Many were higher than those concentrations predicted by
SCI-GROW or observed in other monitoring studies (D291747).  The results
of this study are valid, but they probably do not represent conditions
under more typical conditions.  The sodium acifluorfen was applied in a
single 0.75 lb ai/acre application, the soil at the study site had a low
organic carbon content, low clay content, and water holding capacity;
and with predominately permanently charge surfaces.  Irrigation water
was applied based upon “estimated consumptive use” and irrigated
whether it rained or not.  Acifluorfen and the two primary degradates
were analyzed for (amino acifluorfen, desnitro acifluorfen) in the
study. No (sodium acifluorfen) degradates were detected, acifluorfen
concentrations decreased with time in the soil samples, the suction
lysimeters were effective in collecting water samples which contained
acifluorfen residue, and acifluorfen residue was eventually detected
ground-water monitoring well samples.  The fact that no degradates were
detected suggests that the acifluorfen residues were leached out of soil
and into ground water (D280710).

Survey Monitoring

	The Pesticides in Ground Water Data Base (PGWDB) (USEPA, 1992)
summarizes the results of a number of ground-water monitoring studies. 
Four of 1185 wells sampled, in one study, for acifluorfen reported
concentrations ranged from 0.003 to 0.025 μg/L.  The studies reported
in the PGWDB may reflect conditions where no lactofen or acifluorfen had
been used or where there is a low susceptibility to ground-water
contamination.  Therefore, EFED has low confidence that the monitoring
reflects the potential contamination of ground water from acifluorfen.  

	The maximum acifluorfen concentration was 0.19 µg/L (0.14% of 1476
samples) in the NAWQA study from wells in the mixed land use (major
aquifer surveys)     HYPERLINK
"http://ca.water.usgs.gov/pnsp/pestgw/Pest-GW_2001_Text.html" 
http://ca.water.usgs.gov/pnsp/pestgw/Pest-GW_2001_Text.html .  Since the
USGS NAWQA study is to assess water quality in general and not
specifically lactofen and acifluorfen, there is less confidence in using
these data to assess the potential for lactofen and acifluorfen to
contaminate ground water than the prospective studies. 

Surface Water Monitoring

	For acifluorfen, there have been a small number of detections in
(4.04% of 1233 samples from 48 sites with streams with agricultural land
use) the surface water monitoring program (NAQWA, 2/19/03;   HYPERLINK
"http://ca.water.usgs.gov/pnsp/pestsw/Pest-SW_2001_Text.html" 
http://ca.water.usgs.gov/pnsp/pestsw/Pest-SW_2001_Text.html ).

 μg/L.  Three samples out of 503 samples had acifluorfen residues in
land designated as urban use.  The maximum concentration was 0.060
μg/L.  The estimated values from PRZM/EXAMS tended to be higher than
maximum concentration seen in NAWQA monitoring data.  Because of the
high mobility and long persistence of acifluorfen in water, potentially
"high" concentrations of acifluorfen may exist in surface water bodies. 
Without specifically targeted monitoring data it is not possible to
determine peak environmental concentration.  The monitoring data
demonstrates the potential for acifluorfen to contaminate ground water. 

Citations

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/Environmental Research Laboratory.  U. S. Environmental Protection
Agency. Athens, GA.

Carsel et al.,  1997.  PRZM (Pesticide Root Zone Model) Version 3.12
beta (Compiled (05/24/01).  Environmental Research Laboratory.  U. S.
Environmental Protection Agency. Athens, GA.

Gaston, L.A., and M.A. Locke.  2000.  Acifluorfen sorption, degradation,
and mobility in a Mississippi Delta soil.  Soil Sci. Soc. Am. J.
4:112-121.

Leovey, Elizabeth.  2002.  PRZM Standard Crop/Location Scenarios,
Procedure to Develop and Approve New Scenarios, and PRZM Turf Modeling
Scenarios to Date.   February 27, 2002.

USEPA. OPP. Environmental Fate and Effects Division, Arlington, VA

USEPA. 1989.  Review of final report prospective ground-water monitoring
study. (EFGWB #89701; MRID 411728), 11-20-89. USEPA, OPPTS, OPP, EFED.
Arlington VA.

USEPA. 1992.  Pesticides in Ground Water Database.  A compilation of
monitoring studies: 1971 - 1991 National Summary.  EPA 734-12-92-001. 
U. S. Environmental Protection Agency: Arlington, VA. PRIVATE  

USEPA. 1999. Guidance for Use of the Index Reservoir in Drinking Water
Exposure Assessments. Arlington, VA.

USEPA.   2000. Drinking Water Screening Level Assessment. Part A:
Applying a Percent Crop Area Adjustment to Tier II Surface Water Model
Estimates for Pesticide Drinking Water Exposure Assessments. FQPA
Science Policy Document .Public Comment Draft September 1, 2000. 
Federal Register: October 11, 2000 (volume 65, number 197).  Electronic
copy available at http://www.epa.gov/pesticides/trac/science/ .

USEPA. 2002a. Guidance for Selecting Input Parameters in Modeling the
Environmental Fate and Transport of Pesticides,  Version II (February
28, 2002).   Office of Pesticide Programs, Environmental Fate and
Effects Division, U.S. Environmental Protection Agency. Arlington, VA.

USEPA. 2002b. Pesticide Root Zone Model (PRZM) Field and Orchard Crop
Scenarios: 

Standard Procedures for Conducting Quality Control and Quality
Assurance. Office of Pesticide Programs, Environmental Fate and Effects
Division, U.S. Environmental Protection Agency. Arlington, VA.

USEPA.  2003a.  Report of the Food Quality Protection Act (FQPA)
Tolerance Reassessment Progress and Risk Management Decision (TRED) for
Lactofen.  USEPA. OPPTS, EPA 738-R-04-002.  Washington DC.

USEPA.  2003b. Drinking Water Exposure Assessment For Lactofen, Updated
For Prospective Ground Water (PGW) Monitoring Study (01/21/03), USEPA.
OPPTS.OPP.EFED. Arlington, VA.

USEPA. 2003c   DER. A Small-Scale Prospective Ground Water Monitoring
Study for Lactofen (DP Barcode: D283774; 02/06/03). Office of Pesticide
Programs, Environmental Fate and Effects Division, U.S. Environmental
Protection Agency. Arlington, VA.

USEPA. 2003d. Use of Regional Percent Crop Area Factors in Refined
Drinking Water Assessments. Water Quality Technical Team. Environmental
Fate and Effects Division. USEPA Office of Pesticide Programs,
Arlington, VA. 

 

USEPA. 2003e. Addendum to EFED RED Chapter for sodium acifluorfen. 
Addendum to TRED for lactofen (D291747; September 15, 2003). Office of
Pesticide Programs, Environmental Fate and Effects Division, U.S.
Environmental Protection Agency. Arlington, VA. 

USEPA, 2003f.   SCI-GROW 2.3: Windows Version of SCI-GROW. September 30,
2003. Office of Pesticide Programs, Environmental
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