UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C.  20460

OFFICE OF           

PREVENTION, PESTICIDES

AND TOXIC SUBSTANCES

MEMORANDUM

Date:		12-March-2008

Subject:		Petition:  6F7146.  Glyphosate-Isopropylammonium and
Pyrithiobac Sodium.  Application to Glyphosate-Tolerant Soybeans. 
Summary of Analytical Chemistry and Residue Data.  

Petition:	6F7146	DP #s:	346713, 349700, and 349729

Registration:	352-606 - DuPont Staple Plus Herbicide	Decision #s:	372859
and 388020

40 CFR 180.	364 (glyphosate)

487 (pyrithiobac sodium)	MRID #s:	47007907, 47007908, 47007909,
47007910, 47007911, 47007912, 47119203, 47119204, 47119206, 47119207

PC Codes:	103601 - glyphosate isopropylammonium salt

417300 - glyphosate; free acid

078905 - pyrithiobac sodium





From:		Tom Bloem, Chemist

		Registration Action Branch 1; Health Effects Division (RAB1/HED;
7509P)

Through:		George F. Kramer, Ph.D., Senior Chemist

		RAB1/HED (7509P)

To:		James Tompkins RM 25

		Registration Division (RD; 7505P)

DuPont requested a Section 3 registration for the preplant application
of glyphosate and pyrithiobac sodium to glyphosate-tolerant soybean.  In
addition, the petitioner is requesting that the tolerance expression for
40 CFR 180.364(a) be altered from glyphosate per se to the combined
residues of glyphosate and N-acetyl-glyphosate
(N-acetyl-N-(phosphonomethyl) glycine).  

Executive Summary

Background:  Glyphosate is a nonselective Group 9 herbicide that is
currently registered for pre- and postemergence application to a variety
of fruit, vegetable, and field crops.  Tolerances are currently
established for residues of glyphosate per se resulting from the
application of glyphosate, the isopropylamine salt of glyphosate, the
ethanolamine salt of glyphosate, the ammonium salt of glyphosate, and
the potassium salt of glyphosate in/on various plant commodities at
0.2-400 ppm (40 CFR §180.364(a)).  The Glyphosate Reregistration
Eligibility Decision (RED) document was issued September 1993. 
Pyrithiobac sodium is an acetolactate synthase (ALS) inhibiting
herbicide and is currently registered for application to cotton with
tolerances for residues of parent at 0.02 in/on cottonseed and 0.15 ppm
in/on cotton gin byproducts (40 CFR 180.487(a)); no pyrithiobac sodium
tolerances are established in/on soybean, meat, milk, poultry, or eggs. 

DuPont requested a Section 3 registration for the preplant application
of glyphosate and pyrithiobac sodium to glyphosate-tolerant soybean. 
The petitioner is also working to commercialize a genetically modified
soybean designated as Optimum( GAT( soybean (DP-356Ø43-5).  The
petitioner indicated that Optimum( GAT( soybean was engineered to
express the microbial glyphosate acetyltransferase gene (gat4601), which
confers tolerance to glyphosate via acetylation of the secondary amine
group of glyphosate, and the gm-hra gene, which confers tolerance to
ALS-inhibiting herbicides via encoding for an ALS protein which is not
sensitive to the ALS-inhibiting herbicides.  As a result of the
introduction of this genetically modified soybean, the petitioner is
requesting that the glyphosate tolerance expression (40 CFR 180.364(a))
be altered from glyphosate per se to the combined residues of glyphosate
and N-acetyl-glyphosate; no changes in the pyrithiobac sodium tolerance
expression or tolerances is requested.    

Proposed Uses:  The petitioner submitted proposed supplemental labeling
for the preplant application of DuPont Staple® Plus herbicide (EPA Reg.
No. 352-606; 40.2% glyphosate; 1.7% pyrithiobac sodium; water-soluble
packet/water soluble liquid) to glyphosate-tolerant soybeans (10-month
plant-back interval (PBI)).  Table 6 is a summary of the proposed
application scenario.  HED concludes that the proposed application
instructions are adequate.  HED notes that glyphosate and ALS-inhibiting
herbicide formulated products that are currently registered for
application to soybean may also be applied to Optimum( GAT( soybean.  

Pyrithiobac Sodium - Nature/Magnitude of the Residue (Plants/Livestock):
 The petitioner is proposing preplant application to glyphosate-tolerant
soybean (10-month PBI).  Based on the proposed application scenario and
since pyrithiobac sodium is not currently registered for application to
soybean, HED concludes that the nature of the residue in primary crops
is not relevant to the current petition.  Furthermore, since residues
in/on soybean are expected to be insignificant as a result of the
proposed use (see next paragraph, soybean tolerances for pyrithiobac
sodium will not be required), the nature of the residue in livestock is
also not relevant to the current petition.  

 

The HED Metabolism Assessment Review Committee (MARC) reviewed a
confined rotational crop study and determined that the residue of
concern in rotational crops is pyrithiobac sodium per se (D216002, G.
Kramer, meeting of 1-Jun-1995).  The confined rotational crop study
employed a single bare soil application at 0.125 lb ai/acre (3.9x the
proposed rate) with soybean, carrot, lettuce, and wheat planted 30, 120,
and 240/263 days after application.  For those crops/extracts which
required analysis, residues of pyrithiobac-sodium were ≤0.003 ppm
(D195332, G. Kramer, 13-Jun-1994).  Based on these data and since the
label indicates that glyphosate-tolerant soybean may not be planted for
10 months following application, HED concludes that residues in soybean,
as a result of the proposed use, will be insignificant.  

ALS-Inhibiting Herbicides - Nature/Magnitude of the Residue (Plants): 
As indicated above, ALS-inhibiting herbicide formulated products that
are currently registered for application to soybean may also be applied
to Optimum( GAT( soybean.  The petitioner has not submitted information
concerning the nature/magnitude of these residues in/on Optimum( GAT(
soybean.  The petitioner indicated that the gm-hra gene, which confers
tolerance to ALS-inhibiting herbicides, is a modified version of the
endogenous soybean ALS gene; this modified ALS gene codes for an ALS
protein that is not sensitive to ALS-inhibiting herbicides (ALS
herbicides can not bind with the modified ALS protein).  The petitioner
indicated that the modified protein is >99% identical to the endogenous
soybean ALS protein with two amino acid changes known to confer
herbicide tolerance.  The petitioner submitted a rationale (letter dated
21-Feb-2008, Jacob Vukich, DuPont Crop Protection) concerning the need
for data pertaining to the nature/magnitude of ALS-inhibiting herbicides
in/on Optimum( GAT( soybean (reviewed by the Chemistry Science Advisory
Committee (ChemSAC)).  Since ALS tolerance is conferred via modification
of the endogenous ALS soybean gene such that the plant is no longer
sensitive (i.e., tolerance is not conveyed via metabolism of the
herbicide), HED concludes that the nature/magnitude of the residue data
submitted in support of the registration for application of
ALS-inhibiting herbicides to nontransgenic soybean are applicable for
the application of these compounds to Optimum( GAT( soybean (additional
nature/magnitude of the residue are unnecessary; ChemSAC minutes of
27-Feb-2008 meeting).  

Glyphosate - Nature/Magnitude of the Residue (Plants/Livestock):  As
indicated above, glyphosate formulated products that are currently
registered for application to soybean may also be applied to Optimum(
GAT( soybean.  The petitioner has submitted information concerning the
nature and magnitude of glyphosate residues in/on Optimum( GAT( soybean.
 The petitioner has also submitted information concerning the nature of
N-acetyl-glyphosate, a metabolite found in Optimum( GAT( soybean
following application of glyphosate, in livestock.  

Nature of the Residue – Plants:  Metabolism studies conducted with
nontransgenic corn, cotton, soybeans, and wheat were previously
submitted and reviewed.  Based on these data, HED concluded that the
residue of concern in nontransgenic plants is glyphosate per se (Memo,
R. Perfetti, 19-Oct-1992; RED, R. Perfetti, 27-Oct-1992; Memo, R.
Perfetti, 17-Mar-1994).  Metabolism studies have also been submitted on
glyphosate-tolerant canola (D242628, T. Bloem, 30-Nov-1998) and
glyphosate-tolerant corn (D217539, G. Kramer, 14-Mar-1996).  The
glyphosate-tolerant canola and corn were genetically modified to express
the enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene derived from
Agrobacterium sp. (strain CP4) which codes for an EPSPS protein that has
reduced affinity for glyphosate as compared to the endogenous EPSPS
protein.  The glyphosate-tolerant canola and corn were also genetically
engineered to express the oxireductase gene which converts glyphosate to
the nonherbicidal aminomethylphosphonic acid (AMPA).  Metabolism in
these varieties of transgenic canola and corn was essentially the same
as the nontransgenic plants.  Therefore, it was concluded that the
terminal residue to be regulated, in nontransgenic plants and transgenic
corn and canola modified to express the Agrobacterium sp EPSPS and
oxireductase genes, is glyphosate per se.

Since Optimum( GAT( soybean represents a new variety of
glyphosate-tolerant soybean, the petitioner submitted a summary of what
they termed a "pilot" study conducted on greenhouse-grown Optimum( GAT(
soybean (MRID 47119203).  HED requests that the petitioner submit the
full study as specified in 860.1300.  Based on the submitted data, the
major residues in Optimum( GAT( soybean following a single foliar
glyphosate application at 2.0 lb ae/acre (R2 crop stage) are glyphosate
and N-acetyl-glyphosate (preharvest interval (PHI) of 18 and 68 days). 
Provided the petitioner agrees to submit the requested study and based
on the currently-available data, HED concludes that the residues of
concern in Optimum( GAT( soybean following foliar application of
glyphosate are glyphosate and N-acetyl-glyphosate.

Nature of the Residue – Livestock:  The qualitative nature of the
residue in livestock following dosing with glyphosate and AMPA is
adequately understood.  Studies with lactating goats and laying hens fed
a mixture of glyphosate and AMPA indicate that the primary route of
elimination was by excretion (urine and feces).  These results are
consistent with metabolism studies in rats, rabbits, and cows.  The MARC
determined that the terminal residue to be regulated in livestock is
glyphosate per se (Memo, R. Perfetti, 19-Oct-1992; RED, R. Perfetti,
27-Oct-1992; Memo, R. Perfetti, 17-Mar-1994).  

 analysis was a Tier 1 assessment and resulted in exposures ≤9% HED's
level of concern.  Based on the currently available data, the residues
of concern in livestock following consumption of glyphosate and
N-acetyl-glyphosate, for tolerance expression and risk assessment
purposes, are glyphosate and N-acetyl-glyphosate.  

Magnitude of the Residue – Primary Crops:  The petitioner is proposing
preplant application of glyphosate to glyphosate-tolerant soybean
(10-month PBI).  Based on previously-reviewed confined rotational crop
studies (3.71 lb ai/acre; MRIDs 41543201 and 41543202, A. Abramovitch,
14-Oct-1992), HED concluded that a 30-day PBI was appropriate for all
nonlabeled crops (D200041, G. Kramer, 12-May-1994).  Since the rate
conducted in the confined rotational crop study was 4.9x the proposed
rate and since the label indicates the soybean may not be planted for 10
months following application, HED concludes that residues in soybean, as
a result of the proposed use, will be insignificant.  

The petitioner submitted Optimum( GAT( soybean magnitude of the residue
studies which monitored for residues of glyphosate and
N-acetyl-glyphosate following application of glyphosate at 1x (forage
and hay) or 1.3x (seed) the currently registered rate.  The studies were
conducted in the U.S. (n=6), Chile (n=13), and Argentina (n=2) and
resulted in combined residues of glyphosate and N-acetyl-glyphosate
(expressed as glyphosate) in/on soybean forage, hay, and seed less then
the currently established glyphosate per se tolerances of 100 ppm, 200
ppm, and 20 ppm, respectively (residues were less than the current
tolerance when corrected for exaggerated rate or for residue decline). 
Based on comparison of "growing day units," day length, and minimum
temperature conducted by the petitioner, the U.S. and Chile growing
sites were similar.  The petitioner did not provide a comparison between
the U.S. and Argentina growing sites and did not provide a comparison of
precipitation between the U.S. and Chile sites as the agricultural
production in central Chile is dependent on in-furrow irrigation.  HED
notes that the residues from the Chile and Argentina field trials were
greater than the residues from the U.S. field trials.  This may in part
be explained by the drip and in-furrow irrigation employed at the Chile
and Argentina field trials and the lack of irrigation (precipitation was
sufficient) or overhead irrigation employed at the U.S. field trials. 
Based on a comparison of weather and the resulting residues (residues
from the South America > than those form the U.S. while still being less
than the current tolerances), the trials conducted in South America are
acceptable; no additional field trial data are required.  Based on the
submitted data, HED concludes that the tolerance expression should
change from glyphosate per se to combined residues of glyphosate and
N-acetyl-glyphosate (expressed as glyphosate; numerical value of the
tolerance is acceptable).   

Magnitude of the Residue – Processed Commodities:  The following
soybean processed commodity tolerances for residue of glyphosate per se
are currently established:  soybean hull – 100 ppm and aspirated grain
fractions (AGF) – 100 ppm.  HED has concluded that glyphosate and
N-acetyl-glyphosate residues will be insignificant as a result of the
proposed use.  The petitioner has submitted Optimum( GAT( soybean
processing studies which monitored for residues of glyphosate and
N-acetyl-glyphosate following application of glyphosate at 1.3x or 6.7x
the currently registered rate.  The resulting average processing factors
for the combined residues of glyphosate and N-acetyl-glyphosate in AGF,
hulls, meal, and refined oil were 18.1, 6.9, 0.33, and <0.05,
respectively.  Based on these data and the soybean seed highest-average
field trial (HAFT; 17 ppm), soybean hull and AGF tolerances for the
combined residues of glyphosate and N-acetyl-glyphosate (expressed as
glyphosate) of 120 ppm and 310 ppm, respectively, are appropriate.  A
revised Section F is requested.

Magnitude of the Residue – Livestock:  Based on the data submitted
with the current petition, HED concluded that the residues of concern in
livestock/plants will change from glyphosate per se to the combined
residues of glyphosate and N-acetyl-glyphosate (expressed as
glyphosate); the numerical value of the currently-established plant
tolerances will remain the same for all plant commodities excluding
(from 100 ppm to 120 ppm) and AGF (from 100 ppm to 310 ppm).  The field
trial and processing studies indicated that the principal residue in
Optimum( GAT( soybean is N-acetyl-glyphosate.  The N-acetyl-glyphosate
rat metabolism study (Sprague Dawley; male only) resulted in 66% of the
dosed material being eliminated in the urine and 26% in the feces.  The
glyphosate rat metabolism study (Sprague Dawley) resulted in ~30% and
~62% of the administered dose being eliminated in the urine and feces,
respectively.  Therefore, the N-acetyl-glyphosate metabolite is absorbed
at a greater rate than glyphosate.  

HED notes that the livestock method validation study (MRID 47311011)
referenced poultry and ruminant feeding studies that employed dosing
with N-acetyl-glyphosate; these data have not been submitted to HED. 
HED concludes that the currently available glyphosate per se livestock
feeding studies are sufficient for a conditional registration for the
following reasons (unconditional registration will require the
submission of the aforementioned livestock feeding studies):  (1) based
on the previously calculated dietary burdens (driven by the 400-ppm
alfalfa meal and hay tolerances), the revised Table 1, and the latest
guidance concerning the construction of livestock diets, the potential
dietary burden to N-acetyl-glyphosate relative to the dietary burden
used to calculate the current tolerances is minimal; (2) HED has
determined that N-acetyl-glyphosate is toxicologically equivalent to
glyphosate (see HED risk assessment D345923 (in draft)); and (3) the
previous dietary analysis was a Tier 1 assessment and resulted in
exposures ≤9% HED's level of concern.  Furthermore, based on the
previously calculated dietary burdens (driven by the 400-ppm alfalfa
meal and hay tolerances), the revised Table 1, and the latest guidance
concerning the construction of livestock diets, HED concludes that the
increased soybean hull and AGF tolerances will not result in the need to
increase the current livestock tolerances.   

Analytical Enforcement Method:  HED is not recommending for the
establishment of or changes to the currently established pyrithiobac
sodium or ALS-inhibiting herbicide tolerances; therefore, a discussion
of the enforcement methods for these compounds is unnecessary.  

HED is recommending that the tolerance expression for glyphosate (40 CFR
180.364(a); plant and livestock tolerances) change from glyphosate per
se to the combined residues of glyphosate and N-acetyl-glyphosate
(expressed as glyphosate).  The petitioner has proposed DuPont method
15444 and DuPont method 20009 for enforcement of the plant and livestock
tolerances, respectively (liquid chromatograph/mass spectrometer/mass
spectrometer (LC/MS/MS) methods).  Adequate validation and independent
laboratory validation (ILV) for each of the methods has been submitted. 
The validated limit of quantitation (LOQ) was 0.05 ppm for each analyte
in parent equivalents for plant and livestock tissue commodities and
0.025 ppm for milk and eggs (the reported limits of detection (LODs)
were 0.003-0.02 ppm).  The plant method has been adequately
radiovalidated for residues of glyphosate but no radiovalidation data
for N-acetyl-glyphosate were submitted.  For the livestock method, the
petitioner has submitted radiovalidation data comparing the total
radioactive residues (TRRs) extracted using Method 20009 to the TRRs
extracted from a poultry metabolism study (liver, fat, and muscle; dosed
with 14C-N-acetyl-glyphosate).  Since the poultry metabolism study has
not been submitted to HED, HED is unaware of the adequacy of the
extraction procedures performed in the metabolism study to extract the
residues of concern; therefore, the adequacy of the radiovalidation data
can not be determined.    

The methods have been forwarded to the Analytical Chemistry Laboratory
(ACL) for petition method validation (PMV; D349696, T. Bloem,
5-Mar-2008).  The petitioner is requested to submit radiovalidation data
for N-acetyl-glyphosate (plant method), submit the poultry metabolism
study referenced in the livestock method validation study (MRID
47311011; dosed with 14C-N-acetyl-glyphosate), and revise the plant
method as specified in the ILV (temperature of the water bath used to
precipitate proteins from soybean seed/meal (80-85 °C)); in addition,
the petitioner will be required to make all requested revisions to the
plant and/or livestock methods, if any, requested in the forthcoming
PMV.   

Recommendations:  Provided the petitioner submits a revised Section F
(see below) and the ACL is able to successfully validate the
plant/livestock enforcement methods, HED concludes that the residue
chemistry database supports a conditional registration for the preplant
application of glyphosate and pyrithiobac sodium to glyphosate-tolerant
soybean.  A human-health risk assessment will be prepared as a separate
document.  

A revised Section F specifying the tolerances listed in Table 1 for the
combined residues of glyphosate and N-acetyl-glyphosate (expressed as
glyphosate) resulting from the application of glyphosate, the
ethanolamine salt of glyphosate, the ammonium salt of glyphosate, and
the potassium salt of glyphosate, is requested.  

Table 1:  Tolerance Summary.

Commodity	Proposed 

Tolerance (ppm)	HED-Recommended Tolerance (ppm)	Comments

soybean, hulls	100	120	increase tolerances; change tolerance expression
(see underlined above)

grain, aspirated fractions	100	310

	

The residue chemistry database will support an unconditional
registration upon submission of data that adequately addresses the
following issues:  

●Nature of the Residue - Plants:  The petitioner is requested to
submit the full Optimum( GAT( soybean metabolism study as specified in
860.1300.

●Nature of the Residue - Livestock:  The petitioner is requested to
submit the ruminant and poultry metabolism studies referenced in the
livestock method validation study (MRID 47311011; dosed with
14C-N-acetyl-glyphosate).  

●Plant/Livestock Enforcement Methods:  The petitioner is requested to
submit radiovalidation data for N-acetyl-glyphosate (plant method) and
revise the plant method as specified in the ILV (water bath temperature
used to precipitate proteins (80-85 °C)); in addition, the petitioner
will be required to make all requested revisions to the plant and/or
livestock methods, if any, requested in the forthcoming PMV.  Also, upon
review of the poultry metabolism data, the adequacy of the already
submitted radiovalidation data for the livestock enforcement method will
be evaluated.  

●Meat, Milk, Poultry, and Eggs:  The petitioner is requested to submit
the ruminant and poultry feeding studies referenced in the livestock
validation study (MRID 47311011; dosed with N-acetyl-glyphosate).

HED notes that several of the currently established glyphosate per se
crop tolerances are at 0.1 ppm.  In addition, the glyphosate per se egg
tolerance is at 0.05 ppm.  With the addition of N-acetyl-glyphosate to
the tolerance expression, there is a possibility of over-tolerance
residues if residues of N-acetyl-glyphosate at the LOQ are assumed (LOQ
= 0.05 ppm for crops and 0.025 ppm for egg).  Based on the rationale
provided in attachment 6, HED concludes that the currently established
tolerances are appropriate for combined residues of glyphosate and
N-acetyl-glyphosate (expressed as glyphosate; see attachment 6 for more
information).  

Background

Glyphosate is a nonselective Group 9 herbicide that is currently
registered for pre- and post-emergence application to a variety of
fruit, vegetable, and field crops.  Tolerances are currently established
for residues of glyphosate resulting from the application of glyphosate,
the isopropylamine salt of glyphosate, the ethanolamine salt of
glyphosate, the ammonium salt of glyphosate, and the potassium salt of
glyphosate in/on various plant commodities at 0.2-400 ppm [40 CFR
§180.364(a)].  The RED document was issued September 1993.  The
chemical structure/nomenclature and physicochemical properties of
glyphosate are presented in Tables 2 and 3.  

Pyrithiobac sodium is an ALS-inhibiting herbicide and is currently
registered for application to only cotton with tolerances for residue of
parent at 0.02 in/on cottonseed and 0.15 ppm in/on cotton gin byproducts
(40 CFR 180.487); no pyrithiobac sodium tolerances are established in/on
soybean, meat, milk, poultry, or eggs.  The chemical
structure/nomenclature physicochemical properties of glyphosate are
presented in Tables 4 and 5.  



Common name	Glyphosate (PC code 471300)

Company experimental name	DPX-B2856

IUPAC/CAS name	N-(phosphonomethyl)glycine

CAS registry number	1071-83-6



Table 3:  Physicochemical Properties of the Technical Grade Glyphosate.

Parameter	Value	Reference 1

Melting point/range	189.5 ± 0.5 °C	The Pesticide Manual, 13th Edition

pH	1.9 at 20 °C

	Density	1.705 g/cm3 at 20 °C

	Water solubility	10.5 g/L at 20 °C

	Solvent solubility	acetone		0.078 g/L

methanol		0.231 g/L

hexane		0.026 g/L

ethyl acetate	0.012 g/L

dichloromethane	0.233 g/L

n-octanol		0.020 g/L

propan-2-ol	0.020 g/L

toluene		0.036 g/L	European Commission:  Glyphosate 6511/VI/99-final,
1/21/02

Vapor pressure	1.31 x 10-2 mPa at 25 °C	The Pesticide Manual, 13th
Edition

Dissociation constant, pKa	0.8 (1st phosphoric), 2.3 (carboxylate), 6.0
(2nd phosphoric), and 11.0 (amine)	Knuuttila.  1979 Acta Chem. Scand. B
33:623-626

Octanol/water partition coefficient, Log(KOW)	-3.2 (pH 2-5,  25 °C)
European Commission:  Glyphosate 6511/VI/99-final, 1/21/02

UV/visible absorption spectrum	ε = 0.086 (295nm)

	1 As reported by the petitioner in MRID 47007908.



 

Common name	pyrithiobac (PC code 078905)

Company experimental name	--

CAS name	2-chloro-6-[(4,6-dimethoxy-2-pyrimidinyl)thio]benzoic acid

IUPAC	2-chloro-6-(4,6-dimethoxypyrimidin-2-ylthio)benzoic acid

CAS registry number	123342-93-8 (acid) 123343-16-8 (sodium salt)



Table 5:  Physicochemical Properties of the Technical Grade Glyphosate.

Parameter	Value	Reference

Melting point/range	232.8-234.2  ºC	D195332, G. Kramer, 13-Jun-1994

pH	4.93 (1% m/v)

	Density (22.5 (C)	1.6 g/ml @ 22.5 ºC

	Water solubility (20 (C)	728 ± 27 g/l at 20 ºC

	Solvent solubility (20 (C)	acetone	0.812 ± 0.109

acetonitrile	0.347 ± 0.027

dichloromethane	0.008 ± 0.006

ethyl acetate	0.205 ± 0.097

hexane	0.010 ± 0.007

methanol	270 ± 19

toluene	0.005 ± 0.004

octanol	13.1 ± 3.3

	Vapor pressure (25 (C)	3.6 x 10-11 mm Hg

	Dissociation constant, pKa (20 (C)	pKa = 2.34 ± 0.21

	Octanol/water partition coefficient (KOW)	pH 3.0	132.51 ± 5.50

pH 5.0	4.02 ± 0.50

pH 7.0	0.15 ± 0.01

pH 9.0	0.06 ± 0.01

	UV/visible absorption spectrum	not available

	860.1200 Directions for Use

The petitioner submitted proposed supplemental labeling for the preplant
application of DuPont Staple® Plus herbicide (EPA Reg. No. 352-606;
40.2% glyphosate; 1.7% pyrithiobac sodium; water-soluble packet/water
soluble liquid) to soybeans (10-months PBI).  Table 6 is a summary of
the proposed application scenario.  HED concludes that the proposed
application instructions are adequate.  

 (single rate of ≤1.53 lb ae/acre); and preharvest - 0.77 lb ae/acre
(do not apply more than 2.26 lb ae/acre from emergence to harvest). 
Pyrithiobac sodium is not currently registered for application to
soybean; however, the registered pyrithiobac sodium cotton label
indicates a 10-month PBI for soybean following application to cotton
(cotton is the only registered crop; 0.125 lb ai/acre/year).  Several
ALS-inhibiting herbicide products are registered for application to
soybean.        

Table 6:  Summary of Proposed Glyphosate-Tolerant Soybean Application
Scenario.

App. Timing, Type, 

and Equip.	Formulation

(EPA Reg. No.)	App. Rate

(lb ai/acre)	Max. No. App. per Season	Use Directions and Limitations

preplant burndown,  broadcast sprays using ground (5-20 GPA) or aerial
equipment (≥3GPA) 	water-soluble packet/water soluble liquid 

(352-606)	pyrithiobac sodium  - 0.032

glyphosate - 0.75	1	-Allow at least 10 months between app. and planting
of glyphosate-tolerant soybean.

-App. through irrigation equipment is prohibited.

1  GPA = gallons per acre

860.1300 Nature of the Residue - Plants and Livestock

Pyrithiobac Sodium:  The petitioner is proposing preplant application to
glyphosate-tolerant soybean (10-month PBI).  Based on the proposed
application scenario and since pyrithiobac sodium is not currently
registered for application to soybean, HED concludes that the nature of
the residue in primary crops is not relevant to the current petition. 
Furthermore, since residues in/on soybean are expected to be
insignificant as a result of the proposed use (see rotational crop
section), the nature of the residue in livestock is also not relevant to
the current petition. 

ALS-Inhibiting Herbicides:  As indicated above, ALS-inhibiting herbicide
formulated products that are currently registered for application to
soybean may also be applied to Optimum( GAT( soybean.  The petitioner
has not submitted information concerning the nature/magnitude of these
residues in/on Optimum( GAT( soybean.  The petitioner indicated that the
gm-hra gene, which confers tolerance to ALS-inhibiting herbicides, is a
modified version of the endogenous soybean ALS gene; this modified ALS
gene codes for an ALS protein that is not sensitive to ALS-inhibiting
herbicides (ALS herbicides can not bind with the modified ALS protein). 
The petitioner indicated that the modified protein is >99% identical to
the endogenous soybean ALS protein with two amino acid changes known to
confer herbicide tolerance.  The petitioner submitted a rationale
(letter dated 21-Feb-2008, Jacob Vukich, DuPont Crop Protection)
concerning the need for data pertaining to the nature/magnitude of
ALS-inhibiting herbicides in/on Optimum( GAT( soybean (reviewed by the
ChemSAC).  Since ALS tolerance is conferred via modification of the
endogenous ALS soybean gene such that the plant is no longer sensitive
(i.e., tolerance is not conveyed via metabolism of the herbicide), HED
concludes that the nature/magnitude of the residue data submitted in
support of the registration for application of ALS-inhibiting herbicides
to nontransgenic soybean are applicable for the application of these
compounds to Optimum( GAT( soybean (additional nature/magnitude of the
residue are unnecessary; ChemSAC minutes of 27-Feb-2008 meeting).  

Glyphosate:  The following is a summary of the residue of concern in
plants and livestock.  

Nature of the Residue – Plants:  Metabolism studies conducted with
nontransgenic corn, cotton, soybeans, and wheat were previously
submitted and reviewed.  Based on these data, HED concluded that the
residue of concern in nontransgenic plants is glyphosate per se (Memo,
R. Perfetti, 19-Oct-1992; RED, R. Perfetti, 27-Oct-1992; Memo, R.
Perfetti, 17-Mar-1994).  Metabolism studies have also been submitted on
glyphosate-tolerant canola (D242628, T. Bloem, 30-Nov-1998) and
glyphosate-tolerant corn (D217539, G. Kramer, 14-Mar-1996).  The
glyphosate-tolerant canola and corn were genetically modified to express
the EPSPS gene derived from Agrobacterium sp. (strain CP4) which codes
for an EPSPS protein that has reduced affinity for glyphosate as
compared to the endogenous EPSPS protein.  The glyphosate-tolerant
canola and corn were also genetically engineered to express the
oxireductase gene which converts glyphosate to the nonherbicidal AMPA. 
Metabolism in these varieties of transgenic canola and corn was
essentially the same as the nontransgenic plants. Therefore, it was
concluded that the terminal residue to be regulated, in nontransgenic
plants and transgenic corn and canola modified to express the
Agrobacterium sp. EPSPS and oxireductase genes, is glyphosate per se.

Since Optimum( GAT( soybean represents a new variety of
glyphosate-tolerant soybean, the petitioner submitted a summary of what
they termed a "pilot" study conducted on greenhouse-grown Optimum( GAT(
soybean (MRID 47119203; see below for summary).  HED requests that the
petitioner submit the full study as specified in 860.1300.  Based on the
submitted data, the major residues in Optimum( GAT( soybean following a
single foliar glyphosate application at 2.0 lb ae/acre (R2 crop stage)
are glyphosate and N-acetyl-glyphosate (preharvest interval (PHI) of 18
and 68 days).  Provided the petitioner agrees to submit the requested
study and based on the currently-available data, HED concludes that the
residues of concern in Optimum( GAT( soybean following foliar
application of glyphosate are glyphosate and N-acetyl-glyphosate.

Nature of the Residue – Livestock:  The qualitative nature of the
residue in livestock following dosing with glyphosate and AMPA is
adequately understood.  Studies with lactating goats and laying hens fed
a mixture of glyphosate and AMPA indicate that the primary route of
elimination was by excretion (urine and feces).  These results are
consistent with metabolism studies in rats, rabbits, and cows.  The MARC
determined that the terminal residue to be regulated in livestock is
glyphosate per se (Memo, R. Perfetti, 19-Oct-1992; RED, R. Perfetti,
27-Oct-1992; Memo, R. Perfetti, 17-Mar-1994).  

ious dietary analysis was a Tier 1 assessment and resulted in exposures
≤9% HED's level of concern.  Based on the currently available data,
the residues of concern in livestock following consumption of glyphosate
and N-acetyl-glyphosate, for tolerance expression and risk assessment
purposes, are glyphosate and N-acetyl-glyphosate.  

					

Optimum( GAT( Soybean Metabolism (MRID 47119203):  The Optimum( GAT(
soybean plants were treated with a single foliar application of
14C-glyphosate sequisodium salt at a rate of 2.0 lb ae/acre (location of
radiolabel was not indicated; treated at the R2 stage - full flowering
with some pods present, BBCH65).  Crop samples were collected 18
(immature foliage and pods with beans) and 68 (straw, pods, and beans)
days after foliar application.  The harvested samples were extracted
(solvent was not indicated) with TRRs determined as the sum of TRRs in
the extracts and the unextracted material.  The extracts were analyzed
via a high-performance liquid chromatograph (HPLC); the day-68 straw,
pods, and bean extracts were also subjected to enzyme digestion and
analyzed a second time via HPLC (released additional glyphosate (2-13%
TRR) from straw, pods, and beans and additional N-acetyl-glyphosate (4%
TRR) from straw).  Table 7 is a summary of the identified residues and
Attachment 3 is the petitioner proposed metabolic pathway in Optimum(
GAT( soybean.  

Table 7:  Summary of Identified Residues from the GAT Soybean Metabolism
Study.

	day-18 foliage

(2.09 ppm)	day-18 pods/bean

(0.43 ppm)	day-68 straw

(13.54 ppm)	day-68 pods

(2.89 ppm)	day-68 bean

(1.35 ppm)

	% TRR	ppm	% TRR	ppm	% TRR	ppm	% TRR	ppm	% TRR	ppm

Glyphosate1	60.2	1.26	16.9	0.07	56.2	7.61	17.5	0.54	2.2	0.03

N-acetyglyphosate2	22.0	0.46	60.0	0.26	28.9	3.92	55.8	1.61	59.2	0.80

AMPA	2.8	0.06	not detected	3.6	0.48	not detected	not detected

N-acetyl-AMPA	not detected	4.6	0.02	not detected	2.1	0.06	12.7	0.17

unknown3	not detected	6.0	0.02	6.0	0.82	8.0	0.23	13.5	0.18

total identified	85.0	1.78	81.5	0.35	88.7	12.01	75.4	2.21	74.1	1.00

unextracted	not provided

1  The day 68 samples were subjected to enzyme digestion with 2-13% of
the identified glyphosate formed after enzyme digestion.

2  The day 68 samples were subjected to enzyme digestion with 4% of the
identified N-acetyl-glyphosate in straw formed after enzyme digestion.

3  One or more unidentified components each <5% TRR.

Rumen Fluid Incubation (MRID 47007907):  Selected extracts of GAT
expressing corn and tobacco plants containing glyphosate and
N-acetyl-glyphosate were incubated with active rumen fluid for up to 24
hours (pH 7, 37 (C).  No significant change in the chromatographic
profile was observed in pre- and post-incubation samples. 

Fertile Hen Egg Incubation (MRID 47007907):  Fertile hen eggs (day -6
fertility) were dosed with an aqueous solution of
14C-N-acetyl-glyphosate a ca 1 mg/egg and incubated for 9 days (37 (C). 
The dose was injected into the albumen sac of the eggs.  The
distribution of radioactivity was 24% ,4%, and 62% of the dose in the
allantoic fluid, embryo, and yolk, respectively. Approximately 91% of
the dose was recovered.  N-acetyl-glyphosate (96% TRR) was the only
significant component in the allantoic fluid, embryo, and yolk extracts.


	

Rat Liver S9 Supernatant Incubation (MRID 47007907): 
14C-N-acetyl-glyphosate was incubated in pH 7.4 phosphate buffer
containing rat liver S9 (MoltoxTM, Sprague Dawley male rat) supernatant
for 24 hours (37 (C).  No metabolites of N-acetyl-glyphosate were
observed.  

Rat Metabolism (MRID 47007907):  The absorption, metabolism, and
elimination of N-acetyl-glyphosate were evaluated in male rats following
administration of 14C-N-acetyl-glyphosate.  Following a single oral dose
of 14C-N-acetyl-glyphosate to male rats (15 mg/kg acid equivalents),
approximately 66% of the dose was excreted in urine, and approximately
26% in feces.  Over 90% of the radioactivity was excreted within 48
hours post dose.  Minimal metabolism occurred, with unchanged
14C-N-acetyl-glyphosate representing more than 99% of the total
administered radioactivity detected in urine and feces.  Trace amounts
of 14C-glyphosate (<1% of dose) were detected in feces. 
14C-N-acetyl-glyphosate was the only radioactive component in plasma,
and was eliminated from blood and plasma with half-lives of 20.1 and
15.6 hours, respectively.

860.1340 Residue Analytical Methods

47007908.der.doc; 47311011.der.doc

Pyrithiobac Sodium and ALS-Inhibiting Herbicides - HED is not
recommending for the establishment of or changes to the currently
established pyrithiobac sodium or ALS-inhibiting herbicide tolerances;
therefore, a discussion of the enforcement methods for these compounds
is unnecessary.  

Glyphosate:  HED is recommending that the tolerance expression for
glyphosate (40 CFR 180.364(a); plant and livestock tolerances) change
from glyphosate per se to the combined residues of glyphosate and
N-acetyl-glyphosate (expressed as glyphosate) and is recommending for an
increase in the soybean hull (from 100 ppm to 120 ppm) and AGF (from 100
ppm to 310 ppm) tolerances.  The petitioner has proposed DuPont method
15444 and DuPont method 20009 for enforcement of the plant and livestock
tolerances, respectively.  Adequate validation and ILV for each of the
methods has been submitted.  The plant method has been adequately
radiovalidated for residues of glyphosate but no radiovalidation data
for N-acetyl-glyphosate were submitted.  For the livestock method, the
petitioner has submitted radiovalidation data comparing the TRRs
extracted using Method 20009 to the TRRs extracted from a poultry
metabolism study (liver, fat, and muscle; dosed with
14C-N-acetyl-glyphosate).  Since the poultry metabolism study has not
been submitted to HED, HED is unaware of the adequacy of the extraction
procedures performed in the metabolism study to extract the residues of
concern; therefore, the adequacy of the radiovalidation data can not be
determined.    

The methods have been forwarded to the ACL for petition method
validation (PMV; D349696, T. Bloem, 5-Mar-2008).  The petitioner is
requested to submit radiovalidation data for N-acetyl-glyphosate (plant
method), submit the poultry metabolism study referenced in the livestock
method validation study (MRID 47311011; dosed with
14C-N-acetyl-glyphosate), and revise the plant method as specified in
the ILV (temperature of the water bath used to precipitate proteins from
soybean seed/meal (80-85 °C)); in addition, the petitioner will be
required to make all requested revisions to the plant and/or livestock
methods, if any, requested in the forthcoming PMV.   

Plant Data Collection/Enforcement Method (DuPont method 15444;
47007908.der.doc):  Briefly, samples of soybean seed, forage, hay, AGF,
hulls, and meal (solid matrices) were extracted with aqueous 0.1% formic
acid:methanol (96/4, v/v).  The extract was partitioned with methylene
chloride, and the aqueous fraction was collected and filtered through a
C18 solid-phase extraction (SPE) cartridge.  For soybean seed and meal,
the extract was heated to precipitate sample matrix (proteins) prior to
filtration.  For determination of glyphosate and N-acetyl-glyphosate, an
aliquot of the C18 SPE eluate was purified through an anion-exchange
(MAX) SPE cartridge and the eluant was analyzed via LC/MS/MS.  For
determination of AMPA and N-acetyl-AMPA, an aliquot of the C18 SPE
eluate was purified through a cation-exchange (MCX) SPE cartridge and
the eluant was analyzed via LC/MS/MS.  Soybean oil was sequentially
extracted with 0.02 M phosphoric acid:methylene chloride (1:1, v:v) and
0.02 M phosphoric acid and centrifuged.  The aqueous fractions were
combined and analyzed via LC/MS/MS.

Quantification was via the internal or external standard method.  HED
notes that the glyphosate and/or AMPA stable isotope internal standards
are added prior to LC/MS/MS analysis.  The validated LOQ was 0.05 ppm
for each analyte in parent equivalents, and the reported LODs were
0.003-0.02 ppm.

Livestock Enforcement Method (DuPont method 15444; 47311011.der.doc): 
Briefly, Milk and egg commodities are extracted with aqueous 0.1% formic
acid/methanol (96/4, v/v) and partitioned with hexane followed by
methylene chloride.  The aqueous layer is collected and an aliquot
filtered through a C18 SPE cartridge followed by MAX and/or MCX SPE
cartridge, depending on the matrix and analytes to be examined.  The
resulting eluants are collected and analyzed via LC/MS/MS.  Tissue
commodities are blended with C18 sorbent material and extracted with a
0.1N HC1 in water/methanol (96/4; v/v).  The extract is collected and
purified using MAX SPE cartridge and/or MCX SPE cartridge, depending on
matrix and analytes to be examined.  The resulting eluants are collected
and analyzed via LC/MS/MS.  

Quantification is via the internal or external standard method.  HED
notes that the glyphosate and/or AMPA stable isotope internal standards
are added to extracts prior to ion exchange SPE purification.  The
validated LOQ is 0.025 ppm for each analyte in egg and milk commodities
and 0.05 ppm in livestock tissue commodities; the LODs were 0.003-0.015
ppm.  

860.1360 Food and Drug Administration (FDA) Multiresidue Methods (MRMs)
Protocols

47133201.der.doc

Pyrithiobac sodium:  Pyrithiobac sodium was tested with the FDA MRM
Protocols.  Protocols A, D and E were not applicable.  Protocol C was
not suitable due to insufficient response.  Protocol B afforded a 43%
recovery for a 0.2 ppm fortification and a 0% recovery for a 0.02 ppm
fortification.  These data were forwarded to the FDA (G. Kramer,
15-Nov-1993).

Glyphosate:  The FDA Pestrak database (1990) indicate that recoveries
are not likely for glyphosate under the FDA MRMs.  As part of the
current action, data concerning the behavior of N-acetyl-glyphosate
under the FDA MRMs was provided (47133201.der.doc).  Using Protocol A,
N-acetyl-glyphosate was determined not to be naturally fluorescent. 
Using Protocols B and C, derivatized (methylated) and underivatized
N-acetyl-glyphosate were tested using the nitrogen-specific Modules DG5
(DB-1 column) and DG17 (DB-17 column) which employ a nitrogen-
phosphorus detector (NPD) and the more general Module DG18 (DB-225
column) which employs an electron-capture detector (ECD). 
N-acetyl-glyphosate was not chromatographable using DB-1, DB-17 or
DB-225 columns by NPD or ECD; therefore, no testing was performed under
Protocols D, E, or F.  Because the test substance is not a substituted
urea, no testing under Protocol G is required.  The results indicate
that the multiresidue methods are not suitable for the determination of
N-acetyl-glyphosate.  These data were forwarded to the FDA (D349698, T.
Bloem, 5-Mar-2008).

860.1380 Storage Stability

47007913.der.doc

The petitioner submitted a soybean storage stability study which
indicated that residues of glyphosate, N-acetyl-glyphosate, and AMPA are
stable in/on soybean forage, hay, and seed when stored frozen (-20 ºC)
for 6 months (47007913.der.doc).  The soybean forage, hay, and seed used
in this study were obtained from genetically modified soybean plants
containing the gat4601 and the gm-hra genes (DP-356Ø43-5).  The
petitioner has previously submitted storage stability data which
indicated the following (D166777, R. Perfetti, 2-Apr-1992):  (1)
glyphosate is stable in/on sorghum straw, corn grain, and soybean forage
for at least 24 months and (2) AMPA is stable in/on corn grain and
sorghum forage for 24 months and is relatively stable for up to 12
months in/on sorghum straw.

The field trial and processing studies were conducted with genetically
modified soybean plants containing the GAT and gm-hra genes and employed
frozen storage intervals of 10, 8, 8, <1, <1, <1, <1, and <1 month(s)
for soybean hay, forage, seed, AGF, hull, meal, and oil samples,
respectively.  Based on the storage stability data summarized in the
previous paragraph and/or since the processed commodities were stored
frozen for <1 month from collection to analysis, HED concludes that the
currently-available storage stability data are sufficient to validate
the field trial and processing studies.  HED notes that one of the
processing studies also monitored for N-acetyl-AMPA and that storage
stability data for this compound are not available; since HED has
determined that N-acetyl-AMPA is not a residue of concern in Optimum(
GAT( soybean, HED concludes that these data are unnecessary.  

860.1480 Meat, Milk, Poultry, and Eggs

Pyrithiobac-sodium:  HED has concluded that the proposed preplant
soybean application scenario will result in insignificant residues in/on
soybean commodities (see rotational crop section); therefore, a
discussion of the magnitude of pyrithiobac sodium residues in/on
livestock commodities is unnecessary. 

 

ALS-Inhibiting Herbicides:  HED concludes that the nature/magnitude of
the residue data submitted in support of the registration for
application of ALS-inhibiting herbicides to nontransgenic soybean are
applicable for the application of these compounds to Optimum( GAT(
soybean (additional nature/magnitude of the residue are unnecessary;
ChemSAC minutes of 27-Feb-2008 meeting) therefore, conclusions
previously made concerning the magnitude of ALS herbicides in/on
livestock commodities remain appropriate.  

Glyphosate:  Based on the data submitted with the current petition, HED
concluded that the residues of concern in livestock/plants will change
from glyphosate per se to the combined residues of glyphosate and
N-acetyl-glyphosate (expressed as glyphosate); the numerical value of
the currently-established plant tolerances will remain the same for all
plant commodities excluding soybean hull (from 100 ppm to 120 ppm) and
AGF (from 100 ppm to 310 ppm).  The field trial and processing studies
indicated that the principal residue in Optimum( GAT( soybean is
N-acetyl-glyphosate.  The N-acetyl-glyphosate rat metabolism study
(Sprague Dawley; male only) resulted in 66% of the dosed material being
eliminated in the urine and 26% in the feces.  The glyphosate rat
metabolism study (Sprague Dawley) resulted in ~30% and ~62% of the
administered dose being eliminated in the urine and feces, respectively.
 Therefore, the N-acetyl-glyphosate metabolite is absorbed at a greater
rate than glyphosate.  

er 1 assessment and resulted in exposures ≤9% HED's level of concern. 
Furthermore, based on the previously calculated dietary burdens (driven
by the 400-ppm alfalfa meal and hay tolerances), the revised Table 1,
and the latest guidance concerning the construction of livestock diets,
HED concludes that the increased soybean hull and AGF tolerances will
not result in the need to increase the current livestock tolerances (see
below).   

Poultry:  The previously calculated poultry MTDB was 74 ppm with alfalfa
meal (carbohydrate concentrate (CC); 400 ppm tolerance) and soybean
hulls (roughage (R); 100 ppm tolerance) being significant contributors
(D256740, W. Donovan, 6-Aug-2000).  HED notes that soybean seed (protein
concentrate (PC)), meal (PC), and hulls (R) are fed to poultry.  Based
on the latest guidance, poultry diets are comprised of CC (75-80%) and
PC (20-25%).  Since the current review is not resulting in an increase
in soybean seed or meal tolerances, HED concludes that the application
of glyphosate to Optimum( GAT( soybean will not result in combined
residues of glyphosate and N-acetyl-glyphosate (expressed as glyphosate)
in/on poultry commodities greater then the currently established
glyphosate per se tolerance.  

Hog:  The previously calculated hog MTDB was 65 ppm with alfalfa meal
(CC; 400 ppm tolerance) and barely grain (CC; 20 ppm tolerance) being
significant contributors (D256740, W. Donovan, 6-Aug-2000).  HED notes
that soybean seed (PC) and meal (PC) are fed to hogs.   Since the
current review is not resulting in an increase in soybean seed or meal
tolerances, HED concludes that the application of glyphosate to Optimum(
GAT( soybean will not result in combined residues of glyphosate and
N-acetyl-glyphosate (expressed as glyphosate) in/on hog commodities
greater then the currently established glyphosate per se tolerance.  

Cattle (beef and dairy):  The previously calculated dairy/beef cattle
MTDBs were 210/220 ppm with alfalfa hay (R; 400 ppm tolerance) being the
significant contributor (D256740, W. Donovan, 6-Aug-2000).  HED
concludes that the consumption of glyphosate treated Optimum( GAT(
soybean will not result in combined residues of glyphosate and
N-acetyl-glyphosate (expressed as glyphosate) in/on beef/dairy cattle
commodities greater then the currently established glyphosate per se
tolerance for the following reasons:  (1) the high tolerance value for
alfalfa hay (400 ppm) and since this commodity occupies 40% of the total
beef/dairy cattle diet; (2) the soybean hull tolerance is only
increasing from 100 ppm to 120 ppm and soybean hulls will occupy at most
20% of the beef/dairy cattle dietary burdens; and (3) AGF occupy at most
5% of the beef cattle dietary burden (not fed to dairy cattle).    

860.1500 Crop Field Trials

47007909.der.doc; 47007910.der.doc; 47007911.der.doc

Based on the proposed preplant soybean application scenario (10-month
PBI), residues of glyphosate and pyrithiobac sodium in/on soybean
commodities are not anticipated (see rotational crop section).  As
previously indicated, ALS-inhibiting herbicide and glyphosate products
that are currently registered for application to soybean may also be
applied to Optimum( GAT( soybean.  The following text is a summary of
potential ALS-inhibiting herbicide and glyphosate residues in/on
Optimum( GAT( soybean from these sources. 

ALS-Inhibiting Herbicides:  HED concludes that the nature/magnitude of
the residue data submitted in support of the registration for
application of ALS-inhibiting herbicides to nontransgenic soybean are
applicable for the application of these compounds to Optimum( GAT(
soybean (additional nature/magnitude of the residue are unnecessary;
ChemSAC minutes of 27-Feb-2008 meeting) therefore, conclusions
previously made concerning the magnitude of ALS herbicides in/on soybean
commodities remain appropriate.  

Glyphosate:  Glyphosate is registered for preplant, at planting,
preemergence, and postemergent (including harvest aid) application to
soybean (see OPPTS 860.1200 Directions for Use section for registered
rate).  The following tolerances for residues of glyphosate per se are
also established:  soybean seed - 20 ppm; soybean forage - 100 ppm; and
soybean hay - 200 ppm.  The petitioner submitted three soybean field
trial studies conducted with noncommercial soybean containing the
DP-356Ø43-5 event (containing the gat4601 and gm-hra genes).  The
following text is a summary of these data (see 47007909.der.doc,
47007910.der.doc, and 47007911.der.doc for complete reviews).  

The studies were conducted in the U.S. (n=6), Chile (n=13), and
Argentina (n=2).  The pre-emergent, cracking to flowering, and
preharvest application rates were conducted at 0.8x, 1x, and 1x the
currently registered rates, respectively.  However, the total
post-emergent application rate was 1.3x the registered rate.  Therefore,
the soybean hay and forage samples received 1x the post-emergent
application rate and the soybean seed samples received 1.3x the
post-emergent rate.  Soybean forage and hay samples were collected 1-21
days (n=70) and 1-27 days (n=70) after the third application,
respectively.  Soybean seed samples were harvested 13-23 days after the
fourth application (n=42).  HED notes that a 14-day PHI is established
for soybean forage, hay, and seed. The harvested samples were analyzed
for residues of glyphosate, N-acetyl-glyphosate, and AMPA using an
adequately validated method (storage intervals have also been
validated).  

Combined residues of glyphosate and N-acetyl-glyphosate in/on soybean
forage and hay were ≤94 ppm (PHI of 1-21 days) and ≤249 ppm (PHI of
1-27 days) after application at the proposed rate (see Table 8). 
Therefore, residues in soybean forage were less than the currently
established tolerance while residues in soybean hay were greater than
the currently established tolerance.  HED notes that residues in soybean
hay harvested 13-27 days after application were ≤117 ppm and based on
the residue decline data (see attachments 4 and 5) the remaining soybean
hay residues would have been <200 ppm if the samples were harvested at
the proposed 14-day PHI.  Combined residues of glyphosate and
N-acetyl-glyphosate in/on soybean seed were ≤23 ppm (PHI of 13-23
days) following post-emergent application at 1.3x the proposed rate
(preharvest application rate was 1x).  A comparison of the 68-day PHI
bean (TRR = 1.35 ppm) with the 68-day pod (2.89 ppm) residues from the
Optimum( GAT( soybean metabolism study indicate that glyphosate residues
are readily translocated throughout the plant; therefore, HED concludes
that the 1.3x post-emergent seasonal application rate did impact
residues in/on soybean seed and that residues should be adjusted to a
1x.  Adjusting the maximum 23-ppm residue to a 1x rate yields a 18-ppm
residue which is less than the currently established tolerance. 
Therefore, HED concludes that combined residues of glyphosate and
N-acetyl-glyphosate (expressed as glyphosate) in/on Optimum( GAT(
soybean forage, hay, and seed samples from the submitted field trials
were less than the currently established tolerances when corrected for
residue decline an exaggerated rate.   

Generally, HED request 20 soybean field trials for a U.S. registration
(Zones 2 (n=2), 4 (n=2), and 5 (n=15)).  The petitioner inquired if 6
trials conducted in the U.S. and the remaining trials conducted in the
southern hemisphere would be acceptable to establish a U.S. soybean
registration. The petitioner was informed that southern hemisphere
trials should include information concerning soil type, rainfall, and
temperatures.  If these data demonstrate that the trials conducted in
the southern hemisphere experienced similar growing conditions as that
in the U.S., then the data will be considered acceptable (ChemSAC
minutes of 16-Nov-2005 meeting).

  

Based on comparison of "growing day units," day length, and minimum
temperature conducted by the petitioner, the U.S. and Chile growing
sites were similar.  The petitioner did not provide a comparison between
the U.S. and Argentina growing sites and did not provide a comparison of
precipitation between the U.S. and Chile sites as the agricultural
production in central Chile is dependent on in-furrow irrigation.  HED
notes that the residues from the Chile and Argentina field trials were
greater than the residues from the U.S. field trials.  This may in part
be explained by the drip and in-furrow irrigation employed at the Chile
and Argentina field trials and the lack of irrigation (precipitation was
sufficient) or overhead irrigation employed at the U.S. field trials. 
Based on a comparison of weather data and since residues from the South
America trials were greater than those form the U.S. while still being
less than the current tolerances (less than the current tolerance when
corrected for residue decline an exaggerated rate), HED concludes that
the trials conducted in South America are acceptable; no additional
field trial data are required. Based on the submitted data, HED
concludes that the tolerance expression should change from glyphosate
per se to combined residues of glyphosate and N-acetyl-glyphosate
(expressed as glyphosate; numerical value of the tolerance is
acceptable). 

Table 8:  Summary of Residue Data from Crop Field Trials with
Glyphosate.

Commodity	Total App. Rate (lb ae/acre)	PHI

(days)	Residue Levels1 (ppm)



	n	Min.	Max.	HAFT	Median	Mean	Std. Dev.

Glyphosate

Soybean forage	5.08-5.92	1-8	52	1.9	55	36	21	23	12



10-21	18	0.24	16	12	5.8	6.0	4.2

Soybean hay

1-7	48	3.4	100	86	53	55	23



13-27	22	0.31	31	30	9.3	12	11

Soybean seed	5.66-6.71	13-23	42	<0.05	0.45	0.43	0.12	0.13	0.09

N-acetyl-glyphosate

Soybean forage	5.08-5.92	1-8	52	4.5	67	58	32	33	12



10-21	18	6.2	37	29	18	18	7.3

Soybean hay

1-7	48	15	161	134	92	96	32



13-27	22	11	106	105	69	63	28

Soybean seed	5.66-6.71	13-23	42	<0.05	23	22	5.7	8.7	7.5

AMPA

Soybean forage	5.08-5.92	1-8	52	0.12	1.9	1.6	0.90	0.90	0.38



10-21	18	<0.05	1.3	1.0	0.67	0.57	0.37

Soybean hay

1-7	48	0.41	5.0	4.4	3.7	3.3	1.2



13-27	22	<0.05	3.6	2.8	1.4	1.3	1.1

Soybean seed	5.66-6.71	13-23	42	<0.05	0.27	0.27	0.09	0.12	0.07

Combined glyphosate and N-acetyl-glyphosate

Soybean forage	5.08-5.92	1-8	52	6.4	94	82	53	56	19



10-21	18	6.4	53	41	23	24	11

Soybean hay

1-7	48	21	249	219	147	151	52



13-27	22	11	117	110	82	75	32

Soybean seed	5.66-6.71	13-23	42	<0.10	23	22	5.9	8.8	7.6

1  For calculation of the HAFT, median, mean, and standard deviation,
the LOQ was used for any residues reported as ND or between the LOQ and
LOD in Table C.3.

860.1520 Processed Food and Feed

47119207.der.doc; 47007912.der.doc

Based on the proposed preplant soybean application scenario (10-month
PBI), residues of glyphosate (combined residues of glyphosate and
N-acetyl-glyphosate (expressed as glyphosate)) and pyrithiobac sodium
in/on soybean commodities are not anticipated (see rotational crop
section).  As previously indicated, ALS-inhibiting herbicide and
glyphosate products that are currently registered for application to
soybean may also be applied to Optimum( GAT( soybean.  The following
text is a summary of potential ALS-inhibiting herbicide and glyphosate
residues in/on Optimum( GAT( soybean from these sources. 

ALS-Inhibiting Herbicides:  HED concludes that the nature/magnitude of
the residue data submitted in support of the registration for
application of ALS-inhibiting herbicides to nontransgenic soybean are
applicable for the application of these compounds to Optimum( GAT(
soybean (additional nature/magnitude of the residue are unnecessary;
ChemSAC minutes of 27-Feb-2008 meeting) therefore, conclusions
previously made concerning the magnitude of ALS herbicides in/on
livestock commodities remain appropriate.  

Glyphosate:  Glyphosate is currently registered for preplant, at
planting, preemergence, and postemergent (including harvest aid)
application to soybean (see OPPTS 860.1200 Directions for Use section
for registered rate).  Tolerances for residues of glyphosate per se are
currently established in/on soybean hull and AGF at 100 ppm.  The
petitioner has submitted two soybean processing studies conducted with
noncommercial soybean containing the DP-356Ø43-5 event (containing the
gat4601 and gm-hra genes) The following text is a summary of these data
(see 47119207.der.doc and 47007912.der.doc for complete reviews).  

The studies were conducted in the U.S. (n=2) and Chile (n=1).  At one of
the U.S. trials and at the Chile trial, the pre-emergent, cracking to
flowering, and preharvest application rates were conducted at 0.8x, 1x,
and 1x the currently registered rates, respectively (total post-emergent
application rate of 1.3x).  At the second U.S. trial, the pre-emergent,
cracking to flowering, and preharvest application rates were conducted
at 4.0x, 5.0x, and 5.1x the currently registered rates, respectively
(total post-emergent application rate of 6.7x the registered rate). 
Soybean seed samples from the U.S. trials were collected 12-14 days
after application (harvest date for the Chile trials were not provided).
  The harvested samples were processed into hull, meal, refined oil,
and/or AGF using simulated commercial practices and analyzed for
residues of glyphosate, N-acetyl-glyphosate, AMPA, and N-acetyl-AMPA
using an adequately validated method.  The following discussion pertains
to only combined residues of glyphosate and N-acetyl-glyphosate as these
were the only residues identified as of concern in Optimum( GAT(
soybean.  The storage intervals and conditions for glyphosate and
N-acetyl-glyphosate have been validated for all the relevant matrices.  

Based on the residues in the RAC (>LOQ in/on all samples) and processed
commodities, the processing factors listed in Table 9 for the combined
residues of glyphosate and N-acetyl-glyphosate were calculated.  The
soybean seed HAFT for the combined residues of glyphosate and
N-acetyl-glyphosate is 17 ppm (22 ÷ 1.3 = 17; field trials were
conducted at a 1.3x rate); Based on these data soybean hull and AGF
tolerances for the combined residues of glyphosate and
N-acetyl-glyphosate (expressed as glyphosate) of 120 ppm and 310 ppm
respectively, are appropriate.  A revised Section F is requested.    

Table 9:  Soybean Processing Factors for  Combined Residues of
Glyphosate and N-acetyl-glyphosate.

Commodity	Processing Factor

AGF	5.9, 43, 5.5; average = 18.1

Hull	5.4, 8.4; average = 6.9

Meal	0.23, 0.42; average = 0.33

Refined Oil	<0.05, <0.002, average = <0.05



860.1850 & 1900 Confined and Field Accumulation in Rotational Crops

Pyrithiobac-Sodium:  The MARC  reviewed a confined rotational crop study
and determined that the residue of concern in rotational crops is
Pyrithiobac sodium per se (D216002, G. Kramer, meeting of 1-Jun-1995). 
The confined rotational crop study employed a single bare soil
application at 0.125 lb ai/acre (3.9x the proposed rate) with soybean,
carrot, lettuce, and wheat planted 30, 120, and 240/263 days after
application.  For those crops/extracts which required analysis, residues
of pyrithiobac-sodium were ≤0.003 ppm.  Based on these data and since
the label indicates that glyphosate-tolerant soybean may not be planted
for 10 months following application, HED concludes that residues in
soybean, as a result of the proposed use, will be insignificant.  

Glyphosate:  Based on previously-reviewed confined rotational crop
studies (3.71 lb ai/acre; MRIDs 41543201 and 41543202, A. Abramovitch,
14-Oct-1992), HED concluded that a 30-day PBI was appropriate for all
nonlabeled crops (D200041, G. Kramer, 12-May-1994).  Since the rate
conducted in the confined rotational crop study was 4.9x the proposed
rate and since the label indicates the soybean may not be planted for 10
months following application, HED concludes that residues in soybean, as
a result of the proposed use, will be insignificant.  

860.1550 Proposed Tolerances

The current glyphosate tolerance expression in plant/livestock is for
residues of glyphosate per se (40 CFR 180.364(a)).  HED has concluded
that the residues of concern in Optimum( GAT( soybean are glyphosate and
N-acetyl-glyphosate (expressed as glyphosate).  Rather than establishing
a separate section within 40 CFR 180.364, the petitioner requested that
the 40 CFR 180.364(a) tolerance expression be changed to include
glyphosate and N-acetyl-glyphosate.  HED concludes that changing the
tolerance expression for 40 CFR 180.364(a) is acceptable.  However, a
revised Section F specifying the tolerances listed in Table 10 for the
combined residues of glyphosate and N-acetyl-glyphosate (expressed as
glyphosate) resulting from the application of glyphosate, the
ethanolamine salt of glyphosate, the ammonium salt of glyphosate, and
the potassium salt of glyphosate, is requested.  HED notes that there
are Codex, Canadian, and Mexican maximum residue limits for residues of
glyphosate per se or combined residues of glyphosate and AMPA.  Since
the residues of concern differ, harmonization is irrelevant.    

Table 10:  Tolerance Summary.

Commodity	Proposed 

Tolerance (ppm)	HED-Recommended Tolerance (ppm)	Comments

soybean, hulls	100	120	increase tolerances; change tolerance expression
(see underlined above)

grain, aspirated fractions	100	310

	

  SEQ CHAPTER \h \r 1 RDI: RAB1 Chemists (5-Mar-2008)

T. Bloem:S10945:Potomac Yard 1:703-605-0217:7509P:RAB1

Attachment 1 - Chemical Structures

  SEQ CHAPTER \h \r 1 Attachment 2 - International Residue Limit Status
Sheet

Attachment 3 - Petitioner Proposed Pathway in Soybean Genetically
Modified to Express the GAT and gm-hra Genes (designated DP356Ø43-5).

Attachment 4 - Forage Residue Decline Data

Attachment 5 - Forage Residue Decline Data

Attachment 6 - Tolerances

Attachment 1 - Chemical Structures

compound	structure

Glyphosate

 

N-acetyl-glyphosate

 

AMPA

 

N-acetyl-AMPA

 



Attachment 2 - International Residue Limit Status sheet

INTERNATIONAL RESIDUE LIMIT STATUS

Chemical Name: 

N-(phosphonomethyl)glycine	Common Name:

glyphosate

	X Proposed tolerance

( Reevaluated tolerance

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ਁ砃愀϶xЀimits)	U. S. Tolerances

( No Codex proposal step 6 or above

(No Codex proposal step 6 or above for the crops requested	Petition
Number: 352-606 - DuPont Staple Plus Herbicide 

DP Number:  346713

Other Identifier:

Residue definition:   Residue for compliance with MRLs in plant and
animal commodities: glyphosate. (Residue for estimation of dietary
intake: sum of glyphosate and AMPA expressed as glyphosate.)

	Reviewer/Branch: Tom Bloem/RAB1

	Residue definition: glyphosate and N-acetyl-glyphosate
(N-acetyl-N-(phosphonomethyl)glycine)

Crop (s)	MRL (mg/kg)	Crop(s) 	Tolerance (ppm)

Soya bean (dry)	20	soybean seed	20



soybean forage	100



soybean hay	200



soybean hulls	100



aspirated grain fractions	100

Edible offal (mammalian)	5	kidney (cattle, goat, hog, horse, sheep)	4.0



liver (cattle, goat, hog, horse, sheep)	0.5

Eggs 	0.05 (*)	egg	0.05

Poultry meat	0.05 (*)	poultry meat	0.1

Poultry edible offal of 	0.5	poultry meat byproducts	1.0

Limits for Canada	Limits for Mexico

(  No Limits

( No Limits for the crops requested	(   No Limits

(   No Limits for the crops requested

Residue definition:  N-(phosphonomethyl)

glycine, including the

metabolite aminomethylphosphonic

acid

	Residue definition:  glyphosate

Crop(s)	MRL (mg/kg)	Crop(s)	MRL (mg/kg)

Soybean seed	20	Soy bean	6

Kidney of cattle, goats, hogs, poultry, and sheep	2



Liver of cattle, goats, hogs, poultry and sheep	0.2







	Notes/Special Instructions: S.Funk, 01/15/2008. 

 Attachment 3 - Petitioner Proposed Pathway in Soybean Genetically
Modified to Express the GAT and gm-hra Genes (designated DP356Ø43-5).

 

    

Attachment 4 - Forage Residue Decline Data

Attachment 5 - Hay Residue Decline Data

Attachment 6 - Tolerances

HED notes that several of the currently established glyphosate per se
crop tolerances are at 0.1 ppm.  With the addition of
N-acetyl-glyphosate to the tolerance expression, there is a possibility
of over-tolerance residues (e.g., glyphosate per se residue of 0.08 ppm
and <LOQ N-acetyl-glyphosate residue (LOQ = 0.05 ppm) would yield a
residue of <0.13 ppm).  However, the 0.1- ppm tolerances are based on
combined residues of glyphosate and AMPA; when the AMPA was dropped from
the tolerance expression the numerical value of the tolerance stayed the
same. The table below is a summary of the residue data upon which the
0.1 ppm glyphosate per se tolerances were based on.  HED notes that the
proposed plant tolerance enforcement method has an LOQ for glyphosate
and N-acetyl-glyphosate of 0.05 ppm and that the LOQ for glyphosate and
AMPA in the previous plant tolerance enforcement method was also 0.05
ppm..

HED also notes that the current glyphosate per se egg tolerance is 0.05
ppm.  This tolerance is based on the 74 ppm poultry MTDB and the poultry
feeding study which indicated a transfer coefficient for glyphosate per
se of 0.000278.  Therefore, the expected glyphosate per se residue is
0.021 ppm (0.000278 x 74 = 0.021).  As part of the current review, HED
is adding N-acetyl-glyphosate to the tolerance expression with the
proposed analytical enforcement method having an LOQ of 0.025 ppm for
glyphosate and N-acetyl-glyphosate.  Based on the conservative nature of
the MTDB calculations (tolerance-level residues), HED concludes that the
0.05 ppm egg tolerance is sufficient for the combined residues of
glyphosate and N-acetyl-glyphosate (expressed as glyphosate).   

Crop	Tolerance (ppm)	Rational

borage, seed	0.1	Glyphosate per se tolerance translated from sunflower
seed residue data (D262424, W. Donovan, 18-Jan-2000).

The original sunflower 0.1 ppm tolerance was for the combined residues
of glyphosate and AMPA (29-July-1987, N. Dodd; D219017, N. Dodd,
1-Nov-1995). 1

crambe, seed	0.1

	jojoba, seed	0.1

	lesquerella, seed	0.1

	meadowfoam, seed	0.1

	mustard, seed	0.1

	sesame, seed	0.1

	gourd, buffalo, seed	0.1

	fruiting vegetables, group 8	0.1	Based on the glyphosate RED (D183202,
R. Perfetti, 27-Oct-1992) and the 1994 40 CFR 180.364, the fruiting
vegetable tolerance is based on combined residues of glyphosate and
AMPA. 1  

grain, cereal, group 15 (except barley, field corn, sorghum, and oat
grain)	0.1

	palm, oil	0.1

	peanut	0.1

	pineapple	0.1

	1  Based on the glyphosate RED (D183202, R. Perfetti, 27-Oct-1992), the
LOQ for glyphosate and AMPA for the tolerance enforcement method was
0.05 ppm for each.  

Glyphosate and Pyrithiobac Sodium    	Summary of Analytical Chemistry
and Residue Data	DP Number:  346713

 PAGE   1  of   NUMPAGES  27 

