<Notice of Filing for MCPB [4-(2-methyl-4-chlorophenoxy) butyric acid]
on mint

Pesticide Tolerance Petition:		Notice of Filing

Agency:				Environmental Protection Agency (EPA)

Action:					Notice of Filing

Summary:	This notice announces the filing of a pesticide petition
proposing the establishment of a regulation for residues of the
pesticide 4-(2-methyl-4-chlorophenoxy) butyric acid in or on the raw
agricultural commodity mint at 0.25 ppm.

EPA has received a pesticide petition (PP#7E7257) from Interregional
Research Project Number 4 (IR-4), 500 College Road East, Suite 201-W,
Princeton, NJ  08540 proposing, pursuant to section 408(d) of the
Federal Food, Drug, and Cosmetic Act (FFDCA), 21 U.S.C. 346a(d), to
amend 40 CFR part 180.318 by establishing a tolerance for residues of
4-(2-methyl-4-chlorophenoxy) butyric acid in or on the raw agricultural
commodity mint tops (leaves and stems) at 0.25 parts per million (ppm). 
EPA has determined that the petition contains data or information
regarding the elements set forth in section 408 (d)(2) of  FDDCA;
however, EPA has not fully evaluated the sufficiency of the submitted
data at this time or whether the data supports granting of the petition.
Additional data may be needed before EPA rules on the petition.

<A. Residue Chemistry>

<	1. Analytical method. The samples were analyzed using the method
“Gas Chromatographic/Mass Spectrometric Method for Analysis of
Chlorophenoxy Acid Herbicides: MCPB and MCPA in Peas, Hengel, M. J.;
Mourer, C.R. and Shibamoto, T., Journal of Environmental Chemistry, 8
(3), pp.: 429-433, 1998”. Minor modifications to the reference method
re listed on pages 9-10 of the Analytical Summary Report.   The samples
were analyzed for both MCPB [4-2-methyl-4-chlorophenoxy) butyric acid]
and MCPA [2-methyl-4-chlorophenoxyacetic acid].

MCPB and MCPA residues were extracted from the mint top samples with
acetone and acetone/water homogenization.  After centrifugation, an
aliquot of the extract was acidified and extracted into petroleum ether.
 After evaporation, the concentrate was re-dissolved in hexane and
re-evaporated to dryness. The concentrate was derivatized with
diazomethane and then subject to florisil column clean-up. The samples
were analyzed by GC-MSD.

For the mint oil samples, 2 g of mint oil sample was dissolved in hexane
and extracted into 0.01 N NaOH (containing NaCl).  The aqueous layer was
then acidified and extracted into dichloromethane/hexane fraction was
dried by passing through anhydrous Na2SO4.  After evaporation of the
organic phase, the concentrate was derivatized with diazomethane and
then subject to florisil column clean-up.  The samples were analyzed by
GC-MSD. 

The overall method recoveries ranged from 86% to 117% for MCPB in/on
mint tops, 72% to 88% for MCPA in/on mint tops, 98% to 122% for MCPB
in/on mint oil and 63% to 92% for MCPA in/on mint oil. 

For MCPB in/on mint tops, the LOD for the method was calculated to be
0.004 ppm and the LOD for the method was calculated to be 0.003 ppm and
the LOQ was calculated to be 0.009 ppm.  The lowest level of method
validation (LLMV) for both MCPB and MCPA in/on mint tops.

For MCPB in/on mint oil, the LOD for the method was calculated to be
0.015 ppm and the LOQ was calculated to be 0.044 ppm and for MCPA in/on
mint oil, the LOD for the method was calculated to be 0.013 ppm and the
LOQ was calculated to be 0.039 ppm.  The lowest level of method
validation (LLMV) for both MCPB and MCPA in/on mint oil was 0.05 ppm.

Analytical sets typically consisted of calibration standards,
unfortified controls, fortified controls, and treated samples.  A
calibration standard was injected at the beginning and the end of each
analytical set.

>

<	2. Magnitude of residues. The residue trials were conducted with two
broadcast applications (per trial) made to the treated mint plots.  The
first application was made in the fall when the mint was dormant.  The
second application was made at 38 to 40 days before harvest.  For the
first application, the rates ranged from 0.961 to 1.042 lb ae/A.  For
the second application, the rates ranged from 0.745 to 0.789 lb ae/A. 
The total rate ranged from 1.706 to 1.807 lb ae/A.  All applications
were made using appropriate spray equipment, and the spray volume was
sufficient to provide adequate dispersal of the test substance. At all
trials, samples were harvested 38-40 days after the last application.

In the mint top samples, the residues of MCPB  ranged from < 0.05 ppm to
0.134 ppm in samples harvested 38 – 40 days after the last application
(38-40 days PHI).  No detectable residues of MCPA (< 0.05 ppm) were
found in the mint top samples. 

In the mint oil samples, no detectable residues of either MCPB or MCPA
(< 0.05 ppm) were found in the oil distilled from the mint top samples
harvest 38 – 40 days after last application (38 – 40 day PHI).  

At all trials, either CO2 or compressed air was used as the propellant
and with a tractor or ATV mounted sprayer.  All applications were made
as broadcast applications.  

The WA trials were conducted on light soils (% sand ranging from 58% to
78%) such as sandy loam or loamy sand and the WI trials were conducted
on heavier soils (silt loam) with 25% sand and 55% organic matter.  A
closer look of the residue results indicates that the mint top samples
grown in soils with lower percentage of sand (58% or less) showed
residues of MCPB whereas, the mint top samples grown in soils with
higher percentage of sand (> 70%) did not show any detectable residues
of MCPB (< 0.05 ppm).  No detectable residues of either MCPB or MCPA
(<0.05 ppm) were observed in any of the mint oil samples.

The weather conditions were generally normal at all field locations with
slight deviations from normal conditions.

The samples were analyzed using the method “Gas Chromatographic/Mass
Spectrometric Method for Analysis of Chlorophenoxy Acid Herbicides: MCPB
and MCPA in Peas, Hengel, M. J.; Mourer, C.R. and Shibamoto, T., Journal
of Environmental Chemistry, 8 (3), pp.: 429-433, 1998”. Minor
modifications to the reference method re listed on pages 9-10 of the
Analytical Summary Report.   The samples were analyzed for both MCPB
[4-2-methyl-4-chlorophenoxy) butyric acid] and MCPA
[2-methyl-4-chlorophenoxyacetic acid].

Method suitability was evaluated both prior to sample analysis (method
validation), and concurrently with the sample analysis and the method
was found to be suitable for the analysis of MCPB and MCPA in mint tops
and mint oil.

The recoveries for the mint top storage stability samples ranged from
87% to 91% for MCPB and 81% to 86% for MCPA Concurrent recoveries for
spikes analyzed along with the storage and stability samples ranged from
89% to 104% for MCPB and 74% to 82% for MCPA.

The recoveries for the mint oil storage stability samples ranged from
93% to 98% for MCPB and 65% to 98% fro MCPA.  Concurrent recoveries for
spikes analyzed along with the storage stability samples ranged from
100% to 107% for MCPB and 74% to 88% for MCPA.

This data indicates that the residues of MCPB and MCPA are stable in
both mint tops and mint oil under the conditions that the samples were
held between harvest and analysis.

The acceptable method validation and concurrent recoveries as well as
the storage stability results indicate that the residue results reported
are reliable.  

>

<B. Toxicological Profile>

<	1. Acute toxicity.  MCPB  has a low to moderate acute toxicity profile
(Toxicity Category III to IV.  The acute oral LD50 for MCPB is between
1570 to 4300 mg/kg in rats.  LD50 results for MCPB acute dermal toxicity
is greater than 2,000 mg/kg (and greater than) 10,000 kg/mg in rats and
rabbits respectively.  The acute inhalation is also in toxicity category
III with the LC50 greater than 1.14 mg/L.   MCPB is moderately
irritating to the eyes of rabbits (toxicity category III) but is
non-irritating to the skin (toxicity category IV). Lastly, MCPB is not a
dermal sensitizer.>

<	2. Genotoxicty. There is no relevant genotoxic potential in vitro or
in vivo.>

<	3. Reproductive and developmental toxicity. Developmental and
reproductive studies do not indicate sensitivity or susceptibility to
young animals.>

<	4. Subchronic toxicity. The NOAEL in a 90 day oral study in rats was
100 ppm (6.3 mg/kg bw/d); The NOAEL in a 90 day oral study in dogs was
80 ppm (2 mg/kg bw/d).>

<	5. Chronic toxicity. The established chronic RfD of 0.015 mg/kg/day
for MCPB, based on a NOAEL of 4.4 mg/kg/day in a chronic toxicity study
in rats.  The observed effects were liver and kidney toxicity.  >

<	6. Animal metabolism. MCPB has a high bioavailability (approximately
85%) within 48 hours (usually within 24 hours) in rats.  MCPB is
uniformly distributed and shows no accumulation.  MCPB is rapidly
excreted in urine (80%) and in feces (6%) within 48 hours.>

	

<	7. Endocrine disruption. There is no data suggesting that MCPB causes
endocrine disruption.  >

<C. Aggregate Exposure>

<	1. Dietary exposure. To estimate the dietary exposure and risk from
incidental ingestion of food and water containing MCPB residues, EPA
used surface water model (since residues of PCPB are higher in surface
waters than ground water) combined with the food exposure model.  At the
95th percentile, the acute and chronic risks were well below 100% acute
Population Adjusted Dose (aPAD) and 100% chronic Population Adjusted
Dose (cPAD), EPA’s level of concern.  The dietary exposure resulted in
a 1.7% aPAD and a 2.8%CPAD for the acute and chronic exposures,
respectively.  The aPAD and CPAD for infants younger than 1 year old was
5.9% and 10% respectively.>

<	i. Food. The results of a dietary exposure and risk estimate study
conducted by EPA for MCPB for the general population and the most highly
exposed population subgroup of infants < 1 year old show that at the
95th percentile of exposure, the risk estimates are below EPA’s level
of concern. The most exposed group is infants less than 1 year old at 2%
of the aPAD and 4% of the cPAD.>

<	ii. Drinking water. In EPA’s Tier II screening model, Pesticide Root
Zone Model and Exposure Analysis Modeling System was used to estimate
MCPB residues in surface water.  EPA assumed that MCPB would be applied
once a year at 1.5 pounds of acid equivalent per acre.  EPA concluded
that an acute exposure to MCPB in surface water is 54.7 ppb, and the
chronic exposure to be 13.5 ppb, based on application to peas.  EPA
utilized the Tier 1 Screening Concentrations in Ground Water model in
estimating MCPB concentrations in ground water, assuming a maximum
annual use of 1.5 lb ae/A.  EPA estimated the acute and chronic exposure
from ground water to be 0.86 ppb, on applications to peas.>

<	2. Non-dietary exposure. Workers are potentially exposed to MCPB while
mixing, loading, handling, or applying MCPB and when entering treated
sites.  The risk to the workers and handlers is estimated by a Margin of
Exposure (MOE) which is used to determine how close the occupational
exposures comes to a No Observed Adverse Effect level (NOAEL), from
animal studies.  NOAEL’s greater than 100 do not exceed EPA’s level
of concern.

EPA estimates the workers/handlers are exposed to MCPB for only short
(one day to one month) and intermediate-term (one to six months)
occupational exposures based from labeling directions for use and since
MCPB is used only once a year.

For the MCPB occupational risk assessment, the short and intermediate
term dermal endpoint was selected from a 21-day dermal toxicity study in
rabbits.  The short and intermediate term inhalation endpoint was
selected from a developmental toxicity study with MCPB in rabbits.  The
risk assessment resulted in the short and intermediate term NOAEL for
both the dermal and inhalation exposure equal to 100.

The MCPB MOEs considered the following scenarios for occupational
handler exposures:

Mixing/loading liquid formulations,

Performing aerial applications,

Performing ground boom applications, and

Flagging for aerial applications.

The Dermal and Inhalation MOEs for the above scenarios range from 580-
1700 and 560-9800 respectively and are over the Agency’s level of
concern (less than 100).>

<D. Cumulative Effects   SEQ CHAPTER \h \r 1  EPA has not made a common
mechanism of toxicity finding for MCPB. 

>

             <E. Safety Determination>

<	1. U.S. population. EPA has determined that the MCPB established
tolerances meet safety requirements set forth in the FQPA amendments to
Section 408 (b)(2)(D) of the FFDCA and that there is reasonable
certainty that no harm will result to the general population or special
populations from MCPBs use.>

<	2. Infants and children. EPA has determined that the MCPB established
tolerances meet safety requirements set forth in the FQPA amendments to
Section 408 (b)(2)(D) of the FFDCA and that there is reasonable
certainty that no harm will result to infants and children.  In the
Agency database for MCPB, which is bridged from MCPA, included
developmental and reproductive toxicity studies and there is no evidence
of sensitivity or susceptibility to newborns.  As previously discussed,
the total acute and chronic dietary risks are well below the Agency’s
level of concern, which is less than 100% of the PAD.  The highest
exposed infant subgroup was less that 4% of the aPAD and 10% of the
cPAD.>

<F. International / Existing Tolerances>

<	In Europe and Canada, there are no established maximum residue limits
(MRLs) for MCPB.  MRLs for MCPB exist in Australia at 0.02 ppm for
cereal grains and legumes.>

Tolerances are established under 40 CFR § 180.318 for residues of the
pesticide 4-(2-methyl-4-chlorophenoxy) butyric acid in or on the
following raw agricultural commodities:

Commodity	Parts per Million

Pea	0.1 ppm



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