United States Office of Pesticides and Toxic Substances
Environmental Protection Office of Pesticide Programs (H7508C)
Agency Washington, DC 20460
4>EPA Pesticide
Fact Sheet
540/FS-89-070
Name of Chemical: HCPA
Reason for Issuance: REGISTRATION STANDARD (SRR)
Date Issued: SEP 2 2 1989
Fact Sheet Number: 203
Description of Chemical
Generic name: 2-methyl-4-chlorophenoxyacetic acid, and
its sodium salt, esters and organic amines
Common name: MCPA
Trade names: ACME MCPA AMINE 4, AGRITOX, AGRO ONE,
BORDERMASTER, BH MCPA, CHIPTOX, BED-WEED,
EMPAL, KILSEM, MEPHANAL, METHOXONE, PHOMENE,
RHONOX, and WEEDAR
EPA Pesticide Chemical (Shaughnessy) Number:
MCPA acid - 030501
Sodium salt - 030502
Diethanolamine salt - 030511
Dimethylamine salt - 030516
Butoxyethyl Ester - 030553
Isobutyl Ester - 030562
Isooctyl Ester - 030563
Isopropyl Ester - 030566
Chemical Abstracts Service (CAS) Number:
MCPA acid - 94-74-6
Year of Initial Registration: 1973
Pesticide Type: Herbicide
Chemical Family: Phenoxy herbicides
U.S. Registrant: Dow Chemical
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2. Use Patterns and Formulations
Application sites: Terrestrial food crop use on small grains f
(wheat, oats, barley, rye), peas, beans, pasture grasses,
grain sorghum, alfalfa and clovers.
Terrestrial nonfood crop use on homelawns, ornamental turf,
flax, grass seed crops, noncrop areas, pasture grasses,
rangeland grasses, and forestry.
Aquatic food use on rice.
Aquatic nonfood use on aquatic weeds.
Formulations: Granular (MCPA acid and isooctyl ester) ;
soluble concentrate/liquid (sodium salt, diethanolamine
salt, dimethylamine salt); Technical (MCPA acid, Butoxyethyl
ester, isooctyl ester); Formulation Intermediate (Butyl
ester, isobutyl ester, isopropyl ester, dimethylamine salt,
MCPA acid); Ready-To-Use (Dimethylamine salt); and
Emulsifiable Concentrate (Butoxyethyl ester, isooctyl
ester). There are 117 federally registered products
containing MCPA as an active ingredient either by itself or
itself or in combination with other pesticides.
Methods of application: Aerial and ground equipment, knapsack
sprayers, pressure and hose-end applicators, and lawn
spreaders.
Application rates: 0.2 - 3.0 Ib active ingredient per acre.
Mode of activity: MCPA is absorbed through both leaves and
roots and is readily translocated throughout the plant.
MCPA stimulates nucleic acid and protein synthesis affecting
the activity of enzymes, respiration and cell division.
Broadleaf plants exhibit malformed leaves, stems and roots.
3. Science Findings
This review of MCPA^acid, its salts, and esters, is the
second intensive evaluation of the compound. In its original
Registration Standard, issued in 1982, the Agency summarized the
available data supporting the registration of MCPA and concluded
that additional data were needed to fully evaluate the pesticide.
The Agency has since received and reviewed the data on these
compounds.
The Agency has registered 9 salts, esters and amines of MCPA
in addition to the acid. From a toxicological standpoint the
acid and the sodium salt are essentially identical. The
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registrants, however, must show that the other derivatives would
be equivalent to MCPA acid under testing conditions. Otherwise,
a complete set of data must be submitted on each derivative to
support their continued registration. The following scientific
assessment discusses the Agency's knowledge on MCPA acid. If the
data refers to a derivative, the derivative is identified.
Chemical/Physical Characteristics of the Technical Material
MCPA is white to light brown and can be a solid,
flakes, crystal powder or liquid. It has no odor or can be
slightly phenolic smelling. The melting point is 114 to
119°C and is soluble to varying degrees in various solvents.
Toxicology Characteristics
Acute Oral. Toxicity Category III (LD50 1.38 g/kg in male
rats, 0.76 g/kg in female rats).
Acute Dermal. Toxicity Category III (LD50 > 4000 mg/kg in
the rat).
Acute Inhalation. Toxicity Category III (LC50 > 6.36 mg/L
in the rat).
Primary Eye Irritation. Toxicity Category I (corneal
opacity with irritation of conjunctive observed 21 days
post-instillation with rabbits).
Skin Sensitization. Not a skin sensitizer in guinea pigs.
Testing on other species required.
Acute Delayed Neurotoxicity. MCPA is not an
organophosphate, therefore a study is not required.
Subchronic Oral. Sufficient data are available to satisfy
the requirements of a subchronic oral study in rodents
and nonrodents. In beagles there was evidence of dose-
related liver and kidney toxicity. A NOEL for systemic
effects was set at 1 mg/kg/day. In rats, the mid- and
high-dose males exhibited increased kidney weights and
both sexes had indications of kidney disfunction.
Hepatotoxicity, based on prolongation of clotting times
and decreased cholesterol concentrations occurred in high
dose males. The NOEL for systemic effects is set at 2.5
mg/kg/day.
Subchronic Dermal. Data gap. A 21-day dermal toxicity
study is required.
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Chronic Toxicity. Sufficient data are available to satisfy
the requirements for the chronic feeding studies in two
species for technical MCPA acid. In beagles, after one
year, kidney and liver toxicity was observed at the mid-
and high dose levels. The systemic NOEL was set at 0.15
ing/kg/day, LDT.
In a 2 year rat study, hepatotoxicity was observed with
elevated triglycerides, decreased cholesterol, and kidney
nephropathy. The NOEL for systemic toxicity was set 1.0
mg/kg/day.
Oncogenicity. Rat and mouse studies were reviewed and
found acceptable. MCPA is considered to be non-
oncogenic. No additional studies are required.
Teratogenic. The studies available to the Agency are
unacceptable under current guideline requirements. While
these studies showed no developmental alterations, the
Agency is requiring teratology studies in two species.
Reproduction. In a two-generation reproduction study with
rats, there were indications of a potential postnatal
growth effect. The NOEL is set at 7.5 mg/kg/day. No
additional reproduction studies are required.
Mutaaenicity. The Agency has data to satisfy the
Structural Chromosomal Aberration study and.the DNA
Damage and Repair study. MCPA acid was found to be non-
mutagenic in the first study and weakly mutagenic in the
second. The Agency is requiring a gene mutation study.
Metabolism. In a rat study, MCPA did not appear to be
significantly metabolized in vivo (82 and 88% were
recovered in male and female rat .urine, respectively).
Repeat dosing did not generally indicate biŠaccumulation
in any site except the kidney, primarily in male rats.
Fat appeared to be the site for some MCPA sequestration.
No additional metabolism studies are required.
Special Neurotoxicity Testing. MCPA is structurally
related to 2,4-D which is suspected of causing neuropathy
in humans. Special neurotoxicity testing of 2,4-D is
. currently required. Because of this structural
similarity to 2,4-D, the Agency is also requiring special
neurotoxicity testing of MCPA.
Toxicology Profile of Other MCPA Formulations. As stated
previously from a toxicological standpoint one may expect
the acid and sodium salt to be identical. The organic
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amines and esters may be significantly different and
lacking data to show otherwise, may have different
toxicological properties. The major exposure to these
compounds is during application therefore acute
toxicology data are required on the various derivatiyes.
The Agency has some acute testing on these derivatives
and they fall in toxicity Category III. Additional acute
testing is required.
Human Exposure. The greatest potential for direct human
exposure comes during mixing and loading operations.
Exposure would be minimized by wearing of protective
equipment. The Agency is requiring protective eyewear
for mixers, loaders, and home users of MCPA acid
products. No specialized protective language other than
those required in 40 CFR 156 is required for other MCPA
derivative homeowner use products. There have been no
poisoning incidences with MCPA reported in California
since 1974. Reentry data are not required since MCPA is
generally in Toxicity Category III for acute studies.
Environmental Characteristics. Preliminary data have shown
that MCPA degrades under aerobic laboratory conditions
with a half-life of less than a week to 50 days. Under
aerobic conditions 89% of parent MCPA remained undegraded
for 374 days. MCPA is stable to hydrolysis and to
photolysis in soils. MCPA salts are highly stable in
water. Available data are insufficient to fully assess
the environmental fate of MCPA and its various
derivatives.
Groundwater Concerns. MCPA appears to be mobile from
preliminary leaching studies. MCPA was found,in well
water in Missouri. Groundwater contamination appears to-
be associated with point sources. A special groundwater
precautionary statement on labels is being imposed.
Ecological Effects
Based on available data, MCPA acid has been determined
to be moderately toxic to avian species, slightly toxic to
freshwater fish, practically nontoxic to freshwater
invertebrates and estuarine and marine organisms. Additional
ecological effects data are required on MCPA and its
derivatives. The following data comes from acceptable
studies:
o Acute LD50 377 mg/kg for Bobwhite quail
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o Dietary LC50 > 2000 ppm for mallard, bobwhite, and
ring-necked pheasant
o LC50 rainbow trout = 89 ppm
o LC50 bluegill = 97 ppm
o LC50 Daphnids > 180 ppm
o LC50 Atlantic silverside = 179 ppm
o LC50 Oyster Larvae = 155 ppm
Effects on Plants. The Agency has no data for toxicity to
nontarget plants. A complete battery of tests are
required using MCPA and all its derivatives.
Potential Problems Related to Endangered Species. Because
of MCPA's demonstrated toxicity to nontarget species and
its intended use pattern, several endangered species
could be put at risk from the application of MCPA acid
and its derivatives. The Agency has proposed a
comprehensive Endangered Species Protection program
(Federal Register 54(126) July 3, 1989).
Nontarget Insects. MCPA acid and its sodium salt
derivative are relatively nontoxic to honeybees. Data
are required on the dimethylamine salt and isooctyl ester ,
as their use patterns allow for significant potential "
exposure to bees.
Product Chemistry. The Agency is requiring that all
product chemistry data be. resutmitted. Further, MCPA may
be contaminated with dioxins or dibenzofurans, and the
amine salts of MCPA may be contaminated with n-
nitrosamines. Therefore, analytical data, are required
for certain products.
Tolerance Assessment
Tolerances for residues of MCFA per se in or on food and
feed commodities are published in 40 CFR 180.339(a).
Tolerances for residues of MCPA and its metabolite 2-methyl-
chlorophenoxyacetic acid in or on animal commodities are
published in 40 CFR 180.339(b).
The residue data reviewed in support of these tolerances
showed the following:
- Data on metabolism of MC'PA in plants available for
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review in the 1982 document indicated that MCPA is readily
taken up and translocated by plants. Additional data are
required on the identity and quantities of residue in or on
plants. The nature of the residue is not adequately
understood.
- Data pertaining to the residues of MCPA in animals were
reviewed for the 1982 document. That document did not
require additional data on animal metabolism. Current
Guidelines specify that terminal residues in animals be
identified and quantified using radioactive material. The
metabolism of MCPA in animals is not adequately understood
and additional data are required.
- The current residue analytical methods in PAM I are
adequate for enforcement of tolerances for residues in plants
and animals.
- Data depicting the stability of MCPA residues in
storage were not required in the 1982 document. Current
Guidelines specify that storage stability data must be
submitted in support of established tolerances.
- There are available data to support the established
tolerances for MCPA in or on canarygrass seed and straw.
Additional residue data are required on dried beans,
peas (succulent and dry), pea vines and hay, rice grain,
sorghum grains, wheat grains, rice straw, sorghum forage and
fodder, wheat straw, annual canarygrass, pasture and
rangeland grasses, grass hay, alfalfa and alfalfa hay,
flaxseed, and flax straw.
- The data requested on wheat grain, forage, and straw
may, by translation, support the established tolerances for
residues of MCPA in or on the grain, forage, and straw of
barley, oats, and rye. The data requested on alfalfa and
alfalfa hay may, by translation, support the established
tolerances for residues of MCPA in or on clover and clover
hay, lespedeza and lespedeza hay, trefoil and trefoil hay,
and vetch and vetch hay.
Processing data are needed on rice grain, sorghum
grain, wheat grain, and flaxseed. The requirements for
processing data on barley, oat, and rye grain may be
satisfied by the data requested on wheat.
- Tolerances need to be proposed for residues of MCPA in
or on bean vines and hay, barley hay, oat hay, rye hay, wheat
forage and hay, and canarygrass forage.
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- Upon receipt of the data requested on animal metabolism
and livestock feed items, the established tolerances for the
combined residues of MCPA and 2-methyl-4-chlorophenol in the
meat, fat, and meat by-products of cattle, goats, hogs,
horses, and sheep and in milk will be assessed and the need
for tolerances for residues in poultry tissues and eggs will
be determined.
- A provisional acceptable daily intake (PADI, RfD) of
0.0015 mg/kg/day for MCPA has been established based on a 1-
year feeding study (dog, NOEL 0.15 mg/kg). The value given
is a PADI because of the teratology data gaps. However, when
the teratology studies are submitted and found acceptable,
they are not expected to greatly alter the RfD calculations.
A safety factor of 100 was utilized. The dietary exposure
was calculated using the published tolerances in 40 CFR
180.339. A dietary exposure for the U.S. population is
calculated to be 0.001547 mg/kg/day, corresponding to 103
percent of the RfD. The population subgroups with the
highest calculated exposure were nonnursing infants (0.007405
mg/kg/day, 493% of the RfD) and children 1 to 6 years of age
(0.004069 mg/kg/day, 271% of the RfD). A dietary exposure
was also conducted using the published tolerances factored by
the percent of crop treated with MCPA. The dietary exposure
for the U.S. population is then 10% of the RfD, for
nonnursing infants, 51% of the RfD, and for children 1 to 6
years of age, 27% of the RfD.
4. Summary of Regulatory Positions and Rationales
..- MCPA is not a candidate for special review.
- MCPA does not meet the criteria for restricted use
classification.
Precautionary labeling is required to minimize any hazard
to nontarget organisms.
The Agency is requiring data on MCPZv acid as well as its
derivative amines and esters.
- A special groundwater warning statement is required on the
label because of MCPA's potential to contaminate these
waters.
- MCPA does not meet the criteria to require a reentry
interval.
The Agency will consider establishment of significant new
food use tolerances for MCPA.
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Required Unique Labelina
A. Groundwater Advisory Statements
B. Environmental Hazards Statement
C. Feeding and/or Grazing Restrictions
D. Protective Clothing .Statement
E. Nontarget Species Precautionary Statements
Summary of Outstanding Data Requirements
Toxicology
Environmental Fate/Exposure
Ecological Effects
Residue Chemistry
Product Chemistry
Timeframe Ranges
1-4 years
1-4 years
2 years
2-4 years
1-2 years
Contact Persons at EPA
Product Specific Inquiries;
Joanna Miller
Acting Product Manager (23)
Fungicide Herbicide Branch
Registration Division (H-7505C)
Office of Pesticide Programs
Environmental Protection Agency
401 M Street, s.W.
Washington, B.C. 20460
Office location and telephone number:
Room 245, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, VA 2202
(703) 557-1800
Reregistration Standard Document Inquiries;
Philip T. Hundemann
Review Manager
Reregistration Branch
Special Review and Reregistration Division (H-7508C)
Environmental Protection -Agency
401 M Street, S.W.
Washington, D.C. 20460
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Office location and telephone number:
Room 1124, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, VA 22202
(703) 557-0933
DISCLAIMER: The information in this Pesticide Fact Sheet is a
summary only and is not be used to satisfy data requirements for
pesticide registration and reregistration. The complete
Reregistration Document for the pesticide may be obtained from
the National Technical Information Service. Contact the Review
Manager listed above for further information.
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