MCPA (Chiptox, Dow MCP) Herbicide Profile 9/89
EPA Pesticide Fact Sheet
Name of Chemical: MCPA
Reason for Issuance: REGISTRATION STANDARD (SRR)
Date Issued: SEP 22, 1989
Fact Sheet Number: 208
1. 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, DED-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
2. USE PATTERNS AND FORMULATIONS
- Terrestrial food crop use on small grains
(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.
- 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
- Methods of application: Aerial and ground equipment, knapsack
sprayers, pressure and hose-end applicators, and lawn spreaders.
- Application rates: 0.2 - 3.0 lb 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 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 degrees C and is soluble to varying
degrees in various solvents.
- 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
- Primary Eye Irritation. Toxicity Category I (corneal opacity with
irritation of conjunctive observed 21 days post-instillation with
- 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
- 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 mg/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
- Mutagenicity. 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
- Metabolism. In a rat study, MCPA did not appear to be significantly
metabolized in vivo (82 and 38% were recovered in male and female rat
urine, respectively). Repeat dosing did not generally indicate
bioaccumulation 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 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 derivatives. 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
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
- Acute LD50 377 mg/kg for Bobwhite quail
- Dietary LC50 > 2000 ppm for mallard, bobwhite, and ring-necked
- LC50 rainbow trout = 89 ppm
- LC50 bluegill = 97 ppm
- LC50 Daphnids > 180 ppm
- LC50 Atlantic silverside = 179 ppm
- 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
- 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 resubmitted. 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
Tolerances for residues of MCPA 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
- Data on metabolism of MCPA in plants available for 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
- 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
- There are available data to support the established tolerances for
MCPA in or on canary grass 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 canary-
grass, 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
- 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
- The Agency is requiring data on MCPA 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.
4. REQUIRED UNIQUE LABELING
A. Groundwater Advisory Statements
B. Environmental Hazards Statement
C. Feeding and/or Grazing Restrictions
D. Protective Clothing Statement
E. Nontarget species Precautionary Statements
6. SUMMARY OF OUTSTANDING DATA REQUIREMENTS
Toxicology 1 - 4 years
Environmental Fate/Exposure 1 - 4 years
Ecological Effects 2 years
Residue Chemistry 2 - 4 years
Product Chemistry 1 - 2 years
7. CONTACT PERSONS AT EPA
Product Specific Inquiries:
Acting Product Manager (23)
Fungicide Herbicide Branch
Registration Division (H-7505C)
Office of Pesticide Programs
Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
Office location and telephone number:
Room 245, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, VA 2202
Reregistration Standard Document Inquiries:
Philip T. Hundemann
Special Review and Reregistration Division (H-7508C)
Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
Office location and telephone number.
Room 1124, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, V 22202
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