United States            Office of Pesticides and Toxic Substances
                 Environmental Protection      Office of Pesticide Programs (TS-766C)
                 Agency               Washington, DC 20460
vvEPA      Pesticide
                 Fact Sheet
                 Name of Chemical: Methiocarb
                 Reason for Issuance: Registration Standard
                 Date Issued:  March, 198?
                 Fact Sheet Number:   120
1.  Description of  Chemical

    Chemical Name:   4-methylthio-3,5-xylylmethylcarbamate

    Common Name  :   methiocarb

    Trade  Names :   mercaptodimethur,  metmercapturnon,
                    mesurol, methiocarbe,  Bay 37344,  and H-321

    OPP (Shaughnessy) Number:  100501

    Chemical Abstracts  Service (CAS) Number:   2032-65-7

    Year of Initial  Registration:  1972

    Pesticide Type:  Insecticide, acaricide; molluscicide;
                    and bird and rodent repellent

    Chemical Family:  Carbamate

    U.S. Producer:   Mobay Chemical Corporation

2.  Use Patterns and Formulations

    Application Sites:  Corn and sunflower fields, fruit,
                       orchards, blueberries, ginseng,
                       avocadoes, peppers, ornamentals,
                       greenhouses, lawns and turf

    Types of Formulation:  Dust, granular, wettable powder and

    Types/Methods of Application: Soil-incorporated,  foliar,
                                 aerial and  broadcast.

3. Science Findings
Summary Science Statement
Technical methiocarb is highly acutely toxic by the oral
route and of relatively low acute toxicity by the dermal
route. Methiocarb’s primary mechanism of toxicity is
cholinesterase inhibition. Methiocarb sulfoxide, a
cholinesterase—inhibiting metabolite of methiocarb was
shown to be more acutely toxic than methiocarb in an
acute rat toxicity test (7 mg/kg in female rats and 9
mg/kg in male rats). Results of cholinesterase studies
suggest that methiocarb sulfoxide may be more toxic than
methiocarb. A 30—day dog feeding study conducted with
methiocarb sulfoxide is required to assess the cholines—
terase inhibition of this metabolite. Available studies
are not sufficient to complete the assessment of methio—
carb and its metabolites. Data gaps exist for acute
inhalation; 21—days dermal; mouse oncogenicity; reproduction;
mutagenicity; and general metabolism studies. Methiocarb
is very highly acutely toxic to avian species, to both
coidwater and warmwater fish, and to freshwater invertebrates
on an acute basis. It is slightly toxic to practically
non toxic to avian species on a subacute dietary basis.
Field testing, an avian repellency study and an aquatic
residue monitoring study are required for completion of
the Agency’s assessment of the potential risk to avian
and aquatic species.
Chemical Characteristics :
Physical State: Crystalline solid
Color: White
Odor: Slight mercaptan—like
Boiling Point: Not distillable
Melting Point: 121°C
Bulk Density: 35—40 lb/cu ft.
ph: N/A (not soluble enough)
Toxicology Characteristics :
Acute oral toxicity (rat) 14—30 mg/kg; Toxicity
Category I
Acute derinal toxicity (rabbits) > 2000 mg/kg; Toxicity
Category III

Acute delayed neurotoxicity
(hen) Negative at 380 mg/kg
Chronic feeding (rat) NOEL for cholinesterase
inhibition 67 ppm (3.35
Chronic feeding (dog) NOEL for cholinesterase
inhibition = 5 ppm (0.125
Oncogenicity (rat) not oncogenic up to 600 ppm
Teratology (rat) negative up to 10 mg/kg/day
Teratology (rabbit) negative up to 10 mg/kg/day
Physiological and Biochemical Characteristics:
Metabolism and persistence in plants and animals :
Radiolabeled studies on the uptake, translocation and
metabolism of methiocarb in plants show that methiocarb
undergoes two routes of metabolic breakdown in plants.
Methiocarb may be oxidized to the sulfoxide (MSO) and
thereafter hydrolyzed to methiocarb sulfoxide phenol (MSOP).
These metabolites may be further oxidized and hydrolyzed
to yield methiocarb sulfone (MSO 2 ) or rnethiocarb sulfone
phenol (MSO 2 P). A secondary metabolic route is the
hydrolysis of methiocarb to the phenol (MP). The metabo-
lism of methiocarb in animals is not well understood.
Available information again suggests two pathways of
metabolism. The major route in both chickens and ruminants
appears to be hydrolysis to methiocarb phenol (MP)
followed by oxidation to methiocarb sulfoxide phenol
(MSOP). Additional metabolism studies in ruminants and
poultry are required.
Mechanism of pesticidal action : cholinesterase—inhibition
Environmental Characteristics :
Adequate data are not available to assess the environ-
mental fate of methiocarb; data are not adequate to
assess methiocarb’s potential for contaminating groundwater.
Ecological Characteristics :
Avian acute oral toxicity: mallard duck 12.8 mg/kg
Subacute dietary toxicity: mallard duck; 1071 ppm and
ring—necked pheasant; greater
than 5000 ppm.

Avian reproductive effects: mallard duck; negative at
100 ppm and bobwhite quail;
negative at 50 ppm.
96—hour fish toxicity: rainbow trout; 0.436 ppm and
bluegill sunfish; 0.734 ppm
48—hour fresh water invertebrate toxicity: Daphnia magna;
.019 mg/kg
Tolerance Reassessment
Tolerances have been established for residue of methiocarb
and its cholinesterase—inhibiting metabolites in or on
blueberries (5.0 ppm), cherries (5.0 ppm), citrus fruits
(0.02 ppm), corn (0.03 ppm), and peaches (15.0 ppm). The
tolerances for blueberries and cherries are interim tol-
erances, due to expire on March 31, 1989. Refer to 40 CFR
The food additive tolerances listed for methiocarb
under 21 CFR 193.145 and 21 CFR 561.175 were temporary
tolerances established to cover residues in or on grape
food and feed items resulting from application of the
pesticide to grapes under an experimental use permit.
These tolerances and experimental use permit expired
December 31, 1980.
Tolerances are expressed in terms of methiocarb and its
cholinesterase — inhibiting metabolites.
Available data are not sufficient to conduct a full
tolerance assessment. Data gaps exist for the residue
analytical method; field residue studies and animal
metabolism studies.
4. Required Unique Labeling and Regulatory Position Summary
Use classification — All outdoor commercial and agri-
cultural uses have been classified restricted use
under this Standard; all on the basis of avian toxicity;
and all, with the exception of the corn seed treatment,
on the basis of fish and aquatic species toxicity. This
is an interim precautionary measure pending submittal and
evaluation of the avian repellency and field studies, and
the aquatic residue monitoring studies.
Endangered species labeling — Labeling tor seed treatment
to corn; bait application to corn; and golf course and
sod farm uses will be required pending concurrence on
proposed labeling by the Fish and Wildlife Service, U.S.
Department of the Interior.

Reentry interval — A 24—hour reentry interval is imposed
pending submittal and evaluation of reentry data. This
reentry labeling restriction is being imposed for use of
rnethiocarb on commercial turf; commercially grown orna-
mentals; agricultural crops (except seed treatment); and
in greenhouses.
Tolerances — no additional permanent tolerances will be
established pending the approval of a residue analytical
method. Tolerances above 5.00 ppm cannot be toxicologically
supported and the existing tolerance of 15.0 ppm in/on
peaches will be revoked.
5. Summary of major data gaps:
Toxicology — generic Date Due
Acute inhalation — rats October 1987
21—day derinal October 1987
30—day feeding (dog) October 1987
methiocarb sulfoxide (acceptable protocol)
Mouse oncogenicity study October 1990
Reproductive effects December 1988
Mutagenicity testing February 1988
General metabolism study April 1989
Residue Chemistry
Livestock metabolism —
(ruminants and poultry) October 1988
Analytical methodology
for plants and animals July 1988
Data on levels of residues in: **
citrus fruits, cherries,
blueberries, and corn
Tolerance proposals and/or residue **
data to support the following uses:
avocados; pepper and sunflower seed
crops; preplant application for
agricultural crops, and non—bearing
deciduous fruit trees.
** Submittal due dates for these data are contingent on the
submittal and evaluation of the analytical methodology data.

Ecological Effects
Field testing for mammals
and birds
Avian repellency test
Acute toxicity for estuarine
and marine organisms
Fish early life stage
Aquatic invertebrate
life cycle
Aquatic residue monitoring
Environmental Fate :
— water and soil
Soil metabolism
— aerobic and anaerobic
Leaching and
adsorption/desorpt ion
Soil dissipation
Confined rotational crop
Fish accumulation
Reentry studies
6. Contact Person at EPA :
William H. Miller, (PM—16)
Insecticide—Rodenticide Branch (TS—767)
401 M Street, SW.
Washington, DC 20460
Tel. No. (703) 557—2600
October 1987
(acceptable protocol)
April 1988
August 1987
November 1987
November 1987
April 1988
January 1988
May 1987
July 1989
August 1987
November 1988
November 1989
April 1988
December 1987
DISCLAIMER: The information presented in this chemical
Information Fact Sheet is for informational purposes only and
may not be used to fulfill data requirements for pesticide
registration and reregistration.