Unh«e Statw
Environment!) Protection
Agtncy
Offlct of P«rtiad* and Toxic Sub tancn
Otflc* of Pwttdd* Proonm* (TS-766CI
Wvhington. DC 2O460
&EPA Pesticide
Fact Sheet
Name of Chemical:
Reason for Issuance:
Date Issued: ..*,
Fact Sheet Number:
MALATHION
REGISTRATION STANDARD
152
1. DESCRIPTION OF CHEMICAL
Generic Name:
(Chemical)
O,0-dimethyl phosphorodithioate of diethyl
mercaptosuccinate
Common Name: Malathion
Trade and
Other Names: S-l,2-bis(ethoxycarbonyl)ethyl O,O-dimethyl
phosphorodithioate; diethyl'( dimethoxy-
phosphinothioyDthiobutanedioate;
diethyl mercaptosuccinate S-ester with 0,0-
dimethyl phosphorodithioate; O,O-dimethyl
dithiophosphate of diethyl mercaptosuccinate;
[S-(1,2-dicarbethoxyethyl) O,O-dimethyl
phosphorodithioate; diethyl mercaptosuccinic
acid, S-ester with 0,0-diraethyl phosphoro-
dithioate; American Cyanamid Co. (USP 2578 652)
Code No. EI4049; Calmathion; Celethion; Cythion
(deodorized grade); Chemathion; Malaspray;
Detmol MA 96% (Albert & Co., Germany);
Emmatos; Eromatos Extra; For-Mal (Forshaw
Chemicals); Fyfanon; Hilthion; Karbofos;
Kop-Thion; Kypfos; Malamar; Malaphele;
Malathion ULV Concentrate; Malatol; Maltox
(All-India Medical); Prentox Malathion 95%
Spray; Sumitox; Vegfru Malatox; Zithiol;
Maimed.
EPA Pesticide Chemical Code (Shaughnessy Number): 057701
Chemical Abstract Service (CAS) Number: 121-75-5
Year of Initial Registration: 1956
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Pesticide Type: Insecticide and Miticide
Chemical Family: Oraanophosphate
U.S. and Foreign Producers: American Cyanamid Company, A/S
Cheminova, McLaughlin Gormley King Company, Prentjss
Drug and Chemical Corp., Inc., Carmel Chemical Corp.,
Amvac Chemical Corp., Prochjmje International Inc.,
Gowan Co., Wesley Industries Inc., Trans Chemic Industries
Inc. , Southern Mill Creek Products Co. , Inc. , Octagon
Process Inc., FMC Corp., and Aceto Chemical. Co. Inc.
2. USE PATTERNS AND FORMULATIONS
Application Sites: Terrestrjal food crop use on alfalfa, almond,
anise, apple, apricot, asparagus, avocado, barley, beets,
beets (seed crop), bermudagrass, blackberry, blueberry,
boysenberry, broccoli, brussels sprouts, cabbage, cantaloupe,
carrot, casaba melons, cauliflower, celery, cherry, chestnut,
citrus fruits (nursery stock), clover, collards, corn cotton,
cowpeas (hay), crenshaw melons, cucumber, currant, dandelion,
date, dewberry, eggplant, endive, fig, filbert, flax, garlic,
gooseberry, grapefruit, grapes, grass, grass hay, green bear s,
guava, honeydew melons, honey ball melons, horseradish, kale,
kidney beans, kohirabi, kumquat, leek, lemon, lespedeza,
lettuce, lima beans, lime, loganberry, lupine, macadamia nut,
mango, muskmelons, mustard greens, navy beans, nectarine,
oats, okra, onion, onion (green), onion (seed crop), papaya,
parsley, parsnip, passion fruit, pasture grasses, peach,
peanuts, pear, peas, pecan, peppermint, peppers, persian
melons, pineapple, range].and grasses, raspberry, rutabaga,
rye, safflower, salsify, shallot, snap beans, sorgum, soybeans,
spearmint, spinach, squash, strawberry, sugar beets, sweet
potato, Swiss chard, tangelo, tangerine, tomato, turnips,
vetch, walnut, watercress, watermelons, wax beans, and wheat;
Terrestrial non—food crop use on tobacco, tobacco (transplant)
beds), ornamental flowering plants , ornamental lawns and turf,
ornamental nursery stock, ornamental woody plants, pine seed
orchards and Uncultivated non—agricultural areas;
Greenhouse food crop use on asparagus, beans, beets, celery,
cole crops (includina broccoli , cabbage, kale mustard greens,
and turnips), corn cucumber, eggplant, endive, lettuce,
melons, mushrooms, onion, peas, peppers, potato, radish,
spinach, squash, summer scuash, tomato, and watercress;
Greenhouse non—food crop use on ornamental plants and Epcot
display crops;
Aquatic food crop uses on cranberry and rices
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Aquatic non—food uses on intermittently fooded areas,
irrigation systems, and sewage systems;
Forestry uses on forest trees (including Douglas fir,
eastern pine, hemlock larch, pines, red pine, spruce, and
true fir);
Indoor uses on stored commodity treatment for almonds,
barley, field corn, field or garden seeds, grapes (raisin),
oats, peanuts, rice rye, sorghum, sunflower, wheat., bagged
citrus pulp, and cattle feed concentrate blocks (non—medicated);
pet and domestic animal uses for beef cattle, cats, chickens,
dairy cattle (lactating and non—lactating), dogs, ducks,
geese, goats, hogs, horses (including ponies), pigeons,
sheep, and turkeys; animal p temise uses for dairy and
livestock barns, stables and pens, feed rooms, poultry
houses, manure piles, garbage cans, garbage dumps, kennels,
rabbits on wire, beef cattle feed lots and holding pens,
cat sleeping quarters, dog sleeping quarters, poultry
houses; agricultural premise uses for cull fruit and vegetable
dumps; household uses for indoor domestic dwellings, human
clothing (woolens and other fabrics), mattresses; and
commercial and industrial uses for bagged flour, cereal
processing plants, edible and inedible commercial establish-
ments, dry milk processing plants, edible and inedible eating
establishments, edible and inedible food processing plants,
packaged cereals, pet foods and feed stuff.
Methods of Application: Sprays, aerosols and fogging equipment,
ground and aerial equipment (including ULV), baits, paints,
pet collars, dips, soil, bark and foliar application, dormant
and delayed dormant application, animal dust bags and oilers,
and cattle feed concentrate blocks.
Formulations: Wettable powders, dusts, granules, emulsifiable
concentrates, liquids, solids, impregnated materials, and
pressurized sprays, pellets/tablets, liquids (ready to use).
3. SCIENCE FINDINGS
Summary Science Statement
Technical malathion Is a mildly acutely toxic pesticide,
which is placed in Toxicity Category III based on the oral,
derrnal and inhalation routes of exposure. Technical malathion
is non—sensitizing and only mildly irritating to the eyes and
skin (Toxicity Category III and IV, respectively). Additional
data are required to assess the neurotoxic potential of malathion.
Malathion is a cho].inesterase inhibitor, reducing plasma and
red blood cell cholinesterase.
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Although the Agency possesses a number of studies on the
chronic effects of malathion and its principal metabolite
malaoxon, sever3l of these studies are deficient scientifically,
and must repeated.
Of five studies concerning the oncogenicity of malathion
and its metabolite, three are acceptable, and demonstrate that
malathion is not carcinogenic in two species of rats, and that
its metabolite malaoxon is not carcinogenic in mice. Because
of questionable liver findings in the malathion mouse study and
the malaoxon rat study, new studies must be conducted in these
species.
An acceptable rabbit teratploqy study demonstrated no
teratogenicity at dosages up tolOO mg/kg/day. However,
developmental and maternal toxicity were noted at dosaqes of
50 mg/kq/day. A similar study in rats was unacceptable and
must be repeated. A 3—generation reproduction study was also
unacceptable.
Laboratory data show that technical malathion is potentially
highly toxic to aquatic invertebrates, bees, and aquatic life
stages of amphibians; moderately toxic to birds, and slightly
toxic to fish. Based on theoretical calculations, both terrestrial
and aquatic uses of malathion may pose significant risk to
aQuatic fauna. Reported fish kills and results of field studies
suggest that adverse effects to both aquatic and terrestrial
fauna may result from normal use of malathion. However, these
studies are not adequately documented to enable EPA to propose
restrictions on the use of malathion. EPA will reassess the
impacts of malathion use on nontarget organisms after the
recuired environmental fate and ecological effects data have
been received and reviewed.
The Agency is unable to assess the potential for malathion
to contaminate groundwater because the environmenal fate of
malathion is largely uncharacterized. Preliminary data indicate
that malathion is very mobile in loamy sand and loam soils.
Additional data are needed in order for t’he Agency to assess
its fate in the environment and potential for contaminating
aroundwater.
A tolerance reassessment of malathion is not possible at
this time, since most of the tolerances are not adequately
supported, and because there are gaps in the chronic toxicoloqy
data base (chronic feeding studies, teratolocy study, reproduction
study, mutagenicity studies, and a metabolism study). The
Theoretical Maximal Residue Contribution (TMRC) for the U.S.
population average is 0.1014 mg/kg/day and the Provisional
Acceptable Daily Intake (PADI) is 0.02 mg/kg/day based on a
human study in which plasma and red blood cell cholinesterase
were monitored and a 10—fold uncertainty factor was used. The
TMRC occupies 507% of the PADI.
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Chemical/Physical Characteristics of the Technical Material
Chemical/Physical Color: colorless, yellow, amber, or
Character ist ics brown
(technical grade) Physical state: Liquid
Odor: Mercaptan—like
Specific gravity: 1.2315 at 25°C
Boiling point: 156—157°C at 0.7 mm Hg
Solubility: 145 ppm in water at 25°C;
completely soluble in most
alcohols, esters, high
aromatic solvents, and
ketones; poor solubility in
aliphatic hydrocarbons.
Vapor pressure: 0.00004 mm Hg at 30°C
Miscibility: miscible with most organic
solvents
Stability: may gel in contact with iron,
terreplate or tinplate
Toxicology Characteristics
Acute Oral: Toxicity Category lit (ranges from 1546 to 1945 mg/kg
in female rats and 1522 to 1650 mg/kg in male rats).
Acute Dermal: Toxicity Category III (>2000 mg/kg in female and
male rats and rabbits).
Acute Inhalation: Toxicity Category III based on toxicity values
ranging from 1.7 to >4.0 mg/rn 3 in rats.
Primary Dermal Irritation: Toxicity Category IV based on mild
dermal irritation reported in a rabbit
study
Primary Eye Irritation: Toxicity Category III based on findings
of mild conjunctival reactions 72 hours
post application in rabbits’ eyes.
Skin Sensitization: Non—sensit izing
Delayed Neurotoxicity: Data gap.
Subchronic Inhalation: Data gap.
Oncogenicity: Data gaps for mouse (using malathion) and rat
(using malaoxon).
Chronic Feeding: Data gaps for rodent and nonrodent (using
malathion) and rodent (using malaoxon).
Metabolism: Data gap.
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Teratogenicity:
Reproduction:
Data gap for rat.
NOEL = 25 mg/kg for
was not teratogenic
Dose Tested was 100
Data gap.
Data in rabbit indicated a
developmental effects; it
in any dose group (Highest
mg/kg).
Mutagenicj.ty: Data gap.
Environmental Characterjst ics
Data gaps exist for environmental fate. Data reviewed by the
Agency indicate that malathion is very mobile in laomy sand and
loam soils. Adsorption ratios reported (amount adsorbed/initial
concentration) were 0.73 to O.9 . Data are needed before the
Agency can assess the potential for malathion to contaminate
groundwater.
Ecological Characteristics
Avian oral toxicity
(8—day LD 50 )
Avian dietary toxicity
(8—day LC 50 )
Freshwater fish acute
toxicity (96—hr LC 50 )
Freshwater invertebrate
toxicity (48—hr EC 50 )
Estuarine invertebrate
toxicity
Tolerance Assessment
(technical grade)
167 ppm for ring—necked pheasant
and 1485 ppm for mallard.
Acute toxicity value of 3497 ppm
for bobwhite and >5000 ppm for
mallard
200 ppm for rainbow trout and 40
to 103 ppm for bluegill
1 ppm for Daphnia magna
>1000 ppm for Eastern oyster
The available data pertaining to metabolism of malathion
in plants are inadequate. Additional data are required on the
uptake, distribution, and metabolism of malathion in alfalfa,
cotton, soybeans, and either wheat or rice. The data Pertaining
to metabolism of malathion in animals are inadequate. Additional
metabolism studies are required that utilize ruminants and
poultry. Metabolism studies using cattle, poultry, and swine
reflecting direct animal treatment are also required.
Analytical methodology for determining the levels of
residues of malathion in plants and animals is adequate.
Malathion is detected by the FDA—USDA rnultiresidue protocols.
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Storage stability data demonstrate that residues of
malathion in or on frozen plant commodities are stable up to
185 days after application and in nilk stored at —10°C for 98
days after application. No data are currently available for
animal tissues and are required. Additional storage stability
data are also re uired in order to evaluate the adequacy of the
malathion tolerance.s.
Insufficient data are available on the magnitude and levels
of residues of malathion in or on all commodities listed n 40
CFR 180.111 except flax seed, hops, wild rice, and non—medicated
cattle feed concentrate blocks. Processing studies are required.
Tolerances must be proposed and appropriate supporting
residue data submitted for the following feed items: beanvines
and hay; lentil forage and hay; cowpea seed; soybean straw;
barley forage, hay and straw; corn forage and fodder; oat
forage, hay and estraw; rice straw; rye forage and straw; straw
of wild rice; sorghum fodder; lespedeza forage; lupine forage;
cotton forage; mint hay; peanut hulls, hay and vines; and
pineapple forage.
Feed additive tolerances are required for residues of
malathion in or on dried hops and spent hops. A tolerance for
residues of malathion In or on anise must be proposed together
with supporting residue data. Data are needed to support the
use of malathion in food handling establishments. In addition,
data reflecting the use of malathion on stored, unfinished
tobacco are required.
Based on a study in humans in which red blood cell and
plasma cholinesterase activity were inhibited at a dose of 0.34
mg/kg (the lowest effect level or LEL), a NOEL has been
extrapolated to 0.2 mg/kg/day. A provisional acceptable daily
intake (PADI) of 0.02 mg/kg/day has been calculated using a
10—fold uncertainty factor. The PADI is provisional because
the existing data base on malathion Is lacking chronic toxicity
studies, an acceptable teratology study In rats, an acceptable
reproduction study, mutagenicity studies, and a metabolism
study.
The Theoretical Maximal Residue Contribution (TMRC) for
the U.S. population average is 0.1014 mg/kg/day, occupying 507%
of the PAD!. For children 1 to 6 years of age, the TMRC occupies
1133% of the PAD!. The TMRC is based upon current tolerance
levels and an assumption that 100% of the sites are treated.
Actual exposure levels are likely to be much lower. When the
required data are submitted, the Agency will conduct a full
tolerance reassessment.
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4. SUMMARY OF REGULATORY POSITIONS AND RATIONALES
o No referral to Special Review is being made at this time.
o No new tolerances for raw agricultural commodities or
significant new uses will be granted until the Agency has received
data sufficient to perform a tolerance reassessment. Significant
new uses will not be granted until the data gaps have been
filled.
• The Agency is concerned about the potential hazards to
aquatic organisms. However, no regulatory action is being
considered at this time for fish and wildlife concerns. EPA
will reassess the impacts of malathion use on nontarget organisms
after the required environmental fate and ecological effects
data have been received and reviewed.
o The Office of Endangered Species (OES) in the U.S. Fish
and Wildlife Service has determined that certain uses of mala-
thion may jeopardize the continued existence of endangered
species or critical habitat of certain endangered species.
No additional labeling is required at this time; however,
EPA is developing a program to reduce or eliminate exposure
to these species, and may require labeling revisions when
the program is developed.
o In order to meet the statutory standard for continued
registration, the Agency has determined that malathion products
must bear revised and updated fish and wildlife toxicity warnings.
o The Agency is deferring decisions concerning malathion’s
potential for contamination of groundwater until the environmental
fate data have been submitted and reviewed.
o The Agency is not restricting the use of malathion products
for retail sale only to certified applicators. Malathion does
not meet any of the criteria of 40 CFR 162.11 and therefore
products containing malathion do not warrant restricted use
classification.
o The Agency is not establishing a longer reentry interval
for agricultural uses of malathion beyond the minimum reentry
interval for all agricultural uses of pesticides (sprays have
dried, dusts have settled and vapors have dispersed). The
Agency will reassess the need for reentry data/reentry intervals
upon receipt of the required toxicology data.
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5. SUMMARY OF OUTSTANDING DATA REQUIREMENTS
Toxicology Time Frame
Delayed neurotoxicity 9 mos.
21—day dermal toxicity 9
90—day inhalation — rat 15
Chronic toxicity (rodent and non-rodent)-- 50
using malathion)
Chronic toxicity (rodent)——using malaoxon 50
Oncogenicity (mouse)-—using malathion 50
Oncogenicity (rat)——using malaoxon SO
Teratogenicity — rat 15
Reproductive effects — rat (2—generation) 39
Mutagenicity 9—12 mos
Metabolism 24 mos
Domestic animal, safety testing 15
Environmental Fate/Exposu’e
Hydrolysis 9 mos
Aerobic and anaerobic soil metabolism 27
Aerobic and anaerobic aquatic metabolism 27
Leaching and adsorption/desorption 12
Terrestrial field dissipation 27
Long—term field dissipation 50
Forestry dissipation 27
Aquatic (sediment) — field study 27
Phhotodegradation in water, soil, air 9
Volatility (lab) 12
Rotational crops (confined) 39 5
Accumulation in irrigated crops 39
Accumulation in fish 12
Accumulation in aquatic nontarget organisms 12
Spray drift 18
Residue Chemistry
Storage stability data 18 mos
Plant and animal metabolism 18
Residue data — raw agricultural commodities 18
Processing studies 24
Residue data on stored, unfinished tobacco 18
Residues in water 15
Residue data on food handling establishments 12
Product Chemistry Time Frame
All 9—15 x s
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Fish and Wildlife
Acute toxicity to freshwater invertebrates 9 mos
Acute toxicity to estuarine and marine organisms 12
Avian reproduction 24
Fish early life stage is
Aquatic invertebrate life cycle is
Honeybee - toxicity of residues on foliage 15
6. CONTACT PERSON AT EPA
William H. Miller
Product Manager (16)
Insectjcjde—Rodentjcjde Branch
Registration Division (TS—762C)
Office of Pesticide Programs
Environmental Protection Agency
401 M Street, SW.
Washington, DC 20460
Office location and telephone number:
Rm. 211, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, VA
(703) 557—2600
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.
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