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E X T O X N E T
Extension Toxicology Network
Pesticide Information Profiles
A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the
University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan
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Impact Assessment Program.
EXTOXNET primary files maintained and archived at Oregon State University
TRADE OR OTHER NAMES: The active ingredient diclofop-methyl is found in a variety of commercial herbicides.
Trade names for products containing diclofop-methyl include Hoelon, Illoxan, Hoe-Grass,and One Shot (diclofop plus
bromoxynil plus MCPA) (1, 300).
REGULATORY STATUS: Some or all uses of diclofop-methyl may be classified as a restricted use pesticide (RUP).
Check with specific state regulations for local restrictions which may apply. Restricted products containing diclofop-methyl
must carry the Signal Word "Danger" on their label; others may carry the Signal Word "Caution" (58).
CHEMICAL CLASS: diphenylether/chlorophenoxy herbicide
INTRODUCTION: Diclofop-methyl is a selective post-emergence herbicide for control of wild oats and annual grassy
weeds found among brassicas, carrots, celery, field beans, french beans, broad beans, barley, wheat, parsnips, peas,
potatoes, soy beans, oilseed rape, onions, sugar beet, and lettuce (1).
The herbicide comes in emulsifiable concentrate formulations (1, 242). It is compatible with herbicides derived from urea,
i.e. asulam, ioxynil, etc., although mixing with dinoseb and growth-regulating herbicides leads to decreased effectiveness
- Acute Toxicity: The acute oral LD50 for rats ranged between 563-693 mg/kg (in sesame oil). The acute dermal LD50
for female rats was greater than 2,000 mg/kg. The no effect level (NEL) for a 90-day feeding to rats was 12.5 mg/kg and
8 mg/kg for a 15-month feeding to dogs (1, 242, 300). The acute percutaneous LD50 for rats was greater than 5,000
mg/kg (242). The acute inhalation toxicity for rats exposed to technical diclofop-methyl was greater than 3.83 mg/l/hour
(300). Rats exposed to the product Hoelon 3EC (contains diclofop-methyl) had an oral LD50 value of greater than 2,000
mg/kg. The acute dermal LD50 for exposure to the same product was greater than 5,000 mg/kg (300). The inhalation
LC50 in rats for a 36%EC formulation of diclofop-methyl over a four-hour period was 8.3 mg/l air (1). Inhalation: a rate
of 4,800 ml of a 5% solution in a 4 cubic meter container for four hours was studied. Deaths occurred with rabbits, but
not with rats, guinea pigs or cats at this high rate. The 4-hr LC50 for rats was 8,274 mg/m3 (300). The acute dermal
LD50 for rabbits was reported to be 640 mg/kg. A diclofop-methyl study on rabbits indicated no skin irritation at 24, 48
and 72 hours. Eye irritation in rabbits was found to be zero at 3, 7, or 24 hours (300). Other studies have reported eye
irritation in rabbits as corneal opacity spots and conjunctival irritation in both rinsed and non-rinsed groups. Reversibility
was observed in all but one animal in each group at 7 days. A 10% solution produced corneal opacity in some of the
animals that was completely reversible in 72 hours (300, 207). The acute dermal LD50 for rabbits was found to be 640
- Chronic Toxicity: In 2-year feeding trials the NEL for rats was 20 mg/kg diet. The 15 month NEL for dogs was 8
mg/kg diet (242). Repeated absorption of chlorinated diphenyl ethers has resulted in liver damage in animals (301).
Reproductive Effects The NEL in a three-generation study of technical diclofop-methyl in rats was greater than 30 ppm
- Teratogenic Effects: In a rat teratology study, the teratogenic No-Observable-Effect-Level (NOEL) was 100 ppm, the
highest dose tested. A rabbit teratology study reported a teratogenic NOEL of 3 mg/kg/day, the highest dose tested, and
a NOEL for fetotoxicity of 3.0 mg/kg/day (303).
- Mutagenic Effects: Ames assay testing revealed no mutagenic effects using four bacterial strains with and without
enzyme activation in dose ranges up to 5 miligrams (300). A micronucleus test in mice indicated no mutagenic effect in a
strain with known sensitivity. In a dominant lethal assay, the NOEL was greater than 100 mg/kg. No impairment in
fertility of the male mice and no difference in the number of live and dead implantations in the female animals were noted
- Carcinogenic Effects: No information was available.
- Organ Toxicity: No information was available.
- Fate in Humans and Animals: Diclofop-methyl is metabolized in mammals via hydroxylation. Chlorophenoxy
compounds are absorbed across the gut wall, lung and skin. They are not significantly stored in fat and urinary excretion
is the principal route of elimination. Elimination as a conjugate is within 96 hours (1).
- Effects on Birds: The acute oral LD50 to bobwhite quail was 4,400 mg/kg (300); and greater than 10,000 mg/kg for
Japanese quail (242). The eight-day dietary LC50 value for coturnix quail was greater than 20,000 ppm; 13,000 ppm for
bobwhite quail; and greater than 20,000 ppm for mallard ducks (300).
- Effects on Aquatic Organisms: The 96-hour LC50 for technical diclofop-methyl in rainbow trout was 0.35 mg/l water
(242). The 96-hour LC50 in rainbow trout for the formulated product Hoelon 3EC was 1.38 ppm; and 2.60 ppm for carp
(300). The 48-hour LC50 in the crustacean Daphnia for the formulated product Hoelon 3EC was 4.03 ppm (300).
- Effects on Other Animals (Nontarget species): The LD50 for honeybees in a lab test of the formulated product
Hoelon 3EC indicated it was nontoxic at the highest dose tested; 48 kg/ha (43 lb ai/acre) (300).
- Breakdown of Chemical in Soil and Groundwater: Under aerobic conditions, diclofop-methyl hydrolyzes in a matter
of days in the soil to 2-[4-(2',4'-dichlorophenoxy)phenoxy] propanoic acid which in turn is degraded relatively quickly
with a half-life of 10 days in sandy soils and about 30 days in sandy clay soils. Small amounts of 4-(2,4
dichlorophenoxy)phenol are also produced (300, 302). Field studies of application rates up to 3.4 kg active ingredient
per hectare (3.0 lb ai/acre) showed very low finite residues in soil. At harvest, small finite residues were present in the
0-7.5 cm (0-3 in) soil level and rare small residues were present above the 15 cm (6 in) level. These studies indicate that
diclofop-methyl does not leach downward or move laterally, and dissipates quickly in soil (300).
- Breakdown of Chemical in Surface Water: No information was available.
- Breakdown of Chemical in Vegetation: Diclofop-methyl is absorbed via the leaves and in damp soil there is slight
absorption via the roots. The compound inhibits root growth (1).
PHYSICAL PROPERTIES AND GUIDELINES
- Appearance: colorless crystals (1)
- Chemical Name: methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]propanoate (1)
- CAS Number: 51338-27-3 (1)
- Molecular Weight: 341.2
- Water Solubility: 50 mg/l at 22 degrees C (1)
- Solubility in Other Solvents: readily soluble in common organic solvents, e.g. acetone 40, xylene 50, methanol 40 (all
in g/100 ml at 22 degrees C) (1)
- Melting Point: 39-41 degrees C (1, 300)
- Vapor Pressure: 3.4 x 10 to the minus 7 mbar at 30 degrees C; 3.8 x 10 to the minus 5 mbar at 54.3 degrees C (1)
- Partition Coefficient: Not Available
- Adsorption Coefficient: Not Available
- ADI: Not Available
- MCL: Not Available
- RfD: 0.002 mg/kg/day (1)
- PEL: Not Available
- HA: Not Available
- TLV: Not Available
P.O. Box 2500
Somerville, NJ 08876-1258
- Fax: 908-231-4452
- Telephone: 908-231-2000
- Emergency: 800-228-5635
References for the information in this PIP can be found in Reference List Number 10
DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide
product label/ing or other regulatory requirements. Please refer to the pesticide product label/ing.