E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/95
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)
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
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, 2). 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 (1).
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, 2, 3). The acute percutaneous LD50
for rats was greater than 5,000 mg/kg (2). The acute inhalation toxicity for
rats exposed to technical diclofop-methyl was greater than 3.83 mg/l/hour (3).
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 (3). 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 (3).
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
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 (3, 5).
The acute dermal LD50 for rabbits was found to be 640 mg/kg (3).
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 (2). Repeated absorption of chlorinated
diphenyl ethers has resulted in liver damage in animals (6).
The NEL in a three-generation study of technical diclofop-methyl in rats
was greater than 30 ppm (3, 8).
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 (8).
Ames assay testing revealed no mutagenic effects using four bacterial
strains with and without enzyme activation in dose ranges up to 5 miligrams
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
No information was available.
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 (3); and greater
than 10,000 mg/kg for Japanese quail (2). 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 (3).
Effects on Aquatic Organisms
The 96-hour LC50 for technical diclofop-methyl in rainbow trout was 0.35
mg/l water (2). The 96-hour LC50 in rainbow trout for the formulated product
Hoelon 3EC was 1.38 ppm; and 2.60 ppm for carp (3).
The 48-hour LC50 in the crustacean Daphnia for the formulated product
Hoelon 3EC was 4.03 ppm (3).
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)
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 (3, 7).
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 (3).
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
|CAS No.: ||51338-27-3 (1)
|Chemical name: ||methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]propanoate (1)
|Chemical Class/Use: ||diphenylether/chlorophenoxy herbicide, preemergence and postemergence herbicide (5)
|Specific gravity: ||1.3 gm/cm3 at 40 degrees C (3)
|Solubility in water: ||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, 3)
|Boiling point: ||173-175 degrees C at 0.1 mbar (1)
|Decomposition temperature: ||288.4 degrees C (3)
|Flashpoint: ||38 degrees C (closed cup) (4)
|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)
|Koc: ||4.89 (7)
P.O. Box 2500
Somerville, NJ 08876-1258
Review by Basic Manufacturer:
Comments solicited: October, 1994
The Agrochemicals Handbook. 1983. The Royal Society of Chemistry, The
University, Nottingham, England.
Worthing, C. R. (ed.). 1983. The Pesticide Manual: A World Compendium.
Seventh edition. Published by The British Crop Protection Council.
Herbicide Handbook of the Weed Science Society of America. 1989. Sixth
edition. Champaign, IL.
Farm Chemicals Handbook. 1994. Meister Publishing Co. Willoughby, OH.
Thomson, W. T. 1992. Agricultural Chemicals. Book II: Herbicides.
Thomson Publications, Fresno, CA.
OHS Database. June, 1994. MSDS for Diclofop-Methyl. MDL Information
Systems Inc., San Leandro, CA.
Montgomery, J. H. 1993. Agrochemicals Desk Reference: Environmental
Data. Lewis Publishers. Chelsea, MI.
U. S. Environmental Protection Agency. 1986. Pesticide Tolerance for
Diclofop-Methyl. Federal Register. Vol. 51, No. 102. Rules and Regulations.
Wednesday, May 28, 1986.