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 ethephon is found in a variety of commercial
herbicides. Trade names for products containing ethephon include Arvest,
Bromeflor, Etheverse, Flordimex, Flordimex T-Extra, Cerone, Etherel, Chipco
Florel Pro and Prep (4, 10).
Ethephon is a general use pesticide (GUP). Check with specific state
regulations for local restrictions that may apply. Products containing
ethephon carry the Signal Words "Danger," "Warning," or "Caution" depending on
the product (4).
Ethephon is a plant growth regulator. Its use varies with plant species,
chemical concentration, and time of application. Ethephon regulates phases of
plant growth and development by application to various growth sites (1). It
is currently registered in the U.S. for use on apples, barley, blackberries,
bromeliads, cantaloupes, cherries, coffee, cotton, cucumbers, grapes, guava,
macadamia nuts, ornamentals, peppers, pineapples, rye, squash, sugarcane,
tobacco, tomatoes, walnuts, wheat, etc. (1, 4, 5). Ethephon's mode of action
acts via liberation of ethylene, which is absorbed by the plant and interferes
in the growth process (1). It is also used in the acceleration of ripening of
fruits and vegetables (8).
Ethephon comes in RTU (ready-to-use), emulsifiable concentrate and
aqueous solution formulations (4, 10). It may also be used in combination
with Terpal (with mepiquat-chloride) and Terpal C (chlormequat-chloride) (4).
The amount of ethephon that is lethal to one-half (50%) of experimental
animals fed the material is referred to as its acute oral lethal dose fifty,
or LD50. The acute oral toxicity of ethephon in rats ranged from 3400 mg/kg
(6) to 4229 mg/kg (2, 4, 8).
Acute animal toxicity studies in a few species show that via the oral and
dermal routes, ethephon is relatively non-toxic except in hens. An acute
study with rats showed an oral LD50 of 1.6 g/kg (EPA toxicity category III).
An acute dermal study using rabbits showed a dermal LD50 of greater than 5
g/kg (EPA toxicity category III) (9).
In a rat study, ethephon was administered by gavage for 13 weeks to 20
rats per sex per dose level at 0, 50, 100, and 200 mg/kg/day. Plasma
cholinesterase and brain cholinesterase activity were found to be different
from the controls at all dose levels. However, red blood cell cholinesterase
activity did not differ from the controls in either sex of any dose group (9).
The acute oral LD50 of 24% ethephon solution in propylene glycol for rats
was reported to range between 3,400 mg/kg (RTECS, 1985) to 4,229 mg/kg (Hartly
and Kidd, 1987) (8). The dermal LD50 for the same 24% solution for rabbits
was 5,730 mg/kg. Irritation of mucous membranes in rabbits was also reported.
The same study indicated that the inhalation LC50 for rats was greater than 5
mg/l of air (1, 2, 6).
EPA reported the acute oral LD50 to be 1.6 g/kg for rats; the acute
dermal LD50 for rabbits to be greater than 5 g/kg; and the primary skin
irritation score for rabbits to be 6.75 (corrosive) (10).
The oral LD50 for mice fed technical ethephon was 2850 mg/kg; 5,000 mg/kg
for rabbits; 4,200 mg/kg for guinea pigs; and an unreported 4,200 mg/kg for
In a dog study, ethephon was administered in the food to 4 dogs per sex
per dose level at 0, 5.0, 25.0, or 187.5 mg/kg/day for 13 weeks. Plasma
cholinesterase activity was depressed in both males and females at all dose
levels. Red blood cell activity was depressed in the males (at all dose
levels except 5.0 mg/kg/day at 8 weeks) and at the 25.0 and 187.5 mg/kg/day
dose levels in the females. Brain cholinesterase activity was significant
only in females dosed at 187.5 mg/kg/day (9).
A chronic toxicity/oncogenicity study using Swiss albino mice included 85
mice fed diets containing 0, 4.5, 45, or 150 mg/kg/day of ethephon for 78
weeks. Inhibition of plasma cholinesterase activity was significant at the
45 and 150 mg/kg/day dose levels in males and females. The No Observable
Effect Level (NOEL) for plasma cholinesterase activity is 4.5 mg/kg/day for
both sexes and the Lowest Effect Level (LEL) for this effect was 45 mg/kg/day
for both sexes (9).
There appeared to be a dose-related decrease in red blood cell
cholinesterase activity in females. There was significant depression in RBC
cholinesterase activity at the 45 and 150 mg/kg/day dose levels, while females
in the 4.5 mg/kg/day dose groups exhibited depression in RBC cholinesterase
activity at 52 weeks and 78 weeks, which was not considered statistically
significant. Because of the apparent dose-related decrease in RBC
cholinesterase activity in females in the 4.5 mg/kg/day dose group, the NOEL
for this effect in females is considered to be below 4.5 mg/kg/day, the lowest
dose tested (9).
RBC cholinesterase activity was nominally decreased in males at the mid-
and high-dose groups.
Brain cholinesterase activity was not different from control values at
any dose level in males or females.
In two-year feeding studies, rats receiving greater than or equal to
12,500 mg/kg diet showed no ill-effect except at top dose levels toward the
end of the trial (2). The highest dose without adverse effects reported in
rats was 375 mg/kg/day for 90 days (1).
A developmental toxicity study was conducted on New Zealand white
rabbits. The doses tested were 50, 100, or 150 mg/kg. The teratogenic NOEL
was greater than 50 mg/kg/day (LDT or lowest dose tested). The number of
litters at termination of the study were insufficient to determine teratogenic
effects at the 100 and 150 mg/kg/day levels. The embryotoxic NOEL was 50
mg/kg/day (LDT); an increased average number of resorptions occurred. The
maternal toxic NOEL was 100 mg/kg, while the maternal LEL was 250 mg/kg (HDT
or highest dose tested); decreased body weight, food consumption and increased
mortality occurred at this dose level. The fetal toxic NOEL was reported to be
50 mg/kg/day. The fetotoxic LEL was 100 mg/kg/day, at which decreased fetal
viability was reported (7).
In another study, doses of 0, 200, 750, and 1,500 ppm of 39% ethephon
were tested in a multigeneration rat reproduction study. The NOEL was
reported to be greater than 1500 ppm (highest dose tested) (7).
The NOEL for rat teratogenic effects is 600 mg/kg/day, while in the
rabbit, the NOEL was reported to be 50 mg/kg/day based on fetal resorptions at
higher dose levels tested (7, 10).
Ethephon studies in Salmonella typhimurium indicated no mutagenic effect
up to 1,000 micrograms/100 microliters, without enzyme activation (10).
A carcinogenicity study was conducted in mice using 70.6-72.1% ethephon.
The doses were administered in feed at 0, 15.5, 156 or 1630 mg/kg/day to CD-1
mice for 78 weeks. No dose-related evidence of carcinogenicity/oncogenicity
was reported (7).
No information currently available.
Fate in Humans and Animals
No information currently available.
Effects on Birds
Data indicate that technical-grade ethephon is slightly toxic on an acute
oral basis to bobwhite quail, and slightly toxic on a subacute dietary basis
to bobwhite quail and mallard ducks. The acute oral LC50 in bobwhite quail is
from 596 to 804 mg/kg. The acute oral LC50 is 3,750 ppm for mallard ducks and
greater than 2,160 ppm in bobwhite quail. The average acute oral toxicity for
formulated products is greater than 10,000 ppm in bobwhite quail, or
practically non-toxic (9, 10). Another source reported the oral LD50 for
bobwhite quail to be 1,000 mg/kg (2).
The chronic toxicity LC50 for birds was reported to be 804 mg/kg for
quail and 3,750 ppm for ducks (4); and the LC50 (8 days) for mallard ducks was
greater than 10,000 mg/kg diet.
Effects on Aquatic Organisms
Laboratory and field studies indicate that ethephon is slightly toxic to
fish. Studies indicated LC50 values for fish of 170 mg/l for rainbow trout;
and 180 mg/l for bluegill sunfish. Also, a 96-hour LC50 for rainbow trout
ranged from 254 mg/l to 350 mg/l and for bluegill sunfish 222 mg/l to 300 mg/l
(Worthing and Hance, 1991) (1, 2, 10).
Effects on Other Animals (Nontarget species)
Two studies using ethephon were conducted in humans. In the first study,
some symptoms characteristic of anticholinesterase activity were observed.
Five humans of each sex were dosed with ethephon at an average dose level of
1.8 mg/kg/day. Subjects receiving the test compound reported the following
symptoms and/or signs; sudden onset of diarrhea or an urgency of bowel
movements, stomach cramps or gas and increased urgency or frequency of
urination, and either an increase or decrease in appetite. None of the
control subjects had complaints similar to the test group. Plasma CHE and RBC
CHE activities were similar to or higher than initial values in test subjects
In the second human study, 10 humans of each sex were administered
ethephon at 0.5 mg/kg/day for 16 days, followed by a 2-week recovery period.
Dose related effects occurred in plasma cholinesterase activity, but not in
red blood cell cholinesterase activity. The effect was reversible within 15
days. When the control group and test groups were compared, the decreased
plasma cholinesterase activity was statistically significant. No dose-related
effects were seen in hematology, blood chemistry, or urine analysis. Based on
this study, the NOEL for plasma cholinesterase inhibition in humans is less
than 0.5 mg/kg/day (9).
Ethephon usage has resulted in four cases of skin injury (irritation)
reported from 1980 through 1986 in California due to exposure to field
Ethephon is considered relatively non-toxic to honeybees (1, 9).
Breakdown of Chemical in Soil and Groundwater
Ethephon was found to have low to moderate mobility in soils ranging in
texture from loamy sand to peat and silt loam based on soil thin layer
chromatography tests. Therefore, the potential for contamination of
groundwater appears to be low to moderate (9).
In soil, rapid degradation to phosphoric acid, ethylene, and chloride
ions was reported (Hartley and Kidd, 1987) (1, 8).
Breakdown of Chemical in Surface Water
No information currently available.
Breakdown of Chemical in Vegetation
In plants, ethephon rapidly degrades to phosphate, ethylene, and chloride
(1, 9). Ethephon and the ethylene gas it produces are the major metabolites
in plants (9).
Residues of monochloroacetic acid may be found in ethephon-treated
commodities. Monochloroacetic acid is a potential degradation product of an
impurity in ethephon, monochloroethyl ester of (2-chloroethyl)-phosphonic acid
PHYSICAL PROPERTIES AND GUIDELINES
|CAS No.: ||16672-87-0
|Chemical name: ||2-chloroethylphosphonic acid (IUPAC, CA) (1)
|Chemical Class/Use: ||organic phosphorus compound/plant growth regulator
|Specific gravity: ||1.58 (2, 6)
|Solubility in water: ||readily soluble in water
|Solubility in other solvents: ||readily soluble in methanol, ethanol, isopropanol, acetone, ether and other polar organic solvents. Slightly soluble in non-polar solvents such as benzene and toluene (1)
|Melting point: ||74-75 degrees C (165-167 degrees F) (1, 2, 6, 8)
|Flammability: ||nonflammable (8)
|Vapor pressure: ||<10 to the minus 7 mbar at 20 degrees C (1); 7.5 x 10 to the minus 5 mmHg at 20 degrees C (8)
|Koc: ||0.29 (calculated) (8)
P.O. Box 12014
2 T.W. Alexander Drive
Research Triangle Park, NC 27709
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. Sixth
edition. 1989. 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. August, 1993. MSDS for Ethephon. MDL Information
Systems Inc., San Leandro, CA.
U.S. Environmental Protection Agency. 1992. Office of Pesticides. TOX
Oneliners -- ethephon. September, 1992.
Montgomery, J. H. 1993. Agrochemicals Desk Reference: Environmental
Data. Lewis Publishers. Chelsea, MI.
U.S. Environmental Protection Agency. September, 1988. Guidance for
the Reregistration of Pesticide Products Containing Ethephon as the Active
Ingredient. US EPA, Office of Pesticide Programs, Registration Div.,
U.S. Environmental Protection Agency. September 29, 1988. Pesticide
Fact Sheet Number 176: Ethephon. US EPA, Office of Pesticide Programs,
Registration Div., Washington, DC.