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 phosalone is found in a variety of commercial
insecticides. Trade names for products containing phosalone include Azonfene,
Benzofos, Rubitox, Zolone and RP 11974 (4, 10, 18).
The common name phosalone is generally recognized, except in the Soviet
Union, where the common name benzphos is used (14, 15).
Phosalone is no longer for sale in the U.S. (5). Phosalone was a general
use pesticide (GUP). Products containing phosalone had the Signal Word
"Warning" on their label.
Phosalone was introduced in 1963 by Rhone-Poulenc company as a
nonsystemic insecticide and acaricide for use on deciduous fruit trees, market
garden crops, cotton, potatoes and rape (14, 15). It is a broad-spectrum
pesticide with rapid killing ability. Approximately 12-20 days control may be
Phosalone is a member of the organophosphate family of insecticides. It
is used as both an insecticide and acaricide. It comes in emulsifiable
concentrate, wettable powder and dust formulations (7). It is used on nut
crops, citrus, pome fruits, stone fruits, grapes, potatoes, artichokes, roses
and arborvitae (18). It is active against the red spider mite on apples and
pears. It controls a wide range of caterpillars and beetles on crops of
economic importance as well as a number of hemiptera and hymenoptera (12).
Phosalone is a compound of moderate toxicity (14, 15). The acute oral
LD50 values ranged between 82-205 mg/kg for male rats; and between 90-170
mg/kg for female rats (7, 17, 18). The acute dermal LD50 values for rats
ranged between 350 mg/kg and 390 mg/kg (17, 18). The acute percutaneous LD50
for rats is 1,500 mg/kg (9).
Acute oral toxicities reported for mice ranged between 73 - 205 mg/kg
(10, 17); between 82-380 mg/kg for guinea pigs
(9, 10, 17); 112 mg/kg for cats
(14, 15); and greater than 1,600 mg/kg for dogs (11).
Studies on rabbits exposed to phosalone reported the dermal LD50 to be
greater than 2,000 mg/kg and the percutaneous LD50 to be greater than 1,000
mg/kg (9, 17).
The primary dermal irritation was found to be mildly irritating to intact
and abraded skin and moderately irritating to the skin and eyes (14, 15, 18).
Feeding of phosphate to rats at dietary levels of 25, 50 and 250 ppm and
to dogs at 100, 200 and 1,000 ppm resulted in dosage-dependent inhibition of
red blood cell and plasma cholinesterase, but no signs of illness. In rats,
50 ppm or about 2.4 mg/kg/day was the highest level with no effect on
cholinesterase. In fact, rats and dogs tolerated oral dosages of 7.5 and 15
mg/kg/day for a month, and rats tolerated a dietary level of 250 ppm (about 12
mg/kg/day) for 1 year with no abnormality of growth, behavior, or hematology.
Rats and cats tolerated repeated exposure to an atmospheric concentration of
9.34 mg/cubic meter (14, 15).
Another two-year feeding study on rats receiving 250 mg/kg diet and on
dogs receiving 290 mg/kg diet indicated neither group suffered ill effects
Dogs fed doses of 0, 100, 200 and 1,000 ppm for two years showed
vacuolation and histological changes of the smooth muscle cells of the small
intestine, and the ratios organ/body weight were increased, i.e. liver/body
weight, at the 1000 ppm level. Effects on cholinesterases were evident at all
levels of feeding compared to the control group. Rats fed 0, 25, 50, and 250
ppm dietary levels for two years exhibited depression of plasma cholinesterase
at 50 ppm but not at 25 ppm (11).
Oral administration of a 30% phosalone formulation to rats at doses up to
50 mg/kg/day on days 6 through 15 of gestation did not produce maternal
toxicity (14, 15). Phosalone was found to have no effect on reproduction in
rats at doses of 0, 25 and 50 ppm (11).
Oral administration of a 30% phosalone formulation to rats at doses up to
50 mg/kg/day on days 6 through 15 of gestation did not produce teratogenic
effects (14, 15). Phosalone was not found to be teratogenic in chickens, rats
or rabbits (11).
No information currently available.
A 104-week feeding study was conducted on mice. Fifty animals per sex
were used. The dietary doses given were 0, 5, 50, and 100 ppm. Female mice
demonstrated an increased incidence of leiomyomas and leiomyosarcomas of the
uterus and of the Harderian gland adenomas (19).
No information currently available.
Fate in Humans and Animals
In general, the biotransformation of phosalone is similar to that of
other organic phosphorous compounds. However, in studies where rats were
given a single dose of labeled phosalone, 65.4 % of the labeled carbon was
recovered within 4 days as carbon dioxide in the expired air, while only 32.4%
was excreted in the urine and feces (14, 15).
Phosalone is rapidly absorbed and excreted by mice following oral
administration. Within 24 hours, less than 1 percent phosalone residues were
found in the body. Phosalone is a weak inhibitor of cholinesterase. Its
oxygen analog is 2-3 times more active, especially in inhibiting serum
No clinical effect was observed, and no phosalone or metabolite was found
in the urine of fourteen men working in an orange grove beginning 14-17 and
21-23 days after the application of phosalone at a rate of 13.5 kg/ha. Plasma
cholinesterase also remained normal. The red cell cholinesterase level was
depressed by 15% compared to that of the control group on day 15, but returned
to normal on day 17 (14, 15).
A study of peach pickers indicated that in spite of estimated dosage
rates as high as 14 mg/person/hour, the red cell cholinesterase was inhibited
only about 4%. It was estimated that 98-99% of the workers' exposure was
dermal, mainly to the hands and upper extremities. Four of six workers
exposed to air concentrations of 5.32 mg/cubic meter had their acetyl-
cholinesterase depressed by only 16 to 29% (14, 15).
Effects on Birds
Delayed neurotoxicity was negative in hens (18). Acute subcutaneous LD50
for chickens is 350 mg/kg (11)
The avian oral toxicity indicated phosalone was slightly toxic to
waterfowl; the acute oral LD50 for mallards was greater than 2,150 mg/kg (18).
The oral toxicity for pheasants was 290 mg/kg (9). The 8-day avian dietary
toxicity indicated phosalone was slightly toxic to waterfowl and upland game
birds. Subacute toxicity for mallard ducks was 1,659 ppm and 2,033 ppm for
bobwhite quail (18).
Effects on Aquatic Organisms
The 96-hour freshwater fish acute toxicity found phosalone to be very
highly toxic to warmwater fish and highly toxic to coldwater fish. The acute
LC50 for bluegill sunfish was 0.05 ppm; 0.63 ppm for rainbow trout (18); and
3.4 ppm for harlequin fish (16). Other LC50 values for phosalone indicated the
toxicity for goldfish was 2 mg/l; 0.11 mg/l for bluegill sunfish; and 0.3-0.63
mg/l for rainbow trout (7). One-fifth of the 24-hour LC50 values caused
hemorrhage in bluegills (3).
The 48-hour freshwater invertebrate toxicity indicated phosalone to be
very highly toxic to aquatic invertebrates. The acute value for Daphnia magna
was 0.0012 ppm (18). Immediate toxicity to crustaceans is considered very
Effects on Other Animals (Nontarget species)
Phosalone rates of 700 g/ha were not found to be hazardous to honeybees,
provided they were not actively foraging at the time of spraying (9).
Insecticides, one of which was phosalone, applied to host eggs at field
rates in the laboratory were highly toxic to Trichogramma brasiliensis
released on the eggs, causing 84-100% mortality in 24 hours. However,
percentage parasitism after 4 days was higher with phosalone (36 - 73%) than
with other insecticides studied, and emergence from treated host eggs did not
appear to be affected. Phosalone had little or no effect on adults or cocoons
of Apanteles plutellae (13).
Breakdown of Chemical in Soil and Groundwater
Phosalone rapidly degraded (t1/2 = 3-7 days) in flooded Metapeake loam
and Monmouth fine sandy loam. Mineralization to carbon dioxide accounted for
only 10% of the loss (7).
The primary degradative pathway proceeded by oxidation of phosalone to
give phosalone oxon. Subsequent cleavage of the O, O-diethyl methyl
phosphorodithioate linkage gave 6-chloro-2-benzoxazolinone (7).
Phosalone is stable at pH 5 and 7, but is hydrolyzed at a pH of 9 with a
half-life of 9 days (18). Phosalone does not move in soil and degrades
rapidly when compared to parathion (5).
Aerobic soil metabolism studies demonstrate half-life values of 1-7 days.
Field dissipation studies showed half-life values of 1-9 weeks. Phosalone was
essentially immobile in a soil column test. Based on this preliminary data,
phosalone appears unlikely to contaminate groundwater (18).
Breakdown of Chemical in Surface Water
Phosalone rapidly dissipates in untreated waters (18).
Breakdown of Chemical in Vegetation
Phosalone degrades in plants to chlorbenzoxazolone, formaldehyde, and
diethyl phosphorodithioate (7, 11). It persists on plants about 14 hours,
being converted to the corresponding phosphorothioate which is rapidly
hydrolyzed (9). Phosalone is not phytotoxic under normal conditions (12).
PHYSICAL PROPERTIES AND GUIDELINES
Phosalone is stable under normal storage conditions. It is compatible
with most other pesticides and is noncorrosive. It is incompatible with
alkaline materials such as calcium arsenate and lime sulfur (14, 15).
Phosalone emits toxic fumes of chlorine, phosphorus, nitrogen, and sulfur
oxides when heated to decomposition (7).
|Appearance: ||colorless crystals with a garlic-like odor (7, 14)
|CAS No.: ||2310-17-0 (1, 4, 6, 7, 18) 2279-71-2 (10)
|Chemical name: ||S-6-chloro-2, 3-dihydro-2-oxobenzoxazol-3-ylmethyl O, O-diethyl phosphorodithioate (IUPAC);
S-[(6-chloro-2-oxo-3(2H)-benzoxazolyl)methyl] O, O-diethyl phosphorodithioate (CA);
3-(O, O-diethyldithiophosphorylmethyl)-6-chlorobenzoxazolone (1), O,O-diethyl-S-(6-chloro-2-oxobenzoxazolin-3-yl-methyl)-phosphorodithioate (14, 15)
|Molecular weight: ||367.82 (10)
|Molecular formula: ||C12H15ClNO4PS2 (7, 10)
|Chemical Class/Use: ||organophosphate insecticide-acaricide (5)
|Solubility in water: ||ca. 0.01 g/l (1); 10 g/l (2); 0.0010 at 20 degrees C (6); 1.2, 2.6 and 3.7 mg/l at 10, 20 and 30 degrees C respectively (7); 10 mg/l at room temperature (9)
|Solubility in other solvents: ||Soluble (ca. 1000 g/l) in ethyl acetate, acetone, acetonitrile, benzene, chloroform, methylene chloride, cyclohexane, dioxane, methyl ethyl ketone, toluene, xylene (all at 20 degrees C) (1, 6, 11).
In methanol and ethanol, ca. 200 g/l at 20 degrees C (1, 7)
|Melting point: ||45-48 degrees C (1, 3, 11, 14); 117-118 degrees F (47-48 degrees C) (6)
|Vapor pressure: ||very low (at 20 degrees C, practically negligible) (1); negligible at room temperature (2, 9, 6, 14) 5.03 x 10 to the minus 7 mmHg at 25 degrees C (7)
|KH: ||7.6 x 10-8 atm cubic meter/mol at 25 degrees C (approximate - calculated from water solubility and vapor pressure) (7)
|log Kow: ||3.77 - 4.38 (7)
|log Koc: ||3.41 (calculated) (7)
Rhone Poulenc Ag. Co.
P. O. Box 12014
Research Triangle Park, NC 27609
Review by Basic Manufacturer:
Comments solicited: October, 1994
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