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Phosalone

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).

REGULATORY STATUS

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.

INTRODUCTION

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 expected (5).

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).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

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).

CHRONIC TOXICITY

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 (9).

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).

Reproductive Effects

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).

Teratogenic Effects

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).

Mutagenic Effects

No information currently available.

Carcinogenic Effects

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).

Organ Toxicity

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 cholinesterase (11).

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).

ECOLOGICAL EFFECTS

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 high (8).

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).

ENVIRONMENTAL FATE

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

Exposure Guidelines:

ADI: for man 0.006 (11)

Physical Properties:

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)

BASIC MANUFACTURER

Rhone Poulenc Ag. Co.
P. O. Box 12014
Research Triangle Park, NC 27609
Telephone: 919-549-2000

Review by Basic Manufacturer:

Comments solicited: October, 1994
Comments received:

REFERENCES

  1. The Agrochemicals Handbook. 1983. The Royal Society of Chemistry, The University, Nottingham, England.
  2. Worthing, C. R. (ed.). 1983. The Pesticide Manual: A World Compendium. Seventh edition. Published by The British Crop Protection Council.
  3. Murty, A. S. 1986. Toxicity of Pesticides to Fish Vol. II. CRC Press, Boca Raton, FL.
  4. Farm Chemicals Handbook. 1994. Meister Publishing Co. Willoughby, OH.
  5. Thomson, W. T. 1992. Agricultural Chemicals. Book I: Insecticides. Thomson Publications, Fresno, CA.
  6. OHS Database. 1993. Occupational Health Services, Inc. 1993 (August) MSDS for Phosalone. OHS Inc., Secaucus, NJ.
  7. Montgomery, J. H. 1993. Agrochemicals Desk Reference: Environmental Data. Lewis Publishers. Chelsea, MI.
  8. Briggs, S. A. 1992. Basic Guide to Pesticides: Their Characteristics and Hazards. Hemisphere Publishing Corp., Washington, Philadelphia, London.
  9. Worthing, C. R. (ed.). 1987. The Pesticide Manual: A World Compendium. Eighth edition. Published by The British Crop Protection Council.
  10. Fairchild, E. J. (ed.) 1977. Agricultural Chemicals and Pesticides: A Subfile of the Registry of Toxic Effects of Chemical Substances. U. S. Department of Health, Education, and Welfare, Cincinnati, OH.
  11. Organophosphorus Pesticides: Criteria (Dose/Effect relationships) for Organophophorus Pesticides. 1977. Published for the Commission of the European Communities by Pergamon Press.
  12. Spencer, E.Y. 1981. Guide to the Chemicals Used in Crop Protection. 7th edition. Publication 1093. Research Branch. Agriculture Canada.
  13. Elzen, G. W. 1989. Sublethal Effects of Pesticides on Beneficial Parasitoids. In: Pesticides and Non-target Invertebrates. Ed. by Paul C. Jepson. Intercept Ltd. Dorset, England. pp 129-150.
  14. Hayes, W.J. Jr. and E.R. Laws (ed.). 1990. Handbook of Pesticide Toxicology, General Principles, Vol. 1 and 2. Academic Press, Inc., NY.
  15. Hayes, W. J., Jr. 1982. Pesticides Studied in Man. Williams and Wilkins. Baltimore, London.
  16. Pimentel, David. 1971. Ecological Effects of Pesticides on Non-Target Species. Cornell University, Ithaca, NY.
  17. Canada Department of Agriculture. 1968. Registration of Phosalone. Canada Department of Agriculture, Production and Marketing Branch, Plant Products Division, Ottawa, Ontario.
  18. U.S. Environmental Protection Agency. November 30, 1987. Pesticide Fact Sheet Number 148. US EPA, Office of Pesticide Programs, Registration Div., Washington, DC.
  19. U.S. Environmental Protection Agency. November, 1987. Guidance for the Reregistration of Pesticide Products Containing Phosalone. US EPA, Office of Pesticide Programs, Registration Div., Washington, DC. 145 pp.