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Monocrotophos

Publication Date: 9/95

TRADE OR OTHER NAMES

Trade names for products containing monocrotophos include Azodrin, Bilobran, Crisodrin, Monocil 40, Monocron, Nuvacron, Pillardrin, and Plantdrin (1, 2, 3).

REGULATORY STATUS

Use of monocrotophos on potatoes and tomatoes was withdrawn in 1985 (3). All applications of monocrotophos were discontinued in the United States in 1988 (4). Before its withdrawal, monocrotophos was a Restricted Use Pesticide (RUP) (5).

INTRODUCTION

Monocrotophos is an organophosphorus insecticide and acaricide which works systemically and on contact. It is extremely toxic to birds and is used as a bird poison (1). It is also very poisonous to mammals. It is used to control a variety of sucking, chewing and boring insects and spider mites on cotton, sugarcane, peanuts, ornamentals, and tobacco (2, 3). The EPA classifies monocrotophos as a class I toxicity - highly toxic. Products containing monocrotophos bear the Signal Word "Danger" (6). Monocrotophos is available in other countries as a soluble concentrate or an ultra-low volume spray (3).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Monocrotophos is a direct acting cholinesterase inhibitor capable of penetration through the skin (10). The dose which kills half of the test animals, the LD50, is 17-18 mg/kg for male rats and 20 mg/kg for female rats. The LD50 for dermal exposure is 126 mg/kg for male rats, 112 mg/kg for female rats, and 354 mg/kg for rabbits (3, 7). The concentration in air at which half of the test animals die, the LC50, is 0.8 mg/l air. Monocrotophos is not irritating to skin and eyes (2).

Symptoms of monocrotophos poisoning are similar to those of other organophosphate compounds. Its cholinesterase inhibiting activity causes nervous system effects. Cases of human poisoning are characterized by muscular weakness, blurred vision, profuse perspiration, confusion, vomiting, pain, and small pupils. There is a risk of death due to respiratory failure (8, 11).

CHRONIC TOXICITY

Reproductive Effects

Rats who received doses of 2 mg/kg/day monocrotophos produced fetuses with lower than average length and weight (9). This dose is much higher than expected from normal application of this pesticide.

Teratogenic Effects

No teratogenic effects were found at 2 mg monocrotophos/kg/day in rats, the highest dose tested (9).

Mutagenic Effects

Studies show that monocrotophos may be weakly mutagenic (9).

Carcinogenic Effects

Monocrotophos is not carcinogenic in rats at 0.45 mg/kg/day, the highest dose tested (9). No significant carcinogenic lesions were observed when rats were exposed to monocrotophos aerosol at concentrations from 97-308 mg/m3 for one hour (10).

Organ Toxicity

Monocrotophos affects the central nervous system by inhibiting cholinesterase, an enzyme essential for normal nerve impulse transmission.

Fate in Humans and Animals

Monocrotophos is metabolized and excreted rapidly and does not appear to accumulate within the body (10). In mammals, 60-65% is excreted within 24 hours, predominantly in the urine (8).

ECOLOGICAL EFFECTS

Effects on Birds

Monocrotophos is highly toxic to birds (3). The LD50 is 0.76 mg/kg for California quail, 0.94 mg/kg for bobwhite quail, 1.58 mg/kg for Canada goose, 3.3 mg/kg for European starling and 4.76 mg/kg for mallard ducks (1).

Effects on Aquatic Organisms

Monocrotophos is moderately toxic to fish (3). The LC50 (48 hrs) is 7 mg/l for rainbow trout and 23 mg/l for bluegill sunfish (2). Monocrotophos causes reproductive damage to crustaceans exposed for long periods of time (4).

Effects on Other Animals (Nontarget species)

Monocrotophos is highly toxic to bees (2). It may also kill non-target birds which eat insects poisoned with monocrotophos (1).

ENVIRONMENTAL FATE

Breakdown of Chemical in Soil and Groundwater

Monocrotophos has a low environmental persistence. It does not accumulate in soil because it is biodegradable. Its half-life is less than 7 days in soil exposed to natural sunlight (1, 3, 9).

Breakdown of Chemical in Surface Water

No information is currently available.

Breakdown of Chemical in Vegetation

Monocrotophos has a half-life of 1.3 to 3.4 days on plant foliage (13). It causes slight injury to some varieties of apple, pear, cherry, peach and sorghum (8).

PHYSICAL PROPERTIES AND GUIDELINES

Monocrotophos is a reddish brown crystalline solid with a mild odor (10). It is stable when stored in glass or polyethylene containers at room temperature. It is relatively stable in sunlight and is non-volatile. Hydrolysis is slow and the half-life for monocrotophos in solution is 23 days at pH 7 and 38 degrees C (9).

Physical Properties:

CAS #: 2157-98-4 (mixed isomers)
Chemical Name: dimethyl (E)-1-methyl-2-(methylcarbamoyl)vinyl phosphate
Melting point: 54-55 degrees C (10)
Boiling Point: 125 degrees C (10)
Solubility in water: Soluble in water (3)
Solubility in other solvents: Soluble in acetone and alcohol (3)

Exposure Guidelines:

ADI: 0.0006 mg/kg (2, 12)
NOEL: 0.03 ppm (rat) 1.6 ppm (dog) (cholinesterase inhibition) (9)
OSHA PEL: PEL-TWA: 0.25 mg/m3 (10)
TLV-TWA: 0.25 mg/m3 (10)

BASIC MANUFACTURER

CIBA Agricultural Division
P.O. Box 18300
Greensboro, NC 27419-8300
Telephone: 919-632-6000

Review by Basic Manufacturer:

Comments solicited: October, 1994
Comments received: January, 1995

REFERENCES

  1. Smith, G. J. 1993. Toxicology & Pesticide Use in Relation to Wildlife: Organophosphorus & Carbamate Compounds. C.K. Smoley. Boca Raton, FL.
  2. The Agrochemicals Handbook, Third Edition. 1994. Royal Society of Chemistry Information Systems, Unwin Brothers Ltd., Surrey, England.
  3. Meister, R.T. 1992. Farm Chemicals Handbook '92. Meister Publishing Company. Willoughby, OH.
  4. Briggs, Shirley. 1992. Basic Guide to Pesticides. Hemisphere Publishing. Washington, DC.
  5. Darcy Miller, Publisher. 1985. Protection Chemicals Reference. Chemical and Pharmaceutical Publishing Corp. New York, NY.
  6. Meister, R.T. 1994. Farm Chemicals Handbook '94. Meister Publishing Company. Willoughby, OH.
  7. Budavari, Susan (ed.). 1989. The Merck Index, Eleventh Edition. Merck and Company Inc. Rahway, NJ.
  8. Hayes Jr., Wayland and E. R. Laws, Jr. (eds.). 1991. Handbook of Pesticide Toxicology. Academic Press, Inc. New York, NY.
  9. U.S. Environmental Protection Agency. 1985. Pesticide Fact Sheet No. 72: Monocrotophos. U.S. EPA. Washington, DC.
  10. American Conference of Governmental Industrial Hygienists. 1991. Documentation of the Threshold Limit Values and Biological Exposure Indices: Sixth Edition, Volume I. ACGIH. Cincinnati, OH.
  11. Senanayake, N. and L. Karalliedde. "Neurotoxic Effects of Organophosphorus Insecticides, An Intermediate Syndrome." New England Journal of Medicine. Vol. 316, No.13. pp. 761-763.
  12. Baker, Scott and C. F. Wilkinson (eds.). 1990. The Effect of Pesticides on Human Health. Volume XVIII of Advances in Modern Environmental Toxicology. Princeton Scientific Publishing Co. Princeton, NJ.
  13. Chambers, Janice and Patricia Levi. 1992. Organophosphates Chemistry, Fate and Effects. Academic Press, Inc. New York, NY.