Pesticide Profile - Monocrotophos

In 1996,American Bird Conservancy organized a meeting in Washington D.C. of concerned scientists, non-governmental organizations, and the manufacturers of monocrotophos, to address the alarming mortality of migratory Swainson's Hawks in Argentina. This meeting led to the eventual governmental cancellation of monocrotophos in Argentina and laid the groundwork for future collaborations among pesticide stakeholders from all corners.

Quick Facts

• Chemical name: dimethyl (E)-1-methyl-2-(methylcarbamoyl)vinyl phosphate

• Trade names: Azodrin, Bilobran, Crisodrin, Monocil, Monocron, Nuvacron, Pillardrin, Plantdrin, Susvin, Ulvair, Dominator, Macabre, Suncrotophos, Monopaz

• Pesticide Type: insecticide

• Class: organophosphate

• Mechanism of action: cholinesterase inhibitor.

• Major routes of exposure: works systemically and on contact. Monocrotophos can be absorbed following ingestion, inhalation, and skin contact.

• U.S. regulatory status: All use registrations were cancelled by the EPA in 1991.

• Current use: International - manufacturers exist in Taiwan, China, India, Mexico, Greece, Israel, Singapore, South Korea. Approximately 30,000 tons of monocrotophos are used annually. India (43%), South America (26%), China (15%), and Southeast Asia (9%) account for 90% of the use, internationally.

• Monocrotophos is included in the PIC (Prior Informed Consent) procedure, an international convention that recognizes certain acutely hazardous pesticides as human health risks under conditions of use in developing countries.

• Monocrotophos is weakly mutagenic in vitro, as determined mainly from studies assessing DNA damage/repair and sister chromatid exchange.

• Monocrotophos has documented use in the following Latin American or Caribbean countries: Brazil, Venezuela, Costa Rica, and Surinam. Monocrotophos registrations have been canceled in Argentina and Jamaica.

Chemical Structure

Background

Monocrotophos is one of the most avian-toxic substances ever developed, with LD50s for Golden Eagles and American Kestrels of 0.2 and 1.5 mg/kg bodyweight, respectively. It has been responsible for perhaps more avian mortality incidents than any other pesticide since its initial registration in the United States in 1965. The potential for extreme environmental harm was noted in the U.S. a decade ago and the EPA canceled all registered uses of monocrotophos in 1991. The largest U.S. manufacturer of the chemical has voluntarily begun phasing-out production. However, monocrotophos is still used internationally and poses an unacceptable risk to migrating and resident birds of the Americas, specifically. Scientific evidence indicates that raptor species are sometimes hyper-susceptible to the effects of organophosphates, an exception to the general laboratory and field observations that support the notion that smaller birds typically succumb to the effects of pesticides at lower doses than larger birds, like raptors. Studies have yet to be completed to show the overlap of monocrotophos use and raptor habitat worldwide or in Latin America. It is likely that many species of raptors are at continued risk of exposure to monocrotophos (Hooper, 2000, unpublished), and, if certain analyses are correct, there may not be a safe level of monocrotophos application for birds under any circumstance (Mineau, 2000, unpublished).

Human Health Effects

As are all organophosphate pesticides, monocrotophos is toxic to humans. Extensive regulations on application methods and strict guidelines for the period of time before it is safe for people to enter a field treated with monocrotophos have not abolished accidental exposure to applicators, harvesters, or consumers. An epidemiological study in the Philippines showed an increased mortality of 27% in age and sex classes occupationally exposed to pesticides (rice growing). Monocrotophos was one of the 4 most common pesticides used in the area (PIC). In Parana State, Brazil, monocrotophos caused 107 of 412 reported incidents of accidental poisoning in one year, 1990 (Dinham, 1993). And, in a 1991 study conducted by the FDA on pesticide residues on imported fruits and vegetables into the U.S., monocrotophos accounted for 69 of 88 violations, a violation rate of 0.28% of samples taken.

Repeated daily high-level exposure may gradually lead to poisoning. Monocrotophos may cause delayed symptoms beginning 1 to 4 weeks after an acute exposure that may or may not have caused symptoms. In such cases, numbness, tingling, weakness and cramping may appear in the lower limbs and progress to paralysis. Improvement may occur over months or years, but some residual impairment will remain (PIC Joint Meeting on Pesticide Residues, 1993).

Environmental Effects

Fate

• Persistence: Monocrotophos has a low environmental persistence. It does not accumulate in the soil because it is biodegradable under most field conditions. Its half-life is less than 7 days in soil exposed to sunlight (US EPA, 1985).

• Solubility: highly soluble in water, acetone, and alcohol.

• Bioaccumulation: monocrotophos is metabolized and excreted rapidly and does not appear to accumulate within the body. The primary conversion products in mammals are dimethylphosphate, O-desmethyl monocrotophos, and N-desmethyl monocrotophos. N-desmethyl monocrotophos is more toxic than monocrotophos.

Ecotoxicity

• Monocrotophos is moderately toxic to fish,EC50 48 hrs. for rainbow trout is 7mg/l, for bluegill sunfish EC50 is 23mg/l.

• EC50 48 hours for the aquatic invertebrate Daphnia is 0.023 mg/

• Extremely toxic to birds.

                                    California Quail:         LD50 0.78 mg/kg
                                    Northern Bobwhite:    LD50 0.87 mg/kg
                                    Canada Goose:          LD50 1.58 mg/kg
                                     European Starling:     LD50 3.73 mg/kg
                                     Mallard:                   LD50 4.00 mg/kg
                                     Golden Eagle:            LD50 0.19 mg/kg

Incidents

• Texas, 1985. 45 Franklin's gulls were found dead in a sugarcane field that had been aerially sprayed with monocrotophos. The gulls were feeding on emerging cicada larva. Brain AchE in the gulls was inhibited between 86-98% of the controls.

• Arizona, 1967. U.S. Fish and Wildlife Service officials searched 4 miles of cotton field edge that had been treated with monocrotophos the previous day. A total of 96 dead or severely affected birds were found. Species included Gambel's Quail, Mourning Doves, Vesper, Chipping and unidentified sparrows, Orange-crowned Warblers, Western Tanager, Spotted Sandpiper, and Northern Harrier. 36 of 40 carcasses tested for brain AchE activity showed severe inhibition compared to controls.

• Germany, 1970. A field study to test avian toxicity of monocrotophos when used in corn found 30 dead birds in one test plot, and 44 dead or paralyzed birds in another. The test plots were treated with different concentrations of monocrotophos and were quite small (1 hectare) so the numbers of dead birds found were significant. Species included Ring-necked Pheasant, Blackbird, Song Thrush, Great Tit, Sedge Warbler, shrikes, Yellowhammer, Corn Bunting, Chaffinch, Greenfinch, as well as House and Tree Sparrows.

• New Mexico, 1987. In a study where cornfields were sprayed with monocrotophos and compared with a nearby control plot, 26 bird carcasses were found only in the non-crop strips of edge habitat in the sprayed fields. Search efforts were begun two days after spraying; details of the search methods and frequency are unavailable. Species include: Northern Bobwhite, Killdeer, Mourning Dove, Horned Lark, Mockingbird, Chipping and House Sparrow. Scavengers removed 90% of placed carcasses indicating that the true kill rate was actually much higher. Brain AchE tests were performed with an average AchE depression of 84% of all birds tested compared to control birds.

• Israel, 1979. In an attempt to control voles in alfalfa fields, farmers sprayed with monocrotophos at twice to three times the recommended rate. Massive bird kills were observed over a four-year period from 1975-1979. Raptors were particularly hard-hit. In 1976, authorities recovered 219 individual raptors of 13 species dead or paralyzed. Spotted, Lesser Spotted, and Imperial Eagle, Long-legged and Common Buzzard, Black Kite, Marsh, Hen, and Pallid Harriers, Kestrel, Short-eared, Long-eared, and Barn Owl. In 1977 the carnage continued at similar rates with four added species: White-tailed Sea Eagle, Merlin, Sparrowhawk, and Eagle Owl.

• Argentina, 1996. Researchers described at least 14 different incidents of hawk kills in the Pampas region of Argentina, thought to comprise the 'core' wintering site for Swainson's Hawks. The different kills ranged in number of birds killed from just a few to over 3000 at one site. One scientist estimated that up to 20,000 Swainson's Hawks were killed that year, alone.