Pesticide Profile - Dicrotophos

Quick Facts:

Background

Note: Since one of the primary degradates of dicrotophos is monocrotophos, all the data presented in the monocrotophos profile on this website is relevant. 

Dicrotophos was introduced in 1956 as a contact and systemic insecticide and acaricide. The dermal and oral toxicity is high for mammals, aquatic invertebrates, non-target insects such as pollinators, and birds. The human health risk is significant, and the California Department of Pesticide Regulation has banned the use of dicrotophos in California because of human exposure risks.

In the United States, dicrotophos is only registered for use on cotton. In the past, it was used on soybean, sorghum, and against the elm bark beetle which transmits Dutch Elm disease. Internationally, dicrotophos is used extensively on rice, coffee, and citrus. Dicrotophos, like monocrotophos, is so acutely toxic to birds that any bird in contact with treated crops or with insects that have fed on treated vegetation is likely to be killed or severely affected. Sub-lethal effects are also well-documented. Most of the cotton treated with dicrotophos in the United States is grown in the Mississippi Valley: a highly diverse aquatic and terrestrial ecoregion which underlies the Central Flyway, a flight route used by neotropical migratory birds. A scientific investigation that looked at the number of species of birds in cotton fields recorded 182 different species. These species were oftentimes found in large numbers in cotton fields. Dicrotophos is easily washed into surface and ground waters near treated cotton fields. The persistence of dicrotophos in aquatic environments poses grave risks to the ecosystems of the Mississippi River, its floodplains and tributaries, and other small waterways of the region.

Environmental Effects

Fate

• Persistence: dicrotophos degradation rates in soils are rapid, with a half-life of 3 days in Hanford sandy loam soil. It is moderately mobile in soil, increasing the possibility for surface and groundwater contamination. Dicrotophos is moderately persistent in water, with half-lives of 117, 72, and 28 days for pH 5, 7, and 9 water at 25 C, respectively.

• Solubility: Highly soluble in water and most common organic solvents.

• Bioaccumulation: dicrotophos does not appear to bioaccumulate in animal tissue. The potential for bioconcentration in aquatic organisms is minimal.

• Mobility: highly mobile in soils, which may facilitate surface water contamination.

Ecotoxicity 

• Dicrotophos is highly toxic to mammals. The oral LD50 for rats is 16-21mg/kg. The dermal LD50 is 42-43mg/kg for rats.

• Dicrotophos is very highly toxic to birds.

  California quail    LD50 1.89 mg/kg
  House sparrow   LD50 3.00 mg/kg
  Mallard              LD50 4.24 mg/kg

Dicrotophos is teratogenic and has been shown to cause significant deformities in bird embryos and surviving chicks. Sub-lethal effects have been documented in scientific studies. European starlings given an oral sub-lethal dose of dicrotophos in corn oil made significantly fewer trips to the nest to feed their young and remained away from the nest for longer periods of time than did starlings dosed with corn oil only. The brain cholinesterase levels in dosed birds were 50% of normal controls. Parental care is significantly impaired with exposure to dicrotophos. Additional studies showed that starling nestlings were nearly twice as sensitive to dicrotophos as adults, as measured by brain cholinesterase activity. Young birds fed contaminated insects at the nest are particularly vulnerable to organophosphate exposure. While dicrotophos is not greatly concentrated in tadpoles exposed at 5mg/L, ducklings fed contaminated tadpoles had cholinesterase inhibition of 70%. Given the relative persistence of dicrotophos in freshwater, there is a high risk of secondary exposure of aquatic birds to contaminated amphibians, fish, and invertebrates. Terrestrial organisms exposed to dicrotophos are likely to poison avian consumers, as well.

Incidents

• Matagorda County, Texas, 1982. Approximately 1100 birds representing 12 species died from dicrotophos poisoning. Rice grains impregnated with dicrotophos were placed near rice fields to attract and kill birds. Species killed include: great-tailed grackle, mourning dove, common snipe, vesper sparrow, mottled duck, common moorhen, blue-winged teal, redhead, and ruddy turnstone. The mortality from this incident continued for a three-week period. The practice of illegally treating rice seed with organophosphates appears to be infrequent but widespread.

• West, Texas, 1983. Thirty great-tailed grackles died from exposure to dicrotophos. Confirmation of the cause of death was made when dicrotophos residues were identified in the GI tracts of two of the birds.

Plan of Action

ABC is currently working with the EPA to ensure that the environmental and ecological hazards of dicrotophos are not overlooked in the EPA re-registration process. ABC is seeking complete cancellation of all uses of dicrotophos in the United States. ABC is initiating efforts to document use of dicrotophos in Latin America so that alternatives can be explored until which time dicrotophos and other highly toxic pesticides can be banned from use.