Pesticide Profile - Aldicarb

Quick Facts:

• Chemical name: 2-methyl-2-(methylthio)propionaldehyde O-methylcarbamoyloxime

• Trade names: Temik, ENT 27093, OMS 771, Sanacarb, UC 21149, Ambush

• Pesticide type: systemic insecticide, nematicide, acaricide

• Class: carbamate

• Mechanism of action: cholinesterase inhibitor

• Current registration in U.S.: restricted use only on potatoes, citrus, cotton, peanuts, sorghum, soybeans, sugar beets, sugarcane, coffee, sweet potatoes, pecans, and various other crops. Use on bananas was revoked during special review process due to concerns about high residues.

• Formulation: granular only, due to extreme toxicity

•  Use: approximately 4 million pounds of active ingredient were applied mainly on cotton, peanuts, sugar beets and citrus in 1992, according to the USGS

• Routes of exposure: aldicarb is directly toxic through oral, dermal, and inhalation; it is toxic when plants systemically exposed are consumed and secondary poisoning occurs when exposed prey items, such as insects, rodents, and birds, are consumed by preators and scavengers. 

• Aldicarb is very highly toxic to birds and other organisms. Aldicarb is persistent and may remain in soils and plant material over the entire growing cycle.

• Aldicarb is highly soluble in water and highly mobile in soil, making it a pesticide of concern for ground and surface water contamination.

• Aldicarb has been shown to be mutagenic in human peripheral lymphocytes (white blood cells) assays. Aldicarb exposure in vitro led to an increase in the number of chromatid and chromosome breaks. A positive dose response was noted in relating the amount of aldicarb to the degree of chromosome damage.

• Aldicarb is a suspected endocrine disrupter.

Chemical Structure

Background

Aldicarb is a systemic carbamate pesticide used on a variety of crops. Acute oral toxicity data indicate that aldicarb may be the most toxic of all organophosphate and carbamate pesticides to mammals. It is also among the most toxic of all pesticides to birds, aquatic invertebrates, fish, and insect pollinators, such as bees. The hazards aldicarb presents to the environment are compounded by its high degree of persistence in both natural waters and soil, and the extreme toxicity of its degradates. Aldicarb sulfoxide, the major metabolite, has 76 times greater anticholinesterase activity than aldicarb, itself. Aldicarb is dermally active and residues on food or in drinking water pose grave risks to humans. While the effects of carbamate poisoning are reversible if caught in time, death can be rapid. In one instance where 1300 people consumed residues on watermelon, aldicarb caused two stillbirths in exposed pregnant women, and grand mal seizures in an exposed boy.

Aldicarb and its metabolites can persist in the soil and carry over into the following year's crops. With new application of the pesticide in the spring, extremely high levels may accumulate in the soils and in plants, which rapidly absorb aldicarb. Risk assessments are mathematical models used by the EPA to determine "safe" application rates for pesticides. The EPA bases its risk assessments for wildlife on pesticides residues measured after only one application, in most cases. The potential for aldicarb to persist in the environment adds to the residues found in crops used by wildlife, above what is predicted by the risk assessment. Residue levels used to compute the risk assessments for wildlife are, therefore, unrealistic, in this scenario. Risks to wildlife are much higher with persistent pesticides when residues accumulate from season to season, and from application to application.

Aldicarb is highly soluble in water and mobile in soils, creating a high degree of risk of contamination of ground and surface waters. It is a known contaminant in Wisconsin groundwater. Women from Wisconsin who had consumed groundwater from the contaminated area were found to have altered immune function when compared to a control group of unexposed women (Fiore, MC et al., 1986). Aldicarb is very highly acutely and chronically toxic to marine invertebrates and fish. Species diversity and numbers of organisms are affected when aldicarb reaches fresh and saltwater streams, lakes, estuaries, and rivers. These aquatic organisms form the base of the food chain for other wildlife that will be indirectly affected by a reduction in food items due to aldicarb toxicity.

Environmental Effects

Fate

•   Persistence: Aldicarb is moderately persistent in soil, with half-lives ranging from 9 to 60 days, depending on soil type and conditions. The sulfone, sulfoxide, and demeton degradation products are more persistent and have been found to remain in soils for much longer periods of time than the parent conpound. For aldicarb-sulfone, the half-life is 56 days for clay, 112 days in greenhouse soil, and 154 days in peat. Aldicarb residues have been detected in soils 406 days after application. Data from the Food and Drug Administration indicate that the half-life of aldicarb in soil may be up to 28 weeks. In water, aldicarb is stable and does not degrade in neutral and acidic pH's. Insufficient data exists for the degradation of aldicarb in natural waters and for the degradation of aldicarb breakdown products. 

• Solubility: highly soluble in water, also soluble in acetone, zylene, ethyl, ether, toluene, and other organic solvents.

• Bioaccumulation: bioaccumulation in animal tissue does not appear to be an important fate process as predicted by aldicarb's high solubility in water. However, toxic metabolites are produced when plants systemically absorb aldicarb and may persist for over a year, according to a field study reported by Tashiro and Beaver, 1967.

• Soil Mobility: Aldicarb is highly mobile in most soils. Contamination of groundwater has been well documented. In 1979, aldicarb was found in substantial concentrations (up to 515 ug/L) in Long Island, New York. Contamination was due to use on nearby potato fields. Levels of aldicarb in drinking water which exceed the health advisory level of 10 ppb established by Office of Drinking Water at EPA have been recorded from California, Maine, Wisconsin, Florida, Virginia, Connecticut, Delaware, Maryland, New Jersey, New York, and Rhode Island.

Ecotoxicity 

• Mammals: Aldicarb is one of the most acutely toxic pesticides to mammals in use today. Unlike most carbamates, aldicarb is toxic through dermal contact. The oral LD 50 for the female rat is 0.65 mg/kg. Studies that examined the effect of plant absorbed aldicarb found that 3.0 grams of mint treated with a 10% granular formulation killed a rabbit within 2 hours. Numerous instances of mortality due to secondary exposure from predators and scavengers ingesting contaminated rodents have been reported.

• Aquatic invertebrates: Aldicarb is very highly toxic to aquatic invertebrates such as Daphnia magna and freshwater mussels.

• Fish: Aldicarb is very highly toxic to fish and has been found to cause pathological deformations of vital organs. Aldicarb appears to be able to produce a wide array of histopathological impairments in fish at sub-lethal concentrations, according to one study (Kumar S and Pant SC, 1984.) Given the persistent nature of aldicarb in water, it should be considered an extreme risk to all aquatic animal life.

• Birds: Aldicarb is very highly toxic to birds. Representative oral LD 50's:

  northern bobwhite            2.0 mg/kg
  California quail                2.58 mg/kg
  mallard                           1.0 mg/kg
  starling                         4.21 mg/kg
  |red-winged blackbird      1.78 mg/kg
  common grackle              0.75 mg/kg
  house sparrow                0.75 mg/kg

  Very few studies exist which examine the chronic effects of aldicarb on birds. Given the persistence of aldicarb in the environment, chronic effects such as immunosuppression, weight-loss, and reproductive and behavioral changes need to be thouroughly examined.