Aldicarb

Topic editor

Dan Becker
Lead author: Steven G. Gilbert

Managing Group: Chemicals Group

Overview


Aldicarb is a multi-use pesticide that controls populations of agriculturally-harmful insects and nematodes. Belonging to the carbamate family of pesticides, aldicarb inhibits the production of cholinesterase in these various organisms. Primarily an insecticide, aldicarb was first synthetically produced by Union Carbide under the trade name Temik. Since then, because of the chemical's high toxicity, aldicarb has become highly regulated, being marked as a "Restricted Use Pesticide" in the United States. According to the Environmental Protection Agency, aldicarb is "one of the most acutely toxic Pesticides registered" (#Cox 1992). Only certified applicators are allowed use of the pesticide, and, regardless, all products containing aldicarb must be labeled "Poison." 

 

Chemical Description


Aldicarb belongs to the carbamate class of chemicals. In its pure form, the chemical takes on the appearance of a white crystalline solid, which scientifically is known as 2-methyl-2-(methylthio)propionaldehyde O-methylcarbamoyloxime (#ExtoxnetPip). However, because of aldicarb's acute toxicity, discussed several sections below, this pesticide must always be formulated as a granular mix that contains only 10 to 15 percent of this active chemical ingredient.

Chemical Structure

 
Structure retrieved from Wikimedia Commons.
 

Uses


Aldicarb is primarily used as an insecticide on a range of insects in agricultural and horticultural settings. Additionally, this pesticide also functions as an acaricide and nematicide, the latter being those chemicals applied towards the elimination of parasitic nematodes such as the root-knot nematode. Aldicarb's most common derivative in agriculture is Temik, although the chemical's other trade names include ENT 27093, OMS 771, and UC 21149. In all products and settings, aldicarb is applied in granule form below the surface of soils. Plants and new seedlings absorb these soluble materials as they take in water, and the pesticide moves throughout the organism, killing the various insects that consume these flora (#Cox, 1992).

This method is commonly used to control populations of aphids, whiteflies, spider mites, leaf miners, and the above-mentioned nematodes on a variety of plants including dry beans, pecans, beets, potatoes, onions, hops, coffee, bananas, strawberries, citrus fruits, and soy. On its own, cotton accounts for 83 percent of aldicarb usage in the United States (EPA; #Tomlin, 1997). The chemical can also be applied to household and ornamental gardens (PAN).


 

Pharmacology and Metabolism


As noted above, insects are exposed to aldicarb through both dermal and oral routes. Like other carbamates, aldicarb is a cholinesterase inhibitor, which prevents both the breakdown of Acetylcholine and the production of the enzyme cholinesterase in cells throughout the body. This results in an excess of acetylcholine and produces the symptoms of neurotoxicicity that are outlined in the section below (#Risher, et al, 1987).

The potency and severity of aldicarb poisoning depend upon the derivative of the chemical that is ingested. However, in general cases, aldicarb is readily absorbed in the bodies of animal models. Laboratory studies demonstrate that in rats, symptoms of poisoning present only five minutes after a dose of the pesticide is administered. In the same rodent models, after 24 hours up to 80 to 90 percent of chemical isotopes from aldicarb were excreted in urine, while two to five percent were fully metabolized in feces (#Risher, et al, 1987). Similar data have been shown in cows (#ExtoxnetPip). While aldicarb seems to be easily eliminated from the gut in these experiments, the skin toxicity of this chemical is roughly 1,000 times that of other members of the carbamate family (#ExtoxnetPip).

Aldicarb may impact humans through dermal, oral, and inhalation routes of exposure. In human testing, signs and symptoms of aldicarb poisoning abate quickly and the victim's senses return to normal after approximately six hours, unless the exposure was severe enough to incapacitate. In one case of occupational exposure from Temik handling and burning that resulted in the victim's death, the man died in less than two hours, and the excretion of isotopes was already occurring at his death (#Risher, et al, 1987).

 

Health Effects


Aldicarb is one of the most acutely toxic pesticides registered in the United States (#Cox, 1992). Carbamate insecticide poisoning has signs and symptoms similar to organophosphate poisoning, although the symptoms of the former are not as prolonged. These symptoms generally subside within a six hour period, unless the victim has been exposed to an extremely large amount of the chemical (#Risher et al, 1987).

As noted above, this pesticide can harm humans through dermal and oral routes, and through inhalation of granules. However, the primary route of human exposure to aldicarb comes from the consumption of contaminated food and drinking water. In terms of the former, most cases stem from poor product handling, while in the latter, instances of aldicarb poisoning are due to contaminated wells (#ExtoxnetPip). When aldicarb was still a commonly available insecticide, it routinely manifested itself in food crops, and in July of 1985 nearly two thousand people in Oregon and California became ill from eating contaminated watermelons. Similar fates fell upon consumers in Nebraska, British Columbia, and California in the subsequent years (#Cox, 1992). And as with other pesticides, many of the health effects associated from aldicarb use also stem from improper handling of the product itself. 

Cholinesterase inhibition is the primary cause of aldicarb's range of symptoms. If the production of the specific  cholinesterase enzyme decreases by 30 percent, acute effects begin to present. These signs and symptoms can be organized into two groups:

Muscarinic Signs are those that result from the stimulation of muscarinic receptors found in smooth muscles, especially around the heart and glands. Symptoms include

  • Tightness in chest and difficulty breathing due to bronchoconstriction
  • Increased bronchial secretions, sweating, and salivation
  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal cramps
  • Involuntary urination
  • Miosis (pupil constriction)

In contrast, Nicotinic Signs result from the accumulation of Acetylcholine at the endings of motor nerves that communicate with skeletal muscles and ganglia. They include

  • Muscular effects - fatigue, weakness, and cramps.
  • High blood pressure and hyperglycemia

For a more comprehensive analysis of these signs and symptoms, see #Risher et al, 1987.

The EPA notes that although these effects are real and scientifically demonstrated, forcing aldicarb to be classified as a WHO acute health hazard (PAN), they are also reversible after exposure. In contrast, aldicarb does have the potential to cause neurological effects such as sweating pupillary constriction, and leg weakness. Some additionally classify aldicarb as a potential endocrine disruptor (PAN). However, as with other pesticides, the specific kinds of health effects this chemical has are often debated and are not unified (#ExtoxnetPip). On such example, supplied by the EPA, is the current inadequate and ununified body of data to label aldicarb as a carcinogen (EPA). Luckily, some health dimensions of aldicarb are clear; according to the EPA and EXTOXNET, no teratogenic, mutagenic, or reproductive effects have been associated with the chemical's use in both animals and humans.

 

Environmental Effects


Aldicarb has negative effects on the soil, surrounding organisms, and groundwater wherever this chemical is applied. The chemical characteristics of aldicarb advance its chances to leach into water; additionally, the chemical is highly water soluble and mobile in soils. Aldicarb does not degrade in groundwater under aerobic conditions unless a relatively high pH exists, such as at pH 7.7 (#ExtoxnetPip). Therefore, when applied to farmland, aldicarb may easily be carried off into nearby bodies of water through rain and runoff. Because of these properties, aldicarb can easily contaminate human drinking water supplies, and has been detected in wells of over 12 states in concentrations far above the health standard of 10 parts per billion (#ExtoxnetPip).

Aldicarb also demonstrates high degrees of bioaccumulation within the ecosystems where it is applied. While the compound is degraded by bacteria, sunlight, and eventually, water, it has been found to rapidly build up in wild flora. However, aldicarb does not appear to bioaccumulate in aquatic organisms. This does not imply, though, that the chemical does not harm aquatic life. On the contrary, aldicarb is not only acutely toxic to these organisms, but also can cause liver damage, changes in blood cells, and increases in cholesterol levels. The same is true for other aquatic organisms, such as shrimp (#Cox, 1992).

In addition, aldicarb is acutely toxic to birds; one granule of Temik, in one study, was sufficient to kill over eighty percent of house sparrows and forty percent of blackbirds in sample populations (#Cox, 1992). These organisms are primarily exposed to the chemical through absorbing granules of Temik or consuming earthworms contaminated with Temik (ExtoxnetPip). Laboratory studies have also demonstrated that the chemical has the ability to alter the biological structure of certain species of bacteria (#Cox, 1992).

Lastly, aldicarb, in the process of eliminating agricultural and horticultural pests, also kills beneficial insects such as honeybees and earthworms, both of which are necessary for the well-being of gardens and crop yields. However, in terms of this specific impact, aldicarb has one other agricultural cost to take into account. As a nematicide, aldicarb targets nematodes, of which there are two main groups in agricultural settings: predatory and pest species. While this chemical aims to eliminate the latter, which harm crops and can act as vectors for plant viruses, aldicarb also limits the population of the former, which serve as forms of bio-control by preying on garden pests such as cutworms. Therefore, by using aldicarb as a nematicide, agriculturally-beneficial species of nematode may be eliminated, and their associated benefits will be lost.

 

Regulation


Aldicarb is classified as a Restricted Use Pesticide (RUP) in the United states. RUPs may be purchased and used only by certified applicators. Because aldicarb is rated as highly toxic, products containing aldicarb bear the signal word DANGER-POISON on the label (#ExtoxnetPip). Additionally, a European Commission ruled in January of 2007 that aldicarb could no longer by used as an active ingredient in Temik (#Farmers Weekly, 2007).

 

Current Events


January 11, 2007

Robbers poisoned fourteen dogs and two cats to ease entry into residences. See the iafrica.com article.

January 8, 2007

Farmer's Weekly article highlighting the impact of the recent decision by a European Commission that outlawed the use of aldicarb in commercial growing.

 

External Links


References


"Aldicarb Removal Prompts Grower Rethink".Farmer's Weekly, January 8, 2007. Accessed on 1-25-07.
Cox, Caroline. "Aldicarb". Journal of Pesticide Reform 12, 1992.

CDC. "Epidemiologic Notes and Reports Aldicarb Food Poisoning from Contaminated Melons - California". Morbidity and Mortality Weekly Report. Accessed on 1-30-07.

ExtoxnetPip. Retreived on 1-24-07.
Farm Chemicals Handbook. Meister, 2001.

Risher, John F., Franklin L. Mink, and Jerry F. Stara. "The Toxilogical Effects of the Carbamate Insecticide Aldicarb in Mammals: A Review". Environmental Health Perspectives 78, p267-281, 1987.
Tomlin, C.D.S. ed. The Pesticide Manual 11 ed. British Crop Protection Council, 1997.

Picture of aldicarb granules was retreived from Veterinery Services and Animal Health. Accessed on 1-25-07.