Organocarbamate Pesticides

Organocarbamate Pesticides

Potential exposure

Organocarbamate pesticides are one of several classes of insecticides,

including compounds such as carbaryl, aldicarb, and zectran. The

organocarbamates are not broad-spectrum insecticides, and some common

household insect pests are relatively immune to the effects of these chemicals.

Unlike the organophosphate insecticides, most of the organocarbamate

insecticides have low dermal toxicities. However, due to the high toxicity of

aldicarb by both the oral and dermal routes, it has restricted use in the United

States and is recommended only for limited use in greenhouse operations.

Aldicarb is released to soil as a systemic insecticide for soil use. Carbaryl is a

widely employed insecticide used against a variety of insect pests of cotton,

fruits, vegetables, ornamental trees and shrubs, and animals and livestock. It is

also used as a molluscicide. Humans may be exposed to organocarbamate

insecticides in contaminated air, soils, water, and food by inhalation, dermal

contact, and ingestion exposure routes.

The persistence of organocarbamates in the environment varies with each

individual compound and the chemical properties of the surrounding soils and

water. The reported persistence of carbaryl ranges from nonpersistent in aerobic

conditions, with effectiveness lasting from a few hours to several days, but rarely

more than 12 weeks, to moderately persistent, with effectiveness ranging from 1

to 18 months (Briggs and Council 1992). The reported persistence of aldicarb

ranges from nonpersistent, with effectiveness lasting from a few hours to several

days, but rarely more than 12 weeks, to persistent, retaining toxicity for years

(Briggs and Council 1992). Neither of these compounds bind strongly to soil and

both have potential to leach to groundwater.

Physical and chemical properties of carbaryl

Property

Value

Molecular weight

201.22 g/mol

32 mg/L at 20 C

Water solubility

1.36 10-6 mm Hg at 25 C

Vapor pressure

Koc

370 to 390

log Kow

2.36

Henry's Law Constant 1.28 10-8 atm-m3/mol at 20 C

Toxicity

The mode of action of the organocarbamates, like the organophosphates, is

inhibition of acetylcholinesterase. Inhibition of acetylcholinesterase results in

accumulation of endogenous acetylcholine, a chemical transmitter of neural

impulses in nerve tissue and effector organs. This results in an overactivity of

cholinergic components of the autonomic nervous system, inhibition of

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Appendix D Toxicological Profiles