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Toxicity, Hydrocarbon Insecticides
Updated: Oct 29, 2009
Introduction
Background
Chlorinated hydrocarbon (organochlorine) insecticides, solvents, and fumigants are widely used in the United States. This class comprises a variety of compounds containing carbon, hydrogen, and chlorine. These compounds can be highly toxic, and some agents, such as DDT, have been banned in the United States because of their unacceptably slow degradation and subsequent bioaccumulation.
The toxicity of these agents varies according to their molecular size, volatility, and effects on the CNS. In general, they cause either CNS depression or stimulation, depending upon the agent and dose.1
These compounds are separated into 6 groups, as follows:
- Dichlorodiphenyltrichloroethane (DDT)
- Hexachlorocyclohexane (ie, benzene hexachloride) and isomers (eg, lindane, gamma-hexachlorocyclohexane)
- Cyclodienes (eg, chlordane, heptachlor, aldrin, dieldrin, endrin, endosulfan, isobenzan)
- Chlordecone, kelevan, and mirex
- Toxaphene
- Dicofol and methoxychlor
Pathophysiology
Absorption and metabolism
Organochlorines are well absorbed orally and by inhalation. Transdermal absorption is variable. For example, DDT is poorly absorbed transdermally, whereas cyclodienes have significant transdermal absorption rates.2 Cyclodienes have high absorption levels when taken orally as in the case of food contamination with these pesticides.3 Lindane is also absorbed after topical application. Studies have shown that the young, malnourished, and those with frequent application are at increased risk for toxicity.4
Organic chlorines are strongly lipid soluble and sequestered in body tissues with high lipid content, such as the brain and liver. Consequently, blood levels tend to be much lower than fatty tissue levels.2 The lipophilic tendency of organochlorines accounts for prolonged systemic effects in overdose. The half-life of DDT has been measured in months or years, whereas other organic chlorines are metabolized faster, like lindane, with a half-life of 21 hours.5
Mechanism of toxicity
Toxicity in humans is largely due to stimulation of the central nervous system. The organochlorines disturb the neuronal membrane causing hyperexcitability of the nervous system. Specifically, cyclodienes, hexachlorocyclohexanes, and toxaphene organochlorines inhibit the GABA receptor and prevent chloride influx in the CNS, while DDT affects potassium and voltage-dependent sodium channels. This effect results in agitation, confusion, and seizures. Cardiac effects have been attributed to sensitization of the myocardium to circulating catecholamines.
Some of the more volatile hydrocarbons can be inhaled while in vapor form or swallowed while in liquid form. Inhalation of toxic vapors or aspiration of liquid after ingestion may lead to atelectasis, bronchospasm, hypoxia, and a chemical pneumonitis. In severe cases, this can lead to pulmonary edema, hemorrhage, and necrosis of lung tissue. In liquid form, they are easily absorbed through the skin and GI tract.
- Highly toxic organochlorines
- Moderately toxic hydrocarbons
- Chlordane
- DDT (banned by the EPA)
- Heptachlor
- Kepone
- Lindane
- Mirex
- Toxaphene
Frequency
United States
Organochlorine pesticides are now only rarely used in the developed world, and poisonings have become correspondingly more rare. Lindane is still used as a second-line topical prescription treatment for head lice and scabies.
In the United States, approximately 42,000 cases of pesticide poisoning occur annually. In 2007, the Annual Report of the American Association of Poison Control Centers' National Poison Data System reported pesticide exposure as the ninth most common substance frequently involved in human exposures.9 In 2007, 16 pesticide poisoning fatalities were reported. None of these were due to organochlorine pesticides.9
International
An estimated 3 million cases of severe pesticide poisoning and 220,000 deaths occur each year worldwide. Organochlorine poisoning accounts for only a small fraction of pesticide poisoning. Approximately 95% of fatal pesticide poisonings occur in developing countries.
Mortality/Morbidity
Toxic doses are variable, and reports of poisonings are limited.
Age
Adults are most likely to have serious intentional poisonings, and children are most likely to have accidental poisonings.
Clinical
History
The history of exposure is by far the most important piece of information to obtain. In most cases, the exact history of pesticide exposure is known to the physician, and all efforts to resuscitate the patient can focus upon the specific hydrocarbon to which the patient was exposed. At times, the physician may not have the benefit of knowing the initiating event. CNS depression and excitation are the primary effects observed from organochlorine toxicity; therefore, the patient may appear agitated, lethargic, intoxicated, or even unconscious. Organochlorines lower the seizure threshold, which results in increased seizure activity. Initial euphoria with auditory or visual hallucinations and perceptual disturbances are common in the setting of acute toxicity. Patients may have pulmonary complaints or may be in severe respiratory distress. Cardiac dysrhythmias may complicate the initial clinical presentation.
- Other symptoms include the following:
- Cough
- Shortness of breath
- Nausea
- Vomiting
- Diarrhea
- Abdominal pain
- Skin rash
- Headache
- Dizziness
- Paresthesias of face, tongue, and extremities
Physical
Because of the high lipid solubility, duration of toxicity can be prolonged. Life-threatening complications are secondary to seizures or hypoxia secondary to prolonged CNS stimulation.
- Ingestions
- Nausea and vomiting
- Confusion, tremor, myoclonus, coma, and seizures
- Respiratory depression or failure
- Unusual odor - Toxaphene may have a turpentinelike odor; endosulfan may have a sulfur odor.
- Skin absorption or inhalation
- Ear, nose, and throat irritation
- Blurred vision
- Cough
- Pulmonary edema
- Dermatitis
- Chronic exposure
- Anorexia
- Hepatotoxicity
- Renal toxicity
- CNS disturbances
- Skin irritation
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Further Reading
Keywords
chlorinated hydrocarbon insecticides, organochlorines, pesticide poisoning, insecticide toxicity, hydrocarbon insecticide toxicity, hydrocarbon insecticide poisoning, dichlorodiphenyltrichloroethane, DDT, hexachlorocyclohexane, benzene hexachloride, lindane, gamma-hexachlorocyclohexane, cyclodienes, chlordane, heptachlor, aldrin, dieldrin, endrin, endosulfan, isobenzan, chlordecone, kelevan, mirex, toxaphene, dicofol, methoxychlor, organochlorine poisoning, organochlorine insecticides
