Chlordane is a synthetic organochlorine compound classified as a cyclodiene insecticide. Used extensively from the late 1940s through the 1980s, its most prominent application was the subsurface treatment of soil around residential structures for termite control. Chlordane is recognized internationally as a Persistent Organic Pollutant (POP) due to its high resistance to environmental breakdown.
Sources of Human Exposure
Human contact with Chlordane today primarily results from residual contamination left over from its historical use. The most common pathway is through the soil surrounding homes that were treated for termites before the 1988 ban. The chemical was injected directly into the ground to create a lasting barrier, and residue levels near treated homes sometimes reached thousands of parts per million. People encounter this residue through gardening or contact with contaminated soil near the foundation of older structures.
A significant contemporary exposure route is the inhalation of vapors within older residential buildings. As a semi-volatile compound, Chlordane slowly evaporates from the treated soil beneath the foundation and migrates upward into the indoor air, particularly in basements and crawlspaces. These low-level fumes can persist for years, subjecting occupants to continuous exposure. Ingestion remains a potential pathway, as the chemical bioaccumulates in the fatty tissues of animals and fish, allowing it to enter the food supply. Before the ban, workers who manufactured or applied the pesticide experienced high levels of occupational exposure, often through dermal contact and inhalation.
Acute and Short-Term Health Impacts
Exposure to high concentrations of Chlordane, often resulting from accidental ingestion or significant inhalation, primarily targets the central nervous system (CNS). The compound acts as a neurotoxin by interfering with the inhibitory signals in the brain. Chlordane acts as a non-competitive antagonist of the Gamma-aminobutyric acid (GABA) receptor.
GABA is the main inhibitory neurotransmitter in the brain; its receptors open chloride channels to quiet nerve activity. By binding to the picrotoxinin site on the GABA-A receptor, Chlordane blocks the chloride flux, preventing the inhibitory signal from taking effect. This disruption leads to an over-excitation of the nervous system, resulting in a hyperexcitability syndrome.
Initial symptoms of high-dose exposure often include gastrointestinal distress, headaches, and confusion. As the neurotoxicity progresses, patients may experience tremors, irritability, and poor balance. In the most severe instances, the uncontrolled nerve activity can lead to tonic-clonic convulsions or seizures, which may occur hours or even a full day after the initial exposure.
Chronic and Long-Term Health Risks
The long-term health risks are the primary concern for the general population due to prolonged, low-level exposure from environmental residue. The Environmental Protection Agency (EPA) classifies Chlordane as a Group B2, probable human carcinogen. This designation is based on evidence of tumor development in laboratory animals, particularly liver cancer in mice.
In human studies, exposure to Chlordane has been associated with an increased risk of specific blood cancers, such as non-Hodgkin lymphoma. The chemical’s tendency to accumulate in body fat allows it to persist for decades, leading to chronic biological effects. One of the most consistent non-cancer effects observed is liver toxicity.
The compound induces the production of certain hepatic enzymes, such as cytochrome P-450, leading to changes in liver cell structure and enlargement. This liver burden is a characteristic response to many chlorinated hydrocarbon pesticides. Chlordane and its metabolites, like oxychlordane, function as endocrine disruptors.
These endocrine-disrupting properties mean the compound can interfere with the body’s natural hormone systems, potentially impacting reproductive and developmental health. Children and developing fetuses are particularly susceptible due to their rapid development and lower body mass. The chemical’s ability to cross the placenta and affect the developing nervous system is a concern for neurological outcomes later in life.
Current Regulatory Status and Environmental Persistence
The United States phased out most uses of Chlordane in 1983, with the final ban on all uses, including termite control, taking effect in 1988. Internationally, the compound is listed under the Stockholm Convention on Persistent Organic Pollutants, which aims to globally eliminate or restrict the production and use of hazardous substances. This reflects the compound’s ability to travel long distances in the atmosphere and its documented toxicity.
Despite the decades-old ban, Chlordane remains a concern because it is highly resistant to breaking down in the environment. It has an extremely long half-life in soil, often persisting for more than 20 years. This environmental legacy means the chemical continues to volatilize from contaminated soil and remains a source of low-level exposure in many older residential areas. Monitoring and awareness remain necessary to mitigate the ongoing health risks.