Chlordane is an organochlorine insecticide that was widely used in the United States from 1948 to 1988, primarily to kill termites in and around homes. All uses of chlordane have been banned in the U.S. since 1988 due to serious health concerns, but the chemical persists in soil and building foundations for decades after application. If you’re searching for information on chlordane, you likely live in a home built before the late 1980s, are dealing with a real estate transaction, or want to understand your potential exposure.
What Chlordane Is
Chlordane is not a single chemical. It’s a mixture of pure chlordane (50 to 75 percent) and more than 100 related compounds, including heptachlor and heptachlor epoxide. It belongs to the organochlorine family, a class of synthetic pesticides that includes DDT and dieldrin. These chemicals share a common trait: they’re extremely persistent in the environment and accumulate in fatty tissue over time.
Chlordane doesn’t occur naturally. It was manufactured as a thick, amber-colored liquid with a mild chemical odor, then typically diluted and applied in liquid form to soil around and beneath buildings.
How It Was Used
Chlordane served two main purposes during its decades on the market: agricultural pest control and structural termite treatment. It was used on crops and lawns from 1948 through 1983, when the EPA restricted agricultural applications. Its primary role, however, was as a termiticide, and this use continued until the full ban in 1988.
For termite control, applicators typically soaked the soil directly beneath buildings, under slab foundations, and around foundation perimeters during new construction. In existing homes, it was applied underneath the building (if the crawl space was accessible), around the outside perimeter of the foundation, in trenches dug along foundations, or injected through holes drilled next to the foundation or through flooring near walls. Hawaii used chlordane more heavily than most states because of the islands’ severe termite pressure, but the practice was common across the mainland as well.
The chemical was effective precisely because it lasted so long in the soil. A single application could deter termites for years. That same persistence is now the core problem: chlordane applied in the 1960s or 1970s can still be detected in soil and can still release vapors into living spaces.
How Chlordane Affects the Body
Chlordane is a neurotoxin. It works by interfering with a key chemical messenger in the brain called GABA, which normally acts as a brake on nerve signaling. Chlordane blocks GABA from doing its job, leaving nerve cells in a state of uncontrolled excitation. This is essentially the same mechanism the chemical used to kill insects, and at high enough doses, it produces the same type of disruption in humans.
Significant exposure by any route, whether inhaled, swallowed, or absorbed through the skin, can cause central nervous system excitation, convulsions, and respiratory depression. The body stores chlordane in fat tissue, which means repeated low-level exposures can build up over time rather than being quickly eliminated.
Health Risks From Exposure
Chlordane exposure affects multiple organ systems. The Agency for Toxic Substances and Disease Registry identifies four primary areas of concern: the nervous system, the liver, the blood-forming system, and developmental effects during periods when organs are still forming (relevant for fetuses and young children).
Acute poisoning from a single large exposure is rare today since the chemical is no longer commercially available. The more realistic modern concern is chronic, low-level exposure from living in a home where chlordane was applied to the foundation decades ago. The chemical can migrate from treated soil into indoor air as vapor, particularly through cracks in slab foundations or from crawl spaces. People in these homes may be exposed continuously without realizing it.
Chlordane is classified as a probable human carcinogen. Both the EPA and the International Agency for Research on Cancer have flagged it based on evidence from animal studies and epidemiological data. The liver is the primary target organ for cancer risk, though research has also explored links to blood cancers.
Why It Was Banned
The EPA moved against chlordane in stages. Agricultural and lawn uses were cancelled in 1983 after mounting evidence of environmental persistence, bioaccumulation in the food chain, and health risks to applicators and residents. Termite treatment, the last remaining permitted use, was banned in 1988. Since that date, all uses of chlordane have been illegal in the United States.
Internationally, chlordane is listed under the Stockholm Convention on Persistent Organic Pollutants, a global treaty that targets chemicals considered too dangerous and too long-lasting for use anywhere. Most countries that are party to the convention have eliminated chlordane entirely.
Exposure Risks in Older Homes
The most common way people encounter chlordane today is by living in a home built before 1988 where the chemical was applied to the foundation. Because chlordane binds tightly to soil particles and resists breakdown, treated soil beneath or around a home can remain contaminated for 20 years or more. In some cases, measurable levels persist far longer than that.
Vapors from contaminated soil can enter indoor air through foundation cracks, gaps around plumbing penetrations, and crawl space vents. The risk is highest in homes with slab-on-grade foundations where the chemical was applied directly beneath the concrete. Renovations, foundation repairs, or demolition of older buildings can also disturb contaminated soil and release chlordane into the air at elevated levels.
If you’re buying or living in a pre-1988 home and are concerned about chlordane, environmental testing companies can sample soil around the foundation and test indoor air for chlordane vapors. Soil testing is the most reliable way to confirm whether the chemical was used at a specific property. For homes with confirmed contamination, mitigation strategies focus on sealing foundation cracks, improving ventilation beneath the structure, and in some cases, removing and replacing contaminated soil.
Environmental Persistence
Chlordane’s environmental behavior is what makes it fundamentally different from most modern pesticides. It does not dissolve easily in water, does not break down quickly in sunlight, and binds so tightly to soil that it resists being washed away by rain. Its half-life in soil, the time it takes for half of the applied amount to degrade, can exceed 20 years under typical conditions.
In the food chain, chlordane accumulates in the fat tissue of animals that consume contaminated organisms. Fish in contaminated waterways, for instance, can carry chlordane concentrations many times higher than the surrounding water. This bioaccumulation effect is one of the reasons the chemical was targeted by both domestic regulators and international treaties. Even though it hasn’t been applied in the U.S. for more than three decades, chlordane continues to be detected in environmental monitoring programs, in soil near treated structures, and occasionally in the tissue of wildlife.