Chlordane

Chlordane was introduced in 1947 as part of the organochlorine pesticide revolution following DDT's success [1]. It became the pesticide of choice for termite control and was applied to an estimated 30–35 million homes in the US from the late 1940s through 1988 — primarily by injecting it into soil around and beneath foundations. The volatility of chlordane means it continues evaporating from treated soil and entering homes through foundation cracks and soil gas for years after application [2]. By the 1980s, the evidence of chlordane's persistence, bioaccumulation, and carcinogenicity in animal studies led the EPA to cancel its use for termite control. The pesticide's manufacturer, Velsicol Chemical, resisted restrictions for years. Chlordane was also used on golf courses, turf, and food crops before these uses were also cancelled [3]. Japan accepted a contaminated shipment of corn from chlordane-treated American farms in 1986, causing an international incident that accelerated the US cancellation process.

Inhalation of chlordane vapors in homes that were treated for termites before 1988 is the primary ongoing exposure pathway [1]. Chlordane is highly persistent in soil and has a half-life of 20–30 years under typical conditions — meaning soil around a house treated in 1980 still contains substantial chlordane today. This chlordane volatilizes and enters homes, particularly through crawl spaces, basements, and foundation cracks. Studies in the 1980s and 1990s found detectable chlordane in indoor air in a significant fraction of treated homes, sometimes at concentrations above health guidelines [2]. Dietary exposure occurs through consumption of contaminated fish and shellfish from areas where chlordane use was heavy, and through root vegetables grown in contaminated soil. People who live in homes with crawl spaces or slabs over treated soil are at greatest risk from volatilization [3].

Chlordane is a probable human carcinogen (IARC Group 2A), with the strongest evidence for liver cancer, leukemia, and non-Hodgkin lymphoma in occupationally and residentially exposed populations [1]. Like DDT, chlordane is an organochlorine that accumulates in fatty tissue and disrupts steroid hormone signaling. It activates estrogen receptors and interferes with normal immune function, potentially increasing cancer susceptibility through multiple mechanisms [2]. Acute high-level exposure causes seizures, liver damage, and can be fatal — several poisoning cases occurred when chlordane was applied improperly inside homes. Neurological effects including tremors, headaches, and cognitive effects are reported in people with prolonged residential exposure [3].

People who live in homes constructed before 1988 that received termite treatments — especially if the home has a crawl space or basement that is inadequately ventilated — may still be exposed to chlordane today [1]. Homes in the South and Southeast, where termites are most prevalent and treatments were most common, have the highest prevalence of historical chlordane application. Frequent consumers of sport fish from contaminated coastal and inland waterways where chlordane use was heavy face dietary exposure [2]. Children in treated homes face higher exposure per body weight and have longer lifetime exposure periods.

Test indoor air and crawl space air in pre-1988 homes, especially if you have reason to suspect termite treatment history (ask the seller, check permit records, look for injection ports around the foundation) [1]. Seal cracks in foundations and between the crawl space and living area to reduce vapor migration. Improve crawl space ventilation and consider vapor barriers. Some states and localities have programs to assist homeowners with chlordane testing [2]. Avoid growing root vegetables in soil around homes treated before 1988. Follow state fish consumption advisories for water bodies in areas with historical heavy chlordane use. If you discover you live in a heavily contaminated home, consult your state environmental agency about remediation options [3].