What is Chlordane and Why Does It Matter?

Chlordane is a pesticide that was widely used in the United States from the 1940s through the 1980s. Farmers applied it to crops, and homeowners used it to kill termites in the soil around their foundations. The EPA banned it in 1988, but that ban came too late to prevent lasting contamination. Chlordane doesn't break down quickly. It binds tightly to soil particles and can persist in the ground for decades — slowly leaching into groundwater and eventually into drinking water supplies.

The health risks from chlordane are serious, even at low levels. The EPA classifies it as a possible human carcinogen (cancer-causing agent), based on studies linking it to liver cancer and neurological damage in animals (EPA). The Environmental Working Group (EWG) goes further, setting a health guideline of just 0.0005 ppb — far stricter than the EPA's legal limit of 2 ppb. Long-term exposure, even at trace amounts, has been associated with immune system disruption, hormonal interference, and nervous system effects. Children and pregnant women face the greatest risk, since developing bodies are more vulnerable to persistent organic pollutants like chlordane.

The gap between the EPA's legal limit and the EWG's health guideline tells an important story. The EPA's limit of 2 ppb was set decades ago, based on older science. The EWG's guideline of 0.0005 ppb reflects more recent research on cancer risk and long-term low-dose exposure. Across 34 water systems tested, 22 — nearly two-thirds — showed chlordane levels above the EWG health guideline. The average detected level was 0.116 ppb, which is 232 times higher than the EWG guideline. The highest recorded level reached 0.84 ppb, which is 1,680 times above that same guideline. Technically, those levels may still fall within the EPA's legal limit. But "legal" doesn't always mean "safe."

Florida and North Carolina account for the largest share of affected systems, with 13 and 8 affected systems respectively. Delaware, Oklahoma, and Georgia each show 2 affected systems. This geographic pattern isn't random. These states have long agricultural histories and warm, humid climates where chlordane was heavily used for decades. Termite pressure in the Southeast is high, which drove widespread residential use before the ban. Older homes in these regions — especially those built before 1988 — often sit on soil that still holds chlordane residue. When rain moves through that soil and into groundwater, it can carry traces of the pesticide along with it. If your home draws from a private well in one of these states, testing your water is a smart first step.

The good news is that chlordane can be removed effectively from drinking water. Activated carbon filtration — the kind found in high-quality under-sink filters — captures chlordane and other organic compounds before they reach your glass. Reverse osmosis (RO) systems are even more thorough, removing up to 99% of persistent pesticides and other contaminants. Echo Water's reverse osmosis systems are designed specifically to address contaminants like chlordane that linger long after their original source has been eliminated. If you're in Florida, North Carolina, or another high-risk state — or if you live in an older home with a history of termite treatment — an RO system gives you a reliable layer of protection. At a minimum, get your water tested so you know what you're actually dealing with. Knowledge is the first filter.

Regulatory Standards for Chlordane

Cities With the Highest Chlordane Levels

States Most Affected by Chlordane

Frequently Asked Questions

Related Contaminant Guides