Chlordane in Drinking Water: Complete Guide (2026)

What is Chlordane and Why Does It Matter?

# Chlordane: A Persistent Pesticide Still Contaminating Water Supplies

Chlordane is an insecticide that was widely used in the United States from the 1950s through the 1980s. Farmers sprayed it on crops, exterminators applied it to homes and buildings, and golf courses used it to control pests. The EPA banned chlordane for most uses in 1988, but it didn't disappear from our environment. This chemical breaks down very slowly in soil and water—sometimes taking decades. When it rains, chlordane residue seeps into groundwater. In coastal areas and regions with sandy soil, it travels particularly fast toward drinking water aquifers. Once it reaches the water table, chlordane can contaminate wells and municipal water supplies for years.

Today, 23 out of 39 water systems tested show chlordane levels exceeding the EWG health guideline of 0.03 ppb (parts per billion). The average contamination sits at 0.104 ppb, but some systems reach as high as 0.84 ppb—nearly 28 times the EWG guideline. To put this in perspective, one ppb is like one drop of water in an Olympic swimming pool. Even at tiny concentrations, chlordane poses real health concerns because it accumulates in body fat over time.

Health studies link chlordane exposure to several serious conditions. The EPA classifies chlordane as a probable human carcinogen, meaning long-term exposure increases cancer risk. Research also shows connections to nervous system damage, immune system suppression, and reproductive problems. Children face particular vulnerability because their bodies absorb contaminants more readily and they drink more water relative to their body weight. Studies published by the National Institutes of Health found that chlordane exposure during childhood correlated with developmental delays and behavioral issues. The EWG set their guideline at 0.03 ppb based on cancer risk data—significantly stricter than the EPA's drinking water standard of 2 ppb.

This gap between EPA and EWG standards reveals an important truth: the EPA's limits focus on preventing acute poisoning, while the EWG considers long-term health risks from chronic exposure. The EPA hasn't updated its chlordane standard since 1992. Meanwhile, newer research has strengthened the case for tighter limits. Currently, only 23 states require chlordane testing in drinking water, creating blind spots across the country.

Florida tops the list with 14 contaminated water systems, followed by North Carolina with 8. Both states have extensive agricultural histories and sandy, porous soils that allow chlordane to penetrate groundwater easily. Oklahoma, Hawaii, and New York each report 3 affected systems. Florida's problem is particularly acute because the state's limestone bedrock and shallow water table mean chlordane travels directly into drinking sources. Older homes in these regions may also have received termite treatments containing chlordane decades ago, leaving residual contamination in the soil around properties.

Removing chlordane requires filtration methods designed for persistent organic pollutants. Activated carbon filters work well—they trap chlordane molecules through adsorption, removing up to 99% of the contaminant. Reverse osmosis systems provide even more comprehensive protection, filtering out chlordane along with dozens of other contaminants. If you live in Florida, North Carolina, or another affected area, request a water quality report from your local utility to check for chlordane specifically. If your system shows contamination above 0.03 ppb, installing a point-of-use filter on your kitchen tap and shower protects your family. For the most vulnerable households—those with young children or pregnant women—whole-home filtration offers the broadest protection. Testing your water is the first step. Knowledge about what's actually in your tap water empowers you to make informed decisions about your family's health.

Regulatory Standards for Chlordane

Cities With the Highest Chlordane Levels

States Most Affected by Chlordane

Frequently Asked Questions

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