Hexachlorobenzene (HCB) in Drinking Water: Complete Guide (2026)

What is Hexachlorobenzene (HCB) and Why Does It Matter?

# Hexachlorobenzene (HCB): A Persistent Pesticide in Your Water

Hexachlorobenzene (HCB) is a synthetic chemical that was once widely used as a fungicide to treat seeds before planting. It's also a byproduct of industrial processes that manufacture other chemicals. HCB entered the environment decades ago and refuses to leave. This chemical breaks down extremely slowly in soil and water, meaning contamination from decades-old sources still shows up in water supplies today. HCB doesn't dissolve easily in water, but it binds to sediment and organic matter, allowing it to travel through groundwater and accumulate in aquifers that serve drinking water systems.

Nineteen water systems across the United States have detected HCB in their supplies, with 5 systems exceeding the EPA's safety guideline. The maximum concentration found was 1.0 ppb (parts per billion), while the average across all detections was 0.077 ppb. Florida accounts for the majority of detections with 10 systems affected, followed by Colorado with 2 systems. Single detections also appear in Indiana, Oregon, and South Carolina. These geographic clusters suggest that HCB contamination often reflects historical industrial activity or agricultural practices in specific regions.

Health effects from HCB exposure depend on how much you consume and for how long. The EPA classifies HCB as a probable human carcinogen, meaning long-term exposure increases cancer risk. Animal studies show that HCB damages the liver and kidneys, disrupts hormone systems, and affects immune function. Children are particularly vulnerable because their bodies are still developing and they drink more water per pound of body weight than adults. The Environmental Working Group (EWG) sets a health guideline of 0.06 ppb for HCB — stricter than the EPA's 1.0 ppb limit. This gap exists because the EWG factors in cancer risk over a lifetime of exposure, while the EPA uses different assumptions about safe levels.

The EPA's drinking water standard of 1.0 ppb hasn't changed since 1992, despite growing scientific evidence about HCB's health risks. The EWG's 0.06 ppb guideline reflects more recent research on cancer and developmental effects. This means water that meets EPA standards might still exceed what independent scientists consider safe, especially for vulnerable groups like pregnant women and young children. Some states have adopted their own standards, but many rely solely on federal limits. The disconnect between regulatory and scientific recommendations leaves homeowners uncertain about actual risk levels in their water.

If your water system has detected HCB, or if you live in Florida or Colorado where detections are most common, a whole-house activated carbon filter or reverse osmosis system can remove this contaminant effectively. Activated carbon filters work well for HCB because the chemical binds readily to carbon surfaces. Reverse osmosis systems achieve even higher removal rates, typically eliminating 95-99% of HCB along with other persistent chemicals. Point-of-use filters for your kitchen sink are less effective for HCB alone but provide a lower-cost option if combined with other water safety measures. Check your water quality report or request one from your local water utility to learn if HCB has been detected in your area. If levels exceed the EWG guideline, a filtration system gives you direct control over your family's exposure while regulators work to update standards.

Regulatory Standards for Hexachlorobenzene (HCB)

Cities With the Highest Hexachlorobenzene (HCB) Levels

States Most Affected by Hexachlorobenzene (HCB)

Frequently Asked Questions

Related Contaminant Guides