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

Hexachlorobenzene (HCB) is a man-made chemical that was once widely used as a pesticide to protect grain seeds from fungal disease. It was banned in the United States in 1965, but that doesn't mean it's gone. HCB persists in soil and sediment for decades, slowly leaching into groundwater and surface water supplies. Industrial processes that involve chlorine — including the production of certain pesticides, solvents, and rubber — still release HCB as an unintended byproduct. Once it enters the water supply, it binds to organic matter and doesn't break down easily.

The health concerns around HCB are serious enough that the EPA classifies it as a probable human carcinogen. Even at low levels, long-term exposure has been linked to liver damage, immune system disruption, and hormonal interference. HCB is what scientists call a "persistent organic pollutant," meaning it accumulates in body fat over time rather than being flushed out. Studies cited by the Environmental Working Group (EWG) connect chronic HCB exposure to increased cancer risk, particularly liver cancer. Children and pregnant women face the highest risk, since HCB can cross the placenta and has been detected in breast milk in populations with elevated exposure.

Here's where the regulatory picture gets complicated. The EPA's legal limit for HCB in drinking water is 1 part per billion (ppb). That number sounds protective, but the EWG sets its health guideline far lower — at just 0.0002 ppb — based on a one-in-a-million cancer risk standard. The gap between those two numbers is enormous. Of the 17 water systems across the country where HCB has been detected, 5 tested above the EWG health guideline. The average detected level was 0.085 ppb, and at least one system hit the EPA's maximum of 1.0 ppb. Technically legal doesn't always mean safe, and that distinction matters when you're making decisions for your family.

Geographically, Florida stands out by a wide margin. Nine of the 17 affected water systems are located in Florida — more than half of all detections nationwide. That pattern isn't random. Florida's long agricultural history, combined with its sandy soil and high water table, creates conditions where old pesticide residues migrate into groundwater more easily than in other states. Industrial activity along Florida's Gulf Coast also contributes to ongoing HCB releases. Indiana, Oregon, South Carolina, and New York each had one affected system, suggesting that while HCB contamination is concentrated in Florida, it isn't exclusively a Southern problem. Anyone relying on well water near former agricultural land or industrial sites should take this seriously, regardless of their state.

The good news is that HCB is very effectively removed by the right filtration technology. Activated carbon filters — especially granular activated carbon (GAC) — can significantly reduce HCB levels in drinking water. Reverse osmosis (RO) systems go even further, removing up to 99% of HCB and hundreds of other contaminants in a single pass. If your water comes from a system that has detected HCB, or if you live near agricultural land with a history of pesticide use, an under-sink RO system is the most reliable protection you can get at the tap. Echo Water's reverse osmosis systems are independently tested to NSF/ANSI standards, so you know exactly what's being removed. At minimum, check your annual Consumer Confidence Report — your water utility is required to send it every year — to see whether HCB has been detected in your supply. Knowledge is the first step, and filtration is the practical next one.

Regulatory Standards for Hexachlorobenzene (HCB)

Cities With the Highest Hexachlorobenzene (HCB) Levels

States Most Affected by Hexachlorobenzene (HCB)

Frequently Asked Questions

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