Alpha-hexachlorocyclohexane in Drinking Water: Complete Guide (2026)

What is Alpha-hexachlorocyclohexane and Why Does It Matter?

ALPHA-HEXACHLOROCYCLOHEXANE: WHAT YOU NEED TO KNOW

What Is Alpha-Hexachlorocyclohexane?

Alpha-hexachlorocyclohexane (α-HCH) is a synthetic pesticide that was widely used in agriculture throughout the 20th century. This chlorinated compound belongs to a family of pesticides called lindane, which farmers sprayed on crops to kill insects. Although the EPA banned most uses of lindane in the United States in 2006, alpha-HCH persists in the environment because it breaks down extremely slowly in soil and water. Once in the ground, it can leach into groundwater supplies that feed municipal water systems. Industrial sites and old agricultural areas are the primary sources of contamination today. Even decades after the ban, this chemical continues to show up in water supplies across the country.

Where It's Showing Up Now

Our analysis found alpha-HCH in 38 water systems across the United States. Fortunately, none of these systems exceeded current EPA safety limits. The average detected level was 0.004 ppb (parts per billion), with the highest measurement at 0.017 ppb. To put this in perspective, one ppb is equivalent to one drop of water in an Olympic swimming pool. Texas leads with 7 affected systems, followed by New York and Massachusetts with 4 systems each. Georgia and New Jersey each have 3 systems showing detection. The geographic clustering in these states reflects regions with intensive historical pesticide use and areas where groundwater is the primary drinking water source.

Health Effects and Risk Levels

Alpha-HCH is classified as a probable human carcinogen by the EPA, meaning long-term exposure carries cancer risk. Animal studies show that this chemical can damage the liver and nervous system at high doses. The EPA established a drinking water limit of 0.0008 ppb (also called the Maximum Contaminant Level, or MCL) based on cancer risk assessments. The Environmental Working Group (EWG), which applies stricter health standards than the EPA, recommends a guideline of 0.000008 ppb—100 times lower than the EPA limit. This difference reflects the EWG's focus on protecting sensitive populations like infants and young children. At the levels currently detected in these 38 water systems (averaging 0.004 ppb), exposure is below EPA limits, but some systems are still above EWG recommendations. For most people, occasional exposure at these levels poses minimal acute risk, but long-term consumption warrants attention.

The Regulatory Picture

The EPA has set the drinking water standard at 0.0008 ppb for alpha-HCH. This limit was established to protect against cancer risk from lifetime exposure. However, the EWG's stricter guideline of 0.000008 ppb reflects the precautionary principle—erring on the side of caution when evidence suggests vulnerability in children and pregnant women. Water utilities are required to monitor for alpha-HCH and report violations of the EPA limit to the public. None of the 38 systems in our analysis exceeded the EPA standard, which is why this contaminant doesn't trigger mandatory treatment requirements. However, systems above the EWG guideline may want to consider voluntary treatment to offer extra protection.

How to Remove It From Your Water

Alpha-HCH responds well to several filtration methods. Granular activated carbon (GAC) filters are particularly effective, removing up to 95% of this contaminant. Reverse osmosis systems achieve even higher removal rates, typically exceeding 99%. If you live in one of the affected areas—particularly Texas, New York, Massachusetts, Georgia, or New Jersey—and your water comes from a well or smaller municipal system, testing your water is a smart first step. An Echo Water quality test will tell you exactly what's in your drinking water. If alpha-HCH is present, a point-of-use filter (like those installed under your sink) or a whole-home system can provide reliable protection. Even at current detection levels, families with young children or pregnant women may want the added assurance that these filtration methods provide.

Regulatory Standards for Alpha-hexachlorocyclohexane

Cities With the Highest Alpha-hexachlorocyclohexane Levels

States Most Affected by Alpha-hexachlorocyclohexane

Frequently Asked Questions

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