1,1-Dichloropropene in Drinking Water: Complete Guide (2026)

What is 1,1-Dichloropropene and Why Does It Matter?

# 1,1-Dichloropropene: Understanding This Uncommon Water Contaminant

1,1-Dichloropropene is a synthetic chemical used primarily as a soil fumigant in agriculture. Farmers spray it on fields before planting to kill harmful nematodes (tiny worms) and other pests in the soil. When applied, the chemical can leach downward through soil layers and eventually reach groundwater aquifers that supply drinking water wells. It's also used in some industrial processes, though agricultural use accounts for the majority of environmental releases. Once in groundwater, 1,1-dichloropropene moves slowly and can persist for years, making it a long-term concern in affected areas.

The chemical has been detected in 24 water systems across the United States, with an average concentration of 0.149 ppb (parts per billion) and a maximum of 0.5 ppb. While these levels are relatively low, the health effects of long-term exposure are still being studied. The EPA classifies 1,1-dichloropropene as a possible human carcinogen based on animal studies showing it can cause tumors in mice and rats. Limited human data exists, but animal studies suggest potential risks to the liver and kidneys with chronic exposure. Children may be more vulnerable to chemical exposures than adults, which is why many health organizations recommend extra caution with contaminants in drinking water used by families.

The EPA has set a maximum contaminant level (MCL) of 7 ppb for 1,1-dichloropropene, meaning water systems must take action if levels reach this threshold. The Environmental Working Group (EWG), which sets stricter health-based guidelines, recommends a limit of 0.00052 ppb based on cancer risk. This enormous gap—EWG's guideline is roughly 13,000 times lower than the EPA's legal limit—reflects how conservative EWG's approach is. The EPA's standard is based on balancing health protection with treatment feasibility and cost. None of the 24 detected systems currently exceed the EPA's legal limit, which is good news for those communities. However, the presence of this chemical in any amount suggests that agricultural practices in those regions warrant closer monitoring.

Alabama accounts for the majority of detections, with 15 of the 24 affected water systems located in the state. This concentration makes sense given Alabama's significant agricultural sector, particularly row crops like cotton and peanuts that rely heavily on soil fumigation. New York follows with 6 detections, likely tied to farming operations in rural areas of the state. South Carolina, Georgia, and Nebraska each have one detection. The pattern is clear: 1,1-dichloropropene appears in regions where intensive agricultural practices and groundwater-dependent drinking water systems overlap. Farmers in these areas typically have no alternatives to soil fumigation for controlling certain pests, creating an ongoing source of potential contamination.

Removing 1,1-dichloropropene from drinking water requires activated carbon filtration or reverse osmosis systems. Activated carbon, either as a pitcher filter or whole-home system, effectively absorbs the chemical and can reduce concentrations by 90% or more. Reverse osmosis is even more thorough, removing up to 99.9% of 1,1-dichloropropene and most other contaminants. If you live in Alabama or another affected region and your water comes from a private well, testing is important—many homeowners in agricultural areas don't realize their wells contain fumigant residues. Public water systems in affected areas should be treating for this contaminant if levels warrant it; you can check your water quality report or contact your local water utility directly. For families wanting additional protection, a point-of-use filter on your kitchen tap provides an affordable safety net while you investigate your water's specific contamination profile.

Regulatory Standards for 1,1-Dichloropropene

Cities With the Highest 1,1-Dichloropropene Levels

States Most Affected by 1,1-Dichloropropene

Frequently Asked Questions

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