Dioxane has an  of 5170 mg/kg in rats. It is irritating to the eyes and respiratory tract. Exposure may cause damage to the central nervous system, liver and kidneys. In a 1978 mortality study conducted on workers exposed to 1,4-dioxane, the observed number of deaths from cancer was not significantly different from the expected number. Dioxane is classified by the National Toxicology Program as "reasonably anticipated to be a human carcinogen". It is also classified by the IARC as a Group 2B carcinogen: possibly carcinogenic to humans because it is a known carcinogen in other animals. The United States Environmental Protection Agency classifies dioxane as a probable human carcinogen (having observed an increased incidence of cancer in controlled animal studies, but not in epidemiological studies of workers using the compound), and a known irritant (with a no-observed-adverse-effects level of 400 milligrams per cubic meter) at concentrations significantly higher than those found in commercial products. Under California Proposition 65, dioxane is classified in the U.S. State of California to cause cancer. Animal studies in rats suggest that the greatest health risk is associated with inhalation of vapors in the pure form. The State of New York has adopted a first-in-the-nation drinking water standard for 1,4-Dioxane and set the maximum contaminant level of 1 part per billion.
It tends to concentrate in the water and has little affinity for soil. It is resistant to abiotic degradation in the environment, and was formerly thought to also resist biodegradation. However, more recent studies since the 2000s have found that it can be biodegraded through a number of pathways, suggesting that bioremediation can be used to treat 1,4-dioxane contaminated water.