1,1-Dichloroethane (Ethylidene dichloride)

1,1-Dichloroethane (1,1-DCA) was historically used as a solvent and fumigant, and is produced industrially by hydrochlorination of vinyl chloride [1]. Its primary contemporary environmental significance is as a degradation product: 1,1,1-trichloroethane (TCA) decomposes under alkaline conditions to produce 1,1-DCA, meaning sites contaminated with TCA (a common degreaser) invariably also contain 1,1-DCA [2]. Similarly, 1,1-dichloroethylene can be reduced to 1,1-DCA under anaerobic conditions by certain bacteria [1]. The result is that 1,1-DCA is found in groundwater at virtually every chlorinated solvent Superfund site in the United States — a widespread, persistent groundwater contaminant [2].

Private well users near former industrial solvent facilities and Superfund sites face groundwater exposure [1]. Vapor intrusion — volatilization of 1,1-DCA from contaminated groundwater through soil and into building basements — is a recognized exposure pathway [2]. Historical occupational exposure in solvent applications [1].

1,1-DCA is metabolized by CYP2E1 to chloroacetaldehyde and dichloroethanol, both hepatotoxic metabolites [1]. Animal studies showed liver, kidney, and mammary tumors; EPA classifies 1,1-DCA as a Group C possible human carcinogen [2]. It is less acutely toxic than many related chlorinated solvents but causes CNS depression at high concentrations [1].

Private well users near chlorinated solvent Superfund sites [1]. People in buildings with vapor intrusion from contaminated groundwater [2].

1. Test your well if near former industrial or dry cleaning sites [1]. 2. Conduct indoor air testing if your building is on or near contaminated groundwater [2]. 3. Activated carbon block filters for drinking water [1].