1,2-Dichloropropane

1,2-Dichloropropane (also called propylene dichloride) was developed in the mid-twentieth century for use as a grain fumigant, lead scavenger in leaded gasoline, and solvent for oils, fats, waxes, and resins [1]. It was also a chemical intermediate in manufacturing chlorinated propylene compounds. Its use as a degreasing solvent in the printing industry — particularly for cleaning offset printing plates — was common in Japan through the 1990s and 2000s [2]. The printing industry connection became tragically apparent when clusters of cholangiocarcinoma emerged among offset printing workers in Japan in the 2010s; epidemiological investigation identified 1,2-dichloropropane as the causative agent, and IARC upgraded its cancer classification to Group 1 (definite human carcinogen) in 2014 [1]. U.S. production and use have declined but it remains a groundwater contaminant at industrial sites [2].

Occupational inhalation in enclosed workspaces with poor ventilation is the most dangerous exposure route — as demonstrated by the Japanese printing worker cases [1]. Contaminated groundwater near industrial facilities, former gas stations (where it was a gasoline additive), and solvent disposal sites can reach drinking water supplies [2]. Vapor intrusion into buildings on contaminated land is documented. Consumer exposure through commercial cleaning products containing chlorinated solvents is possible but typically at lower concentrations [1]. Agricultural exposure historically occurred during grain fumigation, though this use has largely been discontinued in the U.S. [2].

IARC's 2014 Group 1 classification — based primarily on the Japanese printing worker cholangiocarcinoma cluster — makes 1,2-dichloropropane one of the few chemicals elevated to definite human carcinogen status based on occupational evidence [1]. Cholangiocarcinoma (bile duct cancer) is normally extremely rare; incidence in affected printing workers was orders of magnitude above background [2]. The proposed mechanism involves reactive metabolites formed during hepatic metabolism that alkylate DNA in bile duct epithelial cells. The compound also causes liver damage, narcosis at high acute doses, and lung irritation [1]. EPA has classified it as a probable carcinogen (Group B2) for other cancer sites based on animal evidence [2].

Workers in printing, metalworking, and cleaning industries who use 1,2-dichloropropane-containing solvents in poorly ventilated spaces are at highest risk for bile duct cancer [1]. Communities near contaminated industrial sites or former gas stations with groundwater pollution are at risk from drinking water exposure [2]. People in buildings on contaminated land where vapor intrusion occurs face chronic inhalation. Agricultural workers who handled the compound as a grain fumigant historically had elevated exposures [1]. Given its carcinogenic potency, any occupational or environmental exposure merits attention [2].

1. If you work with chlorinated solvents, request Safety Data Sheets from your employer and verify whether 1,2-dichloropropane is present; advocate for substitution with less hazardous alternatives [1]. 2. Ensure adequate industrial ventilation (local exhaust, not just general dilution) when using any chlorinated solvent cleaners in enclosed spaces. 3. Test your well or tap water if you live near former industrial facilities, gas stations, or Superfund sites [2]. 4. Activated carbon and reverse osmosis filters reduce chlorinated solvents in drinking water. 5. Check EPA's Envirofacts database (enviro.epa.gov) to identify Superfund sites and TRI-reporting facilities near your address [1]. 6. If you suspect vapor intrusion, contact your state environmental agency for an assessment [2].