Quinoline

Quinoline was first isolated from coal tar by German chemist Friedlieb Ferdinand Runge in 1834, making it one of the earliest identified aromatic compounds [1]. Coal tar — the dark, viscous byproduct of heating coal to produce coke for steel production — contains hundreds of polycyclic and heterocyclic aromatic compounds including quinoline. Quinoline is also found in tobacco smoke, petroleum fractions, and shale oil [2]. Industrially, it has been used as a solvent, a starting material for pharmaceuticals and dyes, and a food flavoring agent in trace amounts. It is produced in quantities large enough to contaminate soils and groundwater at former manufactured gas plant (MGP) sites — thousands of which operated in U.S. cities from the 1880s through the 1950s, leaving quinoline-contaminated soil beneath many urban neighborhoods and parks [1]. EPA classifies it as a probable human carcinogen (Group B2) [2].

Urban residents living near former manufactured gas plant sites and coal tar contaminated areas face soil and groundwater exposure [1]. Tobacco smoke is a significant exposure route for smokers and people exposed to secondhand smoke [2]. Workers in coking operations, coal tar processing, and shale oil refining have historically had the highest occupational exposures. Quinoline has been identified in grilled and smoked foods, and in certain herbal medicines containing quinoline-rich plant extracts [1]. Some contaminated drinking water sources near coal tar Superfund sites contain quinoline [2].

Quinoline is metabolized in the liver to 5,6-epoxy-5,6-dihydroquinoline — a reactive epoxide that alkylates DNA and causes hepatocellular carcinoma in rats and liver and nasal tumors in mice in NTP bioassays [1]. The compound is also mutagenic in several bacterial and mammalian cell test systems. While direct human carcinogenicity data are limited (quinoline rarely occurs in isolation from other polycyclic aromatic compounds in real-world exposures), the mechanistic data support EPA's probable carcinogen classification [2]. Quinoline also accumulates in soil because it binds to organic matter and clay; it resists biodegradation under aerobic conditions and can persist for years [1].

People living near former manufactured gas plant sites — often located in older urban neighborhoods — are at risk from soil and groundwater quinoline contamination [1]. Smokers and those exposed to secondhand tobacco smoke receive ongoing exposures with every cigarette [2]. Coking and coal tar industry workers had the highest historical occupational exposures; contamination monitoring and dust suppression have improved at remaining facilities [1]. People who consume herbal medicines containing quinoline-rich botanicals (some Cinchona bark preparations, for example) are a smaller risk group [2].

1. Check EPA's Superfund site list and your state's brownfield registry for former manufactured gas plant sites in your neighborhood; many have active remediation programs [1]. 2. If you live near a suspected MGP site, avoid gardening in potentially contaminated soil without testing; contact your state environmental agency for guidance on soil screening [2]. 3. Don't smoke, and minimize secondhand smoke exposure — tobacco is one of the few everyday quinoline sources for the general population. 4. If you purchase property in an older urban area, request an environmental site assessment as part of due diligence [1]. 5. Check EPA's Envirofacts database for TRI-reporting facilities in your area that handle quinoline or coal tar [2].