Bacterial mutagenicity of pyrolysis tars produced from chloro-organic fuels

Droplets of toluene and three chlorinated organics, ortho-dichlorobenzene, 1,2-dichloroethane, and trichloroethylene, were pyrolyzed in pure nitrogen. The composition and bacterial mutagenicity of the product tars were measured. The presence of organic chlorine was found to affect both pyrolysis product tar composition and total tar mutagenicity. Pyrolysis in the absence of chlorine produced tars whose bacterial mutagenicity was found to be largely due to the presence of cyclopenta[cd]pyrene, fluoranthene, and benzo[a]pyrene. Small amounts of chlorine in the fuel (i.e., Cl/H molar ratios of less than 0.3) enhanced the formation of highly condensed polycyclic aromatic hydrocarbons (including cyclopenta[cd]pyrene) and increased tar mutagenicity. Larger amounts of organic chlorine (Cl/H ratios of between 0.3 and 0.6) resulted in significant yields of mono- and dichlorinated aromatics and higher levels of tar mutagenicity, which could not be accounted for by the presence of mutagens produced by pyrolysis in the absence of chlorine. Furthermore, unlike tars containing little or no chlorine, tars containing aryl chlorine were more mutagenic in the absence of added enzymes (intended to mimic in vivo mammalian metabolism) than in their presence. We hypothesize that at least one of the chlorinated aromatic products is strongly mutagenic. Two specific conditions that gave notably different results were a) the low-temperature (i.e., below 1400 K) pyrolysis of ortho-dichlorobenzene, which produced tri- and tetrachlorinated biphenyls almost exclusively; and b) the chlorine-rich pyrolysis of trichloroethylene, during which mostly perchloroaromatics were formed. Neither of these tars was found to mutate bacteria.