Chloropicrin (trichloronitromethane), a fumigant and former chemical warfare agent, has been identified as a disinfection byproduct associated with chlorination of nitrite-containing waters. However, nitrite in source waters is typically insufficient to account for chloropicrin formation. Subsequent observations pointed to ozonation upstream of chlorination as a promoter of chloropicrin in nitrite-free waters, but the mechanism has remained unidentified. This work investigated chloropicrin formation by ozone/chlorine, and identified primary and secondary amines as the principal targets of ozone leading to chloropicrin formation. Model compound studies with a primary aliphatic amine (lysine) and aromatic amine (aniline) allowed direct observation of the products of amine ozonation, which were the nitro-analogues of the precursors (e.g., nitrobenzene from aniline). Further model compound studies assessed chloropicrin formation by ozone/chlorine across a range of amine structures including primary, secondary, and tertiary aliphatic amines and alkanolamines; cyclic amines; and aromatic amines. These experiments revealed aniline as an ideal chloropicrin precursor, suggesting an important role for aromatic amines precursors in natural waters. Ozonation/chlorination of a natural freshwater confirmed the importance of primary and secondary amines as precursors: Water pretreated with di-tert-butyl dicarbonate ((Boc)2O), a compound used to protect primary and secondary amines with a tert-butoxycarbonyl group, reduced chloropicrin after ozonation/chlorination from 11 �g/L to undetectable levels (< 1 �g/L), suggesting that primary and secondary amines are the most important chloropicrin precursors in natural water. Ozone demand data confirmed that this decrease was not attributable to ozone scavenging by the derivatizing agent. Addition of radical scavengers increased chloropicrin formation, implicating direct reactions of amines with molecular ozone, rather than hydroxyl radicals.

Ozone promotes chloropicrin formation in natural waters by oxidizing amines to nitro compounds

248th National Meeting (2014)

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