Previously
four chlorinated and brominated halo-benzoquinones were
reported as new disinfection byproducts (DBPs) in drinking water,
which have drawn great concern due to their high toxicity. In this
study, three new iodinated halobenzoquinones, including 2-chloro-6-iodo-1,4-benzoquinone
(2,6-CIBQ), 2-bromo-6-iodo-1,4-benzoquinone (2,6-BIBQ), and 2,6-diiodo-1,4-benzoquinone
(2,6-DIBQ), were detected and identified in drinking water for the
first time. Their cytotoxicity was evaluated, and their formation
under various conditions was examined. Since they were not stable
during chloramination, their further decomposition during chloramination
was also explored. The results indicated that the concentrations of
2,6-CIBQ, 2,6-BIBQ, and 2,6-DIBQ in drinking water were in the ranges
of 0.7–1.3, 1.8–8.0, and 0.4–15.9 ng/L, respectively.
Compared with 2,6-dibromo-1,4-benzoquinone, the iodinated halobenzoquinones
were generally more cytotoxic. The formation of 2,6-DIBQ during chloramination
was significantly affected by the iodide concentration, pH, and natural
organic matter. The five tested iodinated halobenzoquinones decomposed
during chloramination following pseudo-first-order decay, with the
decomposition rate constants in the rank order of 2,6-CIBQ > 2,6-BIBQ
> 2,6-DIBQ > 2,3-diiodo-1,4-benzoquinone >2-iodo-1,4-benzoquinone.
Nine polar halogenated intermediates as well as ten aliphatic halogenated
DBPs were detected as the decomposition products of 2,6-DIBQ during
chloramination, based on which the decomposition pathways of 2,6-DIBQ
during chloramination were proposed and verified.