Carbonyl
compounds are an important class of by-products that are
generated in disinfection reactions. These chemicals are ingredients
contributing to toxicology in the drinking water system, the compositions
and structures of which are worthy of attention. In this study, a
chemical derivatization method based on simultaneous light/heavy isotope
labeling was established for general recognition of carbonyl compounds
and carbonyl disinfection by-products (DBPs) as per the humic substance
reference standard (Suwannee river fulvic acid II, SRFA) before and
after ozonation, chlorination, and chloramination. Decomposition of
macromolecular components into polar carbonyl species was observed
to be the most prominent pathway in ozone treatment due to the efficient
reactivity of ozone with phenols and alkoxy aromatic rings. As a result,
alteration of molecular characteristics was noticed. For instance,
ozone-induced carbonyl DBPs in the highly oxygenated compound classes
(0.67 ≤ O/C ≤ 1.2, 0.6 < H/C ≤ 1.5) possessed
higher O/C but contained less oxygen numbers and carbon numbers. Cl/Br-carbonyl-DBPs
were identified after chlorination and chloramination, and I-carbonyl-DBPs
were found in ozone and chloramine treatments. Several major halogenated
carbonyl homologues were further recognized, including halogenated
4-oxobutenoic acid analogues, halogenated 2,5-dioxohex-3-enoic acid
analogues, and halogenated 4-cyclopentene-1,3-diones analogues. These
findings illustrate the presence of abundant carbonyl DBPs in water
disinfection, and hence their impacts on human health deserve further
investigation.
With
diminishing pristine water, wastewater-affected waters that
contain complex anthropogenic compounds are becoming important sources
of drinking water and the compounds will inevitably react with disinfectants
to form disinfection byproducts (DBPs). Secondary amines such as diphenylamine
(DPA) analogues are considered as potential precursors of N-nitrosamines. In this study, an in situ 14N/15N-labeling and screening workflow was used to systematically
investigate the formation of nitrogenous DBPs (N-DBPs) and putative
reaction pathways. Twenty-four pairs of N-DBPs were generated and
identified from chloramination of DPA through two main pathways, in
which chloramines reacted with the amino and phenyl functional groups
to form N-nitrosodiphenylamine and monochlorinated
5,10-dihydro-phenazine (Cl-DiH-Phe), respectively. Cl-DiH-Phe could
further produce phenazine and the coupling products with another DPA
molecule. Selective N-DBP formation was pH and dose-dependent, and
the same reactions were observed for additional two aromatic DPA analogues.
Effects of alkyl substituents on the formation pathways were investigated
using a series of dialkyl and N-alkyl aromatic analogues.
Only the amino pathway to form nitrosamines was noticed for dialkyl
amines, nevertheless, both the main reactions occurred for N-alkyl aromatic amines. These findings suggested that the
reaction with chloramines through a phenyl pathway was likely to be
crucial for novel nitrogenous heterocyclic byproducts.
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