In recent years, dozens of halogenated
disinfection byproducts
(DBPs) with cyclic structures were identified and detected in drinking
water globally. Previous in vivo toxicity studies
have shown that a few new cyclic DBPs possessed higher developmental
toxicity and growth inhibition rate than common aliphatic DBPs; however, in vitro toxicity studies have proved that the latter exhibited
higher cytotoxicity and genotoxicity than the former. Thus, to provide
a more comprehensive toxicity comparison of DBPs from different endpoints,
11 groups of cyclic DBPs and nine groups of aliphatic DBPs were evaluated
for their comparative in vitro and in vivo toxicity using human hepatoma cells (Hep G2) and zebrafish embryos.
Notably, results showed that the in vitro Hep G2
cytotoxicity index of the aliphatic DBPs was nearly eight times higher
than that of the cyclic DBPs, whereas the in vivo zebrafish embryo developmental/acute toxicity indexes of the cyclic
DBPs were roughly 48–50 times higher than those of the aliphatic
DBPs, indicating that the toxicity rank order differed when different
endpoints were applied. For a broader comparison, a Pearson correlation
analysis of DBP toxicity data from nine different endpoints was conducted.
It was found that the observed Hep G2 cytotoxicity and zebrafish embryo
developmental/acute toxicity in this study were highly correlated
with the previously reported in vitro CHO cytotoxicity
and in vivo toxicity in aquatic organisms (P < 0.01), respectively. However, the observed in vitro toxicity had no correlation with the in
vivo toxicity (P > 0.05), suggesting
that
the toxicity rank orders obtained from in vitro and in vivo bioassays had large discrepancies. According to
the observed toxicity data in this study and the candidate descriptors,
two quantitative structure–activity relationship (QSAR) models
were established, which help to further interpret the toxicity mechanisms
of DBPs from different endpoints.
Identifying disinfection byproducts
(DBPs) with high health risk
is an unresolved challenge. In this study, six members of a new class
of aromatic nitrogenous DBPs2-chloroaniline, 2-bromoaniline,
2,4-dichloroaniline, 2-chloro-4-bromoaniline, 4-chloro-3-nitroaniline,
and 2-chloro-4-nitroanilineare reported as DBPs in drinking
water for the first time. Haloanilines completely degraded within
1 h in the presence of chlorine (1 mg/L), while about 20% remained
in the presence of chloramine (1 mg/L) after 120 h. Haloanilines showed
high stability in the absence of disinfectants, with <30% degradation
at pH 5–9 over 120 h. Eight haloanilines were determined in
chloraminated finished water and tap water at total concentrations
of up to 443 ng/L. The most abundant was 2-bromoaniline, with a median
concentration of 104 ng/L. The cytotoxicity of eight haloanilines
and regulated trichloromethane and dichloroacetic acid (DCAA) was
evaluated using Hep G2 cell assay. The EC50 values of eight
haloanilines were 1–2 orders of magnitude lower than those
of the regulated DBPs. The lowest toxic concentration of 2-chloro-4-nitroaniline
was 1 μM, 500 times lower than that of DCAA. The formation and
control of haloanilines in drinking water warrant further investigation.
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