Disinfectants inactivate pathogens in source water; however, they also react with organic matter and bromide/iodide to form disinfection byproducts (DBPs). Although only a few DBP classes have been systematically analyzed for toxicity, iodinated and brominated DBPs tend to be the most toxic. The objectives of this research were (1) to determine if monochloramine (NH2Cl) disinfection generated drinking water with less toxicity than water disinfected with free chlorine (HOCl) and (2) to determine the impact of added bromide and iodide in conjunction with HOCl or NH2Cl disinfection on mammalian cell cytotoxicity and genomic DNA damage induction. Water disinfected with chlorine was less cytotoxic but more genotoxic than water disinfected with chloramine. For both disinfectants, the addition of Br(-) and I(-) increased cytotoxicity and genotoxicity with a greater response observed with NH2Cl disinfection. Both cytotoxicity and genotoxicity were highly correlated with TOBr and TOI. However, toxicity was weakly and inversely correlated with TOCl. Thus, the forcing agents for cytotoxicity and genotoxicity were the generation of brominated and iodinated DBPs rather than the formation of chlorinated DBPs. Disinfection practices need careful consideration especially when using source waters containing elevated bromide and iodide.
Granular activated carbon (GAC) adsorption
is well-established
for controlling regulated disinfection byproducts (DBPs), but its
effectiveness for unregulated DBPs and DBP-associated toxicity is
unclear. In this study, GAC treatment was evaluated at three full-scale
chlorination drinking water treatment plants over different GAC service
lives for controlling 61 unregulated DBPs, 9 regulated DBPs, and speciated
total organic halogen (total organic chlorine, bromine, and iodine).
The plants represented a range of impacts, including algal, agricultural,
and industrial wastewater. This study represents the most extensive
full-scale study of its kind and seeks to address the question of
whether GAC can make drinking water safer from a DBP perspective.
Overall, GAC was effective for removing DBP precursors and reducing
DBP formation and total organic halogen, even after >22 000
bed volumes of treated water. GAC also effectively removed preformed
DBPs at plants using prechlorination, including highly toxic iodoacetic
acids and haloacetonitriles. However, 7 DBPs (mostly brominated and
nitrogenous) increased in formation after GAC treatment. In one plant,
an increase in tribromonitromethane had significant impacts on calculated
cytotoxicity, which only had 7–17% reduction following GAC.
While these DBPs are highly toxic, the total calculated cytotoxicity
and genotoxicity for the GAC treated waters for the other two plants
was reduced 32–83% (across young–middle–old GAC).
Overall, calculated toxicity was reduced post-GAC, with preoxidation
allowing further reductions.
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