Preferential
Halogenation of Algal Organic Matter
by Iodine over Chlorine and Bromine: Formation of Disinfection Byproducts
and Correlation with Toxicity of Disinfected Waters
posted on 2021-12-28, 17:33authored byChao Liu, Young-Hwan Shin, Xiao Wei, Mahmut S. Ersan, Elizabeth Wagner, Michael J. Plewa, Gary Amy, Tanju Karanfil
The
increasing occurrence of harmful algal blooms (HABs) in surface
waters may increase the input of algal organic matter (AOM) in drinking
water. The formation of halogenated disinfection byproducts (DBPs)
during combined chlorination and chloramination of AOM and natural
organic matter (NOM) in the presence of bromide and iodide and haloform
formation during halogenation of model compounds were studied. Results
indicated that haloform/halogen consumption ratios of halogens reacting
with amino acids (representing proteins present in AOM) follow the
order iodine > bromine > chlorine, with ratios for iodine generally
1–2 orders of magnitude greater than those for chlorine (0.19–2.83
vs 0.01–0.16%). This indicates that iodine is a better halogenating
agent than chlorine and bromine. In contrast, chlorine or bromine
shows higher ratios for phenols (representing the phenolic structure
of humic substances present in NOM). Consistent with these observations,
chloramination of AOM extracted from Microcystis aeruginosa in the presence of iodide produced 3 times greater iodinated trihalomethanes
than those from Suwannee River NOM isolate. Cytotoxicity and genotoxicity
of disinfected algal-impacted waters evaluated by Chinese hamster
ovary cell bioassays both follow the order chloramination > prechlorination-chloramination
> chlorination. This trend is in contrast to additive toxicity
calculations
based on the concentrations of measured DBPs since some toxic iodinated
DBPs were not identified and quantified, suggesting the necessity
of experimentally analyzing the toxicity of disinfected waters. During
seasonal HAB events, disinfection practices warrant optimization for
iodide-enriched waters to reduce the toxicity of finished waters.