Chlorine
radicals, including Cl• and Cl2
•–, can be produced in sunlight waters (rivers,
oceans, and lakes) or water treatment processes (e.g., electrochemical
and advanced oxidation processes). Dissolved organic matter (DOM)
is a major reactant with, or a scavenger of, Cl• and Cl2
•– in water, but limited
quantitative information exists regarding the influence of DOM structure
on its reactivity with Cl• and Cl2
•–. This study aimed at quantifying the reaction
rates and the formation of chlorinated organic byproducts produced
from Cl• and Cl2
•– reactions with DOM. Laser flash photolysis experiments were conducted
to quantify the second-order reaction rate constants of 19 DOM isolates
with Cl• (k
DOM–Cl•) and Cl2
•– (k
DOM–Cl2•–), and compare those with
the hydroxyl radical rate constants (k
DOM–•OH). The values for k
DOM–Cl• ((3.71 ± 0.34) × 108 to (1.52 ± 1.56)
× 109 MC
–1 s–1) were orders of magnitude greater than the k
DOM–Cl2•– values ((4.60 ± 0.90) ×
106 to (3.57 ± 0.53) × 107 MC
–1 s–1). k
DOM–Cl• negatively correlated with the weight-averaged
molecular weight (M
W) due to the diffusion-controlled
reactions. DOM with high aromaticity and total antioxidant capacity
tended to react faster with Cl2
•–. During the same experiments, we also monitored the formation of
chlorinated byproducts through the evolution of total organic chlorine
(TOCl) as a function of chlorine radical oxidant exposure (CT value).
Maximum TOCl occurred at a CT of 4–8 × 10–12 M·s for Cl• and 1.1–2.2 × 10–10 M·s for Cl2
•–. These results signify the importance of DOM in scavenging chlorine
radicals and the potential risks of producing chlorinated byproducts
of unknown toxicity.