Kinetics of Haloacetaldehydes’ Reactions with Radicals Produced in Radiolysis of Water

Halogenated acetaldehydes (HALs) are abundant disinfection byproducts (DBPs) in drinking water with some congeners being more cyto/genotoxic than EPA-regulated DBPs. Advanced oxidation/reduction processes (AOPs/ARPs) are an attractive option for eliminating HALs from water sources; however, kinetic data for their reactions with AOP hydroxyl radicals (HO • ) and ARP hydrated electrons (e aq – )/hydrogen atoms (H • ), are limited. Using electron pulse radiolysis bimolecular rate constants at pH 7 and 24–25 °C for five important HALs (chloro-, dichloro-, trichloro-, bromo-, and dibromoacetaldehyde) were determined. HO • radicals react by hydrogen atom abstraction from the gem-diol (hydrate) form with k HO• values of (1.36 ± 0.07) × 10 9, (1.77 ± 0.01) × 10 9, (3.07 ± 0.14) × 10 9, (1.11 ± 0.01) × 10 9 and (3.01 ± 0.21) × 10 9 M –1 s –1, respectively. Corresponding HAL k eaq- rate constants monitored at 720 nm were (2.45 ± 0.33) × 10 9, (5.81 ± 0.45) × 10 9, (1.50 ± 0.08) × 10 10, (9.05 ± 0.53) × 10 9 and (1.56 ± 0.12) × 10 10 M –1 s –1 . These structure-dependent kinetics were consistent with electron reductive dehalogenation. Chlorinated HAL k H• values measured by electron paramagnetic resonance methods were 100× slower than for e aq – . These data successfully modeled the steady-state 60 Co irradiation of an O 2 -saturated chloroacetaldehyde solution, validating their use for computer optimization of HO • -driven AOPs to mitigate HALs at larger scale.