Absolute kinetics and reaction efficiencies of hydroxyl-radical-induced degradation of methyl isothiocyanate (MITC) in different quality waters

Abstract

Methyl isothiocyanate (MITC), a toxic and corrosive skin and respiratory irritant, is a common soil fumigant byproduct which has become an atmospheric, aqueous, and soil contaminant. The work described here examines the degradation and potential removal of MITC from contaminated waters via free radical reactions. We have measured the oxidizing hydroxyl radical ( ·OH) reaction rate constant with MITC over a range of temperatures relevant to wastewater treatment conditions, determining a room temperature value of (5.69 ± 0.56) × 10 8 M −1 s −1 and a corresponding Arrhenius activation energy of 12.90 ± 0.82 kJ mol −1. Hydroxyl radical reaction efficiencies with MITC in pure water, an associated matrix of model real-world waters, and a reverse osmosis permeate water have also been determined. While solutions containing these constituents had significantly decreased MITC removal efficiencies (5.5–14.7%) as compared to pure water (54.4 ± 3.4%), relative rate calculation corrections showed that the ·OH radical efficiencies for solutions containing DOM were the same as in pure water. However, the slightly higher efficiencies for carbonate-containing solutions indicated that some additional MITC degradation occurred from carbonate radical reactions.