Photochemical degradation of short-chain chlorinated paraffins in aqueous solution by hydrated electrons and hydroxyl radicals.

Short-chain chlorinated paraffins (SCCPs) are a complex mixture of polychlorinated alkanes (C-C, chlorine content 40-70%), and have been categorized as persistent organic pollutants. However, there are knowledge gaps about their environmental degradation, particularly the effectiveness and mechanism of photochemical degradation in surface waters. Photochemically-produced hydrated electrons (e) have been shown to degrade highly chlorinated compounds in environmentally-relevant conditions more effectively than hydroxyl radicals (·OH), which can degrade a wide range of organic pollutants. This study aimed to evaluate the potential for e and ·OH to degrade SCCPs. To this end, the degradation of SCCP model compounds was investigated under laboratory conditions that photochemically produced e or ·OH. Resulting SCCP degradation rate constants for e were on the same order of magnitude as well-known chlorinated pesticides. Experiments in the presence of ·OH yielded similar or higher second-order rate constants. Trends in e and ·OH degradation rate constants of the investigated SCCPs were consistent with those of other chlorinated compounds, with higher chlorine content producing in higher rate constants for e and lower for ·OH. Above a chlorine:carbon ratio of approximately 0.6, the e second-order rate constants were higher than rate constants for ·OH reactions. Results of this study furthermore suggest that SCCPs are likely susceptible to degradation in sunlit surface waters, facilitated by dissolved organic matter as a source of photochemically produced e and ·OH.