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-10-C-13, 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((aq))(-)) have been shown to degrade highly chlorinated compounds in environmentally-relevant conditions more effectively than hydroxyl radicals ((OH)-O-center dot), which can degrade a wide range of organic pollutants. This study aimed to evaluate the potential for e((aq))(-) and (OH)-O-center dot to degrade SCCPs. To this end, the degradation of SCCP model compounds was investigated under laboratory conditions that photochemically produced e((aq))(-) or (OH)-O-center dot. Resulting SCCP degradation rate constants for e((aq))(-) were on the same order of magnitude as well-known chlorinated pesticides. Experiments in the presence of & BULL;OH yielded similar or higher second-order rate constants. Trends in e((aq))(-) and (OH)-O-center dot 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((aq))(-) and lower for (OH)-O-center dot. Above a chlorine:carbon ratio of approximately 0.6, the e((aq))(-) second-order rate constants were higher than rate constants for (OH)-O-center dot 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((aq))(-) and (OH)-O-center dot.

Automated summary

Short-chain chlorinated paraffins (SCCPs) are persistent organic pollutants. This study evaluated the potential for photochemically-produced hydrated electrons (e((aq))(-)) and hydroxyl radicals ((OH)-O-center dot) to degrade SCCPs. The results showed that SCCPs can be degraded by both e((aq))(-) and (OH)-O-center dot, with higher chlorine content leading to higher rate constants for e((aq))(-).