NSF Award
1808054
This award from the Environmental Chemical Sciences Program in the Division of Chemistry supports Dr. Christoph Aeppli at Bigelow Laboratory for Ocean Sciences. The goal of this project is to study how sunlight determines the fate of short-chain chlorinated paraffins (SCCPs) in surface water of lakes and oceans. These compounds have been classified as persistent organic pollutants, but there are insufficient scientific data to assess their fate in the aqueous phase. Specifically, there are knowledge gaps about a process called indirect photolysis of SCCPs. In this project, this process is studied in the laboratory under environmentally relevant conditions. The degradation of SCCPs is mediated by two primary species responsible for indirect photolysis: the so-called hydrated electron and the hydroxyl radical. The mechanisms and rates of these reactions are being determined. There are indications that the pathway mediated by hydrated electrons is highly effective for degrading hydrophobic pollutants, especially in surface water. In such systems, the presence of dissolved organic matter is expected to facilitate the transformation reaction. The anticipated outcome of this research is a better understanding of the loss and persistence of an important class of pollutants in lakes and oceans. Undergraduate students from Colby college participate in this research both in the summer and during the academic year. They gain intense hands-on research experience in laboratory environmental chemistry. A postdoctoral researcher learns about the intersection of photochemistry, high-end analytical techniques, and computational chemistry. <br/><br/>This project investigates whether hydrated electrons are the active species for the photolysis of SCCPs in surface water. It is hypothesized that this photochemical degradation with hydrated electrons occurs in dissolved organic matter (DOM) aggregates. Irradiation experiments are conducted using DOM-containing systems as well as clean systems that allow a separate investigation of the SCCP photolysis by hydrated electrons as well as by hydroxyl radicals. Comprehensive two-dimensional gas chromatography is used to quantify degradation of the highly complex mixture of SCCP congeners. To interpret results from the DOM-containing photolysis experiments, the affinity of individual SCCP congeners into the DOM phase is being estimated using quantum chemical-based computational chemistry tools. Overall, this project advances the understanding of the photochemical fate of hydrophobic pollutants in surface waters. The project also improves the fundamental knowledge of a so-far understudied photoreactive species, the hydrated electron. Furthermore, this project trains the next generation of researchers and includes a significant undergraduate education component. Additionally, there is an active outreach program to educate the broader community on the relevance of the research.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
