The role of dissolved organic matter in arctic surface waters in the photolysis of hexachlorobenzene and lindane



[1] Terrestrially derived dissolved organic matter (DOM) can impact the fate of persistent organic pollutants (POPs) that are transported to the Arctic via global distillation. Interactions between DOM and POPs through hydrophobic binding processes may influence their photofate in arctic surface waters. We examined the DOM-mediated photodegradation of γ-hexachlorocyclohexane (lindane) and hexachlorobenzene (HCB) in arctic surface waters. These two halogenated organic compounds are commonly detected in the Arctic. We examined how different sources of DOM affect the indirect photolysis of these compounds. We conducted our study using DOM from arctic streams and lakes near the Toolik Lake Long-term Ecological Research Site. HCB or lindane was irradiated in the presence and absence of DOM from these sources, both at the surface of an arctic lake and at 10 cm depth, to investigate the indirect phototransformation of these two compounds and the depth dependence of the observed chemistry. In both artificial and natural sunlight, two of four DOM sources studied stimulated the photodegradation of HCB but not of lindane, suggesting that the indirect phototransformation is a selective process depending on the interactions between DOM and POPs. Through solubility studies, we found that HCB readily partitions to isolated Toolik Lake DOM, while lindane shows no affinity for DOM, findings that corroborate results previously reported in the literature. We demonstrate for the first time DOM's role as a sensitizer for photodegradation of some POPs under field conditions, thus confirming that this process may be an important control on the fate of POPs exhibiting a strong affinity for DOM.