ENVIRONMENTAL FATE AND PHOTOTRANSFORMATION OF AN ORGANOCHLORINE PESTICIDE IN ARCTIC SYSTEMS (Invited Presentation)

Organohalogen contaminants that undergo long-range transport to high latitudes are subjected to a slew of environmental processes that affect their persistence, bioavailability, and ultimately ecological and health impacts. We investigated the specific role of Arctic-derived dissolved organic matter (DOM) in mediating the photodegradation and sorption of chlorpyrifos. DOM was isolated from two geographically close but hydrologically different Arctic lakes in Alaska (Toolik Lake and Fog Lake). SPR-W5-WATERGATE ¹H NMR revealed compositional differences between isolated humic substances, particularly in the aromatic and carboxyl-rich regions. Differences were also observed in isolates collected at different points in the summer season for Toolik Lake waters, whereby isolates extracted earlier in the season had higher aromatic signal, possibly from surface inputs into the lake after melt. Chlorpyrifos was found to readily partition into DOM, with Toolik Lake being the most favorable carbon pool exhibiting a K_DOC of 3.7- 3 .9, and Suwannee River fulvic acid the least favorable (K_DOC of 3.2). Likewise, solar simulator experiments with chlorpyrifos also found differences with respect to DOM composition, by lake or point in summer isolated. In the presence of DOM, apparent quantum yields for chlorpyrifos degradation increase by a factor of 2 relative to direct photolysis controls at neutral pH for all isolates except Toolik Lake at freshet, the only isolate which exhibits no photolysis enhancement. DOM from Toolik and Fog Lakes promote differing amounts of hydroxyl radical, singlet oxygen, and triplet excited state contributions to indirect photodegradation rates. Transformation products were consistently observed across multiple experiments, coinciding with differing mechanisms of degradation, which aided in their potential identification. Correlation between solubility and photodegradation enhancement by DOM was analyzed to determine the factors driving the fate and transformation of this contaminant more broadly in the water column, in order to better understand its overall environmental health impacts in sensitive Arctic ecosystems.