Photolysis and Detection of Contaminants of Emerging Concern In Minnesota Waterways

Abstract

Contaminants of emerging concern, or CECs, are a new classification of pollutants which are biologically active even at low concentrations. CECs are degraded by multiple processes in the environment, two of which are direct and indirect photolysis. While indirect photolysis in natural waters has been previously characterized, photolysis in effluent discharges from wastewater treatment plants requires further study. This work has determined that the organic matter in effluent waters are very similar across different treatment plants, more so than with natural organic matter from different locations. This includes the production of photochemically produced reactive intermediates in the effluents. It was found that effluent organic matter produces these intermediates at a higher efficiency than natural organic matter. Thus, as effluent discharge becomes a larger portion of surface water flows, the processing of CECs via photolysis may change. One group of CECs that has received limited attention is strobilurin fungicides, or strobins. Strobins are approved for many crops in the United States, and their unregulated use has been allowed in areas where severe fungal attack may occur. Strobins, however, are toxic to non-target aquatic species including Daphnia magna, fish, and freshwater mussels. Five strobin fungicides were detected in the Whitewater River in Minnesota, and their concentration often correlated with agricultural land use. While indirect photolysis of strobins is limited, direct photolysis is potentially a major pathway for strobins in sunlit surface waters. Three strobins, azoxystrobin, fluoxastrobin, and picoxystrobin, produce an isomer before decaying into multiple products. This work yields greater understanding of previously overlooked issues regarding photolysis of CECs.