USING LOW COST, IN SITU MEASUREMENTS OF OPTICAL BRIGHTENERS TO IDENTIFY WASTEWATER INPUTS INTO A SUBURBAN STREAM

Untreated wastewater entering the environment through leaking infrastructure, faulty septic systems, and sewer overflows threatens both human and aquatic health. Water managers need low cost field methods to detect wastewater contamination in real time to promptly employ mitigation strategies. While wastewater is traditionally detected in the environment using chemical or microbial tracers that allow it to be distinguished from natural water, these analyses are often expensive and performed in the lab. Optical brighteners, synthetic brightening compounds present in laundry detergents and paper products, are emerging as ideal tracers of wastewater because they can be quickly and inexpensively detected in the field. To test the utility of optical brighteners as standalone and in situ wastewater tracers, optical brightener levels were compared with traditional wastewater indicators (e.g., B, F^-, E. coli, microbial source tracking) in a suburban watershed (Fishpot Creek near St. Louis, Missouri). Stream samples were collected monthly across the watershed (26 sites) and weekly from a single outlet site from June 2019 to October 2020 to understand the utility of optical brighteners as tracers. Three mixing models using our wastewater tracers assessed the wastewater fraction in streamflow across the basin. Optical brightener values in the watershed were 6.3 - 59.7 RFU for the monthly samples, while influent wastewater averaged 142.7 ± 56.5 RFU. A significant (α = 0.05), positive correlation between optical brighteners and E. coli existed, but a low r value of 0.3 for the correlation suggested other sources of E. coli to the watershed (e.g., wildlife, pet waste). Of the wastewater tracers we used, only optical brighteners had a significant, positive correlation with wastewater infrastructure density (r = 0.6), indicating their utility to detect wastewater. Our mixing models also showed a significant, positive correlation between the wastewater fraction and sewer pipe density at each site. While using optical brighteners as wastewater tracers has limitations (e.g., photodecay, organic matter interferences), we find that they are more robust tracers than traditional wastewater indicators. Thus, optical brighteners are a good screening tool for identifying wastewater contributions to the environment.