Over the last two decades, there has been a growing urgency to determine both the source and fate of emerging contaminants such as pharmaceuticals and personal care products (PPCP) in our waterways. In particular, many studies have focused on the widely used antimicrobial agent triclosan, due to both its link to antimicrobial resistant bacteria in aquatic communities and its potential role as an endocrine disruptor. However, these initial studies have solely utilized sampling locations downstream of municipal sewage treatment systems, thus overlooking potential inputs from other point sources such as small privately operated sewage systems and non-point sources (i.e., leach fields associated with septic systems) (hereafter referred to as non-traditional sources). Once delivered to aquatic systems, triclosan is susceptible to various degradation pathways, including photochemistry routes that have been shown to lead to the formation of dioxin-like products. Natural dissolved organic matter can mediate this surface photochemistry, but it has recently been shown that the organics present in treatment system effluents exhibit very different reactivity than traditionally studied autochthonous and allochthonous sources8. How triclosan photochemical degradation might be impacted within treatment plant effluents is unclear. The purpose of this project is to address these knowledge gaps using a multi-faceted biogeochemical approach to determine the non-traditional sources of triclosan in a rural to urban watershed and determine how interactions with in-stream dissolved organic matter affects its residence time in the system.