Chlorpyrifos selectively alters fluvial dissolved organic carbon composition and ecosystem dynamics

Chlorpyrifos is a widely used organophosphate pesticide with known aquatic toxicity to freshwater macroinvertebrates. However, less is known about the impact of its presence on stream ecosystem dynamics at environmentally relevant concentrations. This study, through the use of artificial streams, investigated the impact of both chlorpyrifos and dissolved organic matter (DOM) content at (5 μg L^-1 and 5 mg C L^-1 respectively) on both stream ecology and DOM composition. Chlorpyrifos dramatically suppressed insect emergence and preferentially sorb into biofilms. In addition, the loss of grazers in those streams allowed stream primary production, as measured by chlorophyll-a, to proliferate. Excitation-emission fluorescence and parallel factor (PARAFAC) modeling indicated that the presence of chlorpyrifos/lack of grazers allowed for more release of DOM components associated with microbial processes, and an overall shift in DOM composition as related by fluorescence and redox indices. These shifts in composition thus potentially alter DOM's ability to perform its ecosystem functions. This is the first study to our knowledge to systematically study and observe the consequences of chlorpyrifos at environmentally relevant concentrations on ecosystem dynamics in freshwater streams at a molecular level.