THE IMPORTANCE OF PLASTIC DEBRIS AS A SOURCE OF MICROPLASTICS IN RICHLAND CREEK, NORTH CAROLINA

The widespread use and subsequent release of plastic polymers to the environment has raised concerns about their potential ecological impacts on aquatic systems. In spite of these concerns, little is known about the concentrations, sources, transport, deposition and storage of plastics within riverine environments. A common assumption, however, is that macro- (>2.5 cm) and meso-plastic (0.5-2.5 cm) debris degrades by means of physical and (photo) chemical processes to produce a portion of the microplastic (<0.5 cm) particles in river water, the latter of which are thought to pose the most risk to biota. During this study, we surveyed the quantity and type of macro- and meso-plastic debris within the riparian zone of 7 reaches of Richland Creek and its tributaries, a headwater drainage system in the Blue Ridge province of western North Carolina. Plastic debris was abundant along all 7 reaches; abundances ranged from 0.08 to 0.12 items/m², or about 1.4 items per linear meter of riparian zone. At most sites, the most common types of debris included shopping bags and food wrappers, which in combination accounted from about 30 to 50 % of the items. The debris was generally fragmented, and primarily composed of thin, white, or transparent films. Other items included tires, carpet, clothing, geotextile, plastic sheeting, Styrofoam, and bottles, among others. In contrast, river waters collected over a range of discharge conditions at multiple sites revealed that microplastics were dominated by black, blue, and purple fibers (>95% of total) and were also abundant (ranging from ~1 to 30 items/L). Preliminary results from simple shaker experiments revealed that the majority of macro- and meso-plastic debris does not decompose to form such fibers. The exception was the occurrence of various types of fabric (rugs, clothing) and geotextile used in bank and stream restoration projects, both of which produce significant quantities of fibers. An additional source of likely importance was the atmospheric deposition of fibers. Bucket collectors found that microplastics were deposited over an adjacent area in western North Carolina at rates of about 10 to >200 items/m²/day and were dominated by black and blue fibers.