IMPLICATIONS OF SITE SPECIFIC, SHORT-TERM SPATIAL AND TEMPORAL VARIATIONS IN MICROPLASTIC CONCENTRATIONS TO SAMPLE COLLECTION, RICHLAND CREEK, WESTERN NORTH CAROLINA

Microplastics (MPs), pieces of plastic polymers <5 mm in size, represent a contaminant of emerging concern on a global scale. However, the analysis of MPs in freshwater environments is still in its infancy. In fact, widely accepted protocols for the collection and analysis of water samples have yet to be developed. Such protocols required a sound understanding of (1) the spatial distribution of MPs in stream waters at a cross-section at the moment of sampling, and (2) the short-term variations in concentrations at a given point in the cross-section. During this study, the short-term spatial and temporal variations in the concentrations and character (color, shape, composition) of MPs were investigated at multiple sites along Richland Creek, a headwater basin in the southern Blue Ridge Mountains of western North Carolina. MP concentrations ranged from 0 to ~57 MPs/L, about 90 % of which were dark-colored (black, blue, red, purple) fibers. These are some of the highest concentrations reported worldwide in rivers and lakes. The simultaneous collection of multiple samples at differing water depths and locations across the channel showed that MP concentrations were spatially variable (with sample differences often exceeding an order of magnitude) at any given time. Samples collected with ISCO automated samplers from a single point in the channel at ~1-minute intervals were more consistent, but characterized by frequent outlier concentrations. We hypothesize that the observed variations in concentration are due to differences in MP compositions and density (which range above and below that of water, 1 g/cm³) as well as to the agglomeration of MPs with natural mineral and organic matter such that multiple MPs were associated with a single particle. The collected data illustrate the need for composite sampling that spatially collects water from multiple depths and locations across the channel during the collection of grab samples, and that temporally combines water collected at differing times over a relatively long timeframe from a single point in the channel.