Microplastic Particles in Dust-on-snow, Upper Colorado River Basin, Colorado Rocky Mountains, 2013-16

Atmospheric dust deposited to snow cover in the Upper Colorado River basin, Colorado Rocky Mountains, was examined for the types of particulate matter that absorb solar radiation thereby advancing the onset and accelerating the rate of snow melt, effects that challenge management of downstream water resources. In each of 38 samples (14 sites) from the last remaining dust layer during the melt season (late spring) of 2013-16, microplastic filaments and fragments were identified by size, shape, and color, and their relative amounts were estimated visually using stereomicroscopy and a novel technique in imaging spectroscopy. The most common forms of observed microplastic were translucent filaments, typically 10 µm in diameter and as long as 0.5 mm; blue, red, green, and black filaments were also present. Among the many sources of microplastics is road-tire wear. Some of the microplastic particles in dust-on-snow were identical to those in samples of road dust collected from asphalt highways. Estimated amounts suggested relatively more microplastic deposition during snow accumulation in 2015 and 2016 compared with deposition during 2013 and 2014. Examination of subsequent dust-on-snow layers will determine interannual variation in microplastic abundance, test for trends in such abundance, and elucidate the possible role of microplastics for diminishing snow-surface albedo in the Upper Colorado River basin using spectroscopic techniques.