![]() The net mesh size was 333 μm, a commonly used size in microplastic studies. Samples were collected using a 1.5 m long neuston net with an opening 100 cm wide by 40 cm high (Sea-Gear Corp., Miami, FL, USA). The sampling methods and equipment were consistent with those previously used in the Great Lakes, (30) with some modifications for the river setting. Samples from each tributary were collected at least 1 week apart, and typically more than a month apart, to minimize serial correlation. All samples were collected during daylight hours. Runoff-event samples were triggered by observation of rainfall and snowmelt patterns in each watershed and verified by examination of the hydrographs (streamflow data from ref 32). Runoff-event conditions were defined as increased streamflow resulting from rainfall or snowmelt. Results from this study add to the body of information currently available on microplastics in different environmental compartments, including unique contributions to quantify their occurrence and variability in rivers with a wide variety of different land-use characteristics while highlighting differences between surface samples from rivers compared with lakes.Įach tributary was sampled three or four times, capturing low-flow and runoff-event conditions. Fibers, the most frequently detected particle type, were not associated with urban-related watershed attributes, wastewater effluent contribution, or hydrologic condition. Fragments, films, foams, and pellets/beads were positively correlated with urban-related watershed attributes and were found at greater concentrations during runoff-event conditions. Ninety-eight percent of sampled plastic particles were less than 4.75 mm in diameter and therefore considered microplastics. Plastics were found in all 107 samples, with a maximum concentration of 32 particles/m 3 and a median of 1.9 particles/m 3. Plastic particles were sorted by size, counted, and categorized as fibers/lines, pellets/beads, foams, films, and fragments. Tributaries were sampled three or four times each using a 333 μm mesh neuston net. This study characterized the quantity and morphology of floating micro- and macroplastics in 29 Great Lakes tributaries in six states under different land covers, wastewater effluent contributions, population densities, and hydrologic conditions. Plastic debris is a growing contaminant of concern in freshwater environments, yet sources, transport, and fate remain unclear. ![]()
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