Plastic Debris in 29 Great Lakes Tributaries: Relations to Watershed Attributes and Hydrology

Plastic debris is
a growing contaminant of concern in freshwater
environments, yet sources, transport, and fate remain unclear. 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. Tributaries were sampled three
or four times each using a 333 μm mesh neuston net. Plastic
particles were sorted by size, counted, and categorized as fibers/lines,
pellets/beads, foams, films, and fragments. Plastics were found in
all 107 samples, with a maximum concentration of 32 particles/m3 and a median of 1.9 particles/m3. Ninety-eight
percent of sampled plastic particles were less than 4.75 mm in diameter
and therefore considered microplastics. Fragments, films, foams, and
pellets/beads were positively correlated with urban-related watershed
attributes and were found at greater concentrations during runoff-event
conditions. Fibers, the most frequently detected particle type, were
not associated with urban-related watershed attributes, wastewater
effluent contribution, or hydrologic condition. 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.