Neuston samples were collected at 21 stations during an ~700 nautical mile (~1300
km) expedition in July 2012 in the Laurentian Great Lakes of the United States using
a 333 μm mesh manta trawl and analyzed for plastic debris. Although the average abundance
was approximately 43,000 microplastic particles/km², station 20, downstream from two
major cities, contained over 466,000 particles/km², greater than all other stations
combined. SEM analysis determined nearly 20% of particles less than 1 mm, which were
initially identified as microplastic by visual observation, were aluminum silicate
from coal ash. Many microplastic particles were multi-colored spheres, which were
compared to, and are suspected to be, microbeads from consumer products containing
microplastic particles of similar size, shape, texture and composition. The presence
of microplastics and coal ash in these surface samples, which were most abundant where
lake currents converge, are likely from nearby urban effluent and coal burning power
plants.