We intuitively know that much of the plastic litter on our city streets will be carried by stormwater runoff to our creeks and rivers. We also know that macro plastic breaks down into microplastics (< 5 mm) and that researchers have found elevated levels in freshwater and marine waters across the globe.
Unfortunately there is little peer reviewed research into the direct link between stormwater runoff and microplastic levels in river and coastal bays.
Two California microplastic studies conducted by Algalita Marine Research Foundation (link) conducted in 2000 – 2001 demonstrate the role that stormwater runoff plays in Southern California coastal water and shows why we need aquatic microplastic research  in the Schuylkill – Delaware Basin.
Here are images of the 2 papers:
