The topic of marine debris is well detailed in New York Sea Grant's fact sheet on"Microplastics" (pdf):
"For years people have worried about the environmental impacts from
plastics left behind in the oceans and Great Lakes,"
"Pictures
of birds tangled in six-pack rings or turtles choking on plastic bags
have documented the danger of discarded plastics that linger in the
environment."
Attention has since turned to small
plastic particles and microbeads that have been found in waterways, in New York and elsewhere, though.
"Some
plastic particles result from the breakdown of larger plastic items, but
others are small plastic spheres known as microbeads."
Microbeads, the tiny pieces of plastic commonly used in personal care
products, are showing up in waterways across the nation. These tiny
particles are considered potentially dangerous to the environment
because of their tendency to absorb toxins in the water and then get
consumed by fish and other organisms.
For more on the topic, click on the related "News" links to the left.