This is such a more complex topic that the mainstream press can deal with. Gord is right, the term "plastic" is so generic as to be useless in any evaluation of risk/benefit.
There are plastics that float, and some that sink. I seriously doubt the ones that sink to the bottom of the ocean are significantly more of an hazard that the silica in the sand, on the other hand they will be there a long time. Plastics that float stay in the "biosphere" longer, but are also more exposed to the UV degradation. If the plastic degrades from a "macro plastic" to a "micro plastic" it doesn't magically stop there. In fact, micro plastics are even less stable because they have such a huge surface area relative to volume.
Finally, one thing that is NEVER mentioned is that many "plastics" contain a LOT of non-plastic.. Some "plastics" contain more inorganic "filler" like calcium carbonate ("limestone") or calcium sulfate (gypsum) than actual polymer, in the same way that our FRP boat
hulls contain a large fraction by weight of glass along with the plastic. In a lot of studies that try to do a material balance on plastic in the ocean this fact is ignored by people who really should know better.
Like so many things, the impact of plastics on the environment is likely to be MORE significant than presented by people who make their living making plastic, and just as likely to be LESS significant than presented by people who make a living from donations and research
grants. Always follow the money
We have been on a lot of remote
leeshores in the world. And there is a lot of plastic washed up, which I have to assume is a reasonable sample of the macro bits of plastic in the ocean. Commercial fishing gear
is the most common by volume, shoes are probably the single
most common consumer item. Despite looking, we have never, ever, seen a single
plastic drinking straw. That is a silly place to waste effort at reducing pollution. It is a classic
of making people feel good without having a useful impact.