I was just looking at Charlie Moore's presentation about the alleged "Great Pacific Garbage Patch." The concept sounds really nasty until you look at the Wikipedia entry that contains the information that they go on about. It tends to prove that the ocean is really big and environmentalists are really nitpicky. The high concentration of garbage is about 3.34 pieces per "square meter" with an average weight of 5.1 milligrams per square meter. My calculator says that's 17.034 milligrams per square meter. I'm presuming that this is floating garbage and that there is little or nothing in between the surface and the depths. It either sinks or it floats.
One manufacturer of molds for bottle-caps says that their plastic bottlecaps weight 2.35 grams. The average mass figure is satisfied by a floating bottle-cap in every 138 square meters, one bottle-cap in a square about 33 feet on a side. If we actually do have this 17 milligrams per square meter, that's 17,000 kilograms per square kilometer, about 37,400 pounds. That sounds impressive except that a cubic meter of sea water weighs 1000 kilograms and a square kilometer of ocean, to a depth of a meter, weights 1,000,000,000 kilograms or 2.2 billion pounds. 17 milligrams of plastic in one billion milligrams (one cubic meter) of seawater equals 17 parts per billion plastic versus seawater in the notorious "garbage path" of the Pacific, and that's just going to a depth of one meter.
There is a lot of doom and gloom in the predictions but this has been going on for more than 20 years and there are still millions of albatrosses out there, the bird that seems most affected by the garbage. Perhaps we're just making a smarter albatross by weeding out those that can't tell food from garbage.
We're never really sure how thin the justifications are for a new "measure" proposed by the environmentalists until we actually run the numbers. This sounds thin to me.