The study found concentrations of plastics of 3.34 pieces with a mean mass of 5.1 milligrams per square meter
But still that's about 20mg per square meter. Over a square km of ocean that is 20 tonnes, which sounds a lot more impressive. Assuming it extends to a depth of 1m there is about a million tonnes of water so that's 20 parts per million. Mercury thermometers have been banned for less!
So there you go, environmentalists, don't say I never do anything for you!