The scale of the ocean-plastic problem is hard to process. Eight million tonnes of plastic ends up in the ocean every year, washing up on beaches, choking, entangling and poisoning fish, birds and mammals. Most of it bobs in five giant ocean garbage patches. By some estimates, the largest one, in the north Pacific, could cover Canada. And then there’s micro-plastics, the tiny fragments broken off bigger pieces, washed off synthetic clothing and from facial scrubs.