Practically every type of plastic material and plastic object we use today can be found there: cigarette filters, shopping bags, plastic bottles, stirring sticks for coffee, etc. Packaging makes up the majority of the litter. The most noticeable type are the patches that are so dense they cover the surface of the water, making them highly visible – like sheets and bags made of polyethylene.
Yet they, too, can eventually sink to the ocean floor when organisms settle on them. Though higher-density plastics like PVC, polyester and polyamide sink immediately, a great deal of plastic litter initially floats on the surface. The longer these plastics spend in the water, the more they are subjected to ultraviolet radiation from sunlight, and to the salt in the seawater. Battered into smaller and smaller pieces by the waves, the resulting fragments eventually break down into tiny particles ranging from only a few micrometres to one millimetre in size – which explains why they’ve been dubbed microplastics.
To better estimate and analyse the amounts of plastic litter and micro-particles, they are most often divided into different size classes: macroplastics (larger than 25 millimetres), mesoplastics (5 to 25 millimetres), large microplastic particles (1 to 5 millimetres) and small microplastic particles (micrometres to 1 millimetre).