Sewage plants also contribute to plastic pollution in the oceans, because they use plastic pellets known as Bio-Beads in wastewater treatment that spill into the UK’s coastal waters.

https://www.theguardian.com/environment/2017/nov/03/dramatic-rise-in-plastic-seabed-litter-around-uk


Dramatic rise in plastic seabed litter around UK

Average of 358 items per square kilometre found in 2016, of which more than three-quarters were plastic