Where does this plastic come from? And how does it end up in the seas? It is broadly accepted that 80% of plastic flows from land-based sources. The other 20% is plastic littered at sea, from fishing and shipping. Beyond this broad distinction, the sources of ocean plastic can become slightly more complicated.
From land to sea
It can be confusing to think that even litter from inland towns and cities is a source of ocean plastic. The crucial thing here is that the sea is downhill from all water sources, so litter entering rivers or waterways can quite easily reach the ocean. Take a plastic bottle in a town as an example. The bottle is put in a rubbish bin on the street, it blows from the trash can into the street and then into a storm drain, and from here it can enter a river and be carried out to the sea. There are numerous sources of land-based litter:
- Inland litter, from rubbish bins and storm water drains.
- Coastal litter, either items dropped directly on the beach, or through poor management of coastal waste. For example, overflowing bins where litter can easily be blown into the water.
- Leakage from waste management systems, e.g. landfill sites, especially those near rivers or the coastline.
- Sewage flushed straight into the water system, e.g. wet wipes or sanitary products that often contain plastic.
This all shows us that when we throw items "away", there really is no such thing.
Looking further at plastic waste from land-based sources, research by the Ocean Conservancy and McKinsey highlighted that plastic leakage in five countries studied could broadly be split into two types: uncollected and collected waste. Uncollected waste (e.g. litter left on streets or beaches) accounted for 75% and the remaining 25% was from collected waste that leaked back out from the waste management system. This could be due to the waste management system having insufficient controls in place or from storing waste in unfit locations, such as too close to waterways.
This study is just one example from around the world – ocean plastic is truly a global issue. The findings highlight that a crucial first step in managing plastic waste is establishing effective collection methods on land. What these methods look like is different around the world, but success is often seen in systems in which “waste” materials are given a value. For example, in a deposit return system, in which a refundable deposit is added to the price of a beverage, an empty bottle is no longer waste – it has a monetary value to be redeemed. It is a simple, but effective shift in thinking: from waste, to value.
A big proportion of the plastic that enters the ocean is larger items such as plastic bags, plastic bottles/lids, and food packaging. While these may enter as bigger items, we know that the plastic will degrade over time into tiny microplastics that can be hard to see, and harder to clean up. Indeed, one study from Eunomia has highlighted that barely 1% of marine plastics are found floating at or near the ocean surface, with an average global concentration of less than 1kg/km.