Around 80% of marine litter starts on land and rivers help transport it out to sea. In this way, plastic pollution is not just a problem for the distant open ocean – it’s an issue on our doorstep.
There are currently no estimates for the amount of plastic in the Thames, but the world’s rivers are estimated to carry up to 4,000 kg of plastic out to sea every day. Despite much of the plastic in the Thames making it to the North Sea, a portion is permanently accumulating in the catchment.
After 20 river cleans on the foreshore of the Thames in 2019, nearly 9,000 plastic items were recovered, almost all of which were single-use. These were most often wet wipes, sanitary products and food packaging, which accumulate in the sediment or are deposited on the inside of bends in the river.
On the Thames foreshore at Hammersmith in early 2019, 23,000 wipes were collected, averaging 201 wipes per square metre. You may have heard of wet wipes forming “fatbergs” in sewers, but on the banks of the Thames there are wet wipe reefs that are slowly changing the shape of the river itself.
As part of my PhD, I’m researching the accumulation of microplastics in the Thames food web. When I trawl in the Thames for fish the nets are full of plastic, especially tangles of wet wipes. It’s extremely rare that we bring in a net with no litter at all.
Despite its murky appearance, the Thames is a diverse ecosystem that’s full of life. It supports over 120 species of fish as well as many marine mammals, such as grey seals, common seals, dolphins and porpoises. Microplastics in the river can be ingested by all animals in the food web. Negative impacts on one part of this system can potentially cause a cascade which affects other species.
Microplastics contain chemical additives which are released as they degrade and can act as harmful pollutants in water. These toxic chemicals can be transferred to organisms if they ingest them. This forces the animal to use their energy to treat the problem, rather than growing, feeding or reproducing.
The amount of plastic in an animal’s gut is likely to increase higher up the food web that the animal feeds. If amphipods near the base of the foodweb ingest a few pieces of plastic then fish eating large numbers of amphipods would gradually accumulate more as they feed. Seals at the top of the foodweb, which ingest lots of fish, would be exposed to a greater concentration still.
During my research I found that 80% of all plastic extracted from animals was fibres. which originate from our fabrics. Although wastewater treatment plants catch the majority of these fibres, a significant number are still entering the river and making their way out to sea.
We may rightly fret about the impact of our plastic on life in the ocean, but it’s time we realised that the plastic pollution crisis is a lot closer to home than we care to think.
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