A British research team exploring deep ocean trenches have found plastics in the digestive systems of organisms that live there. This is the first evidence that plastic has entered the deep sea food chain, suggesting that this ecosystem could become the final sink for marine plastic debris.

In 2018, a plastic bag was found at the bottom of the Mariana Trench, the deepest place on Earth at more than 7-miles deep. This is deeper than Mount Everest is tall. Now, plastics have also been found inside the organisms dwelling there. The research team studied amphipods, which are mini crustaceans a bit like shrimp that scavenge on the seafloor, detecting food odours using taste buds on their legs. The team’s findings, which were published in the journal Royal Society Open Science, were that more than 80% of amphipods had plastic fibres or particles in their stomachs, and that the deeper the organism was caught, the more fibres present. In the Mariana Trench, 100% of amphipods dissected had plastics within them.

What is worrying is that the team found plastics in amphipods across the globe, from Japan to Chile, suggesting that plastics have spread to all corners of the ocean. At the sea surface, forces such as wave action and UV radiation can break plastic down but in the deep ocean this does not occur. It has been suggested that these deep ocean trenches could become the final sink for marine plastic, with nowhere else to go. As one scientist put it: ‘what you put in the trench stays in the trench’.

The amphipods studied are near the bottom of the food chain, and are eaten by larger fish, which are eaten by even larger predators and so on. As the amphipods contain plastics, these contaminants will be passed onto predators when the amphipod is eaten, so it is expected that plastics are spreading throughout the food chain. Is this a problem? That is the question which the researchers will address next, to see if the plastic ‘is causing any harm’. Previous studies have shown that toxins stick to and accumulate on plastics, which can have harmful effects on the organisms that ingest them such as changing hormone levels, altering gene expression and disrupting reproduction.

Research will continue, but as Anela Choy of the University of California said: ‘we certainly don’t need decades of further scientific study to necessitate more responsible behaviour and policies now’. Action is needed to stop plastic pollution at the source. This doesn’t necessarily mean that plastic is evil or shouldn’t be used, just that it doesn’t belong in the environment. We must be mindful of and clever with the ways that we use plastic, focusing on reducing use, recycling and reusing. Let’s not let the deep ocean become a plastic wasteland.

Author: Liz Heard