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NEW study co-authored by a Plymouth University professor has revealed that discarded plastic bags – even biodegradable ones – are smothering marine life.The plastic litter has been found to dramatically reduce the number of organisms in coastal marshes, causing a knock-on effect on the surrounding eco-system.

The study, led by Dr Dannielle Green, of Trinity College Dublin was recently published in an academic paper and describes the worrying ecological effects of discarded plastic carrier bags.

The experiment showed that in just nine weeks, plastic bags smothered the surface of coastal sediment, preventing oxygen and nutrient flow, and blocking light.This caused a substantial reduction in the amount of 'microalgae' beneath the bags. These tiny algae form the base of the food webs in these habitats, which means their proliferation is important for animals higher up the food chain, including worms and bivalves, which, in turn, are food for commercially important fish that feed within the marsh during high tides.

Dr Green said: "The same effects were there regardless of whether the plastic in question was biodegradable or not.

"While biodegradable plastics are produced because they are thought to be better for the environment because their persistence is shorter, our study suggests that the rate at which they break down may not be fast enough to have any meaningful advantage over conventional bags in marine habitats."