Plastic not fantastic for marine life.

• Position: POLLUTION

Plastic litter can smother marine life, dramatically reducing the numbers of organisms in coastal marshes, and compromising the valuable ecosystem services they provide. In addition, the same negative effects are seen whether or not the bags are biodegradable. Those are the key messages to emerge from a collaborative study led by Dannielle Green, a fellow in the Biogeochemistry Research Group at Trinity College, Dublin, Ireland. Green is the lead author on a paper published in Environmental Science and Technology, which 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, prevented oxygen and nutrient flow, and blocked 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, such as clams and mussels. These species, in turn, are food for commercially important fish that feed within the marsh when the tide is in.

Because some of the animals affected during this study are known to be hardy and resilient to other types of pollution, other, more sensitive groups of animals, like those living in coral reefs, could be more strongly affected from smothering by plastic waste.

"The same effects were there regardless of whether the plastic in question was biodegradable or not," says Green. "Biodegradable plastics are produced because they are thought to be better for the environment because their persistence is shorter, but 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."

Adds coauthor Richard...