SEABIRDS are often found with stomachs full of plastic, and now researchers in the US think they know why – degrading plastic smells like food to them.
Albatross, petrels and other so-called tube-nosed seabirds rely on their sense of smell to find food, and one of the main olfactory cues is dimethyl sulphide, a compound released by algae when it is being eaten by a type of small, shrimp-like creature called krill. Krill are a major food source for seabirds, and this chemical produced by krill eating is the birds’ clue as to where to find them. The researchers at the University of California, Davis, led by Matthew Savoca, found that three of the most common types of plastic, high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP), release dimethyl sulphide when they begin to decompose, leading birds to think the plastic is food and eat it. The seabirds that use the smell of dimethyl sulphide to feed have previously been shown to be six times more likely to eat plastic than birds which use other methods to find food.
Savoca and the team in the UC Davis ecology group took samples of the three types of plastic and placed them in specially sewn mesh bags which were left in the sea for three weeks. The researchers used an unusual method to determine what was attracting the birds to the degrading plastic – a chemical analyser in the UC Davis Department of Viticulture and Enology used for analysing flavour and scent compounds given off by wine. The analyser picked up the dimethyl sulphide, and the researchers found that it was being emitted by biofilms of algae on the surface of the plastic.
An analysis in 2014 suggested that 250m t of plastics are suspended in the world’s oceans, and plastics have been found in the stomachs of fish, turtles and marine mammals, as well as birds. As more plastic is used and discarded, the problem is likely to get worse. Savoca has called on chemists and chemical engineers to help tackle the problem.
“First, perhaps there is some way to physically alter the surface of plastic materials to make them less habitable environments for biofouling, since it is indeed the biofouling of marine plastics by algae that gave our plastic samples their signature dimethyl sulphide odour. Second, if there is a way to produce plastics that harmlessly biodegrade and/or can be consumed by microorganisms like bacteria, with no ill effects to the microorganisms themselves, that could also be a good direction for the plastics industry to focus on,” he told The Chemical Engineer.
Science Advances DOI: 10/bsz7
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