Results from the study: Experimental degradation of polymer shopping bags (standard and degradable plastic, and biodegradable) in the gastrointestinal fluids of sea turtles [1]

Biodegradable plastics – which can be plant or oil based – can contribute to a more sustainable use of plastic. The merits of the current generation of biodegradable plastics to mitigate plastic marine litter, however, are controversial. The reason is that the label biodegradable should not be understood as an invitation to carelessly dispose the material in the environment. In a controlled composting situation it will already take several weeks for biodegradable plastics to completely break down; seawater provides a much less favourable environment for degradation. Current generation biodegradable plastics therefore still form a threat to marine ecosystems if waste systems fail to keep this material ‘in the loop’.

A recent study by researchers from the universities of Freiberg (Germany) and Queensland (Australia) investigated just how big the difference is between standard and biodegradable plastics [1]. Not only in seawater, but also in the intestinal fluids of sea turtles, mimicking the fate of both types of plastics when ingested. Sea turtles mistake plastic bags for jellyfish, and are particularly vulnerable for plastic marine litter [2,3].

To assess the degradability of plastics the researchers recorded the loss in mass of different types of plastic shopping bags over a period of 7 weeks. In an industrial composting situation, this period allows for complete degradation of the biodegradable plastic. In seawater, however, the weight loss was only 3-9%. As one would expect, standard plastic does not degrade at all.

Above: Loggerhead turtle (credit: Damien du Toit).
Below: Green turtle (credit: Mila Zinkova)

So what happens in the intestines of the sea turtles? Again, standard plastic is not degraded, whereas the fate of the biodegradable plastics depends on the species of sea turtle. The herbivorous Green turtle has an increased capacity to digest biodegradable plastics relative to the carnivorous Loggerhead turtle. Still, in the Green turtle the digestion of biodegradable plastic is much slower than the digestion of the plant material that forms the basis of its diet. The authors therefore conclude that sea turtles do not digest biodegradable plastics rapid enough to prevent morbidity.

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[1] Müller, C., Townsend, K., Matschullat, J. (2011) Experimental degradation of polymer shopping bags (standard and degradable plastic, and biodegradable) in the gastrointestinal fluids of sea turtles, Science of The Total Environment, In press, doi: 10.1016/j.scitotenv.2011.10.069. <http://www.sciencedirect.com/science/article/pii/S0048969711012630>

[2] Wabnitz, C., & Nichols, W. J. (2010). Editorial: Plastic pollution: An ocean emergency. Marine Turtle Newsletter, 129, 1-4. http://www.seaturtle.org/plasticpollution/MTN129p1-4.pdf

[3] Wurpel, G., Van den Akker, J., Pors, J. & Ten Wolde, A. (2011). Plastics do not belong in the ocean. Towards a roadmap for a clean North Sea. Chapter 4, IMSA Amsterdam. http://www.plasticmarinelitter.eu/media/publications