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Plastic, the new natural stone?

Marine biologists at the Marine and Environmental Research Center (MARE) on the Portuguese island of Madeira reported on “plasticrust”, a veneer of plastic encrusted on shoreline rocks.

Plastic waste is everywhere. Cities are littered with bottles and wrappers, and the same goes for nature, whether it is on land or in the ocean. And while we don’t deal with it, the earth does it in the way it knows best: by absorbing it into its system. Birds and bees have been known to use the material to make warm nests, but it is not just animals that recycle plastic, it is also absorbed into the crust of the earth.

Back in 2006, a sea captain and oceanographer for the Algalita Marine Research Institute in California called Charles Moore discovered stone that contains mixtures of sedimentary grains and other natural debris, held together by hardened molten plastic.

Plastiglomerate, as the material is dubbed, is formed along shorelines where natural sedimentary grains and organic debris are glued together by molten plastic created probably during campfire burnings. The material has been found on Kamilo Beach on the island Hawaii. Whether or not the material will become part of sedimentary record is cause for speculation, as some geologists and geophysicists think that the material mat revert back to a source of oil in the right conditions.

Plasticrust, on the other hand, is not created by heat and pressure. Discovered by Ignacio Gestoso, a marine biologist at the MARE, first noticed the veneers on Madeira’s shoreline rocks, resembling old, light blue chewing gum. With his team, Gestoso found more crusts, in different colours, and they collected samples.

Over three years, the crusts went from a single sighting to covering nearly 10 per cent of the rocks’ surfaces. The material is made of polyethylene, one of the most common single use plastics.

The crusts likely originate from the crash of plastic pieces against the rocky shore, where the plastic stays behind like a crust on the coarse surface, similarly to algae or lichens.

Not only are plastiglomarate and plasticrust evidence of the Anthropocene – the proposed epoch dating from the commencement of significant human impact on Earth’s geology and ecosystems – especially plasticrust has a larger impact. The plastic veneer is slowly replacing natural biological crusts on the rocks. These surfaces are the home to species that eat algae or lichen, like sea snails and barnacles, which ingest the plastic through the algae on top. As we know from the many stories of dead marine creatures, from seagulls to whales, with stomachs filled of plastic, this cannot be good news.

Gestoso and his team are still researching the potential risk the plasticrust poses, as well as how widespread the problem is.

Photos: Ignacio Gestoso / Aaikevanoord

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