Beijing, China

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A strange and new kind of rock containing plastics has been found across the globe. They are deposits mainly formed by compressing rock and plastic polymers discarded by humans. So far, these plastic rocks have been found on the coast and inland in 11 countries across five continents. 

These bizarre plastic rocks are an alarming sign of global plastic pollution. A researcher told Newsweek that these rocks are harmful to ocean sustainability and human health. 

What are these plastic rocks called?

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There has been a debate among the scientific community about what to call these plastic rocks. Among the various terms proposed, there are "plastistone," "plastiglomerate," "plasticrust," "plastitar," "plastisandstone" and "anthropoquinas." These different terms describe how the plastic rocks develop in specific ways. 

First samples of plastic rocks

Geologist Patricia Corcoran reported the first example of a plastic rock nearly a decade ago in Hawaii and termed it "plastiglomerate."

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Deyi Hou, the author of a recent paper, Plastistone: An emerging type of sedimentary rock, said, "Molten plastic, sand grains, clasts from rock, coral, shells, and wood debris were held together after campfire burning on Kamilo Beach, Hawaii, USA." However, the paper called these plastic rocks "plastistones."

Hou, an associate professor of environment at Tsinghua University in China, added, "Since then, they have been frequently found on beaches, both on islands and mainland coastlines."

Hou and his team were the first to report the discovery of plastic rocks in the inland region. They were also the first to mention the chemical bonding between plastic and rock. Their most recent review summarised that plastic rocks exist across five continents and 11 countries. 

How are plastic rocks formed?

Hou and his team explained that plastic rocks can form via a wide range of methods. "Burning is a commonly proposed mechanism, where plastic debris is melted during campfire or waste burning and then held within the mineral matrix when it cools down," Hou said.

He added, "When waves crash against intertidal rocks, plastic debris from maritime sources can become physically adhered to the rock surface."

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Another way these plastic rocks form is when oil that contains a massive amount of plastic reaches a beach after a leak. This material attaches firmly to the host rock matrix and then undergoes partial evaporation and solidification process, Hou explained.

"Finally, our study found that chemical binding contributed to plastistone generation in an inland region," said Hou. According to their hypothesis, sunlight irradiation causes plastic oxidation, leading to chemical binding between the plastic and rock material. 

Plastic rocks have been found in Bangladesh, Brazil, China, Hawaii, India, Italy, Japan, Peru, Portugal, the Spanish Curry Island and the United Kingdom. 

Plastic pollution has become a complex problem

Gabriel Enrique De-la-Torre, a plastic pollution researcher at Universidad San Ignacio de Loyola in Peru, said, "Plastistone has emerged as a new term to describe plastics that have been incorporated into rocks." This will alter the fate of plastics in the environment, he said. "All in all, these findings show how complex the problem of plastic pollution has become," he added. 

However, the direct reason behind the formation of plastic rocks is the plastic pollution humans are pouring into the environment. According to the study, humans contribute roughly 22-48 million metric tonnes annually. "From a geologic perspective, the mass of plastic deposited by modern human beings is not trivial," Hou and his team wrote.

Furthermore, he believes that these plastic rocks will continue to increase as a part of natural geographical processes and stick around for a long time. They are likely to increase in places where plastic pollution is worse, like cities, mulched agricultural soils, and plastic waste dumping sites. 

"Plastistones can be made from a variety of plastic wastes. Plastic bags, bottles, fishing gear, maritime ropes, and agricultural mulching films can undergo lithification with rocks, giving rise to the formation of plastistones," Hou said.

How are plastic rocks harmful to us?

According to the study, plastic rocks alter the microbial communities within the soil and neighbouring environment. This way the plastic rocks directly affect the local ecosystems. 

"We observed a lower microbial diversity in the plastistone compared to the adjacent soil. Furthermore, we identified several microorganisms that showed a preference for colonising the plastistone," Hou said. However, the potential ecological risks associated with the phenomenon are still unexplored.

But the most dangerous fact about these plastic rocks is that they shed microplastics, tiny pieces of pollution which have spread across the globe and even into human and animal bodies. 

"The occurrence of plastiglomerate in pristine coastal islands such as those found in India increases the possibility of release of microplastic as well as associated chemical forms from the same due to weathering and waves," biogeochemist professor Punyasloke Bhadury of the Indian Institute of Science Education and Research told Newsweek.

"The released microplastic will end up in the ocean, reaching higher trophic levels such as marine mammals and humans through predominantly edible fish," he added. 

(With inputs from agencies)