Chinese researchers discover plastic waste chemically bonded to rocks

17 Apr 2023 --- Chinese researchers at Tsinghua University, Beijing, have found plastic films chemically bonded to rocks, marking a discovery of a new type of plastic material in the environment.

Deyi Hou, one of the study’s authors and soil and groundwater scientist, said the research is the first to uncover chemical bonds between plastic and rocks in the environment. 

The plastic rock complexes form when debris irreversibly absorbs into a rock after a flood. The complexes comprise LDPE or PP films stuck onto quartz-dominated mineral matrices.

The study writes that “future research should evaluate this phenomenon regarding ecosystem fluxes, fate and transport and impacts of plastic pollution,” indicating that more research is needed to draw concrete conclusions about the plastic rocks. 

Plastic films found integrated into rocks (Image credit: Deyi Hou & Liuwei Wang/Tsinghua University).Newfound plastic rocks
The study was published in Environmental Science and Technology. The source of the plastic waste was accumulated around a creek in Hechi City, China. The plastics discovered were PP and PE films.

The plastics became chemically bonded to the rocks through carbon atoms at the surface of the PE films connected to silicon in the rock with the help of oxygen atoms.

The scientists believe the bonding between the plastic films and rocks was driven by ultraviolet light from the sun or by the metabolic activity of microbes living on the plastic rocks. 

However, the PP films appeared to be attached to the rocks by physical forces, not chemical bonds.

“People in the twentieth and twenty-first century are creating new geological records,” Hou says to Nature.

Plastics in China 
Rocks such as these could leak microplastics into the environment. To test the potential damage, the researchers detached parts of the films and exposed them to wet and dry cycles to mimic the creek’s periodic floods. 

The team found rates of microplastic generation greater than reported in lab tests mimicking plastic shedding in landfill, seawater and marine sediment.

According to reports, China is the world’s biggest producer and consumer of plastics. The country is also the largest producer and exporter of single-use and virgin plastics. 

Additionally, in 2020, China produced about 60 million metric tons of plastic waste, of which 16 million metric tons were recycled, according to the China National Resources Recycling Association. Rocks bonded with plastic were discovered in a creek in Hechi City, China.

According to The Value of China’s Legislation on Plastic Pollution Prevention in 2020 report, on average, about 17% of the used plastic in China is recycled. 

China has also been accused of being the biggest contributor to marine plastic waste, while other studies have named the Phillippines the largest. The large amounts of ocean plastics can be attributed to the countries’ waterway systems that lead directly into the oceans.  

Brazil’s plastic rocks
Last month in Brazil’s volcanic Trindade Island, Fernanda Avelar Santos, a Federal University of Parana geologist, discovered rocks made from plastic debris. 

“This is new and terrifying at the same time because pollution has reached geology,” says Santos.

The island is located 1,140 km (708 miles) from the southeastern state of Espirito Santo, which researchers say is evidence of humans’ growing influence over the earth’s geological cycles.

The rocks made of a mixture of sedimentary granules and debris held together by plastic were called “plastiglomerates.” The pollution was identified to have mainly come from fishing nets. 

Santos told Agence France-Presse she was “disturbed” and “upset” to make the discovery.

By Sabine Waldeck