“We need a text that addresses the issue of legacy, of existing pollution, which will wash up on our shores even after we turn off the famous plastic tap.”This is what Inger Andersen, director of the United Nations Environment Programme (UNEP), has just said about the future international treaty on plastic (SudOuest with AFP, September 23, 2024).
Indeed, annual plastic production has more than doubled in twenty years to reach 460 million tonnes, and could triple by 2060 if nothing is done (Organisation for Economic Co-operation and Development, February 2022).
“Some of this plastic is released into the ocean, where it degrades into microplastics.”underlines Suppakarn Jandang in a press release from Kyushu University in Japan. A professor at the Institute of Applied Mechanics, he is the first author of a study published in the journal Science of the Total Environment (September 18, 2024).
Extracting microplastics from coral samples
He and his colleagues at Chulalongkorn University in Thailand wanted to explore the fate of particles resulting from the fragmentation of waste in the marine environment, and thus contribute to solving the mystery of the “missing plastic” in the oceans. Their hypothesis: some of the “microplastics” would actually accumulate in the organism of coral, this reef-building animal.
“Coral has three main anatomical parts: the surface mucus (exterior of the body), the tissue (internal part) and the skeleton, that is, the hard deposits of calcium carbonate that the animal produces”explains Professor Jandang. “Our first step was to develop a way to extract and identify microplastics from our coral samples.”
On the coastal reefs of Si Chang Island in the Gulf of Thailand, the researchers collected and studied some 27 coral samples from four different species. After a series of chemical washes to “break down” each anatomical layer of the coral before filtering out its contents, they counted a total of 174 microplastic particles.
Most of these particles were between 101 and 200 μm in size, close to the width of a human hair, the study details. Their distribution was as follows: 38% in surface mucus, 25% in coral tissues, and 37% in the coral skeleton. Nylon, polyacetylene and polyethylene terephthalate (PET) were the three most common types of materials.
A “plastic well” for hundreds of years?
According to these worrying results, coral could represent a “sink” of plastic in the ocean, like trees absorbing atmospheric CO2 and sequestering part of the carbon in their wood and roots. However, further studies will be necessary to verify the importance of this coral sequestration on a global scale, compared to other possible accumulation sites.
“Since coral skeletons remain intact after death, these deposited microplastics can potentially be preserved for hundreds of years, much like mosquitoes trapped in amber”compare Suppakarn Jandang.
“We do not know the effects of microplastics on the health of corals and the entire reef community. Much more work needs to be done to accurately assess the impact of microplastics on the ecosystem.”adds Professor Atsuhiko Isobe, who led this work (press release).
Previous work had also pointed to the existence of a “plasticrust”, a fusion of plastic and coral which releases dangerous contaminants into the ocean.
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