Wednesday, 04 November 2020
An international research project has discovered that sediments and mangroves are trapping much of the plastic that ends up in the world oceans.
Edith Cowan University has contributed to an international research team led by King Abdullah University of Science and Technology (KAUST) scientists, who have demonstrated a pattern of plastic sedimentation gleaned from core samples collected from the Red Sea and Arabian Gulf.
Global plastic production began to rise precipitously around 1950. Since that time production has grown at around 8.5 per cent annually. Unfortunately, due to poor recapture and recycling globally, much of that plastic has ended up in the world’s oceans.
Strangely, locating plastic with surveys of the world’s oceans has proven difficult. In fact, plastic has been conspicuously absent in surface waters, where only 1 per cent of the expected stock is found.
Sediment samples analysed by the research team align closely with the history of global production of plastics, a trend that has increased exponentially since the midpoint of the 20th century.
Mangroves are highly efficient at sequestering carbon and have increasingly come to be referred to as Blue Carbon habitats.
They are also, according to the team’s research, highly efficient at locking up microplastics in coastal soil as well.
“Our research brings light to the mystery of missing marine plastic to reveal that mangroves, Blue Carbon habitats, are hugely efficiently at trapping plastics and burying them in their soils where they cannot harm vulnerable marine life or their human consumers” said Carlos Duarte, KAUST professor of marine science who supervised the research.
Plastic waste is durable. It does not degrade fully, but rather, accumulates in the environment over time. These properties have long been at odds with the low concentrations of plastic found in surface waters.
Recent research has shed light on how marine organisms ingest a small portion of global plastic waste. And it is widely reported that marine plastics wash up on global shores in large quantities.
But these forces still do not account for most of the plastic that has been released into the environment over the decades.
“The burial of plastic in mangrove sediments has increased at a pace similar to the global plastic production, indicating that the plastic that was sequestered by mangrove sediments since the 1950s has persisted there for decades,” said lead author Dr Cecilia Martin from KAUST.
The scientific community long postulated, and now has strong evidence thanks to this research, that “burial in sediments is thought to be the major sink of plastics in the marine environment.
The signature of plastics in the sediment record provides stratigraphic evidence that, since the mid-20th century, we have entered a new epoch, the Anthropocene,” or the era of man, according to the paper’s introduction.
Professor Pere Masque led the contribution by the Environmental Radioactivity Laboratory of the Centre for Marine and Ecosystems Research at Edith Cowan University.
“We use radioactive isotopes that are naturally occurring in the environment, namely Pb-210, to model the rate at which sediments accumulate in the sea floor,” said Professor Masque.
“This allowed us to calculate the rate at which microplastics have been deposited in the sediments of the region during the last decades.”
The project was a collaboration between KAUST, Edith Cowan University, Universitat Autònoma de Barcelona, The UN International Atomic Energy Agency, Aarhus University, King Fahd University of Petroleum and Minerals and Imam Abdulrahman Bin Faisal University.
The research paper “Exponential increase of plastic burial in mangrove sediments as a major plastic sink” can be read in full on the Science Advances website.
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