Fine MPs of 0.3 to 5 mm that have flowed into the marine environment have been viewed as a problem due to their impact on the ecosystem, such as being accidentally ingested by marine organisms. Long-term records of past MP contamination are necessary to predict the future impact of MP, but there is no data that continuously records the situation before the dawn of MP research (2000s) at the same point, and there is no reliable data. There has never been a sufficient stratigraphic record of MP.

　Therefore, from 2017 to 2019, this group collected multiple columns of seafloor sediment at a depth of 70m in Beppu Bay, extracted MPs, and estimated the age of the sedimentary layer of the sediment.

　As a result, the amount of MP deposition from 1940 to 2015 was clarified with the highest level of precision in the world based on accurate dating.The first MP was found in the 1958-1961 sedimentary layer during the high growth period.From then until 2015, the amount of MP deposition gradually increased while fluctuating in a 20-year cycle.It is speculated that phytoplankton in seawater is involved in this 20-year variation. It was confirmed that the amount of phytoplankton in seawater was also high during the periods when the amount of MP deposition was particularly high (around 1970, around 1990, and around 2015). The sedimentation of MPs is thought to be promoted by the formation of biofilms) and the capture of MPs by various aggregates such as feces.

　The history of MP pollution over the past 75 years revealed in this study is useful for constructing a computational model for future prediction of MP pollution.In addition, the appearance of plastic in the stratum is a clue to the arrival of the geological epoch known as the "Anthropocene," in which man-made materials spread for the first time on a global scale. Attention.

Paper information:[Science of The Total Environment] A 75-year history of microplastic fragment accumulation rates in a semi-enclosed hypoxic basin