The fate of micro plastics in the most fiery ocean

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The fate of micro plastics in the ocean: they finally went to the bottom of the sea. On October 8, Beijing time, according to foreign media reports, the ocean contains a large number of particles from organisms, including living or dead plankton and their excreta. These so-called biogenic particles interact and often form clumps (known academically as "aggregates"), many of which sink directly to the seafloor. In addition to these natural particles, there are also a large number of plastic particles with a size of less than 5mm in the ocean (i.e. micro plastics in the face of fluctuations in the vanadium market). These particles have existed in the ocean for a long time

▲ biofilm formed by bacteria and microalgae on the surface of marine microplastics. The samples were collected in Kiel Fjord, Germany, and imaged by confocal microscope

although new microplastics continue to enter the ocean, and some kinds of plastics float on the sea surface due to their low density, the concentration of microplastics on the sea surface is often lower than originally expected. In addition, microplastic particles have been found many times in deep-sea sediments in recent years. What has happened to the micro plastics on the ocean surface? How did they sink deeper? Jan Michels, a member of the cluster of excellence "the future ocean" in Germany and the first author of the study, said: "our hypothesis is that micro plastics form polymers together with biogenic particles in seawater, and these polymers are likely to sink to a deeper water layer." The research was published in the recent proceedi3 of the Royal Society B

to test this hypothesis, the researchers used polystyrene beads with a size of 700 to 900 microns to observe the agglomeration behavior of these beads in the presence or absence of biogenic particles. The experiment gives clear results. Anya &mid, head of the research team of the Helmholtz Kiel Oceanographic Research Center (geomar) in Germany, this experimental machine is designed and manufactured dot according to the relevant standards of gb/t328 (2) 007 series; Anja Engel described that "the presence of biogenic particles is crucial to the formation of polymers. Although microplastic particles hardly aggregate alone, they can form very obvious and stable polymers with biogenic particles within a few days."

"in addition, we hypothesized that biofilms on the surface of microplastics play a role in the formation of polymers," Michels explained. Michels led these studies while working at geomar and now works at Kiel University. Biofilms on the surface of micro plastics are formed by microorganisms, usually bacteria and unicellular algae, and are relatively viscous. In order to understand the impact of these microorganisms on the polymer, the researchers conducted a comparative experiment. One group used clean plastic beads, and the other group used plastic beads covered with biofilm. Michels said: "after only a few hours, the micro plastics covered with biofilm and biogenic particles formed the first polymer, which was earlier and faster than the micro plastics in the clean state at the beginning of the experiment." On average, 91% of the microplastics covered with biofilm were encapsulated in polymers after 3 days

"in the laboratory, if the micro plastics are wrapped by biofilm and there are biogenic particles at the same time, the micro plastics and biogenic particles will quickly form a stable polymer," Michels concluded. In many sea areas, the coexistence of a large number of biogenic particles and biofilms on the surface of micro plastics is likely to be very common. Professor Kai Wirtz of the Helmholtz Zentrum Geesthacht, a research participant, explained: "this is why the polymerization process observed in our laboratory experiments is likely to occur in the sea, which has a great impact on the transportation and distribution of micro plastics." In the future, scientists can further study these problems by collecting polymers in the ocean and then systematically analyzing the existence of micro plastics

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