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Downward migrating microplastics in lake sediments are a tricky indicator for the onset of the Anthropocene
Summary
Researchers studying lake sediment cores in northeastern Europe found that microplastics had migrated downward through sediment layers over time, appearing in layers that predate the era of plastic production. This means microplastics cannot be used as a reliable geological marker for the start of the modern era (Anthropocene), because the particles move through sediment rather than staying in place. The finding also highlights that microplastics can travel deeper into soil and sediment than previously assumed, potentially reaching groundwater.
Plastics are a recent particulate material in Earth's history. Because of plastics persistence and wide-range presence, it has a great potential of being a global age marker and correlation tool between sedimentary profiles. In this research, we query whether microplastics can be considered among the array of proxies to delimit the Anthropocene Epoch (starting from the year 1950 and above). We present a study of microplastics deposition history inferred from sediment profiles of lakes in northeastern Europe. The sediments were dated with independent proxies from the present back to the first half of the 18th century. Regardless of the sediment layer age, microplastic particles were found throughout the cores in all sites. Depending on particles' aspect ratio, less elongated particles were found deeper, while more elongated particles and fibers have reduced mobility. We conclude that interpretation of microplastics distribution in the studied sediment profiles is ambiguous and does not strictly indicate the beginning of the Anthropocene Epoch.