PLASTIC DEBRIS: A GLOBALLY PERSISTENT ANTHROPOGENIC MARKER HORIZON IN THE SEDIMENTARY RECORD

Many tangible examples of human interaction with Earth’s natural systems have the potential to become preserved in the geologic record, but none may be as globally persistent as plastic debris. Plastic litter has been found in all oceans and along shorelines on every continent. The characteristics that make plastics so durable are also the aspects responsible for its lengthy degradation rates. Where readily exposed to UV radiation (photo oxidation) and mechanical erosion, such as on beaches, polymers become embrittled and break down into microscopic fragments. However, polymers that are buried in sediment have greater potential to remain intact and to become part of a global stratigraphic horizon marking the currently informal Anthropocene epoch. Plastiglomerate is an indurated substance composed of natural sedimentary grains, plastic debris and organic material agglutinated by melted plastic. Its formation on Kamilo Beach, HI and in other locations is a direct result of an anthropogenic action (burning) in response to an anthropogenic problem (plastics pollution). Combining plastic with natural sediment results in density increase of the polymer, thereby extending its residence time and enhancing burial potential. Similarly, plastic debris in lake and ocean bottom sediments has great potential to be preserved because it is shielded from UV radiation by overlying sediment and the water column, and is subjected to temperatures that are much cooler than those on land. Recent investigations have revealed abundant microplastics in bottom sediments of Lake Ontario, Canada, which indicates that anthropogenic debris is accumulating and being preserved in fresh water basin deposits. Considering the amount of plastics in aquatic-related habitats, combined with the debris that is regularly incorporated into soils at landfills and building sites, plastics may be the most widely distributed anthropogenic markers in Earth’s natural environments.