A review of the use of microplastics in reconstructing dated sedimentary archives

Buried microplastics (plastics, <5 mm) have been documented within the sediment column of both marine and lacustrine environments. However, the number of peer-review studies published on the subject remains limited and confidence in data reliability varies considerably. Here we critically review the state of the literature on microplastic loading inventories in dated sedimentary and soil profiles. We conclude that microplastics are being sequestered across a variety of sedimentary environments globally, at a seemingly increasing rate. However, microplastics are also readily mobilised both within depositional settings and the workplace. Microplastics are commonly reported from sediments dated to before the onset of plastic production and researcher-derived microplastics frequently contaminate samples. Additionally, the diversity of microplastic types and issues of constraining source points has so far hindered interpretation of depositional settings. Therefore, further research utilizing high quality data sets, greater levels of reporting transparency, and well-established methodologies from the geosciences will be required for any validation of microplastics as a sediment dating method or in quantifying temporally resolved microplastic loading inventories in sedimentary sinks with confidence.