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

In this review, the global deposition of microplastics across a variety of sedimentary environments is presented. Available literature was critically reviewed to investigate microplastic loading inventories in dated sediment and soil profiles. Even though field studies investigating microplastics in natural archives are scare, important information on the data generated from such studies is presented. We highlight that microplastics are not only readily mobilised within depositional settings, but they are also present in the workplace with researcher-derived microplastics frequently contaminating samples, stressing the need for rigorous laboratory procedures. Microplastics are commonly reported from sediments dated to before the onset of plastic production and the microplastic emissions' record in sediments is often incomplete. Data quality issues are also prevalent in microplastic sedimentation publications.

We found that 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. This paper contributes to a PhD research project where Dr. Amy Lusher, NIVA, is a co-supervisor. The PhD project of Jake Martin (NTNU, Trondheim, Norway) is investigating the role of microplastics in major coastal sedimentary processes, identifying potential accumulation `hotspots` and significant transportation pathways, whilst working towards optimising and harmonising methodological approaches in these complex environmental settings.