Historical microplastic records in marine sediments: current progress and methodological evaluation

Plastic production has increased continuously since its massification in the 1950s. Microplastics (MPs), plastic particles smaller than 5 mm, are contaminants widespread across all environmental compartments, including remote ecosystems. Thus, MPs could serve as geological proxies of the Anthropocene, a proposed geological epoch characterized for the human-derived influence on the environment. MP investigation in sedimentary records requires specific sampling and analytical procedures exclusive to this line of research. Failing to properly conduct one or many of the standardized procedures compromises the veracity of the data obtained. In the present review, we assessed the current advances and notorious results in studies investigating MPs in the sedimentary record, a recent area of research. Also, a method-based diagnosis was conducted by critically analyzing the sampling and dating, MP extraction, polymer identification, and contamination prevention steps. We aimed to provide recommendations to future research based on critical analyses of the current state of the art and to present prospective outlooks regarding MPs as geological markers of modern civilization.