What rejecting the Anthropocene means for the microplastic research community?

It is well known that the Anthropocene Working Group proposed the addition of the Anthropocene as a time interval to the International Chronostratigraphic Chart (ICC). Despite the existence of a substantial body of evidence pointing to the end of the Holocene epoch and the subsequent entry into the Anthropocene, the proposal was formally rejected by a vote of the members of the Subcommission on Quaternary Stratigraphy in March 2024. Following this rejection, a significant number of studies have continued to be published within the Anthropocene, and the scientific community has continued to use the term. Microplastics which have been in manufacture since around the mid-20th century, are regarded as potential indicators of the Anthropocene strata. Microplastics, which have been manufactured since around the mid-20th century, are considered potential indicators of Anthropocene stratigraphy. Microplastics are characterised by their small size (< 5 mm) and variability in physical and chemical properties. This includes variations in size, shape, colour, polymer type and chemical additives. They are characterised by a long lifespan in ecosystems, which is in line with other novel materials (e.g. concrete) and chemical compounds (e.g. persistent organic pollutants) that are recognised markers in the context of the Anthropocene. However, it is not straightforward to integrate microplastics with other established markers in the context of the Anthropocene. For example, the identification of microplastics within sedimentary layers is challenging. Visual analysis alone has been shown to consistently overestimate the number of microplastics, as it is difficult to distinguish them from natural particles. When spectroscopic techniques (e.g. FTIR, Raman) are used, identification is dependent on the libraries used for identification. Potential post-burial changes in polymer chemistry, for example, can lead to misinterpretation of results. In general, the failure of microplastic researchers to consider the taphonomic processes that control the pathways of microplastics after they reach the sea, as well as the diagenetic processes after their deposition and burial, leads to a simplification of the expected profiles of microplastics in sediments. Thus, there are a number of issues that remain to be explored within the microplastics-Anthropocene issue. Taken together, they have the potential to improve our understanding of the use of microplastics as markers of the Anthropocene. The rejection of the Anthropocene for formal inclusion in the ICC provides an opportunity for the microplastics scientific community to explore the issue in depth and ultimately accept microplastics as indicators of the Anthropocene when it is reconsidered for formal inclusion in the geological time scale.