The use of microplastics as a reliable chronological marker of the Anthropocene onset in Southeastern South America

Microplastics (MPs) represent an emergent contamination marker. For this reason, we analyzed the vertical distribu-tion of MPs in six sediment cores retrieved from the Patos-Mirim System, the world's largest coastal lagoonal system. The sediment cores span from mid Holocene to present times according to both radiocarbon and lead dating and are located close to both urban/industrial and agricultural regions. We identified a basal pre-disturbance MP-free zone in all cores and an uppermost contaminated 70-cm-zone, where a general increasing trend in MPs content resembling the human anthropization process was recorded. The predominant format of MPs was fiber, followed by fragments. The most commonly identified polymers were rayon, PVC, acrylate, polycarbonate and cellophane. Urban/industrial and agricultural activities were shown as clear sources of MPs, leading to comparable MPs concentration values in the sediment cores. Thus, MPs are collectively a reliable indicator of the Anthropocene onset, and in the Patos-Mirim System the most appropriate chronology can be assigned to the beginning of 1970s, matching the intensification of anthropogenic activities in the area.

Automated summary

We analyzed the vertical distribution of microplastics (MPs) in sediment cores from the Patos-Mirim System. The cores spanned from mid Holocene to present times and were located near urban/industrial and agricultural regions. We found a MP-free zone at the base and a contaminated zone at the top, indicating the increasing human impact. The main types of MPs were fibers and fragments, with commonly identified polymers being rayon, PVC, acrylate, polycarbonate, and cellophane. Urban/industrial and agricultural activities were identified as key sources of MPs.