The Sink is Leaking! - Enabling Citizen Science for Global Mapping of Microplastic Leakage from Coastal Soils

Microplastic pollution is among the most urgent environmental challenges of our time, yet its movement through soil, particularly at the land-sea interface remains poorly understood.This study provides the, to our knowledge, first documented evidence for the potential of microplastic-leakage from polluted coastal soils back into the ocean and presents a simple, low-cost framework for quantifying it.By combining soil core sampling in the field, rainfall simulation, and fluorescence microscopy using the accessible Nile Red method to quantify microplastics within leachate, we show that coastal soils can act as temporary sinks -slowly re-emitting large amounts of microplastics into surrounding waters.The methodological workflow developed here offers a globally accessible tool for mapping microplastic-leakage, enabling both researchers and citizen scientists to generate comparable data at low cost.This democratization of environmental monitoring bridges the gap between academic research and community participation, allowing schools, local groups, and researchers in resourcelimited settings to contribute to our shared global plastic pollution knowledge.Beyond its scientific contribution, this work aims to empower citizens to engage directly in all stages of the research, from sample collection to data analysis, in similar projects of their choice within their local area, fostering environmental literacy and building public trust in science.The findings also provide policymakers with new evidence on the importance of considering soil-ocean fluxes in pollution models.Together, these advances lay the groundwork for an international network of collaborative mapping and monitoring initiatives to better understand microplastic-leakage along the world's coastlines.