Citizen Science for Monitoring Plastic Pollution from Source to Sea: A Systematic Review of Methodologies, Best Practices, and Challenges

Citizen science provides a valuable approach for tracking plastic pollution; however, its effectiveness is often limited by methodological inconsistencies, concerns about data quality, and a persistent gap between data collection and policy implementation. This systematic review addresses the key question: What constitutes a comprehensive set of best practices for addressing these issues and enhancing the scientific and societal impact of citizen science in monitoring plastic pollution from source to sea? Analyzing 84 studies, from beach cleanups to microplastic sampling, this review synthesizes best practices and identifies remaining gaps. It presents a structured framework designed to enhance data quality and volunteer participation. Key challenges include the ‘microplastic analytical bottleneck,’ the ‘digital divide,’ and notable geographical and demographic disparities that hinder the integration of policies. While citizen science is effective for large-scale data collection, its main challenge is translating data into actionable policies. The main contribution of this review is a series of practical recommendations aimed at improving methodological consistency, ensuring fair volunteer participation, and facilitating the transition from citizen data to evidence-based environmental management, thereby enhancing the effectiveness and impact of citizen science.