Microplastics in water: challenges in measurement and regulation, and a path towards mass-based metrics

Abstract

Microplastics (MPs) have become a ubiquitous environmental pollutant, with water acting as the main vector for their transport and widespread dissemination across natural and engineered systems. Municipal wastewater treatment plants (WWTPs) play a pivotal role as both major sinks and continuous point sources of MPs, as incomplete removal during treatment, combined with high effluent flow rates and sludge reuse, leads to significant emissions to aquatic and terrestrial environments. Growing awareness of this issue is driving the development of increasingly stringent regulatory frameworks in the water sector. However, the absence of standardized and policy-relevant analytical methodologies has so far hindered the explicit regulation of MPs. Current monitoring strategies rely predominantly on particle-based approaches using visual and spectroscopic techniques, which are labor-intensive, observer-dependent and prone to substantial underestimation, particularly for small particles. Therefore, they are poorly suited for regulatory implementation and process control. While thermoanalytical techniques such as pyrolysis- and thermodesorption-gas chromatography coupled to mass spectrometry (Py-GC/MS and TD-GC/MS) provide valuable insights into polymer composition and mass-based information, they remain costly, time-consuming and limited in their ability to deliver rapid, comprehensive quantification of total plastic content in complex (waste)water matrices. This Perspective critically reviews the state of the art in MP quantification, highlights the urgent need for robust mass-based metrics compatible with regulatory and operational requirements, and introduces a practical, cost-effective mass-based method developed by our research group and Captoplastic S. L., and commercialized through the start-up Captoplastic S.L. Its applicability is finally demonstrated through a municipal WWTP case study.