Harmonious assessment of mesh effect in water sieve sampling for fibrous microplastics abundance

Fibrous microplastic pollution in natural water is increasingly concerning because these particles could carry and release toxic substances, and be bioavailable of microplastics less than 100 μm, posing significant risks to ecosystems and human health. Effective monitoring and accurate data sharing are hampered by a lack of standardized sampling methods, particularly for assessing the impact of mesh size (hereafter referred to as mesh opening) on microplastics abundance. This study investigated the efficiencies of various mesh openings (50-500 μm) in water sieve sampling of fibrous microplastics using a continuous multi-layer filtration device. Surface water samples from Zhanqiao Pier, China, were processed, and the geometric properties of the collected microplastics were analyzed. The retention of fibrous microplastics was calculated using logistic models, and Monte Carlo simulations were employed to estimate the amounts of microplastics that were not retained. Data from previous studies were re-evaluated to develop a harmonious assessment protocol for estimating fibrous microplastics abundance. The results showed that larger mesh openings significantly underestimate the abundance of microplastics, missing up to 14.6 (500 μm), 8.8 (315 μm), and 2.0 (150 μm) times more fibers compared to the finest mesh opening (50 μm). Thus, coarser meshes fail to capture smaller, yet numerous, microplastics fibers. Moreover, the re-evaluated results were used to develop correction factors of the harmonious assessment and highlight the need for finer mesh openings in sampling nets and sieves to ensure more accurate data collection. Such improvements could be used to establish a globally standardized methodology for microplastics monitoring.