Global measurement of surface water microplastics using a unified size threshold

Extensive studies have documented microplastics in global surface waters, but varying particle size thresholds compromise data reliability. To address this, we compiled microplastic abundance data and conducted a comprehensive analysis to establish a unified threshold. Our findings showed a significant correlation between microplastic abundance and population density (p < 0.05). Using a 100 μm threshold, we estimated global surface water microplastic abundance at 1.81 × 10⁴ items/m³, notably lower than previous reports. Estuarine environments had the highest abundance (5.56 × 10⁴ items/m³), exceeding freshwater (1.79 × 10⁴ items/m³) and marine environments (8.47 × 10³ items/m³). Additionally, surface water microplastic levels were about 13 times higher in developing countries (2.30 × 10⁴ items/m³) compared to developed countries (1.73 × 10³ items/m³). Therefore, we recommend using a 100 μm threshold for assessing microplastic pollution to enhance understanding globally while addressing the need for standardized protocols in future research.