Critical reassessment of microplastic abundances in the marine environment

Microplastics (MPs) pose a growing concern in the marine environment, but their global prevalence remains largely unknown due to the absence of precise and standardized detection methods. This review critically evaluates existing techniques for quantifying MP abundances in marine field studies, addressing inaccuracies resulting from the exclusion of particle sizes, polymer types, or limitations in identification methods. These traced inaccuracies were considered to recalculate MP abundances for particle sizes from 10 to 5000 μm, providing the first corrected global overview of MP distribution that enables quality assessment and reliable comparisons between adjusted data. The recalculations indicate that MP abundances are up to 15 times higher in marine waters (average (1.5 ± 36.2) × 10⁵ items m^-3) and up to 11 times higher in the marine sediments (average (2.7 ± 117.9) × 10⁵ items kg^-1) than previously reported in the literature. The Australasian Mediterranean Sea (average (1.2 ± 10.6) × 10⁶ items m^-3) and the North Atlantic (average (2.1 ± 37.6) × 10⁵ items kg^-1) emerged as the most polluted regions in marine waters and sediments, respectively, with primary contributors being the coasts of Southeast Asia and East America. This review demonstrates that previous field studies, global estimates, and models have significantly underestimated MP levels in marine environments in many cases, which could result in misinterpretations of both local and global pollution levels. This work highlights the critical need for precise handling of microplastic samples and urges future researchers to adopt standardized protocols for MP analysis to avoid inaccurate and misleading outcomes.