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From macro to meso: Latitudinal distribution of plastic fragments from the Arctic to the tropics and influence of the environmental conditions
Summary
Scientists studying beaches from the Arctic to the tropics found that warmer, sunnier areas break plastic litter into small fragments (mesoplastics) 16 times faster than icy, cloudy regions—heat and UV light act like a plastic shredder. This matters because these smaller pieces are a step toward the microplastics that end up in seafood, drinking water, and eventually our bodies, so understanding where breakdown happens fastest can help predict pollution hotspots and guide cleanup efforts as global temperatures rise.
The aim of the study was to assess the influence of geographical and climatic factors on the fragmentation of plastic litter on sea beaches along the latitude gradient from the Arctic to the tropics (80°N - 20°N). For the first time, a comparable study of macro- (>2.5 cm) and mesoplastics (0.1-2.5 cm) was conducted at 26 sites of eight marine areas of Russia and China (Barents, Kara, Chukchi, White, Baltic, East China and South China Seas, Pacific Ocean). Unified monitoring methods (OSPAR, GESAMP, MSFD) and statistical analysis (Spearman correlations, Kruskal-Wallis, Mann-Whitney tests) were used to assess the relationship of plastic density with temperature, UV index, cloud cover, wave height and duration of ice cover. A statistically significant increase in the density of mesoplastics from high to low latitudes (p = 0.007) was found: in the Tropics (0.141 items/m) it is 16 times higher than in the Arctic (0.009 items/m). Significant positive correlations of mesoplastic density with average annual temperature (ρ = 0.469, p = 0.018) and UV index (ρ = 0.399, p = 0.048), and negative correlations with cloud cover (ρ = -0.482, p = 0.015) were revealed. In the temperate zone (Baltic Sea), a seasonal change of mechanisms has been recorded: mechanical degradation prevails in spring (proportion of small macroplastics up to 48.1%), photooxidative degradation prevails in summer-autumn (reaching 74.2% of mesoplastics). Sandy beaches accumulate mesoplastics 4-5 times more efficiently than pebble beaches (p = 0.013). The work provides the first quantitative basis for a comparative analysis of the mechanisms of plastic degradation in different climatic zones and can be used in the development of regional monitoring strategies and for predicting secondary microplastic generation across climatic gradients. It can serve as a foundation for modeling microplastic fluxes across latitudinal gradients, enabling predictions of secondary microplastic generation under different environmental scenarios and supporting the development of regional monitoring strategies and targeted mitigation efforts.