Study of the influence of fluvial dynamics on the distribution and transport of microplastics.

The global reliance on water and the exponential increase in plastic production have led to significant microplastic water pollution. The recent COVID-19 pandemic and financial crises have worsened this issue, with rising plastic use polluting aquatic ecosystems and increasing disregard for the environment. Microplastics, polymer particles smaller than 5mm, classified as primary, created with a certain purpose, or secondary, formed through plastic waste fragmentation, have proven to be an even greater problem. However, their impact on organisms and human health, as well as their behaviour and path, remain under-researched. Thus, this work explores the complex relationship between river dynamics, microplastic transport, and their distribution in aquatic environments. It is known that rivers are key in transporting microplastics to oceans and coasts. Hence, understanding riverine microplastic behaviour is essential for the development of strategies to mitigate their environmental effects and address the broader issue of plastic pollution. This study was conducted in the Cávado River, from the Amares municipality to the river mouth, encompassing a diverse range of environmental conditions. It involved 17 strategically chosen sites at which the riverbeds were sampled. The samples underwent drying in a laboratory oven and density separation using a CaCl2 solution. The supernatant was then analysed under a microscope, leading to the identification of 571 microplastic particles. Sites MP012B, MP009, MP005, and MP003 had the highest counts, with a notable increase in microplastic prevalence from upstream to downstream. Statistically significant differences among groups confirmed that fluvial dynamics influence microplastic behaviour. The study also examined correlations between fluvial pressure factors (urbanisation, wastewater treatment, agriculture, and industry) and microplastic abundance. Potential cross-contamination sources, such as airborne particles and clothing fibres, along with the lack of organic matter digestion and filtering, were acknowledged. Therefore, reassessment of laboratory procedures is recommended. Also see: https://micro2024.sciencesconf.org/559668/document