Plastic occurrence in Macaronesia: Three years of monitoring on forty-six beaches across nineteen islands in an Atlantic region

In recent decades, plastic pollution has reached alarming levels in all environmental compartments of the planet, with the oceans being one of the most affected. Despite being far from any major direct source of pollution, the Macaronesian region (North Atlantic Ocean) is highly exposed to marine litter, mostly plastics. In this study, a total of 46 beaches on 19 islands of 4 archipelagos in Macaronesia were seasonally monitored between 2020 and 2023 in a total of 430 field expeditions to study the presence and extent of micro-, meso-, and macroplastics pollution. Overall, a total of 271,203 plastic items were collected, weighted, and classified according to their size, shape, colour, and chemical composition. The results showed the presence of plastic marine litter on all the beaches studied, with an average concentration of 1760 items/m² and 15.30 g/m² for microplastics, 315 items/m² and 15.58 g/m² for mesoplastics, and 35 items/m² and 11.81 g/m² for macroplastics, with the Canary Islands being the archipelago with the highest concentrations. Fragments (83.3 %), with a predominance of white and colourless (62.9 %), and polyethylene and polypropylene as the main types of polymer, 81.2 % and 11.4 %, respectively, were the plastic particles mainly found. Monitoring of 28 previously unstudied beaches revealed the presence of 5 new hotspots of plastic arrival. Statistical analysis revealed that beaches with northwest to east orientations were receiving a higher concentration of plastic litter than the opposite orientations. However, in the central group of the Azores, a notable hotspot was found on a beach oriented toward the southwest. These spatial patterns clearly reflect the influence of prevailing ocean currents associated with the North Atlantic Subtropical Gyre, which plays a key role in transporting plastic debris throughout the region. These results may contribute to a better understanding of plastic transport phenomena in a vast oceanic region such as Macaronesia and provide a foundation for further studies in other areas.