Microplastic occurrence, distribution, and zonation at Paraná's beaches-South of Brazil.

Microplastics are emerging pollutants that are increasingly reported on beaches and potentially impacting the environment and ecosystems. This study presents the first assessment of microplastic (MP) abundance and distribution on oceanic beaches of Paraná, South Brazil. Surface sediments samples retrieved from different beach zones across four beaches were analyzed for their MP (in the 1 to 5 mm size fraction-large microplastics) abundance, morphotype, and polymer composition. MP were found on all the studied beaches, totaling 846 particles, with mean concentrations of 51.9 MP/m² or 2.3 MP/kg dw. The most common morphotypes were fragments (40%), styrofoam (28%), and foams (10%), mainly composed of polyethylene (35%) and polypropylene (29%). MP concentration distribution significantly differed between beach zones, and morphotype distribution showed differences between beaches. MP distribution followed a cross-shore pattern, with the backshore as a main accumulation area. Our study suggests that natural environmental factors such as grain size and beach slope primarily control MP distribution and accumulation along sandy shores. At the same time, the proximity of potential MP sources influences morphotype variation among beaches.