INVESTIGATIONS OF MICROPLASTICS IN THE UNIQUE COASTAL ENVIRONMENT OF GUANAJIBO BEACH, PUERTO RICO: NEW CONSTRAINTS IN A POLLUTED ENVIRONMENT

Microplastic plastics are defined as synthetic polymer particles smaller than 5 mm in diameter, and in the last decade, intense interest has arisen across the scientific community regarding their occurrence, sources, fate and transport. While they are recognized as ubiquitous, marine environments are most affected where aquatic organisms bioaccumulate this pollutant with ease. Despite high interest, there is a need for expanded study of microplastics in sediment. This project is an initial investigation of microplastics in sands in two Puerto Rican beaches: the dark sands of Guanajibo and the lighter sands of Buye beach. The sands from both beaches have already been characterized through X-ray diffraction, polarized light microscopy, inductively coupled mass spectroscopy, and grain size analysis, which provide good geogenic control. The dark sands of Guanajibo have a greater abundance of mafic components, such as olivine and pyroxene, while Buye Beach sands are carbonate. The sands of Guanajibo beach and associated macroplastic pollution has been evaluated through reflective spectroscopy, potentially assisting in relating parent material to microplastic pollution. Both sands underwent microplastic separation via zinc chloride flotation, with select samples being exposed to heat (70° C) and 30% hydrogen peroxide prior to separation. Samples were concentrated using a set number of repeated siphonings of the top layer, followed by a wash and filtering using DI water. Point counts were obtained on glass slides using light microscopy and categorized into three main groups: fibrous, globular, and black. Although not certain, the black microplastics are most likely from vehicle tire parent material. Guanajibo beach is highly polluted by tires, and this could potentially lead to a greater abundance of darker microplastics. Refinements of methods are underway to better account for background microplastics in deionized water and biogenic organic matter in sands. Despite these limitations, there are observed high concentrations of microplastics in these beach sands. Future work aims to further quantify and identify microplastics from this beach and other systems.