44 Environmental Geoscience (Posters)

Wednesday, 11 March 2026
9:00 AM - 12:00 PM
RCC, Lower Level Hall

A survey of microplastics in Puerto Rican sands using sodium chloride and zinc chloride solution separation methods and Nile red optical staining

Paper number: 44-6
Program: Technical Sessions
Time: 9:00 AM – 9:00 AM

Authors

Abstract

Plastic pollution is a widely recognized environmental problem due to their increased  abundance, especially in marine and other aquatic environments. Plastics can cause extensive harm to marine organisms through entanglement and ingestion. Furthermore, plastics break down into microplastics through environmental weathering. Microplastics, ranging from 1 micron to 5 mm in diameter, have been shown to both bioaccumulate and biomagnify in marine food webs. Thus, identifying and monitoring the scope of this pollution crisis is necessary. Puerto Rico is an area where these pollutants are comparatively understudied and therefore sands from three of its beaches were investigated for microplastic contamination. The locations include Guanajibo Beach shore and delta, Buye Beach, and El Faro Beach berm and shore. Sodium chloride solution and stereo microscopy were used to acquire preliminary data. Approximately 30 g of dried beach sands were placed in a clean glass beaker with about 300 mL of the sodium chloride solution (1.2 g/cm³). After separation, these solutions were filtered through a 20 micrometer cellulose filter paper, followed by observation under a dissecting microscope. This process was completed for each of the locations in triplicates, and the microplastics were counted and characterized. The findings show that the average number of microplastics per kg dry weight vary amongst the beaches/locations. For Guanajibo Beach the average concentration for the shore and delta are 128 p/kg and 130 p/kg respectively. For Buye Beach, the average concentration is 174 p/kg. At El Faro, the average concentrations for the berm and shore are 98 p/kg and 19 p/kg respectively. Guanajibo is a recognized site with extensive macroplastic pollution whereas the other sites are not, thus indicating that microplastic pollution may be more variable in these environments than expected. A zinc chloride solution (1.5 g/cm³) was also used to separate plastics, with three of the five sites having over double the estimated concentration from that of NaCl separation. This indicates that the population of plastics at these sites are quite dense, and likely have a different source or pathway of deposition than that of other lighter plastics at these locations. This study provides new constraints for microplastic pollution in Puerto Rico.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411625

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