Tourism-associated short-term variability of large microplastics on a tropical sandy beach in the Southern Gulf of...

Tourism-associated coastal activities represent an important source of plastic-derived debris in tropical environments; however, baseline information on large microplastics (> 0.84 mm) remains limited in the Southern Gulf of Mexico. This study evaluated short-term variability in the composition and abundance of confirmed large microplastics in beach sediments from Playa Azul, Centla, Tabasco, comparing two contrasting visitation periods. Two 1-week monitoring campaigns representing low- and high-visitation conditions were conducted to assess changes in daily beach debris generation and large-microplastic characteristics. Results showed a marked increase in total beach debris during the high-visitation period, reaching values approximately 25-fold higher than those recorded during the low-visitation period. In contrast, confirmed large-microplastic abundance showed only limited short-term variation, while morphological composition differed between campaigns. Foams and fragments predominated during the low-visitation period, whereas films and fibres increased during the high-visitation period. Carbonaceous particles were recorded separately as non-plastic anthropogenic residues because their polymeric origin was not confirmed by FTIR. Polymer characterization using Fourier-transform infrared spectroscopy (FTIR) revealed high spectral matches for high-impact polystyrene (HIPS) in foams (95-98%), high-density polyethylene (HDPE) in fragments (90-95%), and polyethylene (PE) in fibres (90-92%). The Microplastic Pollution Index (MPPI) was interpreted as a descriptive screening indicator rather than as a definitive long-term pollution classification. Overall, the findings provide a short-term baseline indicating that visitor pressure was clearly associated with increased total beach debris, whereas large-microplastic abundance and morphology require broader temporal and spatial replication before robust long-term or causal conclusions can be drawn.