Interaction between microplastics and physicochemical properties of sediment: A multi-ecosystem analysis in a...

The Los Flamencos Fauna and Flora Sanctuary (SFF Los Flamencos), located on the Colombian Caribbean coast (La Guajira), comprises five connected ecosystems exposed to anthropogenic pressures, including tourism, wastewater discharge, artisanal fishing, and inadequate waste management. This study presents the first multi-ecosystem assessment of microplastic (MP) contamination in sediments along a land-sea gradient within a protected area of the Colombian Caribbean. Thirty sediment samples were collected during the dry season across marine, beach, dry forest, mangrove, and lagoon ecosystems. MP abundance ranged from 241.58 ± 27.41 MPs·kg^-1 in marine sediments to 447.91 ± 18.01 MPs·kg^-1 in dry forest sediments, following the gradient: dry forest > beach (303.03 ± 18.93 MPs·kg^-1) > mangrove (290.81 ± 21.09 MPs·kg^-1) > lagoon (279.10 ± 60.11 MPs·kg^-1) > marine. Dry forest sediments showed significantly higher MP abundance than marine sediments (p = 0.026). Fibers dominated across ecosystems (73.7%), mainly blue and black, while 70% of MPs measured <1 mm. μATR-FTIR analysis identified 12 polymer types, with polymeric blends (synthetic/natural) and polyethylene terephthalate predominating across all ecosystems, reflecting inputs from textile fibers and packaging materials. Principal component analysis revealed sediment granulometry as the main factor controlling MP accumulation. Sandy, low-conductivity ecosystems, particularly the dry forest and beach, functioned as preferential accumulation zones, whereas mangrove sediments exhibited alternative biological retention associated with root structures and reduced hydrodynamic energy. These findings demonstrate that SFF Los Flamencos operates as an integrated MP retention-transport system, representing a potential ecological risk for benthic fauna and coastal wildlife.