Turf-forming seaweeds as potential bioindicators of microplastic pollution in a southwestern estuary

Turf-forming Gelidium species are perennial seaweeds that trap sediments and provide habitat for benthic organisms. This study aims to assess, for the first time, the occurrence, composition, and potential environmental risks of plastic debris associated with surface water and Gelidium spp. turfs in the Bahía Blanca Estuary (BBE), Argentina. In water, only microplastics (MPs) were detected, with abundances ranging from 1 to 12 items/L. In Gelidium spp. turfs, macro, meso, and MPs were identified, with fibers being the dominant morphotype, and transparent particles were the most common color category. In the clean Gelidium biomass, MP concentrations ranged from 0.47 ± 0.36 to 1.20 ± 0.34 items/g w.w., whereas in the sediment extracted from the Gelidium turfs, they ranged from 0.17 ± 0.08 to 0.57 ± 0.02 items/g. Polymer analysis using μ-FTIR identified cellulose (CE) and polyester (PES) in both water and seaweed, while polyacrylonitrile (PAN) and polypropylene (PP) were exclusive to the seaweed. The polymer hazard index (PHI) indicated low environmental risk in water but high risk in Gelidium turfs, primarily for the presence of PAN. Although the overall particle size posed a low risk, the retention of high-hazard polymers in seaweed suggests the potential for trophic transfer. Due to its perennial nature, Gelidium appears to be a promising passive biomonitor of synthetic fiber pollution in coastal ecosystems. • Gelidium turfs contain significant amounts of microplastics • Meso and microfibers were the most abundant type of shape found in Gelidium algal turfs • Polyester, cellulose, and polyacrylonitrile fibers were identified, with polyacrylonitrile contributing to ecological risk