Industrial marine sponges as natural sinks of microplastics: A hidden risk for the global marine bioeconomy

Marine sponges are a unique example of living aquatic filters and are important players in marine benthic ecosystems worldwide efficiently capturing suspended particulate matter from the surrounding water column. Today, however, their filtering activity has turned these organisms, including industrial species, into unique environmental sinks and collectors of microplastics (MPs). For the first time, we investigate the occurrence, diversity, and structural integration of microplastics found within the spongin-based skeletons of the industrial sponges Spongia tubilifera and Hippospongia communis , originating from the Caribbean and Mediterranean seas, respectively. To achieve a comprehensive characterization of MPs retained within the sponge skeletons, a suite of complementary analytical approaches were applied encompassing structural analysis (digital, fluorescence and scanning electron microscopy), quantitative evaluation (digital image analysis, differential scanning calorimetry, and thermogravimetric analysis), and polymer identification (FTIR, Raman, and laser direct infrared spectroscopy). Our results confirm the presence multiple synthetic polymers such as polyethylene (PE), polyamide (PA), polypropylene (PP), poly(ethylene terephthalate) (PET), polystyrene (PS), polyurethane (PU), low-density polyethylene (LDPE), polyacrylonitrile (PAN), and poly(methyl methacrylate) (PMMA), occurring as fibers, particles, and films embedded within the porous three-dimensional spongin skeletons. Our findings demonstrate that spongin-based sponge skeletons can act as long-term repositories for diverse microplastic debris originating from the surrounding aquatic environment. This improves our understanding of the interactions between microplastics (MPs) and marine sponges, which is critical for predicting the long-term ecological impacts of plastic pollution and highlights the potential of sponges as natural biomonitors for assessing microplastic pollution in marine waters.