Identifying a suitable digestion protocol for microplastic extraction from Isidella elongata (Esper, 1788): New insights for cold-water corals

The persistence and widespread distribution of microplastics (MPs) in marine ecosystems raise concerns about their ecotoxicological impact on biota. Monitoring MP pollution requires standardized methodologies, particularly for smaller particles and those targeting invertebrates. Most studies on MP impacts in anthozoans are based on mesocosm experiments, while field data are scarce and rely on unvalidated protocols. This study aims to identify and document a suitable digestion protocol for small-sized MP isolation from Anthozoa and to validate the method according to standardized protocols using the bamboo coral Isidella elongata , a key Mediterranean deep-sea species. Two protocols were adapted and compared in terms of digestion efficiency, with the most effective combining sodium hypochlorite and hydrochloric acid. Its effects were investigated on 105 particles of three polymers (polyethylene, PE, polypropylene, PP, and polystyrene, PS) ranging from 50 to 1000 μm, with and without coral tissue. Spiked MPs were analyzed before and after digestion steps to assess recovery rate and potential alterations in size, morphology, and polymer composition. After chemical digestion, 87.6 % of particles were recovered, most of which preserved their integrity. Only minor deviations in average size were reported, while no discoloration and minimal or absent degradation and deformation occurred. In contrast, fragmentation was a common alteration in PS given the inherent properties of the polymer. According to FT-IR spectral analysis, polymer composition was well preserved after digestion. These results suggest that the proposed approach represents a reliable methodology for future MP monitoring in cold-water corals, paving the way for standardized biomonitoring approaches for assessing MP pollution in deep-sea benthic fauna. • A chemical digestion protocol was validated for microplastic extraction from Isidella elongata . • 105 PE, PP, and PS particles (50–1000 µm, five size classes) were tested. • The method ensured high digestion efficiency while preserving particle morphology and chemistry. • First validated protocol for Mediterranean cold-water coral and aids MP monitoring standardization in deep-sea fauna.