Experimental development of a new protocol for extraction and characterization of microplastics in fish tissues: First observations in commercial species from Adriatic Sea

• A new method was optimized for extraction of microplastics from marine organisms.
• Density gradient separation and oxidation treatment allow a yield higher than 90%.
• Translocation of particles was shown from stomach to liver of exposed fish.
• Microplastics in commercial fish species have higher frequency in benthic species.
• Polyethylene is the most abundant polymer in Adriatic fish species.

The presence of microplastics in the marine environment has raised scientific interest during the last decade. Several organisms can ingest microplastics with potentially adverse effects on the digestive tract, respiratory system and locomotory appendages. However, a clear evidence of tissue accumulation and transfer of such microparticles in wild organisms is still lacking, partially hampered by technical difficulties in isolation and characterization protocols from biological samples. In this work, we compared the efficacy of some existing approaches and we optimized a new protocol allowing an extraction yield of microplastics from fish tissues ranging between 78% and 98%, depending on the polymer size. FT-IR analyses confirmed that the extraction procedure did not affect the particles characteristics. The method was further validated on the fish mullet, Mugil cephalus, exposed under laboratory conditions to polystyrene and polyethylene; the particles were isolated and quantified in stomach and liver, and their presence in the hepatic tissue was confirmed also by histological analyses. A preliminary characterization revealed the presence and distribution of microplastics in various fish species collected along the Adriatic Sea. FT-IR analyses indicated polyethylene as the predominant polymer (65%) in the stomach of fish. The overall results confirmed the newly developed method as a reliable approach to detect and quantify microplastics in the marine biota.