Determination of microplastic content in seafood: An integrated approach combined with the determination of elemental contaminants

A method for the determination of microplastic (MP) content in seafood is proposed based on the selective digestion of seafood without the degradation of MP. A simple approach was developed using diluted acid with microwave-assisted wet digestion. The following parameters were evaluated: nitric acid concentration (0.5 to 14.4 mol L), digestion temperature (180 to 220 °C), irradiation program holding time (10 to 30 min), MP particle size (0.3 to 5 mm), and the seafood mass (0.5 to 2 g). To develop a reliable method for the determination of MP amount, up to 2 g of an in natura seafood sample were spiked with a known amount of MP (100 mg of mixed MP). Suitable conditions were obtained using 1 mol L HNO at 200 °C (10 min holding time). Digests were filtered and the plastic content was gravimetrically determined. The heating program was 20 min, which represents a significant reduction in the time normally reported in the literature for MP analysis (from few hours up to 3 days). The proposed method allowed gravimetric determination of eight plastic types (polyethylene terephthalate, polystyrene, expanded polystyrene, polypropylene, high and low density polyethylene, polycarbonate and polyvinyl chloride) with particle size ≥0.3 mm. Up to 2 g of an in natura seafood sample (shark species, acoupa weakfish, tuna fish, trahira, and pink shrimp) were efficiently digested, which opened the possibility of using the proposed digestion method for determining elemental contaminants (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, La, Mg, Mn, Mo, Ni, Pb, and Zn). Thus, as the main feature of the proposed digestion method is the possibility of determining MP and elemental contaminants using the same digestion protocol, saves time and reagents and provides accurate and precise information about different classes of marine pollutants (MP and elemental contaminants).