Release of heavy metals during in vitro fish gastrointestinal digestion from microplastics collected at Calabrian coasts

Migration of different environmentally relevant elements (Pb, Cd, Cr, As, Sb, Sn, Zn, and Hg) from microplastics collected at different points on the Calabrian coast (areas of both Tyrrhenian and Ionian seas) during simulated fish digestion processes has been studied. The effect of particle size and polymer composition on migration processes has been studied using three different polymers (low density polyethylene (LDPE), polypropylene (PP), and polyvinyl chloride (PVC)) as models. In vitro fish digestion simulation consists of two different phases: gastric (simulated gastric fluid (SGF)) and intestinal (simulated intestinal fluid (SIF)). In general, larger percentages of released metal were found during the gastric phase with respect to the intestinal, likely due to the more acidic conditions along the gastric phase. The total amount of migrated metals after the whole process (SGF + SIF) was also measured, being lower than the initially migrated during the gastric step. In comparison, the amounts of metals migrated during the intestinal phase were not significant for most of the metals studied, diluting consequently the concentration of the metals at the end of the process. Reduction of the polymeric material size (from diameters of several mm (pellets) to 300-500 μm in average (milled)) leads to higher concentrations released during both digestion phases for most of the metals studied. Plastics collected on the Calabrian coast also show metal migration during digestion simulations, being significant for chromium, lead, cadmium and zinc. Particulates containing lead were also detected by single particle ICP-MS, which may correspond to solid deposits on plastic surfaces released during digestion simulations.