Assessment of metals associated with virgin pre-production and freshwater microplastics collected by an Italian river

Recently, microplastics (MPs) have been detected in almost all environmental matrices (water, soil, air, biota). Their presence is of concern due to high environmental persistence and their ability to release or bind pollutants. In light of this, the present work aimed to quantify a poorly studied pollutant category associated with MPs: metals. This analysis was conducted on virgin MPs, used as raw materials in the plastics' production process and on environmental MPs taken from the Ofanto river in Southern Italy. The MP samples were initially grouped for colour, shape and ageing and following mineralised by a microwave digestor. The metals and metalloids Pb, Ba, Sb, Sn, Cd, Mo, Se, Zn, Cu, Ni, Co, Cr, Fe, Mn, Ti, Al, V, Ca, K, Mg, Na were subsequently quantified with ICP-MS. All the analysed elements were found on both types of samples (virgin and environmental MPs), with higher concentrations detected on environmental samples (above 14,400 μg/g) rather than on pristine ones (above 5000 μg/g). Many of these inorganic compounds are probably adsorbed by the surrounding environment, and others are intentionally added during the plastic production process to improve their properties (e.g. additives). Noticeable differences were detected concerning the metal's distribution and amount observed in the two types of MP particles analysed. Moreover, trace element concentrations were also linked to the colour and shape of the environmental particles analysed. Most abundant levels of metals were quantified on aged black fragments, followed by coloured and transparent fragments and black pellets. Our concluding remarks underline the role of MPs as a vehicle for the transport of metals, with significant differences between the high abundance of these pollutants examined in our particles collected in a freshwater environment and the significantly lower concentrations revealed previously in marine MPs.