Studio comparativo di assorbimento di inquinanti organici persistenti su resin pellet di polipropilene e polietilene e su mitili (Mytilus galloprovincialis)

Abstract

The International Pellets Watch (IPW) [1] aims to map world marine pollution from POPs using resin pellets (virgin plastic granules) as no-living tracers, instead of standard pollution tracers, i.e. filtering organisms and, first of all, mussels. At the base of this project is the excellent correlation obtained (Pearson coefficient equal to 0.755, [1]) between the concentration of PCBs in pellets and mussels sampled in the same area and at the same time. Since pellets can now be found everywhere in the sea and on the beach and presenting few transport, storage and analysis difficulties, their use as pollution tracers would be an advantage from many points of view. However, IPW is based on what was obtained in a previous 2005 study [2], in which a small number of very degraded and yellowed polyethylene (PE) pellets were correlated with a high concentration of PCBs, hence the idea of sampling only yellowed PE pellets and using them as tracers for these substances. Subsequent studies investigated the absorption of PAHs and heavy metals by pellets [3, 4], but have not established the validity of the correlation between yellowing and concentration of pollutants in PE pellets with an adequate statistical basis. Further objections to mapping marine pollution with pellets instead of mussels derive from the fact that the latter are sedentary, while the former are easily transported by the currents and removed from the spill sites. This happens in particular for those of PE and PP (polypropylene), whose density 1.03 kg/m3 favors flotation in the marine surface micro-layer; this fact poses a further problem, since on the surface the concentration of POPs is also 106 times higher than that of the deeper areas of the water column, where mussels generally live [5]. In order to clarify these controversial points, a study has been started divided into two phases: 1) collection, parameterization (color, polymer, state of degradation) and extraction of pollutants (IPA and PCBs) from 400 pellets collected in 4 sites of the Tyrrhenian coast and 2) comparison of the absorption rate of PAHs and PCBs by mussels and pellets in an in situ experiment carried out in three different sites in the Gulf of La Spezia. The experiment, started by ISZTO - Genoa, ISMAR - La Spezia, UNIPI and IGV - Portovenere, started in April 2019 and will last for one year.