The human body is exposed to the ingestion of microplastics that are often contaminated with other substances, which can be released into our body. In this work, a dynamic in-vitro simulator of the gastrointestinal tract based on a membrane reactor has been used for the first time to study the release, bioaccessibility, and bioavailability of chromium (Cr) and lead (Pb) from polyethylene and polypropylene microplastics previously contaminated in the laboratory. The results showed that 23.11% of the initial Cr and 23.17% of the initial Pb present in microplastics were able to cross the tubular membrane, simulating the intestinal absorption phase. The pH evolution during the gastric phase and the duodenal phase, the interaction mechanisms with physiological fluids, and the properties of the polymers, such as specific surface, porosity, and/or surface degradation, affected the kinetics of release from the microplastics and the behavior of both heavy metals. Cr was released very early in the gastric phase, but also began simultaneously to precipitate quite fast, while Pb was released slower and in less quantity than Cr, and did not precipitate until the beginning of the duodenal phase. This study shows, for the first time, how useful the dynamic gastrointestinal simulator is to study the behavior of microplastics and some problematic heavy metals along the human gastrointestinal tract, and can serve as a reference for future studies focused on the effects of these substances in the human body.

The excessive use of plastic in our society is causing a massive accumulation, since it is a non-biodegradable product and with still poor recycling rates. This effect can be observed in the seas, which more and more plastic waste are accumulating. The present work is a critical review, based on all currently available literature, that reports environmental status of marine plastic pollution, especially microplastic pollution, in Spain. The three Spanish water areas with the highest presence of plastics are the Alboran Sea, the Gulf of Alicante and the vicinity of Barcelona probably related to fishing and industrial activities and high population densities. With regard to microplastic contamination on beaches in Spain, annual monitoring by the Spanish government shows contamination along the entire coast of the country, with particularly high concentrations in the Canary Islands (between 800 and 8800 particles/m² in spring). Between 40 and 50% of the particles analyzed were pellets and the main factors postulated for the distribution of these particles are marine currents and the geomorphological characteristics. With regards to biota, ingestion of microplastics by fish has been intensely confirmed and, important differences were observed between the locations of the sampling, being bogues (Boops boops) one of the fish species more studied in Spain. Finally, the work includes a revision of European and Spanish legislation about plastics and marine pollution and some strategies to reduce this kind of contamination in Spain.

In Spain, biomethane is emerging as one of the great keys, not only for the transformation of the energy mix in the short term, but also to advance towards the decarbonisation of the economy.