Pollution in the Marine Environment: Plastics, Microplastics and Organic Pollutants

Abstract

Marine debris (MDs) produces a wide variety of negative environmental, economic, safety, health and cultural impacts, thus further research should focus on these kinds of waste. The present work has three main purposes: First, characterization of the MDs has been carried out in terms of their plastic composition, and their pollutant content (PAHs, ClBzs, ClPhs, BrPhs, PCDD/Fs and PCBs). Thermogravimetry has been used to identify the main constituents of the debris, using kinetic modelling to fit the proportion of each plastic. The decomposition of MDs is compared with that of their neat constituents, i.e. polyethylene (PE), polystyrene (PS), polypropylene (PP), nylon and polyethylen-tereftalate (PET). Furthermore, the analysis of pollutants in the samples reveal that MDs is not a highly contaminated waste. In addition, thermal decomposition of MD materials has been studied in a thermobalance at different atmospheres and heating rates. Second, a method for reusing the MDs is presented, consisting on the hydrothermal carbonization (HTC) of the wastes and the seawater where they are found. The plastics, once removed from the sea, cannot usually be recycled or reused. This debris has high net calorific value (NCV) what makes them suitable as a fuel. For this reason, a mixture of plastic materials was treated by HTC using seawater as a solvent, to examine the characteristics of the final products obtained and to test the feasibility of converting marine plastic debris to fuel. Results showed that an increase in the temperature of the process reduces the content of the inorganic anions and increases the NCV of the hydrochar (HTC char). The content of inorganic compounds in the HTC-liquor was measured, which increases as the process temperature rises. Organic compounds were also analyzed, being amides, alcohols and alkanes the major compounds in all cases. Finally, worried about the way in which these plastics reach the human being, microplastics where measured in sea products, more specifically in salt samples. In this sense, 21 different samples of commercial table salt from Spain have been analyzed for MP content and nature. The samples comprise sea salts and rock salts, before and after packing. Results indicate that even though the micro-particles might originate from multiple sources, there is a background presence of microplastics in the environment.