Impacts of weathered microplastics on bioavailability of pollutants in Paracentrotus lividus and Danio rerio: molecular and ecotoxicological approaches

Plastic materials provide countless applications in every sector of human life, from food and health preservation to textiles and electronics industry (Cole et al., 2011;Thompson et al., 2009) which is resulting in huge amount of plastic waste. Recently, it was estimated that plastics account for the 80-90% of the whole marine litter (Derraik, 2002) and over 5 trillion microscopic plastic fragments are floating on the surface of the World Oceans (Eriksen et al., 2014). The predominant form of marine plastic litter is called “Microplastics (MPs)", terminology by Thompson et al. 2004, used to indicate small plastic fragments, fibers and granules of microscopic size (1 μm to 5 mm in diameter). Being small in size, they are likely to be ingested and accumulate by different classes of organisms (Wright et al., 2013), even can be consumed by algae and bacteria (Mattsson et al., 2015; Bouwmeester et al., 2015). Their presence, therefore, can represent a growing threat to ecosystems and to organisms for which it can represent a hazard (Galloway and Lewis, 2016). MPs are known to interact with a variety of chemicals in the environment through many sorption mechanisms (Yu et al., 2019). Owing to their ability to sorb xenobiotic chemicals, MPs are regarded as vectors of hazardous contaminants to aquatic organisms (Torres et al., 2021). The study of the interactions and the sorption mechanisms occurring between the sorbent (microplastic polymer) and sorbate (chemical contaminant) are important to improve our understanding of MP-mediated contaminant transfer as well as the impact of MPs on the marine environment, especially considering MPs from natural environment. MPs in natural environments undergo weathering processes due to physico-chemical interactions with environmental stress, including with biota. Over time, these stressors may lead to a progressive degradation of plastic polymers and affect their sorption capacity as well as their behavior in aquatic environments. In this context, it is key to know the bioavailable fraction able to determine a potential ecotoxicity in organisms, and to investigate the role of MPs in transferring bioavailable hazardous chemicals to aquatic biota. A multidisciplinary approach to evaluate the influence of the different factors altering plastic surface as well as to investigate the interactions behind the complex mixtures between toxicants and MPs should be considered. The aim of this chapter is to review the main MPs properties focusing particular reference on the sorption mechanisms of MPs, the factors that influence those mechanisms, the sorption behavior of a wide range of chemical contaminants and toxicity associated to combined exposures to MPs and pollutants. An overview of studies that allow relating toxicity to the sorption to MPs and help understand its importance for the bioavailability of chemical compounds is included. A pilot study carried out to evaluate the sorption, over time, of different metals and BDE-47 on a pristine model MP is described. Finally, the objectives of this thesis are presented.