Plastics are considered to be biochemically inert because of their macromolecular structures; they neither react with nor penetrate the cell membrane of an organism [4]. However, most plastics are not pure. Besides their polymeric structure, they consist of a variety of chemicals that all contribute to certain properties of the plastics they comprise [4]. Additives are mostly of small molecular size and are often not chemically bound to a polymer and are, therefore, able to leach from the plastics. Being primarily lipophilic, they penetrate cell membranes, interact biochemically and cause toxic effects. Moreover, plastics debris in the marine environment not only contains additives, but also contains chemicals (contaminants) adsorbed from the surrounding water [4]. The hydrophobic surface of plastics has an affinity for various hydrophobic contaminants, and these are taken up from the surrounding water and accumulate on, and in, the plastics debris. This mechanism receives great attention for microdebris or microplastics, because they are easily ingested by organisms and constitute a pathway for chemicals to enter an organism [103].

Plastics debris in the marine environment can contain two types of possible toxic contaminants, additives and hydrophobic chemicals, that become adsorbed from the surrounding water [56]. In the marine environment, absorption of contaminants by polymers is primarily studied with meso-plastic and microplastic debris. Absorption reduces the transport and diffusion of contaminants. Hydrophobic organic contaminants have a greater affinity for plastics like polyethylene, polypropylene and polyvinyl chloride (PVC) than for natural sediments [56]. Flame retirements are also present as additives in plastics and are added to many common products. The majority of flame retardants are widely used in plastics products because they affect material properties in only a minor way and are very effective in preventing ignition.

However, they are also present as contaminants almost everywhere in the world’s environment; they exist in air, rivers and waters up to the Arctic regions.

Ingestion of plastic fragments by seabirds and fish may be the source of bioaccumulation of heavy metals, polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and other toxins [72]. Absorption and transfer of these chemicals by filter-feeding organisms and invertebrates may lead to reproductive disorders, disease, altered hormone levels or death at higher trophic levels [25,72,147,148].

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