Pathways for degradation of plastic polymers floating in the marine environment

Abstract

Each year vast amounts of plastic are produced worldwide. When released to the environment, plastics accumulate, and plastic debris in the world's oceans is of particular environmental concern. More than 60% of all floating debris in the oceans is plastic and amounts are increasing each year. Plastic polymers in the marine environment are exposed to sunlight, oxidants and physical stress, and over time they weather and degrade. The degradation processes and products must be understood to detect and evaluate potential environmental hazards. Some attention has been drawn to additives and persistent organic pollutants that sorb to the plastic surface, but so far the chemicals generated by degradation of the plastic polymers themselves have not been well studied from an environmental perspective. In this paper we review available information about the degradation pathways and chemicals that are formed by degradation of the six plastic types that are most widely used in Europe. We extrapolate that information to likely pathways and possible degradation products under environmental conditions found on the oceans' surface. The potential degradation pathways and products depend on the polymer type. UV-radiation and oxygen are the most important factors that initiate degradation of polymers with a carbon-carbon backbone, leading to chain scission. Smaller polymer fragments formed by chain scission are more susceptible to biodegradation and therefore abiotic degradation is expected to precede biodegradation. When heteroatoms are present in the main chain of a polymer, degradation proceeds by photo-oxidation, hydrolysis, and biodegradation. Degradation of plastic polymers can lead to low molecular weight polymer fragments, like monomers and oligomers, and formation of new end groups, especially carboxylic acids.

Microplastic-Associated Biofilms: A Comparison of Freshwater and Marine Environments

“…1 Physical, chemical, and biological factors likely to affect the formation and composition of plastisphere microbial assemblages. Only a limited selection of these parameters has been investigated with specific reference to microplastics facilitate biofilm formation [24,25]. Plastic-colonizing microorganisms have also been found to influence the surface properties and buoyancy of polymers [12,20,26].…”

“…Since microplastics are likely to be transported into marine environments via WWTP, rivers, and streams [6,7], factors contributing to initial colonization (such as surface roughness and attachment by pioneering colonizers) can be hypothesized to be particularly important within freshwaters. The impacts of particle age and/or weathering on plastisphere consortia may be comparatively pronounced within marine ecosystems where the residence times of plastic often exceed those within rivers and streams [24]. However, microplastics additionally accumulate within environments such as lakes, where they may persist for decades (similar to timescales predicted for marine habitats) and can be exposed to high levels of UV radiation [2,27,28].…”

Photodegradation of Polymer Materials Used for Film Coatings of Controlled‐Release Fertilizers

“…The -CH-group in the polymer chain is active and is easily stimulated by UV irradiation to form radicals that react with other -CHgroups (Scheme 2). As a result, the polymer chains inside the microspheres were further cross-linked [36,37]. This resulted in an increased hardness and density of the polymers inside the microspheres.…”

Micro-and macro-plastics in marine species from Nordic waters

“…Current understanding is that plastics are persistent in the environment due to their inert nature (Gewert et al, 2015), even if they become brittle and fragment, the particles will remain in the environment in a smaller size. Furthermore, plastics can be transported over long ranges, as is evidenced by accumulation of plastics in areas far from the source locations (Law et al, 2010;van Sebille et al, 2015).…”