Plastics and the Ocean. Группа авторов

in the environment can originate from either textile manufacturing or fabric laundering (Cesa et al. 2020), especially when using top‐loading washing machines. A single wash cycle of a garment (a fleece jacket) in detergent‐free water in a household washing machine releases about 0.3% of its weight as MFs (Hartline et al. 2016) while studies have found 1079 to 10⁶ fibers per kg fabric in five repeated washes to be released into wastewater (Zambrano et al. 2019; Falco et al. 2019). Furthermore, textile fibers such as nylon or polyester can undergo fragmentation consequent to weathering on exposure to solar UVR (Sait et al. 2021). These microfibers can be micro‐ (<100 μm) as well as nanoscale (<100 nm) (Mintenig et al. 2017) and pose a similar threat to marine biota as MPs (Henry et al. 2019). How much fiber exists as debris in the ocean, is difficult to assess, especially because textile fibers are denser than seawater. A recent estimate places it at ~0.2 MMT released annually; as with MPs, the ecological significance of MFs does not scale with the tonnage but with the particle abundance of these in seawater. However, fibers found in seawater collected from six ocean basins turned out to be predominantly (79.5%) cellulosic with synthetic fibers constituting only 8.2% of the microfibers (Cesa et al. 2017). This observation is inconsistent with >50% volume production being synthetic recalcitrant fibers; but the denser synthetics fibers are more likely to be in the sediment. The high percentage of inherently biodegradable cellulosic fiber in the ocean is yet to be explained.

A summary compilation of available datasets on the abundance of MPs in the ocean (particles/m³) is shown in Figure 1.6 for particles in the size scale of 100–5000 μm. But floating‐stock assessments are invariably underestimates because of the size limit imposed by the mesh size of the sampling nets and the collecting effectiveness of different sampling gear (Zheng et al. 2021). Lindeque et al. (2020) found the MPs concentrations to be an order of magnitude larger when sampling with a 10 μm mesh as opposed to a 500 μm mesh net. For instance, N. Atlantic surface water sampled at 23 sites using a 10 μm mesh net (Enders et al. 2015) yielded MPs in the size range of 10–150 μm,while using a 200 μm mesh net to collect samples at 141 sites during a global circumnavigation cruise (Cozar et al. 2014), yielded MPs in the size range of 0.4–15 mm. Even taking into account the differences in location and identification, these samples likely belong to statistically different populations. Regardless of such drawbacks, however, all efforts at quantifying sea‐surface plastics will still capture only ~1% of the total influx of plastics into the ocean as most would have sunk into the sediment.

Figure 1.6 Density (log particles/m³) of MPs (100–5000 μm) in the different oceans. Horizontal line: median; box boundaries: 25th and 75th percentiles; bars: range of observed values; dots and asterisks: potential outliers.

      Source: Courtesy Beiras and Schönemann (2020).

      Because 1.5–4.1% of the annual production can end up in the ocean (Jambeck et al. 2015), 7800 MMT of plastics hitherto produced should have resulted in at least 57–160 MMT of plastics in the ocean. However, inventories find less than 0.25 MMT of plastics in surface waters (Eriksen et al. 2014; Van Sebille et al. 2015) and their abundance does not correlate with production volumes over the recent years (Thompson 2004). This disparity has led to the notion of a “missing fraction” of MPs, especially the smaller fragments in the ocean (Kvale et al. 2020; Woodall et al. 2014). However, floating plastics essentially represent a “snapshot” view of the MPs in the short window of time they float before extensive fouling sink them into the water column. Also, the search for a missing fraction assumes that all floating MPs will be larger than the mesh size of collecting gear (around 330 μm) excluding most of the small MPs and NPs from the count. The missing fraction reflects limitations of the sampling gear and not taking into account the MPs below the surface water level, especially in the sediment (Kanhai et al. 2019; Nakki et al. 2019; Ramirez‐Llodra et al. 2011). A recent estimate (though based on only six sampling sites) estimates 14 MMTs of MPs that are >50 μm in the sediment (Barrett et al. 2020).

Beaches worldwide routinely accumulate plastic debris, including large amounts of microplastics (Kako et al. 2020; Koongolla et al. 2018; Tavares et al. 2020). Unlike larger plastic litter, the MPs are not removed during beach clean operations, or routinely collected on managed beaches. Worldwide beach clean exercises (Ocean Conservancy 2019) annually covering 36,000 miles of coastline yield a consistent list of highly abundant plastic litter items, with cigarette filters topping the list with 5.7 million collected. Plasticized cellulose acetate fibers used in cigarette filters are recalcitrant in the ocean environment, explaining their ubiquity in coastlines around the world. All of the top seven beach litter items reported are made of plastic; if MPs and NPs could also be somehow included in the count, the abundance of beach plastic debris would be higher by several orders of magnitude. Table 1.1 summaries the seven most abundant plastic debris items found in beach cleaning operations in different parts of the world by the Ocean Conservancy, Washington DC, in 2018. Their global beach cleaning operation is an annual event.

Table 1.1 Abundance of the top seven items found in global coastal cleanup by Ocean Conservancy (Washington DC) and types of plastics commonly used in them.

Litter item	Count in millions	Plastics typically used
Candy wrappersCigarette filtersBeverage bottlesBottle capsStraws and stirrersCups and platesBags	5.72 3.73 3.67 1.97 1.75 1.39 0.94	PE, PP, PET Cellulose acetate PET PP PE PE, PS, EPS PE

      Data pertain to 36 000 miles of coastline in different global locations. Based on data by Ocean Conservancy on the 2018 Coastal Cleanup.

      1.2.3 Chemicals in Plastic Debris

      Plastics used in products typically include a suite of chemicals intimately mixed with the base resin. These include (i) intentionally added chemicals or additives to modify the properties of the base resin to suit the needs of the product (Groh et al. 2019; see Chapter 2); (ii) low levels of the relevant residual monomer trapped in the plastic (not an issue with PE or PP with gaseous monomers, but relevant with PS, PVC or polycarbonate [PC]); and (iii) unintended compounds sorbed from seawater and concentrated by partition (Hüffer and Hofmann, 2016; Pascall et al. 2005; Rochman et al. 2013; see Chapter 9). Some of these sorbed chemicals are persistent organic pollutants (POPs) that are toxic compounds as well, and remain in the environment for extended durations, allowing them to be widely distributed via water, soil, and air. These tend to accumulate in the fatty tissue of animals that ingest them and may bio‐magnify as they move to higher trophic levels. Any POPs in seafood are of special interest to human consumers. Despite their very low dissolved concentration in seawater, the equilibrium concentration of POPs in the MPs and NPs tends to be very high, reaching concentrations that are ~2 to 6 orders of magnitude higher than in sediment (Mato et al. 2001) or seawater (Wright et al. 2013). Sorption cleans the water of these pollutants but in the process, also generates MPs loaded with POPs, heavy metal compounds, and pharmaceuticals, ingestible by marine biota.

1.3 Ingestion of Microplastics Marine Organisms

That the marine environment contains numerous natural particles in the same size range as MPs/NPs that in any event constitute only a small fraction of all particles, is often pointed out. Marine organisms having evolved in this particle‐rich environment are reasonably expected to be not particularly affected by them. However, it is the high level of both sorbed