•Very low concentrations offloating macro and microplastics found around Antarctica.•Mean densities of 0.03 macrolitter items·km−2 and 187.6 microplastics·km−2.•Plastic densities are one order of ...magnitude lower than in adjacent temperate waters.•The Subtropical Front seems to be a barrier to the dispersal of drifting plastics.
While macroplastics have been washing up on Southern Ocean islands for decades and microplastics have been found in seabirds from the region since 1960, there are still relatively few quantitative data on the amount of plastic pollution, especially with regard to floating plastics, at high southern latitudes. We present a baseline estimate of the abundance of floating plastics around the Southern Ocean from a survey of floating macro-, meso- and microplastic pollution conducted during the Antarctic Circumnavigation Expedition in 2016/17. A total of 40 net trawls and 626 h of observation were performed during this survey. Of these, 33 net samples and 552 h of observation were made in polar waters south of the Subtropical Front (STF). Only 5 microplastics and 17 macrolitter items were observed south of the STF, confirming the Southern Ocean as the region with the lowest concentrations of plastic pollution globally. The mean concentrations of floating macrolitter (0.02–0.03 items·km−2) and small plastic fragments (188 ± 589 particles·km−2) south of the STF were one order of magnitude lower than in adjacent temperate waters north of the STF, which suggests that the STF acts as a barrier to the southward transport of floating debris. Despite their much lower density, the mass of macroplastics was similar to that of floating microplastics in the Southern Ocean.
Microfibers are ubiquitous contaminants of emerging concern. Traditionally ascribed to the "microplastics" family, their widespread occurrence in the natural environment is commonly reported in ...plastic pollution studies, based on the assumption that fibers largely derive from wear and tear of synthetic textiles. By compiling a global dataset from 916 seawater samples collected in six ocean basins, we show that although synthetic polymers currently account for two-thirds of global fiber production, oceanic fibers are mainly composed of natural polymers. µFT-IR characterization of ~2000 fibers revealed that only 8.2% of oceanic fibers are synthetic, with most being cellulosic (79.5%) or of animal origin (12.3%). The widespread occurrence of natural fibers throughout marine environments emphasizes the necessity of chemically identifying microfibers before classifying them as microplastics. Our results highlight a considerable mismatch between the global production of synthetic fibers and the current composition of marine fibers, a finding that clearly deserves further attention.
In the context of marine anthropogenic debris management, monitoring is essential to assess whether mitigation measures to reduce the amounts of waste plastic entering the environment are being ...effective. In South Africa, baselines against which changes can be assessed include data from the 1970s to the 1990s on microplastics floating at sea, on macro- and microplastic beach debris, and interactions with biota. However, detecting changes in the abundance of microplastics at sea is complicated by high spatial and temporal heterogeneity in net samples. Beach debris data are easier to gather, but their interpretation is complicated by the dynamic nature of debris fluxes on beaches and the increase in beach cleaning effort over time. Sampling plastic ingested by biota is a powerful approach, because animals that retain ingested plastic for protracted periods integrate plastics over space and time, but there are ethical issues to using biota as bioindicators, particularly for species that require destructive sampling (e.g. turtles, seabirds). Bioindicators could be established among fish and invertebrates, but there are technical challenges with sampling microplastics smaller than 1 mm. Fine-scale debris accumulation on beaches provides an index of macroplastic abundance in coastal waters, and offers a practical way to track changes in the amounts and composition of debris in coastal waters. However, upstream flux measures (i.e. in catchments, rivers and storm-water run-off) provide a more direct assessment of mitigation measures for land-based sources. Similarly, monitoring refuse returned to port by vessels is the best way to ensure compliance with legislation prohibiting the dumping of plastics at sea.
Significance:
Monitoring is required to assess whether mitigation measures to reduce waste plastics at sea are making a difference.
Monitoring the leakage of plastic from land-based sources is best addressed on land (e.g. in storm drains and river run-off) before the plastic reaches the sea.
Illegal dumping from ships is best addressed by monitoring the use of port waste reception facilities.
Sampling plastic ingested by biota is a powerful approach, using fish and invertebrates as bioindicators for larger microplastic fragments.
Twenty-four of 40 (60%) loggerhead turtle Caretta caretta post-hatchlings (carapace<9cm) that died within 2months of stranding on southern Cape beaches in April 2015 contained ingested anthropogenic ...debris. Plastic comprised of 99% of debris: 77% hard plastic fragments, 10% flexible packaging and 8% fibres; industrial pellets comprised only 3%, compared to ~70% in 1968–1973, when 12% of stranded post-hatchlings contained plastics. Turtles selected for white (38%) and blue (19%) items, but translucent items (23%) were under-represented compared to beach mesodebris. Ingested loads did not decrease up to 52days in captivity, indicating long retention times. Plastic killed 11 turtles by blocking their digestive tracts or bladders, and contributed to the deaths of five other turtles. Our results indicate that the amount and diversity of plastic ingested by post-hatchling loggerhead turtles off South Africa have increased over the last four decades, and now kill some turtles.
•60% of post-hatchling loggerhead turtles stranded in South Africa contained plastic.•The incidence of ingestion and diversity of plastic has increased since the 1970s.•Turtles favoured blue and white plastic items, but clear items were under-represented.•Turtles retained ingested plastic for up to 2months in captivity.•Plastic ingestion contributed to the deaths of at least 16 of 40 turtles
Limited work to date has examined plastic ingestion in highly migratory seabirds like Great Shearwaters (
Ardenna gravis
) across their entire migratory range. We examined 217 Great Shearwaters ...obtained from 2008–2019 at multiple locations spanning their yearly migration cycle across the Northwest and South Atlantic to assess accumulation of ingested plastic as well as trends over time and between locations. A total of 2328 plastic fragments were documented in the ventriculus portion of the gastrointestinal tract, with an average of 9 plastic fragments per bird. The mass, count, and frequency of plastic occurrence (FO) varied by location, with higher plastic burdens but lower FO in South Atlantic adults and chicks from the breeding colonies. No fragments of the same size or morphology were found in the primary forage fish prey, the Sand Lance (
Ammodytes
spp.,
n
= 202) that supports Great Shearwaters in Massachusetts Bay, United States, suggesting the birds directly ingest the bulk of their plastic loads rather than accumulating via trophic transfer. Fourier-transform infrared spectroscopy indicated that low- and high-density polyethylene were the most common polymers ingested, within all years and locations. Individuals from the South Atlantic contained a higher proportion of larger plastic items and fragments compared to analogous life stages in the NW Atlantic, possibly due to increased use of remote, pelagic areas subject to reduced inputs of smaller, more diverse, and potentially less buoyant plastics found adjacent to coastal margins. Different signatures of polymer type, size, and category between similar life stages at different locations suggests rapid turnover of ingested plastics commensurate with migratory stage and location, though more empirical evidence is needed to ground-truth this hypothesis. This work is the first to comprehensively measure the accumulation of ingested plastics by Great Shearwaters over the last decade and across multiple locations spanning their yearly trans-equatorial migration cycle and underscores their utility as sentinels of plastic pollution in Atlantic ecosystems.
Most studies report the abundance of plastic items in the environment, but mass is an equally important currency for monitoring plastic pollution, particularly given attempts to balance the global ...plastic budget. We determined the size/mass composition of litter stranded on a remote, infrequently-cleaned sandy beach on the west coast of South Africa. Traditional surveys of superficial macrolitter were augmented by sieved transects for buried macrolitter (8-mm mesh), mesolitter (2-mm mesh) and sediment cores for microlitter. Aggregating the data across all sampling scales, the total density was ~1.9x10^5 anthropogenic particulate pollutants per linear metre of beach, 99.7% of which were microfibres (most of which are likely not ‘plastic’). Plastics comprised 99.6% of beach macro- and mesolitter by number and 89% by mass. Small items dominated samples numerically, but were trivial relative to larger items in terms of their mass. Buried litter accounted for 86% of macroplastic items, but only 5% of the mass of macroplastics, because smaller items are buried more easily than large items. The total density of plastic (~1.2 kg·m–1), at least half of which was from fisheries and shipping, is much lower than predicted by global models of plastic leakage from land-based sources. Ongoing degradation of plastic items already in the environment, particularly on beaches, is likely to result in a marked increase in plastic fragments, even if we stop leaking additional plastic. The collection of large items from beaches is a useful stop-gap measure to limit the formation of microplastics while we formulate effective steps to prevent plastic leakage into the environment.
Rivers are assumed to be one of the major conduits for plastics entering the sea, but little is known about the interchange of plastic litter between rivers and coastal waters. We measured the amount ...of litter stranding on the beach around the mouth of a seasonal river in Cape Town, South Africa, to infer litter dispersal distances. Prior to the mouth opening, litter was fairly uniformly distributed along the 2.4 km study beach. Once the mouth was opened for the first major winter storm, most litter stranded within 0.5 km of the river mouth. Beach litter loads peaked during rain events and decreased after the first rainfall event, presumably due to flushing of accumulated litter in the coastal wetland. However, litter loads within the wetland remained high, indicating that only a proportion of litter flushes during floods. Experimental deployments of marked litter items confirmed that most floating litter strands close to the mouth, although less buoyant items travelled farther than more buoyant items. Exchanges occurred in both directions, with marine litter found up to 1.2 km inland in the estuary. On a rising tide, more litter items moved into the estuary than into the sea, despite strong offshore winds. Our results illustrate the complex interplay of litter between rivers and the sea, and suggest that a large proportion of floating litter carried down small rivers washes ashore shortly after entering the sea. Cleaning beaches around river mouths, especially after rain events, will help to reduce leakage of plastic from land-based sources into the sea.
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•Most (>90%) floating litter from a small seasonal estuary washes ashore.•Floating litter mostly strands within 500 m of the estuary mouth.•Litter loads are linked to rainfall and peak after the first winter storm.•Some litter items move from the sea into the estuary.
Much of the plastic waste entering the sea is thought to be transported from land by rivers, yet little is known about the distances over which rivers transport plastic. To address this knowledge ...gap, we collected surface water samples from the Orange-Vaal River at the end of the wet and dry seasons. The Vaal River drains South Africa's main urban-industrial centre, whereas the upper Orange River is sparsely populated. Below their confluence, the river flows through increasingly arid regions with very low human populations before entering the Atlantic Ocean. We collected bulk water samples from 33 bridges to test for microplastic and microfibre (0.025–1 mm) pollution and conducted observations for macrodebris (>50 mm). Where possible, we sampled for plastic fragments (>1 mm) using a neuston net. Microfibres and microplastics were found at every site (1.7 ± 5.1 L−1, >99% fibres) and accounted for 99% of the number of items recorded. Microfibres and microplastics were particularly abundant in the lower reaches during the period of low flow prior to the wet season flush. Macrodebris and larger microplastics were orders of magnitude less abundant (observations: 0.0002 ± 0.0007 items·m−2; neuston net: 0.34 ± 0.93 items·m−2). However, at sites where larger items were found, they comprised most of the mass of plastic. Larger plastics were found mostly at sites in the upper reaches of the Vaal River. Our results suggest that, while the Orange-Vaal River system may be a source of microfibres to the Atlantic Ocean, larger plastic items typically only travel short distances. The Orange-Vaal River system therefore does not appear to be a major source of plastics into the Atlantic Ocean, at least under regular flow conditions.
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•Microfibres found at all sites and in 90% of replicates•Macroplastics and larger microplastics retained close to point sources•Mostly microfibres found at the Orange River mouth•Estimated annual export of 1.7 (1.1–3.1) t of microfibres to the Atlantic Ocean
Identifying the sources of small plastic fragments is challenging because the original source item seldom can be identified. South Africa provides a useful model system to understand the factors ...influencing the distribution of beach litter because it has an open coastline with four equally-spaced urban-industrial centres distant from other major source areas. We sampled mesodebris (∼2–25 mm) at 82 South African beaches in 1994, 2005 and 2015. Plastic items comprised 99% by number and 95% by mass of litter items. Industrial pellets were the most abundant plastic items, but fragments of rigid plastic items comprised most of the mass of debris. Strong correlations between industrial pellets and other plastic items indicate that common factors influence the distribution of both pellets and secondary mesoplastics. The abundance of mesodebris at beaches also was correlated in successive surveys, suggesting that beach-specific factors (e.g. aspect, slope, local currents, etc.) influence the amounts of debris on each beach. Sample year had no effect on mesodebris abundance, indicating that there has been little change in the amounts of mesodebris over the last two decades. There were consistently higher densities of both industrial pellets and other plastic items at beaches close to urban-industrial centres; there were only weak correlations with human population density and no correlation with local runoff. The size of industrial pellets decreased away from local urban centres, further supporting the conclusion that, like macroplastic litter, most mesoplastic pollution on continental beaches derives from local, land-based sources. This finding means that local actions to reduce plastics entering the sea will have local benefits, and that it may be possible to assess the efficacy of mitigation measures to reduce marine inputs of mesoplastic items.
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•Plastic items comprise 99% by number and 95% by mass of sandy beach mesodebris.•Correlations between plastic pellets and other mesodebris indicate common sources.•There is no evidence of an increase in mesodebris loads over the last two decades.•Mesodebris is concentrated around local urban centres.•The efficacy of local mitigation measures should be fairly easy to assess.
Mesoplastic pollution (∼2–25 mm) on South African beaches is concentrated around urban-industrial centres, which indicates the importance of local sources and suggests that actions to reduce marine inputs of mesoplastic items will have local benefits.
Rivers can be major sources of plastics into coastal seas, but it is unclear whether dams retain floating plastics, thus reducing the amount reaching the sea. To test if dams trap microplastics, we ...collected bulk water and neuston net samples from five dams on the Orange–Vaal River system, South Africa. Most manufactured items were microfibres and densities of microplastics were modest (bulk water: 0.21 ± 0.27 items·L−1; net: 0.04 ± 0.16 items·m−2). There was an interaction between dam and season: dams on the densely populated Vaal River had higher microplastic concentrations during dry than wet conditions, whereas the opposite pattern occurred on the less industrialised Orange River. Overall there was no difference in microplastic concentration at sites above vs below dam walls nor was there a strong correlation between microplastic concentration and distance to the wall. Our results therefore suggest that dams do not trap floating microplastics or microfibres.
•Concentrations of microplastics and microfibres were low.•Most manufactured items were microfibres.•There was no difference in plastic and microfibre concentrations at sites above versus below dam walls.•Dams do not appear to trap floating microplastics and microfibres.
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