Understanding the sources of marine litter in remote islands: The Galapagos islands as a case study

Determining the sources of marine litter is necessary to mitigate this increasing global problem. Plastic bottles are useful tracers of marine litter and constitute the main item (24%) stranding on remote beaches in the Galapagos Islands. The aim of this study was to estimate the abundance of plastic bottles in remote beaches and inferred their sources. To do so, we collected plastic bottles at 60 remote Galapagos Island beaches from 2018 to 2022. 76% of beaches were qualified as badly polluted, with >34 bottles·100 m-1. Most identified bottles came from Peru (71%), followed by China (17%) and Ecuador (9%). Although most locally-sold products are made in Ecuador, they contribute little to beach litter loads. Polyethylene terephthalate bottles with lid (necessary for litter dispersal) represented 88% of all bottles, demonstrating that most of the litter reaching the Galapagos comes from distant sources, mainly from South America. However, bottle ages indicate that at least 10% of Peruvian, 26% of Ecuadorian, and all Chinese bottles likely were dumped from ships. Reducing marine litter reaching the Galapagos Islands requires tackling litter leakage from land-based sources in South America and better compliance with regulations banning the dumping of plastics and other persistent wastes from ships.

Proximity to coast and major rivers influence the density of floating microplastics and other litter in east African coastal waters

Floating anthropogenic litter occurs in all ocean basins, yet little is known about their distribution and abundance in the coastal waters off east Africa. Neuston net and bulk water sampling shows that meso- and micro-litter (8567 ± 19,684 items∙km^-2, 44 ± 195 g∙km^-2) and microfibres (2.4 ± 2.6 fibres∙L^-1) are pervasive pollutants off the coasts of Tanzania and northern Mozambique, with higher litter loads off Tanzania. Densities of meso- and micro-litter at the start of the rainy season were greater close to the coast and to major river mouths, suggesting that much litter likely originates on land. However, the mass of litter increased with distance from the six major coastal cities. By number, 95% of meso- and micro-litter was plastic, but only 6% of microfibres. Our results highlight the need to reduce plastic use and improve solid waste management in the region.

Buoyancy affects stranding rate and dispersal distance of floating litter entering the sea from river mouths

Rivers are a major source of litter entering the sea but our understanding of the transport and fate of plastics in estuarine environments is poor. Marked blocks of varying buoyancy were released at three river mouths in South Africa. Of the 1400 blocks released, 80% were recovered on nearby beaches, with a higher recovery rate for more buoyant blocks. Dispersal distances increased with decreasing buoyancy at all sites; median dispersal distance of stranded items ranged from 20 to 90 m for expanded polystyrene (EPS) to 70-90 m for wood and 60-1042 m for high density polyethylene (HDPE) blocks. Floating litter in estuaries is subject to bidirectional flow and export is largely controlled by hydrodynamic conditions such as tides, winds, and wave action, as well as coastal structure and vegetation. Cleaning beaches around river mouths will help to reduce leakage of plastic and other litter into the sea.

Are we underestimating the sources of microplastic pollution in terrestrial environment?

Microplastics (MPs, plastic particles < 5 mm) are an ever-increasing global issue due to their widespread occurrence in the environment and negative effects on organisms. Currently, more than 96 % of MPs studies are related to marine systems. However, the majority of marine MPs pollution has been confirmed to originate from land-based sources, evidence of MPs in the terrestrial system cannot be overlooked. In this manuscript, up-to-date knowledge regarding the sources and occurrence of MPs from the terrestrial system is comprehensively reviewed. According to the different studies both in China and abroad, microfibers derived from textile washing attributed approximately 35 % of the MPs identified in the aquatic system. Additionally, personal care and cosmetic products, tires, agricultural plastic films, artificial turfs and road paints, landfill, littering, packaging and construction industry can also release MPs to the environment. The aquatic system plays an important role in MPs transport. By using a one-way ANOVA test, polypropylene (PP) and polyethylene (PE) accounted for significantly higher percentages than other polymer compositions in surface water. Polyamide (PA) and PP accounted for the majority of polymers in soils. PP, PE, and polystyrene (PS) presented an overwhelming proportion in sediment. Atmospheric deposition presents a new vehicle for entering into the wider environment. More research is urgently required on the topic of exposure risk of atmospheric MPs via inhalation. Morphological characteristics including shapes, sizes, and colors have been discussed among waters, soils, sediments and airborne. These source-occurrence implications continuum summaries can bring us new insights that we cannot underestimate the severity of MPs from land-based sources and should pay more attention to MPs contamination in the terrestrial ecosystem.

Limited long-distance transport of plastic pollution by the Orange-Vaal River system, South Africa

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.

Consistent patterns of debris on South African beaches indicate that industrial pellets and other mesoplastic items mostly derive from local sources

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.

Marine litter from beach-based sources: Case study of an Eastern Mediterranean coastal town

Marine litter has been a serious and growing problem for some decades now. Yet, there is still much speculation among researchers, policy makers and planners about how to tackle marine litter from land-based sources. This paper provides insights into approaches for managing marine litter by reporting and analyzing survey results of litter dispersal and makeup from three areas along an Arab-Israeli coastal town in view of other recent studies conducted around the Mediterranean Sea. Based on our results and analysis, we posit that bathing beach activities should be a high priority for waste managers as a point of intervention and beach-goers must be encouraged to take a more active role in keeping beaches clean. Further, plastic fragments on the beach should be targeted as a first priority for prevention (and cleanup) of marine litter with plastic bottle caps being a high priority to be targeted among plastics. More survey research is needed on non-plastic litter composition for which amounts and geographic dispersal in the region vary greatly from place to place along Mediterranean shores. In general, findings of this study lead us to recommend exploring persuasive beach trash can design coupled with greater enforcement for short term waste management intervention while considering the local socio-economic and institutional context further for long-term efforts.