Marine Litter Sources and Distribution Pathways

Summary

Marine litter has been a global concern for many decades. It is important to understand marine litter sources and distribution pathways for the development of targeted and effective interventions and strategies. These have been relatively less researched on the African continent. This chapter focuses on (1) the sources of litter items from macro to nanoscale entering the marine environment and (2) the distribution and accumulation of these items within the environment, focusing on the African marine setting. Case studies are used to showcase specific examples and highlight knowledge/data gaps that need to be addressed within Africa. The potential pathways going forward are discussed and what may be expected in the future, in light of the challenges and successes examined.

2.1 Introduction

Whilst marine litter has been a global concern for many decades. It has been relatively less researched on the African continent (Akindele and Alimba, 2021; Alimi et al., 2021). The majority of quantification studies took place in South Africa, dating back to the 1980s (Ryan, 1988). However, the global spotlight on this issue has seen more studies being conducted across the continent (Fig. 2.1a, b).

Fig. 2.1

a Total number of marine litter quantification studies published across Africa in peer-reviewed journals (excluding ingestion and entanglement studies, which are covered in Chap. 3). *As of December 2021, detailed list in Annex 2.1. b Total number of marine litter quantification studies, by size fractionate, published across Africa in peer-reviewed journals (excluding ingestion and entanglement studies, which are covered in Chap. 3). *As of December 2021, detailed list in Annex 2.1

2.2 Sources of Marine Litter

Marine and freshwater litter (e.g., plastics, ceramics, cloth, glass, metal, paper, rubber, wood) are evident throughout Africa (Chitaka & von Blottnitz, 2019, 2021; Dunlop et al., 2020; Ebere et al., 2019; Moss et al., 2021; Weideman et al., 2020a). The sheer volume littering coasts or floating down rivers highlights its prevalence and the predominance of and leakage from various sources in the region. Sources and release pathways can be linked to land-based or sea-based activities, with the former including municipal solid waste management, direct littering, wastewater and sludge release, agricultural activities, industrial production, harbour/port activities, and others (Fig. 2.2). Sea-based activities include the fishing industry and aquaculture sector and sea-based dumping from ships and off-shore platforms (Fig. 2.2).

Fig. 2.2

Sources, pathways, and sinks of marine litter from macro- to micro-sized items

2.2.1 Land-Based Sources

2.2.1.1 Municipal Solid Waste Management and Direct Littering

A major source of litter entering the environment in Africa results from the lack of adequate and appropriate solid waste management, which pervades every country of the continent (UNEP, 2018b). Municipal solid waste generation rates vary across Africa (Hoornweg & Bhada-Tata, 2012; Kaza et al., 2018), however, overall daily capita rates were considered to be 0.78 kg in 2012, compared to a global average of 1.2 kg per capita per day (UNEP, 2018b). Higher waste generation rates have been associated with some African island states (i.e., Seychelles, Mauritius, and Cabo Verde), which have been attributed to the tourism industry and a reliance on imported resources and associated packaging (Andriamahefazafy & Failler, 2021; Hoornweg & Bhada-Tata, 2012).

Increases in waste generation rates are driven by factors that include rapid population growth and urbanisation, a growing middle class with associated changing consumption habits, economic development, and global trade, which encourages imports of consumer goods into Africa (Jambeck et al., 2018). See Chap. 1 for further details on projections for Africa. Despite these projections, service delivery remains poor and is unlikely to improve at rates needed to support the populace. In Sub-Saharan Africa, for example, only about 44% collection rate of waste, on average, is achieved (Kaza et al., 2018). Waste collection and disposal methods are primarily crude. It is estimated that the treatment processes across the region are: open dumping and/or burning (69%), unspecified landfilling (12%), sanitary landfilling (11%), controlled landfilling (1%), and recycling (7%) (Kaza et al., 2018). 19 of the world’s 50 biggest dumpsites are in Africa, with six located in Nigeria (UNEP, 2018b). Corresponding data for the North African sub-region alone are not readily available as the area is often combined with that for the Middle East. In this regard, the Middle East and North Africa region had an estimated average waste generation rate of 0.81 kg per capita per day, which amounted to 129 million tonnes in 2016 (Kaza et al., 2018). The average collection rate was 82% for this combined region but varied significantly amongst the countries. Waste treatment in the region was estimated to be: open dumping (52%), unspecified landfilling (10%), sanitary landfilling (11%), controlled landfilling (14%), recycling (9%), and composting (4%) (Kaza et al., 2018). Waste management data from African Small Island Developing States (SIDS) is limited. However, it is well understood that due to lack of space and infrastructure and disposal sites near the marine environment, SIDS are often disproportionately affected by waste leakage into the environment (see Chap. 3 for more detail). This is often compounded by debris littering beaches brought by ocean currents and higher generation of waste by visiting tourists (UNEP, 2019).

Open spaces where solid waste has been dumped indiscriminately result in high leakage of hazardous and non-hazardous waste into drains and finally into rivers, lakes, and estuaries. The closer the source of mismanaged waste to river networks and coastal zones, the greater the chances of marine litter. Many populated inland cities are located on rivers’ banks, which form a rich network of waterways that criss-cross the continent (Grid-Arendal, 2005; Lane et al., 2007; UNEP, 1999). Thus, Africa’s inland rivers and estuaries may provide a pathway for a portion of land-derived litter to enter the sea (Lane et al., 2007; Moss et al., 2021; Naidoo & Glassom, 2019; Weideman et al., 2020c) (Fig. 1.1a). Africa has many densely populated coastal cities, of which several have been linked to large litter inputs to the marine environment (Ryan, 2020a, 2020b; Ryan et al., 2021). Lack of adequate affordable housing in Africa may be, for example, a source of litter entering nearby environments, especially as waste is often used as part of informal and temporary structures and shelters (GESAMP, 2019). The coupling between mismanaged waste and affordable housing needs to be investigated further, along with more work on the role coastal cities across Africa play as a source of litter to the surrounding marine environment.

Direct littering and dumping by households in parts of Africa, has also resulted in solid waste entering open drains, river watercourses, and coastal beaches. Beaches in most parts of the world, but especially those in many low-income countries, have been littered with waste by tourists and local persons involved in recreational activities (Lamprecht, 2013; Lane et al., 2007; Tsagbey et al., 2009; UNEP, 2019). Common items include drink bottles, water sachets, single-use food packaging, cigarette butts, and an array of miscellaneous materials. Many beaches in different parts of Africa have been recorded as frequently littered by tourists, especially during peak holiday months (Tsagbey et al., 2009) or specific sporting/entertainment events (Ahmed et al., 2008).

Once in the environment, larger plastic litter items are physically, biologically, and chemically broken down and degraded into secondary fragments/films/foams that include meso, micro, and nano sizes (Bond et al., 2018; Cooper & Corcoran, 2010). The most common polymers detected in African microplastic studies were polyethylene (PE) and polypropylene (PP) (Alimi et al., 2021; Mayoma et al., 2020; Missawi et al., 2020; Vetrimurugan et al., 2020; Wakkaf et al., 2020; Zayen et al., 2020), which are widely used in the packaging sector (PlasticsSA, 2018). More targeted studies are needed to investigate the role open or unmanaged dumpsites (Bundhoo, 2018; Nel et al., 2021) and incineration sites, where litter is managed through informal burning (Yang et al., 2021), play in microplastic generation and release. Especially, as these sites may become significant legacy sources, leaching microplastics to the surrounding environment long after site closure.

2.2.1.2 Wastewater and Sludge

Domestic and industrial wastewater is a well-recognised source of litter that may get deposited in marine environments (Conley et al., 2019; Freeman et al., 2020; GESAMP, 1991; Kay et al., 2018; Okoffo et al., 2019). Domestic and industrial wastewater serve as conduits for litter, which has been purposely dumped/flushed or originated from added products. Once discharged into streams and rivers (or in some countries directly into the marine environment), litter may be carried into the marine environment. In high-income countries with efficient processing plants, the impact of wastewater discharge on the marine environment is usually mitigated by pre-treatment purification steps (biological, chemical, and mechanical). However, whilst such wastewater treatment plants (WWTPs) may remove most macrolitter and a relatively large portion of microlitter, the smaller (<100 µm) litter fractions remain in the effluent, subsequently entering aquatic environments through discharge (Conley et al., 2019; Iyare et al., 2020; Talvitie et al., 2017). Additionally, although microlitter may get removed before the effluent is discharged into aquatic environments, evidence shows that contaminated sludge/biosolids are spread over terrestrial and agricultural land (De Falco et al., 2019; Mahon et al., 2017; Okoffo et al., 2020) which then leach microlitter during runoff events (Okoffo et al., 2019). The release of raw/untreated sewage directly into the ocean is an additional source of marine litter. Domestic and industrial wastewater in Africa may be an understudied yet a significant source for all sizes of litter, this is detailed in Box 2.1.

Box 2.1: Domestic and Industrial Wastewater as an Understudied Source for Litter from Macro to Nano

Domestic and industrial wastewater are potential sources of marine litter. An investigation of macrolitter flows in three WWTPs in Cape Town, South Africa, found cotton bud sticks in the discharged effluent, which passed through the primary screens designed to trap debris (Chitaka, 2020). Investigations conducted by Nel et al. (2018) and Dalu et al. (2021) of river sediments upstream and downstream of WWTP effluent discharges in South Africa suggested that WWTPs are point-sources for microplastics and microfibres. Research in the Bizerte Lagoon, Tunisia, and the adjacent coastline identified microplastic hotspots potentially linked to wastewater facilities (Wakkaf et al., 2020).

In most African countries, wastewater management facilities are non-existent (AfDB/UNEP/Grid-Arendal, 2020). Where they exist, they are mostly aging, inadequate, dis-used, or derelict due to high maintenance and replacement costs (Nikiema et al., 2013). Inadequate provisions for sanitation are a significant problem for most African urban, peri-urban, and rural communities. In most African countries, 72–92% of wastewater was untreated in 2015 (WWAP, 2017). Domestic wastewater from households, hospitals, academic institutions, government offices, etc., is rarely discharged into sewers. Instead, most households discharge directly into soak-away pits that contaminate groundwater or open land and public drainage gutters, contaminating rivers, streams, and ultimately marine environments (AfDB/UNEP/Grid-Arendal, 2020; Mafuta et al., 2018; Wang et al., 2014). In some coastal cities, sewage is directly discharged into the sea. SIDS are no exception. Although many households are provided with a supply of water, a wastewater collection/connection is far less common within SIDS (UNEP, 2019). More research needs to be conducted across Africa to assess how the lack of services and poor maintenance of wastewater infrastructure results in the release of all sizes of litter to the natural environment. Thus, allowing us to inform which mitigation methods to prioritise and importantly, which solutions have been effective (Image 2.1).

Image 2.1

Evidence of debris in the a dissolved air flotation tank and b effluent of a Cape Town WWTP (Chitaka, 2020)

Domestic and industrial wastewater may contain primary microplastics, intentionally incorporated into some products. For example, ‘microbeads’ made from polyurethane (PU) spheres or PE particles are found in a range of personal care and cosmetic products (Amec Foster Wheeler Environment & Infrastructure UK Limited, 2017; UNEP, 2015). This type of contaminant has gained attention across the globe as a result of the ‘Beat the Microbead’ campaign (Dauvergne, 2018), which highlighted how these products can get released into the environment via wastewater systems. Microplastics may also be intentionally added to or used in the production of paints/coatings, detergents, slow- and controlled-release fertilisers, and industrial abrasives, and depending on the product, will get released into the environment via wastewater, leaching, and/or stormwater runoff (Amec Foster Wheeler Environment & Infrastructure UK Limited, 2017). Although very high concentrations of microbeads have been recorded within some aquatic environments, for example in sediment from the St. Lawrence River, Canada (10³ microbeads L⁻¹; Castaneda et al., 2014) and throughout the Irwell and Mersey catchments in the United Kingdom (<70,000 microbeads kg⁻¹; Hurley et al., 2018), similar hotspots have not been detected in Africa. Microbeads associated with personal care products range in size, shape, and colour (Cheung & Fok, 2017). White granule-like PE fragments in face washes may be more challenging to detect than brightly coloured (blue and green) spherical beads found in other cosmetic products (Nel et al., 2019). This difference in detection may result in some microbead granules being overlooked. Regardless, the potential for contamination is apparent, resulting in several countries banning their use in rinse-off products (Guerranti et al., 2019). However, no African country has banned the inclusion of plastic particles in cosmetic products, though discussions have occurred, and some industries (such as the South African cosmetics industry) have implemented some voluntary initiatives to replace microbeads with other materials (Verster & Bouwman, 2020).

Synthetic and natural microfibres can enter the environment as a result of industrial activities (textile factories), individual consumer activities (washing of clothes by hand or using household/communal machines), and wastewater management (sewage effluent, sewage sludge) (Mishra et al., 2019). Marine microplastic studies in South Africa (De Villiers, 2018, 2019; Nel & Froneman, 2015; Nel et al., 2017) and Tunisia (Wakkaf et al., 2020) found microfibres were the most dominant type of microlitter detected. However, by mass of debris they account for <0.01% (Ryan et al., 2020d). Researchers have suggested that microfibres should be classed as their own contaminant independent of ‘microplastics’. Anthropogenic fibres recorded in the environment can be plastic in origin. Washing synthetic textile materials has been shown to release large amounts of microfibres into wastewater (Browne et al., 2020; De Falco et al., 2019, 2020). Microfibres can also be natural/non-plastic in origin e.g., cotton, viscose, linen, jute, kenaf, hemp (Suaria et al., 2020a) or synthetic in origin but made from natural sources of regenerated cellulose e.g., rayon (Kanhai et al., 2017). Reports have suggested microplastic and microfibre removal rates of ~90% for treated wastewater, however the combined global release of microlitter annually from untreated effluent has been estimated at 3.85 × 10¹⁶ (Pedrotti et al., 2021; Uddin et al., 2020). The largely untreated domestic wastewater that pollutes local streams and rivers in Africa may be expected to be loaded with an abundance of these particles.

Microplastic pollution is expected in industrial wastewaters/drainage, either through intentional industrial processes or as accidental leakage from industries manufacturing items that utilise primary microplastics or process pristine/recycled plastic products (Karlsson et al., 2018). Unfortunately, data on microplastic/microfibre abundance and distribution in industrial wastewaters/drainage is scarce in Africa and globally. However, Zhou et al. (2020b) and Chan et al. (2021) both recorded high levels of pollution (~300/500 microfibres L⁻¹) originating from textile processing factories in China.

Pre-production pellets are another primary microplastic. They have been recorded on beaches in Africa since the 1980s (International Pellet Watch, 2021; Ryan & Moloney, 1990). They have been attributed to unintentional factory and transportation leakage (Boucher & Friot, 2017; Karlsson et al., 2018). Pellets in the marine environment have often been associated with urbanisation and industrialisation centres (Hosoda et al., 2014; Naidoo et al., 2015; Ryan & Moloney, 1990; Ryan et al., 2018). However high concentrations have also been located in more rural locations due to historical deposits resulting from long-range transport carrying high densities of pellets from urban centres (Ryan et al., 2018). For example, in South Africa, pellet deposits are seen at 16 mile Beach in the West Coast National Park and Woody Cape at the east end of Algoa Bay (Ryan et al., 2012, 2018). To combat this specific type of contamination the ‘Operation Clean Sweep’ campaign has been adopted by plastic producers and converters worldwide (American Chemistry Council, 2021). In Africa, the Egyptian Plastic Exporters and Manufacturers Association, Ghana Plastics Manufacturers Association and Plastics SA have pledged to follow best practice guidelines outlined by the campaign to minimise pellet, flake and powder loss from the plastic industry.

2.2.1.3 Harbour and Port Activities

Globally, shipping activities are associated with generating large quantities of wastes onboard. At the same time, ports and harbour activities may also generate wastes close to the sea (APWC, 2020; IMO, 1973/1978; Mobilik et al., 2016). Wastes from both sources can contribute to the marine litter problem. Two international conventions, The London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (IMO, 1972), and the MARPOL (1973/1978) Convention for the Prevention of Pollution from Ships (IMO, 1973/1978) have been designed to ensure that ship-sourced wastes are not dumped into the open ocean, but are provided with adequate ports reception facilities for the safe and efficient discharge and treatment of the wastes. In particular, Annex V (Pollution by Garbage from Ships) to the MARPOL convention, which came into force in 1989, specifically bans the dumping of persistent wastes, including plastics, at sea, and requests for countries to operate adequate ports reception facilities that should include garbage reception boats, ships and vehicles, garbage treatment facilities and adequate communication services, amongst others.

Parties and signatories to the MARPOL convention have been provided with adequate guidelines for operating sustainable and efficient national port reception facilities and guidance for ships to practice good housekeeping onboard (Hwang, 2020; IMO, 2013, 2014, 2016; Wallace & Coe, 1998). Unfortunately, whilst in most high-income countries, national ports authorities provide efficient port reception facilities (Argüello, 2020; NOWPAP, 2009; Øhlenschlæger et al., 2013), the same cannot be said of most seaports in Africa. African seaports have been characterised by their inability to provide adequate and sustainable infrastructure and suffer from generally poor management to address the issues of Annex V of the MARPOL Convention. Although the exact amounts of marine litter derived from port and harbour activities have not been quantified yet in Africa, the few available studies on the status of reception facilities at some national ports underscore the need for improvement. For example, several studies examining facilities at the Apapa Port and the TinCan Island Port of Lagos, Nigeria (Onwuegbuchunam et al., 2017a, 2017b; Osaloni, 2019; Peters & Marvis, 2019) have identified the need for improvements to meet MARPOL Convention requirements. In South Africa, a detailed audit of eight major ports, in Durban, Richards Bay, Cape Town, Saldanha, Ngqura, Port Elizabeth, East London and Mossel Bay, and eleven smaller ones (APWC, 2020) found that it was challenging to get a clear picture of the management of ship-generated waste received at commercial ports. Port-generated waste was well managed and regulated, but ship-generated waste had much lower levels of control. A study of ports in the Mediterranean region, including those of Algeria, Egypt, Morocco, Tunisia, and Libya (REMPEC, 2005), also highlighted the need for considerable improvement of port reception facilities in the African countries of that region. The story is not much different in the East African region (Lane et al., 2007).

Various port activities have also been linked with the unintentional release of microplastics into the environment. In 2017 an accidental spill occurred in Durban Harbour, South Africa, wherein two containers carrying PE pellets broke open after falling off a vessel. This resulted in the rapid and widespread distribution of pellets across the South African coastline (Schumann et al., 2019). Although clean-up campaigns were initiated about 82% of the pellets lost were never recovered (Schumann et al., 2019), probably due to seepage into the south Atlantic and the Indian Oceans via dominant ocean currents (Collins & Hermes, 2019) (Fig. 1.1a). Hull scrapings and marine coatings have also been identified as sources of marine microlitter as a result of harbour and port activities (Dibke et al., 2021). Interestingly, Preston-Whyte et al. (2021) suggested harbour/port dredge spoils that may get dumped in nearby coastal zones may be an important and understudied source of microplastics to the marine environment. This is especially important as many harbours in Africa are associated with high microplastic concentrations and a more diverse suite of microplastic particles (Chouchene et al., 2019; Naidoo et al., 2015; Nel et al., 2017; Shabaka et al., 2019). Harbour sediments are also highly contaminated with persistent organic pollutants (POPs), metals, and a whole range of other hazardous substances that have been shown to sorb to microplastics (Torres et al., 2021). Please refer to Chap. 1 for details on these other chemical pollutants.

2.2.2 Sea-Based Sources

2.2.2.1 Shipping Industry

As mentioned in the previous section, the shipping industry is a significant contributor to marine pollution including, dumping hazardous and general waste (Ryan et al., 2019). A long-term study of bottles washing ashore of Inaccessible Island in the South Atlantic Ocean found an increase in the debris of Asian origin; this suggested that dumping from ships played a significant role in marine pollution in that region (Ryan et al., 2019). Additionally, Ryan (2020a) investigated the origin of plastic bottles stranded on nine Kenyan beaches and concluded that most bottles in urban areas were from local sources. The presence of newly manufactured Polyethylene terephthalate (PET) bottles from China implied ship derived waste is still an important component. Further evidence of ship-based waste was observed in South Africa, wherein foreign bottles accounted for up to 74% on some beaches (Ryan et al., 2021).

2.2.2.2 Fishing and Aquaculture Industry

A meta-analysis of 68 publications estimated that annual losses of fishing nets, traps, and lines are around 6%, 9%, and 29%, respectively (Richardson et al., 2019). An analysis of the Great Pacific Garbage Patch estimated that fishing nets accounted for 46% of the mass of all plastics (Lebreton et al., 2018) whilst fishing related debris was commonly observed on the seabed across all areas of the West European coastal shelves (Maes et al., 2018).

In Africa, fishing gear has also been found to be a major contributor to marine litter from coastal to oceanic waters (Alshawafi et al., 2017; Loulad et al., 2017; Ryan, 2014; Scheren et al., 2002) and on the seabed (Ryan et al., 2020c; Woodall et al., 2015). In Morocco, plastic fishing gear accounted for 94% by number of all collected plastic items on the seafloor (Loulad et al., 2017). Whereas, in South Africa, fishery waste accounted for 22% by number and 73% by mass (Ryan et al., 2020c). In cases where fishing gear has been located close to shore, this is mainly related to small-scale fishing operations. Cardoso and Caldeira (2021) investigated the source of plastic pollution found on the Macaronesian Islands. They concluded that the high proportion of fishing gear littering Cabo Verde (Aguilera et al., 2018) originates predominantly from activities off Western Sahara, Mauritanian and Senegalese coasts, with the east coast of North America a secondary source (Cardoso & Caldeira, 2021).

Aquaculture has also been identified as a potential source of plastic into the marine environment through discarded or lost gear (e.g., polyvinyl chloride (PVC) tubes, nets, and cages) as a result of mismanagement and/or accidental losses during extreme weather events (Huntington, 2019). Aquaculture is also a potential source of microplastics leakage resulting from the fragmentation of plastic gear over time and contaminated fishmeal (Lusher et al., 2017; Thiele et al., 2021; Zhou et al., 2020a). The extent to which aquaculture contributes to marine pollution has not been a research focus in Africa, which may be attributed to the industry’s small size (see details in Chap. 1). However, as African aquaculture is projected to increase (see Chap. 1, Fig. 1.2a, b), this could be an increasing source of marine litter.

2.2.2.3 Oil and Gas Industry

There is global concern about the contribution of the oil and gas industry to plastic pollution, especially at sea (Ahmed et al., 2021). Studies are limited however, a case study from the Norwegian continental shelf found higher microplastic concentrations in both sediment and tube-dwelling polychaete worms near offshore oil and gas installations compared to more remote reference sites (Knutsen et al., 2020). The European Union has recently commissioned studies on identifying all material inputs and activities of this industry that may contribute to the environmental burden of microplastics. It is already well known that microplastics are used in the following applications in the oil and gas sector: cement additives and loss circulation material for drilling, wax inhibitors in production, and crosslinking chemicals in pipelines (Amec Foster Wheeler Environment & Infrastructure UK Limited, 2017). Mega and macroplastic leakage from the oil and gas industry is unquantified. Current Oil-producing, coastal African countries (Algeria, Angola, Republic of Congo, Egypt, Equatorial Guinea, Gabon, Libya, Nigeria, and recently Ghana) often have offshore, and coast-based oil industry installations and are liable to release plastics of all sizes into the marine environment. Though oil production is currently concentrated on the north and west coasts of Africa, oil fields, which may be exploited in the future, do exist on the east coast. Gas-producing coastal countries occur all around Africa and are also liable to release plastics of all sizes into the marine environment. However, studies and data quantifying releases from this industry have been sparse despite this knowledge, in Africa and globally.

2.3 Abundance and Distribution of Marine Litter

The abundance, accumulation rates, and characteristics of marine litter can be investigated in different environmental compartments (shorelines, in coastal waters, and the open ocean from the surface to the seabed) using various methods. Watercourses (e.g., rivers, stormwater drains, and WWTP outlets) are also an area of interest as they provide a conduit for litter transportation into the marine environment. Fluxes between compartments are dynamic, and sinks can become sources to other areas and vice versa depending on various abiotic and biotic processes. As such, it is important to understand these fluxes between land and sea, from rivers, estuaries, and the nearshore surface water to the deep sea, to interpret data trends accurately. More importantly, Ryan et al. (2020b) suggest that when monitoring the effectiveness of mitigation measures, sites close to sources are better as they give a more rapid and accurate measure.

Models used to estimate current, and future risk scenarios predict flow and accumulation. These are often associated with high levels of uncertainty, especially due to an incomplete understanding of marine litter inputs and distribution processes and limited and incomparable datasets (Lebreton et al., 2017; Schmidt et al., 2017). A good demonstration of the uncertainty associated with estimating plastic flows into the marine environment is the case of South Africa. Based on estimates of total waste production and proportion of mismanaged waste, Jambeck et al. (2015) estimated that 90,000–250,000 tonnes of plastic flowed into the ocean from South Africa during 2010. A subsequent estimate by Verster and Bouwman (2020), using more robust data, put forth a more conservative range of 15,000–40,000 tonnes per year, highlighting that the amount of plastic flowing into the environment, though less, is still a point of concern. This last estimate was better aligned with observed amounts of plastic washing up on beaches (Weideman et al., 2020b). Global studies using a Lagrangian model have attempted to estimate marine litter hotspots, suggesting the Mediterranean Sea and the coastal zone around southern Africa as regions of concern (Eriksen et al., 2014; Lebreton et al., 2012; Van Sebille et al., 2015). Models can also assist with where litter has originated. For example, Van Der Mheen et al. (2020) investigated the distribution patterns of particles released into the Northern Indian Ocean (NIO). They suggested that depending on the particle beaching probability, the east coast of Africa and many SIDs can be severely affected by pollution released by countries in south-east Asia. This is supported by direct evidence of long-distance drift of high-density-PE bottles and lids, mainly from Indonesia, found on beaches in Kenya, South Africa, and various western Indian Ocean (WIO) island states (Duhec et al., 2015; Ryan, 2020a; Ryan et al., 2021).

2.3.1 Rivers

Freshwater environments are also contaminated with litter, with rivers considered a major pathway for land-based litter to enter the marine environment (Schmidt et al., 2017; Van Calcar & Van Emmerik, 2019). River basins can also retain high levels of litter (buried beneath sediment, trapped along rocky outcrops and vegetated areas), particularly during low-flow conditions. There have been a handful of studies in Africa looking at macrolitter associated with rivers. In South Africa, visual observations of litter flowing down three rivers into Algoa Bay estimated discharge rates of 22–1500 items day⁻¹ (Moss et al., 2021). Weideman et al. (2020c) investigated the long-distance transport of litter within the Orange-Vaal River system and found limited downstream distribution, with macrolitter often linked to local sources. Ryan and Perold (2021) showed limited debris dispersion from a river into the ocean, with deposition concentrated on beaches within 1 km of the river mouth. They also observed the litter exchange between the sea and the river, with marine litter, found up to 1.2 km inland. Rivers also can be long-term sinks for litter (Ryan & Perold, 2021; Tramoy et al., 2020) however, this is dependent on climatic and hydrological conditions within the catchment. For more information on monitoring litter in rivers and lakes, please see the UNEP (2020) report on harmonised approaches.

Rivers as a major transportation pathway for litter has made it a key point of focus for intervention efforts. Several catchment litter management options exist (Armitage & Rooseboom, 2000), using river booms as a popular intervention method (Box 2.2).

Box 2.2: The Litterboom Project, South Africa

Interception booms made of sun-proof high-density PE have been placed in series across several inland rivers in Durban and Cape Town, collecting a minimum of 14,000 kg per site annually. The litter booms are designed to float on the water’s surface, catching floating plastic and other debris as they move downstream, bound for the open ocean. The booms are placed at an angle to ensure waste flows towards the most accessible bank for easier and safer collection. Litter is recycled where possible or landfilled. Litter booms are easy to maintain for teams in the community and very effective when cleared daily. However, retention can be poor when flow rates are high, for example during rainfall events. Such projects have been useful also for raising community awareness on the impact of indiscriminate disposal and littering. In addition, the collected waste data can be used to inform city-wide efforts to stop ocean-bound plastics (Image 2.2).

Image 2.2

The Litterboom Project (Photo Credit). The initiative is credited to the partnership of The Litterboom Project (TLC) with Parley, the City of Cape Town and Pristine Earth Collective

Micro and nano-plastic and fibre abundances have also been assessed in some freshwater rivers across the continent (Alimi et al., 2021), with most studies in South Africa (Dahms et al., 2020; Dalu et al., 2021; Nel et al., 2018) and Nigeria (Adeogun et al., 2020; Akindele et al., 2019; Ebere et al., 2019; Oni et al., 2020). Microplastics were generally partitioned into the water, river bed/bank sediment, and biota. They were characterised to be mostly derived from PE, PP, PU, polystyrene (PS), and polyester materials (Alimi et al., 2021).

Microplastic abundance in inland freshwater systems across the continent is very varied. For the Bloukrans River system in the Eastern Cape of South Africa, Nel et al. (2018) found sediment microplastic concentrations were less in summer (6.3 ± 4.3 particles kg⁻¹) than in winter (160 ± 140 particles kg⁻¹). In Tunisia, Toumi et al. (2019) investigated the sediments of the Bizerte Lagoon and surrounding areas and found 2340–6920 particles kg⁻¹ in streams, and 3000–18,000 particles kg⁻¹ in the lagoon. For Lake Victoria, Egressa et al. (2020) found 0.02–2.19 particles m⁻³ in the water. For the same lake, in Kenya, Migwi et al. (2020) found 1.56–5.38 particles m⁻³ in the water. Concentrations are often difficult to compare directly due to different authors’ variable sampling and analysis methodologies with no standard or harmonised approach available to date.

What drives microplastic distribution, immobilisation and remobilisation, and burial in freshwater systems is still understudied. Depending on various in-stream abiotic and biotic processes, these particles may become temporarily immobilised within riverbed sediments and other in-stream features or float freely within the water column (Drummond et al., 2020; Krause et al., 2021). Floating particles may get distributed further downstream, eventually discharging into the marine environment (Besseling et al., 2017; Drummond et al., 2020; Schmidt et al., 2017; Siegfried et al., 2017). Overall, there are data gaps regarding the extent African rivers contribute litter to marine ecosystems, whether this contribution varies seasonally and how future scenarios may change with the changing climate.

Other data gaps surround where the potentially vulnerable ecosystems are due to litter accumulation. Wetlands, for example, may be potential sinks for both land- and sea-derived litter (Ryan & Perold, 2021). An assessment of macrolitter in two mangrove forests in Mauritius observed mean densities of 0.46 ± 0.24 and 0.24 ± 0.22 items m⁻² (Seeruttun et al., 2021). Additionally, microplastics have been detected in South African mangroves at densities ranging from 18.5 ± 34.4 per 500 g (St. Lucia) to 143.5 ± 93.0 per 500 g (Isipingo estuary) for sediment samples (Govender et al., 2020). Microplastics in water, sediment, and biota were also found associated with the coastal wetland of Sakumo II Lagoon in Ghana (Kanhai et al., 2017). Mangroves situated within 20 km of river mouths are more vulnerable to plastic pollution due to their potential to trap receiving litter (Harris et al., 2021). However, the extent these regions play as litter traps has not yet been established empirically.

2.3.2 Urban Drainage Systems

Few studies have been conducted on urban drainage systems in Africa, including stormwater drains and sewage outlets. Stormwater runoff resulting from rainfall events carries litter from many sources (Image 2.3), flushing debris into streams, rivers, and ultimately the sea. When stormwater occurs around coastal areas, beach litter may be directly washed into the sea. Most of Sub-Saharan Africa experiences stormwater events during the rainy seasons. In South Africa, Arnold and Ryan (1999) quantified urban stormwater runoff in Cape Town, observing macrolitter fluxes of 7–731 items ha⁻¹ day⁻¹. Twenty years later, Weideman et al. (2020a), repeated the study finding little change with fluxes of 5–576 items ha⁻¹ day⁻¹.

Image 2.3

Stormwater drain discharge from Cape Town, South Africa (Photo Credit: T.Y. Chitaka) and stormwater debris deposited at the drainage entrance into the Sierra Leone River in Freetown (Photo Credit: S.K. Sankoh)

Stormwater also carries microlitter deposited from a variety of sources, including fragmented solid waste, city dust, tyre and road wear particles, paint chips, and other industrial and agricultural emissions (Boucher & Friot, 2017; Horton & Dixon, 2018; Liu et al., 2019; Pramanik et al., 2020). Stormwater runoff was considered a major pathway for microlitter to enter aquatic environments and has been shown as an important point source in Durban Harbour, South Africa (Preston-Whyte et al., 2021). Particles released from tyres, and brake pads constitute a major global source of microplastic contamination (Järlskog et al., 2020; Klöckner et al., 2020; Knight et al., 2020; Kole et al., 2017). Evangeliou et al. (2020) estimated that about 64,000 tonnes per year of tyre wear and brake wear particles are directly transported globally through rivers into the ocean, whilst about 140,000 tonnes per year are carried through long-range transport in the atmosphere and deposited into the sea. However, current extraction and spectroscopic techniques used to isolate and identify microplastics are often inadequate for tyre and road wear particle detection (Baensch-Baltruschat et al., 2020). Another source may come from the use of plastic waste in construction and infrastructure, such as roads, that may release plastic fragments over time (Appiah et al., 2017). With the growing economy of many African countries and the significant rise in the number of automobiles in use, some African cities are likely contributing significantly to the local contamination of the environment by microplastics from tyre and brake pad wear.

Runoff from agricultural land may be another pathway by which microlitter enters aquatic environments. Agricultural land may receive microlitter from the degradation of shade cloth, the application of contaminated sewage sludge or biosolids, use of slow-release plastic-encapsulated fertilisers, plastic mulch film, polymer coasted seeds, contaminated irrigation water, and from direct atmospheric deposition to farmland (Katsumi et al., 2021; Okoffo et al., 2021; Qi et al., 2020; Weithmann et al., 2018). Runoff can transport microplastics from farmlands into drainage systems and river courses. Wind can also mobilise soil-deposited microplastics into the atmosphere (Dris et al., 2016; Zhang et al., 2020), which can be especially important in arid zones such as the Sahara Desert where stormwater events are rare, and the wind frequently generates sandstorms that may be transported far beyond the immediate region.

2.3.3 Beaches

Beach litter surveys are the most common monitoring employed in the marine environment. Data gathered are often used to provide initial insight into the composition and quantity of marine litter and to infer the source. Most beach surveys in Africa have been conducted in South Africa, accounting for about 40% of all published studies (Table 2.1). However, the last 20 years have seen studies conducted in Algeria, Ghana, Guinea-Bissau, Kenya, Mauritania, Morocco, Nigeria, Seychelles, Tanzania, and Tunisia.

Table 2.1 Review of observed litter densities across various beaches in Africa for different size fractions (macro, meso, and micro)

Beach litter surveys, using a transect or quadrats, are popular for two reasons; beaches are more accessible than other compartments (e.g., rocky shores, deep-sea, and open ocean) and require fewer resources (Barnardo & Ribbink, 2020, Annex 2.2). Furthermore, beach litter surveys also contribute to awareness-raising and positive behaviour change of those involved (Nelms et al., 2017). There are two general methods; standing stock surveys or accumulation rate surveys, with the latter currently only conducted for macrolitter. Standing stock surveys report the amount of litter at a specific period in time whilst the latter reports the accumulation rate of litter in a given area and can be used as a proxy for litter abundance in adjacent coastal waters subject to inputs from direct littering or exhumation (Cheshire et al., 2009; Ryan et al., 2009). When interpreting the results of beach surveys, it is important to consider the limitations of each method (see Annex 2.2 for further details). Macrolitter monitoring at beaches might be useful to determine the most prevalent items and subsequent actions, for comparable monitoring of status and trends of beach litter across countries and regions. It is also recommended to focus on the larger microplastic fraction (2–5 mm) as a potential legacy contaminant concentrations are likely to increase in the future (Chubarenko et al., 2020; Haseler et al., 2018).

Long-term longitudinal studies of standing stocks may provide indications of gross changes in the types and abundance of litter, as well as distribution patterns (Ryan et al., 2009). For example, Ryan et al. (2018) used a series of surveys conducted across South Africa in 1994, 2005, and 2015 to investigate mesoplastic distribution patterns, concluding that they mostly derive from local, land-based sources. In addition, there was no significant change in mesoplastic abundance over the years. In Kenya, Okuku et al. (2021b) employed standing stock surveys to investigate the influence of monsoons on the abundance and distribution of macrolitter in Mkomani Beach; the results indicated that monsoons influenced both litter abundance and composition.

Accumulation rates are highly site-specific, with variability across beaches and within beaches (Table 2.1). In 2019, accumulation rates of 3.8 ± 3.1–24.9 ± 19.1 items m⁻¹ day⁻¹ were observed in Kenya (Okuku et al., 2020b), whilst 0.0255 ± 0.0086 items m⁻¹ day⁻¹ were observed on Cousine Island, Seychelles (Dunlop et al., 2020) and 0.403 ± 0.061–0.853 ± 0.085 items m⁻¹ day⁻¹ in South Africa (Chitaka & von Blottnitz, 2019). Limited long-term studies investigating litter fluxes have been conducted. In South Africa, Ryan et al. (2014a) conducted daily and weekly accumulation rate surveys over two beaches in 1994, 1995, and 2012, during which a significant increase was observed in litter loads over time. On Cousine Island, Seychelles, Dunlop et al. (2020) conducted what is arguably the longest temporal study of litter fluxes in Africa, conducting 40 surveys from 2003 to 2019 along the same beach, significant increase in litter was observed over time.

To fully appreciate the extent of the marine litter problem, it is important to relate it to waste generation. A study in Cape Town, South Africa, estimated the proportion of products that leaked into the marine environment in 2017. It was found that items associated with food consumed on the go were more prone to leakage (Chitaka & von Blottnitz, 2021). The estimates were based on beach accumulation rates as a proxy for litter flows into the ocean, coupled with waste generation rates. Whilst uncertainty is associated with such estimates, it is important to note the differences in leakage rates for specific product items (Fig. 2.3).

Fig. 2.3

Looking at the big picture: product-specific leakage rates

2.3.4 Coastal and Oceanic Waters

Marine litter has been detected in coastal and oceanic waters off the African coast. However, the presence of marine litter in the ocean remains one of the most understudied compartments from an African perspective, as illustrated in Fig. 2.1a, b.

Seabed trawls conducted in the Mediterranean Sea, off the coast of Morocco, found total macrolitter densities ranging from 0 to 1768 ± 298 kg km⁻² at depths up to 266 m (Loulad et al., 2017). Off the South African coast, only 17% of 235 trawls contained litter with an average density of 3.4 items km⁻². Most litter was located at depths greater than 200 m (Ryan et al., 2020c). From 2012 to 2015, Loulad et al. (2019) conducted sea trawl surveys in the Mediterranean Sea and observed mean densities of 26 ± 68–80 ± 133 kg km⁻², most of which was located closer to the coast. Visual surveys conducted in the South Atlantic Ocean in 2013 observed a decrease in macrolitter density as distance increased from the coast of Cape Town (Ryan, 2014). Furthermore, the survey offered the first evidence of a South Atlantic ‘garbage patch’. Subsequent surveys provided further evidence to support the dispersion and accumulation of litter into this gyre (Ryan et al., 2014b).

Microplastics collected using neuston nets in the open ocean have been predominately made of PE, with higher concentrations closer to the coast (Suaria et al., 2020b; Vilakati et al., 2020). Fibrous microlitter (rayon and polyester) have been detected in seabed sediment south of Madagascar (Woodall et al., 2015). Seabed cores have also been helpful in demonstrating the increase in microplastics in recent years. An example from Durban Harbour in South Africa shows higher concentrations associated with more recent sediment deposits (Matsuguma et al., 2017).

2.4 Litter Characteristics

Internationally, plastic has been found to be a significant contributor to marine litter, and this is the same case in Africa. Assessments of macrolitter have observed plastic proportions ranging up to 99% of collected items by number. In the open ocean, fishing gear makes up a relatively higher proportion than is observed closer to land (Loulad et al., 2017; Ryan et al., 2014b). Moreover, areas with a lot of fishing activity are found to have large proportions of fishing-related litter (Loulad et al., 2017; Ryan et al., 2020d; Scheren et al., 2002). Packaging is often found to be a major contributor across compartments, including rivers (Moss et al., 2021; Weideman et al., 2020c), beaches (Chitaka & von Blottnitz, 2019; Fazey & Ryan, 2016b; Okuku et al., 2020b, 2021b; Van Dyck et al., 2016), as well as coastal and oceanic waters (Ryan, 2014). Most of the packaging is single-use and related to food and beverages, including snack packets, bottles, lids/caps, and sweet wrappers. Common polymer types used to manufacture these items include PE, PP, and PET (PlasticsSA, 2018). Multilayer packaging containing combinations of plastic, paper, or various plastics is also employed particularly for snack packets. However, it must be remembered that the extent to which these items contribute to marine litter is influenced by a variety of factors including consumption rates, consumer behaviours, and solid waste management infrastructure and practices; which vary across the continent (see Boxes 2.3 and 2.4) (Marais & Armitage, 2004; Okuku et al., 2020b; UNEP, 2018a; Weideman et al., 2020b).

Box 2.3: The Scourge of Water Sachets in West Africa

For several decades, the West Africa sub-region has been bedevilled by a special form of plastic waste—sachets used for packaging water, which now serves most people with a safe source of drinking water. It began as an initiative by a local entrepreneur in Nigeria in the 1990s and has grown into a lucrative business throughout West Africa. Its rapid growth stems from the failure of governments to provide clean and safe potable water and sanitation (GIZ, 2019; Stoler, 2017; Thomas et al., 2020; WWAP, 2015).

The water is packed into low-density-PE sachets holding 300–500 ml. National regulations on the production, use, and management of waste derived from this product are largely disregarded by manufacturers and consumers and are not enforced (Vapnek & Williams, 2017). A ‘use and throw away’ culture generally still prevails in the region, resulting in massive littering of street corners, open drains, and streams and rivers. Water sachets are amongst the top contributors to beach litter in Ghana (Nunoo & Quayson, 2003; Tsagbey et al., 2009) and Nigeria (Ebere et al., 2019).

Polymer identification is a very important step in meso and microplastic research as it is used to infer the most likely source/origin, as well as suggest associated risk/hazard. As the source is easier to infer when litter is larger, polymer identification techniques are not regularly employed during macrolitter studies. The lack of spectroscopy equipment hinders the African continents ability to identify polymers (Akindele & Alimba, 2021; Alimi et al., 2021; Nel et al., 2021). In South Africa, the application of the rapid screening technique using a fluorescent dye (Nile Red) (Maes et al., 2017) has proved to be a cost-effective solution for the large scale monitoring of microplastics in marine sediment, water, and fish (Bakir et al., 2020; Preston-Whyte et al., 2021). Shabaka et al. (2019) used differential scanning calorimetry (DSC) to detect a wide range of polymers in Eastern Harbour, Egypt; detecting PP, polyethylene vinyl acetate (PEVA), acrylonitrile butadiene, PS, and polytetrafluoroethylene. There also appears to be capacity using Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) Spectroscopy for the identification of particles > 300 μm (Nel et al., 2021). However, it would be pertinent to build capacity for polymer identification < 300 μm, given that this size range is often linked to increased uptake (Chap. 3).

2.4.1 Factors Influencing Litter Characteristics, Abundance, and Distribution

Several factors have been identified to determine the characteristics, abundance, and distribution of litter in the marine environment. These include, but are not limited to:

• Catchment area characteristics and drainage systems

• Development status and income levels of residents

• Climatic condition (wind, rainfall amount, and flood events)

• Coastal hydrodynamics and ocean currents

• Physical and chemical characteristics of the litter materials.

2.4.1.1 Catchment Area Characteristics and Drainage System

Once litter is in the marine environment, several processes can influence characteristics, abundance, distribution, and fate. Catchment area characteristics (land-use cover, population density) have influenced litter. In South Africa, Arnold and Ryan (1999) and Weideman et al. (2020a) conducted studies quantifying macrolitter discharges from the same three catchment areas (residential, industrial, and mixed commercial/residential) during wetter months in 1996 and 2018–2019. In both cases, macrolitter was most abundant in the industrial area, with the least in the residential area. In general, remote locations are associated with lower macrolitter abundance than those in densely populated areas (Nachite et al., 2019; Okuku et al., 2020b; Ryan, 2020a; Seeruttun et al., 2021). Nevertheless, some remote beaches away from industrial/urban centres have been found to have relatively high litter loads, which suggest long-range transportation does occur (Aguilera et al., 2018; Dunlop et al., 2020; Ryan et al., 2019). In addition, a study by Ryan et al. (2021) found that standing stocks at remote beaches had lower bottle loads than urban beaches but higher loads than semi-urban beaches; this was attributed to the lower inputs of semi-urban beaches vs urban, coupled with greater cleaning efforts at semi-urban beaches than remote beaches.

2.4.1.2 Development Status and Income Levels of Residents

Some studies have suggested an inverse relationship between income level and macrolitter abundance. A study of debris in stormwater drains in South Africa found higher macrolitter loads in low-income areas, which was attributed to the poor waste removal services available (Marais & Armitage, 2004). A similar relationship was suggested by accumulation surveys of five beaches conducted in Cape Town, wherein a beach in a low-income area was associated with relatively high macrolitter loads (Chitaka & von Blottnitz, 2019).

2.4.1.3 Climatic Condition (Wind, Rainfall Amount, and Flood Events)

Litter distribution is influenced by climatic conditions such as wind and rain. Rainfall and flood events can increase litter fluxes from watercourses and waterways as accumulated litter is flushed out of the system (Chitaka & von Blottnitz, 2021; Nunoo & Quayson, 2003; Okuku et al., 2020b; Ryan & Perold, 2021). Wind strength and direction have also influenced litter distribution and deposition (Okuku et al., 2021b; Ryan & Perold, 2021).

2.4.1.4 Coastal Hydrodynamics and Ocean Currents

Ocean currents play a vital role in transporting and distributing litter within the marine environment (Collins & Hermes, 2019; Van Sebille et al., 2015). Trawl surveys have observed variations in litter density according to water depth (Loulad et al., 2017, 2019; Ryan et al., 2020c). There are no clear correlation indicating if this variation is direct (lower depth, less litter) or inverse (lower depth, more litter) variation. Litter distribution within the ocean is also influenced by geomorphology and hydrodynamics (Loulad et al., 2019), additionally, ocean currents influence the deposition of litter on coastlines (Collins & Hermes, 2019; Ryan, 2020b). A study conducted by Chitaka and von Blottnitz (2019) suggested preferential deposition of litter in Table Bay (South Africa) which was attributed to water movements. Further studies on litter deposition along South African coastlines have also suggested that water movements significantly influence the distribution and stranding of litter items (Fazey & Ryan, 2016a, 2016b; Ryan & Perold, 2021). Microplastic distribution and their fate are influenced by ocean currents (Collins & Hermes, 2019; Schumann et al., 2019), biofouling and inclusion within sinking marine snow (Kooi et al., 2017), sequestration along deep-sea canyons (Pohl et al., 2020) and fluxes to the atmosphere via sea breeze (Allen et al., 2020).

2.4.1.5 Physical Characteristics of the Litter Materials

The physical characteristics of an item also influence distribution of litter. Fazey and Ryan (2016a, 2016b) found that size and buoyancy influence debris dispersal, with smaller and less buoyant items observed to disperse over shorter distances. Biofouling was also found to play a role in distribution by decreasing the buoyancy of items (Fazey & Ryan, 2016a). Furthermore, Weideman et al. (2020b) found that rigid plastics were less likely to be deposited and trapped along rocky shorelines, whilst flexible packaging was prone to entrapment in weeds and rocks.

Similar to larger litter items, microplastic distribution is linked to particle size and shape, polymer type, density, surface characteristics, and degradation rates, to name a few. These factors may affect which types of particles the marine environment receives through river inputs. Weideman et al. (2020c) found that fibres were present across the Orange-Vaal river basin but concentrated in the lower reaches. At the same time large plastics and fragments were more closely linked to urban settlements. Chouchene et al. (2019) recorded features indicative of weathering (i.e., pits, fractures, grooves, cracks, and scratches) associated with PE and PP microplastics from Sidi Mansour Harbour sediment samples in Tunisia. There is a need to understand how factors, such as weathering, influence the transport and fate of microplastics. Changes to plastics (bites on bottles, biofouling) can also be used as an indicator of the length of time plastic litter has been at sea and potentially travelled (Ryan, 2020a; Ryan et al., 2021).

Fibres appear more homogenously distributed within the environment (Barrows et al., 2018; Ryan et al., 2020d; Weideman et al., 2019, 2020c). This may reflect their multiple entry points, for example, point sources through WWTP effluent, and diffuse sources via atmospheric deposition and through the spread of sewage sludge or biosolids on agricultural land. Alternatively, fibres may be more widely distributed, especially as their large surface area to volume ratio may lead to reduced settling rates compared to other microplastic shapes (Hoellein et al., 2019; Khatmullina & Isachenko, 2017). More research is needed to corroborate this assumption, using controlled lab-based experiments, such as artificial flumes which can test hydrodynamic scenarios. Visual bias may also lead to conspicuous fibres being detected more frequently than other microlitter types however, few studies have tested this empirically. Nevertheless, it is important for researchers to understand what type of microplastics are being transported down rivers to the marine environment and in what ‘condition’; as they have likely undergone a series of immobilisation and remobilisation events changing their physical and chemical characteristics that in turn will change how they behave in the estuarine and marine environment as they are no longer ‘pristine’. Understanding these processes within the global, let alone the African context is still in its infancy.

Some microplastics and microfibres emitted from different sources are present and suspended in the atmosphere (Dris et al., 2016) and liable to long-range transport to remote places, including parts of Africa (Evangeliou et al., 2020; González-Pleiter et al., 2021; Wright et al., 2020; Zhang et al., 2020). However, no data is published for Africa regarding atmospheric contamination by microplastics and microfibres. Microplastics get deposited onto soil surfaces by gravitational settling and rainout/washout processes during wet precipitation events (Brahney et al., 2020). This is an substantial gap to fill, especially considering atmospheric deposition may be a major diffuse source for aquatic and terrestrial environments (Wright et al., 2020; Zhang et al., 2020).

Box 2.4: Litter and the COVID-19 Pandemic

The COVID-19 pandemic highlighted the usefulness of plastic in our society in the form of Personal Protective Equipment. Unfortunately, the increased consumption of single-use plastics and their improper disposal raised concerns about the impacts on the environment. In Kenya, Okuku et al. (2021a) found that COVID-19 related litter, including masks, gloves, soap wrappers, wet wipes as well as liquid hand wash and sanitiser bottles, were observed along 11 of 14 streets 10-days after the first confirmed COVID-19 case in the country, contributing up to 17% of waste items. In comparison, in South Africa, relatively low amounts of COVID-19 related litter were observed during daily accumulation surveys of urban streets, contributing less than 1% (Ryan et al., 2020a). On Kenyan beaches, COVID-19 litter densities of up to 5.6 × 10⁻² items m⁻² were observed (Okuku et al., 2021a). Interestingly, higher densities were observed at remote beaches, attributed to less compliance with Government instructions to close beaches. This complements findings by Ryan et al. (2020a), who found approximately three times as much litter during less restricted periods of national lockdown compared to periods where movement was strictly monitored. Additionally, the potential of masks as a source of microplastics has been suggested by some researchers (Fadare & Okoffo, 2020; Shruti et al., 2020).

2.5 Key Messages and Future Directions

This chapter demonstrates that current published studies are isolated to a few selected countries. Thus, there is a need for more coordinated research efforts, using harmonised approaches, across Africa. Specifically, it is important to develop baseline datasets which when combined with long-term monitoring studies at the same locales, will enable countries to measure change and mitigation effectiveness. This can only be realised through investment in capacity across the continent, especially equipment and expertise at the smaller size fractions of plastic pollution (micro and nano), which may have legacy impacts.

Knowledge of the pathways and sources for litter release in the environment can facilitate concentrated mitigation efforts and aid in the accurate interpretation of monitoring datasets in the future. There is a need for more field studies quantifying litter inputs, across all size ranges, from various sources. For example, WWTPs are an understudied source of plastics into the environment in Africa, whilst landfill and incineration sites may be important legacy sources in the future if not contained effectively. Rivers are a pathway for the transportation and transformation of plastics however, understanding the role small and larger systems play in retaining plastics is also important for risk-based assessments, clean-up efforts, and interpretation of downstream trends. This will require inter-African collaboration, especially as many rivers are transboundary. Many large and important rivers in Africa, i.e., the Nile, Congo, Niger, Zambezi, and Senegal, have not been extensively studied.

More studies looking at distribution and burial drivers, and underlying fragmentation processes are required. This will enable a deeper understanding of the results of monitoring studies such as beach surveys. For example, the need to assess the  role seasonality plays in litter distribution and burial. Hurley et al. (2018) showed that seasonal changes in catchment hydrology could redistribute microlitter hotspots. This needs to be done across the continent as wet and dry seasons will be regionally relevant and can vary significantly within countries and across the continent. This is especially important as climate change is expected to alter the duration and intensity of various climatic events that could change how litter is immobilised and remobilised in the environment. Other aspects such as the occurrence/degree of biofouling and fragmentation of litter and the hetero-aggregation of micro and nano-plastics may vary with the different current and future climatic conditions found across Africa.

Models looking at how litter gets distributed from urban-industrial centres around Africa or the numerous rivers discharging into the marine environment are important in understanding marine pollution. However, this can only be achieved through various actions such as;

• Hosting workshops whereby researchers working on in situ data collection and those who need data for model validation are gathered to discuss what is required for models versus what is available/achievable.

• The development of an open access database on plastic pollution abundance/loads specific to the African continent.

• Capacity building for more modelling expertise in Africa.

Whilst research is essential to developing an understanding of plastic pollution; this is not to imply that countries should postpone developing strategies to mitigate litter inputs. It is also vital to understand the drivers of littering and inappropriate waste management (with a view to more effectively changing adverse behaviours). We know there is a problem, and efforts should be made to mitigate it by developing product targeted interventions taking into account the leakage propensities of different items (Fig. 2.3a, b). Thus, combining accumulation rate studies with waste generation rates to get a fuller picture of leakage rates into the environment should be encouraged.

Appendices

Annex 2.1: Marine Litter Quantification Studies Published Across Africa in Peer-Reviewed Journals as of December 2021

Country	Total number of studies	Citations
Ghana	7	Scheren et al. (2002), Nunoo and Quayson (2003), Tsagbey et al. (2009), Hosoda et al. (2014), Van Dyck et al. (2016), Chico-Ortiz et al. (2020), Gbogbo et al. (2020)
Cote D’Ivoire	1	Scheren et al. (2002)
Benin	1	Scheren et al. (2002)
Cameroon	1	Scheren et al. (2002)
Nigeria	2	Scheren et al. (2002), Ebere et al., (2019)
Kenya	6	Kosore et al. (2018), Ryan (2020a), Okuku et al. (2020a, 2020b, 2021a, 2021b)
Cousine Island, Seychelles	1	Dunlop et al. (2020)
Alphonse Island, Seychelles	1	Duhec et al. (2015)
Mauritius	1	Seeruttun et al. (2021)
Morocco	7	Alshawafi et al. (2017), Loulad et al. (2017), Maziane et al. (2018), Nachite et al. (2019), Velez et al. (2019), Mghili et al. (2020), Haddout et al. (2021)
South Africa	37	Ryan (1988, 2015, 2020b), Ryan and Moloney (1990), Madzena and Lasiak (1997), Ryan et al. (2014a, 2018, 2020a, 2020b, 2020c, 2020d, 2021), Naidoo et al. (2015), Nel and Froneman (2015), Fazey and Ryan (2016), Matsuguma et al. (2017), Nel et al. (2017, 2018, 2021), De Villiers (2018, 2019), Chitaka and von Blottnitz (2019), Collins and Hermes (2019), Naidoo and Glassom (2019), Schumann et al. (2019), Weideman et al. (2019, 2020a, 2020b, 2020c), Govender et al. (2020), Iroegbu et al. (2020), Vetrimurugan et al. (2020), Verster and Bouwman (2020), Vilakati et al. (2020), Moss et al. (2021), Preston-Whyte et al. (2021), Ryan and Perold (2021)
Algeria	2	Mankou-Haddadi et al. (2021), Taïbi et al. (2021)
Tunisia	5	Chouchene et al. (2019, 2020), Missawi et al. (2020), Wakkaf et al. (2020), Zayen et al. (2020)
Tanzania	2	Mayoma et al. (2020), Maione (2021)
Egypt	1	Shabaka et al. (2019)
Mauritania	1	Lourenço et al. (2017)
Guinea-Bissau	1	Lourenço et al. (2017)
Senegal	1	Tavares et al. (2020)
Atlantic Ocean	4	Ryan (2014), Kanhai et al. (2017), Ryan et al. (2019, 2020b)
Southern Ocean	2	Ryan et al. (2014b), Suaria et al. (2020)
Mediterranean	2	Cózar et al. (2015), Cincinelli et al. (2019)
Indian Ocean	2	Woodall et al. (2014), Connan et al. (2021)

References for Annex 2.1

Alshawafi, A., Analla, M., Alwashali, E., & Aksissou, M. (2017). Assessment of marine debris on the coastal wetland of Martil in the North-East of Morocco. Marine Pollution Bulletin, 117, 302–310. https://doi.org/10.1016/j.marpolbul.2017.01.079

Chico-Ortiz, N., Mahu, E., Crane, R., Gordon, C., & Marchant, R. (2020). Microplastics in Ghanaian coastal lagoon sediments: Their occurrence and spatial distribution. Regional Studies in Marine Science, 40, 101509. https://doi.org/10.1016/j.rsma.2020.101509

Chitaka, T. Y., & von Blottnitz, H. (2019). Accumulation and characteristics of plastic debris along five beaches in Cape Town. Marine Pollution Bulletin, 138. https://doi.org/10.1016/j.marpolbul.2018.11.065

Chouchene, K., da Costa, J. P., Wali, A., Girão, A. V., Hentati, O., Duarte, A. C., et al. (2019). Microplastic pollution in the sediments of Sidi Mansour Harbor in Southeast Tunisia. Marine Pollution Bulletin, 146, 92–99. https://doi.org/10.1016/j.marpolbul.2019.06.004

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Cincinelli, A., Martellini, T., Guerranti, C., Scopetani, C., Chelazzi, D., & Giarrizzo, T. (2019). A potpourri of microplastics in the sea surface and water column of the Mediterranean Sea. TrAC—Trends in Analytical Chemistry, 110, 321–326. https://doi.org/10.1016/j.trac.2018.10.026

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Ryan, P. G., Lamprecht, A., Swanepoel, D., & Moloney, C. L. (2014a). The effect of fine-scale sampling frequency on estimates of beach litter accumulation. Marine Pollution Bulletin, 88, 249–254. https://doi.org/10.1016/j.marpolbul.2014.08.036

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Ryan, P. G., & Perold, V. (2021). Limited dispersal of riverine litter onto nearby beaches during rainfall events. Estuarine, Coastal and Shelf Science, 251, 107186. https://doi.org/10.1016/j.ecss.2021.107186

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Ryan, P. G., Pichegru, L., Perold, V., & Moloney, C. L. (2020a). Monitoring marine plastics—Will we know if we are making a difference? South African Journal of Science, 116, 1–9. https://doi.org/10.17159/sajs.2020/7678

Ryan, P. G., Suaria, G., Perold, V., Pierucci, A., Bornman, T. G., & Aliani, S. (2020b). Sampling microfibres at the sea surface: The effects of mesh size, sample volume and water depth. Environmental Pollution, 258, 113413. https://doi.org/10.1016/j.envpol.2019.113413

Ryan, P. G., Weideman, E. A., Perold, V., Durholtz, D., & Fairweather, T. P. (2020c). A trawl survey of seafloor macrolitter on the South African continental shelf. Marine Pollution Bulletin, 150, 110741. https://doi.org/10.1016/j.marpolbul.2019.110741

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Weideman, E. A., Perold, V., Arnold, G., & Ryan, P. G. (2020a). Quantifying changes in litter loads in urban stormwater run-off from Cape Town, South Africa, over the last two decades. Science of the Total Environment, 724, 138310. https://doi.org/10.1016/j.scitotenv.2020.138310

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Annex 2.2: Marine Litter Monitoring

Marine litter monitoring can be conducted for a number of reasons including changes in abundance and compositions of litter from different sources or in different compartments as well as assessing the effectiveness of mitigation efforts (Ryan et al., 2020). Beach surveys are a common method for monitoring marine litter due to the accessibility of the beaches compared to the open ocean or sea bed. Furthermore, relatively less equipment is required; personal protective equipment is required for participants, receptacles for collecting the litter and sieves for collecting small size fractions. They often focus on macrolitter, due to the difficulty associated with sampling smaller size fractions. Thus, the accessibility of this method makes it an attractive option for initial investigations into marine litter.

In general, either standing stock assessments or accumulation rate surveys are used. The former reports the amount of litter at a specific period in time whilst the latter reports the accumulation rate of litter in a given area. Both methods provide information on the abundance and characteristics of litter. Furthermore, accumulation rate surveys can be used to better understand litter fluxes between compartments (Cheshire et al., 2009; Ryan et al., 2009), whilst simultaneously giving a better reflection of overall standing stock associated with that location. For more details on monitoring refer to Barnardo and Ribbink (2020) and GESAMP (2019).

Standing stock surveys are popular as they are relatively less time intensive as they only require once-off sampling. However, as they provide a snapshot in time the information they provide with regards to marine litter is limited. More specifically, reported litter loads should be approached with caution as their representativeness and thus interpretation is constrained by the limited information regarding litter fluxes, distribution and deposition prior to the collection of litter. For example, an increase in standing stocks over fifty years can be attributed to a number of factors including an increase, decrease or even no change in litter washing ashore, turnover rates of different material types as well as beach cleaning efforts (Ryan et al., 2020). As such, the value of standing stock surveys lies in the litter composition observed rather than amounts.

Accumulation rate surveys are associated with greater investment in time and effort. They require an initial clean-up of the survey area followed by regular sampling of the newly arrived litter. Thus, they are better suited to macrolitter as it is difficult to ensure that smaller size fractions are completely collected during the initial clean-up (Ryan et al., 2020). Studies can be conducted at different intervals including, daily, weekly or monthly. However, observed fluxes are influenced by the chosen sampling frequency. A comparison of daily vs weekly sampling campaigns conducted by Ryan et al. (2014) found that daily surveys yielded 2.1–3.4 times more items than weekly, with observed masses 1.3–2.3 times greater. Furthermore, the study observed that low density items were associated with greater differences with polystyrene foam showing 4–5 times greater values during daily sampling. This demonstrated that different polymer types are associated with varying turnover rates, most likely linked to wind or perhaps to their buoyancy in the water column. In addition, observed accumulation rates can be influenced by water movements and climatic conditions including rain, wind strength and direction (Ryan et al., 2009). Other challenges include exhumation of buried litter either by tides, the weather or beach goers and cleaning efforts on the site (Ryan et al., 2020).

References for Annex 2.2

Barnardo, T., & Ribbink, A. J. (2020). African marine litter monitoring manual. African Marine Waste Network, Sustainable Seas Trust, Port Elizabeth. https://www.wiomsa.org/wp-content/uploads/2020/07/African-Marine-Litter-Monitoring-Manual_Final.pdf

Cheshire, A. C., Adler, E., Barbière, J., Cohen, Y., Evans, S., Jarayabhand, S., et al. (2009). UNEP/IOC guidelines on survey and monitoring of marine litter [UNEP Regional Seas Reports and Studies, No. 186; IOC Technical Series]. https://wedocs.unep.org/xmlui/bitstream/handle/20.500.11822/13604/rsrs186.pdf?sequence=1

GESAMP. (2019). Guidelines or the monitoring and assessment of plastic litter and microplastics in the ocean. IMO/FAO/UNESCO-IOC/UNIDO/WMO/IAEA/UN/UNEP/UNDP/ISA Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection. http://www.gesamp.org/publications/guidelines-for-the-monitoring-and-assessment-of-plastic-litter-in-the-ocean

Ryan, P. G., Lamprecht, A., Swanepoel, D., & Moloney, C. L. (2014). The effect of fine-scale sampling frequency on estimates of beach litter accumulation. Marine Pollution Bulletin, 88, 249–254. https://doi.org/10.1016/j.marpolbul.2014.08.036

Ryan, P. G., Moore, C. J., Van Franeker, J. A., & Moloney, C. L. (2009). Monitoring the abundance of plastic debris in the marine environment. Philosophical Transactions of the Royal Society B-Biological Sciences, 364, 1999–2012. https://doi.org/10.1098/rstb.2008.0207

Ryan, P. G., Maclean, K., & Weideman, E. A. (2020a). The impact of the COVID-19 lockdown on urban street litter in South Africa. Environmental Processes, 7, 1303–1312. https://doi.org/10.1007/s40710-020-00472-1

Ryan, P. G., Pichegru, L., Perold, V., & Moloney, C. L. (2020b). Monitoring marine plastics—Will we know if we are making a difference? South African Journal of Science, 116, 58–66. https://sajs.co.za/article/view/7678/9944

Ryan, P. G., Weideman, E. A., Perold, V., Durholtz, D., & Fairweather, T. P. (2020c). A trawl survey of seafloor macrolitter on the South African continental shelf. Marine Pollution Bulletin, 150, 6. https://doi.org/10.1016/j.marpolbul.2019.110741

Ryan, P. G., Weideman, E. A., Perold, V., & Moloney, C. L. (2020d). Toward balancing the budget: Surface macro-plastics dominate the mass of particulate pollution stranded on beaches. Frontiers in Marine Science, 7, 14. https://doi.org/10.3389/fmars.2020.575395