Quantification and characterisation of microplastics ingested by selected juvenile fish species associated with mangroves in KwaZulu-Natal, South Africa

A first assessment of marine meso-litter and microplastics on beaches: Where does Mauritius stand?

Marine litter is a major global concern that is threatening marine ecosystems. This study assessed the meso-litter and microplastics density around Mauritius Island, South West Indian Ocean (SWIO) region. WIOMSA guidelines were used for meso-litter and microplastics sampling from October to December 2019 at 12 sites. A total of 1095 meso-litter items (weighing 1250 g) was sampled. Plastics were the most abundant litter category. 'Shoreline and recreational activities' were the main meso-litter source. Microplastics density was highest at the vegetation line (VL) zone. Fragments, mostly blue-coloured, were the most encountered type of microplastics, and polyethylene was the most prevalent polymer type. This study provides important baseline data which can be used by relevant authorities for more effective waste management strategies and awareness campaigns that will help further mitigate the marine litter problem in Mauritius, and to check the effectiveness of management measures in place.

The abundance of microplastics in cnidaria and ctenophora in the North Sea

Microplastic (MP) ingestion has been widely recorded in aquatic organisms, but few studies focus on cnidarians and ctenophores, which form a significant contribution to marine trophic interactions. Scyphozoans (Cyanea capillata, C. lamarckii and Aurelia aurita), hydrozoan (Cosmetira pilosella) and ctenophores (Beroe cucumis and Pleurobrachia bachei) collected opportunistically from Orkney, Shetland and the North Sea were thermally disintegrated, with a subsample of ingested plastics analysed using FTIR. A total of 1,986 MPs were counted (94% fibres), the majority (84.4%) in the four cnidarian species. Highest MP concentrations were recorded in B. cucumis (0.956 ml^-1), whilst C. pilosella yielded the lowest (0.014 ml^-1). The main polymers in digestate were PET and PP, with 27% discounted as non-plastics. In feeding trials, A. aurita ingested a greater quantity of PET fibres (60-80%), compared to nylon (0%) and HDPE fibres (0%). This study demonstrates cnidarians and ctenophores, a largely overlooked group, are a potential route for MPs entry into food webs.

Microplastics in fishes from an estuary (Minho River) ending into the NE Atlantic Ocean

Wild fish (Cyprinus carpio, Mugil cephalus, Platichthys flesus) from an estuary of the NE Atlantic coast were investigated for plastic contamination (N = 128). From the 1289 particles recovered from fish samples, 883 were plastics. Among these, 84% were fibres and 97% were microplastics. Thirty-six polymers were identified. The number of microplastics (mean ± SD) per individual fish (MP/fish) was 8 ± 6 in C. carpio, 10 ± 9 in M. cephalus and 2 ± 2 in P. flesus. The means of MP/fish per body site were 6 ± 7 in gastrointestinal tract, 0.5 ± 1.1 in gills, 0.3 ± 0.7 in liver and 0.6 ± 1.2 in muscle samples. A few large fibres in liver (≤ 4841 μm) and muscle (≤ 5810 μm) samples were found. The results evidence the existence of high fish contamination by microplastics and reinforce the need of further research on plastic pollution in estuaries.

Big eyes can't see microplastics: Feeding selectivity and eco-morphological adaptations in oral cavity affect microplastic uptake in mud-dwelling amphibious mudskipper fish

Microplastic contamination is a widespread global problem. Plastic pollution in the oceans has received a lot of news coverage, but there is a significant gap in our knowledge about its effect in estuarine areas and a profound regional bias in available information. Here, we estimated the degree of microplastic pollution, its impact on a selected fish, and its function as a vector for heavy metals in the Ulhas River estuary, which is one of the most fragile, polluted, and anthropogenically impacted estuaries in India. Using mudskipper fish, we have also assessed how the feeding guild and ecomorphological adaptations in the feeding apparatus affected the microplastic intake and life history traits of the fish. Sediment, water and fish samples were collected from three sampling localities (S1, S2 and S3) in the Ulhas River estuary and analysed. Findings showed an increase in microplastic abundance from S1 (suburban) to S3 (urban industrial belt) in sediment (96.67-130.0 particles kg^-1), water (0.28-0.41 particles L^-1) and fish (3.75-6.11 particles per fish). Fragments, followed by pellets and filaments largely contribute to the plastic morphotypes in sediment and water. FTIR analysis revealed polymers of anthropogenic and industrial origin such as polypropylene, Surlyn ionomer, low-density polyethylene, and polyethylene or polybutylene terephthalate. Only filaments were found in the guts of 74% of the mudskippers examined, which may be due to their filter-feeding habit and unique anatomical arrangement of oral structures that effectively filter large microplastic particles. Microplastic abundance showed a strong negative correlation with condition factor, fullness index and hepatosomatic index of fish. SEM-EDS analysis revealed that the microplastic surface topography played an important part in adsorbing heavy metals from a water body containing these contaminants. Results highlight the contamination of vulnerable estuarine habitats, harmful effects on resident biota, and health threats to dependent populations.

Do Freshwater Fish Eat Microplastics? A Review with A Focus on Effects on Fish Health and Predictive Traits of MPs Ingestion

Microplastics (MPs) have received increasing attention in the last decade and are now considered among the most concerning emerging pollutants in natural environments. Here, the current knowledge on microplastic ingestion by wild freshwater fish is reviewed with a focus on the identification of possible factors leading to the ingestion of MPs and the consequences on fish health. Within the literature, 257 species of freshwater fishes from 32 countries have been documented to ingest MPs. MPs ingestion was found to increase with rising level of urbanization, although a direct correlation with MPs concentration in the surrounding water has not been identified. MPs ingestion was detected in all the published articles, with MPs presence in more than 50% of the specimens analyzed in one study out of two. Together with the digestive tract, MPs were also found in the gills, and there is evidence that MPs can translocate to different tissues of the organism. Strong evidence, therefore, exists that MPs may represent a serious risk for ecosystems, and are a direct danger for human health. Moreover, toxicological effects have also been highlighted in wild catches, demonstrating the importance of this problem and suggesting the need for laboratory experiments more representative of the environmental situation.

Microplastics in marine biota: A review

Plastics are the most important component in marine debris. In turn, within plastics, microplastics (<5 mm) are those that most affect marine biota. Thus, this review has as its main objective to show the current state of studies of microplastics, as well as to determine the groups of vertebrates most affected by microplastics, and the type and predominant color of microplastics. For this research, we review a total of 132 articles, from 2010 to May of 2020. Our results show that the group more affected are turtles with 88% of the specimens contaminated by microplastics and median of 121.73 particles/individue. The predominant type is fibers (67.3%), polymer is polyethylene (27.3%), size is less than 2 mm (73.6%), and color is blue (32.9%).

Microplastic pollution in African countries' water systems: a review on findings, applied methods, characteristics, impacts, and managements

ABSTRACT

Owed to their simplicity, flexibility, lightweight, and low cost, plastics have become highly demanded in Africa as well as worldwide. However, the management of plastic wastes, particularly in African countries, is inadequate and most of the plastic debris is gatewayed into the water bodies. Nowadays, environmentalists, organizations, and governments are aware of microplastic pollution in the marine and terrestrial environment. Thus, addressing a compressive literature review in one referenced paper, as they draw up the articles, is essential to propose new research directions, to synthesize the existing theories among the existing studies. The abundance of microplastics is variable depending on the sampling and identification techniques. In this review, the available publications on microplastic pollution in African countries' water systems were retrieved. Investigations found that microplastic pollution levels in the studied water bodies were reported in high concentrations. It was observed that different sampling and analytical methods were applied for the detection of microplastics, and suggestions were raised at it may affect the reliability of the results. Most of the detected and quantified microplastics were confirmed as they are from secondary sources. Most of the microplastic pollution research was conducted dominantly in South Africa, and secondly Nigeria, although other countries should also start conducting in their water systems. Surface water and sediment samples were dominantly carried out, but are limited with biota samples; hence, the risk assessment of microplastics is not yet determined. Some of the African countries have regulations on the prevention of macroplastic wastes, but the implementations are unsuccessful and most have not yet been established resulting in a threat of microplastics pollution. Thus, the research priorities on microplastic detection should be identified, and the African countries' governments should be more proactive in eradicating macroplastic, which ends up as microplastics, pollutions in the water environments.

GRAPHIC ABSTRACT

ARTICLE HIGHLIGHTS

Researches on microplastic pollution in African countries water system is limited .A high microplastics abundance is found in African countries water system.Sampling methods and used analytical techniques for microplastic detection were included.Harmonized standard methods for microplastic pollution research should be established.Combined analytical tools at once should be adopted to detect reliable microplastics.

Full size microplastics in crab and fish collected from the mangrove wetland of Beibu Gulf: Evidences from Raman Tweezers (1-20 μm) and spectroscopy (20-5000 μm)

Microplastic pollution in organisms is a growing environmental concern worldwide. Current methods to identify microplastics (MPs) are subject to the limitations of analytical techniques, and there is no full-scale method to measure MPs in organisms. In this study, Raman Tweezers and spectroscopy methods were combined and applied to identify MPs in organisms within the size range of 1-5000 μm. The abundance of small MPs (1-20 μm) was measured in crab (0.39-2.83 items/individual) and fish (0.35-3.22 items/individual). Most MPs were transparent in color and pellet shape. The proportion of small MPs (1-20 μm) was 35.77%, and analysis revealed the non-inclusion of this fraction will induce large deviations in the overall measurement. The large MPs (20-5000 μm) were identified in crab and fish with abundances ranging from 0.74-4.96 items/individual and 0.72-5.39 items/individual, respectively. Mainly fiber shape items were detected, the dominant particle size ranged from 20 to 100 μm, and most MPs were white. Polyethylene (PE) and polyethylene terephthalate (PET) were the main types of MPs polymers detected. Our study fills the gap to provide a new method to detect MPs in organisms below 20 μm, facilitating study of the migration and transformation of small MPs in the environment.

Quantitative and qualitative determination of microplastics in oyster, seawater and sediment from the coastal areas in Zhuhai, China

Microplastics as a new class of environmental contaminants have become the hot issue of global concern. We conducted quantitative and qualitative experiments to investigate microplastics in oyster, seawater and sediment along the Zhuhai coastline. The soft tissues of oysters were digested with potassium hydroxide (10%) and hydrogen peroxide (30%), seawaters and sediments with hydrogen peroxide (30%) to degrade organic matter, and analyzed using a digital camera, optical microscopy and micro-ATR-FTIR. The abundance of microplastics were in the range of 0.14-7.90 n/g in oysters (wet weight), 10.00-27.50 n/L in seawaters and 0.053-0.26 n/g in sediments. The fiber and fragment shape, black color, 101-500 μm of size and polyethylene composition were all classified as the major constituents of microplastics. The level of contaminants in oysters was correlated to those in their surrounding environments. Therefore, oysters may serve as a promising sentinel species for the indication of microplastic pollution in the coastal zone of Zhuhai.

Toxicokinetic/toxicodynamic-based risk assessment of freshwater fish health posed by microplastics at environmentally relevant concentrations

The pervasive contamination of microplastics (MPs) in freshwater ecosystems is of emerging concern. Mechanistic link between exposure and effect on assessing health risk of freshwater fish posed by environmental MPs, however, is more limited. Our study filled this gap by developing a toxicokinetic/toxicodynamic (TK/TD)-based risk assessment framework to examine health effects of zebrafish and red tilapia responses to environmental concentrations of MPs appraised with a variety of valuable published data on a global scale. We assessed organ-specific TK parameters and mean residence times for polystyrene (PS)-MPs-exposed freshwater fish in size- and concentration-dependent manners. We estimated the relatively sensitive benchmark concentrations (BMCs) of PS-MPs for oxidative stress in zebrafish and detoxification in red tilapia to be ~1.0 and ~119 μg g^-1, respectively. Based on continental scale MPs trends, the high MPs concentrations were over Asia, with a mean value of 36 mg L^-1. Given metabolic disturbances in zebrafish and red tilapia as bioindicators, we found that MPs pollution was highly likely to enhance fish health risks and that this factor must therefore be considered in evaluations of MPs susceptibility of freshwater fish. Our TK/TD-based risk scheme could help inform intensified efforts to mitigate environmental MPs pollution in order to benefit freshwater fish species and people who depend on healthy stocks of different fish.

Microplastics in African ecosystems: Current knowledge, abundance, associated contaminants, techniques, and research needs

Despite Africa ranking top in mismanaged plastic waste, there is insufficient data on the extent of microplastics and its interaction with other contaminants in its ecosystems. Microplastics pollution has been documented globally, however, specific data from the continent is crucial for accurate risk assessment and to drive policies. We critically reviewed 56 articles from 1987 to 2020 and provide an overview of the current knowledge of the abundance and distribution of microplastics and associated contaminants in African aquatic systems and organisms. Most of the studies were carried out in the marine environment and there is currently no available data on the abundance of microplastic pollution in the African terrestrial environment. We show that across all studies, 5-100% of all sampled aquatic organisms contained microplastics. Concerning high levels of microplastics were reported in fish from Egypt compared to other parts of Africa and the world. Across all persistent organic pollutants sampled in microplastics, hopanes and phthalates were present at high concentrations while sodium and zinc were high relative to other trace metals reported. The most frequently occurring plastics were polyethylene followed by polypropylene and polystyrene. We found that most of the studies relied on visual inspection (52%) > FTIR (38%) > Raman spectroscopy (5%) > Scanning electron microscopy (3%) > Differential scanning calorimetry (2%) for identifying microplastics. Major gaps in sampling and identification techniques which may have overestimated or underestimated the current levels were identified. We discuss other research priorities and recommend solutions to address these issues associated with microplastic pollution in Africa.

Microplastics accumulation in sediments and Periophthalmus waltoni fish, mangrove forests in southern Iran

This investigation was aimed to identify microplastics in the sediment and mudskipper fish (Periophthalmus waltoni) in mangrove forests in southern Iran. Sediments and mudskipper samples were collected at high, mid, and low tidal points of five stations. A total of 2657 plastic particles in different size, color, shape, and genera were identified from sediment samples and 15 microplastic were isolated from mudskippers. The highest and lowest abundance of isolated microplastics from sediments was observed in mangrove forests of Bidkhoun (urban area) and Bordkhon, respectively while no microplastics were found in the fish tissue in those stations. The black (60%) and white (7%) color microplastics in the mudskipper had the highest and the lowest frequency. The highest and lowest polymers in mangrove forest sediments were corresponded to polystyrene (26%) and polycarbonate (3%), respectively. Raman and Fourier transform infrared spectroscopy (FT-IR) techniques were used to identify the type of the polymer. Most of the microplastics found were made of polystyrene, polypropylene, and polyethylene terephthalate. The type of studied area and texture of sediment separately affected the frequency of microplastic and mesoplastic (P-value <0.05) in the sediment samples. The abundance of microplastics in the sediment samples of the Bidkhoun mangrove forest was higher than other studied stations due to proximity to urban and industrial areas. The findings of this study raised concerns about microplastic pollution in the mangrove forests of southern Iran, a threat to the ecosystem and public health, which requires careful actions to prevent and diminish its adverse effects.

Characterization of microplastics in mangrove sediment of Muara Angke Wildlife Reserve, Indonesia

An investigation of microplastic abundance and its characteristics was conducted in Muara Angke Wildlife Reserve, a relic mangrove forest in the Jakarta metropolitan, to contribute to marine microplastics' national data inventory. Microplastics were found in all the stations, with an average of 28.09 ± 10.28 particles per kg of dry sediment (n kg^-1). Sediments in the outside mangrove area contained more microplastics than the inside area. Foam form was the most dominant in all the samples and was found more abundant on the outside. More than half of microplastics were of size <1000 μm, and nearly 50% were polystyrenes. This polymer is widely used for food packaging, which is prone to be fragmented. Polypropylene and polyethylene form another 50% of microplastics, which are widely used for textiles and fishing gears. As Jakarta is the largest city in Indonesia, this microplastic dataset may be the benchmark for other mangroves around the country.

Meso- and microplastics monitoring in harbour environments: A case study for the Port of Durban, South Africa

An investigation into the abundance and distribution of meso- and microplastics within the Port of Durban was conducted using a static immersible water pump and particle filtration system to collect meso- and microplastics from the water column, microplastics from sediment samples and corresponding CTD. Microplastics were detected in all samples under investigation. Results suggest that sewage overflow, stormwater drains, port operations, followed by rivers are input areas for mitigation to focus on. Identifying meso- and microplastics inputs, baselines and distribution allow for long term monitoring and management in a harbour environment. This can potentially contribute to the control and regulation of small plastics particles in harbours, and the subsequent transport of these pollutants via dredged material into other ecosystems.

Plastic pollution threat in Africa: current status and implications for aquatic ecosystem health

Rapid population growth and poor waste management practice are among the main drivers of plastic pollution in modern times, thus making Africa a hotspot for plastic pollution both now and in the future. This study is a review of plastic pollution reports from the African aquatic environment with regard to causes, current status, toxicological implications and implications for ecosystem services. A total of 59 plastic pollution studies from 1987 to September 2020 were reviewed. They comprised 15 from North Africa (NA) (Algeria, Egypt, Morocco and Tunisia), six from East Africa (EA) (Ethiopia, Kenya, Tanzania and Uganda), 13 from West Africa (WA) (Ghana, Guinea-Bissau, Mauritania and Nigeria), and 25 studies from Southern Africa (SA) (South Africa). This shows that plastic pollution studies in Africa, according to the sub-regions, are in the order: SA > NA > WA > EA. High human population in the basins of African large aquatic systems is identified as the greatest driver enhancing plastic surge in the aquatic environment. The occurrence of plastics was mostly reported in the estuarine/marine environment (42 studies) compared to the freshwater environment (only 17 studies). Plastics have also been reported in the three compartments of the aquatic environment: water column, benthic sediment and animals. Zooplankton, annelids, molluscs, insects, fishes and birds were reported as bioindicators of plastic ingestion in the inland and coastal waters of Africa. Polyethylene, polyethylene terephthalate (polyester) and polypropylene were the common plastic polymers observed in the African aquatic environment. In situ toxicological implications of the ingested plastic polymers were not reported in any of the studies. However, reports from laboratory-controlled experiments showed that these polymers are deleterious to aquatic animal health. More research efforts need to delineate the plastic pollution status of the East, West and North of Africa. Furthermore, such studies are required to identify the plastic polymers and in situ ecotoxicological impacts of plastics on both animal and human health.

Microplastics pollution in mangrove ecosystems: A critical review of current knowledge and future directions

Over the last decade, microplastics (MPs, plastic particles <5 mm) as emerging contaminants have received a great deal of international attention, not only because of their continuous accumulation in both marine and terrestrial environment, but also due to their serious threats posed to the environment. Voluminous studies regarding sources, distribution characterization, and fate of MPs in the different environmental compartments (e.g., marine, freshwater, wastewater, and soil) have been reported since 2004, whereas MPs pollution in unique marine ecosystems (e.g., coastal mangrove habitat) receives little scientific attention. Mangrove ecosystem, an important buffer between the land and the sea, has been identified as a potential sink of MPs caused by both marine and land-based activities. Moreover, the source and distribution characteristics of MPs in this ecosystem are significantly different from other coastal habitats, mainly owing to its unique features of high productivity and biomass. With the impetus to provide a more integrated view of MPs pollution in mangrove habitats, a literature review was conducted based on the existing studies related to this topic. This is the first review to present the current state of MPs pollution in mangrove ecosystems, specially including (i) the possible sources of MPs in mangrove areas and their pathways entering into this habitat; (ii) MPs pollution in the different mangrove compartments (including surface seawater, sediments, and biotas); and (iii) factors influencing MPs distribution in mangrove areas. Toward that end, the research gaps are proposed to guide for future research priorities.

Towards Characterising Microplastic Abundance, Typology and Retention in Mangrove-Dominated Estuaries

Plastic and, particularly, microplastic (MP) pollution is a growing research theme, dedicated largely to marine systems. Occurring at the land–sea interface, estuarine habitats such as mangroves are at risk of plastic pollution. This study compared MP pollution (level, morphotype, polymer composition, size and colour) across four South African estuaries, in relation to the built and natural environment. Mouth status, surrounding human population densities and land-use practices influenced the level and type of MP pollution. Systems that were most at risk were predominantly open estuaries surrounded by high population densities and diverse land use types. Microplastic levels and the diversity of types detected increased with increasing levels of anthropogenic disturbance. Overall, microfibres dominated in estuarine water (69%) and mangrove sediment (51%). Polyethylene (43%) and polypropylene (23%) were the dominant polymers overall. Weathered fishing gear, weathered packaging items and run-off from urban/industrial centres are probable sources of MP pollution. Increased run-off and river input during the wet/rainy season may explain the markedly higher MP loads in estuarine waters relative to the dry season. By contrast, MP deposition in mangrove sediment was higher during the dry season. Sediment MP abundance was significantly positively correlated with both pneumatophore density and sediment size (500–2000 µm). This study highlights the role of mangroves as MP sinks, which may limit movement of MPs into adjacent environments. However, under conditions such as flooding and extreme wave action, mangroves may shift from sinks to sources of plastic pollution.

Global distribution of microplastics and its impact on marine environment-a review

Microplastics are the major environmental health hazards spotted in almost all the marine habitats and biota of world. The earlier research on microplastics have mainly focused on studying abundance and distribution as well as impacts on organisms, while the existing review articles have reviewed on any one of the above aspects or the environmental fate of microplastics. The current review focuses on all the above facets thereby bringing out the incompleteness in information globally in the respective facets. Our findings suggest that among 192 countries of the world, only 22.9% (44) of the countries have carried out research regarding microplastics, while impacts on organisms have mostly targeted fish (38%), whereas studies on other highly affected organisms such as turtles (1%) are not well documented. Therefore, we suggest expanding research in all the above aspects of microplastics considering that there are several pristine marine environments and organisms that are yet unexplored. Quantifying research in these regards would enable to propose a microplastic threshold level and formulate control measures to reduce the use of plastics and its subsequent threat to the marine environment.

Microplastics in aquatic environment: characterization, ecotoxicological effect, implications for ecosystems and developments in South Africa

Microplastics are small-size plastic piece scales (particles < 5 mm) in sediments and waters which interact with environment and organisms by various means. Microplastics are becoming a universal ecological concern since they may be a source of hazardous chemicals to marine organisms and environments. Recent research suggests microplastics could enable the transfer of hydrophobic aquatic pollutants or chemical additives to biota. Even though microplastic presence and interactions are recently being detected in marine and freshwater systems, the fate of microplastics is still very poorly understood. This literature review is a summary of the sources and transport of microplastics, their interactions with toxic chemicals and the methodologies for chemical quantification and characterization of microplastics. The environmental outcome and impact of microplastics in wastewater treatment plants were assessed as well as the trends and update on microplastic research in the South African aquatic ecosystem.

Impacts of plastic debris on biota and implications for human health: A South African perspective

Entanglement and ingestion of plastics are the main ecological impacts of marine plastic debris on marine biota, but indirect effects such as the transport of alien species and benthic smothering are also important to note. Entanglement of invertebrates, sharks, turtles, birds and marine mammals is mainly caused by macroplastics (>5 mm), and leads to reduced mobility, ineffective foraging and subsequent mortality. The main plastic types associated with entanglement are improperly discarded fishing nets, lines, ropes and straps. In South Africa and surrounding waters, plastic ingestion has been reported in a number of marine species: sharks (n=10), fish (n>=7), turtles (n=1) and birds (n=36). Lethal (macroplastic) and sub-lethal effects (microplastic ≤5 mm) of marine debris on biota have been noted, but at the time of this review there were no published reports on impacts at the population level. Consumed shellfish are possible vectors for the introduction of microplastics into humans. The specific impacts of microplastic ingestion on human health are largely unknown, but additives associated with plastics represent a threat. The research infrastructure in South Africa is insufficient to monitor and characterise marine plastic debris and, in many cases, not in line with global standards. More research effort is needed to understand the impacts of marine plastic debris on humans and marine biota in South Africa, particularly at the population level. Significance • Macroplastics affect marine biota mainly via entanglement and microplastics largely through ingestion. • Macro- and microplastic interactions with biota can result in sub-lethal effects and mortality but no population effects have been reported for South Africa. • Consumed shellfish are a potential source of microplastics for humans but their potential effects in humans remain unknown. • Better infrastructure is needed for improved monitoring and research on the effects of marine debris in South Africa.