Microplastics are highly bioavailable to marine organisms, either through direct ingestion, or indirectly by trophic transfer from contaminated prey. The latter has been observed for low-trophic ...level organisms in laboratory conditions, yet empirical evidence in high trophic-level taxa is lacking. In natura studies face difficulties when dealing with contamination and differentiating between directly and indirectly ingested microplastics. The ethical constraints of subjecting large organisms, such as marine mammals, to laboratory investigations hinder the resolution of these limitations. Here, these issues were resolved by analysing sub-samples of scat from captive grey seals (Halichoerus grypus) and whole digestive tracts of the wild-caught Atlantic mackerel (Scomber scombrus) they are fed upon. An enzymatic digestion protocol was employed to remove excess organic material and facilitate visual detection of synthetic particles without damaging them. Polymer type was confirmed using Fourier-Transform Infrared (FTIR) spectroscopy. Extensive contamination control measures were implemented throughout. Approximately half of scat subsamples (48%; n = 15) and a third of fish (32%; n = 10) contained 1–4 microplastics. Particles were mainly black, clear, red and blue in colour. Mean lengths were 1.5 mm and 2 mm in scats and fish respectively. Ethylene propylene was the most frequently detected polymer type in both. Our findings suggest trophic transfer represents an indirect, yet potentially major, pathway of microplastic ingestion for any species whose feeding ecology involves the consumption of whole prey, including humans.
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•Microplastic trophic transfer in marine top predators is poorly understood.•Use of captive seals and wild caught fish resolved practical limitations of in natura studies.•Extensive contamination controls were implemented throughout.•Half of scat sub-samples and a third of fish contained 1–4 microplastics.•Trophic transfer may represent an indirect, yet major, pathway of microplastic ingestion.
Microplastic trophic transfer in marine top predators is poorly understood; this study using captive seals found that half of the scat sub-samples and a third of the wild caught fish they were fed on contained 1–4 microplastics, indicating transfer from prey to predator.
Microplastics receive significant societal and scientific attention due to increasing concerns about their impact on the environment and human health. Marine mammals are considered indicators for ...marine ecosystem health and many species are of conservation concern due to a multitude of anthropogenic stressors. Marine mammals may be vulnerable to microplastic exposure from the environment, via direct ingestion from sea water, and indirect uptake from their prey. Here we present the first systematic review of literature on microplastics and marine mammals, composing of 30 studies in total. The majority of studies examined the gastrointestinal tracts of beached, bycaught or hunted cetaceans and pinnipeds, and found that microplastics were present in all but one study, and the abundance varied between 0 and 88 particles per animal. Additionally, microplastics in pinniped scats (faeces) were detected in eight out of ten studies, with incidences ranging from 0% of animals to 100%. Our review highlights considerable methodological and reporting deficiencies and differences among papers, making comparisons and extrapolation across studies difficult. We suggest best practices to avoid these issues in future studies. In addition to empirical studies that quantified microplastics in animals and scat, ten studies out of 30 (all focussing on cetaceans) tried to estimate the risk of exposure using two main approaches; i) overlaying microplastic in the environment (water or prey) with cetacean habitat or ii) proposing biological or chemical biomarkers of exposure. We discuss advice and best practices on research into the exposure and impact of microplastics in marine mammals. This work on marine ecosystem health indicator species will provide valuable and comparable information in the future.
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•A timely systematic review of literature on microplastics (MPs) in marine mammals.•Most studies examined the guts of cetaceans or faeces of pinnipeds for MPs.•A range of taxa around the world are exposed to and ingest microplastics.•Several studies attempted to estimate risk of MP exposure for cetaceans.•Robust, standardized protocols are proposed to improve comparability across studies.
Capsule: A first systematic review on microplastics and marine mammals. We summarize and discuss research findings and discuss best practices in the field to guide future research on this topic.
Microplastics (plastic < 5 mm in size) are now known to contaminate riverine systems but understanding about how their concentrations vary spatially and temporally is limited. This information is ...critical to help identify key sources and pathways of microplastic and develop management interventions. This study provides the first investigation of microplastic abundance, characteristics and temporal variation along the Ganges river; one of the most important catchments of South Asia. From 10 sites along a 2575 km stretch of the river, 20 water samples (3600 L in total) were filtered (60 samples each from pre- and post-monsoon season). Overall, 140 microplastic particles were identified, with higher concentrations found in the pre-monsoon (71.6%) than in post-monsoon (61.6%) samples. The majority of microplastics were fibres (91%) and the remaining were fragments (9%). We estimate that the Ganges, with the combined flows of the Brahmaputra and Meghna rivers (GBM), could release up to 1–3 billion (109) microplastics into the Bay of Bengal (north-eastern portion of the Indian Ocean) every day. This research provides the first step in understanding microplastic contamination in the Ganges and its contribution to the oceanic microplastic load.
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•The microplastics identified were dominated by fibers (91%) and fragments (9%).•A greater number of microplastics were found pre-monsoon than post-monsoon•Microplastic concentrations increased from source to sea.•Approximately 1–3 billion microplastic pieces are discharged into the Bay of Bengal daily.
We estimate that up to 1–3 billion microplastics are released into the Bay of Bengal every day.
Rivers worldwide are now acting as major transport pathways for plastic pollution and discharge large quantities of waste into the ocean. Previous oceanographic modelling and current drifter data ...have been used to predict the movement and accumulation of plastic pollution in the marine environment, but our understanding of the transport and fate through riparian systems is still largely unknown. Here we undertook a proof of concept study by applying open source tracking technology (both GPS (Global Positing System) cellular networks and satellite technology), which have been successfully used in many animal movement studies, to track the movements of individual plastic litter items (500 ml PET (polyethylene terephthalate) drinks bottles) through the Ganges River system (known as the Ganga in India and the Padma and Meghna in Bangladesh, hereafter known as the Ganges) and the Bay of Bengal. Deployed tags were successfully tracked through the Ganges river system and into the Bay of Bengal marine system. The "bottle tags" were designed and built (e.g. shape, size, buoyancy) to replicate true movement patterns of a plastic bottle. The maximum distance tracked to date is 2845 km over a period of 94 days. We discuss lessons learnt from the development of these plastic litter tags, and outline how the potential widespread use of this open source technology has the ability to significantly increase understanding of the location of accumulation areas and the timing of large inputs of plastic pollution into the aquatic system. Furthermore, "bottle tags" may act as a powerful tool for stimulating social behaviour change, informing science-based policy, and as valuable educational outreach tools for public awareness.
Rivers play a crucial role in transporting land-based plastic waste to the ocean, with the Ganges reported as the second largest contributing river of plastic pollution globally. To better quantify ...global plastic pollution transport and effectively reduce the sources and risks imposed, a clear understanding of the origin, transport, fate, and effects of riverine plastic debris is important. In this review paper, we discuss the current state of knowledge of plastic pollution in aquatic systems in Bangladesh and evaluate existing research gaps. Bangladesh has been recognized as an internationally significant nation in the plastic pollution crisis, but this paper identifies a major disconnect in knowledge, understanding and capacity to understand and address this critical environmental and public health issue. Here, we review all available scientific publications on plastic pollution in the freshwater and marine environment in Bangladesh and identify key research themes. A total of 24 studies relevant to plastic pollution were published from 2006 to 2019, of which 18 were selected for this study under the authors’ criteria. Nine focused on plastic pollution in the marine environment, eight focused on plastic waste generation and management and only one focused on the freshwater environment. We compared our findings with three other countries in the Global South with comparable per capita gross domestic product (GDP) and mismanaged waste, namely Cambodia, Kenya, and Tanzania, revealing similar knowledge gaps. This lack of research demonstrates a need for further work to monitor and model riverine plastic transport and examine the implications for aquatic organisms. This will facilitate the formulation of national management strategies aimed at addressing plastic pollution.
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•Bangladesh was the first country in the world to ban plastic bags in 2002.•Plastic pollution in the diverse aquatic systems of Bangladesh is an emerging issue.•Bangladesh ranks 10th globally in terms of the levels of mismanaged plastic waste.•Our review finds plastic pollution studies in Bangladesh are very limited and skewed to overall observation/snapshot.•The River Ganges contributes the second largest amount of plastic to oceans, yet only one report exists.
Marine Protected Areas (MPAs) are designated to enable the management of damaging activities within a discrete spatial area, and can be effective at reducing the associated impacts, including habitat ...loss and over-exploitation. Such sites, however, may be exposed to the potential impacts from broader scale pressures, such as anthropogenic litter, due to its diffuse nature and lack of constraint by legislative and/or political boundaries. Plastic, a large component of litter, is of particular concern, due to increasing evidence of its potential to cause ecological and socio-economic damage. The presence of sensitive marine features may mean that some MPAs are at greater potential risk from the impacts of plastic pollution than some non-protected sites. Understanding the abundance, distribution and composition of litter along coastlines is important for designing and implementing effective management strategies. Gathering such data, however, can be expensive and time-consuming but litter survey programmes that enlist citizen scientists are often able to resolve many of the logistical or financial constraints. Here, we examine data collected over 25-years (1994–2018), by Marine Conservation Society volunteers, for spatial patterns in relation to the English MPA network, with the aim of highlighting key sources of litter and identifying management priority areas. We found that MPAs in southeast (Kent) and southwest (Cornwall and Devon) England have the highest densities of shore-based litter. Plastic is the main material constituent and public littering the most common identifiable source. Items attributed to fishing activities were most prevalent in southwest MPAs and sewage related debris was highest in MPAs near large rivers and estuaries, indicating localised accumulation. When comparing inside and outside of MPAs, we found no difference in litter density, demonstrating the need for wider policy intervention at local, national and international scales to reduce the amount of litter.
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•Plastic is the main material constituent of litter in Marine Protected Areas.•No difference in litter density inside MPAs compared with outside.•MPAs may be exposed to the potential impacts of plastic pollution.•Regional variation in sources demonstrates need for locally appropriate management.•Abstract.
Abandoned, lost or otherwise discarded fishing gear represents a substantial proportion of global marine plastic pollution and can cause significant environmental and socio-economic impacts. Yet ...little is known about its presence in, and implications for, freshwater ecosystems or its downstream contribution to plastic pollution in the ocean. This study documents fishing gear-related debris in one of the world's largest plastic pollution contributing river catchments, the Ganges. Riverbank surveys conducted along the length of the river, from the coast in Bangladesh to the Himalaya in India, show that derelict fishing gear density increases with proximity to the sea. Fishing nets were the main gear type by volume and all samples examined for polymer type were plastic. Illegal gear types and restricted net mesh sizes were also recorded. Socio-economic surveys of fisher communities explored the behavioural drivers of plastic waste input from one of the world's largest inland fisheries and revealed short gear lifespans and high turnover rates, lack of appropriate end-of-life gear disposal methods and ineffective fisheries regulations. A biodiversity threat assessment identified the air-breathing aquatic vertebrate species most at risk of entanglement in, and impacts from, derelict fishing gear; namely species of threatened freshwater turtle and otter, and the endangered Ganges river dolphin. This research demonstrates a need for targeted and practical interventions to limit the input of fisheries-related plastic pollution to this major river system and ultimately, the global ocean. The approach used in this study could be replicated to examine the inputs, socio-economic drivers and ecological impacts of this previously uncharacterised but important source of plastic pollution in other major rivers worldwide.
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•Fishing gear is a significant source of plastic pollution in the Ganges River system.•Fisher knowledge provided insights into behavioural drivers of gear disposal.•Waste gear poses a risk to aquatic species of conservation concern.•Targeted and practical solutions are needed to reduce gear input.•Future work should examine plastic pollution from fisheries in other major rivers.
Monitoring beach plastic contamination across space and time is necessary for understanding its sources and ecological effects, and for guiding mitigation. This is logistically and financially ...challenging, especially for microplastics. Citizen science represents an option for sampling accessible sites to support long term monitoring, but challenges persist around data validation. Here we test a simple citizen science methodology to monitor visible microplastic contamination on sandy beaches using a standard quadrat unit (50 cm × 50 cm x 5 cm depth) sieved to 1 mm, to support the analysis of microplastic on two islands within the marine protected area of the Galápagos Archipelago, Ecuador (San Cristóbal and Santa Cruz islands). High school and university students undertook supervised sampling of two beaches in 2019–2020 collecting over 7000 particles. A sub-sample of the suspected microplastics collected (n = 2,213, ∼30% total) were analysed using FTIR spectrometry, confirming 93% of particles >1 mm visually identified by students were microplastics or rubber, validating this method as a crowd-sourced indicator for microplastic contamination. These data provide important insights into the plastic contamination of Galápagos, revealing plastic abundances of 0–2524 particles m−2 over the two beaches (the highest reported in Galápagos). Strong accumulation gradients were measured parallel to the waterline at Punta Pitt (San Cristobal island) and perpendicular to the waterline at Tortuga Bay (Santa Cruz island), where four-fold higher concentrations were recorded at the sea turtle nesting habitat on the back-beach dune. No significant seasonal trends were measured during one year. These results demonstrate the value of citizen science in filling spatiotemporal knowledge gaps of beach contamination to support intervention design and conservation.
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•Citizen scientists correctly identified plastics or rubber in 93% of particles.•Concentrations varied from 0 to >2500 particles m−2 with accumulation gradients.•No significant spatiotemporal microplastic variation was measured over a year.•Localised high densities of polyethylene pellets were recorded on one island.•Simple quadrat/sieve method offers accessible beach microplastic monitoring option.
Rivers are key pathways for the transfer of microplastics (MP) to marine environments. However, there are considerable uncertainties about the amount of microplastics transported by rivers to the ...ocean; this results in inaccuracies in our understanding of microplastic quantity and transport by freshwater systems. Additionally, it has been suggested that rivers may represent long-term sinks, with microplastics accumulating in sediment due to their high density or other biological, chemical, and physical factors. The atmosphere is also an important pathway by which airborne microplastics may enter aquatic habitats. Here, we compare for first time microplastics type and concentration in these key environmental mediums (air, water and sediment) along a major river (Ganges), from sea to source to understand 1) the abundance, 2) the spatial distribution, and 3) characteristics. Mean microplastic abundance settling from the atmosphere was 41.12 MP m−2 day−1; while concentrations in sediment were 57.00 MP kg−1 and in water were 0.05 MP L−1. Across all sites and environmental mediums, rayon (synthetically altered cellulose) was the dominant polymer (54–82 %), followed by acrylic (6–23 %) and polyester (9–17 %). Fibres were the dominant shape (95–99 %) and blue was the most common colour (48–79 %). Across water and sediment environmental mediums, the number of microplastics per sample increased from the source of the Ganges to the sea. Additionally, higher population densities correlated with increased microplastic abundance for air and water samples. We suggest that clothing is likely to be the prominent source of microplastics to the river system, influenced by atmospheric deposition, wastewater and direct input (e.g. handwashing of clothes in the Ganges), especially in high density population areas. However, we suggest that subsequent microplastic release to the marine environment is strongly influenced by polymer type and shape, with a large proportion of denser microplastics settling in sediment prior to the river discharging to the ocean.
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•Microplastics were investigated in water, sediment, and air in a major river system for the first time.•For water and sediment there was an increase of microplastics from source to sea.•Higher population densities correlated with increased microplastic abundance in Air and Water.•It is predicted a large proportion of denser microplastics settle in sediment.•Rayon was the dominant polymer and blue fibres were the dominant colour and shape.
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