Microplastics are a prolific environmental contaminant that pose a risk to marine organisms. Ecotoxicological studies have identified microplastics can cause sub-lethal harm to aquatic biota. However, prior studies often lack comparability and environmental relevance, for example focussing upon monodisperse beads at extremely high concentrations. Copepods are keystone marine taxa that play vital roles in the marine food web and biogeochemical cycling. In this study, we adapted ISO methods to conduct acute and partial life-cycle toxicity tests exposing adult and juvenile life stages of the copepod Acartia tonsa to a fully characterised tri-polymer microplastic blend comprising cryoground polyethylene, polypropylene, and nylon particles (5-100 μm) at concentrations ranging 0-1000 μg L-1. The tests considered the toxicity of microplastics on a wide number of endpoints including adult survival, algal ingestion rates, egg production and size, larval development ratio and juvenile survival. Mortality, egg size and larval development ratio proved to be the most sensitive endpoints. The tri-polymer blend had an LC5072h value of 182 μg L-1 providing a baseline for future toxicity testing using this method.

The pervasive use of plastic in modern society has led to plastic litter becoming ubiquitous within the ocean. Land-based sources of plastic litter are thought to account for the majority of plastic pollution in the marine environment, with plastic bags, bottles, wrappers, food containers and cutlery among the most common items found. In the marine environment, plastic is a transboundary pollutant, with the potential to cause damage far beyond the political borders from where it originated, making the management of this global pollutant particularly complex. In this study, the risks of land-derived plastic litter (LDPL) to major groups of marine megafauna - seabirds, cetaceans, pinnipeds, elasmobranchs, turtles, sirenians, tuna and billfish - and a selection of productive and biodiverse biogenic habitats - coral reefs, mangroves, seagrass, saltmarsh and kelp beds - were analysed using a Spatial Risk Assessment approach. The approach combines metrics for vulnerability (mechanism of harm for megafauna group or habitat), hazard (plastic abundance) and exposure (distribution of group or habitat). Several potential high-risk zones (HRZs) across the North Atlantic were highlighted, including the Azores, the UK, the French and US Atlantic coasts, and the US Gulf of Mexico. Whilst much of the modelled LDPL driving risk in the UK originated from domestic sources, in other HRZs, such as the Azores archipelago and the US Gulf of Mexico, plastic originated almost exclusively from external (non-domestic) sources. LDPL from Caribbean islands - some of the largest generators of marine plastic pollution in the dataset of river plastic emissions used in the study - was noted as a significant input to HRZs across both sides of the Atlantic. These findings highlight the potential of Spatial Risk Assessment analyses to determine the location of HRZs and understand where plastic debris monitoring and management should be prioritised, enabling more efficient deployment of interventions and mitigation measures.

Microplastics are a prolific environmental contaminant. Curbing microplastic pollution requires an array of globally relevant interventions, including source-reduction and curative measures. A novel, nature-based solution to microplastics is proposed, in which mussels are deployed in aquatic ecosystems to act as microplastic biofilters, removing waterborne microplastics and repackaging them into biodeposits that are subsequently captured and removed. Blue mussels (Mytilus edulis) were used to establish the feasibility of such an approach. In the laboratory, mussels were exposed to representative microplastics in a flume tank; at an initial concentration of 1000 microplastics L-1, mussels reduced waterborne microplastic concentrations at an average rate of 40,146 microplastics kg(-1) h(-1). Mussel faeces sank irrespective of microplastic content, with average sinking velocities of 223-266 m day(-1). Modelling predicts similar to 3 x 10(9) mussels deployed on ropes at the mouths of estuaries could remove 4% of waterborne microplastics discharged from rivers. Mussels were successfully deployed in a prototype biodeposit collection system in an urban marina, with 5.0 kg of mussels removing and repackaging 239.9 +/- 145.9 microplastics and anthropogenic particles day(-1) into their faeces. These results provide impetus for further development of nature-based solutions targeting plastic debris.

Microplastics are a prolific environmental contaminant that can adversely impact sensitive marine organisms. Curbing marine microplastic pollution requires an array of globally relevant interventions, both upstream (i.e. reducing waste, preventing waste entering the natural environment) and downstream (i.e. removing waste from the natural environment). We are currently scoping whether a nature-based solution using bivalve shellfish as biofilters could be deployed to remove and sequester microplastics that have entered the marine environment and have the potential to cause harm to sensitive biota. Here, we report the results of a feasibility study in which we: (1) establish microplastic removal rates for mussels ( Mytilus edulis ) under controlled laboratory settings; (2) establish the fate of ingested microplastics; and (3) test the efficacy of a pilot set-up for removing microplastics under environmental conditions. To establish microplastic removal efficacies under controlled conditions, mussels were exposed to representative polystyrene microbeads and nylon microfibres at a combined initial concentration of 1000 microplastics L-1 in a flume tank under low flow conditions; we identified 5.0 kg of mussels have the capacity to remove an average of 651.0 ± 16.6 microplastics L-1 h-1from flowing water. Microplastics consumed by mussels were observed to be subsequently repackaged into mussel faeces; measurement of faecal sinking velocities demonstrated that microplastics have no significant impact on faecal sinking rates and will sink out at rates of 223-266 m day-1. Finally, we deployed a prototype system in a local marina to evaluate the efficacy of using mussels as a nature-based solution to remove and collect microplastics under environmental conditions; our results showed 5.0 kg mussels remove 4.5-fold greater numbers of microplastic than systems without mussels. These results provide a basis for scaling up the use of mussels as a nature-based solution in real-world settings.

Microplastics are ubiquitous in the marine environment, however, the mechanisms governing their uptake by, and burial within, seabed habitats are poorly understood. In this study, microplastic burial and its impact on fauna-mediated sedimentary processes was quantified at three coastal sites, and the potential contribution of burrowing faunal communities to this process assessed via functional trait diversity analysis of field data. In addition, laboratory exposures were used to assess whether sediment-processing undertaken by the brittlestar Amphiura filiformis, a key species in the sampled area, could explain the burial of microplastic fibres. Field observations confirmed broad-scale burial of microplastics across the coastal seabed, consistent across sites and seasons, with microplastic sequestration linked to benthic-pelagic exchange pathways, driven by burrowing fauna. Brittlestars were observed to bury and line their burrow walls with microfibres during experiments, and their burial activity was also modified following exposure to nylon fibres, relative to controls. Collectively, these results indicate that biodiverse and functionally important seabed habitats act as microplastic sinks, with burrowing fauna contributing to this process via well-known benthic-pelagic pathways, the rates of which are modified by plastic exposure.

Plastic litter is found everywhere. Walk onto any beach around the world and you will almost certainly find plastic. The harm that large plastic litter can cause to marine animals is well-known; for example, you may have seen sad pictures of turtles eating plastic bags or seals tangled in discarded fishing nets. However, scientists are also concerned about microscopic-sized plastic that we do not normally see, and the problems these tiny plastic particles can cause to small marine animals called zooplankton. We focus on a group of zooplankton called copepods. These small-but-mighty crustaceans are amongst the most abundant animals on our planet, and they play a vital role in regulating Earth’s climate. In this article, we will explain what happens when copepods encounter this microscopic plastic, why they eat plastic, and the impacts it has on their health and on the wider ecosystem.

Microplastic debris is ubiquitous and yet sampling, classifying and enumerating this prolific pollutant in marine waters has proven challenging. Typically, waterborne microplastic sampling is undertaken using nets with a 333 mm mesh, which cannot account for smaller debris. In this study, we provide an estimate of the extent to which microplastic concentrations are underestimated with traditional sampling. Our efforts focus on coastal waters, where microplastics are predicted to have the greatest influence on marine life, on both sides of the North Atlantic Ocean. Microplastic debris was collected via surface trawls using 100, 333 and 500 mm nets. Our findings show that sampling using nets with a 100 mm mesh resulted in the collection of 2.5-fold and 10-fold greater microplastic concentrations compared with using 333 and 500 mm meshes respectively (P < 0.01). Based on the relationship between microplastic concentrations identified and extrapolation of our data using a power law, we estimate that microplastic concentrations could exceed 3700 microplastics m(-3) if a net with a 1 mm mesh size is used. We further identified that use of finer nets resulted in the collection of significantly thinner and shorter microplastic fibres (P < 0.05). These results elucidate that estimates of marine microplastic concentrations could currently be underestimated. (C) 2020 The Authors. Published by Elsevier Ltd.

Microplastics (1 μm-5 mm) are a ubiquitous marine contaminant of global concern, ingested by a wide range of marine taxa. Copepods are a key component of marine food webs, providing a source of food for higher trophic levels, and playing an important role in marine nutrient cycling. Microplastic ingestion has been documented in copepods, but knowledge gaps remain over how this affects feeding preference and faecal density. Here, we use exposure studies incorporating algal prey and microplastics of varying sizes and shapes at a concentration of 100 microplastics mL-1 to show: (1) prey selection by the copepod Calanus helgolandicus was affected by the size and shape of microplastics and algae they were exposed to; Exposure to nylon fibres resulted in a 6% decrease in ingestion of similar shaped chain-forming algae, whilst exposure to nylon fragments led to an 8% decrease in ingestion of a unicellular algae that were similar in shape and size. (2) Ingestion of microplastics with different densities altered the sinking rates of faecal pellets. Faeces containing low-density polyethylene sank significantly more slowly than controls, whilst sinking rates increased when faeces contained high-density polyethylene terephthalate. These results suggest that C. helgolandicus avoid ingesting algae that are similar in size and/or shape to the microplastic particles they are exposed to, potentially in a bid to avoid consuming the plastic.

Microplastic debris is a pervasive environmental contaminant that has the potential to impact the health of biota, although its modes of action remain somewhat unclear. The current study tested the hypothesis that exposure to fibrous and particulate microplastics would alter feeding, impacting on lipid accumulation, and normal development (e.g., growth, moulting) in an ecologically important coldwater copepod Calanus finmarchicus. Preadult copepods were incubated in seawater containing a mixed assemblage of cultured microalgae (control), with the addition of ∼50 microplastics mL-1 of nylon microplastic granules (10-30 μm) or fibers (10 × 30 μm), which are similar in shape and size to the microalgal prey. The additive chemical profiles showed the presence of stabilizers, lubricants, monomer residues, and byproducts. Prey selectivity was significantly altered in copepods exposed to nylon fibers (ANOVA, P < 0.01) resulting in a nonsignificant 40% decrease in algal ingestion rates (ANOVA, P = 0.07), and copepods exposed to nylon granules showed nonsignificant lipid accumulation (ANOVA, P = 0.62). Both microplastics triggered premature moulting in juvenile copepods (Bernoulli GLM, P < 0.01). Our results emphasize that the shape and chemical profile of a microplastic can influence its bioavailability and toxicity, drawing attention to the importance of using environmentally relevant microplastics and chemically profiling plastics used in toxicity testing.

Microplastic debris is a globally pervasive contaminant, which presents a substantial risk to marine biota, food webs, and ecosystems. Microplastics are heterogeneously distributed, with highest concentrations associated with the oligotrophic subtropical gyres and relatively biologically productive semienclosed seas and coastal waters. Encounter rates between biota and microplastics are driven by their geographic overlap and relative concentrations; the characteristics of the plastic; and the motility, detection capabilities, and feeding strategy of the organism. We identify four main routes via which microplastics can infiltrate marine food webs: ingestion, inhalation, entanglement, and trophic transfer. Drawing upon established research and more recent exposure studies using microplastics, we highlight how plastics can be detected, ingested, processed, and rejected by filter feeders. Finally, we consider how marine organisms can affect microplastics, by incorporating the plastic into biological matrices, through the movement, redistribution, and burial of plastic.

Microplastics (plastic particles, 0.1 μm-5 mm in size) are widespread marine pollutants, accumulating in benthic sediments and shorelines the world over. To gain a clearer understanding of microplastic availability to marine life, and the risks they pose to the health of benthic communities, ecological processes and food security, it is important to obtain accurate measures of microplastic abundance in marine sediments. To date, methods for extracting microplastics from marine sediments have been disadvantaged by complexity, expense, low extraction efficiencies and incompatibility with very fine sediments. Here we present a new, portable method to separate microplastics from sediments of differing types, using the principle of density floatation. The Sediment-Microplastic Isolation (SMI) unit is a custom-built apparatus which consistently extracted microplastics from sediments in a single step, with a mean efficiency of 95.8% (±SE 1.6%; min 70%, max 100%). Zinc chloride, at a density of 1.5 g cm-3, was deemed an effective and relatively inexpensive floatation media, allowing fine sediment to settle whilst simultaneously enabling floatation of dense polymers. The method was validated by artificially spiking sediment with low and high density microplastics, and its environmental relevance was further tested by extracting plastics present in natural sediment samples from sites ranging in sediment type; fine silt/clay (mean size 10.25 ± SD 3.02 μm) to coarse sand (mean size 149.3 ± SD 49.9 μm). The method presented here is cheap, reproducible and is easily portable, lending itself for use in the laboratory and in the field, eg. on board research vessels. By employing this method, accurate estimates of microplastic type, distribution and abundance in natural sediments can be achieved, with the potential to further our understanding of the availability of microplastics to benthic organisms.

Marine debris, mostly consisting of plastic, is a global problem, negatively impacting wildlife, tourism and shipping. However, despite the durability of plastic, and the exponential increase in its production, monitoring data show limited evidence of concomitant increasing concentrations in marine habitats. There appears to be a considerable proportion of the manufactured plastic that is unaccounted for in surveys tracking the fate of environmental plastics. Even the discovery of widespread accumulation of microscopic fragments (microplastics) in oceanic gyres and shallow water sediments is unable to explain the missing fraction. Here, we show that deep-sea sediments are a likely sink for microplastics. Microplastic, in the form of fibres, was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in contaminated sea-surface waters. Our results show evidence for a large and hitherto unknown repository of microplastics. The dominance of microfibres points to a previously underreported and unsampled plastic fraction. Given the vastness of the deep sea and the prevalence of microplastics at all sites we investigated, the deep-sea floor appears to provide an answer to the question-where is all the plastic?