The distinct spatial variability in microplastic concentrations between marine regions and habitats calls for a better understanding about the transport pathways of this omnipresent pollutant in the marine environment. This study provides empirical evidence that a sessile filter feeder, the Blue mussel M. edulis, accelerates microplastic deposition by aggregating them into sinking particulate faeces and pseudofaeces. After settling to the seafloor, the bioturbation of benthic fauna quickly buries these microplastics. Collectively, these results suggest that if such biologically-mediated benthic-pelagic coupling would be integrated into hydrodynamic transport models, the spatial variability and source-sink dynamics of microplastics would be better understood. It is proposed that microplastic pollution is monitored through sampling that takes into account faeces and pseudofaeces underneath filter feeders. The implications of this detrital pathway for microplastic transfer to the seafloor, and the role of shellfish mariculture in this process, are discussed. Studies that consider filter feeders and benthic communities from other regions, and during different seasons, are needed to validate the proposed biological pump mechanism across space and time.

Microplastics are ubiquitous in the marine environment but characterizing them in marine organisms is challenging. Herein we describe a method to detect, identify, and quantify microplastics in marine mussels (Mytilus edulis) using thermal gravimetric analysis – Fourier Transform infrared spectroscopy – gas chromatography mass spectrometry (TGA-FTIR-GC/MS) after extracting and isolating the microplastics using chemical digestion, density separation, and filtration. Combining the three instrumental techniques adds discriminatory power as temperature profiles, chromatograms, and vibrational and mass spectra differ among common plastics. First, we tested several digestion schemes after spiking the mussels with plastics commonly found in the marine environment, including polyethylene (PE), polystyrene (PS), polypropylene (PP) and polyvinyl chloride (PVC). KOH (10%, w/v) was the most suitable reagent, providing good recoveries (>97%) without degrading the microplastics. We show that the technique TGA-FTIR-GC/MS can be optimized to readily determine both the type (polymer) and amount (mass) of microplastics in the sample. Applied to 100 mussels from each of six locations along the coast of China, we found an average of 0.58 mg of plastic per kg of tissue (range 0.16–1.71 mg/kg), with PE being the most abundant type of plastic measured. Among the coastal cities, mussels from Dalian had the highest microplastic content. Overall, we demonstrate that the method is a powerful technique to quantify masses of microplastics in marine mussels, a species commonly used as a bioindicator of pollution, and may be applied to other biota as well.

Freshwater cyanobacteria produce highly toxic secondary metabolites, which can be transported downstream by rivers and waterways into the sea. Estuarine and coastal aquaculture sites exposed to toxic cyanobacteria raise concerns that shellfish may accumulate and transfer cyanotoxins in the food web. This study aims to describe the competitive pattern of uptake and depuration of a wide range of microcystins (MC-LR, MC-LF, MC-LW, MC-LY, [Asp3]-MC-LR/[Dha7]-MC-LR, MC-HilR) and nodularins (NOD cyclic and linear) within the common blue mussel Mytilus edulis exposed to a combined culture of Microcystis aeruginosa and Nodularia spumigena into the coastal environment.Different distribution profiles of MCs/NODs in the experimental system were observed. The majority of MCs/NODs were present intracellularly which is representative of healthy cyanobacterial cultures, with MC-LR and NOD the most abundant analogues. Higher removal rate was observed for NOD (≈96%) compared to MCs (≈50%) from the water phase. Accumulation of toxins in M. edulis was fast, reaching up to 3.4 μg/g shellfish tissue four days after the end of the 3-days exposure period, with NOD (1.72 μg/g) and MC-LR (0.74 μg/g) as the dominant toxins, followed by MC-LF (0.35 μg/g) and MC-LW (0.31 μg/g). Following the end of the exposure period depuration was incomplete after 27 days (0.49 μg/g of MCs/NODs). MCs/NODs were also present in faecal material and extrapallial fluid after 24 h of exposure with MCs the main contributors to the total cyanotoxin load in faecal material and NOD in the extrapallial fluid. Maximum concentration of MCs/NODs accumulated in a typical portion of mussels (20 mussels, ≈4 g each) was beyond greater the acute, seasonal and lifetime tolerable daily intake. Even after 27 days of depuration, consuming mussels harvested during even short term harmful algae blooms in close proximity to shellfish beds might carry a high health risk, highlighting the need for testing.

The biofiltration capacity of bivalve populations is known to alleviate the effects of coastal eutrophication. However, this important ecosystem service could potentially be impaired by the increasing microplastic abundance in near shore environments. It is known that relatively large microplastics (∼500 μm) impair the filtration capacity of bivalves. However, the effect of smaller microplastics, and specifically microfibers, is not known even though they are more common in many natural systems and similar in size to phytoplankton, the main food source of mussels. Here, we investigated the effects of long-term exposure to microfibers (MFs), which are smaller than 100 μm, on the biofiltration capacity of the blue mussel, Mytilus edulis. Our findings show that long-term exposure (here 39 days) to microfibers significantly reduced (21%) the clearance of phytoplankton (Tetraselmis sp). While previous studies have shown that larger microplastics can decrease the filtration capacity of mussels after short-term exposure, our findings suggest that, for smaller MFs, mussel’s clearance capacity is significantly affected after long-term exposure (39 days in this study). This may be due to the accumulation of MFs in the digestive system. In addition, the most efficient phytoplankton consumers were more susceptible to MF accumulation in the digestive system. This suggests that prolonged exposure to MF of coastal mussels could negatively impact the biofiltration of more potent individuals, thus decreasing the ecosystem service potential of the population as a whole.

To get an overview about distribution, levels and temporal trends of polybrominated diphenyl ethers (PBDE) and halogenated flame retardants (HFR) of emerging concern, different types of environmental samples archived in the German Environment Specimen Bank as well as fish filet samples from the Arctic (n = 13) and Antarctica (n = 5) were analysed for 43 substances (24 PBDE, 19 HFR) using a multi-column clean-up and GC-API-MS/MS or GC-MS. Sample types were herring gull egg (n = 3), blue mussel (n = 3) and eelpout filet (n = 3) from the German North- and Baltic Sea, bream filet (n = 7), zebra mussel (n = 6) and suspended particulate matter (SPM, n = 7) from German freshwater ecosystems as well as tree leaves (n = 9)/shoots (n = 10), soil (n = 4), earthworm (n = 4) and deer liver (n = 7) as representatives of German terrestrial ecosystems. PBDE and emerging HFR were present in each investigated matrices from Germany and Polar regions showing their widespread distribution. The presence in Arctic and Antarctic fish samples confirms their long-range transport potential. Average concentrations of total emerging HFR were highest in SPM (26 ng g⁻¹ dry weight (dw)), zebra mussel (10 ng g⁻¹ dw) and herring gull egg (2.6 ng g⁻¹ dw). Lowest levels were measured in fish filet samples from Antarctica (0.02 ng g⁻¹ dw). Average total PBDE concentrations were highest in bream filet (154 ng g⁻¹), herring gull egg (61 ng g⁻¹ dw), SPM (21 ng g⁻¹ dw), and zebra mussel 18 (ng g⁻¹) and lowest in deer liver (0.04 ng g⁻¹ dw). The patterns of non-fauna terrestrial samples (leaves, shoots, soil) as well as SPM were dominated by DBDPE and BDE209. Elevated proportions of DPTE and in most cases the absence of DBDPE characterized all fauna samples with the exception of Polar samples. Overall, emerging HFR appeared to be less bioaccumulative than PBDE. Temporal trends were generally decreasing with few exceptions such as DBDPE.

The discharge of oil well produced water (PW) provides a constant source of contaminants to the marine environment including polycyclic aromatic hydrocarbons, alkylated phenols, metals and production chemicals. High concentrations of PW cause adverse effects to exposed biota, including reduced survival, growth and reproduction. Here we explore the effects of PW on immune function in the blue mussel, Mytilus edulis. Mussels were exposed for 21 days to sublethal PW concentrations (0.125-0.5%) and cellular parameters were measured. Cell viability, phagocytosis and cytotoxicity were inhibited after exposure to 0.25% and 0.5% PW, whilst the 0.125% PW treatment produced significant increases in these biomarker responses. This biphasic response was only observed after 7 days exposure; longer exposure periods led to a reduction in immune parameters. Results indicate that PW concentrations close to the discharge point cause modulation to cellular immunity. The implications for longer-term disease resistance are discussed. Exposure to produced water alters immune function in the sentinel species Mytilus edulis.

Metals sequestered in coastal sediments are normally considered to be stable, but this investigation shows – somewhat surprisingly – that mercury concentrations in a previously contaminated area, Harboøre Tange, Denmark, have decreased since the 1980s. Mercury concentrations were determined in sediment and benthic biota and present values were compared to values in the 1980s and values from areas without known; history of mercury contamination. Concentrations in both the upper 20 cm of the sediments and; biota are considerably lower now compared to latest monitoring (1980s). Sediment.concentrations at most locations have decreased from the 100–300 ng Hg g⁻¹ dry weight (dw) level to levels below the Background Concentration (BC) of 50 ng Hg g⁻¹ dw defined by Oslo-Paris Convention for the Protection of the Marine Environment of the North-East Atlantic; some stations are at the 2–10 ng Hg g⁻¹ dw level characteristic of Danish coastal sediments with no known history of mercury contamination. Concentrations of mercury in the benthic biota along Harboøre Tange have also decreased since the 1980s but despite the lowered mercury concentrations in the sediments, concentrations in most samples of benthic invertebrate fauna still exceed those in uncontaminated coastal areas and also the Environmental Quality Standard (EQS) of 20 ng Hg g⁻¹ wet weight (≈100 ng Hg g⁻¹ dry weight) defined by the European Union’s Water Framework Directive. Concentration ranges in selected organisms are: (Harboøre Tange l980s/Harboøre Tange now/uncontaminated areas - given in ng Hg g⁻¹ dw): Periwinkles Littorina littorea 9000/150–450/55-77, blue mussels Mytilus edulis up to 9000/300–500/40–170, cockles Cerastoderma edule up to 8000/400–1200/200, brown shrimp Crangon crangon 700–2200/150-450/47, eelgrass Zostera marina up to 330/25–70/12. The present results - together with a literature review - show that a simple and straight forward relationship between the concentrations of mercury in sediment and benthic organisms does not necessarily exist.

Microplastics (MPs) are the most numerous debris reported in marine environments and assessment of the amounts of MPs that accumulate in wild organisms is necessary for risk assessment. Our objective was to assess MP contamination in mussels collected around the coast of Scotland (UK) to identify characteristics of MPs and to evaluate risk of human exposure to MPs via ingestion of mussels. We deployed caged mussels (Mytilus edulis) in an urbanised estuary (Edinburgh, UK) to assess seasonal changes in plastic pollution, and collected mussels (Mytilus spp and subtidal Modiolus modiolus) from eight sampling stations around Scotland to enumerate MP types at different locations. We determined the potential exposure of humans to household dust fibres during a meal to compare with amounts of MPs present in edible mussels. The mean number of MPs in M. modiolus was 0.086 ± 0.031 (SE, n = 6)/g ww (3.5 ± 1.29 (SE) per mussel). In Mytilus spp, the mean number of MPs/g ww was 3.0 ± 0.9 (SE, n = 36) (3.2 ± 0.52 (SE) per mussel), but weight dependent. The visual accuracy of plastic fibres identification was estimated to be between 48 and 50%, using Nile Red staining and FT-IR methodologies, respectively, halving the observed amounts of MPs in wild mussels. We observed an allometric relationship between the number of MPs and the mussels wet weight. Our predictions of MPs ingestion by humans via consumption of mussels is 123 MP particles/y/capita in the UK and can go up to 4620 particles/y/capita in countries with a higher shellfish consumption. By comparison, the risk of plastic ingestion via mussel consumption is minimal when compared to fibre exposure during a meal via dust fallout in a household (13,731–68,415 particles/Y/capita).

We studied the uptake of microplastics under field conditions. At six locations along the French–Belgian–Dutch coastline we collected two species of marine invertebrates representing different feeding strategies: the blue mussel Mytilus edulis (filter feeder) and the lugworm Arenicola marina (deposit feeder). Additional laboratory experiments were performed to assess possible (adverse) effects of ingestion and translocation of microplastics on the energy metabolism (cellular energy allocation) of these species. Microplastics were present in all organisms collected in the field: on average 0.2 ± 0.3 microplastics g−1 (M. edulis) and 1.2 ± 2.8 particles g−1 (A. marina). In a proof of principle laboratory experiment, mussels and lugworms exposed to high concentrations of polystyrene microspheres (110 particles mL−1 seawater and 110 particles g−1 sediment, respectively) showed no significant adverse effect on the organisms' overall energy budget. The results are discussed in the context of possible risks as a result of the possible transfer of adsorbed contaminants.