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.

Microplastics (MPs; <5 mm) released into freshwaters from anthropogenic sources accumulate in sediments, where they may pose an environmental threat to benthic organisms, such as nematodes. Several studies have examined the effects of nano- and microplastics on the nematode Caenorhabditis elegans, whereas reduced food availability was suggested as a possible explanation for the observed inhibitory effects. Therefore, this study should clarify whether micro-beads of different sizes (1.0 and 6.0 μm in diameter) and materials (polystyrene PS, silica) are able to interfere with the feeding of C. elegans on its bacterial diet (Escherichia coli), and, by this, lowering its consumption rate within 7 h of exposure. Moreover, it was examined whether an inhibited bacterial consumption was caused by a reduction of the nematode’s pumping rate, as a primary indicator of food ingestion. Bacterial consumption by C. elegans was significantly decreased in the presence of 1.0- and 6.0-μm PS beads (49–67% lower bacterial consumption compared to control), whereas in the presence of 1.0-μm silica beads feeding was not impeded. Interestingly, the pumping rate was significantly lower in the presence of non-ingestible 6.0-μm PS beads with 161 ± 16 pumps min⁻¹, while it was largely unchanged for nematodes exposed to ingestible 1.0-μm PS beads with 205 ± 12 pumps min⁻¹, compared to control conditions with 210 ± 18 pumps min⁻¹, respectively. As reduced bacterial consumption leads to generally lower energy reserves in C. elegans, these results allow to link observed inhibitory effects of MPs on the nematodes to a lower food availability. Such indirect, food-web related, effects of MPs should raise concern of ecological consequences in natural habitats, where temporal food deficiencies can occur. Consequently, disturbances in food availability and feeding efficiency should be regarded as important parameters in environmental risk assessments focusing on MPs.

Microplastics pollution in marine environments is concerning. Microplastics persist and accumulate in various sections of the ocean where they present opportunity for micropollutant accumulation and microbial colonisation. Even though biofilm formation on plastics was first reported in the 1970's, it is only in recent years were plastic associated biofilms have gained research attention. Plastic surfaces pose a problem as they are a niche ready for colonisation by diverse biofilm assemblages, composed of specific bacterial communities and putative pathogens prone to acquiring ARGs and resistance in the biofilm. However, the nature of antibiotic resistance on aquatic plastic debris is not yet fully understood and remains a concern. Given the inevitable increase of plastic production and waste generation, microplastics released into the environment may prove to be problematic. This review explores microplastic waste in the ocean and possible concerns that may arise from the presence of microplastics in conjunction with favourable conditions for the development and dispersal of antibiotic resistance in the ocean and food web.

The presence of microplastics in the various food web raised concerns on human health, but little is known about the target cells and mechanism of toxicity of microplastics. In this study, we evaluated the toxicity of microplastics using relevant cell lines to the oral route of exposure. Approximately 100 μm-sized fragment-type polypropylene (PP) and polystyrene (PS) particles were prepared by sieving after pulverization and further applied the accelerated weathering using ultraviolet and heat. Thus, the panel of microplastics includes fresh PP (f-PP), fresh PS (f-PS), weathered PP (w-PP), and weathered PS (w-PS). The spherical PS with a similar size was used as a reference particle. Treatment of all types of PP and PS did not show any toxic effects to the Caco-2 cells and HepG2 cells. However, the treatment of microplastics to THP-1 macrophages showed significant toxicity in the order of f-PS > f-PP > w-PS > w-PP. The weathering process significantly reduced the reactive oxygen species (ROS) generation potential of both microplastics because the weathered microplastics have an increased affinity to bind serum protein which acts as a ROS scavenger. The intrinsic ROS generation potential of microplastics showed a good correlation with the toxicity endpoints including cytotoxicity and pro-inflammatory cytokines in THP-1 macrophages. In conclusion, the results of this study suggest that the target cell type of microplastics via oral administration can be macrophages and the pathogenic factor to THP-1 macrophages is the intrinsic ROS generation potential of microplastics. Nevertheless, the toxic effect of microplastics tested in this study was much less than that of nano-sized particles.

Mercury (Hg) pollution in the ocean is an issue of global concern, however bioaccumulation regimes of this ubiquitous pollutant in marine apex predators have important knowledge gaps. Our fish length and stable isotope (δ¹⁵N and δ¹³C) normalized data of Greenland halibut (GH) (Reinhardtius hippoglossoides) showed that Hg bioaccumulation in fillet tissue decreased by ~35–50 %, over a ten-year period from 2006 to 2015 (n = 7 individual sampling years). Hg was predominantly in the methylmercury form (>77 %). Results from a Bayesian information theoretic model showed that GH Hg concentrations decreased with time and its associated declines in Hg air emissions, estimated trophic position, and a potentially lower degree of demersal prey use as indicated by temporal trend shifts in nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotope values. GH trophic shifts accounted for about one third of the observed temporal reduction in Hg. Our study demonstrates the importance of simultaneously considering Hg emissions, food web dynamics and trophic shifts as important drivers of Hg bioaccumulation in a marine, deep water fish species and highlights the effectiveness of Hg regulations on ocean apex predator Hg concentrations and overall seafood safety.

Rivers play an important role in the overall transport of microplastic pollution (1 μm to 5 mm), with fluvial dynamics expected to influence biotic interactions, particularly for fish. So far, there have been few assessments of microplastics in freshwater salmonids. The prevalence (i.e. percentage occurrence) and burden (i.e. abundance per fish) of microplastics were assessed in the gastrointestinal tracts (GITs) and stomach contents (SCs) of 58 brown trout Salmo trutta Linnaeus, 1758 sampled at six sites along the River Slaney catchment in south-east Ireland. Sites were divided into two classifications (high and low exposure) based on proximity to microplastic pollution sources, comprising three sites each. Analysis of biological traits (e.g. fish length) and diet was performed on the same fish to determine possible factors explaining microplastic burden. Microplastics were found in 72% of fish having been recovered from 66% of GITs (1.88 ± 1.53 MPs fish⁻¹) and 28% of SCs (1.31 ± 0.48 MPs fish⁻¹). Fibres were the dominant particle type recovered from GITs (67%) and SCs (57%) followed by fragments. No difference in median microplastic burden was observed between fish collected in high and low exposure sites. Microplastic burden was unrelated to fish fork length, while microplastic size distribution (100 ≤ 350 μm, 350 μm to ≤ 5 mm) was unrelated to S. trutta age class estimates. Furthermore, microplastic burden was not explained by dietary intake. Though further research is necessary, this study showed the presence of microplastics in wild S. trutta collected from an Irish riverine system, which could have further implications for top-level consumers that feed on the species, including humans. Further analysis is required to determine possible trophic linkages for the species, with respect to microplastics, and to assess the suitability of S. trutta for monitoring microplastics in river systems.

The present endocrine disrupting chemicals (EDCs) in wastewater effluents due to incomplete removal during the treatment processes may cause potential ecological and human health risks. This study evaluated the removal and uptake of seven EDCs spiked in two types of wastewater effluent (i.e., ultrafiltration and ozonation) and effluent cultivated with the freshwater green alga Nannochloris sp. In ultrafiltration effluent cultivated with Nannochloris sp. for 7 days, the removal rate of 17β-estradiol (E2), 17α-ethinylestradiol (EE2), and salicylic acid (SAL) was 60%; but Nannochloris sp. did not promote the removal of other EDCs studied. The algal-mediated removal of E2, EE2, and SAL was attributed to photodegradation and biodegradation. Triclosan (TCS) underwent rapid photodegradation regardless of adding algae in the effluent with 63%–100% removal within 7 days. Triclosan was also found associated with algal cells immediately after adding algae, and thus the primary mechanisms involved were photodegradation and bioremoval (i.e., bioadsorption and bioaccumulation). After algal cultivation, TCS still has a bioaccumulation potential to pose high risks within the food web and the endocrine disrupting properties of the residual estrogens in the effluent are not eliminated. Algal cultivation can be exploited to treat wastewater effluents but the removal efficiencies of EDCs highly depend on chemical types.

Mercury (Hg) and methylmercury (CH3Hg) bind strongly to micro and nano (NP) particles and this partitioning impacts their fate and bioaccumulation into food webs, and, as a result, potential human exposure. This partitioning has been shown to influence the bioavailability of inorganic Hg to methylating bacteria, with NP-bound Hg being more bioavailable than particulate HgS, or organic particulate-bound Hg. In this study we set out to investigate whether the potential interactions between dissolved ionic Hg (HgII) and CH3Hg and NPs was due to incorporation of Hg into the core of the cadmium selenide and sulfide (CdSe; CdS) nanoparticles (metal exchange or surface precipitation), or due purely to surface interactions. The interaction was assessed based on the quenching of the fluorescence intensity and lifetime observed during HgII or CH3Hg titration experiments of these NP solutions. Additional analysis using inductively coupled plasma mass spectrometry of CdSe NPs and the separated solution, obtained after HgII additions, showed that there was no metal exchange, and X-ray photoelectron spectroscopy confirmed this and further indicated that the Hg was bound to cysteine, the NP capping agent. Our study suggests that Hg and CH3Hg adsorbed to the surfaces of NPs would have different bioavailability for release into water or to (de)methylating organisms or for bioaccumulation, and provides insights into the behavior of Hg in the environment in the presence of natural or manufactured NPs.

The majority of plastics present in the marine environment are microplastics (MPs, <5 mm). Suspension filter feeders are susceptible species to MPs ingestion. Once ingested MPs can be eliminated packed in fecal pellets, or they can be accumulated within tissues, and likely be transferred along the food web. The research on MPs is hampered by the difficulty on their quantification and the lack of standardized methodologies. Indeed, limited information exits about the capacity of marine organisms to ingest, accumulate and eliminate MPs. In this work we investigated the uptake, elimination and accumulation of MPs (irregularly shaped particles of high density polyethylene, ≤22 μm) in mussel. Mussels were exposed to two concentrations of MPs (2 and 4 mm3 l−1), and their uptake, elimination and accumulation in digestive gland was investigated. The results showed that the uptake of MPs increased at the high concentration tested, and that mussels cleared MPs at the same extent than a food item (microalgae) of similar size. Small MPs (2–4 μm) were less efficiently cleared than the larger ones. Large MPs (>10 μm) were faster eliminated than the smaller ones. The global balance showed that after 6 days of depuration mussels eliminated ≈85% of the MPs cleared, and that ≈2–6% of the MPs cleared remained in the digestive gland, essentially those <6 μm. We recorded a long retention time for MPs, contrasting with the lower times assumed to be necessary to empty mussel's gut before quantifying MPs. Our study emphasized the gap of knowledge on the feeding behaviour of mussels in relation to MPs, and the necessity to investigate it in different marine species, and under different exposure scenarios.

Nowadays, microplastics represent one of the main threats to marine ecosystems, being able to affect organisms at different stages of their life cycle and at different levels of the food web. Although the presence of plastic debris has been reported in different habitats and the ability to ingest it has been confirmed for different taxa, few studies have been performed to elucidate the effects on survival and development of marine animals. Thus, we explored the effects of different environmental concentrations of polystyrene microbeads on the early stages of two invertebrate species widespread in the Mediterranean shallow waters: the pelagic planktotrophic pluteus larvae of the sea urchin Paracentrotus lividus and the filter-feeding sessile juveniles of the ascidian Ciona robusta. We evaluated the effects on larvae and juvenile development and determined the efficiency of bead ingestion. The feeding stages of both species proved to be extremely efficient in ingesting microplastics. In the presence of microbeads, the metamorphosis of ascidian juveniles was slowed down and development of plutei altered. These results prompted the necessity to monitor the populations of coastal invertebrates since microplastics affect sensitive stages of life cycle and may have consequences on generation recruitment.