Deep-sea mining: using hyperbaric conditions to study the impact of sediment plumes in the subtidal clam Spisula solida.

With the growing interest to exploit mineral resources in the deep-sea, there is the need to establish guidelines and frameworks to support hazard and risk assessment schemes. The present study used a subtidal species of filter-feeding bivalve, the clam Spisula solida, as a proxy to better understand the impacts of sediment plumes in marine organisms under hyperbaric conditions. Four concentrations of suspended sediments (0 g/L, 1 g/L, 2 g/L, and 4 g/L) were used in a mixture with different grain sizes at 4 Bar for 96 h. Functional (filtration rate-FR) and biochemical endpoints (catalase-CAT, glutathione s-transferase-GST, and lipid peroxidation-LPO) were analyzed in the gonads, digestive gland, and gills of S. solida after a 96-h exposure at 4 Bar (the natural limit of the species vertical distribution). The FR showed a decreasing trend with the increasing sediment concentrations (significant effects at 2 and 4 g/L). Additionally, significant changes were observed for some of the tested oxidative stress biomarkers, which were concentration and tissue-dependent, i.e., CAT activity was significantly elevated in gills (1 g/L treatment), and GST was decreased in digestive gland (1 g/L treatment). Overall, the results show that suspended sediments, at 2 and 4 g/L, have negative functional impacts in the bivalve S. solida providing additional insights to improve hazard assessment of deep-sea mining. These findings represent a step forward to ensure the mitigation of the potential negative effects of deep-sea resource exploitation.

Microplastic distribution in different tissues of small pelagic fish of the Northeast Atlantic Ocean.

The accumulation of microplastics (MP) by marine species of ecological and commercial interest represents a major concern, particularly for those present in human diet. This study analysed the accumulation of MP in three species of coastal pelagic fish with high commercial value, European sardine (Sardina pilchardus), European anchovy (Engraulis encrasicolus) and horse mackerel (Trachurus trachurus), collected along the Western coast of the Iberian Peninsula. The gastrointestinal tract (GT), gills and muscle were analysed and a total of 504 particles were observed. MP were found in all target tissues of the studied species. Horse mackerel exhibited significantly higher concentrations of microplastics in GT compared to other tissues. On the other hand, anchovies and sardines had significantly lower microplastic concentrations in their muscle tissue. The accumulation of microplastics in the gills showed a significant difference between species, with anchovy having significantly higher concentrations compared to horse mackerel. Horse mackerel had the highest percentage of individuals with microplastics in their GT (92 %), followed by sardine (75 %) and anchovy (50 %). Horse mackerel was also the species that registered the highest percentage of individuals with particles in the muscle (63 %), followed by anchovy (40 %) and finally sardine (39 %). MP in the gills of European sardines and anchovies were similar to those found in water samples. The majority of MP found measured <0.5 mm and were blue fibers. Furthermore, the presence of MP in the GT showed a weak and moderated significant negative correlation with the Fulton Condition Index in horse mackerel and European sardine. Our study confirms the ubiquitous extent of MP contamination in the ocean and provides baseline evidence of MP tissue distribution in three small pelagic fish species with distinct feeding behaviour, while correlating this with the presence of MP in water. Importantly, the results of this study contribute to improve the understanding of biological partitioning of MP in open sea fish species with high commercial relevance, and the potential deleterious effects of our increasingly MP contaminated world.

First evidence of microplastic ingestion in the ocean giant sunfish (Mola mola).

Mola mola is the largest teleost inhabiting our ocean and the presence of microplastics (MP) in this flagship species was, before this study, never described. Thus, this investigation focused on analysing MP ingestion in 53 ocean giant sunfish in the Northeast Atlantic Ocean. A total of 116 MP were found in 79% of the specimens, with a median of 1 MP.ind-1, ranging from 0 to 11 MP.ind-1. Seasonal differences were observed, with more fibers registered in specimens caught in autumn. Among the different size classes observed, the smallest category (<300 µm) was the most frequent (43%). Blue (43%) was the most prevalent color, followed by green (29%) and black (10%). The majority of fragments were styrene acrylic copolymer (53%), while most fibers were rayon (78%). These findings emphasize that the ocean sunfish population crossing the southern waters of Portugal is exposed to microplastic pollution and highlight the need for effective management policies to address plastic pollution in marine ecosystems.

A modelling framework to assess multiple metals impacts on marine food webs: Relevance for assessing the ecological implications of deep-sea mining based on a systematic review.

Industrial deep-sea mining will release plumes containing metals that may disperse over long distances; however, there is no general understanding of metal effects on marine ecosystems. Thus, we conducted a systematic review in search of models of metal effects on aquatic biota with the future perspective to support Environmental Risk Assessment (ERA) of deep-sea mining. According to results, the use of models to study metal effects is strongly biased towards freshwater species (83% freshwater versus 14% marine); Cu, Hg, Al, Ni, Pb, Cd and Zn are the best-studied metals, and most studies target few species rather than entire food webs. We argue that these limitations restrain ERA on marine ecosystems. To overcome this gap of knowledge, we suggest future research directions and propose a modelling framework to predict the effects of metals on marine food webs, which in our view is relevant for ERA of deep-sea mining.

Stressors of emerging concern in deep-sea environments: microplastics, pharmaceuticals, personal care products and deep-sea mining.

Although most deep-sea areas are remote in comparison to coastal zones, a growing body of literature indicates that many sensitive ecosystems could be under increased stress from anthropogenic sources. Among the multiple potential stressors, microplastics (MPs), pharmaceuticals and personal care products (PPCPs/PCPs) and the imminent start of commercial deep-sea mining have received increased attention. Here we review recent literature on these emerging stressors in deep-sea environments and discuss cumulative effects with climate change associated variables. Importantly, MPs and PPCPs have been detected in deep-sea waters, organisms and sediments, in some locations in comparable levels to coastal areas. The Atlantic Ocean and the Mediterranean Sea are the most studied areas and where higher levels of MPs and PPCPs have been detected. The paucity of data for most other deep-sea ecosystems indicates that many more locations are likely to be contaminated by these emerging stressors, but the absence of studies hampers a better assessment of the potential risk. The main knowledge gaps in the field are identified and discussed, and future research priorities are highlighted to improve hazard and risk assessment.

Assessing microplastic exposure of the Critically Endangered Mediterranean monk seal (Monachus monachus) on a remote oceanic island.

Microplastics (<5 mm) are a ubiquitous marine pollutant which are highly bioavailable to marine organisms across all trophic levels. Marine predators are especially vulnerable to microplastic pollution through direct and indirect ingestion (e.g., trophic transfer) due to their high trophic position. In particular, oceanic islands are more susceptible to plastic accumulation, increasing the relative number of microplastics in the environment that are available for consumption. The dynamics of microplastic accumulation in marine predators inhabiting remote islands, however, is sparsely documented. Here we describe microplastic exposure in the Critically Endangered Mediterranean monk seal (Monachus monachus) from the Madeira archipelago (Northeast Atlantic) using scat-based analysis. Microplastics were recovered from 18 scat samples collected between 2014-2021 and were characterized to the polymer level using Fourier-Transform Infrared (u-FTIR) spectroscopy. A total of 390 microplastic particles were recovered, ranging between 0.2-8.6 particles g-1 dry weight (mean 1.84 ± 2.14 particles g-1) consisting mainly of fragments (69 %) of various sizes and polymer composition (e.g., PE, PET, PS). Microplastic prevalence (100 % of samples analysed) was higher than what has been previously recorded using scat-based analysis in other pinniped species. Our results suggest that the levels of microplastic pollution in the coastal food-web in the Madeira archipelago are relatively high, placing higher-trophic level organisms at increased risk of microplastic consumption, including humans. This study provides the first insights into microplastic exposure to Madeira's monk seals that may contribute to future management decisions for the species and their long-term survival.

Gadolinium ecotoxicity is enhanced in a warmer and acidified changing ocean as shown by the surf clam Spisula solida through a multibiomarker approach.

Humans have exhaustively combusted fossil fuels, and released pollutants into the environment, at continuously faster rates resulting in global average temperature increase and seawater pH decrease. Climate change is forecasted to exacerbate the effects of pollutants such as the emergent rare earth elements. Therefore, the objective of this study was to assess the combined effects of rising temperature (Δ = + 4 °C) and decreasing pH (Δ = - 0.4 pH units) on the bioaccumulation and elimination of gadolinium (Gd) in the bioindicator bivalve species Spisula solida (Surf clam). We exposed surf clams to 10 µg L-1 of GdCl3 for seven days, under warming, acidification, and their combination, followed by a depuration phase lasting for another 7 days and investigated the Gd bioaccumulation and oxidative stress-related responses after 1, 3 and 7 days of exposure and the elimination phase. Gadolinium accumulated after just one day with values reaching the highest after 7 days. Gadolinium was not eliminated after 7 days, and elimination is further hampered under climate change scenarios. Warming and acidification, and their interaction did not significantly impact Gd concentration. However, there was a significant interaction on clam's biochemical response. The augmented total antioxidant capacity and lipid peroxidation values show that the significant impacts of Gd on the oxidative stress response are enhanced under warming while the increased superoxide dismutase and catalase values demonstrate the combined impact of Gd, warming & acidification. Ultimately, lipid damage was greater in clams exposed to warming & Gd, which emphasizes the enhanced toxic effects of Gd in a changing ocean.

Improved methodology for microplastic extraction from gastrointestinal tracts of fat fish species.

Potassium hydroxide (KOH) digestion protocols are currently applied to separate microplastics from biological samples, allowing efficient digestion with minor degradation of polymers in a time- and cost-effective way. For biota samples with high-fat content, KOH reacts with triglycerides generating an overlying soap layer, making difficult the digestion and solubilization and subsequent microplastics extraction. Here we studied the addition of Tween-20 in different concentrations to evaluate the effect on the soap layer of post-digested samples. Addition of 10 % of Tween-20 presented higher flow rate during filtration, being set as optimal value. Incorporation of Tween-20 in the extraction procedure increased recovery rates of LDPE, PC and PET and appears to have a protective effect on PC and PET degradation. Tween-20 did not interfere in FTIR spectrum of polymers available in the marine environment. Being low-toxic, makes addition of Tween-20 a simple and economical way to optimize KOH digestion protocols for microplastics extraction.

Single and combined ecotoxicological effects of ocean warming, acidification and lanthanum exposure on the surf clam (Spisula solida).

Lanthanum (La) is one of the most abundant emergent rare earth elements. Its release into the environment is enhanced by its use in various industrial applications. In the aquatic environment, emerging contaminants are one of the stressors with the ability to compromise the fitness of its inhabitants. Warming and acidification can also affect their resilience and are another consequence of the growing human footprint on the planet. However, from information gathered in the literature, a study on the effects of ocean warming, acidification, and their interaction with La was never carried out. To diminish this gap of knowledge, we explored the effects, combined and as single stressors, of ocean warming, acidification, and La (15 µg L-1) accumulation and elimination on the surf clam (Spisula solida). Specimens were exposed for 7 days and depurated for an additional 7-day period. Furthermore, a robust set of membrane-associated, protein, and antioxidant enzymes and non-enzymatic biomarkers (LPO, HSP, Ub, SOD, CAT, GPx, GST, TAC) were quantified. Lanthanum was bioaccumulated after just one day of exposure, in both control and climate change scenarios. A 7-day depuration phase was insufficient to achieve control values and in a warming scenario, La elimination was more efficient. Biochemical response was triggered, as highlighted by enhanced SOD, CAT, GST, and TAC levels, however as lipoperoxidation was observed it was insufficient to detoxify La and avoid damage. The HSP was largely inhibited in La treatments combined with warming and acidification. Concomitantly, lipoperoxidation was highest in clams exposed to La, warming, and acidification combined. The results highlight the toxic effects of La on this bivalve species and its enhanced potential in a changing world.

Lanthanum and Gadolinium availability in aquatic mediums: New insights to ecotoxicology and environmental studies.

Studies dealing with Rare Earth Elements (REE) ecotoxicological behavior are scattered and with potential conflicting results. Climate change impacts on aquatic biota and is known to modify contaminants toxicokinetic. Nevertheless, the current knowledge on the potential interactions between climate change and REE is virtually non-existent. Therefore, we focus our research on La and Gd as representatives of Light and Heavy REE that also are of great environmental concern. Experiments on different mediums (fresh-, brackish- and seawater) were designed to run at present-day and near-future conditions (T°=+4 °C, pH=△-0.4). Sampling was taken at different time scales from minutes to hours for one day. The main challenge was to evaluate the availability of La and Gd under environmental conditions closely related to climate changes scenarios. Furthermore, this study will contribute to the baseline knowledge by which future research towards understanding REE patterns and toxicity will build upon. Lanthanum and Gd behave differently with salinity. Temperature also affects the availability of dissolved La in freshwater. On the other hand, pH reduction causes the decrease of Gd in freshwater. In this medium, concentrations reduce sharply, presumably due to sorption processes or precipitates. In the brackish water experiment only the dissolved La levels in the Warming (T°=+4 °C) and Warming & Acidification (T°=+4 °C, pH=△0.4) diminished significantly through time. Dissolved La and Gd levels in seawater were relatively constant with time. The speciation of both elements is also of great relevance for ecotoxicological experiments. The trivalent free ions (La3+ and Gd3+) were the most common species in the trials. However, as ionic strength increases, the availability of other complexes rose, which should be subject of great attention for upcoming ecotoxicological studies.

Rare earth elements biomonitoring using the mussel Mytilus galloprovincialis in the Portuguese coast: Seasonal variations.

Increased Rare earth elements (REE) usage culminates in discharges into the environment. Mussels have been chosen as models in biomonitoring, hence, REE concentrations in Mytilus galloprovincialis from six locations on the Portuguese coast were accessed to determine natural concentrations and possible linkage to local ecosystem characteristics and temporal variations, by determining them in distinct seasons (autumn and spring). Samples from Porto Brandão (located on the south bank of the Tagus estuary) exhibited the highest REE concentrations, while mussels from Aljezur (the southernmost point on the Portuguese coast) exhibited the lowest, in both seasons. Overall, ∑REE concentration was greater in the spring. LREE enrichment relative to HREE occurs and a negative Ce and Eu anomaly was observed. This study constitutes the first assessment of REE composition on this model species in the Portuguese coast, in two distinct seasons and contributes to a better understanding of REE uptake for future biomonitoring studies.

Differential tissue accumulation in the invasive Manila clam, Ruditapes philippinarum, under two environmentally relevant lanthanum concentrations.

Among the environmental emerging concern rare earth elements, lanthanum (La) is one of the most common and reactive. Lanthanum is widely used in numerous modern technologies and applications, and its intense usage results in increasing discharges into the environment, with potentially deleterious consequences to earthlings. Therefore, we exposed the important food resource and powerful monitoring tool Manila clam to two environmentally relevant concentrations of La (0.3 µg L-1 and 0.9 µg L-1) for 6 days, through water, to assess the bioaccumulation pattern in the gills, digestive gland, and remaining body. The La bioaccumulation was measured after 1 (T1), 2 (T2), and 6 (T6) days of exposure. Lanthanum was bioaccumulated after 2 days, and the levels increased in all tissues in a dose-dependent manner. When exposed to 0.3 µg L-1, the enrichment factor pattern was gills > body > digestive gland. However, when exposed to 0.9 µg L-1, the pattern appears to change to gills > digestive gland > body. Tissue portioning appears to be linked with exposed concentration: In higher exposure levels, digestive gland seems to gain importance, probably associated with detoxification mechanisms. Here, we describe for the first time La bioaccumulation in these different tissues in a bivalve species. Future studies dealing with the bioaccumulation and availability of La should connect them with additional water parameters (such as temperature, pH, and major cations).

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.

Elemental composition of whole body soft tissues in bivalves from the Bijagós Archipelago, Guinea-Bissau.

Marine bivalves are bioindicators of coastal environmental pollution, integrating monitoring programs worldwide. Nonetheless, the choice of particular species as an indicator requires validation, achieved by understanding the differences in element concentrations among and within species. The present study compares the chemical composition of whole body soft tissues of four common bivalve species from the Bijagós Archipelago, a pristine region of West Africa. Significant differences were recorded in the concentrations of various elements among studied species, which likely arise from species-specific uptake and bioaccumulation processes. Overall, there was a segregation between a group including the bloody cockle Senilia senilis and oyster Crassostrea tulipa (with high Cd and Zn concentrations) versus the two other species, Austromacoma nymphalis (with low Cu and high Mn, Se, Hg, Pb concentrations) and Diplodonta spp. (with high values of Cu, Al, Fe, V, Cr, Hg, Pb). C. tulipa was sampled in two different substrates (rock beds and mangrove roots), and the two groups revealed different chemical profiles, with significantly higher concentrations of P, Si, Zn and Cr and lower Cu in specimens fixed in mangrove roots. These results strongly suggest the influence of small-scale environmental variability on the accumulation of particular elements. We found extremely high Cd concentrations in S. senilis (27.1 ± 7.53 µg g-1 DW) and identified C. tulipa as another high Cd-accumulating species (ca. 10 µg g-1 DW). Our results suggest a detoxifying mechanism linked with the presence of Se to reduce the potential toxic effects of Cd in these two species. Cadmium concentrations reported for some bivalve species in this area largely exceed the maximum values proposed by the European Union, emphasizing the need for a regular contamination assessment.

Rare earth and trace elements in deep-sea sponges of the North Atlantic.

The available data on trace elements (TE) of deep-sea organisms is scarce and nonexistent for rare earth elements (REE). Hence, this study characterizes REE and TE in five porifera genera (Jaspis, Geodia, Hamacantha, Leiodermatium, Poliopogon) collected in deep-sea areas (between 481 and 2656 m) of the North Atlantic. Aluminium was the most common TE while lead was the less abundant. These sponges showed an increased accumulation of TE compared with other probably influenced by volcanic activity. Poliopogon amadou sampled at the deepest location presented the highest concentration of all REE. All studied species exhibited a Light REE enrichment in comparison to Heavy REE and showed a negative Ce anomaly with a less conspicuous Eu depletion. Besides the establishment of a baseline for future comparisons, this study provides the first record of REE in a sessile deep-sea marine invertebrate group.

Tissue and gender-related differences in the elemental composition of juvenile ocean sunfish (Mola spp.).

Trace elements are potentially critical contaminants of aquatic environments and fish, occupying upper trophic levels, are especially vulnerable to bioaccumulation. Due to public health concerns, however, data on the elemental composition of non-commercially important marine species are particularly lacking. Ocean sunfish (Mola spp.) attain a low commercial value worldwide and information on their elemental composition is limited. In this context, we examined the concentration of 11 trace elements (V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd and Pb) in eight tissues [brain, gills, gelatin (subcutaneous white gelatinous layer), gonads, spleen, liver, white muscle and red muscle] of 20 juvenile specimens (37.5-85.5 cm TL). Gender-related differences were solely found in the gonads and chiefly for essential elements possibly as a result of their importance in embryo development. Overall, Zn and As were the elements observed in greatest concentrations in body tissues. The considerably high presence of As should be related to the dietary preferences of juvenile ocean sunfish. Considerable inter-individual variability in the concentration of each element in any given tissue was observed, especially in the liver, likely originating from the inclusion of both benthic and pelagic prey in the diet of analysed fish. Greatest elemental loads were found in the liver and gills whereas lowest loads were observed in white muscle, brain and gelatin. Moreover, a clear distinction in elemental load and elemental composition was observed between white and red muscles, likely deriving from existing divergent metabolism-related physiological adaptations linked to their different roles in locomotion.

Functional, biochemical and molecular impact of sediment plumes from deep-sea mining on Mytilus galloprovincialis under hyperbaric conditions.

The deep-sea is the biggest ecosystem in the world and despite the extreme conditions that characterize it, is highly biodiverse and complex. Deep-sea mining has been foreseen as a potential and concerning new stressor, and among the deep-sea mining associated stressors, sediment plumes, likely to be released into the water column as a side effect of mining, can reach habitats within a radius of more than a hundred kilometers. The present study examined the effects of suspended sediments of different grain sizes (63-125 µm, 125-250 µm and 250-500 µm) in the model species Mytilus galloprovincialis, at 4 bar, as a proxy to address the potential effects of sediment plumes, in the water column, with different grain sizes under high pressure conditions. Functional (filtration rate - FR), biochemical (catalase - CAT, glutathione s-transferase - GST, lipid peroxidation - LPO) and molecular (gene expression of [actin (ACTN), glutathione S-transferase alpha (GSTA), superoxide dismutase 2 (SOD2), catalase (CAT), heat shock protein 60 (HSP60), cytochrome c oxidase (COI) and DNA mismatch repair protein (MSH6)]) endpoints were studied in juvenile organisms. The FR decreased significantly for all tested grain size ranges, with a more severe effect for the particles with a diameter between 63 and 125 µm. In addition to the FR, significant changes were also observed for all tested biomarkers. Gene expression was significantly downregulated for CAT and ACTN. Overall, this study demonstrated that the smaller sized particles are the ones leading to more severe effects. Given their high dispersion potential and longer suspension periods under mining operation scenarios, particular attention should be given to the release of sediment plumes that may affect deep-sea environments and the water column. It is, therefore, vital to create standards and guidelines for sustainable mining practices.

Warming enhances lanthanum accumulation and toxicity promoting cellular damage in glass eels (Anguilla anguilla).

Cumulative and continuing human emissions of greenhouse gases to the atmosphere are causing ocean warming. Rising temperature is a major threat to aquatic organisms and may affect physiological responses, such as acid-base balance, often compromising species fitness and survival. It is also expected that warming may influence the availability and toxicological effects of pollutants, including Rare Earth Elements. These are contaminants of environmental emerging concern with great economic interest. This group comprises yttrium, scandium and lanthanides, being Lanthanum (La) one of the most common. The European eel (Anguilla anguilla) is critically endangered and constitutes a delicacy in South East Asia and Europe, being subject to an increasing demand on a global scale. Considering the vulnerability of early life stages to contaminants, we exposed glass eels to 1.5 µg L-1 of La for five days, plus five days of depuration, under a present-day temperature and warming scenarios (△T = +4 °C). The aim of this study was to assess the bioaccumulation, elimination and specific biochemical enzymatic endpoints in glass eels (Anguilla anguilla) tissues, under warming and La. Overall, our results showed that the accumulation and toxicity of La were enhanced with increasing temperature. The accumulation was higher in the viscera, followed by the head, and ultimately the body. Elimination was less effective under warming. Exposure to La did not impact acetylcholinesterase activity. Moreover, lipid peroxidation peaked after five days under the combined exposure of La and warming. The expression of heat shock proteins was majorly suppressed in glass eels exposed to La, at both tested temperatures. This result suggests that, when exposed to La, glass eels were unable to efficiently prevent cellular damage, with a particularly dramatic setup in a near-future scenario. Further studies are needed towards a better understanding of the effects of lanthanum in a changing world.

Correction to: Hg and Se composition in demersal deep-sea fish from the North-East Atlantic.

The correct Table 2 is presented in this paper.