Hydrostatic pressure and temperature affect the tolerance of the free-living marine nematode Halomonhystera disjuncta to acute copper exposure

Effects of heavy metal concentration on zooplankton community composition and abundance in the Yellow Sea coast

The coastal area of the Yellow Sea is a highly urbanized and industrialized region in China, which has been severely polluted because of intensive human activities. And the heavy metals (HMs) pollution has posed a serious threat to aquatic environments and ecosystem health. However, most studies have focused on the toxicity and bio-accumulation of HMs in zooplankton, while neglecting their effects on the overall community structure. To address the gap in this field, four research cruises was conducted in 2022 to analyze the concentrations of representative HMs (Hg, As, Cu, Zn, Pb, and Cd) in surface seawater along the Yellow Sea coast, as well as the composition and abundance of zooplankton communities, aiming to assess the potential ecological impacts in the region. The results indicated that the concentrations of the six HMs in the seawater were in the low to moderate range. Analytical results showed that Zn and As were key metals influencing the abundance and community composition of zooplankton along the Yellow Sea coast: an increase in Zn concentration, coupled with a decrease in As concentration, was associated with an increase in total zooplankton abundance and a more diverse community. The most frequently occurring zooplankton in the survey were copepods, which exhibited a higher tolerance to HMs. Additionally, the significant fluctuations of Zn, As, and Hg during spring and autumn led to explosive growth of Noctiluca scintillans. We observed that the influence of HMs on marine zooplankton was not isolated but rather interacts with multiple factors. Overall, this study highlights the possibility of alterations in marine ecological structures due to changes in HMs concentration levels. It underscores the importance of continuous monitoring of heavy metal concentrations in the Yellow Sea for the long-term protection of marine ecosystems.

Toxicology assessment of deep-sea mining impacts on Gigantidas platifrons: A comparative in situ and laboratory metal exposure study

Deep-sea toxicology is essential for deep-sea environmental impact assessment. Yet most toxicology experiments are conducted solely in laboratory settings, overlooking the complexities of the deep-sea environment. Here we carried out metal exposure experiments in both the laboratory and in situ, to compare and evaluate the response patterns of Gigantidas platifrons to metal exposure (copper [Cu] or cadmium [Cd] at 100 μg/L for 48 h). Metal concentrations, traditional biochemical parameters, and fatty acid composition were assessed in deep-sea mussel gills. The results revealed significant metal accumulation in deep-sea mussel gills in both laboratory and in situ experiments. Metal exposure could induce oxidative stress, neurotoxicity, an immune response, altered energy metabolism, and changes to fatty acid composition in mussel gills. Interestingly, the metal accumulating capability, biochemical response patterns, and fatty acid composition each varied under differing experimental systems. In the laboratory setting, Cd-exposed mussels exhibited a higher value for integrated biomarker response (IBR) while in situ the Cu-exposed mussels instead displayed a higher IBR value. This study emphasizes the importance of performing deep-sea toxicology experiments in situ and contributes valuable data to a standardized workflow for deep-sea toxicology assessment.

A comprehensive review of the effects of salinity, dissolved organic carbon, pH, and temperature on copper biotoxicity: Implications for setting the copper marine water quality criteria

In recent years, there has been a growing concern about the ecological hazards associated with copper, which has sparked increased interest in copper water quality criteria (WQC). The crucial factors affecting the bioavailability of copper in seawater are now acknowledged to be salinity, dissolved organic carbon (DOC), pH, and temperature. Research on the influence of these four water quality parameters on copper toxicity is rapidly expanding. However, a comprehensive and clear understanding of the relevant mechanisms is currently lacking, hindering the development of a consistent international method to establish the seawater WQC value for copper. As a response to this knowledge gap, this study presents a comprehensive summary with two key focuses: (1) It meticulously analyzes the effects of salinity, DOC, pH, and temperature on copper toxicity to marine organisms. It takes into account the adaptability of different species to salinity, pH and temperature. (2) Additionally, the study delves into the impact of these four water parameters on the acute toxicity values of copper on marine organisms while also reviewing the methods used in establishing the marine WQC value of copper. The study proposed a two-step process: initially zoning based on the difference of salinity and DOC, followed by the establishment of Cu WQC values for different zones during various seasons, considering the impacts of water quality parameters on copper toxicity. By providing fundamental scientific insights, this research not only enhances our understanding and predictive capabilities concerning water quality parameter-dependent Cu toxicity in marine organisms but also contributes to the development of copper seawater WQC values. Ultimately, this valuable information facilitates more informed decision-making in marine water quality management efforts.

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.

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.

Copper-binding ligands in deep-sea pore waters of the Pacific Ocean and potential impacts of polymetallic nodule mining on the copper cycle

The release of potentially toxic metals, such as copper (Cu), into the water column is of concern during polymetallic nodule mining. The bioavailability and thus toxicity of Cu is strongly influenced by its speciation which is dominated by organic ligand (L) complexation in seawater, with L-complexes being considered less bioavailable than free Cu²⁺. The presence of CuL-complexes in deep-sea sediments has, however, not been systematically studied in the context of deep-sea mining. We thus analyzed the Cu-binding L concentration ([L]) in deep-sea pore waters of two polymetallic nodule provinces in the Pacific Ocean, the Peru Basin and the Clarion-Clipperton-Zone, using competitive ligand equilibration–adsorptive stripping voltammetry. The pore-water dissolved Cu concentration ([dCu]) ranged from 3 to 96 nM, generally exceeding bottom water concentrations (4–44 nM). Based on fitting results from ProMCC and Excel, Cu was predominantly complexed by L (3–313 nM) in bottom waters and undisturbed pore waters. We conclude that processes like deep-sea mining are unlikely to cause a release of toxic Cu²⁺ concentrations ([Cu²⁺]) to the seawater as > 99% Cu was organically complexed in pore waters and the [Cu²⁺] was < 6 pM for 8 of 9 samples. Moreover, the excess of L found especially in shallow pore waters implied that even with a Cu release through mining activities, Cu²⁺ likely remains beneath toxic thresholds.

Are shallow-water shrimps proxies for hydrothermal-vent shrimps to assess the impact of deep-sea mining?

Polymetallic seafloor massive sulphide deposits are potential targets for deep-sea mining, but high concentrations of metals (including copper - Cu) may be released during exploitation activities, potentially inducing harmful impact. To determine whether shallow-water shrimp are suitable ecotoxicological proxies for deep-sea hydrothermal vent shrimp the effects of waterborne Cu exposure (3 and 10 days at 0.4 and 4 μM concentrations) in Palaemon elegans, Palaemon serratus, and Palaemon varians were compared with Mirocaris fortunata. Accumulation of Cu and a set of biomarkers were analysed. Results show different responses among congeneric species indicating that it is not appropriate to use shallow-water shrimps as ecotoxicological proxies for deep-water shrimps. During the evolutionary history of these species they were likely subject to different chemical environments which may have induced different molecular/biochemical adaptations/tolerances. Results highlight the importance of analysing effects of deep-sea mining in situ and in local species to adequately assess ecotoxicological effects under natural environmental conditions.

Geological, Mineralogical and Textural Impacts on the Distribution of Environmentally Toxic Trace Elements in Seafloor Massive Sulfide Occurrences

With mining of seafloor massive sulfides (SMS) coming closer to reality, it is vital that we have a good understanding of the geochemistry of these occurrences and the potential toxicity impact associated with mining them. In this study, SMS samples from seven hydrothermal fields from various tectonic settings were investigated by in-situ microanalysis (electron microprobe (EMPA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)) to highlight the distribution of potentially-toxic trace elements (Cu, Zn, Pb, Mn, Cd, As, Sb, Co, Ni, Bi, Ag and Hg) within the deposits, their minerals and textures. We demonstrate that a combination of mineralogy, trace element composition and texture characterisation of SMS from various geotectonic settings, when considered along with our current knowledge of oxidation rates and galvanic coupling, can be used to predict potential toxicity of deposit types and individual samples and highlight which may be of environmental concern. Although we cannot quantify toxicity, we observe that arc-related sulfide deposits have a high potential toxicity when compared with deposits from other tectonic settings based on their genetic association of a wide range of potentially toxic metals (As, Sb, Pb, Hg, Ag and Bi) that are incorporated into more reactive sulfosalts, galena and Fe-rich sphalerite. Thus, deposits such as these require special care when considered as mining targets. In contrast, the exclusive concern of ultra-mafic deposits is Cu, present in abundant, albeit less reactive chalcopyrite, but largely barren of other metals such as As, Pb, Sb, Cd and Hg. Whilst geological setting does dictate metal endowment, ultimately mineralogy is the largest control of trace element distribution and subsequent potential toxicity. Deposits containing abundant pyrrhotite (high-temperature deposits) and Fe-rich sphalerite (ubiquitous to all SMS deposits) as well as deposits with abundant colloform textures also pose a higher risk. This type of study can be combined with “bulk lethal toxicity” assessments and used throughout the stages of a mining project to help guide prospecting and legislation, focus exploitation and minimise environmental impact.

The last frontier: Coupling technological developments with scientific challenges to improve hazard assessment of deep-sea mining

The growing economic interest in the exploitation of mineral resources on deep-ocean beds, including those in the vicinity of sensitive-rich habitats such as hydrothermal vents, raise a mounting concern about the damage that such actions might originate to these poorly-know ecosystems, which represent millions of years of evolution and adaptations to extreme environmental conditions. It has been suggested that mining may cause a major impact on vent ecosystems and other deep-sea areas. Yet, the scale and the nature of such impacts are unknown at present. Hence, building upon currently available scientific information it is crucial to develop new cost-effective technologies embedded into rigorous operating frameworks. The forward-thinking provided here will assist in the development of new technologies and tools to address the major challenges associated with deep sea-mining; technologies for in situ and ex situ observation and data acquisition, biogeochemical processes, hazard assessment of deep-sea mining to marine organisms and development of modeling tools in support of risk assessment scenarios. These technological developments are vital to validate a responsible and sustainable exploitation of the deep-sea mineral resources, based on the precautionary principle.