Microplastics can aggravate the impact of ocean acidification on the health of mussels: Insights from physiological performance, immunity and byssus properties

Immune and physiological responses of Mytilus unguiculatus to Alexandrium spp. with varying paralytic shellfish toxin profiles

The innate immunity of bivalves serves as the initial defense mechanism against environmental pollutants, ultimately impacting genetic regulatory networks through synergistic interactions. Previous research has demonstrated variations in the accumulation and tolerance capacities of bivalves; however, the specific mechanism underlying the low accumulation of PSTs in M. unguiculatus remains unclear. This study examined the alterations in feeding behavior and transcriptional regulation of M. unguiculatus following exposure to two Alexandrium strains with distinct toxin profiles, specifically gonyautoxin (AM) and N-sulfocarbamoyl toxin (AC). The total accumulation rate of PSTs in M. unguiculatus was 43.64 % (AC) and 27.80 % (AM), with highest PSTs content in the AM group (455.39 μg STXeq/kg). There were significant variations (P < 0.05) in physiological parameters, such as total hemocyte count, antioxidant superoxide activity and tissue damage in both groups. The absorption rate was identified as the key factor influencing toxin accumulation. Transcriptomic analyses demonstrated that PSTs triggered upregulation of endocytosis, lysosome, and immune-related signaling pathways. Furthermore, PSTs induced a nucleotide imbalance in the AC group, with total PSTs content serving as the most toxic indicator. These results suggested that protein-like substances had a crucial role in the stress response of M. unguiculatus to PSTs. This study provided novel perspectives on the impacts of intricate regulatory mechanisms and varying immune responses to PSTs in bivalves.

Potential threats of microplastics and pathogenic bacteria to the immune system of the mussels Mytilus galloprovincialis

As one of the main components of marine pollution, microplastics (MPs) inevitably enter the mussel aquaculture environment. At the same time, pathogenic bacteria, especially pathogens such as Vibrio, can cause illness outbreaks, leading to large-scale death of mussels. The potential harm of MPs and pathogenic bacteria to bivalve remains unclear. This study designed two experiments (1) mussels (Mytilus galloprovincialis) were exposed to 100 particles/L or 1,000 particles/L polymethyl methacrylate (PMMA, 17.01 ± 6.74 μm) MPs and 1 × 107 CFU/mL Vibrio parahaemolyticus at the same time (14 days), and (2) mussels were exposed to 100 particles/L or 1,000 particles/L MPs for a long time (30 days) and then exposed to 1 × 107 CFU/mL V. parahaemolyticus to explore the effects of these two stresses on the mussel immune system. The results showed that after the combined exposure of V. parahaemolyticus and MPs, the lysosomal membrane stability of hemocytes decreased, lysozyme activity was inhibited, and hemocytes were induced to produce more lectins and defensins to fight pathogenic invasion. Long-term exposure to MPs caused a large amount of energy consumption in mussels, inhibited most of the functions of humoral immunity, increased the risk of mussel infection with pathogenic bacteria, and negatively affected mussel condition factor, the number of hemocytes, and the number of byssuses. Mussels may allocate more energy to deal with MPs and pathogenic bacterial infections rather than for growth. Above all, MPs exposure can affect mussel immune function or reduce its stress resistance, which in turn has an impact on mollusk farming.

Effects of ocean acidification and polystyrene microplastics on the oysters Crassostrea gigas: An integrated biomarker and metabolomic approach

The adverse impacts of microplastics (MPs) or ocean acidification (OA) on mollusks have been widely reported, however, little is known about their combined effects on mollusks. The oysters Crassostrea gigas were exposed to two sizes of polystyrene MPs with 1 × 104 particles/L (small polystyrene MPs (SPS-MPs): 6 μm, large polystyrene MPs (LPS-MPs): 50-60 μm) at two pH levels (7.7 and 8.1) for 14 days. The antagonistic effects between MPs and OA on oysters were mainly observed. Single SPS-MPs exposure can induce CAT enzyme activity and LPO level in gills, while LPS-MPs exposure alone can increase PGK and PEPCK gene expression in digestive glands. Ocean acidification can increase clearance rate and inhibit antioxidant enzyme activity, whereas combined exposure of OA and SPS-MPs can affect the metabolomic profile of digestive glands. This study emphasized that the potential toxic effects of MPs under the scene of climate change should be concerned.

Leachate from municipal solid waste landfills: A neglected source of microplastics in the environment

Over the past decade or so, microplastics (MPs) have received increasing attention due to their ubiquity and potential risk to the environment. Waste plastics usually end up in landfills. These plastics in landfills undergo physical compression, chemical oxidation, and biological decomposition, breaking down into MPs. As a result, landfill leachate stores large amounts of MPs, which can negatively impact the surrounding soil and water environment. However, not enough attention has been given to the occurrence and removal of MPs in landfill leachate. This lack of knowledge has led to landfills being an underestimated source of microplastics. In order to fill this knowledge gap, this paper collects relevant literature on MPs in landfill leachate from domestic and international sources, systematically summarizes their presence within Asia and Europe, assesses the impacts of landfill leachate on MPs in the adjacent environment, and particularly discusses the possible ecotoxicological effects of MPs in leachate. We found high levels of MPs in the soil and water around informal landfills, and the MPs themselves and the toxic substances they carry can have toxic effects on organisms. In addition, this paper summarizes the potential impact of MPs on the biochemical treatment stage of leachate, finds that the effects of MPs on the biochemical treatment stage and membrane filtration are more significant, and proposes some novel processes for MPs removal from leachate. This analysis contributes to the removal of MPs from leachate. This study is the first comprehensive review of the occurrence, environmental impact, and removal of MPs in leachate from landfills in Asia and Europe. It offers a comprehensive theoretical reference for the field, providing invaluable insights.

Influence of calcium concentration on larval adhesion in a highly invasive fouling ascidian: From morphological changes to molecular mechanisms

Calcium ion (Ca2+) is involved in the protein-mediated larval adhesion of fouling ascidians, yet the effects of environmental Ca2+ on larval adhesion remain largely unexplored. Here, the larvae of fouling ascidian C. robusta were exposed to different concentrations of Ca2+. Exposures to low-concentration (0 mM and 5 mM) and high-concentration (20 mM and 40 mM) Ca2+ significantly decreased the adhesion rate of larvae, which was primarily attributed to the decreases in adhesive structure length and curvature. Changes in the expressions of genes encoding adhesion-, microvilli-, muscle contraction-, and collagen-related proteins provided a molecular-level explanation for adhesion rate reduction. Additionally, larvae likely prioritized their energy towards immunomodulation in response to Ca2+ stresses, ultimately leading to adhesion reduction. These findings advance our understanding of the influencing mechanisms of environmental Ca2+ on larval adhesion, which are expected to provide references for the development of precise antifouling strategies against ascidians and other fouling species.

The combined effects of phenanthrene and micro-/nanoplastics mixtures on the cellular stress responses of the thick-shell mussel Mytilus coruscus

Pollution with complex mixtures of contaminants including micro- and nano-plastics (MNPs) and organic pollutants like polycyclic aromatic hydrocarbons (PAH) poses a major threat to coastal marine ecosystems. Toxic mechanisms of contaminant mixtures are not well understood in marine organisms. We studied the effects of single and combined exposures to polycyclic aromatic hydrocarbon phenanthrene (Phe) and MNPs mixture with sizes of 70 nm, 5 μm and 100 μm on the immune health and oxidative stress parameters in the thick-shell mussel Mytilus coruscus. Immune cells (hemocytes) were more sensitive to the pollutant-induced oxidative stress than the gills. In hemocytes of co-exposed mussels, elevated mortality, lower lysosomal content, high production of reactive oxygen species (ROS) and decrease mitochondrial were found. Disparate responses of antioxidant enzymes in the hemolymph (e.g. increased superoxide dismutase (SOD) activity without a corresponding increase in catalase (CAT) in Phe exposures and an increase in CAT without a change in SOD in MNPs exposures) suggests misbalance of the antioxidant defense in the pollutant-exposed mussels. Gill lacked pronounced oxidative stress response showing a decline in ROS and antioxidant levels. Tissue-specific single and combined effects of Phe and MNPs suggest variation in bioavailability and/or different sensitivity to these pollutants in the studied tissues. Notably, the combined effects of MNPs and Phe were additive or antagonistic, showing that MNPs do not enhance and occasionally mitigate the toxic effects of Phe on the hemocytes and the gills of the mussels. Overall, our study sheds light on the impact of long-term exposure to MNPs and Phe mixtures on mussels, showing high sensitivity of the immune system and modulation of the Phe toxicity by MNPs co-exposure. These findings that may have implications for understanding the impacts of combined PAH and MNPs pollution on the health of mussel populations from polluted coastal habitats.

Microplastic pollution and ecological risk assessment of Yueqing Bay affected by intensive human activities

Microplastics (MPs) are a widespread environmental problem posing ecological risks in the ocean. We investigated the abundance, spatial distribution, characteristics and ecological risks of MPs in surface seawater, sediments and organisms in Yueqing Bay, China. MPs were detected in both environmental media and organisms. The overall abundance (0.24 items/m3 seawater, 6.13 items/kg dry sediment, 0.77 items/individual in organisms) was low to medium compared with other coastal areas. The MPs were mainly derived from the high-intensity mariculture and shipping in the bay, as well as industrial and human activities along the surrounding coast. The abundance of MPs in water of the left (western) bay (0.39 items/m3) was considerably higher than that of the right (north-eastern) bay (0.07 items/m3) due to the different levels of population and economic development on the left and right coasts. The ecological risk assessment showed generally low to medium risk from MPs pollution in Yueqing Bay, with higher ecological risk index (H) and potential ecological hazards (RI) of MPs polymers in water samples. These data emphasize the need for timely and effective action to reduce the contribution of intensive human activities to MPs pollution and provide information for further ecotoxicological studies, pollution control, and policy development of MPs.

Prepared microplastics interaction with Artemia salina under low pH conditions representing ocean acidification; a simulated environmental exposure

Ocean acidification and microplastic pollution are two of the major ecological concerns. The distribution of large quantities of plastic debris and microplastics all across the oceans emphasises the need to determine the influence of microplastics in ocean acidification and to evaluate its concomitant toxicological effects on aquatic life forms. Studies on the combined impact of both the stressors are very limited, but much needed in the current scenario. Where most of the present-day research use purchased microplastics of defined size and morphology (microspheres, fibres, rods, etc.), the present study employs prepared "true to life microplastics" that resemble the environmental microplastic pollutants in morphology and size heterogeneity. The present study focusses on evaluating the fate and impact of oceanic microplastics on the physiology and development of Artemia salina (Brine shrimp), one among the most ecologically significant zooplankton species. Natural sea water was acidified by controlled perturbation of carbon dioxide using a valve system. The hatching rate of A. salina cysts receded significantly (p < 0.05) upon singular exposures to microplastics and low pH (7.80), whereas combined effect was insignificant. The reactive oxygen species (ROS) elevated as a result of individual exposures to microplastics and low pH. However, only in 0.5 mg mL-1 PE treatments at pH 7.80, an additive impact was reported for ROS activity (p < 0.05). The SOD activities increased significantly but it can be attributed as the individual responses towards exposure to both the stressors. A significant additive impact was not observed for SOD activity (p > 0.05). But during the development, significant morphological anomalies were observed. Changes in the appendages of nauplii and juveniles as a result of combined exposure to microplastics and low pH treatments are significant findings. Our observations suggest that coupled exposure to microplastics and low pH could induce significant oxidative stress in the marine zooplanktons and also adversely affect their normal development. Findings from the current study emphasise the need for further research to understand the coupled toxicological impacts of ocean acidification and predominant pollutants such as microplastics to other marine animals as well.

Defence mechanisms of Pinctada fucata martensii to Vibrio parahaemolyticus infection: Insights from proteomics and metabolomics

Survival of pearl oysters is not only challenged by coastal pollution, but also pathogen infection that may eventually incur substantial economic losses in the pearl farming industry. Yet, whether pearl oysters can defend themselves against pathogen infection through molecular mechanisms remains largely unexplored. By using iTRAQ proteomic and metabolomic analyses, we analysed the proteins and metabolites in the serum of pearl oysters (Pinctada fucata martensii) when stimulated by pathogenic bacteria (Vibrio parahaemolyticus). Proteomic results found that a total of 2,242 proteins were identified in the experimental (i.e., Vibrio-stimulated) and control groups, where 166 of them were differentially expressed (120 upregulated and 46 downregulated in the experimental group). Regarding the immune response enrichment results, the pathway of signal transduction was significantly enriched, such as cytoskeleton and calcium signalling pathways. Proteins, including cathepsin L, heat shock protein 20, myosin and astacin-like protein, also contributed to the immune response of oysters. Pathogen stimulation also altered the metabolite profile of oysters, where 49 metabolites associated with metabolism of energy, fatty acids and amino acids were found. Integrated analysis suggests that the oysters could respond to pathogen infection by coordinating multiple cellular processes. Thus, the proteins and metabolites identified herein not only represent valuable genetic resources for developing molecular biomarkers and genetic breeding research, but also open new avenues for studies on the molecular defence mechanisms of pearl oysters to pathogen infection.

Exposure sources and pathways of micro- and nanoplastics in the environment, with emphasis on potential effects in humans: A systematic review

Microplastics (MPs) are emerging pollutants that are ubiquitous in the environment, and may be a potential threat to human health. This review describes the MP exposure sources and pathways through drinking water, food intake, and air inhalation. The unregulated discharge of MPs in water sources and the absence of required MP filter technology in water treatment plants are important routes of MP exposure through drinking water. The presence of MPs in food may lead to the accumulation of MPs in the body. Exposure to MPs can occur through airborne fallout and dust inhalation in both indoor and outdoor environments. This review summarizes the MP exposure sources and possible pathways in the human body, and illustrates that the intake of drinking water, food consumption, and air inhalation should be assessed in during routine activities. Integr Environ Assess Manag 2023;19:1422-1432. © 2023 SETAC.

Synergistic adverse effects of microfibers and freshwater acidification on host-microbiota interactions in the water flea Daphnia magna

Microfibers are the most common type of microplastics in freshwater environments. Anthropogenic climate stressors, such as freshwater acidification (FA), can interact with plastic pollution to disrupt freshwater ecosystems. However, the underlying mechanisms responsible for the interactive effects of microfibers and FA on aquatic organisms remain poorly understood. In this study, we investigated individual Daphnia magna-microbiota interactions affected by interactions between microfibers and FA (MFA). We found that the accumulated amount of microfibers in pH-treatment groups was significantly higher than in the control groups, resulting in negative consequences on reproduction, growth, and sex ratio. We also observed that MFA interactions induced immunity- and reproduction-related biological processes. In particular, the abundance of pathogenic bacteria increased only in MFA groups, indicating that MFA interactions can cause intestinal damage. Our integrated analysis of microbiomes and host transcriptomes revealed that synergistic adverse effects of MFAs are closely related to changes in microbial communities, suggesting that D. magna fitness and the microbial community are causally linked. These finding may help elucidate the toxicity mechanisms governing the responses of D. magna to microfibers and acidification interactions, and to host-microbiome-environment interactions.

The adverse impact of microplastics and their attached pathogen on hemocyte function and antioxidative response in the mussel Mytilus galloprovincialis

Microplastics (MPs) are widely distributed in marine environments, and they are easily attached by various microorganisms, including pathogenic bacteria. When bivalves mistakenly eat MPs, pathogenic bacteria attached to MPs enter their bodies through the Trojan horse effect, causing adverse effects. In this study, the mussel Mytilus galloprovincialis was exposed to aged polymethylmethacrylate MPs (PMMA-MPs, 20 μm) and Vibrio parahaemolyticus attached to PMMA-MPs to explore the effect of synergistic exposure by measuring lysosomal membrane stability, ROS content, phagocytosis, apoptosis in hemocytes, antioxidative enzyme activities and apoptosis-related gene expression in gills and digestive glands. The results showed that MP exposure alone did not cause significant oxidative stress in mussels, but after long-term coexposure to MPs and V. parahaemolyticus, the activities of antioxidant enzymes were significantly inhibited in the gills of mussels. Both single MP exposure and coexposure will affect hemocyte function. Coexposure can induce hemocytes to produce higher ROS, improve phagocytosis, significantly reduce the stability of the lysosome membrane, and induce the expression of apoptosis-related genes, causing apoptosis of hemocytes compared with single MP exposure. Our results demonstrate that MPs attached to pathogenic bacteria have stronger toxic effects on mussels, which also suggests that MPs with pathogenic bacteria might have an influence on the immune system and cause disease in mollusks. Thus, MPs may mediate the transmission of pathogens in marine environments, posing a threat to marine animals and human health. This study provides a scientific basis for the ecological risk assessment of MP pollution in marine environments.

Behavioral and physiological effects of ocean acidification and warming on larvae of a continental shelf bivalve

The negative impacts of ocean warming and acidification on bivalve fisheries are well documented but few studies investigate parameters relevant to energy budgets and larval dispersal. This study used laboratory experiments to assess developmental, physiological and behavioral responses to projected climate change scenarios using larval Atlantic surfclams Spisula solidissima solidissima, found in northwest Atlantic Ocean continental shelf waters. Ocean warming increased feeding, scope for growth, and biomineralization, but decreased swimming speed and pelagic larval duration. Ocean acidification increased respiration but reduced immune performance and biomineralization. Growth increased under ocean warming only, but decreased under combined ocean warming and acidification. These results suggest that ocean warming increases metabolic activity and affects larval behavior, while ocean acidification negatively impacts development and physiology. Additionally, principal component analysis demonstrated that growth and biomineralization showed similar response profiles, but inverse response profiles to respiration and swimming speed, suggesting alterations in energy allocation under climate change.

Nanoplastics induce epigenetic signatures of transgenerational impairments associated with reproduction in copepods under ocean acidification

Ocean acidification (OA) is one of many major global climate changes that pose a variety of risks to marine ecosystems in different ways. Meanwhile, there is growing concern about how nanoplastics (NPs) affect marine ecosystems. Combined exposure of marine organisms to OA and NPs is inevitable, but their interactive effects remain poorly understood. In this study, we investigated the multi- and transgenerational toxicity of NPs on copepods under OA conditions for ten generations. The findings revealed that OA and NPs have a synergistic negative effect on copepod reproduction across generations. In particular, the transgenerational groups showed reproductive impairments in the F1 and F2 generations (F1T and F2T), even though they were never exposed to NPs. Moreover, our epigenetic examinations demonstrated that the observed intergenerational reproductive impairments are associated with differential methylation patterns of specific genes, suggesting that the interaction of OA and NPs can pose a significant threat to the sustainability of copepod populations through epigenetic modifications. Overall, our findings provide valuable insight into the intergenerational toxicity and underlying molecular mechanisms of responses to NPs under OA conditions.

Addressing the Joint Impact of Temperature and pH on Vibrio harveyi Adaptation in the Time of Climate Change

Global warming and acidification of the global ocean are two important manifestations of the ongoing climate change. To characterize their joint impact on Vibrio adaptation and fitness, we analyzed the temperature-dependent adaptation of Vibrio harveyi at different pHs (7.0, 7.5, 8.0, 8.3 and 8.5) that mimic the pH of the world ocean in the past, present and future. Comparison of V. harveyi growth at 20, 25 and 30 °C show that higher temperature per se facilitates the logarithmic growth of V. harveyi in nutrient-rich environments in a pH-dependent manner. Further survival tests carried out in artificial seawater for 35 days revealed that cell culturability declined significantly upon incubation at 25 °C and 30 °C but not at 20 °C. Moreover, although acidification displayed a negative impact on cell culturability at 25 °C, it appeared to play a minor role at 30 °C, suggesting that elevated temperature, rather than pH, was the key player in the observed reduction of cell culturability. In addition, analyses of the stressed cell morphology and size distribution by epifluorescent microscopy indicates that V. harveyi likely exploits different adaptation strategies (e.g., acquisition of coccoid-like morphology) whose roles might differ depending on the temperature-pH combination.

Impacts of marine heatwaves on byssus production in highly invasive fouling mussels

Marine heatwaves (MHWs) are projected to increase in their frequency, intensity, and duration, causing irreversible and catastrophic consequences for intertidal ecosystems around the world. The highly invasive fouling mussel, Arcuatula senhousia, can cause marked habitat alteration by constructing extremely intense byssal mats, devastating the biodiversity of many intertidal systems, yet very little is known about its fate under conditions of more frequent, hotter and longer MHWs. Here, we assessed impacts of two scenarios of MHWs (low-intensity with 4 °C rise of seawater temperature and high-intensity with 8 °C rise, respectively) on the byssal production of A. senhousia. Mussels exposed to low-intensity MHWs did not show any significant differences in the number, length and diameter of byssal threads, compared with those not thermally stressed. Under high-intensity scenario, the byssus production was significantly depressed, and byssal threads became fewer, shorter and finer, in line with significant decreases in cumulative length and volume. These findings provide a better understanding of responses of invasive fouling mussels such as A. senhousia to MHWs and make a leap forward in linking climate change and biological fouling in marine ecosystems.

Toxic effects of polystyrene microplastics on the intestine of Amphioctopus fangsiao (Mollusca: Cephalopoda): From physiological responses to underlying molecular mechanisms

Microplastics are broadly used and among the most studied environmental pollutants due to their potential impacts on organisms and human health. Amphioctopus fangsiao (Cephalopoda: Octopodidae) is an important commercial species in the Pacific Northwest and is very popular among consumers owing to its rich nutritional value and fresh flavor. However, the toxic effects of microplastic exposure on A. fangsiao, including phenotypical effect and underlying molecular mechanism, remain limited. In this study, the octopus A. fangsiao were exposed to microplastics (polystyrene microplastics, Micro-PS) at concentrations of 100 and 1000 μg/L for 21 days, and then the physiological response, histopathological analysis, biomarkers of oxidative stress and glycolipid metabolism, microbiome perturbations and transcriptomic profiles in the intestines were performed. Results demonstrated that Micro-PS exposure had distinct adverse effects on the food intake of A. fangsiao. Histological analysis revealed that Micro-PS exposure has resulted in histopathological damage, thus causing early inflammation of the intestine. Oxidative stresses, metabolic disorders and microbiome perturbations were also detected in the intestine of A. fangsiao based on physiological biomarkers and microbiome analyses. Moreover, transcriptome analysis detected the differentially expressed genes (DEGs) and significantly enriched KEGG pathways in response to oxidative stress, glycolipid metabolism, DNA damage and transmembrane transport of intestinal cells, revealing distinct toxic effects at the molecular level. In summary, Micro-PS exposure has a strong impact on the intestines of A. fangsiao. For the first time, this study uses multiple approaches based on the physiological and biochemical response as well as transcriptional regulation analysis. The first assessment of the toxic impact of this species under Micro-PS exposure is also reported.