Effects of acute microplastic exposure on physiological parameters in Tubastrea aurea corals

Chronic effects of exposure to polyethylene microplastics may be mitigated at the expense of growth and photosynthesis in reef-building corals

The causes of the physiological effects of microplastic pollution, potentially harming reef-building corals, are unclear. Reasons might include increased energy demands for handling particles and immune reactions. This study is among the first assessing the effects of long-term microplastic exposure on coral physiology at realistic concentrations (200 polyethylene particles L-1). The coral species Acropora muricata, Pocillopora verrucosa, Porites lutea, and Heliopora coerulea were exposed to microplastics for 11 months, and energy reserves, metabolites, growth, and photosymbiont state were analyzed. Results showed an overall low impact on coral physiology, yet species-specific effects occurred. Specifically, H. coerulea exhibited reduced growth, P. lutea and A. muricata showed changes in photosynthetic efficiency, and A. muricata variations in taurine levels. These findings suggest that corals may possess compensatory mechanisms mitigating the effects of microplastics. However, realistic microplastic concentrations only occasionally affected corals. Yet, corals exposed to increasing pollution scenarios will likely experience more negative impacts.

Effect of abamectin on osmoregulation in red swamp crayfish (Procambarus clarkii)

As a widely used pesticide, abamectin could be a threat to nontarget organisms. In this study, the toxic mechanism of abamectin on osmoregulation in Procambarus clarkii was explored for the first time. The results of this study showed that with increasing abamectin concentration, the membrane structures of gill filaments were damaged, with changes in ATPase activities, transporter contents, biogenic amine contents, and gene expression levels. The results of this study indicated that at 0.2 mg/L abamectin, ion diffusion could maintain osmoregulation. At 0.4 mg/L abamectin, passive transport was inhibited due to damage to the membrane structures of gill filaments, and active transport needed to be enhanced for osmoregulation. At 0.6 mg/L abamectin, the membrane structures of gill filaments were seriously damaged, and the expression level of osmoregulation-related genes decreased, but the organisms were still mobilizing various transporters, ATPases, and biogenic amines to address abamectin stress. This study provided a theoretical basis for further study of the effects of contaminations in aquatic environment on the health of crustaceans.

Immunotoxicity of microplastics in fish

Plastic waste degrades slowly in aquatic environments, transforming into microplastics (MPs) and nanoplastics (NPs), which are subsequently ingested by fish and other aquatic organisms, causing both physical blockages and chemical toxicity. The fish immune system serves as a crucial defense against viruses and pollutants present in water. It is imperative to comprehend the detrimental effects of MPs on the fish immune system and conduct further research on immunological assessments. In this paper, the immune response and immunotoxicity of MPs and its combination with environmental pollutants on fish were reviewed. MPs not only inflict physical harm on the natural defense barriers like fish gills and vital immune organs such as the liver and intestinal tract but also penetrate cells, disrupting intracellular signaling pathways, altering the levels of immune cytokines and gene expression, perturbing immune homeostasis, and ultimately compromising specific immunity. Initially, fish exposed to MPs recruit a significant number of macrophages and T cells while activating lysosomes. Over time, this exposure leads to apoptosis of immune cells, a decline in lysosomal degradation capacity, lysosomal activity, and complement levels. MPs possess a small specific surface area and can efficiently bind with heavy metals, organic pollutants, and viruses, enhancing immune responses. Hence, there is a need for comprehensive studies on the shape, size, additives released from MPs, along with their immunotoxic effects and mechanisms in conjunction with other pollutants and viruses. These studies aim to solidify existing knowledge and delineate future research directions concerning the immunotoxicity of MPs on fish, which has implications for human health.

Microplastics in remote coral reef environments of the Xisha Islands in the South China Sea: Source, accumulation and potential risk

Microplastics (MPs) are of great concern to coral health, particularly enhanced biotoxicity of small microplastics (< 100 µm) (SMPs). However, their fate and harm to remote coral reef ecosystems remain poorly elucidated. This work systematically investigated the distributions and features of MPs and SMPs in sediments from 13 islands/reefs of the Xisha Islands, the South China Sea for comprehensively deciphering their accumulation, sources and risk to coral reef ecosystems. The results show that both MPs (average, 682 items/kg) and SMPs (average, 375 items/kg) exhibit heterogeneous distributions, with accumulation within atolls and dispersion across fringing islands, which controlled by human activities and hydrodynamic conditions. Cluster analysis for the first time reveals a pronounced difference in their compositions between the southern and northern Xisha Islands and resultant distinct sources, i.e., MPs in the north part were leaked mainly from local domestic sewage and fishing waste, while in the south part were probably derived from industrial effluents from adjacent countries. Our ecological risk assessment suggests that the ecosystem within the Yongle Atoll is exposed to a high-risk of MPs pollution. The novel results and proposed framework facilitate to effectively manage and control MPs and accordingly preserve a fragile biosphere in remote coral reefs.

The global significance of Scleractinian corals without photoendosymbiosis

Globally tropical Scleractinian corals have been a focal point for discussions on the impact of a changing climate on marine ecosystems and biodiversity. Research into tropical Scleractinian corals, particularly the role and breakdown of photoendosymbiosis in response to warming, has been prolific in recent decades. However, research into their subtropical, temperate, cold- and deep-water counterparts, whose number is dominated by corals without photoendosymbiosis, has not been as prolific. Approximately 50% of Scleractinian corals (> 700 species) do not maintain photoendosymbiosis and as such, do not rely upon the products of photosynthesis for homeostasis. Some species also have variable partnerships with photendosymbionts depending on life history and ecological niche. Here we undertake a systematic map of literature on Scleractinian corals without, or with variable, photoendosymbiosis. In doing so we identify 482 publications spanning 5 decades. In mapping research effort, we find publications have been sporadic over time, predominately focusing on a limited number of species, with greater research effort directed towards deep-water species. We find only 141 species have been studied, with approximately 30% of the total identified research effort directed toward a single species, Desmophyllum pertusum, highlighting significant knowledge gaps into Scleractinian diversity. We find similar limitations to studied locations, with 78 identified from the global data, of which only few represent most research outputs. We also identified inconsistencies with terminology used to describe Scleractinia without photoendosymbiosis, likely contributing to difficulties in accounting for their role and contribution to marine ecosystems. We propose that the terminology requires re-evaluation to allow further systematic assessment of literature, and to ensure it's consistent with changes implemented for photoendosymbiotic corals. Finally, we find that knowledge gaps identified over 20 years ago are still present for most aphotoendosymbiotic Scleractinian species, and we show data deficiencies remain regarding their function, biodiversity and the impacts of anthropogenic stressors.

Biofilm enhances the interactive effects of microplastics and oxytetracycline on zebrafish intestine

The enhanced adsorption of pollutants on biofilm-developed microplastics has been proved in many studies, but the ecotoxicological effects of biofilm-developed microplastics on organisms are still unclear. In this study, adult zebrafish were exposed to original microplastics, biofilm-developed microplastics, original microplastics absorbed with oxytetracycline (OTC), and biofilm-developed microplastics absorbed with OTC for 30 days. The intestinal histological damage, intestinal biomarker response, gut microbiome and antibiotic resistance genes (ARGs) profile of zebrafish were measured to explore the roles of biofilm in the effects of microplastics. The results showed that biofilm-developed microplastics significantly increased the number of goblet cells in intestinal epithelium compared with the control group. The biofilm-developed microplastics also induced the oxidative response in the zebrafish intestines, and biofilm changed the response mode in the combined treatment with OTC. Additionally, the biofilm-developed microplastics caused intestinal microbiome dysbiosis, and induced the abundance of some pathogenic genera increasing by several times compared with the control group and the original microplastics treatments, regardless of OTC adsorption. Furthermore, the abundance of ARGs in biofilm-developed microplastics increased significantly compared with the control and the original microplastic treatments. This study emphasized the significant influence and unique role of biofilm in microplastic studies.

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.

Physical and cellular impact of environmentally relevant microplastic exposure on thermally challenged Pocillopora damicornis (Cnidaria, Scleractinia)

Microplastic pollution is an increasing threat to coral reefs, which are already strongly challenged by climate change-related heat stress. Although it is known that scleractinian corals can ingest microplastic, little is known about their egestion and how microplastic exposure may impair corals at physiological and cellular levels. In addition, the effects of microplastic pollution at current environmental concentration have been little investigated to date, particularly in corals already impacted by heat stress. In this study, the combined effects of these environmental threats on Pocillopora damicornis were investigated from a physical and cellular perspective. Colonies were exposed to three concentrations of polyethylene microplastic beads (no microplastic beads: [No MP], 1 mg/L: [Low MP]; 10 mg/L: [High MP]), and two different temperatures (25 °C and 30 °C) for 72 h. No visual signs of stress in corals, such as abnormal mucus production and polyp extroflection, were recorded. At [Low MP], beads adhered to colonies were ingested but were also egested. Moreover, thermally stressed colonies showed a lower adhesion and higher egestion of microplastic beads. Coral bleaching was observed with an increase in temperature and microplastic bead concentration, as indicated by a general decrease in chlorophyll concentration and Symbiodiniaceae density. An increase in lipid peroxidation was measured in colonies exposed to [Low MP] and [High MP] and an up-regulation of stress response gene hsp70 was observed due to the synergistic interaction of both stressors. Overall, our findings showed that heat stress still represents the main threat to P. damicornis, while the effect of microplastics on coral health and physiology may be minor, especially at control temperature. However, microplastics could exacerbate the effect of thermal stress on cellular homeostasis, even at [Low MP]. While reducing ocean warming is critical for preserving coral reefs, effective management of emerging threats like microplastic pollution is equally essential.

Bioaccumulation of polystyrene nanoplastics and BDE-209 induced oxidative stress, photosynthesis and growth impairments in floating fern Salvinia natans

Aquatic ecosystems are facing increasing exposure to pollutants, posing potential threats to the stability and wellness of aquatic species. This study focused on evaluating the impacts of single and combined exposure to 80 nm polystyrene nanoplastics (PS-NPs, 0.1, 1, 10, 20 mg/L) and decabromodiphenyl ether (BDE-209, 300 ng/L) for 14 days on the bioaccumulation, growth, photosynthesis and oxidative stress in the free-floating fern Salvinia natans. PS-NPs primarily accumulated in the epidermis and trichomes of S. natans. Meanwhile, the levels of superoxide dismutase (SOD) and malondialdehyde (MDA) were significantly increased, while those for peroxidase (POD), catalase (CAT), total antioxidant capacity (T-AOC), and relative growth rate (RGR) decreased. Furthermore, the chlorophyll contents in submerged leaves were decreased, while those in floating leaves were increased at PS-NPs concentrations of 0.1 and 1 mg/L. However, the chlorophyll contents in both submerged and floating leaves displayed a decreasing trend with increasing concentrations of PS-NPs. Under the co-exposure of PS-NPs and BDE-209, the contents of MDA were significantly elevated, whereas CAT, POD, SOD, T-AOC and RGR were significantly decreased (p < 0.05). Our results revealed that, compared to single exposure, more pronounced ecotoxic effects are observed in S. natans under co-exposure to PS-NPs and BDE-209. These findings offer valuable perspectives into the possible environmental risks of BDE-209 and PS-NPs in freshwater ecosystems, contributing to the development of effective management strategies for protecting aquatic organisms and ecosystems. This research highlights the urgent need to understand the toxic effects of emerging contaminants on different aquatic organisms, emphasizing the importance of protecting and preserving aquatic ecosystems.

The comparative effects of chronic microplastic and sediment deposition on the scleractinian coral Merulina ampliata

Despite increasing research into the effects of microplastics on corals, no study to date has compared this relatively novel pollutant with a well-established stressor such as downwelling sediments. Here, Merulina ampliata coral fragments were exposed to polyethylene terephthalate (PET) and calcium carbonate particles (200-300 μm) at two deposition levels, high (115.20 ± 5.83 mg cm-2 d-1, mean ± SE) and low (22.87 ± 1.90 mg cm-2 d-1) in specially-designed Flow-Through Resuspension (FloTR) chambers. After 28 d, there were no significant differences between fragments exposed to sediments and microplastics for coral skeletal growth, Symbiodiniaceae density, and areal or cellular chlorophyll a concentrations. There were also no significant differences between levels of treatments, or with the control fragments. More PET microplastic particles were incorporated into the coral skeletons of fragments exposed to microplastics compared to those exposed to sediment and the control fragments, but there was no difference between fragments exposed to high and low microplastic levels. Together, the results show that M. ampliata appears to be able to cope with both microplastic and sediment stress, and suggests that microplastics do not represent a more serious threat than downwelling sediments at the levels tested.

Effects of copper on gill function of juvenile oriental river prawn (Macrobrachium nipponense): Stress and toxic mechanism

As an important trace element and the accessory factor of many enzymatic processes, heavy metal copper is essential to aquatic animals. The toxic mechanism of copper on gill function of M. nipponense was clarified for the first time in terms of histopathological analysis, physiology, biochemistry and the expression of important genes. The results obtained by present in present research showed that heavy metal copper could affect normal respiratory and metabolic activities in M. nipponense. Copper stress could cause damage to the mitochondrial membrane of gill cells in M. nipponense, and the activity of mitochondrial respiratory chain complex could be inhibited by copper. Copper could affect normal electron transport and mitochondrial oxidative phosphorylation, resulting in the inhibition of energy production. High concentrations of copper could disrupt intracellular ion balance and induce cytotoxicity. The oxidative stress could be induced by copper, leading to excessive ROS. Copper could reduce the mitochondrial membrane potential, lead to the leakage of apoptotic factors, and induce apoptosis. Copper could damage structure of gill, affect normal respiration of gill. This study provided fundamental data for exploring impacts of copper on gill function in aquatic organisms and potential mechanisms of copper toxicity.

Microplastic as an invisible threat to the coral reefs: Sources, toxicity mechanisms, policy intervention, and the way forward

Microplastic (MP) pollution waste is a global macro problem, and research on MP contamination has been done in marine, freshwater, and terrestrial ecosystems. Preventing MP pollution from hurting them is essential to maintaining coral reefs' ecological and economic benefits. However, the public and scientific communities must pay more attention to MP research on the coral reef regions' distribution, effects, mechanisms, and policy evaluations. Therefore, this review summarizes the global MP distribution and source within the coral reefs. Current knowledge extends the impacts of MP on coral reefs, existing policy, and further recommendations to mitigate MPs contamination on corals are critically analyzed. Furthermore, mechanisms of MP on coral and human health are also highlighted to pinpoint research gaps and potential future studies. Given the escalating plastic usage and the prevalence of coral bleaching globally, there is a pressing need to prioritize research efforts on marine MPs that concentrate on critical coral reef areas. Such investigations should encompass an extensive and crucial understanding of the distribution, destiny, and effects of the MPs on human and coral health and the potential hazards of those MPs from an ecological viewpoint.

Distribution and risk assessment of microplastics in typical ecosystems in the South China Sea

Microplastic pollution in the marine environment has attracted worldwide attention. The South China Sea is considered a hotspot for microplastic pollution due to the developed industries and high population density around the South China Sea. The accumulation of microplastics in ecosystems can adversely affect the health of the environment and organisms. This paper reviews the recent microplastic studies conducted in the South China Sea, which novelty summarizes the abundance, types, and potential hazards of microplastics in coral reef ecosystems, mangrove ecosystems, seagrass bed ecosystems, and macroalgal ecosystems. A summary of the microplastic pollution status of four ecosystems and a risk assessment provides a more comprehensive understanding of the impact of microplastic pollution on marine ecosystems in the South China Sea. Microplastic abundances of up to 45,200 items/m³ were reported in coral reef surface waters, 5738.3 items/kg in mangrove sediments, and 927.3 items/kg in seagrass bed sediments. There are few studies of microplastics in the South China Sea macroalgae ecosystems. However, studies from other areas indicate that macroalgae can accumulate microplastics and are more likely to enter the food chain or be consumed by humans. Finally, this paper compared the current risk levels of microplastics in the coral reef, mangrove, and seagrass bed ecosystems based on available studies. Pollution load index (PLI) ranges from 3 to 31 in mangrove ecosystems, 5.7 to 11.9 in seagrass bed ecosystems, and 6.1 to 10.2 in coral reef ecosystems, respectively. The PLI index varies considerably between mangroves depending on the intensity of anthropogenic activity around the mangrove. Further studies on seagrass beds and macroalgal ecosystems are required to extend our understanding of microplastic pollution in marine environments. Recent microplastic detection in fish muscle tissue in mangroves requires more research to further the biological impact of microplastic ingestion and the potential food safety risks.

Impacts of marine debris on coral reef ecosystem: A review for conservation and ecological monitoring of the coral reef ecosystem

Coral reefs are the most spectacular underwater creation of nature. It enhances ecosystem functioning and marine biodiversity while also ensuring the livelihood of millions of coastal communities worldwide. Unfortunately, marine debris poses a serious threat to ecologically sensitive reef habitats and their associated organisms. Over the past decade, marine debris has been regarded as a major anthropogenic threat to marine ecosystems and gained scientific attention around the globe. However, the sources, types, abundance, distribution, and potential consequences of marine debris on reef ecosystems are hardly known. The goal of this review is to provide an overview of the current status of marine debris in various reef ecosystems across the world, with special emphasis on its sources, abundance, distribution, species impacted, major categories, potential impacts and management strategies. Furthermore, the adhesion mechanisms of microplastics to coral polyps, diseases caused by microplastics and are also highlighted.

A global snapshot of microplastic contamination in sediments and biota of marine protected areas

Microplastics (MPs) become ubiquitous contaminants in Marine Protected Areas (MPA) that have been planned as a conservation strategy. The present study provides a comprehensive overview of the occurrence, abundance, and distribution of MPs potentially affecting MPA worldwide. Data on MP occurrence and levels in sediment and biota samples were collected from recent peer-reviewed literature and screened using a GIS-based approach overlapping MP records with MPA boundaries. MPs were found in 186 MPAs, with levels ranging from 0 to 9187.5 items/kg in sediment and up to 17,461.9 items/kg in organisms. Peaked MPs concentrations occurred within multiple-use areas, and no-take MPAs were also affected. About half of MP levels found within MPA fell into the higher concentration quartiles, suggesting potential impacts on these areas. In general, benthic species were likely more affected than pelagic ones due to the higher concentrations of MP reported in the tissues of benthic species. Alarmingly, MPs were found in tissues of two threatened species on the IUCN Red List. The findings denote urgent concerns about the effectiveness of the global system of protected areas and their proposed conservation goals.

Low particle concentrations of nanoplastics impair the gut health of medaka

The environmental occurrence of nanoplastics (NPs) is now evident but their long-term impacts on organisms are unclear, limiting ecological and health risk assessment. We hypothesized that chronic exposure to low particle concentrations of NPs can result in gut-associated toxicity, and subsequently affect survival of fish. Japanese medaka Oryzias latipes were exposed to polystyrene NPs (diameter 100 nm; 0, 10, 10⁴, and 10⁶ items/L) for 3 months, and histopathology, digestive and antioxidant enzymes, immunity, intestinal permeability, gut microbiota, and mortality were assessed. NP exposures caused intestinal lesions, and increased intestinal permeability of the gut. The trypsin, lipase, and chymotrypsin activities were increased, but the amylase activity was decreased. Oxidative damage was reflected by the decreased superoxide dismutase and alkaline phosphatase and increased malondialdehyde, catalase, and lysozyme. The integrated biomarkers response index values of all NP-exposed medaka were significantly increased compared to the control group. Moreover, NP exposures resulted in a decrease of diversity and changed the intestinal microbiota composition. Our results provide new evidence that long-term NPs exposure impaired the health of fish at extremely low particle concentrations, suggesting the need for long-term toxicological studies resembling environmental particle concentrations when assessing the risk of NPs.

Microplastics occurrence, detection and removal with emphasis on insect larvae gut microbiota

Microplastics have been identified in all living forms including human beings, the present need is to restrain its spread and devise measures to remediate microplastics from polluted ecosystems. In this regard, the present review emphasizes on the occurrence, sources detection and toxic effects of microplastics in various ecosystems. The removal of microplastics is prevalent by various physico-chemical and biological methods, although the removal efficiency by biological methods is low. It has been noted that the degradation of plastics by insect gut larvae is a well-known aspect, however, the underlying mechanism has not been completely identified. Studies conducted have shown the magnificent contribution of gut microbiota, which have been isolated and exploited for microplastic remediation. This review also focuses on this avenue, as it highlights the contribution of insect gut microbiota in microplastic degradation along with challenges faced and future prospects in this area.

Effects of microplastic combined with Cr(III) on apoptosis and energy pathway of coral endosymbiont

The combined effect of polyethylene (PE) microplastics and chromium (Cr(III)) on the scleractinian coral Acropora pruinosa (A. pruinosa) was investigated. The endpoints analysed in this study included the endosymbiont density, the chlorophyll a + c content, and the activity of enzymes involved in apoptosis (caspase-1, caspase-3), glycolysis (lactate dehydrogenase, LDH), the pentose phosphate pathway (glucose-6-phosphate dehydrogenase, G6PDH) and electron transfer coenzyme (nicotinamide adenine dinucleotide, NAD⁺/NADH). During the 7-day exposure to PE and Cr(III) stress, the endosymbiont density and chlorophyll content decreased gradually. The caspase-1 and caspase-3 activities increased in the high-concentration Cr(III) exposure group. Furthermore, the LDH and G6PDH activities decreased significantly, and the NAD⁺/NADH was decreased significantly. In summary, the results showed that PE and Cr(III) stress inhibited the endosymbiont energy metabolism enzymes and further led to endosymbiont apoptosis in coral. In addition, under exposure to the combination of stressors, when the concentration of Cr(III) remained at 1 × 10^-2 mg/L, the toxic effects of heavy metals on the endosymbiont were temporarily relieved with elevated PE concentrations. In contrast, when coral polyps were exposed to 5 mg/L PE and increasing Cr(III) concentrations, their metabolic activities were seriously disturbed, which increased the burden of energy consumption. In the short term, the toxic effect of Cr(III) was more obvious than that of PE because Cr(III) exposure leads to endosymbiont apoptosis and irreversible damage. This is the first study to provide insights into the combined effect of microplastic and Cr(III) stress on the apoptosis and energy pathways of coral endosymbionts. This study suggested that microplastics combined with Cr(III) are an important factor affecting the apoptosis and energy metabolism of endosymbionts, accelerating the collapse of the balance between the coral host and symbiotic endosymbiont.

High Heterotrophic Plasticity of Massive Coral Porites pukoensis Contributes to Its Tolerance to Bioaccumulated Microplastics

Scleractinian corals have been observed to be capable of accumulating microplastics from reef environments; however, the tolerant mechanism is poorly known. Here, we examined the response of Porites pukoensis to microplastic pollution by analyzing algal symbiont density, energetic metabolism, and caspase3 activities (representing the apoptosis level) in the coral-Symbiodiniaceae association. The environments of three fringing reef regions along the south coast of Sanya City, Hainan Province of China, were polluted by microplastics (for example, microplastic concentrations in the seawater ranged from 3.3 to 46.6 particles L^-1), resulting in microplastic accumulation in P. pukoensis (0.4-2.4 particles cm^-2). The accumulation of microplastics was negatively correlated to algal symbiont density in the corals but not to caspase3 activities in the two symbiotic partners, demonstrating that P. pukoensis could tolerate accumulated microplastics despite the decrease of algal symbiont density. Furthermore, results from the carbon stable isotope and cellular energy allocation assay indicated that P. pukoensis obtained energy availability (mainly as lipid reserves) using the switch between heterotrophy and autotrophy to maintain energy balance and cope with accumulated microplastics. Collectively, P. pukoensis achieved tolerance to microplastic pollution by maintaining energy availability, which was largely attributed to its high heterotrophic plasticity.

Environmental impact assessment of plastic waste during the outbreak of COVID-19 and integrated strategies for its control and mitigation

During the COVID-19 pandemic, many positive shifts have been observed in the ecosystem, with a significant decrease in the greenhouse gas emissions and air pollution. On the other hand, there were unavoidable negative shifts due to a surge in demand for plastic products such as food and groceries' delivery packaging, single-use plastics, medical and personal protective equipment to prevent transmission of COVID-19. Plastic pollution can be considered as a key environmental issue in world due to the huge footprints of plastics on natural ecosystems and public health. Herein, we presented an overview on the rise of plastic pollution during the COVID-19 pandemic. The potential sources of plastic waste during COVID-19 with its negative effects on the environment such as marine ecosystems and the global economics are highlighted. We also suggested some strategies and recommendations to tackle plastic leakages by applying feedstock recycling, sterilization, and with the use of biodegradable plastics that have become a sustainable alternative to fossil fuel plastics. Also, the importance of elevating public awareness and some recommendations to mitigate plastic generated during the pandemic has been addressed as well.

Evaluation of potential toxicity of polyethylene microplastics on human derived cell lines

Microplastics bare of major concern for environmental conservation and animal welfare in recent years as its use has increased tremendously. Polyethylene microplastics (PE-MPs) are the most common microplastics and could get exposed to humans via different routes with oral>inhalation>dermal. Internalization of MPs through epithelial tissue could expose MPs to various cells such as dendritic cells, macrophages/monocytes, and/or T cells. In this study, we aimed at identifying the effects of two different sized (30.5 ± 10.5 and 6.2 ± 2.0 μm) PE-MPs on different human cell lines representing different tissues or cells that get exposed to MPs directly or indirectly. Six cell lines were cultured with different concentrations of PE-MPs and cell viability, intracellular reactive oxygen species (ROS), nitric oxide (NO), and cytokines were measured. PE-MPs did not substantially lower the cell viability of cells however highest concentration (1000 μg/mL) of both sized MPs slightly reduced cell viability in intestinal epithelial Caco-2 and lung epithelial A549 cells. Both sized PE-MPs induced higher NO in all the cell lines and upregulation of ROS generation was demonstrated at THP-1, Jurkat, and U937 immune cell lines. A pro-inflammatory cytokine response was seen in HaCaT keratinocyte cells when cultured with PE-MPs whereas the opposite effect was observed in THP-1 and U937 cells except with THP-1 cells cultured with larger-sized MPs. We found that the PE-MPs do not have the same effects on all kinds of cells and tissues exposed and the immune modulation is not necessarily inflammatory. Thus, this study gives insight into why more detailed studies focused on exposure routes and organ-specific effects of different MPs need to be carried out.

Plastics in the environment as potential threat to life: an overview

Plastics have become inevitable for human beings in their daily life. Million tons of plastic waste is entering in oceans, soil, freshwater, and sediments. Invasion of plastics in different ecosystems is causing severe problems to inhabitants. Wild animals such as seabirds, fishes, crustaceans, and other invertebrates are mostly effected by plastic entanglements and organic pollutants absorbed and carried by plastics/microplastics. Plastics can also be potentially harmful to human beings and other mammals. Keeping in view the possible harms of plastics, some mitigation strategies must be adopted which may include the use of bioplastics and some natural polymers such as squid-ring teeth protein. This review focuses on the possible sources of intrusion and fate of plastics in different ecosystems, their potential deleterious effects on wildlife, and the measures that can be taken to minimize and avoid the plastic use.

Long-term interactions between microplastics and floating macrophyte Lemna minor: The potential for phytoremediation of microplastics in the aquatic environment

The presence of microplastics (MPs) in the environment has raised many concerns, and therefore approaches and technologies to remove them in situ are of high interest. In this context, we investigated the interactions between polyethylene MPs (fragments with a mean size of 149 ± 75 μm) and an aquatic floating macrophyte Lemna minor in order to assess its potential use for in situ phytoremediation. We first investigated the long-term effects of a high (100 mg/L = 9600 MPs/L), but still environmentally relevant concentration of MPs on L. minor. Subsequently bioadhesion of MPs was studied and the number and strength of MPs adhering to plant biomass were assessed. MPs did not adversely affect various parameters of plants (e.g., specific growth rate, chlorophyll contents, total antioxidant capacity, electron transport system activity, and contents of energy-rich molecules) throughout the duration of the experiment (12 weeks), except for the first week of the experiment, when protein content and total antioxidant capacity were affected. On the other hand, MPs affected the root length of L. minor during the first eight weeks of the experiment, while further exposure resulted in a decrease in the effects, indicating the ability of L. minor to tolerate the presence of MPs for a long period of time. MPs adhered rapidly to the plant biomass and the average percentages of strongly and weakly adhered particles were 6.5% and 20.0%, respectively, of the total MPs applied. In summary, results of this study suggest that L. minor can tolerate hotspot concentrations of MPs and can collect MPs from the water surface. Therefore, phytoremediation using floating plants could be considered as a potential method for in situ removal of MPs from the aquatic environment.

Impact of polyethylene microplastics on coral Goniopora columna causing oxidative stress and histopathology damages

In recent years, the increase of microplastics in the sea exerted a negative impact on coral health. This study has been undertaken to analyze the impact of microplastics on corals. Here, Goniopora columna was exposed to different concentrations of polyethylene microplastics (PE-MP). The daily polyps length and adaptability were recorded. Analysis of the zooxanthellae density and antioxidant activity of coral was done after 1, 3, 5 and 7 days. Further tissue morphology and accumulation of PE-MP were analyzed. The results showed that PE-MP at different concentrations can be adsorbed on the surface of corals and enter inside corals after 7 days. PE-MP at different concentrations reduced polyps length, adaptability and cause the changes in the density of zooxanthellae to be the reason for unbalancing of corals. PE-MP at different concentrations reduced the superoxide dismutase (SOD) activity after exposure to 1 day. PE-MP increased the catalase (CAT) activity at 100 mg/L after exposure; even after reducing the concentration has the same effect. PE-MP at various concentrations increased the glutathione peroxidase (GPx) activity after exposure to 5 and 7 days. It also increased the glutathione transferase (GST) and glutathione (GSH) activity after exposure to 5 and 7 days. PE-MP at different concentrations increased the malondialdehyde (MDA) content after exposure from 1 to 7 days. Analysis of tissue morphology and tissue accumulation shows that different concentrations of PE-MP cause mesenteric atrophy, vacuole, and accumulation in the coral mesenteric. These results indicate that the PE-MP can impact the antioxidant system and hampers the function of enzymes responsible for detoxification of G. columna, increase lipid peroxide content and also cause tissue damage through accumulating in the coral mesenteric.

Transcriptome alterations in zebrafish gill after exposure to different sizes of microplastics

Most studies on microplastics (MPs) focused on gut, liver, and brain, and MPs toxicity was size-dependent, but less has been reported on gill. Here, zebrafish were exposed to three sizes of MPs (45-53 μm, 90-106 μm, and 250-300 μm). Next, comparative transcriptome analysis and determination of physiological indices were performed in zebrafish gills to elucidate the size-associated toxicity of MPs to fish gills. Compared with the control, 60, 344, and 802 differentially expressed genes (DEGs) were identified after exposure to 45-53 μm, 90-106 μm, and 250-300 μm MPs for 5 days, respectively. More DEGs in treatment with bigger MPs suggested that bigger MPs might induce more changes in zebrafish gills than smaller ones. These DEGs were significantly enriched in the FoxO signaling, cellular senescence, circadian rhythm and p53 signaling pathways. Besides, 90-106 μm and 250-300 μm MPs treatments inhibited the cell cycle and prevented the apoptosis. The GSH content significantly increased after MPs exposure, suggesting the induction of oxidative stress. AChE and Na⁺/K⁺-ATPase activities were significantly lowered in all MPs treatments than in the control, suggesting the inhibition of neurotransmission and ion regulation. These changes might negatively influence the normal functioning of gills, such as osmoregulation, ion regulation, and respiration.

Effects of nanoplastic on cell apoptosis and ion regulation in the gills of Macrobrachium nipponense

Nanoplastic, ubiquitous in aquatic environments, are raising concern worldwide. However, studies on nanoplastic exposure and its effects on ion transport in aquatic organisms are limited. In this study, the juvenile oriental river shrimp, Macrobrachium nipponense, was exposed to five levels of nanoplastic concentrations (0, 5, 10, 20, 40 mg/L) in order to evaluate cell viability, ion content, ion transport, ATPase activity, and related gene expression. The results showed that the apoptosis rate was higher in the high concentration nanoplastic group (40 mg/L) compared to the low concentration nanoplastic group (5 mg/L) and the control group (0 mg/L). The ion content of sodium (Na⁺), potassium (K⁺), chloride (Cl^-), and calcium (Ca²⁺) showed a decreasing trend in gill tissue compared to the control group. The Na⁺K⁺-ATPase, V(H)-ATPase, Ca²⁺Mg²⁺-ATPase, and total ATPase activities in the gills of M. nipponense showed a general decrease with the increasement of nanoplastic concentration and time of exposure. When increasing nanoplastic concentration, the expression of ion transport-related genes in the gills of M. nipponense showed first rise then descend trend. As elucidated by the results, high nanoplastic concentrations have negative effect on cell viability, ion content, ion transport ATPase activity, and ion transport-related gene expression in the gills of M. nipponense. This research provides a theoretical foundation for the toxic effects of nanoplastic in aquaculture.

Enhanced microalgal toxicity due to polystyrene nanoplastics and cadmium co-exposure: From the perspective of physiological and metabolomic profiles

As important emerging contaminants, nanoplastics can act as vectors for other environmental pollutants, resulting in their migration throughout ecosystems and altering their toxicity. In this study, the fluorescent dye label aggravated the toxicity of polystyrene (PS) nanoplastics (100 nm diameter particles) to microalgae Euglena gracilis. Therefore, the toxicity of non-fluorescent labelled PS alone and in combination with divalent cadmium (Cd²⁺) on Euglena gracilis in the environmentally relevant concentrations was investigated. Results revealed that co-exposure to 50 μg/L (1.1 × 10¹⁰ particles/L) PS and 50 μg/L Cd²⁺ resulted in synergistic effects, significantly inhibiting microalgal growth by 28.76%. Superoxide dismutase, peroxidase and extracellular polymeric substances were distinctly enhanced in co-exposure treatments compared to the control, indicating that cellular antioxidant defense responses were activated. LC-MS-based metabolomic analysis suggested that PS and Cd²⁺ exposure alone or in combination induced significant disruption to carbohydrate and purine metabolism-related pathways, as compared to controls. As part of the PS and Cd²⁺ stress response, differential metabolites involved in lipid metabolism and amino acid metabolism provide antioxidants and cell membrane protective molecules. Overall, this combined physiological and metabolomic analysis approach provides a better understanding of the potential risks posed by nanoplastics and heavy metal pollution in aquatic ecosystems.

Behaviors and biochemical responses of macroinvertebrate Corbicula fluminea to polystyrene microplastics

Microplastic, a well-documented emerging contaminant, is widespread in aquatic environments resulting from the production and fragmentation of large plastics items. The knowledge about the chronic toxic effects and behavioral toxicity of microplastics, particularly on freshwater benthic macroinvertebrates, is limited. In this study, adult Asian clams (Corbicula fluminea) were exposed to gradient microplastic solutions for 42 days to evaluate behavioral toxicity and chronic biotoxicity. The results showed that microplastics caused behavior toxicity, oxidative stress, and tissue damage in high-concentration treatments. Siphoning, breathing, and excretion was significantly inhibited (p < 0.05) at high-concentration treatments, suggesting that high-concentration microplastics induced behavioral toxicity in C. fluminea. Malondialdehyde content, superoxide dismutase, catalase, and glutathione reductase activities were significantly enhanced (p < 0.05) and the acetylcholinesterase was significantly inhibited (p < 0.05) throughout the exposure period in high-concentration treatments. Enzymes associated with energy supply were significantly higher at high-concentration microplastics treatments on D7 and D21. However, they recovered to a normal level on D42. The instability of the enzymes indicated that high-concentration microplastics induced oxidative stress and disorder in neurotransmission and energy supply. The gills of C. fluminea in treatments underwent cilia degeneration, which indicated that microplastics caused tissue damage in the gills. The analysis of integrated biomarker response values revealed that high-concentration microplastics led to long-term effects on the health of C. fluminea. In conclusion, continuous exposure to microplastics (10 mg L^-1) would damage physical behavior and the antioxidant system of C. fluminea.

Microplastics: impacts on corals and other reef organisms

Plastic pollution in a growing problem globally. In addition to the continuous flow of plastic particles to the environment from direct sources, and through the natural wear and tear of items, the plastics that are already there have the potential to breakdown further and therefore provide an immense source of plastic particles. With the continued rise in levels of plastic production, and consequently increasing levels entering our marine environments it is imperative that we understand its impacts. There is evidence microplastic and nanoplastic (MNP) pose a serious threat to all the world's marine ecosystems and biota, across all taxa and trophic levels, having individual- to ecosystem-level impacts, although these impacts are not fully understood. Microplastics (MPs; 0.1–5 mm) have been consistently found associated with the biota, water and sediments of all coral reefs studied, but due to limitations in the current techniques, a knowledge gap exists for the level of nanoplastic (NP; <1 µm). This is of particular concern as it is this size fraction that is thought to pose the greatest risk due to their ability to translocate into different organs and across cell membranes. Furthermore, few studies have examined the interactions of MNP exposure and other anthropogenic stressors such as ocean acidification and rising temperature. To support the decision-making required to protect these ecosystems, an advancement in standardised methods for the assessment of both MP and NPs is essential. This knowledge, and that of predicted levels can then be used to determine potential impacts more accurately.

Microplastics in mangroves and coral reef ecosystems: a review

Microplastic pollution has recently been identified as a major issue for the health of ecosystems. Microplastics have typically sizes of less than 5 mm and occur in various forms, such as pellets, fibres, fragments, films, and granules. Mangroves and coral reefs are sensitive and restricted ecosystems that provide free ecological services such as coastal protection, maintaining natural cycles, hotspots of biodiversity and economically valuable goods. However, urbanization and industrial activities have started contaminating even these preserved ecosystems. Here we review sources, occurrence, and toxicity of microplastics in the trophic levels of mangrove and coral reef ecosystems. We present detection methods, such as microscopic identification and spectroscopy. We discuss mitigating measures that prevent the entry of microplastics into the marine environment.

Effects of Microplastics Exposure on the Acropora sp. Antioxidant, Immunization and Energy Metabolism Enzyme Activities

Microplastic pollution in marine environments has increased rapidly in recent years, with negative influences on the health of marine organisms. Scleractinian coral, one of the most important species in the coral ecosystems, is highly sensitive to microplastic. However, whether microplastic causes physiological disruption of the coral, via oxidative stress, immunity, and energy metabolism, is unclear. In the present study, the physiological responses of the coral Acropora sp. were determined after exposure to polyethylene terephthalate (PET), polyamide 66 (PA66), and polyethylene (PE) microplastic for 96 h. The results showed that there were approximately 4-22 items/nubbin on the surface of the coral skeleton and 2-10 items/nubbin on the inside of the skeleton in the MPs exposure groups. The density of endosymbiont decreased (1.12 × 105-1.24 × 105 cell/cm2) in MPs exposure groups compared with the control group. Meanwhile, the chlorophyll content was reduced (0.11-0.76 μg/cm2) after MPs exposure. Further analysis revealed that the antioxidant enzymes in coral tissues were up-regulated (Total antioxidant capacity T-AOC 2.35 × 10-3-1.05 × 10-2 mmol/mg prot, Total superoxide dismutase T-SOD 3.71-28.67 U/mg prot, glutathione GSH 10.21-10.51 U/mg prot). The alkaline phosphatase (AKP) was inhibited (1.44-4.29 U/mg prot), while nitric oxide (NO) increased (0.69-2.26 μmol/g prot) for cell signal. Moreover, lactate dehydrogenase (LDH) was down-regulated in the whole experiment period (0.19-0.22 U/mg prot), and Glucose-6-phosphate dehydrogenase (G6PDH) for cell the phosphate pentoses pathway was also reduced (0.01-0.04 U/mg port). Results showed that the endosymbiont was released and chlorophyll was decreased. In addition, a disruption could occur under MPs exposure, which was related to anti-oxidant, immune, and energy metabolism.