Individual and combined toxicogenetic effects of microplastics and heavy metals (Cd, Pb, and Zn) perturb gut microbiota homeostasis and gonadal development in marine medaka (Oryzias melastigma)

Phthalates (PAEs) and reproductive toxicity: Hypothalamic-pituitary-gonadal (HPG) axis aspects

Phthalates (PAEs) are widely used for their excellent ability to improve plastic products. As an essential endocrine axis that regulates the reproductive system, whether dysfunction of the hypothalamic-pituitary-gonadal (HPG) axis is involved in reproductive toxicity mediated by environmental endocrine disruptors PAEs has become a hot topic of widespread concern. This study systematically reviewed the adverse effects of multiple PAEs on the HPG axis in different models and objectively discussed the possible underlying mechanisms. The abnormal release of gonadotropin-releasing hormone and gonadotropin, dysfunction of sex hormone receptors and steroid hormone synthesis, and general damage, including cell proliferation, oxidative stress, apoptosis, and autophagy have been confirmed to be involved in this process. Although it is widely established that PAEs induce HPG axis dysfunction, the specific mechanisms involved remain unclear. From a systematic review of relevant publications, it appears that the abnormal expression of peroxisome proliferator-activated, aryl hydrocarbon, and insulin receptors mediated by PAEs is key upstream event that induces these adverse outcomes; however, this inference needs to be further verified. Overall, this study aimed to provide reliable potential biomarkers for future environmental risk assessment and epidemiological investigation of PAEs.

Toxicity assessment of microplastic (MPs); a threat to the ecosystem

Plastic is now considered part and parcel of daily life due to its extensive usage. Microplastic (MP) pollution is becoming a growing worry and has been ranked as the second most critical scientific problem in the realm of ecology and the environment. Microplastics are smaller in size than the plastic and are more harmful to biotic and as well as abiotic environments. The toxicity of microplastic depends upon its shape and size and increases with an increase in its adsorption capacity and their toxicity. The reason behind their harmful nature is their small size and their large surface area-to-volume ratio. Microplastic can get inside fruits, vegetables, seeds, roots, culms, and leaves. Hence microplastic enters into the food chain. There are different entry points for microplastic to enter into the food chain. Such sources can include polluted food, beverages, spices, plastic toys, and household (packing, cooking, etc.). The concentration of microplastic in terrestrial environments is increasing day by day. Microplastic causes the destruction of soil structure; destroys soil microbiota, cause depletion of nutrients in the soil, and their absorption by plants decreases plant growth. Apart from other environmental problems caused by microplastic, human health is also badly affected by microplastic pollution present in the terrestrial environment. The presence of microplastics in the human body has been confirmed. Microplastic enters into the body of humans in different possible ways. According to their way of entering the body, microplastics cause different diseases in humans. MPs also cause negative effects on the human endocrine system. At the ecosystem level, the impacts of microplastic are interconnected and can disrupt ecological processes. Although recently different papers have been published on several aspects of the microplastic present in the terrestrial environment but there is no complete overview that focus on the interrelationship of MPs in plants, and soil and their effect on higher animals like a human. This review provides a completely detailed overview of existing knowledge about sources, occurrences, transport, and effects of microplastic on the food chain and soil quality and their ecotoxicological effects on plants and humans.

Global hotspots and trends in interactions of microplastics and heavy metals: a bibliometric analysis and literature review

Microplastics (MPs) are identified as emerging contaminants; however, their interactions with heavy metals in the environment have not been well elucidated. Here, the research progress, hotspots, and trends in the interactions of MPs and heavy metals were analyzed at a global scale using a bibliometric analysis combined with a literature review. We comprehensively searched the Web of Science Core Collection database from 2008 to July 5, 2022. A total of 552 articles published in 124 journals were selected, which came from 70 countries and 841 institutions. The most contributing journals, countries, institutions, and authors were identified. Visualization methods were used to identify high co-citation references and hot keywords in the 552 articles. Evolutionary and cluster analyses of hot keywords suggested several research hotspots in the co-contamination of MPs and heavy metals, including their toxicity and bioaccumulation, the adsorption and desorption behaviors, the environmental pollution and risk assessment, and their detection and characterization. Based on the current research status, several directions of priority are recommended to understand the interactions between MPs and heavy metals and their potential risks. This article can help recognize the current research status and future directions in this field.

Toxicity of microplastics and nanoplastics: invisible killers of female fertility and offspring health

Microplastics (MPs) and nanoplastics (NPs) are emergent pollutants, which have sparked widespread concern. They can infiltrate the body via ingestion, inhalation, and cutaneous contact. As such, there is a general worry that MPs/NPs may have an impact on human health in addition to the environmental issues they engender. The threat of MPs/NPs to the liver, gastrointestinal system, and inflammatory levels have been thoroughly documented in the previous research. With the detection of MPs/NPs in fetal compartment and the prevalence of infertility, an increasing number of studies have put an emphasis on their reproductive toxicity in female. Moreover, MPs/NPs have the potential to interact with other contaminants, thus enhancing or diminishing the combined toxicity. This review summarizes the deleterious effects of MPs/NPs and co-exposure with other pollutants on female throughout the reproduction period of various species, spanning from reproductive failure to cross-generational developmental disorders in progenies. Although these impacts may not be directly extrapolated to humans, they do provide a framework for evaluating the potential mechanisms underlying the reproductive toxicity of MPs/NPs.

Influences of chronic copper exposure on intestinal histology, antioxidative and immune status, and transcriptomic response in freshwater grouper (Acrossocheilus fasciatus)

Copper (Cu) contamination is commonly found in both natural water environments and fish farms, and it can cause severe damage to different fish organs, but Cu-induced intestinal damage has been rarely studied. This study subjected three groups of freshwater grouper (Acrossocheilus fasciatus) (initial weight: 1.56 ± 0.10 g) to 0 mg/L, 0.01 mg/L, and 0.04 mg/L Cu2+ for 30 days, named Con, Cu0.01, and Cu0.04 groups, respectively. The histological observation indicated that the Cu0.04 group caused a significant decrease in villus length, lamina propria width, and muscular thickness compared to the Con group (P < 0.05). Additionally, the Cu0.04 group significantly increased intestinal superoxide dismutase (SOD), glutathione peroxidase (GPx), lysozyme (LZM) activities, as well as malondialdehyde (MDA) content than the Con group (P < 0.05). Meanwhile, the Cu0.01 and Cu0.04 groups showed significantly increased immunoglobulin M (IgM), complement 3 (C3), and glutathione (GSH) contents than the Con group (P < 0.05). Transcriptomic analysis revealed a total of 101 differentially expressed genes (DEGs), including 47 up-regulated and 54 down-regulated DEGs, were identified between the Cu0.04 and Con groups. Notably, the DEGs were mainly related to intestinal structure construction, immune functions, apoptosis, and resistance to DNA damage and pathogen infection. The findings suggest that chronic Cu exposure caused intestinal histological alterations, activated the antioxidative and immune systems, and induced systematic adaptation to cope with the physical barrier injury, DNA damage, and potential pathogen growth.

Multiple effects of ZnO nanoparticles on goldfish (Carassius auratus): Skin mucus, gut microbiota and stable isotope composition

The skin and the gut are direct target tissues for nanoparticles, yet attention to effects of metal-based nanoparticles (MNPs) on these two and the discrepancy in these effects remain inadequate. Here, effects of ZnO nanoparticles (nZnO) on skin mucus and gut microbiota of goldfish (Carassius auratus) were investigated, as well as further elements turnover and metabolic variations. After 14 days of exposure, considerable variations in levels of biomarkers (protein, glucose, lysozyme and immunoglobulin M) in skin mucus demonstrated significant stress responses to nZnO. nZnO exposure significantly reduced the abundance of Cetobacterium in the gut while increased that of multiple pathogens, and further leading to down-regulation of pathways such as carbohydrate metabolism, translation, and replication and repair. Decreased δ¹⁵N values indicated declined N turnover in vivo, further demonstrating the negative effect of nZnO on metabolism in the organism. Integration analysis of each biomarker using the biomarker response index version 2 (IBRv2) revealed concentration-dependent effects of nZnO on skin mucus, while effects on physiology in vivo was not, demonstrating the discrepancy in the toxicity pathways and toxic effects of nZnO on different tissues. This work improved our understanding about the comprehensive toxicity of nZnO on aquatic organism.

Size-specific effects of microplastics and lead on zebrafish

Microplastics (MPs) can adsorb heavy metals and induce combined toxicity to aquatic organisms. However, the combined effects on the gut-liver and gut-brain axes are yet to be fully comprehended. This study investigated the combined effects of polystyrene microplastics (PS-MPs) with two concentrations (20 and 200 μg/L) and three sizes (0.1, 10, and 250 μm) and Pb (50 μg/L) on zebrafish through gut-liver and gut-brain axes. The results showed that the combined exposure of 0.1 μm PS-MPs and lead resulted in the most significant changes to the community diversity of gut microbiota. The combined exposures of PS-MPs (0.1 μm and 250 μm PS-MPs) and Pb significantly down-regulated expression of zo-1 and occludin but increased the lipopolysaccharide content in zebrafish liver compared to the PS-MPs or Pb alone exposure groups, indicating impaired gut barrier function. Subsequent studies showed that combined exposure of PS-MPs (0.1 μm and 250 μm) and Pb combined groups induced liver inflammation through the TLR4/NF-κB pathway. Moreover, all exposure groups had an impact on the expression of genes related to bile acid metabolism (cyp7a1, fgf19, abcb11b, and slc10a2) and neurotransmitters (tph1a, tph2, pink, and trh). The findings of this study provide new evidence on the combined effects of MPs and metals, which are significant for their hazard identification and risk assessment.

Early life stage exposure to cadmium and zinc within hour affected GH/IGF axis, Nrf2 signaling and HPI axis in unexposed offspring of marine medaka Oryzias melastigma

Information on transgenerational effects of cadmium (Cd) and zinc (Zn) within hour of exposure is scarce. To the end, larvae of marine medaka Oryzias melastigma at 0 day-post-hatching (dph) were subjected to LC₅₀ for 96-h of Cd or Zn for 0.5 and 6 h, and then transferred into clear water for 95 days until the generation of offspring larvae at 25 dph. Growth, antioxidant capacity and stress response in offspring larvae were examined. Exposure to Zn for 0.5 h or Cd for 0.5 h and 6 h promoted growth performance and reduced total antioxidant capacity (TAC) and activities of superoxide dismutase (SOD) and catalase (CAT). Malondialdehyde (MDA) and cortisol levels declined in larvae following Zn exposure for 0.5 h, whereas Cd exposure increased MDA content and did not affect cortisol levels. These physiological changes could be partially explained by transcription of genes in the hormone/insulin-like growth factor-I (GH/IGF) axis, NF-E2-related factor 2 (Nrf2) signaling, and hypothalamus-pituitary-interrenal (HPI) axis. For example, Zn exposure for 0.5 h up-regulated genes encoding growth hormone (gh) and insulin-like growth factor binding protein (igfbp1) and down-regulated mRNA levels of nrf2, Kelch-like-ECH-associated protein 1 gene (keap1a), keap1b, sod1, mineralocorticoid receptor (mr), corticotropin-releasing hormone receptor (crhr1), corticotropin-releasing hormone binding protein (crhbp), cytochrome P450 (cyp11a1, cyp17a1) and hydroxysteroid dehydrogenase (hsd3b1). Cd exposure for 0.5 and 6 h up-regulated growth hormone release hormone (ghrh) and igfbp1, down-regulated nrf2 and keap1a, and did not affect mRNA levels of HPI axis genes. Taken together, this study demonstrated that short-term metal exposure during larvae phase had positive and negative effects on offspring even after a long recovery.

Dietary berberine against intestinal oxidative stress, inflammation response, and microbiota disturbance caused by chronic copper exposure in freshwater grouper (Acrossocheilus fasciatus)

Berberine (BBR) is known for its strong antioxidant, anti-inflammatory, and capacity to preserve intestinal microbiota balance in fish. This study aimed to investigate the protective effects of berberine against copper-induced toxicity in the intestine of freshwater grouper Acrossocheilus fasciatus. The experiment involved four groups: a control group, a Cu group exposed to 0.02 mg/L Cu²⁺, and two BBR groups fed with 100 or 400 mg/kg of berberine diets and exposed to the same Cu²⁺ concentration. Three replicates of healthy fish (initial weight 1.56 ± 0.10 g) were subjected to their respective treatments for 30 days. Results showed that none of the treatments significantly affected the survival rate, final weight, weight gain, and feed intake (P > 0.05). However, supplementation with 100 and 400 mg/kg of BBR significantly lowered the antioxidant activities, and glutathione peroxidase (gpx) and superoxide dismutase (sod) expression levels, as well as reduced malondialdehyde (MDA) content caused by Cu²⁺ exposure (P < 0.05). Berberine inclusion significantly downregulated proinflammatory factors NLR family pyrin domain containing 3 (nlrp3), interleukin 1 beta (il1β), interleukin 6 cytokine family signal transducer (il6st) but upregulated transforming growth factor beta 1 (tgfβ1) and heat shock 70kDa protein (hsp70) expression. Moreover, berberine at both levels maintained the intestinal structural integrity and significantly improved gap junction gamma-1 (gjc1) mRNA level compared to the Cu group (P < 0.05). Based on 16S rDNA sequencing, the richness and diversity of intestinal microbiota in different groups were not significantly influenced. Berberine reduced the Firmicutes/Bacteroidota ratio and stifled the growth of some specific pathogenic bacteria such as Pseudomonas, Citrobacter, and Acinetobacter, while boosting the richness of potential probiotic bacteria, including Roseomonas and Reyranella compared with the Cu group. In conclusion, berberine showed significant protective effects against Cu²⁺-induced intestinal oxidative stress, inflammation response, and microbiota disturbance in freshwater grouper.

Effects of microplastics and lead exposure on gut oxidative stress and intestinal inflammation in common carp (Cyprinus carpio L.)

Microplastics (MPs) are increasingly being detected in freshwater environments, which have the potential to cause combined toxicity with other contaminants on aquatic organisms. To reveal the ecological risks, the combined effects of lead (Pb) and polyvinyl chloride microplastics (MPs) were explored in the gut of common carp (Cyprinus carpio L.). The results confirmed that exposure of Pb alone accelerated Pb accumulation, increased oxidative stress, and activated the inflammation response of the gut. However, the aforementioned effects all decreased under the co-exposure of Pb and MPs. In addition, MPs altered intestinal microbial community of common carp, especially the abundance of immune system-related species. All measured variables were organized for partial least square path modeling, which revealed the combined effects of Pb and MPs on inflammation response. The results implied that MPs reduced inflammation response in two ways, including the reduction of intestinal Pb accumulation and the alteration of the intestinal microbial community. Overall, this study provides a novel aspect of ecological effects on aquatic animals from Pb and MPs exposure. The interesting results remind us that when exploring the ecological risks of MPs, combined effects from other toxic substances must be considered simultaneously.

Are Microplastics Toxic? A Review from Eco-Toxicity to Effects on the Gut Microbiota

Emerging studies have presented an initial picture of the toxic effects of exposure to environmental micro- and nanoplastics. They have indicated that micro- and nanoplastics may induce toxicity by leading to oxidative stress, energy metabolism disorders, gene damage, and so forth in environmental organisms, marine invertebrates and vertebrates, and laboratory mouse models. In recent years, micro- and nanoplastics have been discovered in human fecal samples, placentas, lung tissue, and even blood; thus, micro- and nanoplastics pose an alarming and ever-increasing threat to global public health. However, current research on the health effects of micro- and nanoplastics and the possible adverse outcomes in humans has only presented the tip of the iceberg. More robust clinical data and basic experiments are still warranted to elucidate the specific relationships and mechanisms. In this paper, we review studies on micro- and nanoplastic toxicity from the perspectives of eco-toxicity, the adverse effects on invertebrates and vertebrates, and the impact of micro- and nanoplastics on the gut microbiota and its metabolites. In addition, we evaluate the toxicological role of micro- and nanoplastic exposure and its potential implications in respect to human health. We also summarize studies regarding preventive strategies. Overall, this review provides insights on micro- and nanoplastic toxicity and its underlying mechanisms, opening up scientific avenues for future in-depth studies.

Recent advances in micro (nano) plastics in the environment: Distribution, health risks, challenges and future prospects

Environmental micro(nano)plastics have become a significant global pollution problem due to the widespread use of plastic products. In this review, we summarized the latest research advances on micro(nano)plastics in the environment, including their distribution, health risks, challenges, and future prospect. Micro(nano)plastics have been found in a variety of environmental media, such as the atmosphere, water bodies, sediment, and especially marine systems, even in remote places like Antarctica, mountain tops, and the deep sea. The accumulation of micro(nano)plastics in organisms or humans through ingestion or other passive ways poses a series of negative impacts on metabolism, immune function, and health. Moreover, due to their large specific surface area, micro(nano)plastics can also adsorb other pollutants, causing even more serious effects on animal and human health. Despite the significant health risks posed by micro(nano)plastics, there are limitations in the methods used to measure their dispersion in the environment and their potential health risks to organisms. Therefore, further research is needed to fully understand these risks and their impacts on the environment and human health. Taken together, the challenges of micro(nano)plastics analysis in the environment and organisms must be addressed, and future research prospects need to be identified. Governments and individuals must take action to reduce plastic waste and minimize the negative impact of micro(nano)plastics on the environment and human health.

Bioaccumulation and Bioremediation of Heavy Metals in Fishes-A Review

Heavy metals, the most potent contaminants of the environment, are discharged into the aquatic ecosystems through the effluents of several industries, resulting in serious aquatic pollution. This type of severe heavy metal contamination in aquaculture systems has attracted great attention throughout the world. These toxic heavy metals are transmitted into the food chain through their bioaccumulation in different tissues of aquatic species and have aroused serious public health concerns. Heavy metal toxicity negatively affects the growth, reproduction, and physiology of fish, which is threatening the sustainable development of the aquaculture sector. Recently, several techniques, such as adsorption, physio-biochemical, molecular, and phytoremediation mechanisms have been successfully applied to reduce the toxicants in the environment. Microorganisms, especially several bacterial species, play a key role in this bioremediation process. In this context, the present review summarizes the bioaccumulation of different heavy metals into fishes, their toxic effects, and possible bioremediation techniques to protect the fishes from heavy metal contamination. Additionally, this paper discusses existing strategies to bioremediate heavy metals from aquatic ecosystems and the scope of genetic and molecular approaches for the effective bioremediation of heavy metals.

Nanoplastics pose a greater effect than microplastics in enhancing mercury toxicity to marine copepods

Due to human activities, high abundances of nano/microplastics (N/MPs) concurrent with metal pollution have become a serious problem in the global marine environment. Because of displaying a high surface-area-to-volume ratio, N/MPs can serve as the carriers of metals and thus increase their accumulation/toxicity in marine biota. As one of the most toxic metals, mercury (Hg) causes adverse effects on marine organisms but whether environmentally relevant N/MPs can play a vector role of this metal in marine biota, as well as their interaction, is poorly known. To evaluate the vector role of N/MPs in Hg toxicity, we first performed the adsorption kinetics and isotherms of N/MPs and Hg in seawater, as well as ingestion/egestion of N/MPs by marine copepod Tigriopus japonicus, and second, the copepod T. japonicus was exposed to polystyrene (PS) N/MPs (500-nm, 6-μm) and Hg in isolation, combined, and incubated forms at environmentally relevant concentrations for 48 h. Also, the physiological and defense performance including antioxidant response, detoxification/stress, energy metabolism, and development-related genes were assessed after exposure. The results indicated N/MPs significantly increased Hg accumulation and thus its toxicity effects in T. japonicus as exemplified by decreased transcription of genes related to development and energy metabolism and increased transcriptional levels of genes functioning in antioxidant and detoxification/stress defense. More importantly, NPs were superimposed onto MPs and produced the most vector effect in Hg toxicity to T. japonicus, especially in the incubated forms. Overall, this study highlighted the role of N/MPs as a potential risk factor for increasing the adverse effects of Hg pollution, and emphasized the adsorption forms of contaminants by N/MPs should doubly be considered in the continuing researches.

Polylactic acid (PLA), polyethylene terephthalate (PET), and polystyrene (PS) microplastics differently affect the gut microbiota of marine medaka (Oryzias melastigma) after individual and combined exposure with sulfamethazine

Microplastics and the antibiotic sulfamethazine (SMZ) are two prevalent pollutants in regions with high human activity, particularly in coastal marine environments. In this study, the individual and joint effects of microplastics (i.e., the bio-based microplastics polylactic acid (PLA), the petroleum-based microplastics polyethylene terephthalate (PET), and the petroleum-based microplastics polystyrene (PS) at 0.5 and 5 mg/g) and sulfamethazine (SMZ, at 5 mg/g) on the gut microbiota of marine medaka (Oryzias melastigma) via dietary route were investigated. For the individual microplastics exposure, two petroleum-based microplastics PET and PS significantly decreased the alpha diversity and the complexity of co-occurrence networks of gut microbiota. Differently, the adverse effects caused by the bio-based microplastic PLA were more modest, suggesting that PLA was less hazardous than PET and PS. For the combined exposure, SMZ alone dramatically impaired the homeostasis of gut microbiota by decreasing the alpha diversity and the complexity of co-occurrence networks, while the presence of PLA or PET alleviated these adverse effects caused by SMZ. Interestingly, such an alleviation effect was not observed in the SMZ + PS groups, suggesting that different types of microplastics might exhibit distinct joint effects with SMZ. Our findings contribute to a better understanding of the ecological risk of different types of microplastics to marine ecosystems, especially in a scenario of combined pollution with antibiotics.

Adverse health effects and mechanisms of microplastics on female reproductive system: a descriptive review

Microplastics (MPs), with a diameter of less than 5 mm, include polymers such as polystyrene, polypropylene, and polyethylene. The MPs occur in different morphologies including fragments, beads, fibers, and films that are swallowed by fresh water and land-based animals and enter their food chain, where they produce hazardous effects such as uterine toxicity, infertility, and neurotoxicity. The aim of this review is to explore the effects of polystyrene MPs (PS-MPs) on the female reproductive system and understand the mechanisms by which they produce reproductive toxicity. Several studies suggested that the exposure to PS-MPs increased the probability of larger ovaries with fewer follicles, decreased the number of embryos produced, and decreased the number of pregnancies in female mice. It also changed sex hormone levels and caused oxidative stress, which could have an impact on fertility and reproduction. Exposure to PS-MPs caused the death of granulosa cells through apoptosis and pyroptosis via activation of the NLRP3/caspase pathway and disruption of the Wnt-signaling pathway. Activation of TL4/NOX2 caused the uterine fibrosis resulting in endometrium thinning. The PS-MPs had a negative impact on ovarian capacity, oocyte maturation, and oocyte quality. Furthermore, the PS-MPs disrupted the hypothalamus-pituitary-gonadal axis in marine animals, resulting in a decrease in hatching rate and offspring body size, causing trans-generational effects. It also reduced fecundity and produced germ-line apoptosis. The main focus of this review was to explore the different mechanisms and pathways through which PS-MPs adversely impact the female reproductive system.

Factors Affecting the Adsorption of Heavy Metals by Microplastics and Their Toxic Effects on Fish

Fish not only constitute an important trophic level in aquatic ecosystems but also serve as an important source of protein for human beings. The health of fish is related to the sustained and healthy development of their entire aquatic ecosystem. Due to the widespread use, mass production, high disposal frequency, and degradation resistance of plastics, these pollutants are released into aquatic environments on a large scale. They have become one of the fastest growing pollutants and have a substantial toxic effect on fish. Microplastics have intrinsic toxicity and can absorb heavy metals discharged into water. The adsorption of heavy metals onto microplastics in aquatic environments is affected by many factors and serves as a convenient way for heavy metals to migrate from the environment to organisms. Fish are exposed to both microplastics and heavy metals. In this paper, the toxic effects of heavy metal adsorption by microplastics on fish are reviewed, and the focus is on the toxic effects at the individual (survival, feeding activity and swimming, energy reserves and respiration, intestinal microorganisms, development and growth, and reproduction), cellular (cytotoxicity, oxidative damage, inflammatory response, neurotoxicity, and metabolism) and molecular (gene expression) levels. This facilitates an assessment of the pollutants' impact on ecotoxicity and contributes to the regulation of these pollutants in the environment.

Exposure to copper nanoparticles or copper sulfate dysregulated the hypothalamic-pituitary-gonadalaxis, gonadal histology, and metabolites in Pelteobagrus fulvidraco

This study evaluated the effects of chronic exposure to copper nanoparticles (Cu-NPs) and waterborne copper (CuSO₄) on the reproductive system of yellow catfish (Pelteobagrus fulvidraco). Juvenile yellow catfish were exposed to 100 and 200 μg Cu/L Cu-NPs and 100 μg Cu/L CuSO₄ for 42 days. The results showed clear reproductive defects in both female and male yellow catfish in the 200 μg Cu/L Cu-NPs and 100 μg Cu/L CuSO₄ groups. Exposure to Cu-NPs or CuSO₄ inhibited folliculogenesis and vitellogenesis in the ovaries, and spermatogenesis in the testes, accompanied by elevation of the apoptotic signal. Ultrastructural observations also revealed damaged organelles of gonadal cells in both testes and ovaries. Most of the hypothalamic-pituitary-gonadal (HPG) axis genes examined and serum sex steroid hormones tended to be downregulated after Cu exposure. Metabolomic analysis suggested that gonadal estradiol level is sensitive to Cu-NPs or CuSO₄. The heat map of gonadal metabolomics suggested a similar effect of 200 μg Cu/L Cu-NPs and 100 μg Cu/L CuSO4 in both the ovaries and testes. Additionally, metabolomics data showed that the reproductive toxicity due to Cu-NPs and CuSO₄ may occur via different metabolic pathways. Cu-NPs tend to dysregulate the metabolic pathways of sphingolipid and linoleic acid metabolism in the ovary and the biosynthesis of amino acids and pantothenate and CoA in the testis. Overall, these findings revealed the toxicological effects of Cu-NPs and CuSO₄ on the HPG axis and gonadal metabolism in yellow catfish.

Effects of bisphenols on lipid metabolism and neuro-cardiovascular toxicity in marine medaka larvae

Bisphenols are environmental endocrine disruptors that have detrimental effects on aquatic organisms. Using marine medaka larvae, this study explored the effects of bisphenol compounds [bisphenol A (BPA), bisphenol S (BPS), bisphenol F (BPF), and bisphenol AF (BPAF)] on the early growth and development of aquatic organisms. Marine medaka larvae were exposed to bisphenol compounds at concentrations of 0.05, 0.5, and 5 μM for 72 h, and changes in heartbeat rate, behavior, hormone levels, and gene expression were determined. Bisphenols were shown to have a toxic effect on the cardiovascular system of larvae and can cause neurotoxicity and endocrine disruption, such as changes to thyroid-related hormones. Functional enrichment showed that bisphenols mainly affect lipid metabolism and cardiac muscle contraction of larvae, which implied that the main toxic effects of bisphenols on marine medaka larvae targeted the liver and heart. This study provides a theoretical foundation for evaluating the toxicological effects of bisphenols on the early development of aquatic organisms.

Heavy metals (HMs) pollution in the aquatic environment: Role of probiotics and gut microbiota in HMs remediation

The presence of heavy metals (HMs) in aquatic ecosystems is a universal concern due to their tendency to accumulate in aquatic organisms. HMs accumulation has been found to cause toxic effects in aquatic organisms. The common HMs-induced toxicities are growth inhibition, reduced survival, oxidative stress, tissue damage, respiratory problems, and gut microbial dysbiosis. The application of dietary probiotics has been evolving as a potential approach to bind and remove HMs from the gut, which is called "Gut remediation". The toxic effects of HMs in fish, mice, and humans with the potential of probiotics in removing HMs have been discussed previously. However, the toxic effects of HMs and protective strategies of probiotics on the organisms of each trophic level have not been comprehensively reviewed yet. Thus, this review summarizes the toxic effects caused by HMs in the organisms (at each trophic level) of the aquatic food chain, with a special reference to gut microbiota. The potential of bacterial probiotics in toxicity alleviation and their protective strategies to prevent toxicities caused by HMs in them are also explained. The dietary probiotics are capable of removing HMs (50-90%) primarily from the gut of the organisms. Specifically, probiotics have been reported to reduce the absorption of HMs in the intestinal tract via the enhancement of intestinal HM sequestration, detoxification of HMs, changing the expression of metal transporter proteins, and maintaining the gut barrier function. The probiotic is recommended as a novel strategy to minimize aquaculture HMs toxicity and safe human health.

Cascading effects of Pb on the environmental and symbiotic microbiota and tadpoles' physiology based on field data and laboratory validation

Heavy metal pollution poses a serious threat to ecosystems. Currently, there is a lack of field data that would enable us to gain a systematic understanding of the influences of heavy metals on aquatic ecosystems, especially the interactions between environments and animals. We studied the relationships between the variations in heavy metal concentrations (10 species including Pb in sediments and surface water), the community structure of environmental and symbiotic microbiota, and the gut traits of Bufo gargarizans tadpoles across 16 sampling sites on the Chengdu Plain through rigorous statistical analysis and laboratory validation. The results show that heavy metal concentrations, especially the Pb concentration of the sediment, are linked to the variations in sediment and tadpoles' gut microbiomes but not to water microbiota. For the sediment microbiota, Pb causes a trade-off between the proportions of Burkholderiales and Verrucomicrobiae and affects the methane, sulfide, and nitrate metabolisms. For tadpoles, a high sediment Pb content leads to a low abundance of gut aerobic bacteria and a large relative gut weight under both field and laboratory conditions. In addition, Pb promotes the growth of B. gargarizans tadpoles under laboratory conditions. These effects seem to be beneficial to tadpoles. However, a high Pb content leads to a low abundance of probiotic bacteria (e.g., Verrucomicrobiae, Eubacteriaceae, and Cetobacterium) and a high abundance of pathogenic bacteria in the gut and environment, suggesting potential health risks posed by Pb. Interestingly, there is a causal relationship between Pb-induced variations in sediment and symbiotic microbiotas, and the latter is further linked to the variation in relative gut weight of tadpoles. This suggests a cascading effect of Pb on the ecosystem. In conclusion, our results indicate that among the heavy metals, the Pb in sediment is a critical factor affecting the aquatic ecosystem through an environment-gut-physiology pathway mediated by microbiota.

Microplastics and their interactions with microbiota

As a new pollutant, Microplastics (MPs) are globally known for their negative impacts on different ecosystems and living organisms. MPs are easily taken up by the ecosystem in a variety of organisms due to their small size, and cause immunological, neurological, and respiratory diseases in the impacted organism. Moreover, in the impacted environments, MPs can release toxic additives and act as a vector and scaffold for colonization and transportation of specific microbes and lead to imbalances in microbiota and the biogeochemical and nutrients dynamic. To address the concerns on controlling the MPs pollution on the microbiota and ecosystem, the microbial biodegradation of MPs can be potentially considered as an effective environment friendly approach. The objectives of the presented paper are to provide information on the toxicological effects of MPs on microbiota, to discuss the negative impacts of microbial colonization of MPs, and to introduce the microbes with biodegradation ability of MPs.

From marine to freshwater environment: A review of the ecotoxicological effects of microplastics

Microplastics (MPs) have been widely detected in the world's water, which may pose a significant threat to the ecosystem as a whole and have been a subject of much attention because their presence impacts seas, lakes, rivers, and even the Polar Regions. There have been numerous studies that report direct adverse effects on marine organisms, but only a few have explored their ecological effects on freshwater organisms. In this field, there is still a lack of a systematic overview of the toxic effects and mechanisms of MPs on aquatic organisms, as well as a consistent understanding of the potential ecological consequences. This review describes the fate and impact on marine and freshwater aquatic organisms. Further, we examine the toxicology of MPs in order to uncover the relationship between aquatic organism responses to MPs and ecological disorders. In addition, an overview of the factors that may affect the toxicity effects of MPs on aquatic organisms was presented along with a brief examination of their identification and characterization. MPs were discussed in terms of their physicochemical properties in relation to their toxicological concerns regarding their bioavailability and environmental impact. This paper focuses on the progress of the toxicological studies of MPs on aquatic organisms (bacteria, algae, Daphnia, and fish, etc.) of different trophic levels, and explores its toxic mechanism, such as behavioral alternations, metabolism disorders, immune response, and poses a threat to the composition and stability of the ecosystem. We also review the main factors affecting the toxicity of MPs to aquatic organisms, including direct factors (polymer types, sizes, shapes, surface chemistry, etc.) and indirect factors (persistent organic pollutants, heavy metal ions, additives, and monomer, etc.), and the future research trends of MPs ecotoxicology are also pointed out. The findings of this study will be helpful in guiding future marine and freshwater rubbish studies and management strategies.

Reproductive toxicity and cross-generational effect of polyethylene microplastics in Paramisgurnus dabryanus

Pollution of microplastics (MPs) has become a global environmental issue due to the difficulty in its degradation and may cause unexpected ecological effects. Nevertheless, little is known about the potential effects of MPs on reproduction toxicity in aquatic species. In this study, adult loach (Paramisgurnus dabryanus, F0 generation) were exposed to two concentrations (1 and 10 mg/L) of polyethylene MPs (PE-MPs) for 15 or 30 days, and the toxic effects in parental loach and the offspring (F1 generation) were examined. Our results showed that PE-MPs exposure could change the indicators content of antioxidant system in the brain, liver, and gonad. PE-MPs can accumulate in the gonads, disrupt the transcription of HPG-axis related genes, alter sex hormone levels, increase cell apoptosis and gonadal pathological lesions, lead to the damage of biological characteristics of semen, and affect the reproduction in F0 generation. PE-MPs remaining in the parental gonads can be transferred to the F1 generation embryos and accumulated on the embryonic chorionic membrane, increasing mortality and malformation rates, accelerating hatching time, and decreasing hatching rate and body length. These results suggest that PE-MPs leads to a potential adverse influence on reproduction and serious impacts on population sustainability. This work provides a new perspective into the effects of MPs on reproductive damage and cross-generational effects in teleost fish, which have implications in fields of freshwater ecology and environmental toxicology.

Microplastics in Commercial Fishes and By-Catch from Selected FAO Major Fishing Areas of the Southern Baltic Sea

According to recent world wide studies, microplastics (MPs) have been found in many fish species; however, the majority of research has focused only on the gastrointestinal tract, neglecting edible organs. This study aimed to assess the presence of microplastics in the non-edible (gills, digestive tract) and edible organs (liver) of three commercial fish species and twoby-catch species from the southern Baltic Sea. Fish (Clupea harengus, Gadus morhua, Platichthy sflesus, Taurulus baublis, Cyclopterus lumpus) were caught in 108 and 103 FAO Fishing Zones belonging to the Polish fishing zone. The abundanceof MPs ranged from 1 to 12 items per fish, with an average of 4.09 items. MPs were observed in different organs, such as the liver, gills, and digestive tract of all five tested species. MPs recognized as fibers were the most abundant. Other shapes of polymers found in fish organs were pellets and particles of larger plastic pieces. The dominant color of the MPs was blue, but there were also red, black, transparent, yellow, green, and white items found. According to dimensions, dominant MPs were between 0.1 and 0.5 mm in size. The chemical characterization of polymers accomplished by the use of Fourier Transform Infrared (FT-IR) Spectroscopy demonstrated the abundance of cellophane, polyamide, polyethylene, polypropylene, polyethylene terephthalate, polyvinyl propionate, polyacrylonitrile, and polyester.

A baseline study of microplastic pollution in a Southern Indian Estuary

Knowledge on the processes controlling the vertical distribution of microplastics (MPs) in estuaries is less. This research was carried out to determine the MP distribution in the surface, middle, and bottom layers of the Udyavara River Estuary in southwest India. The mean (± standard deviation) concentrations were 320.83 (± 98.30), 514.55 (± 352.16), and 755.03 (± 400.96) particles/m³, respectively. Fibres, films, and fragments dominated, and 57 % of the MPs had a size range of 0.3-1 mm, while 43 % had a size of 1-5 mm. The main polymers were high-density polyethylene and polyethylene terephthalate. A positive correlation (r = 0.421, p = 0.0205, n = 30) exists between the MPs and salinity, suggesting that the MPs are held by dense saline waters. The mean pollution load index value was 2.25 indicating severe pollution. Microplastic pollution is due to harbour, fishing, industrial activities, the effects of southwest monsoon rain, and tidal currents.

Polystyrene microplastics enhanced copper-induced acute immunotoxicity in red swamp crayfish (Procambarus clarkii)

Microplastic pollution has attracted a lot of attention in recent years. Not only can it be ingested by animals, but it can easily become a carrier of other pollutants, forming a composite pollutant with potentially toxic effects on organisms. We investigated the effect of Cu on the accumulation of polystyrene microplastics (PS) in the gills of Procambarus clarkii and whether PS exacerbated the immune toxicity of Cu to P. clarkii were exposed to Cu, PS and PS+Cu for 48 h, the accumulation of PS in gill and hepatopancreas immune and antioxidant indices were analyzed. The objective was to investigate the toxic effects of Ps and Cu compound pollutants on P. clarkii and whether the accumulated pollutants would cause food safety problems. The results showed that microplastic particles adhered to each other and aggregated in the PS+Cu group, and the number of microplastic particles in gill in the PS+Cu group was significantly lower than that in the PS group. Compared with the other two treatment groups, SOD, CAT, GPx activities and MDA content increased significantly in the PS+Cu group and were relatively delayed. At 12 h, 24 h, 36 h and 48 h, the SOD mRNA expression levels in the PS+Cu group were all significantly lower than those in the Cu group (P < 0.05). At 24 h and 48 h, CAT mRNA expression in the PS+Cu group was significantly higher than that in the Cu group (P < 0.05). Crustin 4 mRNA expressions in the PS+Cu group was significantly higher than that in the Cu group at 12 h and 36 h (P < 0.05). The results demonstrate that the PS and Cu compound reduced the accumulation of microplastic particles in the gill. PS particles delayed Cu entry into P. clarkii for a short time (12 h) and reduced the toxic effect, but with the increase of exposure time (24 h and 48 h), the toxic effect of PS and Cu complexes on P. clarkii increases, and the large accumulation of PS and Cu complexes may cause food safety problems.

Combined toxicity of micro/nanoplastics loaded with environmental pollutants to organisms and cells: Role, effects, and mechanism

Micro/nanoplastics (MPs/NPs) are ubiquitous in the environment and living organisms have been exposed to these substances for a long time. When MPs/NPs enter different organisms, they transport various pollutants, including heavy metals, persistent organic pollutants, drugs, bacteria, and viruses, from the environment. On this basis, this paper summarizes the combined toxicity induced by MPs/NPs accumulating contaminants from the environment and entering organisms through a systematic review of 162 articles. Moreover, the factors influencing toxic interactions are critically discussed, thus highlighting the dominant role of the relative concentrations of contaminants in the combined toxic effects. Furthermore, for the first time, we describe the threats posed by MPs/NPs combined with other pollutants to human health, as well as their cytotoxic behavior and mechanism. We found that the "Trojan horse" effect of nanoplastics can increase the bioaccessibility of environmental pollutants, thus increasing the carcinogenic risk to humans. Simultaneously, the complex pollutants entering the cells are observed to be constantly dissociated due to the transport of lysosomes. However, current research on the intracellular release of MP/NP-loaded pollutants is relatively poor, which hinders the accurate in vivo toxicity assessment of combined pollutants. Based on the findings of our critical review, we recommend analyzing the toxic effects by clarifying the dose relationship of each component pollutant in cells, which is challenging yet crucial to exploring the toxic mechanism of combined pollution. In the future, our findings can contribute to establishing a system modeling the complete load-translocation toxicological mechanism of MP/NP-based composite pollutants.

Morphological Alterations in the Early Developmental Stages of Zebrafish (Danio rerio; Hamilton 1822) Induced by Exposure to Polystyrene Microparticles

Microplastics (MPs) are emerging pollutants of widespread concern in aquatic environments. The aim of this study was to evaluate the negative impact of pristine MPs of polystyrene of 100 μm on embryo and larvae of Danio rerio exposed to three environmentally relevant concentrations of polystyrene (3.84 × 10^- 6, 3.84 × 10^- 7, and 3.84 × 10^- 8 g/mL). The exposure effect was evaluated through the general morphology score, biometrics, and integrated biomarker response version 2 index. No mortality was observed but the anatomical structure of fishes was affected showing pigmentation deficiency and alterations in the head region as the main affected endpoints. The general morphology score and the integrated biomarker response values were highly sensitive to address the effect of the three concentrations of MPs used here. Our results provide solid evidence of the negative impact of 100 μm pristine polystyrene MPs exposure on early stages of zebrafish.

Assessment of Lead (Pb) Toxicity in Juvenile Nile Tilapia, Oreochromis niloticus-Growth, Behaviour, Erythrocytes Abnormalities, and Histological Alterations in Vital Organs

Lead (Pb) is one of the toxins responsible for the deterioration of ecological health in aquatic environments. The present study investigated the effects of Pb(NO₃)₂ toxicity on growth, blood cell morphology, and the histopathology of gills, liver, and intestine of juvenile Nile tilapia, Oreochromis niloticus. A 30-day long aquarium trial was conducted by assigning three treatment groups T₁ 5.20 mg L^-1, T₂ 10.40 mg L^-1, and T₃ 20.80 mg L^-1, and a control 0 mg L^-1 following the 96 h LC₅₀ of 51.96 mg L^-1 from acute toxicity test. Overall growth performance significantly declined in all the Pb(NO₃)₂ treated groups and the highest mortality was recorded in T₃. Behavioural abnormalities were intense in all the treatment groups compared to the control. Hepatosomatic index (HSI) values were reported as higher in treatment groups. Reduced nucleus diameter and nuclei size in erythrocytes were reported for T₂ and T₃ groups. Dose-dependent histological alterations were visible in the gills, liver, and intestine of all the Pb(NO₃)₂ treated groups. The width of the intestinal villi was highly extended in T₃ showing signs of severe histological alterations. In conclusion, Pb toxicity causes a negative effect on growth performance, erythrocyte morphology, and affected the vital organs histomorphology of juvenile O. niloticus.

Comprehensive analysis of spatial distribution of microplastics in Rawal Lake, Pakistan using trawl net and sieve sampling methods

Occurrence of microplastics (MPs) in freshwater environments, particularly reservoir and lakes, is an emerging concern. There are limited studies in Pakistan on microplastic pollution in the lacustrine environments and those that exist do not provide sufficient information on the spatial distribution of MPs in offshore surface water. The aims of this study were to determine microplastic abundance in Rawal Lake, Pakistan and to ascertain if sampling methodology influences microplastic counts. Surface water samples were collected from 10 sites; 5 tributaries, 2 human settlement and 3 fishing and boating areas using two different sampling techniques: 100 μm mesh trawl and 20 L sample through a 45 μm mesh sieve. A significant difference was observed in the abundance of MPs across two methods with the sieve method yielding 2.8 ± 1.44 particles/L and trawl yielding 0.025 ± 0.024 particles/L. Tributaries and boating/fishing area had higher microplastic abundance than the residential area regardless of sampling method. Filaments were the dominant shape of MPs in both type of samples followed by fragments in trawl samples and films in sieved samples. Microbeads were only detected in trawl samples. MPs within size range 0.1-0.9 mm were mostly fragments (82%). MPs were diverse in colors with white/transparent and black MPs common. Polypropylene was the main type of microplastic in Rawal Lake (40-74%). Scanning Electron Microscopy (SEM) of MPs showed cracks, roughness and striations on the particles. Energy Dispersive Spectroscopy (EDS) detected heavy metals (Fe, Cu, Ni, Pb, Zn, Co and Cr) in MPs. Findings suggest that microplastic pollution in Rawal Lake may pose great risk to aquatic and human life through leaching of inherent/adsorbed heavy metals and therefore requires future investigation.

Effects of bisphenol AF on growth, behavior, histology and gene expression in marine medaka (Oryzias melastigma)

Bisphenol AF (BPAF) is one of the substitutes for bisphenol A (BPA), which has endocrine-disrupting, reproductive and neurological toxicity. BPAF has frequently been detected in the aquatic environment, which has been a long-term threat to the health of aquatic organisms. In this study, female marine medaka (Oryzias melastigma) were exposed to 6.7 μg/L, 73.4 μg/L, and 367.0 μg/L BPAF for 120 d. The effects of BPAF on behavior, growth, liver and ovarian histology, gene transcriptional profiles, and reproduction of marine medaka were determined. The results showed that with the increase of BPAF concentration, the swimming speed of female marine medaka showed an increasing trend and then decreasing trend. BPAF (367.0 μg/L) significantly increased body weight and condition factors in females. BPAF (73.4 μg/L and 367.0 μg/L) significantly delayed oocyte maturation. Exposure to 367.0 μg/L BPAF showed an increasing trend in the transcript levels of lipid synthesis and transport-related genes such as fatty acid synthase (fasn), sterol regulatory element binding protein (srebf), diacylglycerol acyltransferase (dgat), solute carrier family 27 member 4 (slc27a4), fatty acid-binding protein (fabp), and peroxisome proliferator-activated receptor gamma (pparγ) in the liver. In addition, 6.7 μg/L BPAF significantly down-regulated the expression levels of antioxidant-related genes [superoxide dismutase (sod), glutathione peroxidase (gpx), and catalase (cat)], and complement system-related genes [complement component 5 (c5), complement component 7a (c7a), mannan-binding lectin serine peptidase 1 (masp1), and tumor necrosis factor (tnf)] were significantly up-regulated in the 73.4 and 367.0 μg/L groups, which implies the effect of BPAF on the immune system in the liver. In the hypothalamic-pituitary-ovarian axis (HPG) results, the transcription levels of estrogen receptor α (erα), estrogen receptor β (erβ), androgen receptor (arα), gonadotropin-releasing hormone 2 (gnrh2), cytochrome P450 19b (cyp19b), aromatase (cyp19a), and luteinizing hormone receptor (lhr) in the brain and ovary, and vitellogenin (vtg) and choriogenin (chg) in the liver of 367.0 μg/L BPAF group showed a downward trend. In addition, exposure to 367.0 μg/L BPAF for 120 d inhibited the spawning behavior of marine medaka. Our results showed that long-term BPAF treatment influenced growth (body weight and condition factors), lipid metabolism, and ovarian maturation, and significantly altered the immune response and the transcriptional expression levels of HPG axis-related genes.

Unraveling the potential human health risks from used disposable face mask-derived micro/nanoplastics during the COVID-19 pandemic scenario: A critical review

With the global spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), disposable face masks (DFMs) have caused negative environmental impacts. DFMs will release microplastics (MPs) and nanoplastics (NPs) during environmental degradation. However, few studies reveal the release process of MPs/NPs from masks in the natural environment. This review presents the current knowledge on the abiotic and biotic degradation of DFMs. Though MPs and NPs have raised serious concerns about their potentially detrimental effects on human health, little attention was paid to their impacts on human health from DFM-derived MPs and NPs. The potential toxicity of mask-derived MPs/NPs, such as gastrointestinal toxicity, pneumotoxicity, neurotoxicity, hepatotoxicity, reproductive and transgenerational toxicity, and the underlying mechanism will be discussed in the present study. MPs/NPs serve as carriers of toxic chemicals and pathogens, leading to their bioaccumulation and adverse effects of biomagnification by food chains. Given human experiments are facing ethical issues and animal studies cannot completely reveal human characteristics, advanced human organoids will provide promising models for MP/NP risk assessment. Moreover, in-depth investigations are required to identify the release of MPs/NPs from discarded face masks and characterize their transportation through the food chains. More importantly, innovative approaches and eco-friendly strategies are urgently demanded to reduce DFM-derived MP/NP pollution.

Triacontanol priming as a smart strategy to attenuate lead toxicity in Brassica oleracea L

The most prevalent heavy metal pollutant in the environment is lead (Pb). Lead potentially contribute 10% of overall heavy metal contamination. Lead uptake by plants has been found to have an impact on their metabolic functions, photosynthetic activity, growth, and productivity. The current experiment was conducted to investigate the impact of triacontanol (Tria) for attenuating Pb stress in Brassica oleracea var. italic (broccoli). Three different Tria concentrations (10, 20 and 30 µmol L^-1) were used to prime broccoli seeds. Growth of broccoli was reduced when exposed to Pb-driven toxicity. Additionally, Pb had a deleterious impact on the protein quantity, stomatal conductance, transpiration and photosynthetic rate. Nevertheless, plants grown from seeds primed with Tria2 (20 µmol L^-1 Tria) exhibited improved morphological characteristics, uptake of mineral content (Mn⁺², Zn⁺², K⁺¹, Na⁺¹) along with biomass production. There was 1.6-fold increase in photosynthetic rate, the phenol (1.3 folds), and DPPH activity (1.2 folds) in seed primed with Tria2. Additionally, plants treated with Tria2 demonstrated enhanced MTI and gas exchange characteristics that improves plant stress tolerance under Pb stress. Seed priming with Tria can be used to increase plant tolerance to Pb stress as evidenced by the improved growth and biochemical characteristics of broccoli seedlings.

Intestinal flora variation reflects the short-term damage of microplastic to the intestinal tract in mice

The potential toxicity of microplastic (MPs) to organisms has attracted extensive attention. However, due to the subacute toxicity of MPs, the biological effect is hard to verify in short-term exposure experiment. Here, by tracking the dynamics of gut microbes, mice model was utilized to evaluate the toxicity of compositional MPs (PE, PET, PP, PS and PVC). After 7 days digestive exposure, the physiological indicators were normal as the control group that the body weight and serum cholesterol levels were insignificant change. Whereas, through histopathological examination, all the treatment groups suffered colon tissue damage, among which PS had the most inflammatory cells. Moreover, the high-throughput sequencing results revealed great variation of intestinal flora in treated mice. The ratio of Bacteroidetes and Firmicutes in PE, PET and PP treatment groups heighten, and the relative abundance of Ruminococcaceae and Lachnospiraceae increased significantly at family levels. At the genus level, Alistipes bacteria in PS treatment group significantly decreased that is associated with obesity risk. It indicated that MPs induced inflammatory response would further interfere the dynamics of intestinal flora causing health effect in living organisms. This work shed light on MPs toxicity in short-term exposure and supplied research paradigm of MPs health risk assessment.

Early-life chemical exposome and gut microbiome development: African research perspectives within a global environmental health context

The gut microbiome of neonates, infants, and toddlers (NITs) is very dynamic, and only begins to stabilize towards the third year of life. Within this period, exposure to xenobiotics may perturb the gut environment, thereby driving or contributing to microbial dysbiosis, which may negatively impact health into adulthood. Despite exposure of NITs globally, but especially in Africa, to copious amounts and types of xenobiotics - such as mycotoxins, pesticide residues, and heavy metals - little is known about their influence on the early-life microbiome or their effects on acute or long-term health. Within the African context, the influence of fermented foods, herbal mixtures, and the delivery environment on the early-life microbiome are often neglected, despite being potentially important factors that influence the microbiome. Consequently, data on in-depth understanding of the microbiome-exposome interactions is lacking in African cohorts. Collecting and evaluating such data is important because exposome-induced gut dysbiosis could potentially favor disease progression.

Developmental Polyethylene Microplastic Fiber Exposure Entails Subtle Reproductive Impacts in Juvenile Japanese Medaka (Oryzias latipes)

Microplastic pollution has been recognized as a potential threat to environmental and human health. Recent studies have shown that microplastics reside in all ecosystems and contaminate human food/water sources. Microplastic exposure has been shown to result in adverse effects related to endocrine disruption; however, data are limited regarding how exposure to current environmental levels of microplastics during development may impact reproductive health. To determine the impact of environmentally relevant, chronic, low-dose microplastic fibers on fish reproductive health, juvenile Japanese medaka were exposed to five concentrations of polyethylene fibers for 21 days, and reproductive maturity was examined to assess the later life consequences. Fecundity, fertility, and hatching rate were evaluated to determine the organismal level impacts. Gonadal tissue integrity and stage were assessed to provide insights into potential tissue level changes. Expression of key reproductive genes in male and female gonads provided a molecular level assessment. A significant delay in hatching was observed, indicating cross-generational and organismal level impacts. A significant decrease in 11-beta-dehydrogenase isozyme 2 (HSD11 β 2) gene expression in male medaka indicated adverse effects at the molecular level. A decrease in male expression of HSD11 β 2 could have an impact on sperm quality because this enzyme is crucial for conversion of testosterone into the androgen 11-ketotestosterone. Our study is one of the first to demonstrate subtle impacts of virgin microplastic exposure during development on later life reproductive health. The results suggest a possible risk of polyethylene fiber exposure for wild fish during reproductive development, and populations should be monitored closely, specifically in spawning and nursery regions. Environ Toxicol Chem 2022;41:2848-2858. © 2022 SETAC.

Combined effects of micro-/nano-plastics and oxytetracycline on the intestinal histopathology and microbiome in zebrafish (Danio rerio)

Accumulated evidence has demonstrated that microplastics and oxytetracycline (OTC) affect organisms, but few studies have investigated their combined effects on aquatic organisms. In this study, adult zebrafish (Danio rerio) were exposed to single and binary-combined contamination of micro-, nano-sized polystyrene plastics and OTC for 30 days, and the intestinal histopathology, gut microbiota and antibiotic resistance genes (ARGs) of zebrafish were measured. The results showed that the intestinal epithelial damage increase with the decrease of plastic sizes. Nano-sized plastics, OTC and their combined exposure caused intestinal epithelial damage, and co-exposure with micro-sized plastics reduced the intestinal damage caused by single OTC exposure. The gut microbial communities were affected by the combined exposure to microplastics and OTC. Compared with the blank control, the relative abundance of Fusobacteria increased 12.7 % and 21.1 % in OTC combined with 45-85 μm micro-plastics (MOTC) and 40-54 nm nano-plastics (NOTC), respectively, and that of Bacteroidetes increased 26.2 % and 18.6 % in the MOTC and NOTC treatments, respectively. The effects of MOTC and NOTC on the biodiversity of the zebrafish gut microbiome were different; MOTC increased the biodiversity by 11.3 % compared with the blank control, whereas NOTC decreased the biodiversity by 8.8 % compared with the blank control. Furthermore, the abundance of ARGs in 40-54 nm nano-plastics, MOTC and NOTC treatments was increased 96.9 %, 96.6 % and 68.8 % compared with the control group, respectively. Additionally, significant differences were observed in ARGs characteristics between the micro- and nano-plastics treated groups whether combined with OTC or not. These results are essential to further understand the combined ecotoxicological effects of micro- or nano-plastics and antibiotics on aquatic organisms.

Adverse Effects of Co-Exposure to Cd and Microplastic in Tigriopus japonicus

There is increasing concern about the adverse impact of exposure to microplastic, as an emerging pollutant, on wild organisms, and particularly on organisms co-exposed to microplastic and other environmental contaminants. It has been widely reported that the combination of microplastics and heavy metals showed obvious toxicity to organisms in terms their growth and development. The present study was performed to determine the impact of binary metal mixtures of cadmium (Cd) and polystyrene microplastic (PS-microplastic) on Tigriopus japonicus, a typical marine model organism, using a titration design. Increasing concentrations of PS-microplastic (2 μg/L, 20 μg/L, and 200 μg/L) were titrated against a constant concentration of Cd (15.2 μg/L). The results showed no significant impact of exposure to this dose of Cd or co-exposure to Cd and the lowest dose of PS-microplastic examined (2 μg/L). However, the feeding rate, filtration rate, oxygen consumption rate, and hatching number declined significantly in T. japonicus co-exposed to Cd and higher concentrations of PS-microplastic (20 μg/L and 200 μg/L) (p < 0.05). Furthermore, the development of F1 larvae from nauplius stage (N) to adult stage (A) was markedly delayed when co-exposed to Cd and higher doses of PS-microplastic (20 and 200 μg/L), and the effects persisted to the F2 larval stage. Interestingly, the present titration design did not affect the sex ratio or number of oocysts in either the F1 or F2 generation. These results indicated that the current marine environmental concentrations of Cd and microplastic are safe for wild organisms. Further studies are required to address the knowledge gap regarding toxicological effects at the cellular and molecular levels.

Trojan horse in the intestine: A review on the biotoxicity of microplastics combined environmental contaminants

With the reported ability of microplastics (MPs) to act as "Trojan horses" carrying other environmental contaminants, the focus of researches has shifted from their ubiquitous occurrence to interactive toxicity. In this review, we provided the latest knowledge on the processes and mechanisms of interaction between MPs and co-contaminants (heavy metals, persistent organic pollutants, pathogens, nanomaterials and other contaminants) and discussed the influencing factors (environmental conditions and characteristics of polymer and contaminants) that affect the adsorption/desorption process. In addition, the bio-toxicological outcomes of mixtures are elaborated based on the damaging effects on the intestinal barrier. Our review showed that the interaction processes and toxicological outcomes of mixture are complex and variable, and the intestinal barrier should receive more attention as the first line of defensing against MPs and environmental contaminants invasion. Moreover, we pointed out several knowledge gaps in this new research area and suggested directions for future studies in order to understand the multiple factors involved, such as epidemiological assessment, nanoplastics, mechanisms for toxic alteration and the fate of mixtures after desorption.

Ecotoxic effects of microplastics and contaminated microplastics - Emerging evidence and perspective

The high prevalence and persistence of microplastics (MPs) in pristine habitats along with their accumulation across environmental compartments globally, has become a matter of grave concern. The resilience conferred to MPs using the material engineering approaches for outperforming other materials has become key to the challenge that they now represent. The characteristics that make MPs hazardous are their micro to nano scale dimensions, surface varied wettability and often hydrophobicity, leading to non-biodegradability. In addition, MPs exhibit a strong tendency to bind to other contaminants along with the ability to sustain extreme chemical conditions thus increasing their residence time in the environment. Adsorption of these co-contaminants leads to modification in toxicity varying from additive, synergistic, and sometimes antagonistic, having consequences on flora, fauna, and ultimately the end of the food chain, human health. The resulting environmental fate and associated risks of MPs, therefore greatly depend upon their complex interactions with the co-contaminants and the nature of the environment in which they reside. Net outcomes of such complex interactions vary with core characteristics of MPs, the properties of co-contaminants and the abiotic factors, and are required to be better understood to minimize the inherent risks. Toxicity assays addressing these concerns should be ecologically relevant, assessing the impacts at different levels of biological organization to develop an environmental perspective. This review analyzed and evaluated 171 studies to present research status on MP toxicity. This analysis supported the identification and development of research gaps and recommended priority areas of research, accounting for disproportionate risks faced by different countries. An ecological perspective is also developed on the environmental toxicity of contaminated MPs in the light of multi-variant stressors and directions are provided to conduct an ecologically relevant risk assessment. The presented analyses will also serve as a foundation for developing environmentally appropriate remediation methods and evaluation frameworks.

Comprehensive understanding the impacts of dietary exposure to polyethylene microplastics on genetically improved farmed tilapia (Oreochromis niloticus): tracking from growth, microbiota, metabolism to gene expressions

Microplastics (MPs) pollution has been recognized as a threat to sustainable fisheries due to the risks of MPs contamination in the process of feed production and susceptibility of fish to ingest MPs from the aquatic environment. In this study, we applied comprehensive approaches to investigate the impacts of polyethylene microplastics (PE-MPs) on juvenile genetically improved farmed tilapia (GIFT, Oreochromis niloticus) through 9-week dietary exposure based on growth performance, gut microbiota, liver metabolism, and gene expressions in brain and liver tissues. Dietary exposure to two kinds of PE-MPs with different median size (27 μm and 63 μm, respectively) concentration-dependently decreased weight gain (WG), while increased feed conversion ratio (FCR) and hepatosomatic index (HSI) of the tilapia. Dietary administration of PE-MPs also significantly reduced the activities of intestinal protease and amylase. PE-MPs particles of the larger size groups (63 μm) were mainly detected in feces, but those of the smaller ones (27 μm) tended to be accumulated in intestine. PE-MPs ingestion resulted in the alteration of gut microbiota composition, with Fusobacteria, Verrucomicrobia and Firmicutes as the overrepresented bacterial taxa. Metabolomic assays of liver samples in fish fed the diets containing 8 % of PE-MPs revealed the particle size-specific variations in composition of differential metabolites and metabolism pathways such as amino acid and glycerophospholipid metabolism. Gene expressions of brain and liver samples were analyzed by RNA-seq. Photoperiodism and circadian rhythm were the representative biological processes enriched for the differentially expressed genes (DEGs) identified from the brain. Citrate cycle (TCA cycle) was the most enriched pathway revealed by a joint transcriptomic and metabolic pathway analysis for the liver, followed by propanoate and pyruvate metabolism. Furthermore, an integration analysis of the gut microbiome and liver transcriptome data identified significant associations between several pathogenic bacteria taxa and immune pathways. Our findings demonstrated that the sizes and concentrations of PE-MPs are critically related to their toxic impacts on microbiota community, metabolism, gene expressions and thus fish growth.

Occurrence, distribution, and characteristics of microplastics in agricultural soil around a solid waste treatment center in southeast China

PURPOSE

In recent years, microplastic (MP) contamination has raised enormous concern. However, data on the influence of solid waste treatment systems on MP pollution around agricultural soil are lacking. This study investigated the distribution and characteristics of MPs in agricultural soil surrounding a solid waste treatment center in southeastern China.

MATERIALS AND METHODS

Fifty-seven agricultural topsoil samples around the solid waste treatment center were collected. The samples were pretreated by drying, flotation separation using NaCl solution, and digestion by H₂O₂. The abundance and morphological characteristics of MPs were determined by a microscope, followed by Raman spectroscopy analysis identified polymer types and SEM-EDS analysis observed surface morphology and the type of metals accumulated on the MPs.

RESULTS AND DISCUSSION

Soil MPs' abundance ranged from 280 to 2360 items/kg, while a higher abundance of MPs was distributed in the downwind area. The < 1-mm MPs were dominant, and white fragment MPs were widely found. Polyethylene (52.86%) and polypropylene (27.14%) were the most common. Moreover, SEM-EDS images illustrated that MPs were significantly weathered and showed the uneven distribution of metal(loid) elements on the surface, implying that MPs may migrate as heavy metal vectors to threaten agroecosystem safety.

CONCLUSIONS

This study reveals the distribution and characteristics of MPs in agricultural soil surrounding a solid waste treatment center in southeastern China, as well as the potential source of soil MPs, and provides systematic data for further research on MP pollution in agricultural soil.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11368-022-03341-6.

Co-exposure to polystyrene microplastics and lead aggravated ovarian toxicity in female mice via the PERK/eIF2α signaling pathway

Generally, individual microplastics (MPs) or lead (Pb) exposure could initiate ovarian toxicity. However, their combined effects on the ovary and its mechanism in mammals remained unclear. Female C57BL/6 mice were used in this study to investigate the combined ovarian toxicity of polystyrene MPs (PS-MPs, 0.1 mg/d/mouse) and Pb (1 g/L) for 28 days. Results showed that co-exposure to PS-MPs and Pb increased the accumulation of Pb in ovaries, the histopathological damage in ovaries and uterus, the serum malondialdehyde levels and decreased serum superoxide dismutase and sex hormone levels significantly when compared with single PS-MPs and Pb exposure. These observations indicated that co-exposure exerted more severe toxicity to mouse ovaries and uterus. Furthermore, co-exposure to PS-MPs and Pb caused endoplasmic reticulum (ER) stress by activating the PERK/eIF2α signaling pathway in the ovary, which resulted in apoptosis. However, the oxidative and ovarian damage were alleviated, and the mRNA levels of genes related to the PERK/eIF2α signaling pathway were down-regulated to levels of the control mice in the PS-MPs and Pb co-exposed mice administered with ER stress inhibitor (Salubrinal, Sal) or the antioxidant (N-acetyl-cysteine, NAC). In conclusion, our findings suggested that the combination of PS-MPs and Pb aggravated ovarian toxicity in mice by inducing oxidative stress and activating the PERK/eIF2α signaling pathway, thereby providing a basis for future studies into the combined toxic mechanism of PS-MPs and Pb in mammals.

Polystyrene microplastic exposure induces insulin resistance in mice via dysbacteriosis and pro-inflammation

Microplastics (MPs) as emerging contaminants have become a global environmental problem. However, studies on the effects of MPs on metabolic diseases remain limited. Here, we evaluated the effects of polystyrene (PS), one of the most prominent types of MPs, on insulin sensitivity in mice fed with normal chow diet (NCD) or high-fat diet (HFD), and explained the underlying mechanisms. Mice fed with NCD or HFD both showed insulin resistance (IR) after PS exposure accompanied by increased plasma lipopolysaccharide and pro-inflammatory cytokines such as tumor necrosis factor-α and interleukin-1β. Exposure to PS also resulted in a significant decrease in the richness and diversity of gut microbiota, particularly an increase in the relative abundance of Gram-negative bacteria such as Prevotellaceae and Enterobacteriaceae. Additionally, PS with a small particle size (5 μm) accumulated in the liver, kidneys and blood vessels of mice. Further analyses showed inhibition of the insulin signaling pathway in the liver of PS exposed mice, such as inhibition of IRS1 and decreased expression of PI3K. Hence, the mechanism of PS exposure to induce IR in mice might be mediated through regulating gut microbiota and PS accumulation in tissues, stimulating inflammation and inhibiting the insulin signaling pathway. In conclusion, PS might be a potential environmental contaminant that causes metabolic diseases associated with IR.

Developmental and reproductive toxic effects of exposure to microplastics: A review of associated signaling pathways

Microplastics (MPs), small pieces of plastic (∼5 mm), are released into the environment not only as a result of the decomposition of large-sized plastics but also from day-to-day use of plastic products. Chronic exposure to MPs has been attributed to harmful effects on aquatic organisms and rodents. Effects include gastrointestinal toxicity, hepatotoxicity, neurotoxicity, and reproductive and developmental toxicities. Exposure to MPs may also potentially affect human health. Herein, we reviewed the impact of MPs on male and female reproductive systems and the associated mechanisms involved in the reproductive and developmental toxicities of MPs. We performed a literature search in Google Scholar and PubMed using the following keywords: MPs and reproductive toxicity; MPs and developmental studies; MPs and infertility; MPs and aquatics; and MPs and rodents. Evidence of MPs accumulation has been reported in many organs of humans and experimental models. The harmful effects of MPs have been manifested in male and female reproductive systems of mammalian and aquatic animals, including developmental effects on gametes, embryos, and their offspring. This review describes various signaling pathways involved in MPs-associated male and female reproductive and developmental toxicities.

Microplastics in decapod crustaceans: Accumulation, toxicity and impacts, a review

The presence of microplastics in the aquatic environment poses a serious threat not only to aquatic organisms but also to human beings that consume them. The uptake and effects of microplastics have been studied in almost all groups of aquatic organisms. This review details the different aspects of microplastics exposure in an ecologically and economically important group of crustaceans, the Decapods. A majority of Decapod crustaceans such as prawns, shrimp, crabs, lobsters and crayfish are consumed as seafood and play important roles in food chains and food webs. Numerous studies are available on the accumulation of microplastics in tissues such as the gills, hepatopancreas and gastrointestinal tract in these organisms. Experimental studies have also highlighted the toxic effects of microplastics such as oxidative stress, immunotoxicity and reproductive and developmental toxicity in them. This review also summarizes the ecological impacts and implications in human beings as well as lacunae with regard to microplastic uptake in Decapods.

Oxidative stress, apoptosis and serotonergic system changes in zebrafish (Danio rerio) gills after long-term exposure to microplastics and copper

Fish gills are in direct contact with the surrounding pollutants, and thus, potentially more vulnerable to microplastics (MPs) and heavy metals. The present study aimed to evaluate the long-term exposure effects of MPs and copper (Cu) in the gills of adult zebrafish (Danio rerio). To this end, zebrafish were exposed to MPs (2 mg/L), Cu (Cu25, 25 μg/L) and their mixture (Cu25 + MPs) for 30 days, and then oxidative stress, detoxification, antioxidant, metabolic and neurotoxicity enzymes/genes, as well serotonergic system and apoptosis genes, were evaluated in gills. In the mixture group, ROS levels were increased, while CAT and GPx activities were inhibited, indicating the induction of oxidative stress in zebrafish gills. This was followed by an increase of LPO levels and potential oxidative damage in zebrafish gills. The tryptophan hydroxylase 1a (tph1a) and caspase-3 (casp3) genes were significantly upregulated in Cu25 + MPs group, indicating a potential dysregulation of serotonin synthesis and apoptosis pathways, respectively. Overall, the present study contributes to improving the knowledge about the response of aquatic organisms to MPs and the potential ecological risk that these particles represent to the ecosystems.

Untoward Effects of Micro- and Nanoplastics: An Expert Review of Their Biological Impact and Epigenetic Effects

The production of plastic has dramatically increased in the last 50 y. Because of their stability and durability, plastics are ubiquitously incorporated in both marine and terrestrial ecosystems. Plastic is acted upon by biological, chemical, and physical agents, leading to fragmentation into small pieces [i.e., microplastics (MPs) or nanoplastics (NPs)], classified depending on their size. MPs range from 0.1 to 5000 μm and NPs are fragments between 0.001 to 0.1 μm. MPs and, especially NPs, are easily incorporated into living beings via ingestion. The penetration of MPs and NPs into the food system is an important issue, for both food security and health risk assessment. Ingestion of different MPs and NPs has been associated with different issues in the intestine, such as direct physical damage, increased intestinal permeability, diminished microbiota diversity, and increases in local inflammatory response. However, the potential harmful effects of low-dose dietary plastic are still unclear. Some evidence indicates that intestinal uptake of plastic particles is relatively low and is mostly dependent on the particle's size. However, other evidence highlights that NPs dysregulate key molecular signaling pathways, modify the gut microbiota composition, and may induce important epigenetic changes, including transgenerational effects that might be involved in the onset of many different metabolic disorders. Until now, experiments have been mostly performed on marine organisms, Caenorhabditis elegans, and mouse models, but some research indicates accidental plastic dietary consumption by humans, raising the issue of detrimental health effects of MPs and NPs. This review discusses the impact that MPs and NPs could have on the intestinal tract and the biodistribution and systemic, cellular, and molecular levels. Accumulated evidence of MPs' effects on the human gut suggests that large exposure to MPs and NPs may have phenotypical untoward effects in humans, calling for urgent research in this field.

Microplastics impact the accumulation of metals in earthworms by changing the gut bacterial communities

Microplastics (MPs) are defined as plastic debris with particle size smaller than 5 mm, which have been frequently detected in environments. In this study, earthworms (Eisenia foetida) were exposed to three different sized polystyrene (PS; 0.1, 10 and 100 μm) at 10 and 100 mg per kg soil for 21 days. We examined the contents of metals (Cu, Zn, Ni and Pb) and gut microbial communities in earthworms exposed to MPs. Results showed that MPs reduced the accumulation of Ni and Pb in earthworms on the 21st day. The composition of gut bacterial communities was altered in earthworms exposed to MPs, especially 10 μm MPs, featuring a higher relative abundance of Proteobacteria (44.5%) and Bacteroidetes (27.1%) than the control group. Additionally, gut microorganisms including genus Paenibacillus and Achromobacter in earthworms were expected to be potential biomarkers for Cu and Zn. The microbial community networks showed that MPs affected bacterial community connections by size effect, and MPs with smaller size increased the complexity of earthworm microbial community networks. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that metabolism was the main difference in the bacterial communities in different treatments, especially carbohydrate metabolism and amino acid metabolism, which was relevant to the survival and growth of bacteria. This study provides insight into the environmental risks of MPs on terrestrial organisms.