Neurotoxicity, Behavior, and Lethal Effects of Cadmium, Microplastics, and Their Mixtures on Pomatoschistus microps Juveniles from Two Wild Populations Exposed under Laboratory Conditions-Implications to Environmental and Human Risk Assessment

Melatonin prevents histopathologies stem from cadmium chloride in pregnant mice lungs

Heavy metals may cause structural and functional changes in organs. Cadmium, taken into the body through oral and respiratory routes, can lead to lesions. Cadmium may lead to lesions by accumulating in organs. The lungs are significantly affected by cadmium. Melatonin, an antioxidant hormone with therapeutic effects, is secreted by the pineal gland. The aim of the study is to treat cadmium-induced lesions in the lungs of pregnant mice with Melatonin. Four groups were created with 24 pregnant mice, named Control, Cadmium Chloride, Melatonin, and Melatonin + Cadmium Chloride groups (n: 6) Cadmium Chloride (2 mg/kg/bw) and Melatonin (3 mg/kg/bw) were given orally through gavage during pregnancy (21 days) After routine histological procedures, the lung tissues were stained with Hematoxylin-Eosin and evaluated under a light and electron microscope. ANOVA tests were applied for one-way analysis of variance, and LSD tests were applied for pairwise comparisons (p < 0.05) The average lung weight decreased in the Cadmium Chloride group (p: 0.03) The average lung weight in the Cadmium Chloride + Melatonin group was found to be close to the control group (p: 0.06) Cadmium Chloride caused thickening of the lung alveolar wall, inflammatory cell infiltration, and fibrin deposition. Because the lesions were not observed in the Melatonin group, lesions may be prevented by melatonin. Additional studies may be useful to determine the protective effect of Melatonin at different doses of Cadmium Chloride.

Organ-specific bioaccumulation of microplastics in market fish of Dhaka and size-dependent impacts of PVC microplastics on growth of Anabustestudineus

Microplastics (MPs), a growing environmental concern with potential ecotoxicological risks, are ubiquitous in aquatic environment. This study investigated the organ-specific distribution and variation of MPs in commercially caught fishes (7 species, 140 individuals) collected from Dhaka's two main fish distribution hubs (Uttara and Jatrabari). Additionally, the impact of different-sized MPs on fish growth (Anabas testudineus) was examined in a control experiment. Results revealed that kidneys of market fish bioaccumulated the highest concentration of MPs (average, 59.1 MPs/g), followed by liver (24.6 MPs/g) and intestine (18.6 MPs/g). On average, fish from Uttara had a higher MPs concentration (36 MPs/g) compared to Jatrabari (25 MPs/g). Among fish species, Glossogobius giuris showed the highest MPs bioaccumulation due to its feeding habits and morphology. Fiber-shaped MPs were most prevalent in all fishes (79-93%) except Glossogobius giuris (fragments, 51%). Fourier-transform infrared spectroscopy (FTIR) analysis identified 19 different polymer types, with high density polyethylene (HDPE), ethylene vinyl acetate (EVA) and polyamide (PA) being commonly found in all organs. The experimental study confirmed that large-sized PVC MPs (1.18 mm-300 μm) had a greater negative impact on fish growth (length) and caused more physical deformities (particularly intestinal injuries) compared to small-sized PVC MPs (150 μm-75 μm). Moreover, fish exposed to larger diameter MPs experienced highest physical weight and depth loss among exposed groups. Large-sized PVC MPs bioaccumulated highest in fish compared to small-sized PVC MPs. Similar to market fish, kidney in the experimental fish had the highest MPs bioaccumulation (6.5 MPs/g), followed by liver (5.2 MPs/g) and intestine (4.8 MPs/g), with a dominance of fibers despite the presence of high concentration of fragments in the food source. Statistical analysis also supported a clear correlation between increasing MPs size and adverse effects on fish growth and health. Urgent action is needed to curb microplastic pollution and protect ecosystems and human health.

Unveiling population-specific outcomes: Examining life cycle traits of different strains of Chironomus riparius exposed to microplastics and cadmium questions generality of ecotoxicological results

Ecotoxicological tests used for risk assessment of toxicants and its mixtures rely both on classical life-cycle endpoints and bioindicator organisms usually derived from long-term laboratory cultures. While these cultures are thought to be comparable among laboratories and more sensitive than field organisms, it is not well investigated whether this assumption is met. Therefore, we aimed to investigate differential life-cycle endpoints response of two different strains of C. riparius, one originally from Spain and the other from Germany, kept under the same laboratory conditions for more than five years. To highlight any possible differences, the two populations were challenged with exposure to cadmium (Cd), polyvinyl chloride (PVC) microplastics and a co-exposure with both. Our results showed that significant differences between the strains became evident with the co-exposure of Cd and PVC MPs. The German strain showed attenuation of the deleterious Cd effects with microplastic co-exposure in survival and developmental time. Contrary to that, the Spanish strain showed no interaction between the substances. In conclusion, the toxicity-effects of contaminants may vary strongly among laboratory populations, which makes a universal risk assessment evaluation challenging.

Reviewing the use of zebrafish for the detection of neurotoxicity induced by chemical mixtures through the analysis of behaviour

The knowledge and assessment of mixtures of chemical pollutants in the aquatic environment is a complex issue that is often challenging to address. In this review, we focused on the use of zebrafish (Danio rerio), a vertebrate widely used in biomedical research, as a model for detecting the effects of chemical mixtures with a focus on behaviour. Our aim was to summarize the current status of the ecotoxicological research in this sector. Specifically, we limited our research to the period between January 2012 and September 2023, including only those works aimed at detecting neurotoxicity through behavioural endpoints, utilizing zebrafish at one or more developmental stages, from egg to adult. Additionally, we gathered the findings for every group of chemicals involved and summarised data from all the works we included. At the end of the screening process 101 papers were considered eligible for inclusion. Results show a growing interest in zebrafish at all life stages for this kind of research in the last decade. Also, a wide variety of different assays, involving different senses, was used in the works we surveyed, with exposures ranging from acute to chronic. In conclusion, the results of this study show the versatility of zebrafish as a model for the detection of mixture toxicity although, for what concerns behavioural analysis, the lack of standardisation of methods and endpoints might still be limiting.

Role of UV radiation and oxidation on polyethylene micro- and nanoplastics: impacts on cadmium sorption, bioaccumulation, and toxicity in fish intestinal cells

This study investigated the role of ultraviolet (UV) radiation and oxidation in high-density polyethylene microplastics (2-15 μm) and nanoplastics (0.2-9.9 μm) (NMPs) on particle chemistry, morphology, and reactivity with cadmium (Cd). Additionally, toxicity of NMPs alone and with Cd was evaluated using RTgutGC cells, a model of the rainbow trout (Oncorhynchus mykiss) intestine. The role on NMPs on Cd bioaccumulation in RTgutGC cells was also evaluated. Dynamic light scattering indicated that after UV radiation NPs agglomerated size increased from 0.8 to 28 µm, and to 8 µm when Cd was added. Oxidized MPs agglomerated size increased from 11 and 7 to 46 and 27 µm in non-UV- and UV-aged oxidized MPs when adding Cd, respectively. Cd-coated particles exhibited generally significantly higher zeta potential than non-Cd-coated particles, while attenuated total reflectance-Fourier transform infrared spectroscopy showed that the functional chemistry of the particles was oxidized and modified after being exposed to UV radiation. Presence of NMPs resulted in a significant decrease in Cd bioaccumulation in RTgutGC cells (100.5-87.9 ng Cd/mg protein) compared to Cd alone (138.1 ng Cd/mg protein), although this was not quite significant for co-exposures with UV-aged NPs (105.7 ng Cd/mg protein). No toxicity was observed in RTgutGC cells exposed to NMPs alone for 24 h. Moreover, co-exposures with Cd indicated that NMPs reduce the toxicity of Cd. Altogether these results show that UV aging enhances NMP surface reactivity, increasing Cd absorption in solution, which resulted in a reduction in Cd bioavailability and toxicity.

Inhibiting ferroptosis in brain microvascular endothelial cells: A potential strategy to mitigate polystyrene nanoplastics‒induced blood‒brain barrier dysfunction

Polystyrene nanoplastics (PS-NPs), a group of ubiquitous pollutants, may injure the central nervous system through the blood‒brain barrier (BBB). However, whether exposure to PS-NPs contributes to BBB disruption and the underlying mechanisms are still unclear. In vivo, we found that PS-NPs (25 mg/kg BW) could significantly increase BBB permeability in mice and downregulate the distribution of the tight junction-associated protein zona occludens 1 (ZO-1) in brain microvascular endothelial cells (BMECs). Using an in vitro BBB model, exposure to PS-NPs significantly reduced the transendothelial electrical resistance and altered ZO-1 expression and distribution in a dose-dependent manner. RNA-seq analysis and functional investigations were used to investigate the molecular pathways involved in the response to PS-NPs. The results revealed that the ferroptosis and glutathione metabolism signaling pathways were related to the disruption of the BBB model caused by the PS-NPs. PS-NPs treatment promoted ferroptosis in bEnd.3 cells by inducing disordered glutathione metabolism in addition to Fe2+ and lipid peroxide accumulation, while suppressing ferroptosis with ferrostatin-1 (Fer-1) suppressed ferroptosis-related changes in bEnd.3 cells subjected to PS-NPs. Importantly, Fer-1 alleviated the decrease in ZO-1 expression in bEnd.3 cells and the exacerbation of BBB damage induced by PS-NPs. Collectively, our findings suggest that inhibiting ferroptosis in BMECs may serve as a potential therapeutic target against BBB disruption induced by PS-NPs exposure.

The odd couple: Caffeine and microplastics. Morphological and physiological changes in Mytilus galloprovincialis

In recent years, the presence of pharmaceuticals and microplastics (MPs) in aquatic ecosystems has raised concerns about their environmental impact. This study explores the combined effects of caffeine, a common pharmaceutical pollutant, and MPs on the marine mussel Mytilus galloprovincialis. Caffeine, at concentrations of 20.0 μg L-1, and MPs (1 mg L-1, 35-50 μm size range), was used to mimic real-world exposure scenarios. Two hundred M. galloprovincialis specimens were divided into four groups: caffeine, MPs, Mix (caffeine + MPs), and Control. After a two-week acclimation period, the mollusks were subjected to these pollutants in oxygen-aerated aquariums under controlled conditions for 14 days. Histopathological assessments were performed to evaluate gill morphology. Cellular volume regulation and digestive gland cell viability were also analyzed. Exposure to caffeine and MPs induced significant morphological changes in M. galloprovincialis gills, including cilia loss, ciliary disk damage, and cellular alterations. The chitinous rod supporting filaments also suffered damage, potentially due to MP interactions, leading to hemocyte infiltration and filament integrity compromise. Hemocytic aggregation suggested an inflammatory response to caffeine. In addition, viability assessments of digestive gland cells revealed potential damage to cell membranes and function, with impaired cell volume regulation, particularly in the Mix group, raising concerns about nutrient metabolism disruption and organ function compromise. These findings underscore the vulnerability of M. galloprovincialis to environmental pollutants and emphasize the need for monitoring and mitigation efforts. RESEARCH HIGHLIGHTS: The synergy of caffeine and microplastics (MPs) in aquatic ecosystems warrants investigation. MPs and caffeine could affect gill morphology of Mytilus galloprovincialis. Caffeine-exposed cells had lower viability than the control group in the NR retention test. MPs and mix-exposed cells struggled to recover their volume.

Toxicological Research on Nano and Microplastics in Environmental Pollution: Current Advances and Future Directions

This review explains the sources of nanoplastics (NPs) and microplastics (MPs), their release, fate, and associated health risks in the aquatic environment. In the 21st century, scientists are grappling with a major challenge posed by MPs and NPs. The global production of plastic has skyrocketed from 1.5 million tons in the 1950s to an astonishing 390.7 million tons in 2021. This pervasive presence of these materials in our environment has spurred scientific inquiry into their potentially harmful effects on living organisms. Studies have revealed that while MPs, with their larger surface area, are capable of absorbing contaminants and pathogens from the surroundings, NPs can easily be transferred through the food chain. As a result, living organisms may ingest them and accumulate them within their bodies. Due to their minuscule size, NPs are particularly difficult to isolate and quantify. Furthermore, exposure to both NPs and MPs has been linked to various adverse health effects in aquatic species, including neurological impairments, disruption of lipid and energy metabolism, and increased susceptibility to cytotoxicity, oxidative stress, inflammation, and reactive oxygen species (ROS) production. It is alarming to note that MPs have even been detected in commercial fish, highlighting the severity of this issue. There are also challenges associated with elucidating the toxicological effects of NPs and MPs, which are discussed in detail in this review. In conclusion, plastic pollution is a pressing issue that governments should tackle by ensuring proper implementation of rules and regulations at national and provincial levels to reduce its health risks.

A realistic combined exposure scenario: effect of microplastics and atrazine on Piaractus mesopotamicus

Microplastics, considered emerging environmental contaminants resulting from plastic degradation, are discovered in diverse aquatic ecosystems and can be unintentionally ingested by fish. Therefore, it is essential to characterize their interaction with other contaminants, such as agrochemicals, in aquatic environments. This study aimed to assess histological, enzymatic, and genotoxic biomarkers in juvenile pacú (Piaractus mesopotamicus) exposed to polyethylene (PE) microplastic particles and the herbicide atrazine, individually or combined, for 15 days. Four treatments were used: a negative control (CON), PE in the fish diet (0.1% w/w, FPE), atrazine through water (100 μg L-1, ATZ), and the mixture (ATZ+FPE). Results confirmed histological alterations in gills (edema and lamellar fusion) and liver (necrotic areas and congestion) of fish exposed to ATZ and ATZ+FPE. The number of goblet cells increased in the posterior intestine of fish under ATZ+FPE compared to CON and FPE. Enzyme activities (CAT, GST, AChE, and BChE) significantly increased in ATZ+FPE compared to CON. However, no genotoxic effect was demonstrated. These findings provide insights into the complex impacts of simultaneous exposure to atrazine and microplastics, emphasizing the need for continued research to guide effective environmental management strategies against these contaminants that represent a risk to aquatic organisms.

Biochemical basis of resistance to multiple contaminations in the native and invasive populations of Dreissena polymorpha

The zebra mussel Dreissena polymorpha (Pallas, 1771) is an invasive species and a valuable bioindicator in the inland waters. Nevertheless, the biochemical reasons for the unique competitiveness of zebra mussels are not clear. This study aimed to compare the native and invasive populations of D. polymorpha in their ability to withstand the same multiple environmental challenges (i.e. chemical: microplastics and caffeine; physical: temperatures). The specimens from the invasive population in west Ukraine (Tn) and native population at lower streams of river Dnipro (south Ukraine, Kh) were sampled in the August of 2021 y. Molluscs from both populations were treated simultaneously with microplastics (MP, 1 mg L-1, pore size 2 μm); caffeine (Caf, 20.0 μg L-1) at 18 °C, elevated temperature (25 °C) and MP and Caf combinations at 18 °C and 25 °C for 14 days. Untreated molluscs exposed at 18 °C represented control groups. A set of the 20 markers of oxidative stress, biotransformation, detoxification and apoptosis were assayed in the total soft tissues. From the two controls, Kh-group indicated lower stressful impact. However, both populations increased caspase-3 and GST activities and lysosomal instability in most exposures, and cholinesterase and phenoloxidase activities under the heating and combine exposures, indicating the remarkable properties to respond to new challenges and synergistic effect of mixtures. Inter-population differences were related to the metallothionein, cathepsin D, cytochrome P540 and oxidative stress responses that reflect population-dependent adverse outcome pathways. The discriminant analysis separated two populations with a substantially lesser magnitude of responses in the invasive population as a sign of higher resistance.

Toxic vascular effects of polystyrene microplastic exposure

Polystyrene microplastics (PSMPs) are some of the most common microplastic components, and the resulting pollution has become a global problem. Extensive studies have been conducted on the toxic effects of PSMPs on the heart, lungs, liver, kidneys, nerves, intestines and other tissues. However, the impact of PSMPs on vascular toxicity is poorly understood at present. The aim of this study was to reveal the vascular toxicity of microplastics (MPs). Patients were assigned to a calcification group (25 patients) or a non-calcification group (22 patients) based on the presence or absence of calcification in the thoracic aorta wall. We detected 7 polymer types in human feces. Patients with vascular calcification (VC) had higher levels of total MPs, polypropylene (PP) and polystyrene (PS) in feces than patients without VC. The thoracic aortic calcification score was significantly positively correlated with the total MP abundance (Spearman r = 0.8109, p < 0.0001), PP (Spearman r = 0.7211, p = 0.0160) and PS (Spearman r = 0.6523, p = 0.0471) in feces. We then explored the effects of PSMP exposure on normal and vitamin D3 + nicotine (VDN)-treated rats. PSMP exposure induced mild VC in normal rats and aggravated VC in VDN-treated rats. PSMP exposure disturbed the gut microbiota, causing Proteobacteria and Escherichia_Shigella to be the dominant phylum and genus, respectively. It also induced intestinal inflammatory responses in normal rats, aggravated intestinal inflammation in VDN-treated rats, impaired the intestinal mucosal barrier, and increased intestinal permeability. This study provides a theoretical basis for the risk assessment of MP-induced cardiovascular disease.

Incidence and exposure to microplastics in table salt present in the Iran market

Plastics and microplastics (MPs) are toxic, pervasive and threatening the biotic and abiotic components of the earth, and they threaten food safety and food security by moving in the food chain. In this study, the amounts and characteristics of 40 table salt samples with different brands, including sea salt (No = 13), rock (No = 13), bulk (No = 8) and non-standard (No = 6), were investigated with a combination of sieving, filtration, observation and FTIR, Micro-Raman and SEM techniques. The results showed that all the salts were contaminated with MPs. In general, the abundance range of detected particles was 700-5470 MPs/kg. The abundance of MPs was higher in counterfeit and non-standard salts (1825 ± 1808 MPs/kg). Investigating the relationship between the effect of the purification process (Kruskal-Wallis Test, P = 0.841), the type of packaging (Kruskal-Wallis Test, P = 0.609), and the type of salt (Kruskal-Wallis Test, P = 0.942), on the abundance of MPs using a comparison test Kruskal-Wallis was not significant. However, the numerical difference was recognizable. The most identified polymer in the salts was cellulose acetate, which probably causes by unmanaged plastic litter in the environment (especially cigarette butts). The dominant form of particles was fragment-shaped, which is the most abundant form of identified MPs in the environment. Both environmental pollution and secondary pollution (during production and packaging), respectively, contribute to the contamination of salts with MPs. The estimated human dietary intake (EDI) and the amount of estimated annual intake (EAI) for different ages in Iran were obtained EDI = 5-59 MPs/capita/day and EAI = 1967-21563 MPs/capita/year. The surface morphology of the particles showed that the MPs were affected by continuous weathering, mechanical fracture and oxidation. MPs are a threat to human health due to the absorption and transmission of dangerous pollutants and their inherent toxicity. Therefore, a solution must be thought of to prevent the contamination of the food chain through salts by MPs, (with protective measures at the salt source, and by improving its production processes.

The organism fate of inland freshwater system under micro-/nano-plastic pollution: A review of past decade

Micro- and nano-plastics (MPs/NPs) are characterized by their small size and extensive surface area, making them global environmental pollutants with adverse effects on organisms at various levels, including organs, cells, and molecules. Freshwater organisms, such as microalgae, emerging plants, zooplankton, benthic species, and fish, experience varying impacts from MPs/NPs, which are prevalent in both terrestrial and aquatic inland environments. MPs/NPs significantly impact plant physiological processes, including photosynthesis, antioxidant response, energy metabolism, and nitrogen removal. Extended exposure and ingestion to MPs/NPs might cause metabolic and behavioral deviations in zooplankton, posing an extinction risk. Upon exposure to MPs/NPs, both benthic organisms and fish display behavioral and metabolic disturbances, due to oxidative stress, neural toxicity, intestinal damage, and metabolic changes. Results from laboratory and field investigations have confirmed that MPs/NPs can be transported across multiple trophic levels. Moreover, MPs/NPs-induced alterations in zooplankton populations can impede energy transfer, leading to food scarcity for filter-feeding fish, larvae of benthic organism and fish, thus jeopardizing aquatic ecosystems. Furthermore, MPs/NPs can harm the nervous systems of aquatic organisms, influencing their feeding patterns, circadian rhythms, and mobility. Such behavioral alterations might also introduce unforeseen ecological risks. This comprehensive review aims to explore the consequences of MPs/NPs on freshwater organisms and their interconnected food webs. The investigation encompasses various aspects, including behavioral changes, alterations in physiology, impacts on metabolism, transgenerational effects, and the disruption of energy transfer within the ecosystem. This review elucidated the physiological and biochemical toxicity of MPs/NPs on freshwater organisms, and the ensuing risks to inland aquatic ecosystems.

Review of cadmium toxicity effects on fish: Oxidative stress and immune responses

Cadmium (Cd) in aquatic environments can cause environmental toxicity to fish and induce oxidative stress owing to an excessive production of reactive oxygen species in fish bodies. Fish have developed various antioxidant systems to protect themselves from reactive oxygen species; thus, a change in antioxidant responses in fish can be a criterion for evaluating oxidative stress resulting from Cd exposure. Because Cd exposure may be recognized as an exogenous substance by a fish body, it may lead to the stimulation or suppression of its immune system. Various immune responses can be assessed to evaluate Cd toxicity in fish. This review aimed to identify the impacts of Cd exposure on oxidative stress and immunotoxicity in fish as well as identify accurate indicators of Cd toxicity in aquatic ecosystems.

Neurotoxicity of microplastics: a CiteSpace-based review and emerging trends study

Microplastics, as a currently emerging pollutant, are gaining increasing attention from researchers in various fields. The purpose of this study is to summarize research development on microplastics in the field of neurotoxicity using bibliometric tools and visualization methods and to identify current research hotspots. The Web of Science Core Collection (WoSCC) was searched under the topics of "microplastics" and "neurotoxicity." A total of 33 published articles were obtained by exclusion and analyzed using CiteSpace (V6.1.R2). It was found that microplastic neurotoxicity research is currently on the rise, with the most research results being published in China, the most collaboration occurring between Italy and other countries, and the least collaboration occurring between authors. The focus and hotspots of future research on the neurotoxicity of microplastics may revolve around "accumulation" and "integrated biomarker response." These findings demonstrate the trends and frontiers in the field of microplastic neurotoxicity research and provide valuable information for subsequent research directions and potential collaborations.

Combined toxic effects of cadmium and environmental microplastics in Aphanius fasciatus (Pisces, Cyprinodontidae)

Microplastics (MPs), plastic particles smaller than 5 mm in diameter, have received extensive attention as new environmental pollutants with still unexplored potential ecological risks. The main objective of the present study is to see if the concomitant exposure to MPs and Cd is more toxic than that to MPs or Cd separately in Aphanius fasciatus. Immature female were exposed to Cd and/or MPs for 21 days, and the subsequent effects were monitored by a combination of biochemical, histological and molecular toxicity markers. Exposure to Cd, but not to MPs, increased metallothioneins content and mRNA levels of the metallothioneins gene MTA both in liver and gills. In addition, we observed a significant oxidative stress response at histological, enzymatic (Catalase and Superoxide dismutase), non-enzymatic (proteins sulfhydryl and malondialdehyde) and gene expression levels to both toxicants in both tissues, particularly in gills, but no clear evidence for interaction between the two factors. Our results indicate a major effect of MPs on gills at different organizational levels. Finally, exposure to both MPs and Cd induced spinal deformities, although bone composition was only altered by the latter, whereas MTA mRNA bone levels were only increased realtive to controls in doubly-exposed samples. Interestingly, the simultaneous use of both pollutants produced the same effects as Cd and MPs alone, probably due to reduced bioavailability of this heavy metal.

In vitro characterization of cadmium transport across the gastro-intestinal membrane of the fathead minnow (Pimephales promelas) in the presence and absence of microplastics

There is concern that microplastics can act as a vector for cadmium through adsorption and desorption of free-ionic cadmium. Little is known about the uptake of cadmium following ingestion of cadmium-microplastic complexes. This study used an in vitro gut sac technique to investigate the translocation of cadmium across the gut barrier of fathead minnows following the simulated ingestion of cadmium, microplastics, or their complexed mixture. Microplastics did not cross the gut membrane, nor did microplastics alter the rate of cadmium translocation, which was estimated to be 1.2 ± 0.04ngCd / hour. Less cadmium translocated when cadmium-microplastic complexes were injected than the equivalent dose of only cadmium, indicating that the presence of microplastics was protective of dietary cadmium uptake. This work highlights the importance of considering dietary uptake and the role of microplastics acting as a vector for cadmium in aquatic environments and stresses the need to understand how environmental (digestive or ambient) characteristics govern cadmium-microplastic interactions.

Functional Trait-Based Evidence of Microplastic Effects on Aquatic Species

Microplastics represent an ever-increasing threat to aquatic organisms. We merged data from two global scale meta-analyses investigating the effect of microplastics on benthic organisms' and fishes' functional traits. Results were compared, allowing differences related to vertebrate and invertebrate habitat, life stage, trophic level, and experimental design to be explored. Functional traits of aquatic organisms were negatively affected. Metabolism, growth, and reproduction of benthic organisms were impacted, and fish behaviour was significantly affected. Responses differed by trophic level, suggesting negative effects on trophic interactions and energy transfer through the trophic web. The experimental design was found to have the most significant impact on results. As microplastics impact an organism's performance, this causes indirect repercussions further up the ecological hierarchy on the ecosystem's stability and functioning, and its associated goods and services are at risk. Standardized methods to generate salient targets and indicators are urgently needed to better inform policy makers and guide mitigation plans.

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.

Tracking microplastics contamination in drinking water in Zahedan, Iran: From source to consumption taps

Microplastics (MPs) that pollute drinking water are inherently toxic, act as an adsorbent of hazardous pollutants, and threaten human health. So, the fate of microplastics in drinking water from the source to consumption taps (CTs) was assessed in spring and winter in Zahedan city in Iran. Sampling was performed from 4 reservoirs (raw water), before and after two water treatment plants (WTPs), and 10 CTs. The reservoirs were sampled using a plankton net (pore size = 100 μm), and the remaining samples were taken using a sampling device (containing a stainless steel membrane as a filter with pore size = 5 μm). The combination of density separation techniques, digestion, observation, Micro-Raman and FTIR, and SEM analysis was performed to recognize MPs. The average number of MPs in raw water varied between 15.4 and 44.7 MP/m³ (winter) and 22-51.8 MP/m³ (spring). The results before and after the treatment plant showed that about 64 % and 75 % of particles were eliminated in WTP₁ and WTP₂, respectively. The average number of MPs in CTs was more than treatment water (CT_a = 85-390 MP/m³ and CT_b = 75-400 MP/m³), which is a probable confirmation of secondary contamination (abrasion from pipes, installations, and sealing materials). The dominant type of polymer detected in raw water, treated water, and consumption taps were PS. The estimated daily intake for children and adults was about 0.16-15 MP/kg/bw/year and 0.07-5.7 MP/kg/bw/year, respectively. The surface morphology of MPs showed that the particles were affected by continuous weathering, mechanical breakage, and oxidation. MPs threaten the environment and human health due to the adsorption and transport of hazardous pollution and their intrinsic toxicity, so a solution must be thought of to prevent the pollution of drinking water by MPs.

Advances and prospects of carbon dots for microplastic analysis

Microplastics have become the world's most emerging pollutants today due to the ubiquitous use of plastics in everyday life and their ability to migrate from micro to nanoscale to every corner of the natural world, leading to ecological imbalances and global catastrophes. However, a standardized method for separating and analyzing microplastics from actual food or environmental samples has not been established. Therefore, it is necessary to develop a simple, fast, cost-effective, and accurate method that can accurately measure the degree of contamination of microplastics. As one of these methods, fluorometry has been proposed as a cost-effective method to detect, quantify and differentiate individual plastic particles. Therefore, this review discussed the technique for analyzing microplastics using fluorescent carbon dots (CDs). This review provided an overview of the impact of microplastics and the feasibility of using CDs to detect and analyze microplastics. In particular, this review will discuss novel microplastic analysis methods using CD and future application studies. The method using CDs will overcome the limitations of current microplastic analysis technology and may become a new method for detecting and analyzing microplastics.

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.

Effects of the Antidepressant Amitriptyline on Juvenile Brown Trout and Their Modulation by Microplastics

Pharmaceuticals such as antidepressants are designed to be bioactive at low concentrations. According to their mode of action, they can also influence non-target organisms due to the phylogenetic conservation of molecular targets. In addition to the pollution by environmental chemicals, the topic of microplastics (MP) in the aquatic environment came into the focus of scientific and public interest. The aim of the present study was to investigate the influence of the antidepressant amitriptyline in the presence and absence of irregularly shaped polystyrene MP as well as the effects of MP alone on juvenile brown trout (Salmo trutta f. fario). Fish were exposed to different concentrations of amitriptyline (nominal concentrations between 1 and 1000 µg/L) and two concentrations of MP (104 and 105 particles/L; <50 µm) for three weeks. Tissue cortisol concentration, oxidative stress, and the activity of two carboxylesterases and of acetylcholinesterase were assessed. Furthermore, the swimming behavior was analyzed in situations with different stress levels. Exposure to amitriptyline altered the behavior and increased the activity of acetylcholinesterase. Moreover, nominal amitriptyline concentrations above 300 µg/L caused severe acute adverse effects in fish. MP alone did not affect any of the investigated endpoints. Co-exposure caused largely similar effects such as the exposure to solely amitriptyline. However, the effect of amitriptyline on the swimming behavior during the experiment was alleviated by the higher MP concentration.

Short- and long-term single and combined effects of microplastics and chromium on the freshwater water flea Daphnia magna

In this study, we investigated the individual and combined effects of microplastics (MPs) and chromium (Cr) on the freshwater water flea Daphnia magna by measuring mortality, bioaccumulation, antioxidative response, multixenobiotic resistance activity, and sestrin-related mitochondrial biogenesis in short-term assays and in vivo endpoints including reproduction and adult survival rate in long-term assays. Exposure to MPs, Cr, and their combination caused significant deleterious effects and acute toxicity in D. magna. Alterations in oxidative stress occurred in the groups treated with MPs and Cr alone and together. However, upon co-exposure to MPs, the Cr concentration, measured by inductively coupled plasma optical emission spectroscopy, decreased, suggesting that MPs and Cr interact with each other. Based on enzymatic activities, we noted a decrease in MP egestion via inhibition of P-glycoprotein activity in the MP-exposed groups, and multidrug resistance-associated protein activity increased in some of the MP-exposed animals depending on Cr concentration. On the other hand, MP exposure seemed to lead to mitochondrial transcription dysfunction induced by Cr via sestrin-related mitochondrial biogenesis. Overall, these results indicate that co-exposure to MPs and Cr causes acute toxicity in D. magna but lacks the chronic toxicity (21 days) and mitochondrial dysfunction caused by Cr exposure alone.

Stress responses of bivalve mollusc Unio tumidus from two areas to ibuprofen, microplastic and their mixture

Even though bivalve molluscs are recognized as bioindicators of freshwater quality, their responses to multiple stressors are unpredictable. This study aims to elucidate the inter-population peculiarities of the effect in the sub-chronic environmentally relevant exposure to novel contaminants. The specimens of Unio tumidus from reference (Pr) and contaminated (Ct) areas were treated with ibuprofen (IBU, 0.8 µg L^-1), microplastic (MP, 1.0 mg L^-1, size 0.1-0.5 mm), or their combination (Mix) for 14 days. Untreated mussels (PrC- and CtC-groups) served as controls. The PrC-group had higher levels of antioxidants Mn-SOD, Cu,Zn-SOD, catalase, and cholinesterase (AChE) as well as lesser levels of oxidative lesions (TBARS and protein carbonyls) in digestive glands, indicating lower environmental impact than in the CtC-group. However, lysosomal stability was similar in both control groups. Among antioxidants, Mn-SOD activity was affected most prominently, increasing in all exposed Ct-groups. TBARS level was increased only in PrMP-group compared to responsive control. IBU and Mix enhanced protein carbonyl concentration in the Pr-groups, and decreased it in the Ct-groups. AChE was induced in the CtIBU- and PrMix-groups, and lysosomal integrity increased in the CtIBU and CtMix-groups. Discriminant analyses indicated lesser differences between Pr-groups, demonstrating lower cumulative stress compared to Ct-groups. Generally, the most remarkable response was revealed in the CtIBU-group, and distortion of individual effects was established in combined exposures. The qualification of stress-neutral and stress-positive populations was proposed for Pr- and Ct-populations correspondingly. Inter-site peculiarities must be taken into consideration when the environmental impact of MP and pharmaceuticals is evaluated.

Distinct adverse outcomes and lipid profiles of erythrocytes upon single and combined exposure to cadmium and microplastics

The growing accumulation of environmental microplastics (MPs) has become a global concern. MPs are capable to interact with other environmental contaminants leading to altered toxicity. Red blood cells (RBCs), are the target with highest priority for most of toxic xenobiotics after entering blood stream. Whether co-existence of MPs changes the toxicity of cadmium, a typical hemolysis inducer, in RBCs is unknown. We investigated the adverse effects of CdCl₂ and Polystyrene-MPs (PS-MPs) on RBCs in mice. We found that CdCl₂ induced mild microcytic hypochromic anemia while PS-MPs induced polycythemia vera, indicating distinct outcomes between them. Moreover, co-treatment of PS-MPs with CdCl₂ did not change the phenotype of microcytic hypochromic anemia, indicating an antagonistic relationship between CdCl₂ and PS-MPs. However, the lipid profiles were also distinct between single exposure and combined exposure to CdCl₂ and PS-MPs. The significant changed lipids were mainly involved in altering the physiochemical or biological properties of RBCs, including decreased membrane components, disrupted bilayer thickness and intrinsic lipid curvature. These results indicated impaired membrane functions of RBCs. The altered lipid profiles observed in the current study may represent new and previously unrecognized harmful characteristics of cadmium and MPs on erythrocytes at low dose without apparent induction of anemia.

Indication of the impact of environmental stress on the responses of the bivalve mollusk Unio tumidus to ibuprofen and microplastics based on biomarkers of reductive stress and apoptosis

The vulnerability of bivalve mollusks to micropollutants is estimated mainly in single model exposures. However, chronic environmental stress and complex exposures can modulate their responses. To evaluate the impact of population-dependent adaptations on the ability to react to common micropollutants, we compared freshwater bivalves Unio tumidus from two distinct populations, pure (Pr) and contaminated (Ct), in their exposures to microplastics (MP, 1 mg L^-1, size 0.1-0.5 mm), pharmaceutical ibuprofen (IBU, 0.8 μg L^-1), or their combination (Mix) for 14 days. Control groups from both sites showed remarkable differences, with lower levels of total antioxidant capacity (TAC), metallothionein protein (MTSH), NADH and NAD⁺, cytochrome P450-related EROD, glutathione-S transferase (GST), and citrate synthase (CS) but higher levels of GSH, GSSG, caspase-3 and cathepsin D (CTD) in the Ct-control group. These data indicate a chronic stress impact in the Ct population. Under exposures, we found an almost common strategy in both populations for NAD⁺/NADH and MTSH suppression and CTD induction. Additionally, Mix exposure caused an increase in CS, and IBU did not change GSH in both populations. However, the expected response to IBU - the suppression of caspase-3 - was indicated only in PrIBU- and PrMix-mollusks. CTD efflux increased dramatically only in PrMP- and PrMix- groups, and suppression of EROD and GST was detected in the PrMix-group. According to discriminant analysis, exposed Pr-groups were highly differentiated from control, whereas Ct-control and exposed groups had common localization demonstrating high resistance to environmental stress. Thus, the same exposures resulted in different adverse outcome pathways depending on the population.

Microplastics as Contaminants in Water Bodies and Their Threat to the Aquatic Animals: A Mini-Review

Microplastics (MPs), which are particles with a diameter of less than 5 mm, have been extensively studied due to their serious global pollution. Typically, MPs in water originate from terrestrial input. A number of studies have reported the presence of MPs as a stressor in water environments worldwide, and their potential threat to the aquatic animals, affecting the growth, oxidative stress responses, body composition, histopathology, intestinal flora, and immune and reproduction systems. During the plastic degradation process, a large variety of toxic substances are released. MPs have been proposed to be the carriers of toxic chemicals and harmful microorganisms. A study of the literature on MP pollution and stress on the aquatic animals associated with MPs was carried out.

Size-dependent seizurogenic effect of polystyrene microplastics in zebrafish embryos

The effects of polystyrene microplastic (PS-MP) size on neurotoxicity remain to be evaluated at various microsizes, and the seizurogenic effects of PS-MPs are unknown. This study aimed to evaluate the swimming behavior of zebrafish larvae under light-dark transitions after exposure to four PS-MP sizes (i.e., 1, 6, 10, and 25 μm) at concentrations of 500, 5,000, and 50,000 particles/mL. Changes in electroencephalographic signals, seizure-related gene expression, and neurochemical concentrations were measured. Locomotor activity was inhibited only by 10-μm PS-MPs. According to electroencephalographic signals, the number and total duration of seizure-like events significantly increased by 10-μm PS-MPs, which was confirmed by the altered expression of seizure-related genes c-fos and pvalb5. Additionally, an increase in the levels of neurochemicals choline, betaine, dopamine, 3-methoxytyramine, and gamma-aminobutyric acid indicated that the observed hypoactivity and seizure-like behavior were associated with the dysregulation of the cholinergic, dopaminergic, and GABAergic systems. Overall, these findings demonstrate that exposure to PS-MPs can potentially cause seizurogenic effects in developing zebrafish embryos, and we highlight that PS-MPs 10 µm in size dominantly affect neurotoxicity.

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.

Microplastics and copper induce apoptosis, alter neurocircuits, and cause behavioral changes in zebrafish (Danio rerio) brain

The knowledge regarding the neurological and behavioral toxic effects associated with microplastics (MPs) and heavy metals exposure is still scarce. The present study aimed to evaluate the potential chronic (30 days) toxic effects of MPs (2 mg/L) and copper (Cu, 25 µg/L), alone or combined, in the zebrafish (Danio rerio) brain antioxidant system, cell proliferation/death, cholinergic-, serotonergic- and dopaminergic pathways and, consequently, in locomotor, anxiety, and social behaviors. Our findings showed that MPs and Cu exposure modulated the antioxidant system of zebrafish brain, with superoxide dismutase (SOD) and glutathione reductase (GR) having higher activity in the Cu25 +MPs group, but glutathione peroxidase (GPx) being inhibited in MPs, Cu25 and Cu25 +MPs. Moreover, an increase in acetylcholinesterase (AChE) activity was observed in all exposed groups. When considering neurogenesis genes, a downregulation of proliferating cell nuclear antigen (pcna) was noticed in zebrafish exposed to the mixture treatment, while for dopaminergic system-related genes (th and slc6a3) an upregulation was observed in MPs, Cu25 and Cu25 +MPs groups. An increase in apoptosis-related genes expression (casp8, casp9 and casp3) was observed in the MPs exposed group. Changes in zebrafish behavior, particularly in mean speed, total distance moved, inactivity in the aquaria, and social/shoaling behavior was also observed in the MPs and Cu exposed groups. Overall, our results highlight the multiplicity of toxic effects of MPs, alone or combined with Cu, in zebrafish brain, namely apoptosis and alterations in adult neurogenesis, neurocircuits and, consequently, behavior.

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.

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.

Chronic toxicity effects of sediment-associated polystyrene nanoplastics alone and in combination with cadmium on a keystone benthic species Bellamya aeruginosa

Nanoplastics (NPs) are emerging pollutants that may adversely affect aquatic fauna. However, the adverse effects of NPs and heavy metals, both alone and combined on freshwater benthic fauna remain largely unclear. Here, we performed a 28-day sediment toxicity test with Bellamya aeruginosa to examine the effects of exposure to polystyrene nanoplastics (PSNPs) and co-exposure to PSNPs and Cd. Cd bioavailability, the bioaccumulation of PSNPs and Cd, and changes in multiple biomarkers were determined. The results revealed that PSNPs significantly increased Cd bioavailability and thereby facilitated Cd bioaccumulation; however, PSNPs displayed a negligible vector role in Cd uptake by B. aeruginosa. The results demonstrated that PSNPs can accumulate in B. aeruginosa and induce oxidative damage and DNA damage. Co-exposure to PSNPs and Cd significantly enhanced oxidative damage and DNA damage and reduced metallothionein levels. The integrated biomarker response index analysis showed that co-exposure to PSNPs and Cd considerably increased toxic stress in B. aeruginosa compared to single PSNPs or Cd exposure, suggesting that PSNPs may have a synergistic effect with Cd. Collectively, our findings highlight that PSNPs not only cause toxicity to B. aeruginosa but also significantly enhance the toxicity of Cd by increasing Cd bioavailability in the sediment.

Microplastics- and copper-induced changes in neurogenesis and DNA methyltransferases in the early life stages of zebrafish

In this study, zebrafish embryos were exposed to microplastics (MPs, 2 mg/L) and copper (Cu, 60 and 125 μg/L), alone or combined, for 14 days, and the development of motor neurons was assessed through gene expression and immunohistochemistry. DNA methyltransferases (DNMTs) genes expression was also evaluated. The results showed a downregulation of neuronal proliferation (sox2, pcna), neurogenesis (neuroD, olig2), and motor neurons development (islet) related genes, implying potential deficits in the neurogenesis of the exposed zebrafish early life stages. Downregulation of the maintenance and de novo DNMTs expression was also found, indicating that the DNA methylation patterns could be modulated by MPs and Cu. A high relative volume of proliferating cell nuclear antigen (PCNA)-positive cells was found in the fish retina from the MPs exposed group, suggesting that MPs increased the rate of cellular division. In contrast, a significant decrease of PCNA-positive cells, and therefore a lower cell proliferation, was found in the retina and brain of zebrafish exposed to Cu and Cu + MPs, which could lead to cognitive and behavioral functions impairment. No alterations were found in the relative volume of ISL1&2-positive cells. This study contributes to the knowledge of the mechanisms by which MPs and Cu cause neurotoxicity, fundamental for a comprehensive and realistic ecological risk assessment in aquatic populations.

Harmful effects of the microplastic pollution on animal health: a literature review

Background

The environmental pollution by microplastics is a global problem arising from the extensive production and use of plastics. Small particles of different plastics, measured less than 5 mm in diameter, are found in water, air, soil, and various living organisms around the globe. Humans constantly inhale and ingest these particles. The associated health risks raise major concerns and require dedicated evaluation.

Objectives

In this review we systematize and summarize the effects of microplastics on the health of different animals. The article would be of interest to ecologists, experimental biologists, environmental physicians, and all those concerned with anthropogenic environmental changes.

Methodology

We searched PubMed and Scopus from the period of 01/2010 to 09/2021 for peer-reviewed scientific publications focused on (1) environmental pollution with microplastics; (2) uptake of microplastics by humans; and (3) the impact of microplastics on animal health.

Results

The number of published studies considering the effects of microplastic particles on aquatic organisms is considerable. In aquatic invertebrates, microplastics cause a decline in feeding behavior and fertility, slow down larval growth and development, increase oxygen consumption, and stimulate the production of reactive oxygen species. In fish, the microplastics may cause structural damage to the intestine, liver, gills, and brain, while affecting metabolic balance, behavior, and fertility; the degree of these harmful effects depends on the particle sizes and doses, as well as the exposure parameters. The corresponding data for terrestrial mammals are less abundant: only 30 papers found in PubMed and Scopus deal with the effects of microplastics in laboratory mice and rats; remarkably, about half of these papers were published in 2021, indicating the growing interest of the scientific community in this issue. The studies demonstrate that in mice and rats microplastics may also cause biochemical and structural damage with noticeable dysfunctions of the intestine, liver, and excretory and reproductive systems.

Conclusions

Microplastics pollute the seas and negatively affect the health of aquatic organisms. The data obtained in laboratory mice and rats suggest a profound negative influence of microplastics on human health. However, given significant variation in plastic types, particle sizes, doses, models, and modes of administration, the available experimental data are still fragmentary and controversial.

Recent advances in toxicological research and potential health impact of microplastics and nanoplastics in vivo

As emerging pollutants, direct and indirect adverse impacts of micro(nano)plastics (MPs/NPs) are raising an increasing environmental concern in recent years due to their poor biodegradability and difficulty in recycling. MPs/NPs can act as carriers of bacteria, viruses, or pollutants (such as heavy metals and toxic organic compounds), and may potentially change the toxicity and bioavailability of pollutants. Ingested or attached MPs/NPs can also be transferred from low-trophic level organisms to high-nutrient organisms or even the human body through the food chain transfer process. This article reviews the emerging field of micro- and nanoplastics on organisms, including the separate toxicity and toxicity of compound after the adsorption of organic pollutants or heavy metals, as well as possible mechanism of toxicological effects and evaluate the nano- and microplastics potential adverse effects on human health. The inherent toxic effects MPs/NPs mainly include the following: physical injury, growth performance decrease and behavioral alteration, lipid metabolic disorder, induced gut microbiota dysbiosis and disruption of the gut's epithelial permeability, neurotoxicity, damage of reproductive system and offspring, oxidative stress, immunotoxicity, etc. Additionally, MPs/NPs may release harmful plastic additives and toxic monomers such as bisphenol A, phthalates, and toluene diisocyanate. The vectors' effect also points out the potential interaction of MPs/NPs with pollutants such as heavy metals, polycyclic aromatic hydrocarbons, organochlorine pesticides, polychlorinated biphenyls, perfluorinated compounds, pharmaceuticals, and polybrominated diphenyl ethers. Nevertheless, these potential consequences of MPs/NPs being vectors for contaminants are controversial.

Interactions effects of nano-microplastics and heavy metals in hybrid snakehead (Channa maculata ♀ × Channa argus ♂)

The interaction between microplastics and contaminants has potentially generated new undefined risks on animals and ecosystems, and nano-microplastics are considered to be more harmful than microplastics. This experiment investigated the interactions and effects of nano-microplastics with heavy metals cadmium in hybrid snakehead. Different concentrations of nano-microplastics 80 nm (50 μg/L and 500 μg/L) and Cd (50 μg/L) were used for exposure, and four sampling points were set for 24 h, 48 h, 96 h and clear-48 h. Results indicated that the morphology of gill was altered under the influence of nano-microplastics and cadmium, and the damage was aggravated with time. Nano-microplastics and Cd can cause oxidative damage to fish liver partly by effect the activities of antioxidant enzyme, and significantly suppressed the expressions of genes related to the inflammation (IL-1β and TNF-α) and as well as significantly up-regulated the expression of genes HSP70 and SOD. Additionally, the mRNA levels of MT gene can be speculated that the heavy metal cadmium may accumulated in the body over time. And the concentration of heavy metals will also affect their accumulation in the body. Our study elucidated the nano-microplastics and Cd will increase the impact on environmental and organisms that the nano-microplastics contribute to the bioaccumulation of metals, which served as a new support for study the interaction between environmental contaminants.

Sub-acute exposure to nanoplastics via two-chain trophic transfer: From brine shrimp Artemia franciscana to small yellow croaker Larimichthys polyactis

This study investigated the trophic transfer of nanoplastics in marine food chains. We fed nanoplastic-exposed Artemia franciscana (brine shrimp) to Larimichthys polyactis (small yellow croaker) daily for eight days. Subsequently, the overall health condition, histopathological damage to the liver and digestive tract, and swimming ability of the fish were measured. After the sub-acute exposure to nanoplastics via trophic transfer, the fish showed inhibited growth, severe liver damage, as well as a poorer swimming ability compared to the control. The swimming ability was especially affected, in terms of the overall movement as well as thigmotaxis. The results thus clarified that even an indirect exposure to nanoplastics could induce neurotoxic effects and affect the swimming ability of the fish. As fish are well-known human food resources, the possibility of such trophic transfers affecting higher trophic level organisms, such as humans, cannot be ruled out.

Effect of short-term exposure to fluorescent red polymer microspheres on Artemia franciscana nauplii and juveniles

Microplastics (MPs) are ubiquitously present in the world's seas with unknown potential toxic effects on aquatic ecosystems. The aim of this study was to evaluate biochemical responses caused by 1-5 μm diameter plastic fluorescent red polymer microspheres (FRM), under short-term exposure of nauplii and juveniles of Artemia franciscana, using a set of biomarkers involved in important physiological processes such as biotransformation, neuronal transmission and oxidative stress. Two FRM concentrations (0.4 and 1.6 mg mL^-1) present in the water at ecologically relevant concentrations were used to study their toxicity. No significant differences were found in growth, survival and feeding behaviour of nauplii, after 2 days of exposure to both FRM concentrations. However, in juveniles, survival decreased after 5 days of exposure to FRM1.6; but no significant differences were found in either growth or feeding behaviour. It was observed that nauplii and juveniles, under short-term exposure, had the ability to ingest and egest FRM particles, although their accumulation was higher in nauplii than in juveniles, maybe related with the capacity of the latter to empty their gut content faster, in the presence of food. Regarding biomarkers responses in nauplii, all enzymatic activities increased significantly, after short-term exposure to the higher FRM concentration tested (FRM1.6), which could be related with detoxifying MPs-triggered oxidative stress. In juveniles, the inhibition of ChE and the decrease in the activity of antioxidant enzymes, after 5 days of exposure to FRM1.6, might indicate a neurotoxic effect and oxidative damage induced by FRM. This study provides further evidences that accumulation of MPs in the gut by nauplii and juveniles of A. franciscana can induce negative effects on important physiological processes with influence on their health, highlighting the general concern about the negative effects of MPs pollution on aquatic species, as well as the need to understand the mechanism of MPs toxicity and its possible impacts on environmental safety. Graphical abstract.

Effects of nanoplastic on toxicity of azole fungicides (ketoconazole and fluconazole) in zebrafish embryos

The ubiquity of nanoplastics (NPs) raises concerns about their interactions and combined toxicity with other common contaminants. Although azoles are present throughout the natural environment, their interactions with NP are not well known. We investigated the effects of polystyrene (PS) NP on the toxicity of ketoconazole (KCZ) and fluconazole (FCZ) in zebrafish embryos using the developmental toxicity, oxidative-stress-related biochemical parameters, and expression of genes related to neurotoxicity (ache), cardiotoxicity (gata4, bmp4), inflammation (il1b), oxidative stress (sod1, sod2, cyp1a), and apoptosis (bax, bcl2). Co-exposure to NP (1 mg/L) and KCZ/FCZ (1 mg/L) for 96 h reduced the hatching rate, survival rate, and heart rate and increased the malformation rate and catalase activity. The bax/bcl2 ratio, an apoptosis indicator, was higher after NP, KCZ, or FCZ treatment. However, the bax/bcl2 ratio after exposure to NP + KCZ or NP + FCZ was much higher than that after single exposure. Overall, the results indicated that NP aggravated the toxicity of azole by significantly increasing the reactive oxygen species, lipid peroxidation and altering the expression of oxidative-stress- and apoptosis-related genes. The interactive toxicity of PS NP with KCZ/FCZ reported in this study emphasises the need for caution in the release of azole fungicides in the environment.

Microplastics in fishes from an estuary (Minho River) ending into the NE Atlantic Ocean

Wild fish (Cyprinus carpio, Mugil cephalus, Platichthys flesus) from an estuary of the NE Atlantic coast were investigated for plastic contamination (N = 128). From the 1289 particles recovered from fish samples, 883 were plastics. Among these, 84% were fibres and 97% were microplastics. Thirty-six polymers were identified. The number of microplastics (mean ± SD) per individual fish (MP/fish) was 8 ± 6 in C. carpio, 10 ± 9 in M. cephalus and 2 ± 2 in P. flesus. The means of MP/fish per body site were 6 ± 7 in gastrointestinal tract, 0.5 ± 1.1 in gills, 0.3 ± 0.7 in liver and 0.6 ± 1.2 in muscle samples. A few large fibres in liver (≤ 4841 μm) and muscle (≤ 5810 μm) samples were found. The results evidence the existence of high fish contamination by microplastics and reinforce the need of further research on plastic pollution in estuaries.

The time-dependent variations of zebrafish intestine and gill after polyethylene microplastics exposure

Microplastics (MPs) are common environmental contaminants that present a growing health concern due to their increasing presence in aquatic and human systems. However, the mechanisms behind MP effects on organisms are unclear. In this study, zebrafish (Danio rerio) were used as an in vivo model to investigate the potential risks and molecular mechanisms of the toxic effects of polyethylene MPs (45-53 μm). In the zebrafish intestine, 6, 5, and 186 genes showed differential expression after MP treatment for 1, 5, and 10 days, respectively. In the gills, 318, 92, and 484 genes showed differential expression after MP treatment for 1, 5, and 10 days, respectively. In both the intestine and the gills, Gene Ontology (GO) annotation showed that the main enriched terms were biological regulation, cellular process, metabolic process, cellular anatomical entity, and binding. KEGG enrichment analysis on DEGs revealed that the dominant pathways were carbohydrate metabolism and lipid metabolism, which were strongly influenced by MPs in the intestine. The dominant pathways in the gills were immune and lipid metabolism. The respiratory rate of gills, the activity of SOD and GSH in the intestine significantly increased after exposure to MPs compared with the control (p < 0.05), while the activity of SOD did not change in the gills. GSH activity was only significantly increased after MP exposure for 5 days. Also, the MDA content was not changed in the intestine but was significantly decreased in the gills after MP exposure. The activity of AChE significantly decreased only after MPs exposure for 5 days. Overall, these results indicated that MPs pollution significantly induced oxidative stress and neurotoxicity, increased respiratory rate, disturbed energy metabolism and stimulated immune function in fish, displaying an environmental risk of MPs to aquatic ecosystems.

Microplastic pollution in perch (Perca fluviatilis, Linnaeus 1758) from Italian south-alpine lakes

Microplastic particles (MPs) contamination of aquatic environments has raised a growing concern in recent decades because of their numerous potential toxicological effects. Although fish are among the most studied aquatic organisms, reports on MPs ingestion in freshwater environments are still scarce. Thus, there is still much to study to understand the uptake mechanisms, their potential accumulation among the food webs and their ecotoxicological effects. Here, MPs presence in the digestive system of one of the most widespread and commercially exploited freshwater fish, the perch (Perca fluviatilis, Linnaeus 1758), was investigated in four different south-alpine lakes, to assess the extent of ingestion and evaluate its relation to the body health condition. A total of 80 perch specimen have been sampled from the Italian lakes Como, Garda, Maggiore and Orta. Microplastic particles occurred in 86% of the analysed specimens, with average values ranging from 1.24 ± 1.04 MPs fish^-1 in L. Como to 5.59 ± 2.61 MPs fish^-1 in L. Garda. The isolated particles were mainly fragments, except in L. Como where films were more abundant. The most common polymers were polyethylene, polyethylene terephthalate, polyamide, and polycarbonate, although a high degree of degradation was found in 43% of synthetic particles, not allowing their recognition up to a single polymer. Despite the high number of ingested MPs, fish health (evaluated by means of Fulton's body condition and hepatosomatic index) was not affected. Instead, fullness index showed an inverse linear relationship with the number of ingested particles, which suggests that also in perch MPs presence could interfere with feeding activity, as already described for other taxa.

Polystyrene nanoparticles induced neurodevelopmental toxicity in Caenorhabditis elegans through regulation of dpy-5 and rol-6

Micro- and nano- polystyrene particles have been widely detected in environment, posing potential threats to human health. This study was designed to evaluate the neurodevelopmental toxicity of polystyrene nanoparticles (NPs) in Caenorhabditis elegans (C. elegans), to screen crucial genes and investigate the underlying mechanism. In wild-type C. elegans, polystyrene NPs (diameter 50 nm) could concentration-dependently induce significant inhibition in body length, survival rate, head thrashes, and body bending, accompanying with increase of reactive oxygen species (ROS) production, lipofuscin accumulation, and apoptosis and decrease of dopamine (DA) contents. Moreover, pink-1 mutant was demonstrated to alleviate the locomotion disorders and oxidative damage induced by polystyrene NPs, indicating involvement of pink-1 in the polystyrene NPs-induced neurotoxicity. RNA sequencing results revealed 89 up-regulated and 56 down-regulated differently expressed genes (DEGs) response to polystyrene NPs (100 μg/L) exposure. Gene Ontology (GO) enrichment analysis revealed that predominant enriched DEGs were correlated with biological function of cuticle development and molting cycle. Furthermore, mutant strains test showed that the neurodevelopmental toxicity and oxidative stress responses induced by 50 nm polystyrene NPs were regulated by dpy-5 and rol-6. In general, polystyrene NPs induced obvious neurodevelopmental toxicity in C. elegans through oxidative damage and dopamine reduction. Crucial genes dpy-5 and rol-6 might participate in polystyrene NPs-induced neurodevelopmental toxicity through regulation on synthesis and deposition of cuticle collagen.

Combined toxicity of micro/nano scale polystyrene plastics and ciprofloxacin to Corbicula fluminea in freshwater sediments

Plastic pollution has become a global environmental threat, and its potential to affect the bioavailability and toxicity of pharmaceuticals to aquatic organism are of growing concern. However, little is known regarding the combined toxicity of micro/nano-plastics and pharmaceuticals to benthic organisms in sediments. Thus, we employed a freshwater benthic bivalve, Corbicula fluminea (C. fluminea), to investigate the individual and co-toxicity of model plastics, microscopic fluorescent polystyrene (PS) (PS nano-plastic (PS-NP) and PS micro-plastic (PS-MP), 80 nm and 6 μm, respectively) and the common antibiotic ciprofloxacin (CIP) in formulated sediments. Our results suggest that oxidative damage and neurotoxicity were confirmed to occur in C. fluminea in all the treatments. The oxidative damage in the digestive glands reduced the clam ability to scavenge free radicals, causing severe tissue damage to the digestive glands of C. fluminea. Filtration rates of C. fluminea were significantly decreased in a concentration-dependent manner across all the treatments, which might be due to the inhibition of acetylcholinesterase activities. Interactions between CIP and micro/nano-plastic were observed, whereby the presence of PS decreased the toxicity of CIP in the digestive glands but aggravated the C. fluminea siphoning inhibition rate in the nano-plastic co-treatments group; in addition, the CIP toxicity to C. fluminea decreased because that the concentration of free dissolved CIP was lowered by micro/nano-PS. Taken together, the current study could contribute greatly to evaluating the ecological risk of CIP and PS in aquatic environments and sheds light on potential issues of food safety caused by both emerging pollutants.

miR-217 through SIRT1 regulates the immunotoxicity of cadmium in Cyprinus carpio

MicroRNAs (miRNAs) play a critical role in regulating the response of animals exposed to heavy metal stress. As a globally dispersed heavy metal in aquatic ecosystems, cadmium (Cd) is highly toxic to many aquatic species. However, little is known about the miRNA response to Cd stress in fish. To investigate the regulatory effect of miRNAs in response to Cd, common carp (Cyprinus carpio) were exposed to Cd²⁺-containing water (0.005 mg/L, 0.05 mg/L, 0.5 mg/L) for 30 days. After exposure, Cd²⁺ contents were significantly higher in the kidneys of C. carpio compared to other tissues, when exposed to 0.5 mg/L Cd²⁺. Hematoxylin and eosin staining images revealed that elevated Cd induced inflammatory damage in the kidneys of C.carpio. Further, miRNA sequencing revealed nine differentially expressed miRNAs (miR-217, miR-205 and seven novel miRNAs) in the kidneys, between 0.5 mg/L Cd²⁺ exposure and control groups. Potential target mRNAs of miRNAs suggest that miR-217 is involved in immunotoxicity. miR-217 agomir was intraperitoneally administered to C. carpio and RT-PCR revealed that the expression of IL-8 and SIRT1 decreased, while TLR-4, TRAF6, NF-kB, TNF-α, IL-1β, and TGF-β increased in the kidneys of C.carpio. Additionally, the expression of SIRT1 decreased, while the expression of other mRNAs increased in kidneys of C. carpio exposed to Cd. According to mRNAs expression in the agomir and Cd treatment, miRNAs inhibit the expressions of target mRNAs. These results demonstrate that miR-217 via SIRT1 plays a regulatory role in the immunotoxicity of Cd to C. carpio.

Micro/nanoplastics effects on organisms: A review focusing on 'dose'

Microplastics have become predominant contaminants, attracting much political and scientific attention. Despite the massively-increasing research on microplastics effects on organisms, the debate of whether environmental concentrations pose hazard and risk continues. This study critically reviews published literatures of microplastics effects on organisms within the context of "dose". It provides substantial evidence of the common occurrence of threshold and hormesis dose responses of numerous aquatic and terrestrial organisms to microplastics. This finding along with accumulated evidence indicating the capacity of organisms for recovery suggests that the linear-no-threshold model is biologically irrelevant and should not serve as a default model for assessing the microplastics risks. The published literature does not provide sufficient evidence supporting the general conclusion that environmental doses of microplastics cause adverse effects on individual organisms. Instead, doses that are smaller than the dose of toxicological threshold and more likely to occur in the environment may even induce positive effects, although the ecological implications of these responses remain unknown. This study also shows that low doses of microplastics can reduce whereas high doses can increase the negative effects of other pollutants. The mechanisms explaining these findings are discussed, providing a novel perspective for evaluating the risks of microplastics in the environment.

Long-term adverse effects of microplastics on Daphnia magna reproduction and population growth rate at increased water temperature and light intensity: Combined effects of stressors and interactions

In many ecosystems, the zooplankton community has been pressured simultaneously by microplastic pollution and alterations resulting from global climate changes. The potential influence of light intensity rise (from 10,830 lx to 26,000 lx) and water temperature rise (from 20 °C to 25 °C) on the long term-toxicity of microplastics (MPs) to Daphnia magna were investigated. Three 21-day laboratory bioassays with model MPs (1-5 μm diameter) were carried out at (i) 20 °C/10830 lx, (ii) 20 °C/26000 lx, and (iii) 25 °C/10830 lx. In each bioassay, one control (no MPs) and three MP concentrations (0.04, 0.09, 0.19 mg/L) were tested. In all the bioassays, MPs caused parental and juvenile mortality, and reduced the somatic growth, reproduction and population growth rate. The MP EC₅₀s on living offspring (95% confidence interval within brackets) were 0.146 mg/L (0.142-0.151 mg/L) at 20 °C/10830 lx, 0.102 mg/L (0.099-0.105 mg/L) at 20 °C/26000 lx, and 0.101 mg/L (0.098-0.104 mg/L) at 25 °C/10830 lx. Relatively to the respective control group, 0.19 mg/L of MPs decreased the mean of the population growth rate by 27% at 20 °C/10830 lx, 38% at 20 °C/26000 lx and 59% at 25 °C/10830 lx. Based on the population growth rate and in relation to 20 °C/10830 lx (control, no MPs), the interaction between increased light intensity (26,000 lx) and MPs was synergism (at all the MP concentrations tested). The interaction between water temperature rise (25 °C) and MPs was antagonism at 0.04 mg/L of MPs and synergism at 0.09 and 0.19 mg/L of MPs. In the present scenario of climate changes and global MP pollution such findings raise high concern because zooplankton communities are crucial for aquatic biodiversity conservation, ecosystem functioning and services provided to humans. Further studies on the combined effects of MPs, other common pollutants, and alterations due to climate changes are needed.

Cadmium Accumulation and Depuration in the Muscle of Prussian Carp (Carassius gibelio Bloch) after Sub-Chronic Cadmium Exposure: Ameliorating Effect of Melatonin

Simple Summary

Rapid urbanization and industrialization has resulted in substantial contamination of various ecosystems, especially aquatic environments with heavy metals. Heavy metals are classified as either essential (iron, zinc, or copper) or non-essential (cadmium, lead, or mercury) for organisms. Cadmium is a toxic, cancerogenic, and mutagenic metal, occurring as anthropogenic contamination in aquatic environments. The level of cadmium uptake in animals depends on the rate at which they are accumulated and eliminated. Exceeding the permissible levels of cadmium in fish muscle may pose risks for human health in the case of contaminated fish consumption. The aim of the present study was to evaluate the influence of melatonin on cadmium accumulation and elimination in fish muscle. Prussian carps were exposed to two doses of cadmium in the presence or without the melatonin implants. This is the first study to report that melatonin co-administration can effectively protect fish from the accumulation of cadmium in muscle tissue, improve the accumulated cadmium depuration from muscle, and prevent disturbance of the concentration of essential metals in fish body.

Abstract

The aim of this study was to investigate the bioaccumulation of cadmium in the muscle tissue of Prussian carp during 7 and 13 weeks of exposure to different concentrations of this metal in water (0.4 and 4.0 mg/L), and the depuration of cadmium from muscle during the following 6-week depuration period in the presence of melatonin implants. Furthermore, the relationship between cadmium accumulation and the levels of essential bioelements (copper, zinc, iron) in muscle was evaluated, as well as the bioconcentration factor of cadmium. Heavy metal concentration was determined using atomic absorption spectrometry. Cadmium accumulation in fish muscle increased with the duration of exposure. Cd concentrations exceeded the permissible levels for human consumption in groups exposed to the higher concentration of this metal. Moreover, a significant increase of Zn and Fe levels in the muscle was observed. In the fish that received melatonin implants and were exposed to Cd, its level in the muscle was significantly lower. The depuration of accumulated cadmium depended mainly on the duration of the elimination period. This is the first study to report that melatonin co-administration can effectively protect the fish from the accumulation of cadmium in muscle tissue and changes in trace metal levels.