Biomarker responses in zebrafish (Danio rerio) larvae exposed to pristine low-density polyethylene fragments

Size-dependent effects of microplastic on uptake, immune system, related gene expression and histopathology of goldfish (Carassius auratus)

Todays, with the industrialization of human societies, pollution of aquatic ecosystems with plastics derivatives are a serious concern, affecting the life of their organisms. The present study was conducted to investigate the size effects of micro-plastic, polystyrene on some physiological lesions of the goldfish, Carassius auratus. Fish were exposed to two sizes (0.25 and 8 μm) polystyrene at different environmentally relevant concentrations. The exposure trial was done in two steps. First, fish exposed to a stable concentration of 300 mg/L polystyrene for 168 h. Gill, intestine, and liver tissues were sampled every 24 h to investigate the accumulation of polystyrene. Then, fish were exposed in three replicates to 0 (control), 0.05, 0.5, and 5 mg/L polystyrene in two sizes of 0.25 and 8 μm for 28 days. After the exposure period, gill, liver, and intestine tissues were sampled for histological study, also, serum samples were collected for biochemical assays. Fluorescent microscope observations confirmed the accumulation of polystyrene in tissue samples with time. In addition, histological lesions were found in the liver, intestine, and gill of the exposed fish. The severity of lesions showed a size and dose-dependent pattern. Polystyrene induced the antioxidant system of exposed fish through elevating the levels of SOD and CAT activity and significant difference in expression of antioxidant related genes (CAT, SOD and HSP70). In conclusion, the results of the present study confirmed the toxic effects of microplastic, polystyrene on goldfish.

Adaptation of life-history traits and trade-offs in marine medaka (Oryzias melastigma) after whole life-cycle exposure to polystyrene microplastics

Microplastics are ubiquitous in marine environments and may cause unexpected ecological effects. This study adopted a whole life-cycle exposure to illuminate the impact of polystyrene microplastics on life-history strategies of marine medaka (Oryzias melastigma), including the hatching of embryos, growth and reproduction of F₀ generation, and embryonic and larval development of F₁ offspring. Microplastics accumulated on the eggshell and reduced embryonic hatching rate and larval body length and weight. Similarly, 150 days of microplastic exposure decreased body mass and gonadosomatic index of adult fish, but accelerated sexual maturity of female fish, showing a trade-off between growth and reproduction. Microplastic exposure also caused obvious histopathological damages to gonads and decreased egg productions and fertilization rates. Moreover, parental microplastic exposure induced elevated heartbeats, premature hatching, and slow growth in F₁ offspring. Anti-oxidative stress response, sex hormone disruption, and disturbed transcription of steroidogenic genes in the reproductive axis could partially explain the reproduction impairment and transgenerational trade-offs. Furthermore, transcriptome analysis revealed that the steroid hormone biosynthesis and cytochrome P450 pathways in the testes of male fish were significantly affected after 20 μg/L microplastic exposure. These findings suggest that microplastic pollution may be an emerging threat to the sustainability of marine fish population.

Nano and microplastic interactions with freshwater biota - Current knowledge, challenges and future solutions

Current understanding of nano- and microplastic movement, propagation and potential effects on biota in freshwater environments is developing rapidly. Still, there are significant disconnects in the integration of knowledge derived from laboratory and field studies. This review synthesises the current understanding of nano- and microplastic impacts on freshwater biota from field studies and combines it with the more mechanistic insights derived from laboratory studies. Several discrepancies between the field and laboratory studies, impacting progress in process understanding, were identified including that the most prevalent plastic morphologies found in the field (fibres) are not those used in most of the laboratory studies (particles). Solutions to overcome these disparities are proposed to aid comparability of future studies. For example, environmental sampling and separation of biota into its constituents is encouraged when conducting field studies to map microplastic uptake preferences. In laboratory studies, recommendations include performing toxicity studies to systematically test possible factors affecting toxicity of nano- and microplastics, including morphology, chemical makeup (e.g., additives) and effects of plastic size. Consideration should be given to environmentally relevant exposure factors in laboratory studies, such as realistic exposure medium and effects of plastic ageing. Furthermore, based on this comprehensive review recommendations of principal toxicity endpoints for each of the main trophic levels (microbes, primary producers, primary consumers and secondary consumers) that should be reported to make toxicity studies more comparable in the future are given.

Polystyrene microplastics induce apoptosis via ROS-mediated p53 signaling pathway in zebrafish

Microplastic (MP) pollution is ubiquitous and has become an emerging threat to aquatic biota. Recent scientific reports have recorded their toxic impacts at the cellular and organism levels, but the underlying molecular mechanism of their toxicity remains unclear. The present study elucidates an array of molecular events underlying apoptosis in the gills of polystyrene microplastics (PS-MPs) exposed zebrafish (Danio rerio). PS-MPs at different concentrations (10 and 100 μg L^-1) induced the reactive oxygen species (ROS) generation, in turn affecting the oxidative and immune defense mechanism. The expression profile of antioxidant genes cat, sod1, gpx1a and gstp1 were altered significantly. PS-MPs also significantly inhibited the neurotransmission in zebrafish. In addition, the PS-MPs exposure upregulated the expression of p53, gadd45ba, and casp3b resulting in apoptosis. We demonstrate that PS-MPs significantly upregulate the transcriptional pattern of tnfa and ptgs2a which are essential gene markers in inflammatory mechanism. Further, the oxidative damage induced by PS-MPs exposure could lead to cytological damage resulting in altered lamellar structures, capillary dilation, and necrosis in gill histomaps. In conclusion, the findings of this work strongly suggest that PS-MPs induce dose-and time-dependent ROS mediated apoptotic responses in zebrafish. Furthermore, the physiological responses observed in the gills correlate with the above observations and helps in unravelling the potential molecular mechanism underpinning the PS-MPs toxicity in zebrafish.

Single and combined effects of phenanthrene and polystyrene microplastics on oxidative stress of the clam (Mactra veneriformis)

Toxicity of single organic pollutants or microplastics on organisms have been reported widely, however, their combined toxicity on bivalves was rarely investigated. In this paper, single and combined effects of phenanthrene (Phe, 20 μg·L^-1 and 50 μg·L^-1) and polystyrene (PS, 17 μm and 150 μm with 1 mg·L^-1) microplastics on oxidative stress of the clam Mactra veneriformis were assayed under laboratory conditions with biomarkers including superoxide dismutase (SOD), glutathione-S-transferase (GST) and malondialdehyde (MDA). We found that Phe or PS single stress source could induce oxidative stress to clams. Besides, exposed to Phe 50 μg·L^-1 or PS 150 μm caused the reduced expression of SOD and GST activities, leading to potential oxidative injury in clams. At each Phe concentration level, the order of single and combined toxicity on clams was Phe + PS 150 μm > Phe ≈ Phe + PS 17 μm. Phe exhibited a stronger toxic effect on clams than PS. Under joint exposure stress, the toxicity influence of Phe is still dominant. Furthermore, MDA and GST could be considered the most sensitive oxidative stress biomarkers in clams under Phe or PS single and combined exposures, respectively.

Size-dependent adverse effects of microplastics on intestinal microbiota and metabolic homeostasis in the marine medaka (Oryzias melastigma)

Microplastic (MP) is an emerging environmental pollutant and exposure to MPs has been associated with numerous adverse health outcomes in both wild and laboratory animals. The toxicity of MPs depends on concentration, exposure time, chemical composition and size distribution, but the impacts of particle size remain inconclusive yet. In this study, adult marine medaka (Oryzias melastigma) were exposed to different size of polystyrene MPs (PS-MPs) with concentration of 10 mg/L for 60 days and the growth performance, lipid metabolism, immune parameters and gut microbiome were determined. Results indicated that particle size is a dominant factor causing lipid metabolism disorders and hepatic toxicity in PS-MPs-exposed fish. The bodyweight, adipocyte size and hepatic lipid contents were significantly increased in 200 μm PS-MPs-exposed fish, while 2 and 10 μm PS-MPs-exposed fish exhibited liver injury principally manifested asthepresence oflittlefibrosis and inflammation. Given that larger particles could not enter the circulatory system, the impacts of PS-MPs on intestinal microbial biota homeostasis were further investigated. The results not only showed the characterization of gut microbial communities in Oryzias melastigma, but also indicated that microbial diversity and composition were altered in gut of fish exposed to PS-MPs, in particular 200 μm PS-MPs. The differentially abundant bacterial taxa in PS-MPs-exposed fish mainly belonged to the phylum Verrucomicrobia, Firmicutes and Fusobacteria. And furthermore, increased abundance of Verrucomicrobia and Firmicutes/Bacteroidetes ratio and decreased Fusobacteria were correlated with the increased bodyweight. Intestinal microbiome should play a critical role in regulating host lipid metabolism in fish exposed to lager size of PS-MPs.

Toxic effects of naturally-aged microplastics on zebrafish juveniles: A more realistic approach to plastic pollution in freshwater ecosystems

We aim at evaluating the toxicity of naturally-aged polystyrene microplastics (MPs) in Danio rerio at intermediate development stage. Animal models were stactically exposed to 4 × 10⁴ and 4 × 10⁶ microparticles/m³ for five days - this concentration is environmentally relevant. We evaluated MP's impact on animals' nutritional status and REDOX balance, as well as its potential neuro- and cytotoxic action on them. Initially, MPs did not induce any change in total carbohydrates, triglycerides and total cholesterol levels. MP accumulation was associated with oxidative stress induction, which was inferred by the nitrite and thiobarbituric acid reactive substances levels. Furthermore, we observed that such stress was not counterbalanced by increase in the assessed enzymatic (total glutathione, catalase and superoxide dismutase) and non-enzymatic (total thiols, reduced glutathione and DPPH radical scavenging activity) antioxidants. The association between high acetylcholinesterase activity and numerical changes in neuroblasts distributed on animals' body surface confirmed MP's neurotoxic potential. MP's ability to induce apoptosis and necrosis processes in animals' erythrocytes suggested its cytotoxic action; therefore, the present study is pioneer in providing insight on how MPs can affect young freshwater fish at environmental concentrations. It is essential knowing the magnitude of these pollutants' impact on the ichthyofauna.

Long Term Exposure to Virgin and Recycled LDPE Microplastics Induced Minor Effects in the Freshwater and Terrestrial Crustaceans Daphnia magna and Porcellio scaber

The effects of microplastics (MP) are extensively studied, yet hazard data from long-term exposure studies are scarce. Moreover, for sustainable circular use in the future, knowledge on the biological impact of recycled plastics is essential. The aim of this study was to provide long-term toxicity data of virgin vs recycled (mechanical recycling) low density polyethylene (LDPE) for two commonly used ecotoxicity models, the freshwater crustacean Daphnia magna and the terrestrial crustacean Porcellio scaber. LDPE MP was tested as fragments of 39.8 ± 8.82 µm (virgin) and 205 ± 144 µm (recycled) at chronic exposure levels of 1–100 mg LDPE/L (D. magna) and 0.2–15 g LDPE/kg soil (P. scaber). Mortality, reproduction, body length, total lipid content, feeding and immune response were evaluated. With the exception of very low inconsistent offspring mortality at 10 mg/L and 100 mg/L of recycled LDPE, no MP exposure-related adverse effects were recorded for D. magna. For P. scaber, increased feeding on non-contaminated leaves was observed for virgin LDPE at 5 g/kg and 15 g/kg. In addition, both LDPE induced a slight immune response at 5 g/kg and 15 g/kg with more parameters altered for virgin LDPE. Our results indicated different sublethal responses upon exposure to recycled compared to virgin LDPE MP.

Micro-plastic pollution along the Bay of Bengal coastal stretch of Tamil Nadu, South India

In the present-day context, micro-plastic particles in a marine environment are increasingly ubiquitous and of considerable persistence. In line with the micro-plastic pollution, the present contribution is devoted to the investigation of micro-plastic particles (MPs) along the urban sandy beach called Marina, the renowned longest beach in India. Along the sea coast of about 5 km, the quantification of micro-plastic particles using optical microscope evidenced the granular, filamentous, filmy and tubular fragments in a total of 72 marine samples including those filtered in the marine water column (WAT; 24 samples), those found in wet sediment (WET; 24 samples) and those found in dry sand (DSS; 24 samples). The filamentous-typed plastics of 79%, 57% and 52%, respectively in WET, WAT and DSS dominated over the other granular and tubular types. The micro-plastic particles were in the range of 60-820 items per m³, 60-1620 items per kg and 20-1540 items per kg for WAT, WET and DSS, respectively. The standard deviation for the microplastics abundance were 193.1, 396.6 and 364.6 for WAT, WET and DSS respectively. Upon visual inspection, the micro particles were observed in eight different colors and most of the samples were found to contain two different fragment types. Apart from the optical microscopic examination, the micro-plastics particles were studied by scanning electron microscope (SEM) coupled with elemental analysis by energy dispersive spectroscopy (EDS). The energy spectral graphs displayed that the micro-filaments and micro-tubular particles contained polyesters and fluoro-polymers. The presence of few micro-filaments of polypropylene and polyethylene was also evidenced from their atomic percentage values of carbon of about 88% and 93%, respectively. The presence of fluoro-polymers and polyesters was also confirmed by Fourier Transform Infra-Red (FTIR). Excepting the fluoro-polymers, the micro-plastics particles contained elements arising from sea water (Na, Cl, S, Mg, Ca, K). Heavy metals such as Cu, Mn, Mo, Ru and Rh were observed in micro-tubular fragments. Fe and Ti elements were detected with the highest atomic percentage of 17.19 and 19.84 in micro-tubular fragments. All the observations and analyses give a photography of the nature and the spatial distribution of MPs along this Indian beach.

Toxicity of polystyrene microplastics on juvenile Oncorhynchus mykiss (rainbow trout) after individual and combined exposure with chlorpyrifos‎

Microplastic (MP) sorption and transfer of chemical contaminants has been widely reported, yet few studies have investigated combined effects of contaminant-loaded MPs on organisms. This study examined effects of pristine or chlorpyrifos (CPF)-loaded polystyrene (PS)‎ fragments on histopathological and histomorphometrical biomarkers in rainbow trout (Onchorhynchus mykiss)‎. In laboratory, O. mykiss were exposed for 96 h to pristine PS-MPs concentrations (30 or 300 µg/L), concentrations of CPF ‎alone (2 or ‎‎6 µg/L), and the same concentrations of CPF in the presence of PS-MPs in aquaria‎. Results showed the highest histopathological alterations in both CPF concentrations and when combined with PS-MPs in fish gills. Alternatively, high histopathological lesions including massive necrosis, infiltration of inflammatory cells, and shed of villi tips were observed in fish gut in high CPF concentrations combined with high PS-MP concentrations of ‎(6 μg/L CPF+300 μg/L PS-‎MPs). Individual CPF and PS-MP concentrations or combined together showed significant changes in histomorphometrical biomarkers in fish gills, gut and skin. Findings highlight that pristine PS-MPs cause toxicity and increase adverse effects of CPF in O. mykiss, especially in gill tissue. We present evidence that pristine short-term exposure to even low concentrations of PS-MPs has a significant impact on biomarker responses in O. mykiss.

The need to investigate continuums of plastic particle diversity, brackish environments and trophic transfer to assess the risk of micro and nanoplastics on aquatic organisms

Plastic particles are ubiquitous in marine and freshwater environments. While many studies have focused on the toxicity of microplastics (MPs) and nanoplastics (NPs) in aquatic environments there is no clear conclusion on their environmental risk, which can be attributed to a lack of standardization of protocols for in situ sampling, laboratory experiments and analyzes. There are also far more studies concerning marine environments than fresh or brackish waters despite their role in the transfer of plastics from continents to oceansWe systematically reviewed the literature for studies: (1) using plastics representative of those found in the environment in laboratory experiments, (2) on the contamination of plastic particles in the continuum between fresh and marine waters, focusing in particular on estuaries and (3) on the continuum of contamination of plastic particles between species through trophic transfer in aquatic environments. We found that the exposure of aquatic organisms in the laboratory to plastic particles collected in the environment are very scarce. Moreover, plastic exposures of estuarine species in the laboratory are generally carried out for a single salinity and a single temperature that do not reflect the fluctuating environmental conditions of estuaries. Finally, the trophic transfer of plastic particles is mainly studied in the laboratory through simple food chains which are not representative of the complexity of the trophic networks observed in the aquatic environment. We pointed out that future studies in the laboratory should include both MPs and NPs sampled in the environment and focus on the precise characterization of the composition and surface of these plastics as well as on their absorbed pollutants, additives or biofilms. Moreover, investigations must be continued concerning the toxicity of plastic particles in brackish water environments such as estuaries and the trophic transfer of plastic particles in complex food chains.

Toxicological effects induced on early life stages of zebrafish (Danio rerio) after an acute exposure to microplastics alone or co-exposed with copper

Data about the toxicological interactions of MPs and heavy metals in biota is limited, particularly in fish early life stages. This study aimed to evaluate the toxicological effects of MPs and copper (Cu), alone or combined, in zebrafish early life stages. Embryos were exposed from 2 until 96-h post-fertilization (hpf) to MPs (2 mg/L), three sub-lethal concentrations of Cu (15, 60 and 125 μg/L) and binary mixtures containing Cu and MPs (Cu15+MPs, Cu60+MPs, Cu125+MPs). Lethal and sub-lethal parameters, histopathological changes, biochemical biomarkers, gene expression and behavior were assessed. Our findings showed that Cu and Cu + MPs decreased embryos survival and hatching rate. Increased ROS levels were observed in larvae exposed to the two lowest Cu and Cu + MPs groups, suggesting an induction of oxidative stress. An increased CAT and GPx activities were observed in Cu and Cu + MPs, implying a response of the antioxidant defense system to overcome the metal and MPs stress. The sod1 expression was downregulated in all Cu groups and in the two highest Cu + MPs exposed groups. AChE was significantly inhibited in Cu and Cu + MPs groups, indicating neurotoxicity. A disruption of avoidance and social behaviors were also noticed in the Cu125 and Cu125+MPs exposed larvae. Evidences of Cu-toxicity modulation by MPs were observed in some endpoints. Overall, the findings of this study highlight that Cu alone or co-exposed with MPs lead to oxidative stress, neurotoxicity and ultimately behavioral alterations in early life stages of zebrafish, while MPs alone do not produce significant effects on zebrafish larvae.

Micro-contextual identification of archaeological lipid biomarkers using resin-impregnated sediment slabs

Characterizing organic matter preserved in archaeological sediment is crucial to behavioral and paleoenvironmental investigations. This task becomes particularly challenging when considering microstratigraphic complexity. Most of the current analytical methods rely on loose sediment samples lacking spatial and temporal resolution at a microstratigraphic scale, adding uncertainty to the results. Here, we explore the potential of targeted molecular and isotopic biomarker analysis on polyester resin-impregnated sediment slabs from archaeological micromorphology, a technique that provides microstratigraphic control. We performed gas chromatography-mass spectrometry (GC-MS) and gas chromatography-isotope ratio mass spectromety (GC-IRMS) analyses on a set of samples including drill dust from resin-impregnated experimental and archaeological samples, loose samples from the same locations and resin control samples to assess the degree of interference of polyester resin in the GC-MS and Carbon-IRMS signals of different lipid fractions (n-alkanes, aromatics, n-ketones, alcohols, fatty acids and other high polarity lipids). The results show that biomarkers within the n-alkane, aromatic, n-ketone, and alcohol fractions can be identified. Further work is needed to expand the range of identifiable lipid biomarkers. This study represents the first micro-contextual approach to archaeological lipid biomarkers and contributes to the advance of archaeological science by adding a new method to obtain behavioral or paleoenvironmental proxies.

Effects of chronic exposure to microplastics of different polymer types on early life stages of sea trout Salmo trutta

The aim of the present study was to determine the effect of a long-term (113 days) exposure to microplastics on the development and induction of endocrine, geno- and cytotoxic responses in early life stages of sea trout Salmo trutta. Microplastic particles (3000 μm) of three most commonly mass-produced polymers (polystyrene - PS, polyethylene terephthalate - PET and polyethylene - PE) were applied in environmentally realistic concentrations (0.1% of sediment dry weight) in a laboratory experiment imitating the natural environment, typical for sea trout spawning grounds. The exposure of the sea trout, from fertilized eggs to mobile yolk-sac larvae, to microplastics did not affect the hatching success (the survival of embryos), hatching rate and the incubation period. Microplastics of any tested polymer type also had no adverse effect on the larvae survival, growth rate and the rate of yolk sack absorption. Similarly, no changes in frequencies of detected cytotoxicity endpoints compared to the control group were recorded. Exposure to polymer particles induced however the formation of genotoxicity endpoints (nuclear buds, micronuclei and blebbed nuclei cells). The level of total genotoxicity (ΣGentox) in fish larvae erythrocytes increased significantly in the following sequence: PS > PET > PE. No significant changes in the whole body corticosterone, dehydrocorticosterone and cortisone concentrations due to exposure to microplastics were recorded, while cortisol was detected in larvae exposed to PS. Our results show that long-term, non-ingestion related exposure to microplastics does not affect development of S. trutta early life stages but may lead to genotoxic responses. PS seems to be the most hazardous among all polymers studied. This is the first study demonstrating non-ingestion related toxicity of microplastics to the early life stages of fish.

Quality Criteria for Microplastic Effect Studies in the Context of Risk Assessment: A Critical Review

In the literature, there is widespread consensus that methods in plastic research need improvement. Current limitations in quality assurance and harmonization prevent progress in our understanding of the true effects of microplastic in the environment. Following the recent development of quality assessment methods for studies reporting concentrations in biota and water samples, we propose a method to assess the quality of microplastic effect studies. We reviewed 105 microplastic effect studies with aquatic biota, provided a systematic overview of their characteristics, developed 20 quality criteria in four main criteria categories (particle characterization, experimental design, applicability in risk assessment, and ecological relevance), propose a protocol for future effect studies with particles, and, finally, used all the information to define the weight of evidence with respect to demonstrated effect mechanisms. On average, studies scored 44.6% (range 20-77.5%) of the maximum score. No study scored positively on all criteria, reconfirming the urgent need for better quality assurance. Most urgent recommendations for improvement relate to avoiding and verifying background contamination, and to improving the environmental relevance of exposure conditions. The majority of the studies (86.7%) evaluated on particle characteristics properly, nonetheless it should be underlined that by failing to provide characteristics of the particles, an entire experiment can become irreproducible. Studies addressed environmentally realistic polymer types fairly well; however, there was a mismatch between sizes tested and those targeted when analyzing microplastic in environmental samples. In far too many instances, studies suggest and speculate mechanisms that are poorly supported by the design and reporting of data in the study. This represents a problem for decision-makers and needs to be minimized in future research. In their papers, authors frame 10 effects mechanisms as "suggested", whereas 7 of them are framed as "demonstrated". When accounting for the quality of the studies according to our assessment, three of these mechanisms remained. These are inhibition of food assimilation and/or decreased nutritional value of food, internal physical damage, and external physical damage. We recommend that risk assessment addresses these mechanisms with higher priority.

Microbial remediation of micro-nano plastics: Current knowledge and future trends

An alarming rise of micro-nano plastics (MNPs) in environment is currently causing the biggest threat to biotic and abiotic components around the globe. These pollutants, apart from being formed through fragmentation of larger plastic pieces and are also manufactured for commercial usage. MNPs enter agro-ecosystem, wildlife, and human body through the food chain, ingestion or through inhalation, causing blockage in the blood-brain barrier, lower fertility, and behavioural abnormalities among other problems. Hence, it becomes essential to develop novel procedures for remediation of MNPs. Among the numerous existing methods, microbial remediation promises to degrade/recover MNPs via a green route. Since microbial remediation processes mostly depend upon biotic and abiotic factors such as (temperature, pH, oxidative stress, etc.), it becomes easy to influence changes in the plastic pollutants. Hence, with the help of recent technologies, a complete degradation/removal of MNPs can be expected by utilizing the respective carbon content as energy sources for growth of microorganisms. In this review, considering the urgent environmental need, the impact of micro-nano plastics on ecosystem along with its corresponding degradation mechanisms has been brought out. Also, importance of the various recent research approaches in MNPs remediation is highlighted. Finally, the role of enzyme and membrane technology, nanoparticle technology, and metagenomics in remediation of MNPs are discussed for the first time in detail to bring out a novel remedy for the environment.

Microplastics and sorbed contaminants - Trophic exposure in fish sensitive early life stages

The present study evaluated very small microplastic particle (MPs) transfer to zebrafish and marine medaka larvae via prey experimentally exposed to MPs from the onset of feeding. Larvae were fed Paramecium or Artemia nauplii loaded with fluorescent 1-5 or 10-20 μm MP. Pollutant accumulation was analyzed by optically tracking of benzo[a]pyrene (BaP) and recording cyp1a transcription. Paramecium transferred 1-5 μm particles only, whereas Artemia efficiently transferred both MPs. Although zebrafish and medaka larvae fed from the onset of active food intake (2-3 dph, respectively) on Paramecium and from days 6-7 post-hatch on Artemia nauplii, neither MP accumulation nor translocation to tissues was detected. MP egestion started within few hours after ingestion. Cyp1a induction and fluorescent analyses proved BaP bioavailability after transfer via Paramecium and Artemia. Unicellular or plankton organisms ingest contaminants via MPS and transfer effectively these to sensitive early life-stages of vertebrates, giving rise to whole-life exposure.

Polyvinyl chloride (PVC) plastic fragments release Pb additives that are bioavailable in zebrafish

Plastic polymers such as polyvinyl chloride (PVC) may contain chemical additives, such as lead (Pb), that are leachable in aqueous solution. The fragmentation into microplastics (MPs) of plastics such as PVC may facilitate desorption of chemical additives and increase exposure of aquatic animals. In this study, the role of chemical additives in the aqueous toxicity of PVC, high-density polyethylene (HDPE) and polyethylene terephthalate (PET) MPs were investigated in early-life stage zebrafish (Danio rerio) by assessment of changes in expression of biomarkers. Exposure of zebrafish larvae to PVC for 24 h increased expression of metallothionein 2 (mt2), a metal-binding protein, but no changes in expression of biomarkers of estrogenic (vtg1) or organic (cyp1a) contaminants were observed. HDPE and PET caused no changes in expression of any biomarkers. A filtered leachate of the PVC also caused a significant increase in expression of mt2 and indicated that a desorbed metal additive likely elicited the response in zebrafish. Metal release was confirmed by acid-washing the MPs which mitigated the response in mt2. Metal analysis showed Pb leached from PVC into water during exposures; at 500 mg PVC L^-1 in water, 84.3 ± 8.7 μg Pb L^-1 was measured after 24 h. Exposure to a Pb-salt at this concentration caused a comparable mt2 increase in zebrafish as observed in exposures to PVC. These data indicated that PVC MPs elicited a response in zebrafish but the effect was indirect and mediated through desorption of Pb from PVC into the exposure water. Data also indicated that PVC MPs may act as longer-term environmental reservoirs of Pb for exposure of aquatic animals; the Pb leached from PVC in 24 h in freshwater equated to 2.52% of total Pb in MPs leachable by the acid-wash. Studies of MPs should consider the potential role of chemical additives in toxicity observed.

Zebrafish: An emerging model to study microplastic and nanoplastic toxicity

Microplastics (MPs) and nanoplastics (NPs) have received global concern due to its widespread contamination, ingestion in aquatic organisms and the ability to cross the biological barrier. However, our understanding of its bioaccumulation, toxicity, and interaction with other environmental pollutants is limited. Zebrafish is increasingly used to study the bioaccumulation and toxicity of environmental contaminants because of their small size, ease of breed, short life cycle and inexpensive maintenance. The transparent nature of zebrafish embryo and larvae provides excellent experimental advantages over other model organisms in studying the localization of fluorescent-labeled MPs/NPs particles. Zebrafish outplays the traditional rodent models with the availability of transgenic lines, high-throughput sequencing and genetic similarities to humans. All these characteristics provide an unprecedented opportunity to investigate the toxicity of MPs/NPs and associated contaminants. This review summarizes the existing literature on MPs/NPs research in zebrafish and suggests a path forward for future research.

Neonicotinoids caused oxidative stress and DNA damage in juvenile Chinese rare minnows (Gobiocypris rarus)

To assess the effects of neonicotinoid insecticides on fish, juvenile Chinese rare minnows (Gobiocypris rarus) were exposed to 0.1, 0.5, or 2.0 mg/L neonicotinoid insecticides (imidacloprid, nitenpyram, and dinotefuran) for 60 days. The endpoints, including oxidative stress and DNA damage, were determined. The results of oxidative stress assays showed that SOD activities were significantly increased in the 2.0 mg/L imidacloprid and 0.5 mg/L nitenpyram and dinotefuran treatments (p < 0.05). CAT activity was significantly increased with 0.1 mg/L nitenpyram (p < 0.05), whereas it was significantly decreased in the 0.1 and 2.0 mg/L dinotefuran treatment groups (p < 0.05). Moreover, MDA content was significantly decreased in all imidacloprid treatments and in the 0.5 and 2.0 mg/L dinotefuran treatments (p < 0.05); however, it was significantly increased in the 0.1 mg/L nitenpyram treatment (p < 0.05). GSH content was significantly increased at all treatments except for the 0.5 mg/L dinotefuran treatment (p < 0.05). The transcript expression results showed that gstm mRNA expression was significantly inhibited by 0.5 and 2.0 mg/L imidacloprid, and gstp1 mRNA expression was significantly inhibited by all nitenpyram treatments (p < 0.05). In addition, ugt1a mRNA expression was significantly inhibited in the 0.5 mg/L nitenpyram treatment (p < 0.05). The results of the DNA damage assay showed that tail moments were significantly increased by the 2.0 mg/L imidacloprid treatment (p < 0.01), while tail DNA was significantly increased by 0.5 and 2.0 mg/L imidacloprid, 2.0 mg/L nitenpyram and all dinotefuran treatments (p < 0.01). Moreover, olive tail moments were significantly increased by the 0.5 and 2.0 mg/L imidacloprid and 2.0 mg/L dinotefuran treatments (p < 0.01). Therefore, our oxidative stress and DNA damage findings demonstrated that imidacloprid and nitenpyram could cause adverse effects on juvenile rare minnows.

Exposure to pet-made microplastics: Particle size and pH effects on biomolecular responses in mussels

This study aims to evaluate the expression of biomarkers of oxidative stress (LPO, GPx, AtCh, SOD) in mussels (Mytilus galloprovincialis) following the exposure to suspensions of microparticles irregular shaped fibres of Polyethylene terephthalate of different sizes (small 5-60 μm, S-PET; medium 61-499 μm, M-PET; large 500-3000 μm, L-PET) at a single dose of 0.1 g/L. Mussels were tested under two different starting pH conditions of marine water: standard (8.0) and acidified (7.5). The results obtained from this study show that: i) PET microplastics are able to induce biochemical stress in mussels; ii) among the biomarkers tested, LPO and GPx were more effective in detecting the stress induced by microplastic in both initial pH conditions; iii) the expression of biomarkers was influenced by the size of the microparticle. In particular, greater effects were associated with the largest PET particle tested (0.5-3.0 mm); iv) regarding the effect of pH, in experiments starting from 7.5 pH the animals showed a lower biomarker expression than those starting from 8.0 pH.

The plastic brain: neurotoxicity of micro- and nanoplastics

Given the global abundance and environmental persistence, exposure of humans and (aquatic) animals to micro- and nanoplastics is unavoidable. Current evidence indicates that micro- and nanoplastics can be taken up by aquatic organism as well as by mammals. Upon uptake, micro- and nanoplastics can reach the brain, although there is limited information regarding the number of particles that reaches the brain and the potential neurotoxicity of these small plastic particles.

Earlier studies indicated that metal and metal-oxide nanoparticles, such as gold (Au) and titanium dioxide (TiO₂) nanoparticles, can also reach the brain to exert a range of neurotoxic effects. Given the similarities between these chemically inert metal(oxide) nanoparticles and plastic particles, this review aims to provide an overview of the reported neurotoxic effects of micro- and nanoplastics in different species and in vitro. The combined data, although fragmentary, indicate that exposure to micro- and nanoplastics can induce oxidative stress, potentially resulting in cellular damage and an increased vulnerability to develop neuronal disorders. Additionally, exposure to micro- and nanoplastics can result in inhibition of acetylcholinesterase activity and altered neurotransmitter levels, which both may contribute to the reported behavioral changes.

Currently, a systematic comparison of the neurotoxic effects of different particle types, shapes, sizes at different exposure concentrations and durations is lacking, but urgently needed to further elucidate the neurotoxic hazard and risk of exposure to micro- and nanoplastics.

Interaction of Environmental Pollutants with Microplastics: A Critical Review of Sorption Factors, Bioaccumulation and Ecotoxicological Effects

Microplastics have become one of the leading environmental threats due to their persistence, ubiquity and intrinsic toxic potential. The potential harm that microplastics impose on ecosystems varies from direct effects (i.e., entanglement and ingestion) to their ability to sorb a diversity of environmental pollutants (e.g., heavy metals, persistent organic compounds or pharmaceuticals). Therefore, the toxicological assessment of the combined effects of microplastics and sorbed pollutants can produce in biota is one of the hottest topics on the environmental toxicology field. This review aims to clarify the main impacts that this interaction could have on ecosystems by (1) highlighting the principal factors that influence the microplastics sorption capacities; (2) discussing the potential scenarios in which microplastics may have an essential role on the bioaccumulation and transfer of chemicals; and (3) reviewing the recently published studies describing toxicological effects caused by the combination of microplastics and their sorbed chemicals. Finally, a discussion regarding the need for a new generation of toxicological studies is presented.

Enhanced adsorption of tetrabromobisphenol a (TBBPA) on cosmetic-derived plastic microbeads and combined effects on zebrafish

Microplastics (MPs) pollution and its potential environmental risks have drawn increasing concerns in recent years. Among which, microbeads in personal care and cosmetic products has becoming an emerging issue for their abundance as well as the knowledge gaps in their precise environmental behaviors in freshwater. The present study investigated the sorption process of tetrabromobisphenol A (TBBPA), the most widely applied and frequently encountered flame retardant in aquatic environments, on two sources of polyethylene (PE) particles (pristine PE particles and microbeads isolated from personal care and cosmetic products). Significantly enhanced adsorption capacity of microbeads was observed with up to 5-folds higher than the pristine PE particles. The sorption efficiency was also governed by solution pH, especially for the cosmetic-derived microbeads, indicating the strong adsorption of TBBPA on PE was dominated by both hydrophobic and electrostatic interactions. Additionally, combined effects on redox status of zebrafish were evaluated with two environmental relevant concentrations of PE particles (0.5 and 5 mg L^-1) using integrated biomarker response (IBR) index through a 14-d exposure. Co-exposure induced significant antioxidative stress than either PE or TBBPA alone when exposed to 0.5 mg L^-1 of MPs. After 7-d depuration, the IBR value for combination treatments [TBBPA + PE (L)] was 3-fold compared with that in MP-free groups, indicating the coexistence might exert a prolonged adverse effects on aquatic organisms. These results highlight the probability of risk from microbead pollution in freshwater, where toxic compounds can be adsorbed on microbeads in a considerable amount resulting in potential adverse effects towards aquatic organisms.

PET microplastics toxicity on marine key species is influenced by pH, particle size and food variations

This study aims to evaluate effects induced by the exposure of key marine species to leachates and suspensions of different particle-size of PET microparticles, a plastic polymer that is actually considered safe for the environment. Leachates and suspensions of small (5-60 μm); medium (61-499 μm) and large (500-3000 μm) PET were tested on bacteria (V. fischeri; UNI EN ISO 11348-3:2009), algae (P. tricornutum; UNI EN ISO 10253:2016E), and echinoderms (P. lividus; EPA 600/R-95-136/Section 15) species both under standard (8.0) and acidified (7.5) pH conditions. Results obtained show that: i) conversely to larval stage of P. lividus, bacterial and algal tested species are not sensitive to PET pollution under all tested conditions; ii) different tested particle-sizes of PET produce effects that are not always related to their particle-size; iii) differences comparing acidified and standard pH conditions were recorded; iv) concerning echinoderms, food availability produce significant differences compared to fasting conditions; v) special attention on the possible interactions between MPs and other stressors (e.g., food and pH) is needed in order to give a better picture of natural occurring dynamics on marine ecosystems especially in the future frame of global changes.

Single-Cell RNA Sequencing Reveals Size-Dependent Effects of Polystyrene Microplastics on Immune and Secretory Cell Populations from Zebrafish Intestines

Microplastics (MPs) as widespread contamination pose a high risk for aquatic organisms. However, the current understanding of MP toxicity is based on cell population-averaged measurements. Our aim was to gain a comprehensive understanding of the size-dependent effects of polystyrene MPs (PS-MPs) on intestinal cell populations in zebrafish and characterize the interplay of MPs, intestinal cells, and intestinal microbiota. Here, we used single-cell RNA sequencing to determine the transcriptome heterogeneity of 12 000 intestinal cells obtained from zebrafish exposed to 100 nm, 5 μm, and 200 μm PS-MPs for 21 days. Eight intestinal cell populations were identified. Combined with changes in intestinal microbiota, our findings highlight a previously unrecognized end point that all three sizes of PS-MPs induced dysfunction of intestinal immune cells (including effects on phagosomes and the regulation of immune system processes) and increased the abundance of pathogenic bacteria. However, only 100 nm PS-MPs altered the expression of genes related to phagocyte-produced reactive oxygen species (ROS) generation and increased mucus secretion by secretory cells. Microsize PS-MPs specifically changed the lysosome (5 μm) and cell surface receptor signaling (200 μm) processes of the macrophages. Our findings pinpoint to cell-specific and size-dependent responses to PS-MPs in fish intestine, which can provide a reference for future study directions.

Chronic microfiber exposure in adult Japanese medaka (Oryzias latipes)

Microplastic fibers (MFs) pollute aquatic habitats globally via sewage release, stormwater runoff, or atmospheric deposition. Of the synthetic MFs, polyester (PES) and polypropylene (PP) are the most common. Field studies show that fish ingest large quantities of MFs. However, few laboratory studies have addressed host responses, particularly at the organ and tissue levels. Adult Japanese medaka (Oryzias latipes), a laboratory model fish, were exposed to aqueous concentrations of PES or PP MFs (10,000 MFs/L) for 21 days. Medaka egested 1,367 ± 819 PES MFs (0.1 ± 0.04 mg) and 157 ± 105 PP MFs (1.4 ± 0.06 mg) per 24 hrs, with PP egestion increasing over time. Exposure did not result in changes in body condition, gonadosomatic- or hepatosomatic indices. PES exposure resulted in no reproductive changes, but females exposed to PP MFs produced more eggs over time. MF exposure did not affect embryonic mortality, development, or hatching. Scanning electron microscopy (SEM) of gills revealed denuding of epithelium on arches, fusion of primary lamellae, and increased mucus. Histologic sections revealed aneurysms in secondary lamellae, epithelial lifting, and swellings of inner opercular membrane that altered morphology of rostral most gill lamellae. SEM and histochemical analyses showed increased mucous cells and secretions on epithelium of foregut; however, overt abrasions with sloughing of cells were absent. For these reasons, increased focus at the tissue and cell levels proved necessary to appreciate toxicity associated with MFs.

Chronic dietary exposure to polystyrene microplastics in maturing Japanese medaka (Oryzias latipes)

Fish studies report consumption of microplastics (MPs) in the field, and concern exists over associated risks. However, laboratory studies with adult fish are scarce. In this study, outbred and see-through Japanese medaka (Oryzias latipes) were fed diets amended with 500, 1000, or 2000 μg/g 10 μm fluorescent spherical polystyrene microplastics (MPs) for 10 weeks during their maturation from juveniles to spawning adults. No behavioral changes, growth differences, or mortalities occurred. In vivo examinations and histologic sections showed no evidence of translocation of MPs from the gut to other internal organs. Mature females experienced dose-dependent decreases in egg number. Scanning electron microscopic examination of gills and gut revealed MPs in both areas. Swollen enterocytes were observed on apices of gut folds only in exposed fish. These were particularly apparent in foreguts of the high exposure group. Enterocytes with eroded brush borders were found in foregut of high and medium exposure groups. Increased mucus production, in long strands and sheets, was seen over primary and secondary lamellae of gills. Histological analysis showed alteration in buccal cavity, kidney, and spleen. Thickening and roughening of epithelium in headgut and pharynx and cellular alterations in spleen occurred. Head kidney was the primary site of alteration. Glomerulopathy and nephrogenesis were observed in exposed fish, increasing in severity with exposure level.

Polystyrene microplastics cause tissue damages, sex-specific reproductive disruption and transgenerational effects in marine medaka (Oryzias melastigma)

The ubiquity of microplastics in the world's ocean has aroused great concern. However, the ecological effects of microplastics at environmentally realistic concentrations are unclear. Here we showed that exposure of marine medaka (Oryzias melastigma) to environmentally relevant concentrations of 10 μm polystyrene microplastics for 60 days not only led to microplastic accumulation in the gill, intestine, and liver, but also caused oxidative stress and histological changes. Moreover, 2, 20, and 200 μg/L microplastics delayed gonad maturation and decreased the fecundity of female fish. Alterations of the hypothalamus-pituitary-gonadal (HPG) axis were investigated to reveal the underlying mechanisms, and gene transcription analysis showed that microplastic exposure had significantly negative regulatory effects in female HPG axis. Transcription of genes involved in the steroidogenesis pathway in females were also downregulated. This disruption resulted in decreased concentrations of 17β-estradiol (E₂) and testosterone (T) in female plasma. Furthermore, parental exposure to 20 μg/L microplastics postponed the incubation time and decreased the hatching rate, heart rate, and body length of the offspring. Overall, the present study demonstrated for the first time that environmentally relevant concentrations of microplastics had adverse effects on the reproduction of marine medaka and might pose a potential threat to marine fish populations.

Ingestion of polyethylene microbeads affects the growth and reproduction of medaka, Oryzias latipes

Research using various species of wild and cultured fish has identified negative effects of short-term exposure to microbeads. Although wild animals might be contaminated with microbeads and/or other pharmaceuticals, data regarding the long-term effects remain limited. To clearly elucidate the effects of microbeads, studies of long-term exposure using animal models are necessary. Our aim was to elucidate the effects of microbeads alone on the growth and fecundity of medaka following long-term exposure (12 weeks). In experiment 1, fish groups (except controls) were temporarily exposed to polyethylene microbeads (10-63 μm diameter) a low dose of 0.065 microbeads-mg/L and high dose of 0.65 microbeads-mg/L. In experiment 2, see-through medaka and fluorescent polyethylene microbeads (10-45 μm diameter) were used to estimate the retention time of ingested microbeads in the digestive tract, which was 4-9 days. The low dose of microbeads did not affect growth but did decrease the number of eggs and the hatching rate. The high dose decreased growth, the number of eggs, and hatching rate. Growth differences were recognized for the first time at 7 weeks, and differences in the number of eggs at 12 weeks. Thus, long-term tests using medaka indicated that microbeads per se exhibit growth inhibition and reproductive toxicity. These effects could be associated with nutritional factors resulting from the long retention time of microbeads in the digestive tract. We also determined the dose that affects only fecundity. This suggests that normal growth of medaka in the wild does not mean the environment is free from microbead contamination. We are thus attempting to identify new biological indexes for monitoring the status of microbead contamination using our system.

An exploratory ecotoxicity study of primary microplastics versus aged in natural waters and wastewaters

Current understanding of how environmental aging of microplastics contributes to their ecotoxicity is low. We investigated whether incubation of microplastics in waters with different organic load and toxic potential alters the toxicity of microplastics to crustacean Daphnia magna, fish embryos Danio rerio and plant Lemna minor. Polyethylene primary microplastics; specifically microbeads from facial scrub; were subjected to 3-weeks incubation in low affected spring water, river water, effluent from the municipal wastewater treatment plant (WWTP) and municipal landfill leachate. Primary microplastics had no acute effect on D. magna mobility and D. rerio embryos development. While high organic load wastewaters; WWTP effluent and landfill leachate; showed evident toxicity for D. magna and D. rerio embryos, microplastics aged in these wastewaters had no effect. This suggests that adsorption of pollutants from wastewaters to microplastic particles was not high enough to induce acute toxicity to D. magna and D. rerio. On the contrary, primary microplastics affected the root growth of L. minor. Interestingly, aging of microplastics in low organic-load waters mitigated the toxicity of microplastics for L. minor, while microplastics aged in high-organic load waters had the same adverse effect as primary microplastics. Partly, these effects can be explained by different extent of coating on microplastics in different water samples. This study suggests that aging of microplastics in wastewaters and natural waters did not significantly enhance the toxicity to selected test species, but further studies on plants may be of interest.

Acute toxic effects of polyethylene microplastic on adult zebrafish

To identify the physical effects, behavioral changes, and gene expression profiles of the phase 1 detoxification-related gene (cyp 1a) and oogenesis-related gene (vtg 1) induced by microplastics, high-density polyethylene microplastics of various sizes were used because of their dominance in coastal areas and effluent samples in Hong Kong. Adult zebrafish were used as the model organism to identify the upper and lower boundaries of microplastics ingestion and were exposed to individual polyethylene microplastics in five size ranges (10-22 μm, 45-53 μm, 90-106 μm, 212-250 μm, and 500-600 μm) at a concentration of 2 mg/L for 96 h. To study behavioral changes and targeted gene expression profiles via real-time PCR (qPCR), a mixture of microplastics in three size ranges at effluent-related (11 particles/L), moderate (110 particles/L), and high concentrations (1,100 particles/L) were applied for 96 h. The zebrafish behavior was recorded by a video camera and by two observers (interrater reliability, >85%). The results implied that the upper and lower size boundaries for microplastic ingestion were 558.4 ± 26.2 μm (yellow) and 19.7 ± 3.1 μm (red), respectively. In addition, 61 ± 10% of fish in medium concentration treatments and 61 ± 10% of fish in high concentration treatments were found with the microplastic ingestion and remaining in their intestine. In addition, 28 ± 10% of fish in high concentration treatments were found with microplastic retaining in their gills (No. of fishes = 18 in each treatment). The presence of microplastics, which occupied 89 ± 6% of intestine area, reduced the voids inside the intestine for feed. The expression of cyp1a in the intestine (medium concentration) and vtg1 in the liver (medium and high concentration) showed significant up-regulation, and abnormal behavior (i.e., seizures and tail bent downward) was observed (medium and high concentration). In summary, the effects on the aryl hydrocarbon receptor (AHR) pathway, disruption of the oogenesis process, and neurotoxicity could be caused by acute exposure of adult zebrafish to microplastics.

Thyroid endocrine status and biochemical stress responses in adult male Wistar rats chronically exposed to pristine polystyrene nanoplastics

Toxicity evaluations of micro- or nano-sized plastics in rodent species commonly employed for toxicity analyses based on which risk assessment for humans could be performed are still largely lacking. Given this knowledge gap, the present work was aimed at determining the potential impact of chronic exposure to polystyrene nanoplastics (PS NPs) on the thyroid endocrine status and biochemical stress in a rat model. Young adult male rats were orally administered with PS NPs (1, 3, 6 and 10 mg kg^-1 day^-1) for five weeks. Thyroid hormones (THs) l-thyroxine (T4), l-triiodothyronine (T3), l-free triiodothyronine (FT3), and l-free thyroxine (FT4) as well as thyroid stimulating hormone (TSH) serum levels of normal rats and those exposed to PS NPs were compared. Serum levels of high-density lipoprotein (HDL), low-density lipoprotein (LDL), cholesterol, and creatinine, as well as glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) enzymes were also measured. Exposure to PS NPs suppressed the serum levels of T3 and circulating levels of THs, whereas TSH increased significantly. Though exposure to PS NPs did not affect the molar ratios of T3/T4, it induced a slight, but significant, increase in FT3/FT4. In addition, exposure to plastic nanoparticles showed signs of nephrotoxicity induction and kidney injury in exposed organisms as can be inferred from the significantly higher serum levels of creatinine in exposed groups. Our results provide clear evidence of an association between exposure to plastic NPs and thyroid endocrine disruption as well as metabolic deficit, and generate new leads for future research efforts.

First account of plastic pollution impacting freshwater fishes in the Amazon: Ingestion of plastic debris by piranhas and other serrasalmids with diverse feeding habits

Reported here is the first evidence of plastic ingestion by freshwater fishes in the Amazon. Plastic bags, bottles, fishing gear, and other products are entering Amazonian water bodies and degrade into meso- and micro-plastic particles that may be ingested, either directly or indirectly via food chains, by fishes. Examination of stomach contents from 172 specimens of 16 serrasalmid species from lower Xingu River Basin revealed consumption of plastic particles by fishes in each of three trophic guilds (herbivores, omnivores, carnivores). Overall, about one quarter of specimens and 80% of species analyzed had ingested plastic particles ranging from 1 to 15 mm in length. Fourier transform infrared spectroscopy indicated 12 polymer types, including 27% identified as polyethylene, 13% polyvinyl chloride, 13% polyamide, 13% polypropylene, 7% poly(methyl methacrylate), 7% rayon, 7% polyethylene terephtalate, and 13% a blend of polyamide and polyethylene terephtalate. Dimensions of ingested plastic particles varied among trophic guilds, even though the frequency and mass of ingested particles were not significantly different among fishes with different feeding habits.

Chronic brain toxicity response of juvenile Chinese rare minnows (Gobiocypris rarus) to the neonicotinoid insecticides imidacloprid and nitenpyram

Imidacloprid and nitenpyram are widely used neonicotinoid pesticides worldwide and were observed to adversely affect non-target aquatic organisms. In this study, the toxic effect of imidacloprid and nitenpyram on the brain of juvenile Chinese rare minnows (Gobiocypris rarus) was investigated by determining the oxidative stress, 8-hydroxy-2-deoxyguanosine (8-OHdG) content and acetylcholinesterase (AChE) activity. The superoxide dismutase (SOD) activities did not significantly change after long-term exposure to imidacloprid and nitenpyram. A noticeable increase of catalase (CAT) activities was observed on the brain tissues under 0.1 mg/L imidacloprid and under all nitenpyram treatments (p < 0.05). The malondialdehyde (MDA) content increased markedly under 2.0 mg/L imidacloprid and 0.1 mg/L nitenpyram treatments (p < 0.05). The glutathione (GSH) content in the brain significantly increased under 0.5 and 2.0 mg/L imidacloprid (p < 0.05). A significant decrease was observed in the mRNA levels of Cu/Zn-sod under 2.0 mg/L imidacloprid and those of cat under 0.1 and 0.5 mg/L nitenpyram (p < 0.05). The mRNA levels of gpx1 clearly decreased under 2.0 mg/L imidacloprid and under 0.1 mg/L nitenpyram (p < 0.05). The treatments of 0.1 and 0.5 mg/L nitenpyram decreased cat expression levels markedly (p < 0.05). 2.0 mg/L imidacloprid raised the 8-OHdG content. The AChE activities increased markedly under 0.5 and 2.0 mg/L imidacloprid while clearly decreasing under 2.0 mg/L nitenpyram (p < 0.05). Therefore, our results indicate that imidacloprid and nitenpyram might cause adverse effects on juvenile Chinese rare minnows brain. Notably, imidacloprid had greater impacts on juvenile rare minnows compared to nitenpyram.

Oxidative stress, energy metabolism and molecular responses of earthworms (Eisenia fetida) exposed to low-density polyethylene microplastics

Soils are both a sink and a pathway of plastic wastes, but there is a great lack of knowledge regarding their impacts on soil biota. To tackle the mechanisms of toxicity of these contaminants to soil invertebrates, earthworms (Eisenia fetida Savigny, 1826) were exposed during 28 days to different concentrations of low-density polyethylene microplastics (62, 125, 250, 500 and 1000 mg MPs kg^-1 soil_dw) with sizes ranging between 250 and 1000 μm, in an artificial soil. The ecotoxicological responses were evaluated by analysing various oxidative stress biomarkers (catalase, glutathione S-transferase and thiobarbituric acid reactive substances), a biomarker of energy metabolism (lactate dehydrogenase) and overall organism molecular changes by Fourier transform infrared spectrometry (FTIR) and nuclear magnetic resonance (NMR) analyses. Significant effects resulting from an unbalanced oxidative stress system, expressed in terms of thiobarbituric acid reactive substances levels were recorded on earthworms exposed at the three highest concentrations tested. Despite that, no significant changes were recorded on the molecular profiles of earthworms by FTIR-ATR. NMR analysis pointed out for differences from the control, only for earthworms exposed to the lowest concentration of MPs. Considering that stress responses are complex, and involve multiple mechanisms, a cluster analysis taking into account all the parameters assessed, clearly identified two groups of earthworms separated by the concentration of 250 mg MPs kg^-1 soil_dw, above each meaningful effects were recorded.

Dydrogesterone Causes Male Bias and Accelerates Sperm Maturation in Zebrafish ( Danio rerio)

Synthetic progestins are widely used in human and veterinary medicine. They can enter aquatic environments mainly via wastewater discharge and agricultural runoff, thus affecting fish populations in receiving waters. Here, we investigated the chronic effects of dydrogesterone (DDG) on zebrafish from 21 to 140 days post-fertilization (dpf) at 3.39, 33.1, and 329 ng L^-1. The results showed that the male ratio increased with the exposure concentration, and after 120 days of exposure to 329 ng L^-1, 98% of the fish were males. The DDG exposure during sex differentiation significantly increased the transcription of dmrt1 (1.83-fold) and apoptosis-related genes but suppressed the transcription of cyp19a1a (3.16-fold). Histological analysis showed that the exposure to DDG at 329 ng L^-1 caused 61.5% of mature spermatocytes in males, while the exposure to DDG at 33.1 ng L^-1 resulted in 14.7% of atretic follicles in females. Microarray analysis identified spermatogenesis-related gene ontology (endothelial barrier and immune response) in the testes at all concentrations. Genes from phagosome, lysosome, and sphingolipid metabolism pathways were enriched and could be responsible for sperm maturation. The findings from this study demonstrate that DDG in the aquatic environment can cause male bias and accelerate sperm maturation in zebrafish, resulting in potential high ecological risks to fish populations.

Bioindicators for monitoring marine litter ingestion and its impacts on Mediterranean biodiversity

The Mediterranean Sea has been described as one of the most affected areas by marine litter in the world. Although effects on organisms from marine plastic litter ingestion have been investigated in several oceanic areas, there is still a lack of information from the Mediterranean Sea. The main objectives of this paper are to review current knowledge on the impact of marine litter on Mediterranean biodiversity, to define selection criteria for choosing marine organisms suitable for use as bioindicator species, and to propose a methodological approach to assessing the harm related to marine litter ingestion in several Mediterranean habitats and sub-regions. A new integrated monitoring tool that would provide the information necessary to design and implement future mitigation actions in the Mediterranean basin is proposed. According to bibliographic research and statistical analysis on current knowledge of marine litter ingestion, the area of the Mediterranean most studied, in terms of number of species and papers in the Mediterranean Sea is the western sub-area as well as demersal (32.9%) and pelagic (27.7%) amongst habitats. Applying ecological and biological criteria to the most threatened species obtained by statistical analysis, bioindicator species for different habitats and monitoring scale were selected. A threefold approach, simultaneously measuring the presence and effects of plastic, can provide the actual harm and sub-lethal effects to organisms caused by marine litter ingestion. The research revealed gaps in knowledge, and this paper suggests measures to close the gap. This and the selection of appropriate bioindicator species would represent a step forward for marine litter risk assessment, and the implementation of future actions and mitigation measures for specific Mediterranean areas, habitats and species affected by marine litter ingestion.

Effects of pristine polyvinyl chloride fragments on whole body histology and protease activity in silver barb Barbodes gonionotus fry

Silver barb Barbodes gonionotus fry were exposed to polyvinyl chloride (PVC) fragments at increasing concentrations of 0.2, 0.5 and 1.0 mg/L for 96 h, following which whole body histological evaluation and analysis of the digestive enzymes trypsin and chymotrypsin were performed. Whole body trypsin and chymotrypsin activities increased significantly in fish exposed to 0.5 and 1.0 mg/L PVC as compared those exposed to zero or 0.2 mg/L PVC. In fish exposed to all tested concentrations, PVCs were observed in both the proximal and distal intestine, and fish exposed to 0.5-1.0 and 1.0 mg/L PVC, respectively, and these particles were associated with localized thickening of the mucosal epithelium. No tissue damage was evident in any other internal organs or gills. This lack of damage may be attributed to the absence of contaminants associated with the PVC fragments and their relatively smooth surface. The increased whole body trypsin and chymotrypsin activities may indicate an attempt to enhance digestion to compensate for epithelial thickening of the intestine and/or to digest the plastics.

Microplastic does not magnify the acute effect of PAH pyrene on predatory performance of a tropical fish (Lates calcarifer)

Microplastic (MP) leads to widespread pollution in the marine ecosystem. In addition to the physical hazard posed by ingestion of microplastic particles, concern is also on their potential as vector for transport of hydrophobic contaminants. We experimentally studied the single and interactive effects of microplastic and pyrene, a polycyclic aromatic hydrocarbon, on the swimming behaviour and predatory performance of juvenile barramundi (Lates calcarifer). Juveniles (18+ days post hatch) were exposed to MPs, or pyrene (100 nM), or combination of both, and feeding rate and foraging activity (swimming) were analysed. Exposure to MPs alone did not significantly influence feeding performance of the juveniles, while a dose-effect series of pyrene showed strong effect on fish behaviour when concentrations were above 100 nM. In the test of combined MP and pyrene exposure, we observed no effect on feeding while swimming speed decreased significantly. Thus, our results confirm that short-time exposure to pyrene impacts the performance of fish juveniles, while additional exposure to microplastic at the given conditions influenced their activity only and not their feeding rate. Further studies of the combined effects of microplastics and pollutants on tropical fish behaviour are encouraged.

Combined effects of microplastics and chemical contaminants on the organ toxicity of zebrafish (Danio rerio)

Microplastics contamination of the aquatic environment is considered a growing problem. The ingestion of microplastics has been documented for a variety of aquatic animals. Studies have shown the potential of microplastics to affect the bioavailability and uptake route of sorbed co-contaminants of different nature in living organisms. Persistent organic pollutants and metals have been the co-contaminants majorly investigated in this field. The combined effect of microplastics and sorbed co-contaminants in aquatic organisms still needs to be properly understood. To address this, we have subjected zebrafish to four different feeds: A) untreated feed; B) feed supplemented with microplastics (LD-PE 125-250µm of diameter); C) feed supplemented with 2% microplastics to which a mixture of PCBs, BFRs, PFCs and methylmercury were sorbed; and D) feed supplemented with the mixture of contaminants only. After 3 weeks of exposure fish were dissected and liver, intestine, muscular tissue and brain were extracted. After visual observation, evaluation of differential gene expression of some selected biomarker genes in liver, intestine and brain were carried out. Additionally, quantification of perfluorinated compounds in liver, brain, muscular tissue and intestine of some selected samples were performed. The feed supplemented with microplastics with sorbed contaminants produced the most evident effects especially on the liver. The results indicate that microplastics alone does not produce relevant effects on zebrafish in the experimental conditions tested; on the contrary, the combined effect of microplastics and sorbed contaminants altered significantly their organs homeostasis in a greater manner than the contaminants alone.

Microplastic particles cause intestinal damage and other adverse effects in zebrafish Danio rerio and nematode Caenorhabditis elegans

Microplastics have been frequently detected in aquatic environments, and there are increasing concerns about potential effects on biota. In this study, zebrafish Danio rerio and nematode Caenorhabditis elegans were used as model organisms for microplastic exposure in freshwater pelagic (i.e. water column) and benthic (i.e. sediment) environments. We investigated the toxic effects of five common types of microplastics: polyamides (PA), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and polystyrene (PS) particles. Results showed no or low lethality in D. rerio after exposure for 10d at 0.001-10.0mgL^-1 microplastics. The PA, PE, PP and/or PVC microplastics with ~70μm size caused intestinal damage including cracking of villi and splitting of enterocytes. Exposure to 5.0mgm^-2 microplastics for 2d significantly inhibited survival rates, body length and reproduction of C. elegans. Moreover, exposure to microplastics reduced calcium levels but increased expression of the glutathione S-transferase 4 enzyme in the intestine, which indicates intestinal damage and oxidative stress are major effects of microplastic exposure. Among 0.1, 1.0 and 5.0μm sizes of fluorescently labeled PS, 1.0μm particles caused the highest lethality, the maximum accumulation, the lowest Ca²⁺ level in the intestine and the highest expression of glutathione S-transferase 4 in nematodes. Taken together, these findings suggest that intestinal damage is a key effect of microplastics; and that the toxicity of microplastics is closely dependent on their size, rather than their composition.

Microplastics have a more profound impact than elevated temperatures on the predatory performance, digestion and energy metabolism of an Amazonian cichlid

Knowledge on the impacts of microplastics (MPs) pollution on freshwater environments and biota remains limited. Meanwhile, freshwater ecosystems have been threatened by elevated temperatures caused by climate change. To date, no information exists on how MPs-especially under elevated temperature conditions-affect predatory performance, digestive processes and metabolic pathways in freshwater organisms. Here, we examined MPs, elevated temperature and their combined effects on juveniles (0+ group) of an Amazonian cichlid, the discus fish (Symphysodon aequifasciatus). For 30 days, fish were exposed to ambient or elevated temperatures (i.e., 28 or 31 °C) in the absence or presence of MPs (i.e., 0 or 200 μg/L). The following metrics were quantified: MPs accumulation; predatory performance; and biomarkers involved in neurotransmission, digestion and energy production. The results showed that survival rate and body length were not affected by MPs, elevated temperatures or their combination. Elevated temperatures resulted in an increase in MP concentrations in fish bodies. Exposure to MPs decreased the post-exposure predatory performance (PEPP) at ambient temperatures but not at elevated temperatures. Elevated temperatures, however, had no effect on the PEPP but antagonistically interacted with MPs, leading to similar predatory performances under present and future conditions. Acetylcholinesterase (AChE) activity was only affected by MPs and decreased in the presence of MPs, indicating adverse effects in nervous and neuromuscular function and, thus, potentially in predatory performance. Trypsin activity was only influenced by MPs and decreased during exposure to MPs. Elevated temperatures or MPs alone increased the amylase activity but interacted antagonistically. Lipase activity was not influenced by either of the two stressors. In contrast, alkaline phosphatase (ALP) activity was affected by MPs or elevated temperatures alone and decreased with both stressors. Such results indicate deficits in the digestive capabilities of early-stage S. aequifasciatus under elevated temperature conditions and especially during exposure to MPs. Electron transport system (ETS) activity was not influenced by either of the two stressors. Both elevated temperatures and MPs alone increased LDH activity; however, the interaction between the two stressors cancelled activity but was still higher than activity in present conditions. Citrate synthase (CS) activity decreased with elevated temperature but increased during exposure to MPs. Cytochrome c oxidase (COX) activity was only influenced by MPs and increased in the presence of MPs. Thus, S. aequifasciatus juveniles exposed to elevated temperatures and MPs not only relied on anaerobic glycolysis for energy production but also depended on aerobic metabolism in the presence of MPs. Overall, these findings suggested that MPs showed a greater impact than elevated temperatures on the predatory performance, digestion and energy production of S. aequifasciatus. Nevertheless, juvenile survival and growth were minimally impacted, and thus, S. aequifasciatus could cope with near-future temperature increases and MP exposure.

Gaps in aquatic toxicological studies of microplastics

The contamination of aquatic environments with microplastics (MPs) has spurred an unprecedented interest among scientific communities to investigate their impacts on biota. Despite the rapid growth in the number of studies on the aquatic toxicology of MPs, controversy over the fate and biological impacts of MPs is increasingly growing mainly due to the absence of standardized laboratory bioassays. Given the complex features of MPs, such as the diversity of constituent polymers, additives, shapes and sizes, as well as continuous changes in the particle buoyancy as a result of fouling and defouling processes, it is necessary to modify conventional bioassay protocols before employing them for MP toxicity testings. Moreover, several considerations including quantification of chemicals on/in the MP particles, choice of test organisms, approaches for renewing the test solution, aggregation prevention, stock solution preparation, and units used to report MP concentration in the test solution should be taken into account. This critical review suggests some important strategies to help conduct environmentally-relevant MP bioassays.