Interactive effects of polystyrene microplastics and roxithromycin on bioaccumulation and biochemical status in the freshwater fish red tilapia (Oreochromis niloticus)

Acute and chronic combined effect of polystyrene microplastics and dibutyl phthalate on the marine copepod Tigriopus japonicus

Dibutyl phthalate (DBP) is a commonly used additive in plastic products, so it may potentially coexist with microplastics (MPs) in marine environment. The ingestion of MPs might affect the accumulation of DBP in marine organisms. In this study, the marine copepod Tigriopus japonicus was applied to study the combined effect of DBP and polystyrene microplastics (mPS) on the copepod through both acute mortality tests and chronic reproduction tests. The LC₅₀ of DBP was 1.23 mg L^-1 (95% CI: 1.11-1.35 mg L^-1), while exposure to mPS didn't have significant lethal effect on the copepods. Adsorption to MPs led to decreased bioavailability of DBP, resulting in decreased toxicity of DBP. In contrast to the results of acute toxicity tests, DBP didn't affect the reproduction of the copepods at lower exposure concentrations, while mPS reduced the number of nauplii and extended the time to hatch. Similar as acute toxicity tests, antagonistic interaction was observed for mPS and DBP in chronic reproduction tests, which might be attributed to promoted aggregation of mPS at presence of DBP. Overall, antagonistic toxicity effect between the two pollutants was observed for both acute and chronic tests, but the mechanisms of the interaction between DBP and mPS were different. Results of the present study highlighted the importance of long-term exposure when evaluating the toxic effect of MPs and their combined effect with other chemicals.

A review of the toxicity in fish exposed to antibiotics

Antibiotics are widely used in the treatment of human and veterinary diseases and are being used worldwide in the agriculture industry to promote livestock growth. However, a variety of antibiotics that are found in aquatic environments are toxic to aquatic organisms. Antibiotics are not completely removed by wastewater treatment plants and are therefore released into aquatic environments, which raises concern about the destruction of the ecosystem owing to their non-target effects. Since antibiotics are designed to be persistent and work steadily in the body, their chronic toxicity effects have been studied in aquatic microorganisms. However, research on the toxicity of antibiotics in fish at the top of the aquatic food chain is relatively poor. This paper summarizes the current understanding of the reported toxicity studies with antibiotics in fish, including zebrafish, to date. Four antibiotic types; quinolones, sulfonamides, tetracyclines, and macrolides, which are thought to be genetically toxic to fish have been reported to bioaccumulate in fish tissues, as well as in aquatic environments such as rivers and surface water. The adverse effects of these antibiotics are known to cause damage to developmental, cardiovascular, and metabolic systems, as well as in altering anti-oxidant and immune responses, in fish. Therefore, there are serious concerns about the toxicity of antibiotics in fish and further research and strategies are needed to prevent them in different regions of the world.

Immunotoxicity and neurotoxicity of bisphenol A and microplastics alone or in combination to a bivalve species, Tegillarca granosa

Though invertebrates are one of the largest groups of animal species in the sea and exhibit robust immune and neural responses that are crucial for their health and survival, the potential immunotoxicity and neurotoxicity of the most produced chemical bisphenol A (BPA), especially in conjunction with microplastics (MPs), still remain poorly understood in marine invertebrate species. Therefore, the impacts of exposure to BPA and MPs alone or in combination on a series of immune and neural biomarkers were investigated in the invertebrate bivalve species blood clam (Tegillarca granosa). Evident immunotoxicity as indicated by alterations in hematic indexes was observed after two weeks of exposure to BPA and MPs at environmentally realistic concentrations. The expression of four immune-related genes from the NFκB signaling pathway was also found to be significantly suppressed by the BPA and MP treatment. In addition, exposure to BPA and MPs led to an increase in the in vivo contents of three key neurotransmitters (GABA, DA, and ACh) but a decrease in the expression of genes encoding modulatory enzymes and receptors for these neurotransmitters, implying the evident neurotoxicity of BPA and MPs to blood clam. Furthermore, the results demonstrated that the toxic impacts exerted by BPA were significantly aggravated by the co-presence of MPs, which may be due to interactions between BPA and MPs as well as those between MPs and clam individuals.

Biomarker responses in New Zealand green-lipped mussels Perna canaliculus exposed to microplastics and triclosan

Microplastics (MPs) are of increasing concern for filter feeding marine and freshwater species. Additionally MPs can sorb hydrophobic contaminants from the water, potentially providing an additional pathway of exposure of aquatic species to contaminants. An acute 48 h laboratory study was conducted to investigate the effects of microplastics and triclosan, both individually and combined, on New Zealand's green-lipped mussel, Perna canaliculus. Biomarkers included clearance rate, oxygen uptake, byssus production; and superoxide dismutase (SOD) activity, glutathione-S-transferase (GST) activity and lipid peroxidation in the gill tissue. Microplastics and triclosan, both individually and combined significantly decreased oxygen uptake and byssus production. These physiological responses were not observed when the microplastics were spiked with triclosan. Triclosan, both alone and spiked to microplastics, increased mussel oxidative stress markers including SOD activity and lipid peroxidation. An enhanced effect was observed on the SOD enzyme activity when mussels were exposed to microplastics spiked with triclosan. No effects on the biochemical biomarkers were observed for mussels exposed to microplastic only. Microplastics enhanced the uptake of triclosan in mussel tissue compared with triclosan only treatments indicating that microplastics potentially provide an additional pathway of exposure to hydrophobic contaminants.

Toxicological effects of nano- and micro-polystyrene plastics on red tilapia: Are larger plastic particles more harmless?

Nanoplastics (NPs) and microplastics (MPs) are a heterogeneous class of pollutants with diverse sizes in aquatic environments. To evaluate the hazardous effects of N/MPs with different sizes, the accumulation, oxidative stress, cytochrome P450 (CYP) enzymes, neurotoxicity, and metabolomics changes were investigated in the red tilapia exposed to three sizes of polystyrene (PS) N/MPs (0.3, 5, and 70 - 90 μm). After 14-d exposures, the largest particles (70 - 90 μm) showed the highest accumulation levels in most cases. Exposures to PS-MPs (5 and 70 - 90 μm) caused a more severe oxidative stress in red tilapia than PS-NPs. The activity of CYP3A-related enzyme was obviously inhibited by PS-NPs, whereas the CYP enzymes in the liver may not be sensitive to MP exposures. In the brain, only 5 μm PS-MPs significantly inhibited the acetylcholinesterase activity. After exposures, the treatments with 0.3, 5, and 70 - 90 μm N/MPs resulted in 31, 40, and 23 significantly differentially expressed metabolites, respectively, in which the pathway of tyrosine metabolism was significantly affected by all the three PS-N/MP exposures. Overall, the PS particles within the μm size posed more severe stress to red tilapia. Our results suggest that the toxicity of N/MPs may not show a simply monotonic negative correlation with their sizes.

Exposure to microplastics impairs digestive performance, stimulates immune response and induces microbiota dysbiosis in the gut of juvenile guppy (Poecilia reticulata)

Microplastics (MPs) are widely distributing in aquatic environment. They are easily ingested by aquatic organisms and accumulate in digestive tract especially of intestine. To explore the potential effects of MPs on intestine, here we, using juvenile guppy (Poecilia reticulata) as experimental animal, investigated the response characteristics of digestion, immunity and gut microbiota. After exposure to 100 and 1000 μg/L concentrations of MPs (polystyrene; 32-40 μm diameters) for 28 days, we observed that MPs could exist in guppy gut and induce enlargement of goblet cells. Activities of digestive enzymes (trypsin, chymotrypsin, amylase and lipase) in guppy gut generally reduced. MPs stimulated the expression of immune cytokines (TNF-α, IFN-γ, TLR4 and IL-6). Through high throughput sequencing of 16S rRNA gene, decreases in diversity and evenness and changed composition of microbiota were found in guppy gut. PICRUSt analysis revealed that MPs might have effects on intestinal microbiota functions, such as inhibition of metabolism and repair pathway. Our findings suggested that MPs could retain in the gut of juvenile guppy, impair digestive performance, stimulate immune response and induce microbiota dysbiosis in guppy gut. The results obtained here provide new insights into the potential risks of MPs to aquatic animals.

Microplastics combined with tetracycline in soils facilitate the formation of antibiotic resistance in the Enchytraeus crypticus microbiome

Growing evidence suggests that microplastics can adsorb antibiotics and may consequently exacerbate effects on the health of exposed organisms. Our current understanding of the combined effects of microplastics and antibiotics on antibiotic resistance genes (ARGs) in soil invertebrates is limited. This study aimed to investigate changes in the microbiome and ARGs in Enchytraeus crypticus following exposure to a soil environment that contained both microplastics and antibiotics. Tetracycline (TC), polyamide (PA) and polyvinyl chloride (PVC) were used to construct microcosms of polluted soil environments (TC, PA, PVC, PA+TC, PVC+TC). The differences in microbiomes and ARGs were determined by bacterial 16S rRNA gene amplicon sequencing and high throughput quantitative PCR. The results show that compared with the Control or microplastics alone treatments, TC was significantly accumulated in E. crypticus when exposed to TC alone or in combination with microplastics (P < 0.05), but there were no significant differences about TC accumulation between TC, PA+TC, and PVC+TC treated E. crypticus (P > 0.05). Microplastics and TC significantly disturbed the microbial community, and decreased the microbial alpha diversity of E. crypticus (P < 0.05). However, there were no significant differences between TC, microplastics and their combined exposure treatments, and no toxic synergies on the diversity of E. crypticus microbiome between tetracycline and microplastics in soil environment. All the treatments increased the diversity of ARGs in E. crypticus (39-49 ARGs vs. 25 ARGs of control). In particular, treatments combining PVC and TC or PA and TC exposure resulted in greater ARGs abundance than the treatments when E. crypticus was exposed to PVC, PA or TC alone. These results add to our understanding of the combined effects of microplastics and antibiotics on the ARGs and microbiome of soil invertebrates.

A review of the influences of microplastics on toxicity and transgenerational effects of pharmaceutical and personal care products in aquatic environment

PPCPs (pharmaceutical and personal care products) and microplastics (MPs) are two types of emerging pollutants that are ubiquitous and widely concerned in the environment. Both of them can accumulate in fish or aquatic invertebrates and transfer to offspring, thereby producing toxic effects on both parents and offspring, in which the characteristics of MPs also enable them to adsorb PPCPs thus producing carrier effects. In this study, we have conducted a comprehensive review of MPs and PPCPs and found that MPs can act as a carrier of PPCPs to influence the bioaccumulation of PPCPs. MPs and PPCPs have toxicity and transgenerational effects on both fish and aquatic invertebrates in many aspects, and MPs can also affect the toxicity and transgenerational effects of PPCPs due to their carrier effects. This paper revealed that MPs may have an important impact on the bioavailability of PPCPs and the interaction between MPs and PPCPs is a hot topic in future research. This study also puts forward the shortcomings of the current research and related suggestions, and relevant research should be carried out as soon as possible to provide the basis for the prevention and treatment of fresh water.

Uptake and Release Kinetics of Organic Contaminants Associated with Micro- and Nanoplastic Particles

A generic theoretical framework is presented for describing the kinetics of uptake and release of organic compounds that associate with plastic particles. The underlying concepts account for the physicochemical features of the target organic compounds and the plastic particles. The developed framework builds on concepts established for dynamic speciation analysis by solid-phase microextraction and the size-dependent reactivity features of particulate complexants. The theoretical framework is applied to interpretation of literature data, thereby providing more rigorous insights into previous observations. The presented concepts enable predictions of the sink/source functioning of plastic particles and their impact on the dynamic chemical speciation of organic compounds in aqueous environmental media and within biota. Our results highlight the fundamental influence of particle size on the uptake and release kinetics. The findings call for a comprehensive description of the physicochemical features of plastic particles to be provided in experimental studies on micro- and nanoplastics in different types of aquatic environmental media.

Influence of roxithromycin as antibiotic residue on volatile fatty acids recovery in anaerobic fermentation of waste activated sludge

The removal of antibiotics and resistance genes in wastewater treatment plants has attracted widespread attention, but the potential role of residual antibiotics in the disposal of waste activated sludge (WAS) has not been clearly understood. In this study, the effect of roxithromycin (ROX) on volatile fatty acid (VFA) recovery from WAS anaerobic fermentation was investigated. The experimental results showed that ROX made a positive contribution to the production of VFAs. With the increase of ROX dosages from 0 to 100 mg/kg TSS, the maximum accumulation of VFAs increased from 295 to 610 mg COD/L. Mechanism studies revealed that ROX promoted the solubilization of WAS by facilitating the disruption of extracellular polymeric substances. In addition, ROX enhanced the activity of acetate kinase and inhibited the activities of α-glucosidase and coenzyme F₄₂₀, and showed a stronger inhibitory effect on methane production than the hydrolysis process, thus resulting in an increase in VFA accumulation. These findings provide a new insight for the role of antibiotics in anaerobic fermentation of WAS.

Spatiotemporal variation in microplastic contamination along a subtropical reservoir shoreline

Microplastics have become a major environmental concern globally due to their potential impact on ecosystem function. They are known to be ubiquitously present, persistent and bio-accumulative, yet there is a lack of abundance quantifications in freshwater shorelines. Furthermore, there is little understanding of combined effects of seasonality and human population density on the extent of microplastic pollution. In this study, we assessed microplastics in sediment along a subtropical reservoir shoreline across three seasons and seven sites to understand microplastic pollution dynamics along a human population gradient. Multivariable analysis was used to assess relationships among substrate embeddedness, sediment organic matter, human population density and microplastic particle densities and characteristics. Microplastic densities were relatively high during the hot-dry season (mean range 120-6417 particles kg^-1 dwt) whilst the hot-wet season had the lowest densities (mean range 5-94 particles kg^-1 dwt). Microplastic abundances were positively correlated with population density, demonstrating the direct effects of human activity on microplastic contamination. These results highlight the need to further explore microplastic distribution patterns in freshwater ecosystems in the Southern Hemisphere. Furthermore, our findings suggest particular risk for fauna during low rainfall periods through microplastic concentration effects.

Microplastics enhance the developmental toxicity of synthetic phenolic antioxidants by disturbing the thyroid function and metabolism in developing zebrafish

Coexposure of MPs and other contaminants adsorbed from the environment has raised many attentions, but the understanding of the combined effects of MPs and plastic additives are limited. Butylated hydroxyanisole (BHA), a widely used synthetic phenolic antioxidant in plastics, has gained high concerns due to their unintended environmental release and potential threat to aquatic organisms. This study was conducted to reveal the influences of MPs on the bioaccumulation and developmental toxicity of BHA in zebrafish larvae. As a result, MPs promoted the accumulation of BHA in zebrafish larvae and enhanced the toxicity of BHA in larvae development manifested by reduced hatching rates, increased malformation rates and decreased calcified vertebrae. Although the concentration of MPs was not sufficient to cause obvious developmental toxicity, the impacts of MPs on thyroid hormones status might contribute to the aggravated join toxicity. The metabolomic mechanism was revealed to be that the coexposure of BHA and MPs affected the development of zebrafish larvae via disturbing the metabolism of arachidonic acid, glycerophospholipid, and lipids. Our results emphasized that MPs, even at the nontoxic concentrations, in combination with additives caused health risk that should not be ignored.

Involvement of oxidative stress in the sensitivity of two algal species exposed to roxithromycin

Algal species Raphidocelis subcapitata and Chlorella vulgaris are commonly used to test the chemicals with an antibacterial mode of action during marketing authorization process. However, significant differences in the sensitivity toward antibiotic exposure have been reported. The selection of an inappropriate test species would thus underestimate the environmental hazard of target chemicals and pose a potential threat to the ecosystem. Since oxidative stress is a crucial factor determining the inhibition of algal growth, an investigation on oxidative stress and antioxidant defense mechanisms in these two species was performed to explore its roles in species sensitivity. Here, roxithromycin (ROX), a macrolide antibiotic extensively used to treat respiratory, urinary and soft tissue infections, was used for testing. After 7 days exposure to ROX at the low (0.01 mg L^-1) and high (0.09 mg L^-1) concentrations, R. subcapitata was inhibited while the growth of C. vulgaris was stimulated. We investigated the roles of oxidative stress in algae by measuring the oxidative stress biomarkers (MDA), non-enzymatic antioxidants (GSH), and antioxidant enzymes (SOD, CAT, GP, GST). The results suggested that when the growth of algae is inhibited, MDA content as well as activities of oxidative stress enzymes would increase, and thus, activating the antioxidant system. On the contrary, it was inferred that when the growth is stimulated, MDA content and oxidative stress enzymes activities would decrease.

Desorption of pharmaceuticals from pristine and aged polystyrene microplastics under simulated gastrointestinal conditions

Microplastics (MPs) in the environment usually undergo extensive weathering and can transport pollutants to organisms once being ingested. However, the transportation mechanism and effect of aging process are poorly understood. This study systematically investigated the desorption mechanisms of pharmaceuticals from pristine and aged polystyrene (PS) MPs under simulated gastric and intestinal conditions of marine organisms. Results showed that the increased desorption in stomach mainly depended on the solubilization of pepsin to pharmaceuticals and the competition for sorption sites on MPs via π-π and hydrophobic interactions. However, high desorption in gut relied on the solubilization of intestinal components (i.e. bovine serum albumin (BSA) and bile salts (NaT)) and the competitive sorption of NaT since the enhanced solubility increased the partition of pharmaceuticals in aqueous phase. Aging process suppressed the desorption of pharmaceuticals because aging decreased hydrophobic and π-π interactions but increased electrostatic interaction between aged MPs and pharmaceuticals, which became less affected by gastrointestinal components. Risk assessment indicated that the MP-associated pharmaceuticals posed low risks to organisms, and warm-blooded organisms suffered relatively higher risks than cold-blooded ones. This study reveals important information to understand the ecological risks of co-existed MPs and pollutants in the environment.

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.

Perspectives and challenges of micro/nanoplastics-induced toxicity with special reference to phytotoxicity

Plastic pollution has become a global concern for ecosystem health and biodiversity conservation. Concentrations of plastics are manifold higher in the terrestrial system than the aquatic one. Micro/nanoplastics (M/NP) have the ability to alter soil enzymatic system, soil properties and also affect soil borne microorganisms and earthworms. Despite, the knowhow regarding modulatory effects of plastics are acquired from the study on aquatic system and reports on their phytotoxic potentials are limited. The presence of cell wall that could restrict M/NP invasion into plant roots might be the putative cause of this limitation. M/NP inhibit plant growth, seed germination and gene expression; and they also induce cytogenotoxicity by aggravating reactive oxygen species generation. Dynamic behavior of cell wall; the pores formed either by cell wall degrading enzymes or by plant-pathogen interactions or by mechanical injury might facilitate the entry of into roots M/NP. This review also provides a possible mechanism of large sized microplastics-induced phytotoxicity especially for those that cannot pass through cell wall pores. As M/NP affect soil microbial community and soil parameters, it is hypothesized that they could have the potential to affect N₂ fixation and research should be conducted in this direction. Reports on M/NP-induced toxicity mainly focused only on one polymer type (polystyrene) in spite of the toxicological relevancies of other polymer types like polyethylene, polypropylene etc. So, the assessment of phytotoxic potential of M/NP should be done using other plastic polymers in real environment as they are known to intract with other environmental stressors as well as can alter the the soil-microbe-plant interaction.

Antioxidants and molecular damage in Nile Tilapia (Oreochromis niloticus) after exposure to microplastics

Recently, research on the biological effects of microplastics (MPs) has grown exponentially. However, effects of MPs on freshwater fishes and the mechanisms of the biological effects of MPs were limited. So, the purpose of the current study was to clarify the effects of microplastics on oxidative stress response, DNA fragmentation, and proteinogram of the early juvenile stage of Nile Tilapia (Oreochromis niloticus). The fishes were assigned into four groups: one control, three MPs-exposed groups as 1 mg/L of MPs, 10 mg/L of MPs, and 100 mg/L of MPs respectively for 15 days and 15 days of recovery. The activities of superoxide dismutase, catalase, total peroxides, and oxidative stress index (OSI), as well as lipid peroxidation and DNA fragmentation, increased in groups exposed to MPs compared to the control group in a dose-dependent manner. In contrast, the activity of total antioxidant capacity decreased in groups exposed to MPs compared to the control group in a dose-dependent manner. The electrophoretic pattern of muscle proteins revealed alteration in the proteinogram in the MPs-exposed groups compared to control. After the recovery period, the activities of superoxide dismutase, catalase, total peroxides, total antioxidant capacity, lipid peroxidation, DNA fragmentation, and the electrophoretic pattern of muscle proteins returned to normal levels in 1 mg/L of MPs-exposed group. Combined with our previous work, these results suggest that MPs cause the overproduction of reactive oxygen species (ROS) and alters the antioxidants parameters, resulting in oxidative stress and DNA damage. The present study fosters a better understanding of the toxic effects of MPs on Tilapia as a freshwater model. Graphical Abstract.

Interactive effects of roxithromycin and freshwater microalgae, Chlorella pyrenoidosa: Toxicity and removal mechanism

Roxithromycin (ROX) has received increasing concern due to its large usage, ubiquitous detection in environment and high ecotoxicology risk. This study investigated the acute and chronic effects of ROX on the growth, chlorophyll, antioxidant enzymes, and malonaldehyde (MDA) content of Chlorella pyrenoidosa, as well as the removal mechanism of ROX during microalgae cultivation. The calculated 96 h median effective concentration of ROX on yield (E_yC₅₀) and specific growth rate (E_rC₅₀) of C. pyrenoidosa was 0.81 and 2.87 mg/L, respectively. After 96 h exposure, 1.0 ~ 2.0 mg/L of ROX significantly inhibited the synthesis of chlorophyll and promoted the activities of SOD and CAT (p < 0.05). The MDA content increased with the ROX concentration increasing from 0.5 ~ 1.0 mg/L, and then decreased to 105.76% of the control exposure to 2.0 mg/L ROX, demonstrating the oxidative damage could be moderated by the upregulation of SOD and CAT activities. During the 21 d chronic exposure, low concentration of ROX (0.1 and 0.25 mg/L) showed no significant effect on the growth and chlorophyll content of algae during the first 14 d, but significantly inhibited the growth of algae and the synthesis of chlorophyll at 21 d (p < 0.05 or p < 0.01). 1.0 mg/L ROX significantly inhibited the growth of microalgae during 3 ~ 21 d and the synthesis of chlorophyll at 7 ~ 21 d. High concentration and long-term exposure of low concentration of ROX caused the SOD and CAT activities and MDA content to increase, demonstrating a higher level of oxidative damage of microalgae. During the first 14 d, abiotic removal of ROX played a more important role, contributing about 12.21% ~ 21.37% of ROX removal. After 14 d, the biodegradation of ROX by C. pyrenoidosa gradually became a more important removal mechanism, contributing about 45.99% ~ 53.30% of ROX removal at 21 d. Bio-adsorption and bioaccumulation both played minor roles in the removal of ROX during algae cultivation.

Toxicity of Microplastics and Nanoplastics in Mammalian Systems

Fragmented or otherwise miniaturized plastic materials in the form of micro- or nanoplastics have been of nagging environmental concern. Perturbation of organismal physiology and behavior by micro- and nanoplastics have been widely documented for marine invertebrates. Some of these effects are also manifested by larger marine vertebrates such as fishes. More recently, possible effects of micro- and nanoplastics on mammalian gut microbiota as well as host cellular and metabolic toxicity have been reported in mouse models. Human exposure to micro- and nanoplastics occurs largely through ingestion, as these are found in food or derived from food packaging, but also in a less well-defined manner though inhalation. The pathophysiological consequences of acute and chronic micro- and nanoplastics exposure in the mammalian system, particularly humans, are yet unclear. In this review, we focus on the recent findings related to the potential toxicity and detrimental effects of micro- and nanoplastics as demonstrated in mouse models as well as human cell lines. The prevailing data suggest that micro- and nanoplastics accumulation in mammalian and human tissues would likely have negative, yet unclear long-term consequences. There is a need for cellular and systemic toxicity due to micro- and nanoplastics to be better illuminated, and the underlying mechanisms defined by further work.

Microplastics in aquatic environments: Occurrence, accumulation, and biological effects

Microplastics, whether originating directly from industrial and household products or from the degradation of larger plastics, are currently of intense global concern. These particles are present in aquatic environments in high concentrations and may adversely affect aquatic organisms. An additional concern is the ability of microplastics to adsorb inorganic and organic pollutants and subsequently liberate them into marine and freshwater systems. In this review, we report on the occurrence and abundance of microplastics in the global aquatic environment. We then consider the accumulation (uptake, distribution, and elimination) of microplastics in aquatic organisms and the important factors that lead to bioaccumulation. The effects of microplastics on aquatic organisms of different trophic levels are also discussed. Several studies have shown that the size, shape, and surface physicochemical characteristics of microplastics are essential determinants of their biological effects. Finally, we examine the combined effects of microplastics and other pollutants, including persistent organic pollutants and heavy metals. Our review concludes by suggesting future lines of research based on the remaining knowledge gaps in microplastic research.

Bioavailability and toxicity of microplastics to fish species: A review

The prevalence of microplastics in aquatic environments has raised concerns about their availability and risks to aquatic biota. Since fish is an important source of animal protein for human beings, the occurrence and potential impacts of microplastics in fishes deserve special attention. Although there have been an increasing number of studies concerning microplastics ingestion and effects in fish, review papers specifically focusing on this issue are few. This review summarized the current knowledge about the bioavailability and toxicity of microplastics to fish species. By collating literatures, it can be concluded that microplastics contamination could occur in almost all types of aquatic habitats around the globe. Both field and laboratory studies suggest that fishes are very susceptible to microplastics ingestion. Compared with marine species, freshwater fishes have been less studied. Microplastics alone or in combination with other contaminants could cause various health problems to fish after exposure. There still exist some debates over the environmental relevance of the laboratory-based effect studies and the relative contribution of microplastics in increasing the exposure of fish to hazardous chemicals. Hopefully, this review could extend the current knowledge on the ecotoxicological impacts of microplastics contamination to fish and provide guidance for future research.

Effect of nanoplastics on fish health and performance: A review

Small plastic particles are considered emerging pollutants, and this has motivated a considerable number of studies to establish their environmental consequences. At present, the study of the effects of nanoplastics (NPs) on aquatic organisms is still scarce, especially in organisms from higher trophic levels such as fish. This review describes the effects reported in different fish species after exposure to plastic particles smaller than 100 nm. Studies show that NPs can adversely affect fish at different stages of development, with reported accumulation in tissues, decreased locomotor and foraging activities, effects on growth and the immune system and alterations on lipid metabolism and neurotoxicity. However, mortality, effects on hatching success or malformations related to NPs have not been reported to this date.

Functional response quantifies microplastic uptake by a widespread African fish species

Ecological impacts of microplastic remain poorly understood, despite their ubiquity across all habitat types globally. Microplastic concentrations vary significantly across spatiotemporal gradients, however we lack quantitative methodologies to predict species-level responses to differential environmental concentrations. In the present study, we expose a key species, the banded tilapia Tilapia sparrmanii Smith, 1940, to different concentrations of microplastic particles. We apply and develop the functional response approach for quantifications of microplastic uptake by the fish across different environmental densities. Tilapia consumed microplastic even when relatively rare in their environment, and consumption rates related negatively to concentrations supplied, conducive with a saturating Type II (i.e., inversely-density-dependent) functional response. Attack rate (i.e., search efficiency), handling time and maximum feeding rate estimates towards microplastic were estimated, providing key information on feeding behaviour in relation to exposure concentrations. We propose the utility of functional response approaches for predictive quantifications of microplastic uptake rates. In turn, this can better-link laboratory exposure studies to environmental concentrations which are known to cause ecological impact, and provide a means of comparing uptakes among species and across environmental contexts.

Partitioning of chemical contaminants to microplastics: Sorption mechanisms, environmental distribution and effects on toxicity and bioaccumulation

There is an increasing awareness of the threats posed by the worldwide presence of microplastics (MPs) in the environment. Due to their high persistence, MPs will accumulate in the environment and their quantities tend to increase with time. MPs end up in environments where often also chemical contaminants are present. Since the early 2000s, the number of studies on the sorption of chemicals to plastic particles has exponentially increased. The objective of this study was to critically review the literature to identify the most important factors affecting the sorption of chemical contaminants to MPs. These factors include the physicochemical properties of both the MPs and the chemical contaminants as well as environmental characteristics. A limited number of studies on soil together with an increased notion of the importance of this compartment as a final sink for MPs was observed. Therefore, we assessed the distribution of model chemicals (two PCBs and phenanthrene) in the soil compartment in the presence of MPs using a mass balance model. The results showed a high variation among chemicals and microplastic types. Overall, a higher partitioning to MPs of chemical contaminants in soil is expected in comparison to aquatic environments. As sorption to a large extent determines bioavailability, the effects of combined exposure to chemicals and MPs on the toxicity and bioaccumulation in biota are discussed. Finally, some considerations regarding sorption and toxicity studies using MPs are given.

Exposure to microplastics lowers arsenic accumulation and alters gut bacterial communities of earthworm Metaphire californica

Ubiquitous contamination of microplastics and arsenic in soil ecosystems can induce many health issues to nontarget soil organisms, and will also cause many potential threats to the gut bacterial communities of soil fauna. However, the changes in the gut bacterial communities of soil fauna after exposure to both microplastics and arsenic remain unknown. In this study, the toxicity and effects on the gut microbiota of earthworm Metaphire californica caused by the combined exposure of microplastics and arsenic were examined by using arsenic species analysis and high throughput sequencing of gut microbiota. Results showed that total arsenic and arsenic species in the earthworm gut and body tissues after exposure to combination of microplastics with arsenate (As(V)) were significantly different from that treated with As(V) alone. Microplastics lessened the accumulation of total arsenic and the transformation rate of As(V) to arsenite (As(III)). Microplastics alleviated the effect of arsenic on the gut microbiota possibly via adsorbing/binding As(V) and lowering arsenic bioavailability, thus prevented the reduction of As(V) and accumulation of total arsenic in the gut which resulted in a lower toxicity on the earthworm. The study broadens our understanding of the ecotoxicity of microplastics with other pollutants on the soil animals and on their gut microbiota.

Distribution characteristics of microplastics in the seawater and sediment: A case study in Jiaozhou Bay, China

As a newly identified form of pollutant in the ocean, microplastics are receiving more and more attention from researchers. In order to evaluate the potential impact of microplastics, it is important to have comprehensive knowledge of the current microplastic situation. This study analyzed the abundance, polymer type, size, shape and color of microplastics in the seawater and sediments of Jiaozhou Bay, China, a semi-enclosed bay highly affected by surrounding human activities. Qualitative and quantitative analysis of microplastics were carried out using stereo microscope and attenuated total reflection micro-Fourier transform infrared spectrometer (ATR-μ-FT-IR). The abundance of microplastics in the bay seawater samples ranged between 20 items/m³ and 120 items/m³. The abundance of microplastics in sediment samples in the bay were between 7 items/kg d.w. and 25 items/kg d.w. The microplastics were mainly in black and blue colors with fiber being the dominant shape in all samples. All microplastics identified were smaller than 4 mm in this study. Polyethylene terephthalate (PET) was the main type of microplastics, followed by polypropylene (PP) and polyethylene (PE). Both the abundance and types of microplastics show positive correlations between the seawater and sediment samples. Microplastic polymer types in the bay showed close match to the polymer types in the estuaries. Relatively higher abundance of microplastics tended to be found in the area where there were residual currents and sediment transport trends. Our study showed riverine input is an important contributor to the microplastics in the bay and physical factors such as residual currents would greatly affect the aggregation of microplastics.

Sub-lethal toxicity of chlorpyrifos alone and in combination with polyethylene glycol to common carp (Cyprinus carpio)

In the present study, sub-lethal effects of chlorpyrifos, alone (25 and 50 μg L^-1) and in combination with Polyethylene glycol (5 and 10 mg L^-1), on common carp were investigated. Exposure to chlorpyrifos caused significant changes in all blood biochemical parameters compared to control groups. Total protein, triglyceride, glucose levels, as well as lactate dehydrogenase (LDH), gamma-glutamyl transferase (GGT), and creatine phosphokinase (CPK) activities in plasma changed after exposure to 10 mg L^-1 polyethylene glycol (PEG), while fish exposed to PEG did not show any significant difference in aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and acetylcholinesterase (AChE) activities and albumin and globulins levels. Exposure to a combination of chlorpyrifos and PEG caused a significant change in AST, GGT, CPK, LDH and AChE activity, total protein and glucose level. The influence of chlorpyrifos and PEG combination on ALP, cholesterol, triglyceride, albumin, and globulin depends on the concentration of the insecticide and PEG. With a reduction in chlorpyrifos concentration, PEG can maintain ALP activity and albumin at a normal level. Although fish exposure to chlorpyrifos, alone or in combination with polyethylene glycol, significantly increased malondialdehyde (MDA) and catalase (CAT) level, it decreased total antioxidant level (TAN). Exposure to just polyethylene glycol had no impact on CAT activity, TAN and MDA level. According to the results, PEG can have an antagonistic effect on chlorpyrifos toxicity, depending on these two materials concentration. However, chlorpyrifos increased the toxicity of PEG.