Ingestion and Egestion of Microplastics by the Cladoceran Daphnia magna: Effects of Regular and Irregular Shaped Plastic and Sorbed Phenanthrene

State of knowledge and future research needs on microplastics in groundwater

Microplastics (MPs) are widespread in aquatic and soil environments. This study targets the issue of MPs' transfer from soil to groundwater. Scientific papers were collected and analyzed using a text-mining approach that classifies text segments. This allowed the identification of four research topics and the organization of the results into a summarizing table. Those four topics are sources of groundwater MPs, main types of MPs (physico-chemical properties, polymer units, shapes, and size), human exposure (mainly drinking water), and potential environmental and human effects. Compared to the research of MP on aquatic or soil compartments, scientific data on MP in groundwater are less substantial. Current results show a divergence due to differences in context (alluvial aquifer, fractured rock aquifer, karst aquifer, etc), collecting, sampling, and analytical methods. This divergence requires further research with standardized analytic protocols and reference materials. The associated research gaps were identified by using the same approach. The following five topics emerged: (1) the transfer of MPs from soil to underground, (2) the contribution of groundwater to drinking water microplastic pollution, (3) the interaction with other contaminants, (4) the human and environmental effects, and (5) the protective and remediation solutions.

Plastics in scene: A review of the effect of plastics in aquatic crustaceans

Plastic pollution in aquatic environments is present in all compartments from surface water to benthic sediment, becoming a topic of emerging concern due to the internalization, retention time, and its effects on aquatic biota. Crustacea with nearly 70,000 species, broad distribution and different roles in the trophic webs is a significant target of the increasing plastic pollution. At least 98 publications in the last 10 years report the impact of plastics in crustaceans, all suggesting that this taxon is at high risk for ecosystem disadvantage by plastic contamination loads. This review compiles the current knowledge on physiological effects (endpoints) by plastic contamination analyzed in crustaceans in the last 10 years, highlighting their use as model species for ecotoxicological tests, sentinels species and bioindicators. Plastic contamination analyzed in this review includes macroplastic, microplastic, and nanoplastic, in a wide variety of types. The studies were focused on 38 marine species with an economic interest in fisheries and aquaculture; 14 freshwater with a higher frequency in standard test species and 4 estuarial and 3 mangrove species with ecological interest. The publications reviewed were divided into studies describing plastic presence in crustaceans without reporting toxic effects and those with analysis of plastic toxicity. Publications describing the plastic presence in the organisms show that the ingestion in individual effects and food-web transfer in ecological effects were the most frequent endpoints. The publications that analyzed plastic toxicity through survival, nutrition-metabolism-assimilation, and reproduction in individual effects, and bioaccumulation in ecological effects were the most frequent endpoints. This review gathers the available information on the use of crustaceans as model species in environmental impact for toxicity screening and hazard assessment. Besides, identifying knowledge gaps will let us propose some future directions in research and the effects on target fisheries species which involves a possible effect on human health.

Effects of a microplastic mixture differ across trophic levels and taxa in a freshwater food web: In situ mesocosm experiment

The ubiquitous presence of microplastics (MP) in aquatic ecosystems can affect organisms and communities in multiple ways. While MP research on aquatic organisms has primarily focused on marine ecosystems and laboratory experiments, the community-level effects of MP in freshwaters, especially in lakes, are poorly understood. To examine the impact of MP on freshwater lake ecosystems, we conducted the first in situ community-level mesocosm experiment testing the effects of MP on a model food web with zooplankton as main herbivores, odonate larvae as predators, and chironomid larvae as detritivores for seven weeks. The mesocosms were exposed to a mixture of the most abundant MP polymers found in freshwaters, added at two different concentrations in a single pulse to the water surface, water column and sediment. Water column MP concentrations declined sharply during the first two weeks of the experiment. Contrary to expectations, MP ingestion by zooplankton was low and limited mainly to large-bodied Daphnia, causing a decrease in biomass. Biomass of the other zooplankton taxa did not decrease. Presence of MP in the faecal pellets of odonate larvae that fed on zooplankton was indicative of a trophic transfer of MP. The results demonstrated that MP ingestion varies predictably with MP size, as well as body size and feeding preference of the organism, which can be used to predict the rates of transfer and further effects of MP on freshwater food webs. For chironomids, MP had only a low, short-term impact on emergence patterns while their wing morphology was significantly changed. Overall, the impact of MP exposure on the experimental food web and cross-ecosystem biomass transfer was lower than expected, but the experiment provided the first in situ observation of MP transfer to terrestrial ecosystems by emerging chironomids.

Transgenerational effects of polyethylene microplastic fragments containing benzophenone-3 additive in Daphnia magna

Maternal exposure to microplastics (MPs) plays an important role in the fitness of unexposed progeny. In this study, the transgenerational effects of polyethylene MP fragments (17.35 ± 5.50 µm) containing benzophenone-3 (BP-3; 2.85 ± 0.16% w/w) on chronic toxicity (21 d) in Daphnia magna were investigated across four generations. Only D. magna in the F0 generation was exposed to MP fragments, MP/BP-3 fragments, and BP-3 leachate to identify the transgenerational effect in the F3 generation. The mortality of D. magna induced by MP and MP/BP-3 fragments was recovered in the F3 generation, but somatic growth and reproduction significantly decreased compared to the control. Additionally, reproduction of D. magna exposed to BP-3 leachate significantly decreased in the F3 generation. These findings confirmed the transgenerational effects of MP fragment and BP-3 additive on D. magna. Particularly, the adverse effect on D. magna reproduction seemed to be cumulative across four generations for MP/BP-3 fragments, while it was an acclimation trend for BP-3 leachate. However, there was no significant difference in global DNA methylation in D. magna across four generations, thus requiring a gene-specific DNA methylation study to identify different epigenetic transgenerational inheritance.

The first plastic produced, but the latest studied in microplastics research: The assessment of leaching, ecotoxicity and bioadhesion of Bakelite microplastics

Bakelite, the first synthetic plastic, is a rather unexplored material in the field of ecotoxicology, despite its long production and use. The aim of this study was to investigate the ecotoxicity of Bakelite microplastics (before and after leaching) and its leachates on four aquatic organisms: the crustacean Daphnia magna, the plant Lemna minor, the bacterium Allivibrio fischeri and the alga Pseudokirchneriella subcapitata. Bakelite microplastics before and after leaching and leachates affected all organisms, but to varying degrees. Leachates showed increased ecotoxicity to Daphnia magna, while Pseudokirchneriella subcapitata was more affected by particles. For Lemna minor and Allivibrio fischeri, the effects of particles before leaching and leachate were comparable, while the negative effect of particles after leaching was minimal or not present. All leachates were analysed, and phenol and phenol-like compounds were the predominant organics found. In addition, bioadhesion of Bakelite microplastics to the surface of Daphnia magna and Lemna minor was confirmed, but the particles were mainly weakly adhered. Results of this study suggest that, in addition to the recently studied microplastics from consumer products (e.g. from polyethylene and polystyrene), microplastics from industrial plastics such as Bakelite may be of increasing concern, primarily due to leaching of toxic chemicals.

Ingestion and toxic impacts of weathered polyethylene (wPE) microplastics and stress defensive responses in whiteleg shrimp (Penaeus vannamei)

Weathered plastic litter is recognized as hazardous secondary microplastics(MPs) in the coastal and marine ecosystems, which are of high concern due to their greater impact on the environment. The present study aims to elucidate the impacts of environmentally weathered polyethylene (wPE) MPs on ingestion, growth and enzymatic responses in Penaeus vannamei. The Penaeus vannamei was chronically exposed to five varying concentration (0.1 mg-0.5 mg) of wPE particles in the size range between 43 and 32 μm for a period of 25days, followed by 5days depuration. At the end of exposure, a considerable number of wPE particles were observed from <2 to 14 per individual organism. However, around 60% of the wPE particles were removed after the depuration phase. The toxic exposure on P. vannamei resulted in significant changes in the enzymatic and growth responses with increasing concentration and duration. In addition, growth assessment confirmed that wPE exposure inhibited the growth of organism, and the effect was particularly evident at increasing concentrations and prolonged exposure. Also observed an elevated levels of lipid peroxidation, glutathione-S-transferases, whereas lower levels of reduced-glutathione and catalase at all exposed concentrations. This study confirmed that the ingestion of wPE was completely influenced by exposure duration, rather than the concentrations of administered. The present biomarker assay might act as an appropriate oxidative stress index for wPE toxicity. Findings of this study is useful in providing the basic biological information for environmental risk assessments of MPs, which are of high concern due to the rising input of microplastics into the environment.

Polyamide microplastic exposure elicits rapid, strong and genome-wide evolutionary response in the freshwater non-biting midge Chironomus riparius

Susceptibility to hazardous materials and contamination is largely determined by genetic make-up and evolutionary history of affected organisms. Yet evolutionary adaptation and microevolutionary processes triggered by contaminants are rarely considered in ecotoxicology. Using an evolve and resequencing approach, we investigated genome-wide responses of the midge C. riparius exposed to virgin polyamide microplastics (0-180 μm size range, at concentration 1 g kg^-1) during seven consecutive generations. The results were integrated to a parallel life-cycle experiment ran under the same exposure conditions. Emergence, life-cycle trait, showed first a substantial reduction in larval survival, followed by a rapid recovery within three generations. On the genomic level, we observed substantial selectively driven allele frequency changes (mean 0.566 ± 0.0879) within seven generations, associated with a mean selection coefficient of 0.322, indicating very strong selection pressure. Putative selection targets were mainly connected to oxidative stress in the microplastics exposed C. riparius population. This is the first multigenerational study on chironomids to provide evidence that upon exposure to polyamide microplastic there are changes on the genomic level, providing basis to rapid adaptation of aquatic organisms to microplastics.

Microplastic properties and their interaction with hydrophobic organic contaminants: a review

Microplastics (MPs) have been defined as particles of size < 5 mm and are characterized by hydrophobicity and large surface areas. MPs interact with co-occurring hydrophobic organic contaminants (HOCs) via sorption-desorption processes in aquatic and terrestrial environments. Ingestion of MPs by living organisms may increase exposure to HOC levels. The key mechanisms for the sorption of HOCs onto MPs are hydrophobic interaction, electrostatic interaction, π-π interactions, hydrogen bonding, and Van der Waals forces (vdW). Polymer type, UV-light-induced surface modifications, and the formation of oxygen-containing functional groups have a greater influence on electrostatic and hydrogen bonding interactions. In contrast, the formation of oxygen-containing functional groups negatively influences hydrophobic interaction. MP characteristics such as crystallinity, weathering, and surface morphology affect sorption capacity. Matrix properties such as pH, ionic strength, and dissolved organic matter (DOM) also influence sorption capacity by exerting synergistic/antagonistic effects. We reviewed the mechanisms of HOC sorption onto MPs and the polymer and matrix properties that influence the HOC sorption. Knowledge gaps and future research directions are outlined.

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

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

Molecular, biochemical and behavioral responses of Daphnia magna under long-term exposure to polystyrene nanoplastics

The presence and potential toxicity of nanoplastics (NPs) in aquatic ecosystems is an issue of growing concern. Although many studies have investigated the adverse effects of short-term exposure to high concentrations of NPs to aquatic organisms, the information on the consequences caused by the administration of low NPs concentrations over long-term exposure is limited. The present study aimed at investigating the effects induced by a long-term exposure (21-days) to two sub-lethal concentrations of polystyrene nanoplastics (PS-NPs; 0.05 and 0.5 µg/mL) on Daphnia magna. A multi-level approach was performed to assess potential sub-individual (i.e., molecular and biochemical) and individual (i.e., behavioural) adverse effects. At molecular level, the modulation of the expression of genes involved in antioxidant defence, response to stressful conditions and specific physiological pathways was investigated. Oxidative stress (i.e., the amount of pro-oxidants, the activity of antioxidant and detoxifying enzymes and lipid peroxidation) and energetic (i.e., protein, carbohydrate, lipid and total caloric content) biomarkers were applied to assess effects at the biochemical level, while swimming activity was measured to monitor changes in individual behavior. Although the 21-days exposure to PS-NPs induced a slight modulation of gene involved in oxidative stress response, biochemical analyses showed that D. magna individuals did not experience an oxidative stress condition. Significant changes in energy reserves of individuals exposed for 21 days to both the PS-NPs concentrations were observed, but no alterations of swimming activity occurred. Our results highlighted that the exposure to low concentrations of PS-NPs could pose a limited risk to D. magna individuals and suggested the importance of a multi-level approach to assess the risks of NPs on aquatic organisms.

Virgin and UV-weathered polyamide microplastics posed no effect on the survival and reproduction of Daphnia magna

Although evidence suggests that microplastic (MP) particles pose a risk to organisms, the effects of virgin and weathered MP should be evaluated separately as their effects may be different. In this work, we provide new information on the toxic potential of virgin and UV-weathered polyamide, one of the commonly used plastics worldwide. Polyamide MP particles were subjected to UV-weathering in wet conditions over 26 days in a customized irradiation chamber equipped with UV-C light tubes (15 W each, max. wavelength 254 nm). The toxicity of virgin and UV-weathered polyamide MP (< 180 µm in one dimension, 100 and 300 mg L^-1) was evaluated by studying Daphnia magna reproduction in natural lake water spiked with MP, following the 21-day OECD 211 test guideline. In parallel, a nonionic surfactant Tween 20 (7 mg L^-1) was added to the test medium to improve the suspendability of the MP. The results of the tests showed no adverse effects of either virgin or UV-weathered polyamide MP on the reproduction of D. magna. In addition, presence of Tween 20 in the test medium had no effects on the test results. These results bring a new perspective on the potential long-term impact of polyamide particles on aquatic organisms, especially considering that the polyamide has received marginal attention in the ecotoxicological research. However, standard test endpoints (survival and reproduction) may still miss long-term adverse effects of insoluble e.g., plastic particles and additional studies may be necessary.

Acute toxicity of microplastic fibers to honeybees and effects on foraging behavior

Microplastics (MPs) are considered emerging and persistent pollutants, although most of the research has been conducted on marine environments. Declines in honeybee populations have been reported globally, and recently, microplastic pollution has been considered a possible cause of this. Thus, we aimed to determine acute toxicity of polyester fibers and their effects on foraging behavior in honeybees. To test this, we conducted an oral acute toxicity bioassay, testing the effect of MPs on individual honeybees, and we studied the foraging behavior of honeybees when exposed to food and water containing MPs. We observed no mortality in honeybees fed with sucrose solution containing 100 mg MP/L after 24 and 48 h. Upon bee dissection of the digestive tract, we found 1.27 ± 1.5 fibers per bee, showing a mean (±SE) of 0.92 (±1.14) and 0.32 (±0.70) in their gut and crop respectively. The length of these microfibers ranged between 0.05 and 1.24 mm with a mean (±SE) of 0.42 (±0.25) mm. Although we did not find any preference or avoidance of MPs when presented in sucrose solutions and water; bees consumed MP-free solutions faster than solutions with 10 and 100 mg MPs/L. This might be due to changes in the viscosity of the solutions containing plastic and has implications for the impact of microplastic pollution on insects. Results suggest that MPS do not pose a threat to honeybees in the short term, based on the lack of acute mortality. However, bee foraging behavior does not prevent them from ingesting MPs present in water or resources which potentially might cause lethal long-term effects of MPs.

Toxicity of micro and nano tire particles and leachate for model freshwater organisms

Environmental sampling has documented a diversity of microplastics, including high levels of black rubber- generally identified as tire debris. Though organisms have been shown to ingest tire particles (TPs), past research focused on toxicity of leachate alone, overlooking potential effects of particles. To address these gaps, we assessed the toxicity of micro (1-20 µm) and nano (<1 µm) TPs for two model organisms, embryonic Zebrafish Danio rerio and the crustacean Daphnia magna. To assess effects on development, Zebrafish embryos were exposed to concentrations of TPs or leachate ranging from 0 to 3.0 × 10⁹ particles/ml and 0-100% respectively (n = 4). Greater mortality and sublethal malformations were observed following nano TP and leachate exposures as compared to micro TPs. Unique abnormalities between the exposures indicates that there is both chemical and particle-specific toxicity. We also observed D. magna mortality following a 48 h exposure of neonate to TPs or leachate, ranging from 0 to 3.3 × 10⁹ particles/ml and 0-100% respectively (n = 3). Though, particle-enhancement of toxicity was observed for both Zebrafish and D. magna, overall sensitivity to TPs differed. It is important to identify differential toxicities across species to achieve an understanding of the environmental impacts of TPs and the chemicals they leach.

Microplastic Fibers Increase Sublethal Effects of AgNP and AgNO3 in Daphnia magna by Changing Cellular Energy Allocation

The effects of combined exposure to microplastics and contaminants are still not completely understood. To fill this gap, we assessed the effects of polyethylene terephthalate microplastic fibers (100 mg/L; 360 µm average length) on the toxicity of silver nanoparticles (AgNPs; 32 nm) and silver nitrate (AgNO₃ ; 0.1-10 µg Ag/L) to Daphnia magna. Acute immobilization (median effect concentration [EC50]) and cellular energy allocation (CEA; ratio between available energy and energy consumption) were determined in neonates (<24 h old) and juveniles (7 d old), respectively. The 48-h EC50 for AgNP and AgNO₃ (2.6 and 0.67 µg Ag/L, respectively) was not affected by the presence of microplastic fibers (2.2 and 0.85 µg Ag/L, respectively). No decrease in the available energy was observed: lipid, carbohydrate, and protein contents were unaffected. However, a significant increase in energy consumption was observed in animals exposed to AgNO₃ (250% compared with control) and to the combination of microplastic fibers with AgNP (170%) and AgNO₃ (260%). The exposure to microplastic fibers alone or in combination with both Ag forms decreased the CEA (values were 55-75% of control values). Our results show that after short-term exposure (48 h), microplastic fibers increased Ag toxicity at a subcellular level (i.e., CEA), but not at the individual level (i.e., immobilization). These results highlight the importance of combining different levels of biological organization to fully assess the ecotoxicological effects of plastics in association with environmental contaminants. Environ Toxicol Chem 2022;41:896-904. © 2021 SETAC.

The Effect of Submicron Polystyrene on the Electrokinetic Potential of Cell Membranes of Red Blood Cells and Platelets

In recent years, many scientists have studied the effects of polymer micro- and nanostructures on living organisms. As it turns out, plastic can be a component of the blood of livestock, eaten by humans around the globe. Thus, it seems important to investigate possible changes in the physicochemical parameters and morphology of the cell membranes of blood morphotic elements (red blood cells and platelets) under the influence of polymer particles. The article presents research in which cell membranes were exposed to plain polystyrene (PS) and amino-functionalized polystyrene (PS-NH₂) of two different sizes. The polymers were characterized by infrared spectroscopy and dynamic light-scattering methods. To analyze possible changes caused by polymer exposure in the structure of the membranes, their zeta potentials were measured using the electrophoretic light-scattering technique. The concentration of the polymers, as well as the exposure time, were also taken into the consideration during the research. Based on the obtained results, we concluded that 100 and 200 nm PS, as well as 100 nm PS-NH₂, internalize into the cells. On the contrary, 200 nm PS-NH₂ particles attach to cell membranes. Our study clearly shows that particle size and surface chemistry determine the interaction with biological membranes.

Microplastics and Their Impact on Reproduction-Can we Learn From the C. elegans Model?

Biologically active environmental pollutants have significant impact on ecosystems, wildlife, and human health. Microplastic (MP) and nanoplastic (NP) particles are pollutants that are present in the terrestrial and aquatic ecosystems at virtually every level of the food chain. Moreover, recently, airborne microplastic particles have been shown to reach and potentially damage respiratory systems. Microplastics and nanoplastics have been shown to cause increased oxidative stress, inflammation, altered metabolism leading to cellular damage, which ultimately affects tissue and organismal homeostasis in numerous animal species and human cells. However, the full impact of these plastic particles on living organisms is not completely understood. The ability of MPs/NPs to carry contaminants, toxic chemicals, pesticides, and bioactive compounds, such as endocrine disrupting chemicals, present an additional risk to animal and human health. This review will discusses the current knowledge on pathways by which microplastic and nanoplastic particles impact reproduction and reproductive behaviors from the level of the whole organism down to plastics-induced cellular defects, while also identifying gaps in current knowledge regarding mechanisms of action. Furthermore, we suggest that the nematode Caenorhabditis elegans provides an advantageous high-throughput model system for determining the effect of plastic particles on animal reproduction, using reproductive behavioral end points and cellular readouts.

Shape, size, and polymer dependent effects of microplastics on Daphnia magna

The effects of microplastic (MP) pollution on organisms are gaining increasing attention. To date, a variety of polymers of different shapes and sizes are used in ecotoxicology. Although polystyrene (PS) is the predominant polymer type used in effect studies, it is still unclear whether the observed effects derive from the polymer itself or from a certain particle shape and size. To elucidate whether the effects are polymer specific, we conducted a systematic study on Daphnia magna by comparing various PS-MPs to nonplastic control particles with similar properties. In chronic exposure experiments, we used PS beads (6 µm; 20 µm), fibers (Ø 3 µm, length: 75.5 µm), and fragments (5.7 µm; 17.7 µm) in two different size classes and two different concentrations (500 and 5000 particles ml^-1) and in-house-produced control particles of comparable size, shape, concentration and, if possible, density. Although most PS properties did not elicit effects on the tested endpoints, we observed sublethal effects on D. magna life history and morphology for small PS beads and fragments. Interestingly, no adverse effects were detected for any of the control particles. Hence, the observed effects are polymer-specific, related to the size and shape of the polymer, and do not result from particle exposure per se.

Toward a Framework for Environmental Fate and Exposure Assessment of Polymers

Development of risk-assessment methodologies for polymers is an emerging regulatory priority to prevent negative environmental impacts; however, the diversity and complexity of polymers require adaptation of existing environmental risk-assessment approaches. The present review discusses the challenges and opportunities for the fate and exposure assessment of polymers in the context of regulatory environmental risk assessment of chemicals. The review discusses the applicability and adequacy for polymers of existing fate parameters used for nonpolymeric compounds and proposes additional parameters that could inform the fate of polymers. The significance of these parameters in various stages of an exposure-assessment framework is highlighted, with classification of polymers as solid or dissolved being key for identification of those parameters most relevant to environmental fate. Considerations to address the key limitations and knowledge gaps are then identified and discussed, specifically the complexity of polymer identification, with the need for characterization of the most significant parameters for polymer grouping and prioritization; the complexity of polymer degradation in the environment, with the need to incorporate the fate and hazards of degradation products into risk assessment; the requirement for development and standardization of analytical methods for characterization of polymer fate properties and degradation products; and the need to develop exposure modeling approaches for polymers. Environ Toxicol Chem 2022;41:515-540. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Size fractionation of high-density polyethylene breakdown nanoplastics reveals different toxic response in Daphnia magna

Plastic litter is a growing environmental problem. Recently, microplastics and nanoplastics, produced during breakdown processes in nature, have been in focus. Although there is a growing knowledge concerning microplastic, little is still known about the effect of nanoplastics. We have showed that mechanical breakdown of high-density polyethylene (HDPE), followed by filtration through 0.8 µm filters, produces material toxic to the freshwater zooplankton Daphnia magna and affected the reproduction in life-time tests. However, further size fractionation and purification reveals that the nanoplastics fraction is non-toxic at these concentrations, whereas the fraction with smaller sizes, below ~ 3 nm, is toxic. The HDPE nanoplastics are highly oxidized and with an average diameter of 110 nm. We conclude that mechanical breakdown of HDPE may cause environmental problems, but that the fraction of leached additives and short chain HDPE are more problematic than HDPE nanoplastics.

Seeking for a perfect (non-spherical) microplastic particle - The most comprehensive review on microplastic laboratory research

In recent decades, much attention has been paid to microplastic pollution, and research on microplastics has begun to grow exponentially. However, microplastics research still suffers from the lack of standardized protocols and methods for investigation of microplastics under laboratory conditions. Therefore, in this review, we summarize and critically discuss the results of 715 laboratory studies published on microplastics in the last five years to provide recommendations for future laboratory research. Analysis of the data revealed that the majority of microplastic particles used in laboratory studies are manufactured spheres of polystyrene ranging in size from 1 to 50 µm, that half of the studies did not characterize the particles used, and that a minority of studies used aged particles, investigated leaching of chemicals from microplastics, or used natural particles as a control. There is a large discrepancy between microplastics used in laboratory research and those found in the environment, and many laboratory studies suffer from a lack of environmental relevance and provide incomplete information on the microplastics used. We have summarized and discussed these issues and provided recommendations for future laboratory research on microplastics focusing on (i) microplastic selection, (ii) microplastic characterization, and (iii) test design of laboratory research on microplastics.

Comparative role of microplastics and microalgae as vectors for chlorpyrifos bioacumulation and related physiological and immune effects in mussels

Microplastics (MP) are contaminants of concern per se, and also by their capacity to sorb dissolved chemicals from seawater, acting as vehicles for their transfer into marine organisms. Still, the role of MP as vehicles for contaminants and their associated toxicological effects have been poorly investigated. In this work we have compared the role of MP (high density polyethylene, HDPE, ≤22 μm) and of natural organic particles (microalgae, MA) as vehicle for chlorpyrifos (CPF), one of the most common pesticides found in river and coastal waters. We have compared the capacity of MP and MA to carry CPF. Then, the mussel Mytilus galloprovincialis has been exposed for 21 days to dissolved CPF, and to the same amount of CPF loaded onto MP and MA. The concentration of CPF in mussel' tissues and several physiological, energetics and immune parameters have been analyzed after 7 and 21 days of exposure. Results showed similar CPF accumulation in mussel exposed to MP and to MA spiked with CPF. This revealed that MP acted as vector for CPF in a similar way (or even to a lesser extent) than MA. After 21 days of exposure mussels exposed to MP spiked with CPF displayed similar or more pronounced biological effects than mussels exposed to dissolved CPF or to MA loaded with CPF. This suggested that the combined "particle" and "organic contaminant" effect produced an alteration on the biological responses greater than that produced by each stressor alone, although this was evident only after 3 weeks of exposure.

Aggregate exposure pathways for microplastics (mpAEP): An evidence-based framework to identify research and regulatory needs

Microplastics as emerging contaminants have been detected from peaks to poles. High concerns on the risks of microplastic pollution to humans and ecosystems have therefore been raised in the past decade. While a large number of studies have been conducted to investigate the environmental levels and toxicity of microplastics, the information generated to support risk assessment is fragmented and the coherence between different types of study is largely lacking. Here we introduced the Aggregate Exposure Pathway (AEP), a conceptual framework originally proposed for chemical exposure assessment, to facilitate organization, visualization and evaluation of existing information generated from microplastic research, and to efficiently identify future knowledge and regulatory needs. A putative microplastic AEP network (mpAEP) was developed to demonstrate the concept and model development strategies. Two mpAEP case studies, with polyethylene (PE) as a prototype, were then presented based on existing environmental exposure data collected from the Changjiang Estuary and the East China Sea (Case I), and the Oslo Fjord (Case II), respectively. Weight of evidence (WoE) assessment of the mpAEPs were performed for evaluating the essentiality, theoretical plausibility, empirical evidence and quantitative understanding of the evidence and relationships in the AEPs. Both cases showed moderate/high WoE to support the strength of the models, whereas also displayed clear knowledge gaps, thus providing guidance for future investigations and regulations. The mpAEP framework introduced herein presents a novel strategy for organizing fragmented information from diverse types of microplastic research, enhancing mechanistic understanding of causal relationships and facilitating the development of quantitative prediction models for research and regulation in the future.

A comparative investigation of toxicity of three polymer nanoparticles on acorn barnacle (Amphibalanus amphitrite)

Pollution from plastic waste is increasingly prevalent in the environment and beginning to generate significant adverse impact on the health of living organisms. In this study, we investigate the toxicity of polymer nanoparticles exposed to Acorn Barnacle (Amphibalanus amphitrite) nauplii, as an animal model. Highly stable aqueous dispersion of luminescent nanoparticles from three common polymers: polymethylmethacrylate (PMMA), polystyrene (PS), and polyvinylchloride (PVC), were prepared via nanoprecipitation and fully characterised. Exposure studies of these polymer particles to freshly spawned barnacle nauplii were performed within a concentration range from 1 to 25 mg/L under laboratory-controlled conditions. The exposure to PMMA and PS nanoparticles did not show detrimental toxicity and did not cause sufficient mortality to compute a LC₅₀ value. However, PVC nanoparticles were significantly toxic with a mortality rate of up to 99% at 25 mg/L, and the calculated LC₅₀ value for PVC nanoparticles was 7.66 ± 0.03 mg/L, 95% CI. Interestingly, PVC nanoparticle aggregates were observed to adhere to the naupliar carapace and appendages at higher concentrations and could not be easily removed by washings. To explore the possibility of chemical toxicity of polymer nanoparticles, analysis of the polymer powders which was used to prepare the nanoparticles was conducted. The presence of low molecular weight oligomers such as dimers, trimers and tetramers were observed in all polymer samples. The chemical nature and concentration of such compounds are likely responsible for the observed toxicity to the barnacle nauplii. Overall, our study shows that care should be exercised in generalising the findings of exposure studies performed using one type of plastic particles, as the use of different plastic particles may elicit different responses inside a living organism.

Spatial distribution of microplastics in Chinese freshwater ecosystem and impacts on food webs

Over the past two decades, there has been a lot of discussion about the rapid increase of microplastics (MPs) due to their persistence, ubiquity, and toxicity. The widespread distribution of MPs in various freshwater ecosystems makes them available for different trophic levels biota. The ingestion and trophic transfer of MPs may induce potential impacts on freshwater food webs. Therefore, this systematic review is an in-depth review of 51 recent studies to confirm the spatial distribution of MPs in the Chinese freshwater ecosystem including water, sediment and biota, exposure pathways, and impacts on freshwater food webs. The result suggested the white, transparent and colored, Polypropylene (PP) and Polyethylene (PE) of <1 mm fibers were dominant in Chinese freshwaters. The uptake of MPs by various freshwater organisms as well as physiological, biological and chemical impacts on food webs were also elucidated. At last, some limitations were discussed for future studies to better understand the effects of MPs on food webs.

Environmental Impacts of Microplastics and Nanoplastics: A Current Overview

The increasing distribution of miniaturized plastic particles, viz. microplastics (100 nm–5 mm) and nanoplastics (less than 100 nm), across the various ecosystems is currently a subject of major environmental concern. Exacerbating these concerns is the fact that microplastics and nanoplastics (MNPs) display different properties from their corresponding bulk materials; thus, not much is understood about their full biological and ecological implications. Currently, there is evidence to prove that these miniaturized plastic particles release toxic plastic additives and can adsorb various chemicals, thereby serving as sinks for various poisonous compounds, enhancing their bioavailability, toxicity, and transportation. Furthermore, there is a potential danger for the trophic transfer of MNPs to humans and other higher animals, after being ingested by lower organisms. Thus, this paper critically analyzes our current knowledge with regard to the environmental impacts of MNPs. In this regard, the properties, sources, and damaging effects of MNPs on different habitats, particularly on the biotic components, were elucidated. Similarly, the consequent detrimental effects of these particles on humans as well as the current and future efforts at mitigating these detrimental effects were discussed. Finally, the self-cleaning efforts of the planet via a range of saprophytic organisms on these synthetic particles were also highlighted.

Toxicity of nanoplastics to zooplankton is influenced by temperature, salinity, and natural particulate matter

Increases in temperature/salinity promote nanoplastics toxicity, while organic matter/natural colloids mitigate toxicity.

Long-term exposure of Daphnia magna to polystyrene microplastic (PS-MP) leads to alterations of the proteome, morphology and life-history

In the past years, the research focus on the effects of MP on aquatic organisms extended from marine systems towards freshwater systems. An important freshwater model organism in the MP field is the cladoceran Daphnia, which plays a central role in lacustrine ecosystems and has been established as a test organism in ecotoxicology. To investigate the effects of MP on Daphnia magna, we performed a chronic exposure experiment with polystyrene MP under strictly standardized conditions. Chronic exposure of D. magna to PS microparticles led to a significant reduction in body length and number of offspring. To shed light on underlying molecular mechanisms induced by microplastic ingestion in D. magna, we assessed the effects of PS-MP at the proteomic level, as proteins, e.g., enzymes, are especially relevant for an organism's physiology. Using a state-of-the-art mass spectrometry based approach, we were able to identify 28,696 different peptides, which could be assigned to 3784 different proteins. Using a customized bioinformatic workflow, we identified 41 proteins significantly altered in abundance (q-value <0.05) in the PS exposed D. magna. Among the proteins increased in the PS treated group were several sulfotransferases, involved in basic biochemical pathways, as well as GABA transaminase catalyzing the degradation of the neurotransmitter GABA. In the abundance decreased group, we found essential proteins such as the DNA-directed RNA polymerase subunit and other proteins connected to biotic and inorganic stress and reproduction. Strikingly, we further identified several digestive enzymes that are significantly downregulated in the PS treated animals, which could have interfered with the affected animal's nutrient supply. This may explain the altered morphological and life history traits of the PS exposed daphnids. Our results indicate that long-term exposure to PS microplastics, which are frequently detected in environmental samples, may affect the fitness of daphnids.

Variable Fitness Response of Two Rotifer Species Exposed to Microplastics Particles: The Role of Food Quantity and Quality

Plastic pollution is an increasing environmental problem, but a comprehensive understanding of its effect in the environment is still missing. The wide variety of size, shape, and polymer composition of plastics impedes an adequate risk assessment. We investigated the effect of differently sized polystyrene beads (1-, 3-, 6-µm; PS) and polyamide fragments (5–25 µm, PA) and non-plastics items such as silica beads (3-µm, SiO₂) on the population growth, reproduction (egg ratio), and survival of two common aquatic micro invertebrates: the rotifer species Brachionus calyciflorus and Brachionus fernandoi. The MPs were combined with food quantity, limiting and saturating food concentration, and with food of different quality. We found variable fitness responses with a significant effect of 3-µm PS on the population growth rate in both rotifer species with respect to food quantity. An interaction between the food quality and the MPs treatments was found in the reproduction of B. calyciflorus. PA and SiO₂ beads had no effect on fitness response. This study provides further evidence of the indirect effect of MPs in planktonic rotifers and the importance of testing different environmental conditions that could influence the effect of MPs.

Effects of synthetic and natural microfibers on Daphnia magna-Are they dependent on microfiber type?

Microfibers, which are sourced from textiles and some products from the fishery industry, are the biggest contributors to microplastic pollution in aquatic ecosystems. In addition to these synthetic microfibers, naturally derived microfibers can also be found in aquatic environments. However, there are limited studies on the ecotoxicity of natural microfibers. To shed light on this topic, this study assessed and compared the toxicity of natural and synthetic microfibers on Daphnia magna, using lyocell, polyester (PET) and polypropylene (PP) microfibers. To evaluate the adverse effect of microfibers on D. magna, after effects including depuration, food intake, growth, mortality, and immobilization rate were continually observed for up to 96 h after the initial 48 h of exposure to the microfibers. Immobilization rate decreased in the following order: PP, PET, and lyocell. However, the depuration of microfibers in the lyocell and PET treatment groups was similar, with higher mortality rates than in the PP treatment group. Furthermore, despite the high rates of food intake following exposure, the lyocell and PET exposed groups exhibited growth inhibition during the same period. This growth inhibition corresponded with, and was likely due to, reductions in the length of gut microvilli, probably an expression of gut damage, which is believed to have reduced nutrient absorption in the affected individuals. Based on the results of this study, it was confirmed that even natural microfibers, and not just synthetic microfibers, can have adverse effects on aquatic organisms. This study confirmed not only the toxicity of microfibers, but also the consequences of their after effects. These results could be the basis for future research on the after effects of microplastics on aquatic organisms and provide directions for further microplastic ecotoxicity studies.

Particle shape does not affect ingestion and egestion of microplastics by the freshwater shrimp Neocaridina palmata

The ingestion of microplastics (MPs) is well documented for various animals and spherical MPs (beads) in many studies. However, the retention time and egestion of MPs have been examined less, especially for irregular MPs (fragments) which are predominantly found in the environment. Furthermore, the accumulation of such particles in the gastrointestinal tract is likely to determine whether adverse effects are induced. To address this, we investigated if the ingestion and egestion of beads are different to those of fragments in the freshwater shrimp Neocaridina palmata. Therefore, organisms were exposed to 20-20,000 particles L-1 of either polyethylene (PE) beads (41 μm and 87 μm) or polyvinyl chloride (PVC) fragments (<63 μm). Moreover, shrimps were exposed to 20,000 particles L-1 of either 41 μm PE and 11 μm polystyrene (PS) beads or the PVC fragments for 24 h, followed by a post-exposure period of 4 h to analyze the excretion of particles. To simulate natural conditions, an additional fragment ingestion study was performed in the presence of food. After each treatment, the shrimps were analyzed for retained or excreted particles. Our results demonstrate that the ingestion of beads and fragments were concentration-dependent. Shrimps egested 59% of beads and 18% of fragments within 4 h. Particle shape did not significantly affect MP ingestion or egestion, but size was a relevant factor. Medium- and small-sized beads were frequently ingested. Furthermore, fragment uptake decreased slightly when co-exposed to food, but was not significantly different to the treatments without food. Finally, the investigations highlight that the assessment of ingestion and egestion rates can help to clarify whether MPs remain in specific organisms and, thereby, become a potential health threat.

Trophic transfer of microbeads to jellyfish and the importance of aging microbeads for microplastic experiments

Concepts in microplastics studies are not well established due to the emerging nature of microplastic research, especially in jellyfish. We conducted experiments to test whether ephyrae would ingest more microbeads via trophic transfer than direct ingestion and whether medusae would ingest more aged microbeads than virgin microbeads. We exposed ephyrae of Aurelia coerulea to two treatments, aged microbeads and Artemia nauplii that had ingested microbeads. We found that the ephyrae ingested 35 times more microbeads via trophic transfer than by direct ingestion. In the second experiment, medusae of A. coerulea were exposed to virgin microbeads and microbeads in seawater under a 12/12 light/dark cycle or constant darkness. Ingestion rates of microbeads from the light incubation were greater than those from the dark incubation or virgin microbeads, suggesting the likely presence of photosynthetic organisms in biofilms from the light incubation increased the palatability of the microbeads and promoted their ingestion.

Inclusion of shape parameters increases the accuracy of 3D models for microplastics mass quantification

As microplastics may bring about adverse effects on living organisms, it is important to establish more precise quantification approaches to better understand their dynamics. One method to determine the concentration of microplastics is to estimate their mass using three-dimensional (3D) models, but its accuracy is not well known. In this study, we evaluated the shape of the particles and verified the accuracy of a 3D model-based mass estimation using samples from a tidal flat facing Tokyo Bay. The particle shape evaluation suggested that the microplastics were flat and irregular in shape; based on these data, we created two types of models to estimate their mass. As a result, an accuracy of mass estimation by our model was higher than other models that consider the slenderness and flatness of particles. The optimization of mass estimation methods based on 3D models may improve the reliability of microplastic evaluation in monitoring studies.

Microplastic pollution in freshwater systems in Southeast Asia: contamination levels, sources, and ecological impacts

Plastics are synthetic polymers known for their outstanding durability and versatility, and have replaced traditional materials in many applications. Unfortunately, their unique traits ensure that they pose a major threat to the environment. While literature on freshwater microplastic contamination has grown over the recent years, research undertaken in rapidly developing countries, where plastic production and use are increasing dramatically, has lagged behind that in other parts of the world. In the South East Asia (SEA) region, basic information on levels of contamination is very limited and, as a consequence, the risk to human and ecological health remains hard to assess. This review synthesises what is currently known about microplastic contamination of freshwater ecosystems in SEA, with a particular focus on Malaysia. The review 1) summarises published studies that have assessed levels of contamination in freshwater systems in SEA, 2) discusses key sources and transport pathways of microplastic in freshwaters, 3) outlines what is known of the impacts of microplastic on freshwater organisms, and 4) identifies key knowledge gaps related to our understanding of the transport, fate and effects of microplastic.

Exposure to polystyrene microplastics induced gene modulated biological responses in zebrafish (Danio rerio)

The substantial increase in the occurrence of microplastics (MPs) in the aquatic ecosystem has been recognized as an emerging concern today. Studies have revealed the toxicity of microplastics on behavior, physiology, and reproduction of fishes. Despite several reports, there are inadequate literature reports on the impact of microplastics on aquatic forms at the molecular level. The present study was aimed to investigate the adverse effects of polystyrene microplastics (PS-MPs) in adult zebrafish model system. Healthy fishes were exposed to different concentrations (10 and 100 μg L^-1) of PS-MPs for 35 d. The results revealed that PS-MPs exposure induced ROS (Reactive oxygen species) generation disrupting the antioxidant defense system, hepatic enzymology, and neurotransmission. Correspondingly, the histological studies showed PS-MPs induced histopathological lesions, including inflammation, degeneration, necrosis, and hemorrhage, in the brain and liver tissues of zebrafish. Furthermore, PS-MPs exposure significantly upregulated the expressions of gstp1, hsp70l, and ptgs2a gene along with the downregulation of cat, sod1, gpx1a, and ache genes. Therefore, the present study illustrates the potential of PS-MPs to induce different grades of toxic impacts in fishes by altering its metabolic mechanism, histological architecture, and gene regulation pattern through ROS induced oxidative stress.

Reality Check: Experimental Studies on Microplastics Lack Realism

Environmental microplastics are gaining interest due to their ubiquity and the threat they pose to environmental and human health. Critical studies have revealed the abundance of microplastics in nature, while others have tested the impacts of these small plastics on organismal health in the laboratory. Yet, there is often a mismatch between these two areas of research, resulting in major discrepancies and an inability to interpret certain findings. Here, we focus on several main lines of inquiry. First, even though the majority of environmental microplastics are plastic microfibers from textiles, laboratory studies still largely use spherical microbeads. There are also inconsistencies between the measurements of microplastics in the environment as compared to the concentrations that tend to be used in experimental studies. Likewise, the period of exposure occurring in experimental studies and in the environment are vastly different. Lastly, although experimental studies often focus on a particular subset of toxic chemicals present on microplastics, textile microfibers carry other dyes and chemicals that are understudied. They also cause types of physical damage not associated with microspheres. This review will analyze the literature pertaining to these mismatches, focusing on aquatic organisms and model systems, and seek to inform a path forward for this burgeoning area of research.

Ecological risks in a 'plastic' world: A threat to biological diversity?

Microplastics pollution is predicted to increase in the coming decades, raising concerns about its effects on living organisms. Although the effects of microplastics on individual organisms have been extensively studied, the effects on communities, biological diversity, and ecosystems remain underexplored. This paper reviews the published literature concerning how microplastics affect communities, biological diversity, and ecosystem processes. Microplastics increase the abundance of some taxa but decrease the abundance of some other taxa, indicating trade-offs among taxa and altered microbial community composition in both the natural environment and animals' gut. The alteration of community composition by microplastics is highly conserved across taxonomic ranks, while the alpha diversity of microbiota is often reduced or increased, depending on the microplastics dose and environmental conditions, suggesting potential threats to biodiversity. Biogeochemical cycles, greenhouse gas fluxes, and atmospheric chemistry, can also be altered by microplastics pollution. These findings suggest that microplastics may impact the U.N. Sustainability Development Goals (SDGs) to improve atmospheric, soil, and water quality and sustaining biodiversity.

Microplastics as a vehicle of exposure to chemical contamination in freshwater systems: Current research status and way forward

Contamination by microplastics is increasing steadily worldwide, affecting all environments. Additionally, aquatic organisms are often exposed to mixtures of other contaminants, including various chemicals. Numerous studies reported adsorption of chemicals to microplastics, raising concern about their possible role as vehicles of exposure through transfer to biota. Nevertheless, until recently, the studies on the topic were mostly focused on the marine environment. In the past five years, however, plenty of publications contributed empirical data about freshwater ecosystems, raising the need for a critical appraisal of the information. Herein the scientific literature was reviewed and multivariate data analysis was done. The analysed studies employed widely different experimental designs, endpoints, test species, shapes and concentrations of various polymer types and chemicals, often not relevant for the freshwater environment. Our integrated analytical approach revealed unfathomable research gaps, given the theoretical knowledge available and lessons learned from research about the marine environment. Greater harmonization of laboratory studies investigating this topic is needed, as well as testing conditions reflecting real exposure scenarios. Furthermore, standardized testing protocols are urgently required to guide such experiments and improve the comparability of the results obtained.

Microplastics and plankton: Knowledge from laboratory and field studies to distinguish contamination from pollution

Due to their ubiquitous presence, size and characteristics as ability to adsorb pollutants, microplastics are hypothesized as causing a major impact on smaller organisms, such as plankton. Despite this, there is a need to determine whether these impacts just relate to the environmental presence of the materials or their effects on biological processes. Therefore, we aimed to 1) review current research on plankton and microplastics; 2) compare field and laboratory experimental findings, and 3) identify knowledge gaps. The systematic review showed that 70% of the 147 relevant scientific publications were from laboratory studies and microplastics interactions with plankton were recorded in 88 taxa. Field study publications were relatively scarce and the characteristics of microplastics collected in the field were very different from those used in laboratory experiments thereby limiting the comparison between studies. Our systematic review highlighted knowledge gaps in: 1) the number of field studies; 2) the non-comparability between laboratory and field conditions, and 3) the low diversity of plankton species studied. Furthermore, this review indicated that while there are many studies on contamination by microplastics, the effects of this contamination (i.e., pollution per se) have been less well-studied, especially in the field at population, community, and ecosystem levels.

Environmental Microplastic Particles vs. Engineered Plastic Microparticles-A Comparative Review

Microplastic particles (MPs) pose a novel threat to nature. Despite being first noticed in the 1970s, research on this topic has only surged in recent years. Researchers have mainly focused on environmental plastic particles; however, studies with defined microplastic particles as the sample input are scarce. Furthermore, comparison of those studies indicates a discrepancy between the particles found (e.g., in the environment) and those used for further research (e.g., exposure studies). Obviously, it is important to use particles that resemble those found in the environment to conduct appropriate research. In this review, different categories of microplastic particles are addressed, before covering an overview of the most common separation and analysis methods for environmental MPs is covered. After showing that the particles found in the environment are mostly irregular and polydisperse, while those used in studies with plastic microparticles as samples are often not, different particle production techniques are investigated and suggestions for preparing realistic plastic particles are given.

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

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

Ecotoxicological effects of different size ranges of industrial-grade polyethylene and polypropylene microplastics on earthworms Eisenia fetida

The effects of microplastics (MPs) on terrestrial organisms remain poorly understood, even though soil is an important MPs sink. In this study, the earthworms Eisenia fetida were exposed to 0.25% (w/w) of industrial-grade high-density polyethylene (HDPE, 28-145, 133-415 and 400-1464 μm) and polypropylene (PP, 8-125, 71-383 and 761-1660 μm) MPs in an agricultural soil for 28 d. The results showed that HDPE and PP MPs with different size ranges can be ingested by E. fetida. Exposure to different size ranges of HDPE and PP MPs altered the activities of superoxide dismutase, catalase and glutathione S-transferase and induced an increase in the 8-hydroxy-2'-deoxyguanosine level in E. fetida, suggesting that MPs-induced oxidative stress occurred in E. fetida. A size and type-dependent toxicity of MPs to E. fetida was demonstrated by the integrated biological response index. In addition, to obtain detailed molecular information on the responses of E. fetida to MPs exposure, transcriptomic analysis was conducted for E. fetida from HDPE (28-145 μm) and PP (8-125 μm) treatment groups. Transcriptomic analysis identified 34,937 and 28,494 differentially expressed genes in the HDPE and PP MPs treatments compared with the control, respectively. And, exposure to HDPE and PP MPs significantly disturbed several pathways closely related to neurodegeneration, oxidative stress and inflammatory responses in E. fetida. This study provides important information for the ecological risk assessment of different size ranges and types of industrial-grade MPs.

Resolving the effects of environmental micro- and nanoplastics exposure in biota: A knowledge gap analysis

The pervasive spread of microplastics (MPs) and nanoplastics (NPs) has raised significant concerns on their toxicity in both aquatic and terrestrial environments. These polymer-based materials have implications for plants, wildlife and human health, threatening food chain integrity and ultimate ecosystem resilience. An extensive - and growing - body of literature is available on MP- and NP-associated effects, including in a number of aquatic biota, with as yet limited reports in terrestrial environments. Effects range from no detectable, or very low level, biological effects to more severe outcomes such as (but not limited to) increased mortality rates, altered immune and inflammatory responses, oxidative stress, genetic damage and dysmetabolic changes. A well-established exposure route to MPs and NPs involves ingestion with subsequent incorporation into tissues. MP and NP exposures have also been found to lead to genetic damage, including effects related to mitotic anomalies, or to transmissible damage from sperm cells to their offspring, especially in echinoderms. Effects on the proteome, transcriptome and metabolome warrant ad hoc investigations as these integrated "omics" workflows could provide greater insight into molecular pathways of effect. Given their different physical structures, chemical identity and presumably different modes of action, exposure to different types of MPs and NPs may result in different biological effects in biota, thus comparative investigations of different MPs and NPs are required to ascertain the respective effects. Furthermore, research on MP and NP should also consider their ability to act as vectors for other toxicants, and possible outcomes of exposure may even include effects at the community level, thus requiring investigations in mesocosm models.

Negative impacts of realistic doses of spherical and irregular microplastics emerged late during a 42 weeks-long exposure experiment with blue mussels

Microplastics have been found in all compartments of the environment, and numerous life forms are known to take up the anthropogenic particles. Marine filter feeders are particularly susceptible to ingest suspended microplastics, but long-term studies on the potential effects of this uptake are scarce. We exposed juvenile Mytilus spp. to environmentally realistic doses of irregularly shaped polyvinylchloride (PVC) particles (15, 1500, 15,000, 150,000, 1,500,000 particles/individual/week calibrated in the size range 11-60 μm) and regularly shaped polystyrene (PS) beads (15, 1500, 15,000 particles/individual/week, 40 μm) over 42 weeks. During this period, we monitored physiological traits such as clearance rate, byssus production, growth rate, superoxide dismutase (SOD) activity, malondialdehyde (MDA) concentrations, and the condition index (CI). Negative effects of the tested microplastics on mussel performance emerged late in the experiment and were rather weak. Interestingly, even after having received the lowest particle dose of PS, SOD activity in the gill was significantly lower in mussels exposed to microplastics compared to a group of conspecifics that were kept in clean water. However, growth and CI, which are both closely related to the fitness of the mussels, were not found to be impaired at the end of the exposure phase. This is the so far longest laboratory microplastic exposure study on mussels and we worked with particle doses that reflect todays pollution levels. The small effect sizes we observed for the response variables assessed suggest that these specific microplastics pose only a minor threat to blue mussel populations.

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.

Are Honey Bees at Risk from Microplastics?

Microplastics (MPs) are ubiquitous and persistent pollutants, and have been detected in a wide variety of media, from soils to aquatic systems. MPs, consisting primarily of polyethylene, polypropylene, and polyacrylamide polymers, have recently been found in 12% of samples of honey collected in Ecuador. Recently, MPs have also been identified in honey bees collected from apiaries in Copenhagen, Denmark, as well as nearby semiurban and rural areas. Given these documented exposures, assessment of their effects is critical for understanding the risks of MP exposure to honey bees. Exposure to polystyrene (PS)-MPs decreased diversity of the honey bee gut microbiota, followed by changes in gene expression related to oxidative damage, detoxification, and immunity. As a result, the aim of this perspective was to investigate whether wide-spread prevalence of MPs might have unintended negative effects on health and fitness of honey bees, as well as to draw the scientific community’s attention to the possible risks of MPs to the fitness of honey bees. Several research questions must be answered before MPs can be considered a potential threat to bees.

Size-dependent chronic toxicity of fragmented polyethylene microplastics to Daphnia magna

Fragmented microplastics (MPs) are emerging contaminants in freshwater environments; however, long-term assessment of their toxicity remains limited. This study aimed to evaluate and compare the chronic toxicity (21 d) of synthesized polyethylene MP fragments and commercial polyethylene MP beads to Daphnia magna. Ingestion of small- and large-sized MP fragments (17.23 ± 3.43 and 34.43 ± 13.09 μm, respectively) by D. magna was significantly (p < 0.05) higher, by 8.3 and 5.2 times, respectively, than that of MP beads (39.54 ± 9.74 μm). The survival of D. magna exposed to small- and large-sized MP fragments (20 and 60%, respectively) was significantly (p < 0.05) lower than that of individuals exposed to MP beads (90%). In particular, small-sized MP fragments significantly (p < 0.05) reduced algal feeding (from 95% to 76%), body length (from 4.20 mm to 3.98 mm), and the number of offspring (from 109 to 74) in D. magna, when compared with MP beads, likely due to their longer retention time and greater interference in the digestive tract. These findings suggest that fragmentation of MPs into μm-scale particles can pose a significant ecological risk to aquatic organisms; moreover, further studies are required to identify the underlying toxicity mechanism.

Current understanding and challenges for aquatic primary producers in a world with rising micro- and nano-plastic levels

The impacts of micro- and nanoplastics (MNPs) on aquatic animals have been intensively studied; however, the extent and magnitude of potential effects of MNPs on aquatic primary producers are poorly understood. In this study, we quantitatively analyzed the published literature to examine the impacts of MNPs on growth, photosynthesis, pigments, and metabolism of aquatic microalgae. MNPs negatively affected growth of microalgae but usually had a high EC₅₀ (>25 mg/L). However, positively charged MNPs had a much lower EC₅₀ (<1 mg/L). MNPs lowered maximum photochemical efficiency of photosystem II (F_v/F_m) with the effect increasing with concentration of MNPs but diminishing with exposure time, and also reduced chlorophyll a content to enhanced extent with increased MNPs concentration. MNPs induced relatively higher changes in superoxide dismutase (SOD) and malondialdehyde (MDA) levels in marine algae than in freshwater algae. Reactive oxygen species (ROS) levels increased with MNPs concentration and exposure time while SOD levels first increased and then decreased with increasing MNPs concentration. Macrophytes were found to be able to trap MNPs via multiple mechanisms. Future work should focus on the mechanisms behind MNPs impacts on primary productivity and global carbon cycle, and the combined effects of MNPs with other environmental factors.

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.

Relative importance of aqueous leachate versus particle ingestion as uptake routes for microplastic additives (hexabromocyclododecane) to mussels

Microplastic pollution is emerging as a global environmental issue, and its potential for transferring hazardous chemicals to aquatic organisms is gaining attention. Studies have investigated the transfer of chemicals, mainly sorbed chemicals, through ingestion of microplastics by organisms, but limited information is available regarding chemical additives and uptake via the aqueous route through plastic leaching. In this study, we compared two bioaccumulation pathways of the additive hexabromocyclododecane (HBCD) by exposing mussels (Mytilus galloprovincialis) to two different sizes of expanded polystyrene (EPS): inedible size (4.2-5.5 mm) for leachate uptake and edible size (20-770 μm) for particle ingestion and leachate uptake. Over 10 days, the HBCD concentration increased significantly in mussels in the EPS exposure groups, indicating that EPS microplastic acts as a source of HBCD to mussels. The concentration and isomeric profiles of HBCD in mussels show that uptake through the aqueous phase is a more significant pathway for bioaccumulation of HBCD from EPS to mussels than particle ingestion. HBCD levels measured in EPS, leachate and exposed mussels from this study are environmentally relevant concentration. The fate and effects of chemical additives leached from plastic debris in ecosystem requires further investigation, as it may affect numerous environments and organisms through the aqueous phase.