Microplastic consumption and excretion by fathead minnows (Pimephales promelas): Influence of particles size and body shape of fish

Alteration to organismal behavior due to microplastic exposure

Influx of plastics into the biosphere has faced increased public scrutiny in the last twenty years. Plastics fragment into particles at the microscale which can lead them to interact with organisms in unanticipated ways. Research has focused on hazards linked to ingestion of microplastics with little research focused on how secondary effects influence organismal behavior and interspecies relationships. Plastics do not establish homogenous test suspensions; they either float or sink. The present study investigated how the presence of microplastics influenced the behavior of Daphnia magna, and two planktivorous fish, Pimephales promelas and Gambusia affinis. The study investigated two plastic types: fluorescent microspheres and microplastic fragments. The results demonstrated that microplastics influenced the behavior of the organisms with effects dependent on species and plastic type. Microplastics attracted D. magna and decreased their mobility and total swimming distance. Both fish species were more often found at the bottom of the chamber and their behavior was linked to D. magna location. Some changes in fish mobility were observed with fluorescent microspheres. Coloration of microplastics may have influenced the organism's responses results and further research is needed. Results of the present study reveal a potential effect of microplastics on communal distribution of aquatic organisms in natural ecosystems.

Microplastics accumulation in leaf litter: Field evidence for microplastic ingestion and transfer through prey-predatory relationships

Microplastics (MP) contamination of the terrestrial environment is a global concern. The contamination level of MPs in leaf litter and soil fauna that feed on it has not been reported. Moreover, the interspecific relationships among field soil fauna at different trophic levels and their effects on MP loads remain unclear. Thus, we selected a model food chain including a prey-isopod and predatory-spider relationship to evaluate the role of this relationship in the MPs body burden. The results showed that MP concentrations in the fallen leaf litter ranged from 5340 ± 336.15 particles/kg to 10920 ± 432.43 particles/kg dry weight during different seasons of the monitoring year. However, we found MP particles ranged from 1.17 ± 0.25 to 10.11 ± 1.02 particles/ind in isopods and 2.25 ± 0.35 to 4.25 ± 0.35 particles/ind in spiders. All extracted MPs were colored and blue was the most prevalent one. Fiber-shaped polyester (≤500 μm) and (501-1000 μm) were the most common MPs size in tested fauna and leaf litter, respectively. Our findings indicate that MP ingestion by isopods pose a significant risk for higher trophic levels in the terrestrial food chain. Magnification of MPs was observed in the predatory spider with MP concentration increasing from 46.45 ± 16.68 particles/gm wet weight in isopod to 147.51 ± 54.4 particles/gm wet weight in spider, annually. Furthermore, the results indicate that these soil invertebrates may represent a source of MPs to other organisms in the environment.

Occurrence, trophic transfer and risk assessment of microplastics in fishery organisms from the Bohai Sea, China

Marine microplastic (MP) pollution has emerged as a critical environmental issue, posing significant risks to a wide range of marine organisms. However, the trophic transfer of MPs with different characteristics among marine species remain poorly understood. This study investigated the abundances and characteristics of MPs in various fishery organisms from the Bohai Sea, China, and evaluated the influencing factors, trophic transfer and associated risks. Results showed that MP abundances ranged from 0.50 ± 0.52-2.38 ± 1.41 items per individual. Most MPs were smaller than 1 mm (74.6 %), with fiber being the most common shape (80.8 %), and transparent being the dominant color (75.3 %). Among the 13 identified polymer types, cellophane was the most prevalent. MP ingestion by fishery organisms was significantly influenced by body size, biological taxa, and habitat, while showing no correlation with feeding habits. Notably, the trophic transfer and significant biomagnification of MPs occurred through the marine food chain. Specially, MPs within the size ranges from 30 to 500 µm, in fibrous shape, transparent color, and composed of cellophane, PET, PP, and PA polymers, demonstrated enhanced potential for trophic transfer. PHI-based quantitative risk assessment revealed a medium to danger risk of MPs to marine fishery organisms, with hazard indices spanning medium to danger risk levels. These findings provide new insights into the bioaccumulation and risk of MPs across different trophic levels in marine organisms.

Microplastic footprints in sharks and rays: First assessment of microplastic pollution in two cartilaginous fishes, hardnose shark and whitespotted whipray

Microplastic (MP) pollution is an emerging environmental problem worldwide and has caused widespread concern both in terrestrial and aquatic ecosystems due to their potential impacts on the human health, and health of aquatic organisms and the environment. Little is known about the exposure of top marine predators to MP contamination (debris 0.1μm - <5mm, also called MPs). For the first time, MPs have been characterized in carnivore demersal elasmobranch specimens of hardnose shark Carcharhinus macloti, and the whitespotted whipray Maculabatis gerrardi. The specimens were from the Persian Gulf and Sea of Oman, and MPs were extracted from their intestines, gills, and skin. MPs were found in every sampled tissue examined: this is higher pollution than previously reported for elasmobranch. The total MPs for these organs were 12.6 MPs/g body mass of sharks, and 17.8 MPs/g in the whiprays on average. The most common MPs found were fibres (59%), and filaments (35%); pointing towards fishing gears and limited wastewater treatment. Fragments, films, and foams were <2.1 %; a less abundant problem. The most abundant MPs sampled were ∼0.5 mm ≤ L< 1 mm (when the limit of detection was 0.1 mm), and blue was the most common MP color hinting intake due to visual confusion. Polycarbonate and nylon were the most abundant polymers in the MPs recovered. The overall findings show that C. macloti and M. gerrardi are vulnerable to plastic and it reflects the critical state of their habitat.

Exploring the ecotoxicological impacts of microplastics on freshwater fish: A critical review

Microplastics (MPs) have become ubiquitous in the environment, prompting significant concern among ecotoxicologists due to their potential toxic effects. These particles originate from various sources, including the fragmentation of larger plastic debris (secondary microplastics) and consumer products such as liquid soaps, exfoliants, and cleaning agents. The widespread use of plastics, coupled with inadequate waste management, poses a growing threat to ecosystem health worldwide. MPs are plastic particles composed of high-molecular-weight polymers that exhibit biochemical stability. Plastics break down into MPs and even smaller nanoplastics through various degradation mechanisms, such as exposure to UV radiation from sunlight and other environmental factors. Due to their resemblance to certain types of zooplankton and food particles, MPs are often ingested by fish, entering their digestive systems. Once inside, they do not remain solely in the gut; rather, they infiltrate the fish's circulatory and lymphatic systems, eventually distributing throughout various tissues and organs. Microplastics have been found in fish gills, muscles, liver, heart, swim bladders, ovaries, spinal cords, and even brains. The presence of MPs in these organs has been linked to significant adverse effects, including reproductive, neurological, hormonal, and immune system disruptions. This toxicity extends beyond fish, as bioaccumulation and biomagnification of MPs affect other organisms as well, marking MPs as a major anthropogenic stressor that impacts ecosystems at multiple levels. Research indicates that nearly all aquatic environments globally are at risk of MP contamination. Laboratory and field studies highlight fish as particularly susceptible to MP ingestion, though freshwater species have been less extensively studied than marine counterparts. After exposure, fish may suffer various health issues, either directly from MPs or from their interaction with other contaminants. The broader environmental implications of these laboratory findings and the specific role of MPs in increasing fish exposure to harmful chemicals remain topics of ongoing debate. This review aims to contribute to ecotoxicological insights on fish contamination by MPs and outline areas for future investigation.

Microplastic characterization in small freshwater fishes collected in Gyeongan-cheon, a tributary stream of Han River in South Korea: Ingestion and depuration study of Nylon

Plastic inventions have had an impact on various industries, and people easily approach to plastic products, degrading into microplastic (MP). In this study, distribution of MP was evaluated in freshwater fishes collected in a tributary stream of the Han River, Gyeongan-cheon. Totally 38 fishes, mostly Zacco platypus, were used to analyze, and they were collected in two different seasons as the normal and rainy seasons. Fishes contained 34-284 particles/individual. The prevalent size of MP in fishes ranged from 45 to 100 μm, followed by 100-300 and 20-45 μm. Shapes of MP in fishes were mostly fragments, and types of MP were polypropylene (PP) > polyethylene (PE) > polytetrafluoroethylene (PTFE). By 4-day ingestion of Nylon at 100 μg/L (equivalent to 55,000 particles/L, about 20-40 μm) in Zacco koreanus, the treated fish showed MP concentration with an average number of 53 Nylons. Mean retention time value was considered as 13.4 days by the uptake-depuration test using Z. platypus at 500 μg/L Nylon. Taken together, MP concentration found in smaller freshwater fish was dependent on living habitat and MP size. These findings underscore the importance of ongoing monitoring of MPs in freshwater ecosystems and the need to understand MP ingestion and excretion patterns in small freshwater fish species.

Uptake, removal and trophic transfer of fluorescent polyethylene microplastics by freshwater model organisms: the impact of particle size and food availability

As an emerging contaminant, microplastics (MPs) are widely distributed in freshwater ecosystems and pose potential threats to aquatic organisms, attracting significant attention from both the scientific community and the general public. However, there is still uncertainty regarding the mechanisms of MPs transfer within aquatic biota and how particle size and food availability influence their transport patterns. In this study, zebrafish (Danio rerio) were selected as a model organism to investigate the uptake and elimination of fluorescent polyethylene (PE) MPs under different exposure scenarios (waterborne or trophic transfer, with or without food) and varying particle sizes (ranging from 10-300 μm at concentrations of 0.1, 2, and 300 mg/L). Additionally, water fleas (Daphnia magna) were provided as prey for the fish. The dynamic accumulation of PE-MPs sized between 10-20 μm at a concentration of 25 mg/L by daphnia was also determined along with its impact on animal feeding behavior. The results demonstrated that both organisms were capable of ingesting PE-MPs during exposures lasting up to 24 hours for daphnia and up to 72 hours for zebrafish. Furthermore, rapid elimination rates were observed within just 30 minutes for daphnia and between 6-12 hours for zebrafish. The presence of food reduced MPs uptake and removal by daphnia but significantly increased MP elimination by fish. Zebrafish showed a preference for ingesting larger-sized MPs that they could easily recognize; however, trophic transfer from daphnia to fish was found to be the primary route of ingestion specifically for PE-MPs sized between 10-20 μm. The findings suggest that while fish directly ingest fewer invisible MPs from the water column, they still accumulate these particles through predation on contaminated prey organisms. Therefore, it is imperative to prioritize the ecological risks associated with the transfer of MPs from zooplankton to fish.

Accumulation, depuration, and potential effects of environmentally representative microplastics towards Daphnia magna

Microplastic risk assessment often characterizes primary plastics, plastics intentionally manufactured at the micro- and nanoscale, or plastics collected within the natural environment, which often lack repeatability and the volume necessary for reliable hazard characterization. There is limited understanding of how environmentally representative plastics prepared at the microscale impact aquatic organisms. The aim of the present study was to create environmentally representative microplastics and characterize their toxicokinetics and hazards. Plastic cups and forks were micronized to <120 μm particles and Daphnia magna were exposed for 48 h at concentrations ranging from 0.01 mg/L to 100 mg/L. Uptake and depuration experiments were conducted at the highest concentration where accumulation was confirmed. Raman spectroscopy identified that both plastics were polystyrene and had similar size distributions. Microplastics were not acutely toxic but accumulated and rapidly depurated. Toxicokinetics demonstrated that cup MPs were consumed at higher rates than fork MPs despite similar physical characteristics. Daphnia magna preferentially selected smaller particles from the heterogenous suspensions. Future research will need to further explore the relationship between physicochemical properties, particularly size, and ecotoxicity. The study focused on mortality as the primary hazard endpoint. However alternative, sublethal biomarkers may be more appropriate in describing the effects of microplastic exposure.

Contrasting the distribution kinetics of microplastics and nanoplastics in medaka following exposure and depuration

Direct ingestion of micro/nanoplastics (MNPs) results in significant accumulation in gastrointestinal (GI) tract of fish. The breathing process of fish makes MNPs easily retained in their gills. However, the uptake of MNPs in other fish organs remains largely unknown, let alone their kinetic processes. Herein, microplastics (MPs) and nanoplastics (NPs) in vivo imaging and precise quantification in various tissues (GI tract, gill, liver, brain, eye, and skin) of seawater (SW)- and freshwater (FW)- acclimated medaka Oryzias melastigma were achieved at an environmentally relevant concentration. Subsequently, the distribution kinetics of MNPs was investigated over a 96-h uptake and 48-h depuration period. MNPs were quickly and mostly captured in GI tract and gill of O. melastigma, and then transferred to liver and brain likely via blood circulation. Such transport was more efficient for NPs as compared to MPs, as evidenced by the consistently higher bioconcentration factors in both SW and FW conditions. The detection of MNPs in eye and skin of O. melastigma was more of an adsorption process, although the specific mechanisms of adsorption and absorption process can hardly be clearly differentiated. This study presented distribution kinetics of MNPs in O. melastigma and highlighted their possible transportation among tissues.

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

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

Integrating aggregate exposure pathway and adverse outcome pathway for micro/nanoplastics: A review on exposure, toxicokinetics, and toxicity studies

Micro/nanoplastics (MNPs) have emerged as a significant environmental concern due to their widespread distribution and potential adverse effects on human health and the environment. In this study, to integrate exposure and toxicity pathways of MNPs, a comprehensive review of the occurrence, toxicokinetics (absorption, distribution, and excretion [ADE]), and toxicity of MNPs were investigated using the aggregate exposure pathway (AEP) and adverse outcome pathway (AOP) frameworks. Eighty-five papers were selected: 34 papers were on detecting MNPs in environmental samples, 38 papers were on the ADE of MNPs in humans and fish, and 36 papers were related to MNPs toxicity using experimental models. This review not only summarizes individual studies but also presents a preliminary AEP-AOP framework. This framework offers a comprehensive overview of pathways, enabling a clearer visualization of intricate processes spanning from environmental media, absorption, distribution, and molecular effects to adverse outcomes. Overall, this review emphasizes the importance of integrating exposure and toxicity pathways of MNPs by utilizing AEP-AOP to comprehensively understand their impacts on human and ecological organisms. The findings contribute to highlighting the need for further research to fill the existing knowledge gaps in this field and the development of more effective strategies for the safe management of MNPs.

Microplastic ingestion in aquatic and soil biota: A comprehensive review of laboratory studies on edible size and intake pattern

Microplastic contamination is ubiquitous and can be transferred through the food chain to humans. However, studies on microplastic size have mainly focused on large animals with a body length >20 mm. To address this gap, we conducted a comprehensive review of 169 laboratory studies to determine the edible size of microplastics for macrofauna and flora in aquatic and soil biota. Our findings indicate that microplastics with a size of <300 μm and 1 μm, respectively, are edible for these organisms, which are positioned at the base of the food chain. We also analyzed intake and depuration patterns and identified factors affecting microplastic ingestion. Our study fills an important knowledge gap by identifying the range of microplastic sizes that can enter the food chain and be transferred to humans. The study findings have strong implications for the ecological risk assessment of microplastics and suggest a starting point for mitigating this threat.

Polystyrene microplastics interaction and influence on the growth kinetics and metabolism of tilapia gut probiotic Bacillus tropicus ACS1

Gut probiotic bacteria play a significant role in the host health, immunity, and survival. In aquaculture, changes in the gut microbiome of fishes affect the overall productivity and product quality. In the scenario of growing plastic pollution and associated microplastic prevalence, the current study was designed to investigate the interactions and impact of prepared polystyrene microplastics (PS-MPs) of irregular surface morphology on a probiotic bacteria Bacillus tropicus ACS1, isolated from the gut of Oreochromis mossambicus (commonly called as Tilapia). The cell viability was significantly increased along with changes in bacterial growth kinetics upon exposure to varying concentrations of PS-MPs. The microplastic exposure also increased the production of exopolysaccharides (EPS) and induced slight changes in the IR spectra of the EPS. A peak representing a carbonyl linkage that could be attributed to the glycosidic linkages between sugars disappeared following exposure to higher concentrations of PS-MPs. The interaction between the bacteria and the microplastics was visualized using scanning electron microscopy (SEM) and the colonization of the bacteria with active biofilm formation was observed. The investigation of PS-MP induced oxidative stress in the bacteria revealed the generation of reactive oxygen species (ROS) and increase in anti-oxidant enzyme concentrations, superoxide dismutase (SOD), and catalase. The study provides new insights into the effect of microplastics on gut probiotics of an economically significant aquaculture species.

Direct observation and identification of nanoplastics in ocean water

Millions of tons of plastics enter the oceans yearly, and they can be fragmented by ultraviolet and mechanical means into nanoplastics. Here, we report the direct observation of nanoplastics in global ocean water leveraging a unique shrinking surface bubble deposition (SSBD) technique. SSBD involves optically heating plasmonic nanoparticles to form a surface bubble and leveraging the Marangoni flow to concentrate suspended nanoplastics onto the surface, allowing direct visualization using electron microscopy. With the plasmonic nanoparticles co-deposited in SSBD, the surface-enhanced Raman spectroscopy effect is enabled for direct chemical identification of trace amounts of nanoplastics. In the water samples from two oceans, we observed nanoplastics made of nylon, polystyrene, and polyethylene terephthalate-all common in daily consumables. The plastic particles have diverse morphologies, such as nanofibers, nanoflakes, and ball-stick nanostructures. These nanoplastics may profoundly affect marine organisms, and our results can provide critical information for appropriately designing their toxicity studies.

Feeding behavior and species interactions increase the bioavailability of microplastics to benthic food webs

Plastics are pervasive in aquatic ecosystems, in which they circulate in the water column, accumulate in sediments, and are taken up, retained, and exchanged with their biotic environment via trophic and non-trophic activities. Identifying and comparing organismal interactions are a necessary step to improve monitoring and risk assessments of microplastics. We use a community module to test how abiotic and biotic interactions determine the fate of microplastics in a benthic food web. Using single-exposure trials on a trio of interacting freshwater animals (the quagga mussel Dreissena bugensis, a filter feeder; the gammarid amphipod Gammarus fasciatus, a deposit feeder; and the round goby Neogobius melanostomus, a benthivorous fish), we quantify the (1) uptake of microplastics from environmental routes (water, sediment) under six exposure concentrations, (2) the depuration capacities over 72 h, and (3) the transfer of microbeads via trophic (predator-prey) and behavioral interactions (commensalism, intraspecific facilitation). Under 24 h exposures, each animal of our module acquired beads from both environmental routes. The body burden of filter-feeders was higher when they were exposed to particles in suspension, whereas detritivores had similar uptake from either route. Mussels transferred microbeads to amphipods, and both invertebrates transferred beads to their mutual predator, the round goby. Round gobies generally displayed low contamination from all routes (suspension, sedimented, trophic transfer) with a higher microbead load from preying on contaminated mussels. Higher mussel abundance (10-15 mussel per aquaria, i.e., ~200-300 mussels·m2) did not increase individual mussel burdens during exposure, and neither did it increase the transfer of beads from mussels to gammarids via biodeposition. Our community module approach revealed that the feeding behavior of animals allows microplastic uptake from multiple environmental routes, whereas trophic and non-trophic species interactions increased their burden within their food web community.

Differential developmental and proinflammatory responses of zebrafish embryo to repetitive exposure of biodigested polyamide and polystyrene microplastics

Microplastics (MPs) have attracted global concern and are at the forefront of current research on environmental pollution, whereas, little is known about the degradation of ingested MPs in the gastrointestinal environment and repetitive exposure-associated risk of egested MPs to organisms. The present study revealed that polyamide (PA) and polystyrene (PS) MPs exhibited remarkably differential biodegradations in the gastric and intestinal fluids of a model fish (Siniperca chuatsi). Significant disintegration of the skeleton structure, size reduction (from 27.62 to 9.17 µm), benzene ring scission, and subsequent biogenic corona coating and surface oxidation occurred during in vitro digestion, thus increasing the hydrophilicity and agglomeration of PS. Conversely, PA MPs exhibited high resistance to enzymolysis with slight surface erosions and protein adsorption. Relative to the pristine form, the bioaccumulation of digested PS elevated and the musculoskeletal deformity and mortality of juvenile zebrafish were obviously enhanced, but these changes were unobservable for PA. Lipopolysaccharide-triggered inflammation and apoptosis via Toll-like receptor signaling pathways and reduction of extracellular matrix secretions driven by oxidative stress contributed to the aggravated inhibitory effects of digested PS on larval development. These findings emphasize the necessity of concerning the biota digestion in MP risk assessments in natural waters.

Polypropylene microplastics aging under natural conditions in winter and summer and its effects on the sorption and desorption of nonylphenol

Plastics in the environment undergo various aging effects. Due to the changes in physical and chemical properties, the sorption behavior of aged microplastics (MPs) for pollutants differs from that of pristine MPs. In this paper, the most common disposable polypropylene (PP) rice box was used as the source of MPs to study the sorption and desorption behavior of nonylphenol (NP) on pristine and naturally aged PPs in summer and winter. The results show that summer-aged PP has more obvious property changes than winter-aged PP. The equilibrium sorption amount of NP on PP is summer-aged PP (477.08 μg/g) > winter-aged PP (407.14 μg/g) > pristine PP (389.29 μg/g). The sorption mechanism includes the partition effect, van der Waals forces, hydrogen bonds and hydrophobic interaction, among which chemical sorption (hydrogen bonding) dominates the sorption; moreover, partition also plays an important role in this process. Aged MPs' more robust sorption capacity is attributed to the larger specific surface area, stronger polarity and more oxygen-containing functional groups on the surface that are conducive to forming hydrogen bonds with NP. Desorption of NP in the simulated intestinal fluid is significant owning to intestinal micelles' presence: summer-aged PP (300.52 μg/g) > winter-aged PP (291.08 μg/g) > pristine PP (287.12 μg/g). Hence, aged PP presents a more vital ecological risk.

Combined effects of microplastics and benz[a]anthracene on cardiotoxicity in zebrafish (Danio rerio) larvae: Size matters

The size of microplastics (MPs) plays an important role in combined toxic effects including synergistic or antagonistic effects. However, the influence of the size of MPs on the combined toxicity of contaminants remains unclear. In this study, we employed a zebrafish model to investigate the effects of MP size on the combined toxicity of benz[a]anthracene (BaA), a representative polyaromatic hydrocarbon, using three different sizes of polystyrene MPs (PSMPs) (0.2, 1.0, and 10 μm). Treatment of all groups did not result in any mortality of the zebrafish larvae. However, small-sized PSMPs (0.2 μm) enhanced the toxic effect of BaA in larvae such as cardiac defect and disruption of vessel formation. Medium-sized PSMPs (1.0 μm) were boundary in terms of the combined toxic effect; however, large-sized PSMPs (10 μm) alleviated the cardiotoxicity of BaA, including cardiac defect, ROS levels, and cell death. The combined effects showed a correlation with the body burden of MPs and BaA in larvae according to particle size (in the order of 0.2 μm > 1.0 μm > 10 μm). The synergistic effects occurred likely because the small PSMPs facilitated the body burden of BaA, induced excessive ROS by Ahr-mediated activity, and caused cell death in the heart, resulting in increased heart defects in the larvae. In contrast, large PSMPs abated the combined toxic effect through decreased body burden, whereas medium PSMPs form a boundary in combined effects. Therefore, the combined toxic effects of MPs are dependent on their size, which plays an important role in the transport and accumulation of environmental pollutants.

Influencing factors for microplastic intake in abundant deep-sea lanternfishes (Myctophidae)

Plastic debris is ubiquitous in the hydrosphere. Yet, we lack an understanding of contamination among deep-sea species and primarily how each trait can influence microplastic intake. We investigated microplastic contamination in the digestive tract of hyper-abundant mesopelagic lanternfishes (n = 364 individuals) from the Southwestern Tropical Atlantic, captured from 90 to 1000 m depth. Overall, microplastics were detected in most individuals analysed (frequency of occurrence = 68 %). Large microplastics, mostly of a filamentous shape were the most frequent, followed by smaller fragments and foams. Microplastics made of high-density polymers (PET, PVC, PA, SBR rubber) were more prevalent than low-density ones (PE, EVA and PBD rubber), especially under deeper layers. Larger microplastics were detected in lanternfishes captured off the northeastern Brazilian coast (mean 0.88 ± SE 0.06 mm) compared to those from around the Rocas Atoll and Fernando de Noronha Archipelago (0.70 ± 0.07 mm; p≤ 0.05), ∼350 km from the continent. Moreover, lanternfishes that migrate from the upper mesopelagic (200-500 m) to the epipelagic layers (<200 m) had simultaneously the highest intake and the smallest particles (1.65 ± 0.17 particles individual^-1 and 0.55 ± 0.07 mm; p≤ 0.05). Biological mediated transport of microplastics from the epipelagic to the mesopelagic waters was evinced, but fishes foraging in shallower layers had the lowest intake (1.11 ± 0.10 part. ind.^-1; p≤ 0.05). Furthermore, the jaw length was positively associated with an increment in microplastic intake (Incidence Rate Ratio = 1.1; p≤ 0.05). The lanternfishes that preferably prey upon fish larvae are more prone to microplastic intake than their counterparts, which forage mostly on crustaceans and gelatinous zooplankton (p≤ 0.05).

Parasite infection but not chronic microplastic exposure reduces the feeding rate in a freshwater fish

Microplastics (plastics <5 mm) are an environmental contaminant that can negatively impact the behaviour and physiology of aquatic biota. Although parasite infection can also alter the behaviour and physiology of their hosts, few studies have investigated how microplastic and parasite exposure interact to affect hosts. Accordingly, an interaction experiment tested how exposure to environmentally relevant microplastic concentrations and the trophically transmitted parasite Pomphorhynchus tereticollis affected the parasite load, condition metrics and feeding rate of the freshwater fish final host chub Squalius cephalus. Microplastic exposure was predicted to increase infection susceptibility, resulting in increased parasite loads, whereas parasite and microplastic exposure were expected to synergistically and negatively impact condition indices and feeding rates. Following chronic (≈170 day) dietary microplastic exposure, fish were exposed to a given number of gammarids (4/8/12/16/20), with half of the fish presented with parasite infected individuals, before a comparative functional response experiment tested differences in feeding rates on different live prey densities. Contrary to predictions, dietary microplastic exposure did not affect parasite abundance at different levels of parasite exposure, specific growth rate was the only condition index that was lower for exposed but unexposed fish, with no single or interactive effects of microplastic exposure detected. However, parasite infected fish had significantly lower feeding rates than unexposed fish in the functional response experiment, with exposed but unexposed fish also showing an intermediate decrease in feeding rates. Thus, the effects of parasitism on individuals were considerably stronger than microplastic exposure, with no evidence of interactive effects. Impacts of environmentally relevant microplastic levels might thus be relatively minor versus other stressors, with their interactive effects difficult to predict based on their single effects.

Global occurrence, drivers, and environmental risks of microplastics in marine environments

With an increasing quantity of plastic waste being discharged into the oceans, marine microplastic (MP) pollution has received widespread attention. However, the global occurrence characteristics, environmental risks, driving factors, and source-sink relationships remain unclear. In this study, we conducted a meta-analysis based on 165 articles about marine MP pollution. It was found that the global marine MP abundance displayed a significant spatial heterogeneity, and the distribution pattern was influenced by offshore distance, population density, and economic development. The morphological characteristics of MPs showed a significant difference between seawater and marine sediment, and small-size MPs (<1 mm) accounted for the majority of all MPs in the marine environment. The environmental risk assessment revealed that most of the marine MP pollution still remains at low concentrations in the global context, with the Polyurethane (PU), Polyacrylonitrile (PAN), and Polyvinyl chloride (PVC) types of MPs showing high environmental-risk contributions. In addition, land-based waste and marine operations, which were considered to be the dominant sources of marine MPs, primarily aggregated at nearshore submarine areas, in the water column, and in the deep-sea bottom environment. This study suggested that the combination of a meta-analysis and Monte Carlo simulation can provide much valuable information regarding the global occurrence characteristics and environmental risks of marine MPs.

Beyond the exposure phase: Microplastic depuration and experimental implications

Currently, most studies focus on the effect of microplastics (MPs) in the exposure phase, but pay limited attention to the depuration phase. Depuration is a promising practice to achieve safe aquaculture production, which is also helpful to understand the long-term impact of MPs. Therefore, investigating the post-exposure scenarios of MPs has great practical significance. In order to provide implications for future research, this work attempted to systematize the current findings and knowledge gaps regarding the depuration of MPs. More specifically, three methods, including direct fitting, one-compartment kinetic model and interval observation, for estimating the retention time of MPs to further determine the minimum depuration time were introduced, in which the one-compartment kinetic model could also be used to calculate the depuration rate constant and biological half-life of MPs. Moreover, the post-exposure effect of MPs generally presented three scenarios: incomplete reversal (legacy effect), return to control level (recovery) and stimulatory response (hormesis-like effect). In addition, the possible tissue translocation of MPs, the influence of food abundance and body shape on MPs egestion, and the potential interaction with environmental factors, have aroused great scientific concerns and need further exploration and clarification.

Microplastic pollution in sediments of tropical shallow lakes

Forty-eight tropical shallow lakes (depth ≤ 4 m) across a climatic gradient were assessed for microplastic (MPs; <5 mm) pollution based on MPs concentrations in archive samples from lake shore sediments. The MPs were classified by type (fragments or fibres), colour (yellow, black, red, green, blue, white, and transparent), size (0.55 to 4.93 mm), and polymer (polyester, polyethylene, chlorinated polyethylene, and polyamide). Sediments were predominantly medium sand, and all samples (144) contained MPs, consisting of 24 % fragments (6.3 ± 11.3 MPs·300 g^-1) and 76 % fibres (21.25 ± 12.7 MPs·300 g^-1). The lake climate (humid, transitional, or semi-arid), type of surrounding land use (urban, semi-arid, or rural), and distance from the shoreline (0, 5 or 10 m) did not explain the differences in MPs concentrations, partially refuting the initial hypothesis. The only significant difference was between the sample medians for the number of fragments based on the region (H = 7.586; p = 0.0481). The number of fragments in the lakes in the humid region was greater than that in the semi-arid region (p < 0.05). Poor sanitation, sewage effluents, and solid wastes reaching and accumulating in the lakes may be the primary and transversal conditioning factors for this small difference among diverse environments. Freshwater lakes are investigated in all continents, and the present study contributes to the first record of MPs in shallow lake sediments in eastern South America. The 48 shallow lakes assessed showed a relatively low concentration of MPs compared to other lake contaminants reported in the international literature. This information coincides with public policies issued, regarding the control and reduction of plastics and MPs in Brazil, and the study region.

The legacy effect of microplastics on aquatic animals in the depuration phase: Kinetic characteristics and recovery potential

The prevalence of microplastics (MPs) in global aquatic environments has received considerable attention. Currently, concerns have been raised regarding reports that the adverse effect of MPs on aquatic animals in the exposure phase may not be (completely) reversed in the depuration phase. In order to provide insights into the legacy effect of MPs from the depuration phase, this study evaluated the kinetic characteristics and recovery potential of aquatic animals after the exposure to MPs. More specifically, a total of 68 depuration kinetic curves were highly fitted to estimate the retention time of MPs. It was shown that the retention time ranged from 1.26 to 3.01 days, corresponding to the egestion of 90 % to 99 % of ingested MPs. The retention time decreased with the increased retention rate. Furthermore, variables potentially affecting the retention time were ranked by the decision tree-based eXtreme Gradient Boosting (XGBoost) algorithm, suggesting that the particle size and tested species were of great importance for explaining the difference in retention time of MPs. Moreover, a biomarker profile was recompiled to determine the toxic changes. Results indicated that the MPs-induced toxicity significantly reduced in the depuration phase, evidenced by the recovery of energy reserves and metabolism, hepatotoxicity, immunotoxicity, hematological parameters, neurotoxicity and oxidative stress. However, the continuous detoxification and remarkable genotoxicity implied that the toxicity was not completely alleviated. In addition, the current knowledge gaps are also highlighted, with recommendations proposed for future research.

Microplastic loads within riverine fishes and macroinvertebrates are not predictable from ecological or morphological characteristics

Microplastics are a relatively new but important form of freshwater contamination that can be ingested by a range of different species, with particle counts thought to be predictable from species ecology and morphology. Here, we report levels of microplastics in a 26 μm-5 mm size range within the macroinvertebrate and fish community of a lowland river (Dorset Stour, SW England), and test the hypothesis that counts are predictable from characteristics such as feeding guild, body length and trophic position. Macroinvertebrates (n = 257, 12 taxa) and fish (n = 418, 9 species) were collected from distinct river reaches by kick sampling and rod and line angling, respectively. Batches of whole macroinvertebrates and individual fish gastrointestinal tracts were digested with 30% hydrogen peroxide before microplastic screening and FTIR polymer confirmation on a particle subset. Particles were found in 40% of pooled macroinvertebrate batches (taxa incidences: 14-75%) and 39% of fishes (species incidences: 29-47%). Dominant particle feature categories were ≤100 μm, blue/green, fragments and fibres identified as various polyolefins. Although particle counts in macroinvertebrates were highest in Ephemeroptera (mean of 0.74 particles per individual), the relationships between particle loads, batch number and guild were all non-significant. In fishes, particle counts were not significantly related to species, stomach structure, feeding guild or body length, with spatial differences also not apparent across the catchment. Individual fish particle counts were similarly not significantly associated with their trophic positions (calculated from bulk δ¹⁵N values for a subset of fishes) and parasite load of Pomphorhynchus tereticollis. Correlations between fish and macroinvertebrate particle counts within specific river reaches were also not significant. In entirety, these results indicated although loadings of microplastic particles were relatively consistent within the two communities, they were not predictable from any of their ecological or morphological characteristics.

Microplastic accumulation in the gastrointestinal tracts of nestling and adult migratory birds

This study examines the abundance and types of microplastic (MP) content in the digestive system of different bird species to help us better understand MP transfer to birds from their environments. The lower GI tracts of six bird species (Tree Swallow (Tachycineta bicolor), Ovenbird (Seiurus aurocapilla), Dark-eyed Junco (Junco hyemalis), Hermit Thrush (Catharus guttatus), Tennessee Warbler (Leiothlypis peregrine), White-throated Sparrow (Zonotrichia albicollis)) were collected for MP analysis. Tree Swallows were collected from nine locations along three drainages in the Milwaukee area and at a remote lake in Wisconsin, USA and consisted of nestlings not yet fledged. The five other bird species were adult migratory bird fatalities from window strikes at the Loyola University Chicago's Lake Shore Campus. Results of plastic analysis showed that the lower GI tracts of all bird species contained different types of MPs (i.e., fibers, fragment, beads). Fiber was the most dominant, followed by fragment and beads. Microplastics were polyethylene, polyethylene terephthalate, nylon, and polyvinyl base materials. There was no statistically significant difference in the site average MP concentration for nestling Tree Swallows or in the species average concentration for adult migratory birds. However, except for Ovenbird, species of adult migratory birds had a species average MP concentration (20.1) that was statistically higher than the site-average MP concentration for Tree Swallow nestlings (5.9). The presence of MPs in the lower GI tracts of unfledged swallows could suggest that MPs had been transferred to the birds from the environment via their diet, such as flying insects-the food source of the birds. Further study should be conducted to investigate the potential transfer of MPs from aquatic insects to birds.

Seasonal variation and ecological risk assessment of microplastics ingested by economic fishes in Lake Chaohu, China

Microplastic (MP) contaminations in freshwater organisms have attracted substantial attention worldwide. However, seasonal field studies of MPs concentrations in aquatic life are scarce. In this study, we analyzed the seasonal variation and ecological risk of MPs concentrations in economic fish species from Lake Chaohu in China between wet and dry seasons. Within both seasons, MPs in fish were systematically analyzed using methods of KOH digestion, NaCl density floatation and raman spectroscopy. MPs abundance in economic fishes were significantly higher in dry season than that in wet season, which can be ascribed to the MPs' amplification effects in lacustrine ecosystems during dry season. Whereas, our results recorded similar and homogenized characteristic composition of MPs in economic fishes between wet and dry seasons. In both seasons, fiber was the main morphological type, black and blue were the most common MPs color, and MPs ranging from <0.5 mm accounting for the most abundant size. In addition, polypropylene (PP) and polyethylene terephthalate (PET) accounted for the most abundant polymer type detected by economic fishes in both seasons. In terms of feeding groups and habitat preferences, planktivorous and pelagic fish species exhibited sensitive variations of MPs concentrations between wet and dry seasons, thus being highlighted as good bioindicators of MPs contaminants in freshwater ecosystems. Our results revealed higher ecological risks of MPs in wet season than that in dry season when indicating from polymer risk index (H). By providing detailed and direct toxicity information, our study highlights the usage of polymer risk index for ecological risk assessment in aquatic organisms.

Coronas of micro/nano plastics: a key determinant in their risk assessments

As an emerging pollutant in the life cycle of plastic products, micro/nanoplastics (M/NPs) are increasingly being released into the natural environment. Substantial concerns have been raised regarding the environmental and health impacts of M/NPs. Although diverse M/NPs have been detected in natural environment, most of them display two similar features, i.e.,high surface area and strong binding affinity, which enable extensive interactions between M/NPs and surrounding substances. This results in the formation of coronas, including eco-coronas and bio-coronas, on the plastic surface in different media. In real exposure scenarios, corona formation on M/NPs is inevitable and often displays variable and complex structures. The surface coronas have been found to impact the transportation, uptake, distribution, biotransformation and toxicity of particulates. Different from conventional toxins, packages on M/NPs rather than bare particles are more dangerous. We, therefore, recommend seriously consideration of the role of surface coronas in safety assessments. This review summarizes recent progress on the eco-coronas and bio-coronas of M/NPs, and further discusses the analytical methods to interpret corona structures, highlights the impacts of the corona on toxicity and provides future perspectives.

Taking advantage of transparency: A proof-of-principle for the analysis of the uptake of labeled microplastic particles by organisms of different functional feeding guilds using an adapted CUBIC protocol

The analysis of the ingestion of microplastics (MP) by biota is frequently performed through invasive procedures such as chemical digestion protocols or by histological analysis of thin sections. Different, promising approaches for the observation of ingested MP particles pose so called tissue clearing methods. They are currently applied to organs, tissue samples, or whole organisms, rendering the sample transparent and enable to look inside an otherwise opaque environment. To date, there is a lack of methods to detect labeled MP inside an opaque organism's digestive tract without interfering with the sample's integrity. Therefore, our goal was to adapt the CUBIC tissue clearing protocol (Clear, Unobstructed Brain/Body Imaging Cocktails and Computational Analysis) for aquatic and terrestrial organisms of various functional feeding groups for the analysis of the uptake of fluorescent labeled microplastic (MP) particles. We included the buff-tailed bumblebee Bombus terrestris, the compost worm Eisenia fetida, the woodlouse Porcellio scaber, the freshwater shrimp Gammarus roeselii, and the quagga mussel Dreissena bugensis in the analysis. The adapted CUBIC method has led to transparency in all normally opaque organisms. It further offers a simple way of locating fluorescent labeled MP inside the digestive system of the different organisms while leaving them intact.

Size dependent egestion of polyester fibres in the Dublin Bay Prawn (Nephrops norvegicus)

Microplastics (MPs) are an extensive global contaminant in the marine environment, known to be ingested by marine organisms. The presence of MPs in the commercially important marine decapod crustacean Nephrops norvegicus (Dublin Bay Prawn) has been documented for the North-East Atlantic and the Mediterranean, however, uncertainties remain about retention times of MPs in the gastrointestinal tract (GIT) of this species. This study aims to investigate the retention times of polyester MP fibres of three sizes (3, 5, and 10 mm in length) and to determine whether the egestion of MP fibres is size and time dependent. Results suggest that MP fibres of different lengths are retained for different periods of time, with larger MP fibres being retained for longer periods (e.g., minimum 96 h for 10 mm fibres). The present study also assesses for the first time, the size dependent relationship of MP fibres under controlled conditions for N. norvegicus.

Concurrent water- and foodborne exposure to microplastics leads to differential microplastic ingestion and neurotoxic effects in zebrafish

Organisms constantly ingest microplastics directly from the environment or indirectly via trophic transfer due to the pervasiveness of microplastic pollution. However, most previous studies have only focused on waterborne exposure at the individual level, while few studies have investigated the contribution of trophic transfer to the exposure in organisms. We comprehensively evaluated the differences in microplastic ingestion and toxic effects in zebrafish exposed to microplastics via two concurrent routes (waterborne and foodborne). The polyethylene microplastics (40-47 μm, 0.1-10 mg/L) concentration used here was set in a range closed to the environmentally relevant microplastic concentrations, especially considering the extreme high concentration scenarios in wastewater. The concentration of microplastics resulting from foodborne exposure (0.01±0.01 μg/mg; 0.1±0.1 particles/mg) was significantly lower than that through waterborne exposure (0.06±0.02 μg/mg; 0.8±0.3 particles/mg), suggesting the ingestion of microplastics in their tissues occurs mainly through direct environmental uptake rather than food chain transfer (though the initial microplastic concentration was 1000 folds lower). However, more sublethal impacts, including the significant abnormal hyperactive swimming behaviour (107±5% induction; p< 0.05), were observed in the foodborne group than waterborne group. Additionally, ingenuity pathway analysis predicted both exposure routes caused obvious nervous system interference but through opposite modes of action. This was further verified by the alteration of neurotransmitter biomarkers that neurotoxicity mechanisms were completely different for the two exposure routes. The neurotoxic effects of microplastics are non-negligible and can exert together through both water- and foodborne exposure routes, which deserves further attention.

Excretion characteristics of nylon microplastics and absorption risk of nanoplastics in rats

Ingestion of environmental microplastics (MPs) by animals is receiving a great health concern, because of its potential adverse effects on organisms. Most ingested MPs will be excreted, while the health threats depend largely on the excretory dynamics. Although the excretion characteristics of MPs in invertebrates and fishes have been studied, information on the excretion of MPs in mammals remains lacking, especially for the fibrous MPs. Here, fibrous and granular MP and nanoplastic (NP) of nylon polymer (polyamide 66, PA66) were exposed in rats by oral in the first day, then the excretion behavior of ingested PA66 in rats was quantified using mass quantification of liquid chromatography with tandem mass spectrometry (LC-MS-MS) together with the microscope observation. Although most of the ingested PA66-MP or PA66-NP was excreted within 48 h, the three forms of PA66 were not completely cleared by the rats even after seven days excretion. The excretion of PA66 in rats was well-described by a first-order kinetics model, and the calculated half-lives of elimination of PA66 polymer in rats are 19.9 h (fibrous PA66-MP), 23.7 h (granular PA66-MP), and 36.9 h (PA66-NP), indicating rats excrete smaller MPs more slowly than the bigger ones. This was further confirmed by the particle size distribution of granular PA66-MP observed in feces. Besides, approximately 30% of the ingested PA66-NP were failed to be detected in feces, while the occurrence of PA66-NP in rat serum induced by PA66-NP ingestion was found. This indicates that PA66-NP can pass through the gut barrier and entered the blood circulation. Therefore, the health risks of ingested MPs, especially for the NPs, deserve further attention.

Adsorption of environmental contaminants on micro- and nano-scale plastic polymers and the influence of weathering processes on their adsorptive attributes

Increases in plastic-related pollution and their weathering can be a serious threat to environmental sustainability and human health, especially during the present COVID-19 (SARS-CoV-2 coronavirus) pandemic. Planetary risks of plastic waste disposed from diverse sources are exacerbated by the weathering-driven alterations in their physical-chemical attributes and presence of hazardous pollutants mediated through adsorption. Besides, plastic polymers act as vectors of toxic chemical contaminants and pathogenic microbes through sorption onto the 'plastisphere' (i.e., plastic-microbe/biofilm-environment interface). In this review, the effects of weathering-driven alterations on the plastisphere are addressed in relation to the fate/cycling of environmental contaminants along with the sorption/desorption dynamics of micro-/nano-scale plastic (MPs/NPs) polymers for emerging contaminants (e.g., endocrine-disrupting chemicals (EDCs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), pharmaceuticals and personal care products (PPCPs), and certain heavy metals). The weathering processes, pathways, and mechanisms governing the adsorption of specific environmental pollutants on MPs/NPs surface are thus evaluated in relation to the physicochemical alterations based on several kinetic and isotherm studies. Consequently, the detailed evaluation on the role of the complex associations between weathering and physicochemical properties of plastics should help us gain a better knowledge with respect to the transport, behavior, fate, and toxicological chemistry of plastics along with the proper tactics for their sustainable remediation.

Distribution and translocation of micro- and nanoplastics in fish

Microplastics (MPs) and nanoplastics (NPs) are regarded as emerging particulate contaminants. Here, we first summarize the distribution of plastic particles in fish. Field investigations verify the presence of various kinds of fibrous, spherical, and fragmentary MPs in fish gastrointestinal tract and gills, and specifically in muscle and liver. Laboratory works demonstrate that NPs even penetrate into blood vessels of fish and pass onto next generations. Second, we systematically discuss the translocation ability of MPs and NPs in fish. MPs can enter early-developing fish through adherence, and enter adult fish internal organs by intestine absorption or epidermis infiltration. NPs can not only penetrate into fish embryo blastopores, but also reach adult fish internal organs through blood circulation. Third, the cellular basis for translocation of plastic particles, NPs in particular, into cells are critically reviewed. Endocytosis and paracellular penetration are two main pathways for them to enter cells and intercellular space, respectively. Finally, we compare the chemical and physical properties among various particular pollutants (MPs, NPs, settleable particulate matters, and manufactured nanomaterials) and their translocation processes at different biological levels. In future studies, it is urgent to break through the bottleneck techniques for NPs quantification in field environmental matrix and organisms, re-confirm the existence of MPs and NPs in field organisms, and develop more detailed translocating mechanisms of MPs and NPs by applying cutting-edge tracking techniques.

Size Effects of Microplastics on Embryos and Observation of Toxicity Kinetics in Larvae of Grass Carp (Ctenopharyngodon idella)

Microplastics have caused great concern in recent years. However, few studies have compared the toxicity of different sizes of microplastics in fishes, especially commercial fishes, which are more related to human health. In the present study, we revealed the effects of varying sizes of microplastics on grass carp embryos and larvae using scanning electron microscopy (SEM) and fluorescence imaging. Embryos were exposed to 80 nm and 8 μm microplastics at concentrations of 5, 15, and 45 mg/L. Toxicity kinetics of various sizes of fluorescent microplastics were analyzed through microscopic observation in the larvae. Results found that nanoplastics could not penetrate the embryo’s chorionic membrane, instead they conglutinated or aggregated on the chorion. Our results are the first to explore the defense mechanisms of commercial fish embryos against microplastics. Larvae were prone to ingesting their own excrement, resulting in microplastic flocculants winding around their mouth. For the first time, it was found that excreted microplastics could be reconsumed by fish and reaccumulated in the oral cavity. Microplastics of a certain size (1 μm) could be accumulated in the nasal cavity. We speculate that the presence of a special groove structure in the nasal cavity of grass carp larvae may manage to seize the microplastics with a particular size. As far as we know, this is the first report of microplastics being found in the nasal passages of fish. Fluorescence images clearly recorded the toxicity kinetics of microplastics in herbivorous fish.

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.

Behavior of Microplastics in Inland Waters: Aggregation, Settlement, and Transport

Inland waters are the main medium transporting microplastics to the ocean. Aggregation, vertical settlement, and horizontal transport will occur when microplastics enter the inland waterbodies. This paper reviews these behaviors of microplastics in inland waters and their influencing factors. The aggregation of microplastics were divided into homogeneous aggregation and heterogeneous aggregation, which are critical for the settlement of microplastics. The settlement of microplastics in inland water bodies is influenced by microplastic properties (size, density, and shapes) and environmental conditions (microorganisms, sedimental properties, hydraulic conditions, and so on). Horizontal transport of microplastics in water is influenced by hydrologic conditions, rainfall, river morphologies, dams, vegetation, etc. Future perspectives including laboratory simulations and numerical models involving multiple factors, the behaviors of degradable plastics, and the influence of hydrologic conditions have been proposed.

Treatment-level impacts of microplastic exposure may be confounded by variation in individual-level responses in juvenile fish

Microplastic (MP) pollution is a key global environmental issue and laboratory exposure studies on aquatic biota are proliferating at an exponential rate. However, most research is limited to treatment-level effects, ignoring that there may be substantial within-population variation in responses to anthropogenic stressors. MP exposure experiments often reveal considerable, yet largely overlooked, inter-individual variation in particle uptake within concentration treatments. Here, we investigated to what degree treatment-level responses to MP exposure may be affected by variation in MP ingestion rates in the early life stages of a marine fish, the Gilt-head seabream, Sparus aurata. First, we tested whether MP ingestion variation is repeatable. Second, we assessed to what degree this variation may determine individual-level effects of MP exposure on fitness-related behavioural performance (i.e., escape response). We found that consistent inter-individual variation in MP ingestion was prevalent and led to differential impacts within exposure treatments. Individuals with high MP ingestion rates exhibited markedly inferior escape responses, a result that was partially concealed in treatment-level analyses. Our findings show that the measured response of populations to environmental perturbations could be confounded by variation in individual-level responses and that the explicit integration of MP ingestion variation can reveal cryptic patterns during exposure experiments.

Chronic feeding exposure to virgin and spiked microplastics disrupts essential biological functions in teleost fish

Toxicity of polyethylene (PE) and polyvinyl chloride (PVC) microplastics (MPs), either virgin or spiked with chemicals, was evaluated in two short-lived fish using a freshwater species, zebrafish, and a marine species, marine medaka. Exposures were performed through diet using environmentally relevant concentrations of MPs over 4 months. No modification of classical biomarkers, lipid peroxidation, genotoxicity or F0 behaviour was observed. A significant decrease in growth was reported after at least two months of exposure. This decrease was similar between species, independent from the type of MPs polymer and the presence or not of spiked chemicals, but was much stronger in females. The reproduction was evaluated and it revealed a significant decrease in the reproductive output for both species and in far more serious numbers in medaka. PVC appeared more reprotoxic than PE as were MPs spiked with PFOS and benzophenone-3 compared to MPs spiked with benzo[a]pyrene. Further, PVC-benzophenone-3 produced behavioural disruption in offspring larvae. These results obtained with two species representing different aquatic environments suggest that microplastics exert toxic effects, slightly different according to polymers and the presence or not of sorbed chemicals, which may lead in all cases to serious ecological disruptions.

Impacts of microplastics on three different juvenile shrimps: Investigating the organism response distinction

The effects of microplastics (MPs) on aquaculture animals have raised increasing concern, but studies on MPs contamination in cultured shrimp are still limited. Therefore, the responses of three widely farmed shrimp species to MPs, including Penaeus monodon (P. monodon), Marsupenaeus japonicas (M. japonicus) and Litopenaeus vannamei (L. vannamei), were investigated in this study. The results showed that the mortality of P. monodon, M. japonicus and L. vannamei were 47%, 53% and 20% respectively after 48 h of 300 mg/L MPs exposure. After 48 h of 100 mg/L MPs exposure, for P. monodon, the MPs content in water and excreta were significantly different from that in M. japonicus and L. vannamei. For genes expressions, the expression of catalase (Cat) was significantly increased and the expression of apoptosis protein (IAP) was inhibited in these three shrimps, but only the expression of Lysozyme (Lys) was increased in L. vannamei after MPs exposure. After 48 h of depuration, the Cat and IAP expression of P. monodon and M. japonicus was significant decreased while the IAP and Lys expression of L. vannamei still maintained at a high level. The results suggested that the metabolic rate of MPs in P. monodon was significantly higher than that in M. japonicus and L. vannamei. The tolerance of L. vannamei to MPs was higher than that of P. monodon and M. japonicas and their different responses in anti-microbial gene might be one of the reasons for the difference of their mortality. This study provides the first report comparing the organism response distinction in cultured shrimp and enriching to the understanding of the impact of MPs on ecosystem.

The gut retention time of microplastics in barnacle naupliar larvae from different climatic zones and marine habitats

Microplastic ingestion has been widely documented in marine zooplankton, but the retention time of microplastics in their digestive gut are still poorly studied, especially among species from different climatic zones and marine habitats. This study evaluated the ingestion and gut retention time of four sizes of fluorescent microplastic beads (1.3, 7.3, 10.6, and 19.0 μm) in stage II naupliar larvae of nine barnacle species from different habitats (epibiotic on turtles, mangroves, coral reefs, and rocky shores) and climatic zones (subtropical/tropical and temperate). Microbeads were not lethal to all species (climatic zones/habitats) tested from the four sizes of non-fluorescent virgin microbeads (1.7, 6.8, 10.4 and 19.0 μm, each at concentrations 1, 10, 100, and 1000 beads mL^-1). Gut retention time of microplastic beads in barnacle naupliar larvae significantly increased with decreasing size. Microbeads resided in digestive tracts generally 3-4 times longer in rocky shore and coral reef barnacles than in muddy shore and epibiotic ones. However, species from different climatic zone did not differ in retention time. Our results suggested nauplius larvae from rocky shore and coral reef barnacles appear to be more susceptible to the impacts of longer retained microplastics (e.g., toxic chemicals present on the surface).

In situ and low-cost monitoring of particles falling from freshwater animals: from microplastics to parasites

A simple and low-cost method of monitoring and collecting particulate matter detaching from (or interacting with) aquatic animals is described using a novel device based on an airlift pump principle applied to floating cages. The efficiency of the technique in particle collection is demonstrated using polyethylene microspheres interacting with a cyprinid fish (Carassius carassius) and a temporarily parasitic stage (glochidia) of an endangered freshwater mussel (Margaritifera margaritifera) dropping from experimentally infested host fish (Salmo trutta). The technique enables the monitoring of temporal dynamics of particle detachment and their continuous collection both in the laboratory and in situ, allowing the experimental animals to be kept under natural water quality regimes and reducing the need for handling and transport. The technique can improve the representativeness of current experimental methods used in the fields of environmental parasitology, animal feeding ecology and microplastic pathway studies in aquatic environments. In particular, it makes it accessible to study the physiological compatibility of glochidia and their hosts, which is an essential but understudied autecological feature in mussel conservation programs worldwide. Field placement of the technique can also aid in outreach programs with pay-offs in the increase of scientific literacy of citizens concerning neglected issues such as the importance of fish hosts for the conservation of freshwater mussels.

Surfactant stealth effect of microplastics in traditional coagulation process observed via 3-D fluorescence imaging

Microplastics (MPs) have aroused rising social concerns. Although amounts of surfactants exist in wastewater and are expected to alter the surface properties of MPs significantly as they are designed to be adsorbed by hydrophobic particles. However, rare works have been done on the influence of surfactants on the coagulation removal process of MPs which was thought to be an effective way to remove MPs together with other natural particles, such as clay. We used 3-D fluorescence imaging to track the coagulation removal process of polystyrene MPs. Our results indicate that nonionic surfactant, tween 20 in ppm scale, could inhibit the coagulation removal of polystyrene MPs significantly. Residue MPs in the effluent is proportional with the surfactant concentration and increases up to tens of times, which will lead to a dramatic increase in their potential environmental risks. Apparent size effect exists in the coagulation in which smaller MPs can escape from the coagulation removal more easily. Mechanism study suggests that the steric resistance of the hydrophilic flexible polyethylene glycol (PEG) layer formed by tween 20 adsorbed on MP surface inhibits clay deposition and thus hinders subsequent agglomeration and precipitation. A surfactant stealth effect, which is used in the design of nanomedicine to avoid the human immune recognition and clearance of nano-drugs from blood circulation, also exists in the coagulation removal process of MPs. Our finding not only proves the strong influence of surfactants on MPs but also will stimulate related studies on other latent surfactant effects of MPs.