Quantifying the vector effects of polyethylene microplastics on the accumulation of anthracene to Japanese medaka (Oryzias latipes)

Size-dependent vector effects of microplastics on bioaccumulation of hydrophobic organic contaminants in earthworm: A dual-dosing study

The potential of microplastics to act as a vector for anthropogenic contaminants is of rising concern. However, directly quantitatively determining the vector effects of microplastics has been rarely studied. Here, we present a dual-dosing method that simulates the chemical bioaccumulation from soil and microplastics simultaneously, wherein unlabeled hydrophobic organic contaminants (HOCs) were spiked in the soil and their respective isotope-labeled reference compounds were spiked on the polyethylene microplastics. The comparison of the bioavailability, i.e., the freely dissolved concentration in soil porewater and bioaccumulation by earthworm, between the unlabeled and isotope-labeled HOCs was carried out. Relatively higher level of bioavailability of the isotope-labeled HOCs was observed compared to the unlabeled HOCs, which may be attributed to the irreversible desorption of HOCs from soil particles. The average relative fractions of bioaccumulated isotope-labeled HOCs in the soil treated with 1 % microplastics ranged from 6.9 % to 46.4 %, which were higher than those in the soil treated with 0.1 % microplastics. Treatments with the smallest microplastic particles were observed to have the highest relative fractions of bioaccumulated isotope-labeled HOCs, with the exception of phenanthrene, suggesting greater vector effects of smaller microplastic particles. Biodynamic model analysis indicated that the contribution of dermal uptake to the bioaccumulation of isotope-labeled HOCs was higher than that for unlabeled HOCs. This proposed method can be used as a tool to assess the prospective vector effects of microplastics in complex environmental conditions and would enhance the comprehensive understanding of the microplastic vector effects for HOC bioaccumulation.

Non-negligible vector effect of micro(nano)plastics on tris(1,3-dichloro-2-propyl) phosphate in zebrafish quantified by toxicokinetic model

Micro(nano)plastics (MNPs) inevitably interact with coexisting contaminants and can act as vectors to affect their fate in organisms. However, the quantitative contribution of MNPs in the in vivo bioaccumulation and distribution of their coexisting contaminants remains unclear. Here, by selecting tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) as the typical coexisting contaminant, we quantified the contribution of MNPs to bioaccumulation and distribution of TDCIPP with toxicokinetic models. Results indicated that MNPs differentially facilitated TDCIPP bioaccumulation and distribution, and NPs slowed down TDCIPP depuration more significantly than MPs. Model analysis further revealed increasing contributions of MNPs to whole-fish TDCIPP bioaccumulation over time, with NPs (33-42%) contributing more than MPs (12-32%) at 48 h exposure. NPs contributed more than MPs to TDCIPP distribution in the liver (13-19% for MPs; 36-52% for NPs) and carcass (24-45% for MPs; 57-71% for NPs). The size-dependent vector effect might be attributed to the fact that MNPs promote contaminant transfer by damaging biofilm structure and increasing tissue membrane permeability, with NPs exerting stronger effects. This work demonstrated the effectiveness of using modeling tools to understand the relative importance of MNPs as contaminant vectors in the TK process and highlighted the higher contaminant transfer potential of NPs under combined exposure scenarios.

Size effect of polystyrene microplastics on the accumulation of anthracene for Java medaka (Oryzias javanicus)

Pollution by microplastics in aquatic ecosystems is a worldwide problem, and the role of microplastics as vectors of pollutants has been a concern. Although small microplastics are thought to have a greater effect than large microplastics as vectors of pollutants, the impact of the size of microplastics on their ability to serve as vectors of pollutants has not been quantified. In this study, we conducted the 14-day experiment (7 days of exposure and 7 days of depuration) with polystyrene microplastics (2-μm or 10-μm diameter) and anthracene. On the last day of the exposure period, the concentration of anthracene in the muscle of Java medaka exposed to both anthracene and 2-μm polystyrene microplastics was the highest (47.4 ± 15.2 μg/g-muscle) of any group, followed by the group exposed to both anthracene and 10-μm polystyrene microplastics (23.0 ± 4.2 μg/g-muscle) and the group exposed to only anthracene (11.2 ± 2.2 μg/g-muscle). These results demonstrated that the size of microplastics was a critical determinant of their ability to serve as vectors of anthracene. The concentrations of anthracene and fine microplastics in the environment are sufficiently low that the effect of microplastics as vectors of anthracene may be observed only under experimental conditions that are unlikely to occur in the present environment. However, because pollution by plastics is expected to become more serious in the future, careful thought and proactive action will be needed to ensure that the impact of microplastics as vectors of pollutants does not become demonstrable under future environmental conditions.

Combined effect of anthracene and polyethylene microplastics on swimming speed and cytochrome P4501A monooxygenase expression of Java medaka (Oryzias javanicus)

Microplastics have been detected in a variety of aquatic ecosystems, and the combined effect of microplastics and chemical pollutants has become a matter of increasing concern. We conducted a 12-d co-exposure test of anthracene and spherical or fragmented polyethylene microplastics (size 200 µm) on Java medaka (Oryzias javanicus). The accumulation of anthracene in Java medaka muscle reached a plateau on day 5 in all anthracene exposure groups, and no significant differences were detected among the groups (ANT, 20.4 ± 5.5; ANT + SPPE-MP, 24.7 ± 2.7; ANT + FRPE-MP, 24.6 ± 4.7 µg/g). However, co-exposure to anthracene and spherical or fragmented polyethylene microplastics increased the duration of slow swimming in a swimming behavior test (control, 4.1 ± 1.4; ANT, 5.2 ± 2.8; ANT + SPPE-MP, 12.4 ± 3.7; ANT + FRPE-MP, 17.4 ± 5.1 min/30 min), and co-exposure to anthracene and fragmented polyethylene microplastics induced higher cytochrome P4501A monooxygenase (CYP1A) expression in Java medaka livers than the other anthracene exposure groups (ANT, 189 ± 74; ANT + SPPE-MP, 203 ± 75; ANT + FRPE-MP 272 ± 36% of control). Polyethylene microplastics appear to be weak vectors of anthracene at the size tested (200 µm), and the effect of shape (spherical or fragmented) on the vector effect was small. However, the presence of polyethylene microplastics could affect the swimming behavior and CYP1A expression in Java medaka.

Enhancement of photodegradation of polyethylene with adsorbed polycyclic aromatic hydrocarbons under artificial sunlight irradiation

The photodegradation of plastic waste produces microplastics (MPs) in marine environments. Plastics can adsorb hydrophobic organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) and can be transported over long distances. However, the impact of adsorbed pollutants on the photodegradation remains unknown. Here, we show that adsorbed PAHs act as photocatalysts that promote the photodegradation of polyethylene. Upon light irradiation, coloration and surface degradation of the PAH-adsorbed polyethylene sheets were observed, indicating that the PAH-adsorbed polyethylene sheets are less resistant to light. Furthermore, fluorene, phenanthrene, anthracene, benzo[a]anthracene, benzo[a]pyrene, and indeno[1,2,3-cd]perylene adsorbed on polyethylene MP exhibited lower photodegradation rates than the aqueous phase. These results indicate that these PAHs can act as photocatalysts; their role of PAHs may have two adverse effects on marine environment. First, enhanced photodegradation of plastic waste increased the production of MPs. Second, the lifetime of PAHs is extended, thereby enhancing PAHs pollution in marine environments.

The effect of microplastics on the depuration of hydrophobic organic contaminants in Daphnia magna: A quantitative model analysis

Microplastics are emerging pollutants that can absorb large amounts of hydrophobic organic contaminants (HOCs). However, no biodynamic model has yet been proposed to estimate their effects on HOC depuration in aquatic organisms, where the HOC concentrations are time-varying. In this work, a microplastic-inclusive biodynamic model was developed to estimate the depuration of HOCs via ingestion of microplastics. Several key parameters of the model were redefined to determine the dynamic HOC concentrations. Through the parameterized model, the relative contributions of dermal and intestinal pathways can be distinguished. Moreover, the model was verified and the vector effect of microplastics was confirmed by studying the depuration of polychlorinated biphenyl (PCB) in Daphnia magna (D. magna) with different sizes of polystyrene (PS) microplastics. The results showed that microplastics contributed to the elimination kinetics of PCBs because of the fugacity gradient between the ingested microplastics and the biota lipids, especially for the less hydrophobic PCBs. The intestinal elimination pathway via microplastics would promote overall PCB elimination, contributing 37-41 % and 29-35 % to the total flux in the 100 nm and 2 μm polystyrene (PS) microplastic suspensions, respectively. Furthermore, the contribution of microplastic uptake to total HOC elimination increased with decreasing microplastic size in water, suggesting that microplastics may protect organisms from HOC risks. In conclusion, this work demonstrated that the proposed biodynamic model is capable of estimating the dynamic depuration of HOCs for aquatic organisms. The results can shed light on a better understanding of the vector effects of microplastics.

Combined exposure to microplastics and amitriptyline caused intestinal damage, oxidative stress and gut microbiota dysbiosis in zebrafish (Danio rerio)

The potential toxicity of microplastics (MPs) and hydrophilic pharmaceuticals to aquatic organisms has recently raised great public concern, yet their combined effects on aquatic organisms remain largely unknown. Herein, the combined effects of MPs and the commonly prescribed amitriptyline hydrochloride (AMI) on the intestinal tissue and gut microbiota of zebrafish (Danio rerio) were investigated. Adult zebrafish were exposed to microplastics (polystyrene, PS, 440 µg/L), AMI (2.5 µg/L), PS+AMI (440 µg/L PS + 2.5 µg/L AMI), and dechlorinated tap water (control) for 21 days, respectively. Our results showed that zebrafish rapidly ingested PS beads and accumulated them in the gut. Exposure to PS+AMI significantly enhanced the SOD and CAT activities compared to the control group, suggesting that combined exposure might increase ROS production in the zebrafish gut. Exposure to PS+AMI led to severe gut injuries, including cilia defects, partial absence and cracking of intestinal villi. Exposure to PS+AMI caused shifts in the gut bacterial communities, increasing the abundance of Proteobacteria and Actinobacteriota, and decreasing the abundance of Firmicutes, Bacteroidota and beneficial bacteria Cetobacterium, which caused dysbiosis in the gut microbiota, and subsequently may induce intestinal inflammation. Furthermore, exposure to PS+AMI disordered the predicted metabolic functions of gut microbiota, but functional changes in the PS+AMI group at KEGG level 1 and level 2 were not significantly different from those in the PS group. The results of this study extend our knowledge of the combined effects of MPs and AMI on the health of aquatic organisms, and will be helpful in assessing the combined effects of MPs and tricyclic antidepressants on aquatic organisms.

A transcriptomic-based analysis predicts the neuroendocrine disrupting effect on adult male and female zebrafish (Danio rerio) following long-term exposure to tetrabromobisphenol A bis(2-hydroxyethyl) ether

Endocrine-disrupting chemicals (EDCs) are now ubiquitously distributed in the environment. Tetrabromobisphenol A bis(2-hydroxyethyl) ether (TBBPA-DHEE) pollution in environment media poses a significant threat to humans and aquatic organisms as a result of its potential neurotoxicity and endocrine-disrupting effect. The endocrine-disrupting effects of TBBPA-DHEE on aquatic organisms, however, have received limited attention. In this study, the neurotoxicity and reproductive endocrine-disruptive effect of TBBPA-DHEE was evaluated by observing the neurobehavioral changes, vitellogenin (VTG), testosterone, 17β-estradiol and gene expression levels in adult male and female zebrafish exposed to TBBPA-DHEE (0.05, 0.2 and 0.3 mg/L) for 100 days. Furthermore, transcriptomic analysis was conducted to unravel other potential neuroendocrine-disrupting mechanism. Our result showed TBBPA-DHEE significantly (p < 0.05) altered the locomotor behavior and motor coordination abilities in both sexes. Steroid hormone and VTG levels were also altered indicating the neuroendocrine-disrupting effect of TBBPA-DHEE on the hypothalamic-pituitary-gonadal-axis. A total of 1568 genes were upregulated and 542 genes downregulated in males, whereas, 1265 upregulated and 535 downregulated genes were observed in females. The KEGG enrichment analysis showed that cell cycle and p55 signaling pathways were significantly enriched due to TBBPA-DHEE exposure. These pathways and its component genes are potential target of EDCs. The significant upregulation of genes in these pathways could partly explain the neuroendocrine disrupting effect of TBBPA-DHEE. The observed toxic effects of TBBPA-DHEE observed in this study is confirmation of the endocrine-disrupting toxicity of this chemical which would be valuable in biosafety evaluation and biomonitoring of TBBPA-DHEE for public health purposes.

Desorption of polycyclic aromatic hydrocarbons from polyethylene microplastics in two morphologically different digestive tracts of marine teleosts: Gastric red seabream (Pagrus major) and agastric mummichog (Fundulus heteroclitus)

In this study, we elucidated the desorption potency of polycyclic aromatic hydrocarbons (PAHs) sorbed on microplastics (MP; polyethylene) in the digestive tract of two fish species: gastric red seabream and agastric mummichog. In our in vitro assay system using the real gut sample of unexposed fish, the digestive tract was firstly removed from the fish and divided into three parts. Then, MP that had previously been sorbed with 16 PAHs were incubated with extracts of the gut contents or tissue with buffer or only a buffer. The desorption potency of PAHs was individually assessed for gut contents and tissue, which revealed that PAH desorption from MP was elevated in extracts of the gut contents compared with that in the buffer alone for both fish species. PAH desorption potency was the highest in the midgut for gastric red seabream and in the foregut for agastric mummichog, which indicates that PAH desorption from MP varies among different parts of the digestive tract and among fish with distinct gut morphology. In the midgut contents of red seabream and foregut contents of mummichog, the desorption fraction was 5.6% and 8.1% of the total PAHs sorbed on MP, respectively. The desorption fraction enhancement achieved by adding gut contents extracts tended to be greater with an increase in the n-octanol/water partition ratio, suggesting that enhancement of the desorption fraction in the digestive tract depends on the physicochemical properties of PAHs. Thus, morphological differences in digestive tracts and PAH properties should be considered when evaluating the effect of MP vector on pollutant exposure in fish.

Microplastic profusion in food and drinking water: are microplastics becoming a macroproblem?

Microplastics are extremely complex, and as the food chain comes full circle, it is dreaded that these could have a deleterious influence on humans. Although the risk of plastics to humans is not yet established, their occurrence in food and water destined for human consumption has been reported. The prevalence of micro-sized plastics in the ecosystem and living organisms, their trophic transfer along the food web, and the discernment of food species as competent indicators have become research priorities. The scale of the issue is massive, but what are the main culprits and causes, and could there be a solution in sight for this global problem? Despite the massive amount of research in the field, a collation of available data and pertinent hazard evaluation remains difficult. In order to identify the knowledge gaps and exposure pathways, several traits related to food chain assessment are presented with the goal of properly evaluating and managing this emerging risk. We apprehend three possible noxious consequences of small plastic particles, firstly, due to the plastic particles themselves; secondly, due to the extrication of tenacious organic pollutants adsorbed onto the plastics; and thirdly, due to the leaching of components such as monomers and additives from the plastics. The exigency for the standardization of protocols to bring about consistency in data collection and analysis, involving solutions, stakeholder costs, and benefits, are discussed. Harmonized methods will enable meticulous assessment of the impacts and threats that microplastics pose to the biota and increase the comparability between studies. We emphasize the contribution of the "honest broker" in science, providing an overarching analysis to devise the most viable solutions to microplastic pollution for private and public leadership to utilize.

Combined effect of diazepam and polystyrene microplastics on the social behavior of medaka (Oryzias latipes)

The combined effect of microplastics and pharmaceuticals on aquatic organisms is an issue of concern. In this laboratory study, we evaluated the combined effect of polystyrene microplastics (2-μm diameter) and diazepam on the social behavior of medaka (Oryzias latipes) by using the shoaling behavior test with five treatment groups: solvent control, polystyrene microplastics exposure (0.04 mg/L), low-concentration diazepam exposure (0.03 mg/L), high-concentration diazepam exposure (0.3 mg/L), and polystyrene microplastics and low-concentration diazepam co-exposure. After 7 days of exposure, the shoal-leaving behavior of the high-concentration diazepam exposure group (8.9 ± 8.3 counts/medaka) and the co-exposure group (6.8 ± 6.7 counts/medaka) was significantly greater than that in the solvent control group (1.8 ± 2.6 counts/medaka). Even after 5 days of recovery, medaka in the co-exposure group left the shoal more often (7.3 ± 5.0 counts/medaka) than those in the solvent control group (2.6 ± 2.6 counts/medaka), whereas the shoal-leaving behavior in other exposure groups, except for the high-concentration diazepam exposure group, was restored. Our findings show that the combined effects of diazepam and polystyrene microplastics suppressed medaka social behavior, suggesting that the presence of microplastics can enhance the adverse effects of pollutants on the social behavior of aquatic organisms.

Adsorption of Different Pollutants by Using Microplastic with Different Influencing Factors and Mechanisms in Wastewater: A Review

The studies on microplastics are significant in the world. According to the literature, microplastics have greatly specific surface areas, indicating high adsorption capacities for highly toxic pollutants in aquatic and soil environments, and these could be used as adsorbents. The influencing factors of microplastic adsorption, classification of microplastics, and adsorption mechanisms using microplastics for adsorbing organic, inorganic, and mixed pollutants are summarized in the paper. Furthermore, the influence of pH, temperature, functional groups, aging, and other factors related to the adsorption performances of plastics are discussed in detail. We found that microplastics have greater advantages in efficient adsorption performance and cost-effectiveness. In this paper, the adsorptions of pollutants by microplastics and their performance is proposed, which provides significant guidance for future research in this field.

Biomarker responses in zebrafish (Danio rerio) following long-term exposure to microplastic-associated chlorpyrifos and benzo(k)fluoranthene

Continuously increasing plastic production causes a constant accumulation of microplastic particles (MPs) in the aquatic environment, especially in industrialized and urbanized areas with elevated wastewater discharges. This coincides with the release of persistent organic pollutants (polycyclic aromatic hydrocarbons (PAHs), pesticides) entering limnic ecosystems. Although the assessment of potential effects of environmental pollutants sorbed to MPs under chronic exposure scenarios seems vital, data on potential hazards and risk by combined exposure to pollutants and microplastics for aquatic vertebrates is still limited. Therefore, zebrafish (Danio rerio) were exposed over 21 days to the organophosphate insecticide chlorpyrifos (CPF; 10 and 100 ng/L) and the PAH benzo(k)fluoranthene (BkF; 0.78 and 50 µg/L) either dissolved directly in water or sorbed to different MPs (irregular polystyrene, spherical polymethyl methacrylate; ≤ 100 µm), where CPF was sorbed to polystyrene MPs and BkF was sorbed to polymethyl methacrylate MPs. Contaminant sorption to MPs and leaching were documented using GC-EI-MS; potential accumulation was studied in cryosections of the gastrointestinal tract. Enzymatic biomarkers and biotransformation were measured in liver and brain. Overall, exposure to non-contaminated MPs did not induce any adverse effects. Results of fluorescence tracking, CYP1A modulation by BkF as well as changes in acetylcholinesterase activity (AChE) by CPF were less pronounced when contaminants were sorbed to MPs, indicating reduced bioavailability of pollutants. Overall, following exposure to waterborne BkF, only minor amounts of parent BkF and biotransformation products were detected in zebrafish liver. Even high loads of MPs and sorbed contaminants did not induce adverse effects in zebrafish; thus, the potential threat of MPs as vectors for contaminant transfer in limnic ecosystems can be considered limited.

Impacts of Cetylpyridinium Chloride on the Survival, Development, Behavior, and Oxidative Stress of Early-Life-Stage Zebrafish (Danio rerio)

Cetylpyridinium chloride (CPC) is a widely used surfactant that has been detected in various water ecosystems. However, knowledge on the toxicity of CPC to fish remains scarce. Here, we examined the survival, development, behavior, and oxidative stress in the early life stages of zebrafish exposed to CPC (0, 4, 40, 400, and 1200 μg/L) until 120 h post-fertilization (hpf). Results showed that CPC induced significant mortality at 400 and 1200 μg/L, with a 120 h-EC₅₀ value of 175.9 μg/L. CPC significantly decreased the heart rate of embryos (48 hpf; 4–400 μg/L) and larvae (72 hpf; 40 and 400 μg/L). At 120 hpf, CPC exhibited a dual effect on the locomotion activity (decreased at 400 μg/L and increased at 4 and 40 μg/L) and elevated the reactive oxygen species, superoxide dismutase, and glutathione levels in zebrafish larvae at 400 µg/L. In addition, a correlation analysis revealed that CPC-induced oxidative stress might play a critical role in mediating the cardiac and behavioral toxicity of CPC to zebrafish larvae. Our findings suggest that CPC may disturb the fish’s development, behavior, and oxidative status at environmentally relevant concentrations, which should not be ignored when assessing its potential risks to aquatic ecosystems.

Oral Exposure to Tributyltin Induced Behavioral Abnormality and Oxidative Stress in the Eyes and Brains of Juvenile Japanese Medaka (Oryzias latipes)

The widely used compound tributyltin (TBT), which can be continuously detected in aquatic species and seafood, may induce diverse adverse effects on aquatic organisms. However, little is known regarding the mechanistic links between behavioral abnormality and oxidative stress in different fish tissues in response to oral TBT exposure. Herein, juvenile Japanese medaka (Oryzias latipes) were orally exposed to TBT at 1 and 10 ng/g-bw/d for four weeks. After exposure, the locomotor activity and social interaction of juvenile medaka were found to be significantly reduced in the 10 ng/g-bw/d TBT-exposed group. Furthermore, the antioxidant biomarkers in different tissues of juvenile medaka showed different levels of sensitivity to TBT exposure. The eye superoxide dismutase (SOD) activities markedly increased in both groups exposed to 1 and 10 ng/g-bw/d TBT, while the eye and brain malondialdehyde (MDA) levels increased in the higher dose group. Furthermore, the eye and brain ATPase activities markedly declined in the 1 ng/g-bw/d TBT-exposed group. A correlation analysis revealed that the decreased locomotor activity and social interaction in medaka were associated with the eye antioxidant enzyme (i.e., SOD and catalase (CAT)) activity and brain oxidative damage level. Thus, our findings suggested that there might be some mechanistic links between the behavioral abnormality induced by TBT exposure and oxidative stress in the eyes and brains of medaka. Thus, our findings indicate that the impacts of oral exposure to TBT should be considered to better assess its risk to the aquatic ecosystem and human health.