Plastic mulching, and occurrence, incorporation, degradation, and impacts of polyethylene microplastics in agroecosystems.

Polyethylene microplastics have been detected in farmland soil, irrigation water, and soil organisms in agroecosystems, while plastic mulching is suggested as a crucial source of microplastic pollution in the agroecosystem. Plastic mulch can be broken down from plastic mulch debris to microplastics through environmental aging and degradation process in farmlands, and the colonization of polyethylene-degrading microorganisms on polyethylene microplastics can eventually enzymatically depolymerize the polyethylene molecular chains with CO2 release through the tricarboxylic acid cycle. The selective colonization of microplastics by soil microorganisms can cause changes in soil microbial community composition, and it can consequently elicit changes in enzyme activities and nutrient element content in the soil. The biological uptake of polyethylene microplastics and the associated disturbance of energy investment are the main mechanisms impacting soil-dwelling animal development and behavior. As polyethylene microplastics are highly hydrophobic, their presence among soil particles can contribute to soil water repellency and influence soil water availability. Polyethylene microplastics have been shown to cause impacts on crop plant growth, as manifested by the effects of polyethylene microplastics on soil properties and soil biota in the agroecosystems. This review reveals the degradation process, biological impacts, and associated mechanisms of polyethylene microplastics in agroecosystems and could be a critical reference for their risk assessment and management.

Characterization of Microplastic-Associated Biofilm Development along a Freshwater-Estuarine Gradient.

Microplastic contamination is an increasing concern worldwide. Biofilms rapidly develop on surfaces in aquatic habitats, but the processes of biofilm formation and variation in bacterial community succession on different microplastics introduced into freshwater and estuarine environments are not well understood. In this study, the biofilm bacterial communities that developed on three different types of microplastics that are prevalent in the environment, high-density polyethylene (HDPE), polyethylene terephthalate (PET), and polystyrene (PS), was investigated. Virgin microplastics were incubated in microcosms over a period of 31 days with water collected along a freshwater-estuarine gradient of the Raritan River in New Jersey. Through long-read MinION sequencing of bacterial ribosomal operons, we were able to examine biofilm bacterial communities at a species- and strain-level resolution. Results indicated that both salinity level and microplastic type impacted biofilm formation and promoted colonization by distinct microbial communities. Limnobacter thiooxidans was found to be one of the most abundant microplastics colonizing-bacteria, and it is hypothesized that different types of microplastics could select for different strains. Our findings indicate that multiple groups of highly similar L. thiooxidans rRNA operons could be discerned within the community profiles. Phylogenetic reconstruction further established that various Linmobacter species uniquely colonized the different microplastics from the different sampling sites. Our findings indicate that microplastics support abundant and diverse bacterial communities and that the various types of microplastics can influence how different bacterial biofilms develop, which may have ecological impacts on aquatic ecosystems.

Exposure to polystyrene microplastics impairs gonads of zebrafish (Danio rerio).

Microplastic contamination poses a great threat to the health of aquatic species, which may affect their reproduction and result in ecological consequences. There is a need to further elucidate the potential impact microplastics can impose on aquatic species. In this study, the effects of exposure to polystyrene microplastics on reproductive organs, and the underlying response mechanisms, were investigated using zebrafish Danio rerio. After 21 days of continuous waterborne exposure, no significant difference was observed at the lower concentration of 10 µg/L. At concentrations above 100 µg/L, significantly enhanced reactive oxygen species (ROS) level was found in both male and female liver and gonads. At the concentration of 1000 µg/L, significantly increased apoptosis levels were observed in male testes, triggering increased expression of p53-mediated apoptotic pathways; histological alteration in the form of a significant decrease in testis basement membrane thickness was also observed. This study demonstrated that exposure to microplastics can induce molecular responses and histological alterations in fish gonads, implying potential adverse impact on fish reproductive organs. This work provided new insights on the reproductive damage microplastics can cause in fish and have implications in fields of freshwater ecology and environmental toxicology.

Parental exposure to polystyrene microplastics at environmentally relevant concentrations has negligible transgenerational effects on zebrafish (Danio rerio).

Waterborne exposure to highly persistent microplastic pollutants is a major concern for aquatic species worldwide. There are still gaps in knowledge on microplastics' potential transgenerational effects on offspring generation. Using zebrafish, this study investigated the survival and early development of offspring through a 21-day continuous parental treatment with polystyrene microplastics. The results showed that continuous waterborne exposure to high concentrations (>100 µg/L) of polystyrene microplastics (1 µm) for 21 days resulted in notable microplastic accumulation in adult fish intestines. Exposure at microplastic concentrations greater than 100 µg/L also induced significant changes in steroidogenic mRNA expression in zebrafish gonads. However, no significant changes in the cumulative number of eggs spawned and fertilization rate were observed at any parental exposure concentrations when compared to the control. Early development of derived offspring, in terms of hatching rate, body length, malformation rate and mortality rate, did not significantly differ from that of the control. This study showed that transgenerational effects of parental exposure to polystyrene microplastics in zebrafish might be negligible or recoverable. This study provided new results and insights on the transgenerational effects of microplastics on a freshwater fish species and can help to understand impacts of microplastics on freshwater ecosystems.

Bioaccumulation of microplastics and its in vivo interactions with trace metals in edible oysters.

Microplastics have been an emerging threat to marine environments and marine life. Oysters as seafood are popular worldwide, yet also a high-risk group to accumulate pollutants due to their filter-feeding nature. In this study, edible oysters were collected from Yantai, a coastal city in China, to study the uptake, accumulation and translocation of microplastics in marine life, as well as their in vivo interactions with other persistent pollutants. Microplastics were found in all of the studied oyster tissue samples with an average concentration around 4.53 items/g wet weight (24.49 items/g dry weight). Microplastics were mainly translocated and distributed in the gills and mantle of the studied oysters in the form of fibers. The detected microplastics in the oysters were mostly cellophane and polyester as identified by the micro-Fourier transform infrared spectroscope. Cellophane tends to accumulate in gills, mantle and muscle while polyester tends to accumulate in digestive glands of the studied oysters. Excessive concentrations of trace metals (30.484, 4.415, 0.395 and 181.044 µg/g dry weight of Cr, Cd, Pb and Cu, respectively) were detected in the studied oysters using inductively coupled plasma mass spectrometry. Trace metals of Cr, Mn, Ni, Cu, Zn, Cd and Pb were found to be adsorbed on the surface of microplastics isolated from the oysters. There was a correlation between the in vivo concentration of microplastics and the in vivo concentration of four trace metals: Cd, Cr, Cu and Pb, which suggests potential in vivo interactions between microplastics and trace metals. This study can help to understand the impacts of microplastics and their joint toxicity with other pollutants on marine life, especially on aquaculture seafood. This study will be an important reference for the assessment of health risks associated with consumption of edible coastal oysters in China.

Silver Nanoparticles in Zebrafish (Danio rerio) Embryos: Uptake, Growth and Molecular Responses.

Silver nanoparticles (AgNPs) are widely used in commercial applications as antimicrobial agents, but there have recently been increasing concerns raised about their possible environmental and health impacts. In this study, zebrafish embryos were exposed to two sizes of AgNP, 4 and 10 nm, through a continuous exposure from 4 to 96 h post-fertilisation (hpf), to study their uptake, impact and molecular defense responses. Results showed that zebrafish embryos were significantly impacted by 72 hpf when continuously exposed to 4 nm AgNPs. At concentrations above 0.963 mg/L, significant in vivo uptake and delayed yolk sac absorption was evident; at 1.925 mg/L, significantly reduced body length was recorded compared to control embryos. Additionally, 4 nm AgNP treatment at the same concentration resulted in significantly upregulated hypoxia inducible factor 4 (HIF4) and peroxisomal membrane protein 2 (Pxmp2) mRNA expression in exposed embryos 96 hpf. In contrast, no significant differences in terms of larvae body length, yolk sac absorption or gene expression levels were observed following exposure to 10 nm AgNPs. These results demonstrated that S4 AgNPs are available for uptake, inducing developmental (measured as body length and yolk sac area) and transcriptional (specifically HIF4 and Pxmp2) perturbations in developing embryos. This study suggests the importance of particle size as one possible factor in determining the developmental toxicity of AgNPs in fish embryos.

Exposure to microplastics decreases swimming competence in larval zebrafish (Danio rerio).

Microplastics have been frequently detected in both marine and freshwater ecosystems. Their impact on aquatic organisms has raised much concern. This study investigated the impact of microplastics on zebrafish embryos and larvae, with a special focus on their swimming competence. The zebrafish embryos were exposed to microplastics starting from 4 h post fertilization. Microplastics first adhered to the embryo chorion, then entered the stomach and intestinal tract of the larvae later. In the free swimming test, exposure to 1000 µg/L (around 1.91 × 107 particles/L) of microplastics led to a significant decrease in both swimming distance and speed of zebrafish larvae under the dark condition by 3.2% and 3.5% respectively. In the alternating light-to-dark photoperiod stimulation assay, exposure to 100 and 1000 µg/L (around 1.91 × 106 and 1.91 × 107 particles/L) of microplastics caused a 4.6% and 2.6% decrease in swimming distance, and reduced the active speed by 4.9% and 2.8%, possibly as a result of inhibited dark avoidance in treated zebrafish larvae. At the molecular level, exposure to microplastics induced upregulated expression of inflammation (il1b) and oxidative stress (cat) related genes. This study demonstrates that exposure to microplastics significantly decreases larvae swimming competence, which may have significant impacts on its population fitness in the aquatic environment and further ecological consequences.

[Distribution and Settlement of Microplastics in the Surface Sediment of Yangtze Estuary].

This study is designed to understand the microplastic contamination in the coastal area of Yangtze estuary. The abundance and distribution profiles of microplastics in the surface sediment of six sampling sites along the Yangtze estuary were examined throughout one year. The detected average concentration of microplastic, including fibers and fragments, in the surface sediment of Yangtze estuary was (3.42±1.31) items ·g-1 (DW). Sampling during four seasons, in the months of January, April, July, and November, indicated that the highest abundance of microplastics in Yangtze estuary surface sediment occurred in January. A re-suspension experiment showed that microplastics tend to settle in the surface sediment after re-suspension. The distribution and settlement of microplastics along the coastal area has a high concordance with the dynamic erosion-accretion process of the Yangtze estuary. Microplastics tend to settle in accretion sites rather than in erosion sites.

[Contribution of Particle Size and Surface Coating of Silver Nanoparticles to Its Toxicity in Marine Diatom Skeletonema costatum].

Due to the unique antibacterial properties, silver nanoparticles (AgNPs) have been widely used in commercial applications. In this study, the toxicity of three kinds of AgNPs with different sizes and surface coatings to marine diatom Skeletonema costatum (S. costatum) was studied, which was one of the dominant species in estuarine and coastal areas. All three kinds of tested AgNPs inhibited the growth of exposed S. costatum under acute exposure condition, and the order of toxicity was 10 nm-OA > 10 nm-PVP > 20 nm-PVP. Given the condition of similar particle size, oil amine surface coated AgNPs were more toxic than polyvinyl pyrrolidone (PVP) surface coated AgNPs in S. costatum in term of cytotoxicity. With the same surface coating, the toxicity of AgNPs in S. costatum was affected by its hydrodynamic diameter and exposure concentrations. When the concentration of AgNPs was less than 500 µg · L⁻¹, larger sized AgNPs showed greater toxicity; When the concentration was greater than or equal to 500 µg · L⁻¹, smaller AgNPs exhibited greater toxicity. At molecular level, 50 µg · L⁻¹ 10nm-PVP significantly upregulated expression level of 3HfcpA (P < 0.05) and significantly downregulated expression level of Dl (P < 0.05), and 500 µg · L⁻¹ 10nm-OA significantly upregulated 3HfcpA expression (P < 0.05), while 20 nm-PVP treatment group didn't show any significant change. Exposed diatom demonstrated sensitive photosynthesis response to small size and PVP coated silver nanoparticles at molecular level. This study suggested that the toxicity of AgNPs to marine microalgae was largely controlled by the particle size, surface coating, exposure medium, exposure concentration and other factors. The smaller the particle size, the greater the toxicity of AgNPs, and the particle size of AgNPs played an important role in the toxicity of AgNPs in marine diatom S. costatum.

Environmental concentration of carbamazepine accelerates fish embryonic development and disturbs larvae behavior.

Environmental pollution caused by pharmaceuticals has been recognized as a major threat to the aquatic ecosystems. Carbamazepine, as the widely prescribed antiepileptic drug, has been frequently detected in the aquatic environment and has created concerns about its potential impacts in the aquatic organisms. The effects of carbamazepine on zebrafish embryos were studied by examining their phenotype, behavior and molecular responses. The results showed that carbamazepine disturbed the normal growth and development of exposed zebrafish embryos and larvae. Upon exposure to carbamazepine at 1 µg/L, the hatching rate, body length, swim bladder appearance and yolk sac absorption rate were significantly increased. Embryos in treatment groups were more sensitive to touch and light stimulation. At molecular level, exposure to an environmentally relevant concentration (1 µg/L) of carbamazepine disturbed the expression pattern of neural-related genes of zebrafish embryos and larvae. This study suggests that the exposure of fish embryo to antiepileptic drugs, at environmentally relevant concentrations, affects their early development and impairs their behavior. Such impacts may have future repercussions by affecting fish population structure.