Size-dependent transfer of microplastics across the intestinal wall of the echinoid Paracentrotus lividus

Micro-and nano-plastics induce kidney damage and suppression of innate immune function in zebrafish (Danio rerio) larvae

Aquatic environments serve as critical repositories for pollutants and have significantly accumulated micro- and nanoplastics (MNPs) due to the extensive production and application of plastic products. While the disease resistance and immunity of fish are closely linked to the condition of their aquatic habitats, the specific effects of nanoplastics (NPs) and microplastics (MPs) within these environments on fish immune functions are still not fully understood. The present study utilized zebrafish (Danio rerio) embryos and larvae as model organisms to examine the impacts of polystyrene NPs (100 nm) and MPs (5 μm) on fish immune responses. Our findings reveal that NPs and MPs tend to accumulate on the surfaces of embryos and within the intestines of larvae, triggering oxidative stress and significantly increasing susceptibility to Edwardsiella piscicida infection in zebrafish larvae. Transmission electron microscopy examined that both NPs and MPs inflicted damage to the kidney, an essential immune organ, with NPs predominantly inducing endoplasmic reticulum stress and MPs causing lipid accumulation. Transcriptomic analysis further demonstrated that both NPs and MPs significantly suppress the expression of key innate immune pathways, notably the C-type lectin receptor signaling pathway and the cytosolic DNA-sensing pathway. Within these pathways, the immune factor interleukin-1 beta (il1b) was consistently downregulated in both exposure groups. Furthermore, exposure to E. piscicida resulted in restricted upregulation of il1b mRNA and protein levels, likely contributing to diminished disease resistance in zebrafish larvae exposed to MNPs. Our findings suggest that NPs and MPs similarly impair the innate immune function of zebrafish larvae and weaken their disease resistance, highlighting the significant environmental threat posed by these pollutants.

Cellular effects of microplastics are influenced by their dimension: Mechanistic relationships and integrated criteria for particles definition

The definition of microplastics (MPs) is nowadays too generic from a biological perspective, since different characteristics of these particles might influence their effects. To provide experimental evidence that size is an important factor to be considered, Mediterranean mussels Mytilus galloprovincialis were exposed to five size classes of polyethylene fragments (PE-MPs, 20-50 μm, 50-100 μm, 100-250 μm, 250-500 μm, 500-1000 μm). After 10 days of exposure, MPs ingestion and mechanistic relationships between particles size and cellular effects were analysed through a wide panel of biological alterations, including immune system responses, cholinergic function, antioxidant system, lipid metabolism and peroxidation. Results were further elaborated through a Weight of Evidence approach, summarizing the overall biological significance of obtained results in a hazard index based on the number and magnitude of variations and their toxicological relevance. PE-MPs 500-1000 μm were identified as the less biologically reactive size class due to the limited ingestion of particles coupled with the lack of biological effects, followed by PE-MPs 250-500 μm, which slightly altered the cholinergic function and lysosomal membranes. Conversely, PE-MPs smaller than 250 μm provoked a more consistent onset of biological alterations in terms of immune system composition and functioning, redox homeostasis, and lipid metabolism. The overall findings of this study highlight the importance of considering the size of particles for monitoring and risk assessment of MPs, introducing a more integrated evaluation of plastic pollution that, beside particles concentration, should adequately weigh those characteristics triggering the onset of biological effects.

Microplastic ingestion and its effects οn sea urchin Paracentrotus lividus: A field study in a coastal East Mediterranean environment

Microplastics (MPs) are recognized as an increasing threat to the marine environment, but little is known about their effects on benthic organisms, including sea urchins, when ingested. For this purpose, wild sea urchins (P. lividus) and seafloor sediment samples were investigated across three coastal areas of Zakynthos Island (Ionian Sea), each exposed to different anthropogenic pressures, revealing a consistent pattern in MP abundance, shape, and color. Biomarkers related to oxidative stress, neurotoxicity, and genotoxicity showed no significant effects of MP ingestion in the sea urchins, except for a positive correlation between GST activity and ingested MPs, suggesting a possible activation of their detoxification system in response to MP ingestion. While MP concentrations in sea urchins and sediments were within the low range reported in the global literature, it remains crucial to conduct further investigations in areas with MP pollution approaching predicted levels to fully comprehend the potential effects of MP pollution on marine organisms.

The emerging role of microplastics in systemic toxicity: Involvement of reactive oxygen species (ROS)

Plastic pollution is one of the most pressing environmental threats the world is facing currently. The degradation of macroplastics into smaller forms viz. microplastics (MPs) or Nanoplastics (NPs) is a potential threat to both terrestrial and marine ecosystems and also to human health by directly affecting the organs and activating a plethora of intracellular signaling, that may lead to cell death. There is accumulating evidence that supports the serious toxicity caused by MP/NPs at all levels of biological complexities (biomolecules, organelles, cells, tissues, organs, and organ systems) and the involvement of the reactive oxygen species (ROS) in this process. Studies indicate that MPs or NPs can accumulate in mitochondria and further disrupt the mitochondrial electron transport chain, cause mitochondrial membrane damage, and perturb the mitochondrial membrane potential or depolarization of the mitochondria. These events eventually lead to the generation of different types of reactive free radicals, which can induce DNA damage, protein oxidation, lipid peroxidation, and compromization of the antioxidant defense pool. Furthermore, MP-induced ROS was found to trigger a plethora of signaling cascades, such as the p53 signaling pathway, Mitogen-activated protein kinases (MAPKs) signaling pathway including the c-Jun N-terminal kinases (JNK), p38 kinase, and extracellular signal related kinases (ERK1/2) signaling cascades, Nuclear factor erythroid 2-related factor 2 (Nrf2)-pathway, Phosphatidylinositol-3-kinases (PI3Ks)/Akt signaling pathway, and Transforming growth factor-beta (TGF-β) pathways, to name a few. As a consequence of oxidative stress caused by the MPs/NPs, different types of organ damage are observed in living species, including humans, such as pulmonary toxicity, cardiotoxicity, neurotoxicity, nephrotoxicity, immunotoxicity, reproductive toxicity, hepatotoxicity, etc. Although presently, a good amount of research is going on to access the detrimental effects of MPs/NPs on human health, there is a lack of proper model systems, multi-omics approaches, interdisciplinary research, and mitigation strategies.

Microplastics in aquatic species of Anzali wetland: An important freshwater biodiversity hotspot in Iran

Coastal wetlands are sensitive ecosystems that give habitat to large number of species. The extent of the impact of microplastic pollution in the aquatic system and humans is not known. In this study, the occurrence of microplastics (MPs) was assessed in 7 aquatic species from the Anzali Wetland (40 fish and 15 shrimp specimens), a listed wetland on the Montreux record. Specifically, the tissues analyzed were gastrointestinal (GI) tract, gills, skin, and muscles. The total frequency of MPs (all detected MPs in the GI tract, gill and skin samples) varied from 5.2 ± 4.2 MPs/specimen for Cobitis saniae to 20.8 ± 6.7 MPs/specimen for Abramis brama. Among all tissues studied, the GI tract of the Chelon saliens, a herbivorous demersal species, had the greatest level of MPs (13.6 ± 10 MPs/specimen). Significant differences (p < 0.05) were found between the abundance of MPs in different species, tissues, living domains and feeding habit types. The findings support that fish may uptake MPs through adherence in gills (respiration) in addition to ingestion. White/transparent and black/grey polyamide (PA) fibers were the most common type of MP which may be originated from municipal wastewater and intensive fishing activities. About 34% of the MPs were in the range of 250 μm-500 μm, and those >100 μm were not detected in muscles from the study fish. All species had unhealthy weight according to the Fulton's condition index (K). Positive relationships existed between biometric properties (total length and weight) of species and the total frequency of uptaken MPs, pointing to detrimental impact of MPs in the wetland.