Cell size matters: Nano- and micro-plastics preferentially drive declines of large marine phytoplankton due to co-aggregation

Uncovering layer by layer the risk of nanoplastics to the environment and human health

Nanoplastics (NPs), defined as plastic particles with dimensions less than 100 nm, have emerged as a persistent environmental contaminant with potential risk to both environment and human health. Nanoplastics might translocate across biological barriers and accumulate in vital organs, leading to inflammatory responses, oxidative stress, and genotoxicity, already reported in several organisms. Disruptions to cellular functions, hormonal balance, and immune responses were also linked to NPs exposure in in vitro assays. Further, NPs have been found to adsorb other pollutants, such as persistent organic pollutants (POPs), and leach additives potentially amplifying their advere impacts, increasing the threat to organisms greater than NPs alone. However, NPs toxic effects remain largely unexplored, requiring further research to elucidate potential risks to human health, especially their accumulation, degradation, migration, interactions with the biological systems and long-term consequences of chronic exposure to these compounds. This review provides an overview of the current state-of-art regarding NPs interactions with environmental pollutants and with biological mechanisms and toxicity within cells.

Zooming in the plastisphere: the ecological interface for phytoplankton-plastic interactions in aquatic ecosystems

Phytoplankton is an essential resource in aquatic ecosystems, situated at the base of aquatic food webs. Plastic pollution can impact these organisms, potentially affecting the functioning of aquatic ecosystems. The interaction between plastics and phytoplankton is multifaceted: while microplastics can exert toxic effects on phytoplankton, plastics can also act as a substrate for colonisation. By reviewing the existing literature, this study aims to address pivotal questions concerning the intricate interplay among plastics and phytoplankton/phytobenthos and analyse impacts on fundamental ecosystem processes (e.g. primary production, nutrient cycling). This investigation spans both marine and freshwater ecosystems, examining diverse organisational levels from subcellular processes to entire ecosystems. The diverse chemical composition of plastics, along with their variable properties and role in forming the "plastisphere", underscores the complexity of their influences on aquatic environments. Morphological changes, alterations in metabolic processes, defence and stress responses, including homoaggregation and extracellular polysaccharide biosynthesis, represent adaptive strategies employed by phytoplankton to cope with plastic-induced stress. Plastics also serve as potential habitats for harmful algae and invasive species, thereby influencing biodiversity and environmental conditions. Processes affected by phytoplankton-plastic interaction can have cascading effects throughout the aquatic food web via altered bottom-up and top-down processes. This review emphasises that our understanding of how these multiple interactions compare in impact on natural processes is far from complete, and uncertainty persists regarding whether they drive significant alterations in ecological variables. A lack of comprehensive investigation poses a risk of overlooking fundamental aspects in addressing the environmental challenges associated with widespread plastic pollution.

Toxicity of inorganic nanoparticles and commercial sunscreens on marine bacteria

The Balearic Islands, a top tourist destination for sunny beaches, face physical and chemical pressures from human activities, impacting keystone species like the endemic seagrass Posidonia oceanica and its associated microbiome. This study evaluated the effects of ZnO and TiO2 nanoparticles and three commercial sunscreens with varying protection factors (50 or 90) and chemical complexities (1- SPF50_E "eco-friendly"; 2- SPF50 not "eco-friendly"; 3- SPF90 not "eco-friendly") on five heterotrophic bacteria (Pseudomonas azotifigens, Marinobacterium litorale, Thiothrix nivea, Sedimenticola thiotaurini and Cobetia sp) and two autotrophic cyanobacteria (Halothece sp. and Fischerella muscicola) associated to P. oceanica, as well as a natural leaf epiphytic community. Results indicated that TiO2 affected all heterotrophic bacteria, while ZnO was toxic to only two species, while autotrophs were unaffected. Commercial sunscreens impacted three heterotrophs and the natural epiphytic community, while autotrophs were only affected by SPF50. SPF50_E reduced phosphorus uptake, and both SPF50 and SPF90 decreased alkaline phosphatase activity. Reactive oxygen species production was mainly induced by SPF90, followed by SPF50_E and SPF50. Generally, the smallest bacteria were most sensitive to UV-filters (UVFs). This study indicates that UVFs exposure may alter the epiphytic community structure of P. oceanica.

Do weathered microplastics impact the planktonic community? A mesocosm approach in the Baltic Sea

Microplastics (MPs) are ubiquitous pollutants of increasing concern in aquatic systems. However, little is still known about the impacts of weathered MPs on plankton at the community level after long-term exposure. In this study, we investigated the effects of weathered MPs on the structure and dynamics of a Baltic Sea planktonic community during ca. 5 weeks of exposure using a mesocosm approach (2 m3) mimicking natural conditions. MPs were obtained from micronized commercial materials of polyvinyl chloride, polypropylene, polystyrene, and polyamide (nylon) previously weathered by thermal ageing and sunlight exposure. The planktonic community was exposed to 2 μg L-1 and 2 mg L-1 of MPs corresponding to measured particle concentrations (10-120 μm) of 680 MPs L-1 and 680 MPs mL-1, respectively. The abundance and composition of all size classes and groups of plankton and chlorophyll concentrations were periodically analyzed throughout the experiment. The population dynamics of the studied groups showed some variations between treatments, with negative and positive effects of MPs exhibited depending on the group and exposure time. The abundance of heterotrophic bacteria, pico- and nanophytoplankton, cryptophytes, and ciliates was lower in the treatment with the higher MP concentration than in the control at the last weeks of the exposure. The chlorophyll concentration and the abundances of heterotrophic nanoflagellates, Astromoeba, dinoflagellate, diatom, and metazooplankton were not negatively affected by the exposure to MPs and, in some cases, some groups showed even higher abundances in the MP treatments. Despite these tendencies, statistical analyses indicate that in most cases there were no statistically significant differences between treatments over the exposure period, even at very high exposure concentrations. Our results show that weathered MPs of the studied conventional plastic materials have minimal or negligible impact on planktonic communities after long-term exposure to environmentally relevant concentrations.

Exposure to polystyrene nanoplastics induces abnormal activation of innate immunity via the cGAS-STING pathway

Endogenous immune defenses provide an intrinsic barrier against external entity invasion. Microplastics in the environment, especially those at the nanoscale (nanoplastics or NPs), may pose latent health risks through direct exposure. While links between nanoplastics and inflammatory processes have been established, detailed insights into how they may perturb the innate immune mechanisms remain uncharted. Employing murine and macrophage (RAW264.7) cellular models subjected to polystyrene nanoplastics (PS-NPs), our investigative approach encompassed an array of techniques: Cell Counting Kit-8 assays, flow cytometric analysis, acridine orange/ethidium bromide (AO/EB) fluorescence staining, cell transfection, cell cycle scrutiny, genetic manipulation, messenger RNA expression profiling via quantitative real-time PCR, and protein expression evaluation through western blotting. The results showed that PS-NPs caused RAW264.7 cell apoptosis, leading to cell cycle arrest, and activated the cGAS-STING pathway. This resulted in NF-κB signaling activation and increased pro-inflammatory mediator expression. Importantly, PS-NPs-induced activation of NF-κB and its downstream inflammatory cascade were markedly diminished after the silencing of the STING gene. Our findings highlight the critical role of the cGAS-STING pathway in the immunotoxic effects induced by PS-NPs. We outline a new mechanism whereby nanoplastics may trigger dysregulated innate immune and inflammatory responses via the cGAS/STING pathway.

Microalgae-microplastics interactions at environmentally relevant concentrations: Implications toward ecology, bioeconomy, and UN SDGs

Microplastics (MPs) are one of the emerging pollutants, causing potential harm to aquatic ecosystems and serious concern in achieving UN Sustainable Development Goals (SDGs). Realizing the occurrence of varying concentrations of MPs in the environment, this investigation presents multi-dimensional insights into the ecological and bioeconomic implications at environmentally relevant concentrations. We pursued a multi-step approach to gain a comprehensive understanding on the effects of microalgae‒MPs interactions and their expansive implications toward SDGs. Baseline data generated using a model microalga, Raphidocelis subcapitata, and three MPs (polyethylene terephthalate, PET; polyvinyl chloride, PVC; and polystyrene, PS) indicated 10‒15 % reduction in microalgal growth rate relative to the control, pointing to a heightened energy demand. The biochemical impacts displayed concentration-dependent variability. Using the baseline data, we developed a linear regression model to dissect the interaction effects around the primary dimensions of Ecology and Bioeconomy. Notably, a correlation matrix for carbon allocation pinpointed PET as having a more pronounced impact compared to PVC and PS, with the model accounting for 33.72 % of the observed variance. Extending our insights from the model, we adopted an evidence-based methodology to outline the broader implications across the Ecology and Bioeconomy domains, and subsequently identified their associations with specific SDGs. Further probing into microalgae‒MPs interaction effects at environmentally relevant concentration, our model revealed that the selected MPs perturbed the ecological variables. Interestingly, when carbon allocation was assessed to study bioeconomic implications, there were contrasting effects on starch synthesis (beneficially) and lipid synthesis (detrimentally). The present combined analysis revealed that MPs, beyond their traditional association with SDG 14 (Life Below Water), directly and indirectly affect five other SDGs through their interactions with microalgae. This study thus underscores the complex and interconnected nature of MPs pollution at environmentally relevant concentrations and their impacts on ecological and bioeconomic aspects of SDGs, thereby highlighting the urgent need for additional research and effective mitigation strategies.

Toxic effects of pristine and aged polystyrene and their leachate on marine microalgae Skeletonema costatum

The acute toxic effects of pristine and aged polystyrene (P-PS and A-PS) and their leaching solutions (L-PS) on microalgae Skeletonema costatum were investigated by measuring algal density and growth inhibition rate (IR), chlorophyll concentration and photosynthetic efficiency (Fv/Fm) over 96 h. Total protein (TP), superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) were measured to analyze the oxidative damage to microalgae by microplastics and their leachates. Hydrodynamic diameter of microplastics in seawater, FITR and SEM images were used to study the changes of polystyrene during aging. The interaction of algae cell with microplastics and the cellular ultrastructure changes of cells were analyzed combined with electron microscopy for a comprehensive and systematic understanding on the mechanisms of microplastic toxicity to microalgae. Both high concentration and small size of PS had significant inhibitory effect on the growth of microalgae, and the inhibitory effect was greater with increasing exposure time. The inhibition effect of aged microplastics was more obvious, which was speculated to be caused by the synergistic effect of aged PS itself and leaching solution. The negative effect of leaching solution on microalgae was due to the release of some additives during the aging process. The content of MDA reached the highest value of 54.41 nmol/mgprot in 1.0 μm 50 mg/L A-PS treatment group, and A-PS were found to be more prone to heterogeneous aggregation with algae cells by SEM.

Gross Negligence: Impacts of Microplastics and Plastic Leachates on Phytoplankton Community and Ecosystem Dynamics

Plastic debris is an established environmental menace affecting aquatic systems globally. Recently, microplastics (MP) and plastic leachates (PL) have been detected in vital human organs, the vascular system, and in vitro animal studies positing severe health hazards. MP and PL have been found in every conceivable aquatic ecosystem─from open oceans and deep sea floors to supposedly pristine glacier lakes and snow covered mountain catchment sites. Many studies have documented the MP and PL impacts on a variety of aquatic organisms, whereby some exclusively focus on aquatic microorganisms. Yet, the specific MP and PL impacts on primary producers have not been systematically analyzed. Therefore, this review focuses on the threats posed by MP, PL, and associated chemicals on phytoplankton, their comprehensive impacts at organismal, community, and ecosystem scales, and their endogenous amelioration. Studies on MP- and PL-impacted individual phytoplankton species reveal the production of reactive oxygen species, lipid peroxidation, physical damage of thylakoids, and other physiological and metabolic changes, followed by homo- and heteroaggregations, ultimately eventuating in decreased photosynthesis and primary productivity. Likewise, analyses of the microbial community in the plastisphere show a radically different profile compared to the surrounding planktonic diversity. The plastisphere also enriches multidrug-resistant bacteria, cyanotoxins, and pollutants, accelerating microbial succession, changing the microbiome, and thus, affecting phytoplankton diversity and evolution. These impacts on cellular and community scales manifest in changed ecosystem dynamics with widespread bottom-up and top-down effects on aquatic biodiversity and food web interactions. These adverse effects─through altered nutrient cycling─have "knock-on" impacts on biogeochemical cycles and greenhouse gases. Consequently, these impacts affect provisioning and regulating ecosystem services. Our citation network analyses (CNA) further demonstrate dire effects of MP and PL on all trophic levels, thereby unsettling ecosystem stability and services. CNA points to several emerging nodes indicating combined toxicity of MP, PL, and their associated hazards on phytoplankton. Taken together, our study shows that ecotoxicity of plastic particles and their leachates have placed primary producers and some aquatic ecosystems in peril.

The effect of microplastics on the interspecific competition of Daphnia

Microplastic pollution is currently one of the most intensely studied ecological issues. Numerous studies have estimated the distribution and concentration of microplastics in various environments and determine how they affect their inhabitants. Much less effort has been place on assessing the possible effects of microplastics on interactions between organisms, including interspecific competition. Our aim was to test the hypothesis that the presence of microplastics affects the proportion of individuals of coexisting species and the elimination rate of the inferior competitor. The hypothesis was tested in competitive experiments done in the absence and presence of spherical non-biodegradable polystyrene and polyethylene and biodegradable polyhydroxybutyrate in environmentally relevant densities. In each of the experiments, we used three different pairs of closely related planktonic species of the genus Daphnia composed of the superior and inferior competitor: D. pulex and D. magna, D. magna and D. galeata, D. pulex and D. galeata. The results support our hypothesis and demonstrate each microplastic type had a different effect on the density of the competing species. The presence of polystyrene and polyethylene lowered the density of the superior competitor in each of the three pairs, at least partially due to a reduction in the number of gravid females, but not their fecundity. The presence of the polyhydroxybutyrate, in turn, increased the population density of D. magna in the variants with each of the two remaining species. Moreover, the presence of microplastics affected the elimination rate of the inferior competitor, i.e. polystyrene expedited the exclusion of D. magna by D. pulex, and polyhydroxybutyrate hampered the exclusion of D. magna by D. pulex. Our results suggest that long-term exposure to environmentally relevant densities of both non-biodegradable and biodegradable microplastics may affect the relative abundance of co-occurring species in zooplankton communities, and thus the functioning of aquatic ecosystems.

Nano-ecotoxicology in a changing ocean

The ocean faces an era of change, driven in large by the release of anthropogenic CO2, and the unprecedented entry of pollutants into the water column. Nanomaterials, those particles < 100 nm, represent an emerging contaminant of environmental concern. Research on the ecotoxicology and fate of nanomaterials in the natural environment has increased substantially in recent years. However, commonly such research does not consider the wider environmental changes that are occurring in the ocean, i.e., ocean warming and acidification, and occurrence of co-contaminants. In this review, the current literature available on the combined impacts of nanomaterial exposure and (i) ocean warming, (ii) ocean acidification, (iii) co-contaminant stress, upon marine biota is explored. Here, it is identified that largely co-stressors influence nanomaterial ecotoxicity by altering their fate and behaviour in the water column, thus altering their bioavailability to marine organisms. By acting in this way, such stressors, are able to mitigate or elevate toxic effects of nanomaterials in a material-specific manner. However, current evidence is limited to a relatively small set of test materials and model organisms. Indeed, data is biased towards effects upon marine bivalve species. In future, expanding studies to involve other ecologically significant taxonomic groups, primarily marine phytoplankton will be highly beneficial. Although limited in number, the available evidence highlights the importance of considering co-occurring environmental changes in ecotoxicological research, as it is likely in the natural environment, the material of interest will not be the sole stressor encountered by biota. As such, research examining ecotoxicology alongside co-occurring environmental stressors is essential to effectively evaluating risk and develop effective long-term management strategies.

Seasonal variations in the abundance and distribution of microplastic particles in the surface waters of a Southern Indian Lake

Hazardous anthropogenic particles, such as microplastics (MPs) in the lake ecosystems, are a serious concern. In this work, we have investigated the seasonal occurrence and distribution of microplastics in the surface water samples of Lake Manipal in southwest India. The concentration of MPs was found to be higher during the monsoon season (0.423 particles/L) in comparison with the post-monsoon (0.117 particles/L) period. The higher abundance is attributed to the input of storm-water sewers connected to the lake as well as surface runoff during periods of high rainfall. The concentrations of small-sized (0.3-1 mm) microplastics were greater in both seasons. Approximately 96% of the microplastics were fibres, followed by smaller amounts of fragments, pellets, films, and foams. Polyethylene terephthalate (PET) was the principal polymer composition of the microplastics, followed by cellulose. The PET and cellulose fibres were mainly derived from the laundering of clothes in the residential colonies and hostels situated close to the lake. The storm-water sewers were the likely conduit for these PET fibres into the lake. The Pollution Load Index (PLI) data reveals that pollution due to microplastics in Lake Manipal falls within the Level I risk category. The PLI was higher during the monsoon season due to an increased flux of these particles from the nearby region. During the post-monsoon period, the PLI values decreased, suggesting that MPs in the water column may have settled and mixed with the sediments. The baseline data generated in this study is important as different types of birds, amphibians, and other microorganisms are present in the environment of Lake Manipal. We also propose certain policy measures that can be adopted by the regional population to mitigate microplastic pollution in the lake and its vicinity.

Conversion of Plastic Waste into Supports for Nanostructured Heterogeneous Catalysts: Application in Environmental Remediation

Plastics are ubiquitous in our society and are used in many industries, such as packaging, electronics, the automotive industry, and medical and health sectors, and plastic waste is among the types of waste of higher environmental concern. The increase in the amount of plastic waste produced daily has increased environmental problems, such as pollution by micro-plastics, contamination of the food chain, biodiversity degradation and economic losses. The selective and efficient conversion of plastic waste for applications in environmental remediation, such as by obtaining composites, is a strategy of the scientific community for the recovery of plastic waste. The development of polymeric supports for efficient, sustainable, and low-cost heterogeneous catalysts for the treatment of organic/inorganic contaminants is highly desirable yet still a great challenge; this will be the main focus of this work. Common commercial polymers, like polystyrene, polypropylene, polyethylene therephthalate, polyethylene and polyvinyl chloride, are addressed herein, as are their main physicochemical properties, such as molecular mass, degree of crystallinity and others. Additionally, we discuss the environmental and health risks of plastic debris and the main recycling technologies as well as their issues and environmental impact. The use of nanomaterials raises concerns about toxicity and reinforces the need to apply supports; this means that the recycling of plastics in this way may tackle two issues. Finally, we dissert about the advances in turning plastic waste into support for nanocatalysts for environmental remediation, mainly metal and metal oxide nanoparticles.