Can plastics affect near surface layer ocean processes and climate?

Microplastics and climate change: the global impacts of a tiny driver

Microplastic pollution and climate change, the two seemingly distinct phenomena of global concern, are interconnected through various pathways. The connecting links between the two include the biological carbon pumps in the oceans, the sea ice, the plastisphere involved in biogeochemical cycling and the direct emissions of greenhouse gases from microplastics. On one hand, the presence of microplastics in the water column disrupts the balance of the natural carbon sequestration by affecting the key players in the pumping of carbon, such as the phytoplankton and zooplankton. On the other hand, the effect of microplastics on the sea ice in Polar Regions is two-way, as the ice caps are transformed into sinks and sources of microplastics and at the same time, the microplastics can enhance the melting of ice by reducing the albedo. Microplastics may have more potential than larger plastic fragments to release greenhouse gases (GHGs). Microbe-mediated emission of GHGs from soils is also now altered by the microplastics present in the soil. Plastisphere, the emerging microbiome in aquatic environments, can also contribute to climate change as it hosts complex networks of microbes, many of which are involved in greenhouse gas production. To combat a global stressor like climate change, it needs to be addressed with a holistic approach and this begins with tracing the various stressors like microplastic pollution that can aggravate the impacts of climate change.

Enhancing aggregation of microalgae on polystyrene microplastics by high light: Processes, drivers, and environmental risk assessment

Microplastics (MPs) are emerging pollutants, causing potential threats to aquatic ecosystems and serious concern in aggregating with microalgae (critical primary producers). When entering water bodies, MPs are expected to sink below the water surface and disperse into varying water compartments with different light intensities. However, how light influences the aggregation processes of algal cells onto MPs and the associated molecular coupling mechanisms and derivative risks remain poorly understood. Herein, we investigated the aggregation behavior between polystyrene microplastics (mPS, 10 µm) and Chlorella pyrenoidosa under low (LL, 15 μmol·m-2·s-1), normal (NL, 55 μmol·m-2·s-1), and high light (HL, 150 μmol·m-2·s-1) conditions from integrated in vivo and in silico assays. The results indicated that under LL, the mPS particles primarily existed independently, whereas under NL and HL, C. pyrenoidosa tightly bounded to mPS by secreting more protein-rich extracellular polymeric substances. Infrared spectroscopy analysis and density functional theory calculation revealed that the aggregation formation was driven by non-covalent interaction involving van der Waals force and hydrogen bond. These processes subsequently enhanced the deposition and adherence capacity of mPS and relieved its phytotoxicity. Overall, our findings advance the practical and theoretical understanding of the ecological impacts of MPs in complex aquatic environments.

Persistence of algal toxicity induced by polystyrene nanoplastics at environmentally relevant concentrations

Polystyrene (PS) often found in the ocean is one of the most commonly used plastic polymers in the world and can exist in different particle sizes. In particular, PS degrades relatively faster and widely accumulates at the nanoscale. Therefore, the penetration is strong and it is easy to enter the body and cause adverse effects. However, the persistence or recovery of their toxicity remains largely unclear. Here, we designed two subexperiments (exposure and recovery experiments) and investigated the persistence of the toxicity of polystyrene (PS) NPs at a wide concentration range (0.01-10 mg/L) to diatoms (Phaeodactylum tricornutum). PS-NPs significantly inhibited algal growth and clearly wrinkled the surfaces of cells, membrane permeability was significantly increased, and the steady-state state of cell redox and mitochondrial membrane potential was disturbed. However, in the recovery experiment, the increased membrane permeability was observed to persist, but the induced oxidative damage was reversible, and the absorbed NPs could be excreted. Integrated omics techniques (metabolomics and transcriptomics) revealed that PS-NPs significantly disrupts cell metabolism, including disturbances in fatty acid biosynthesis and enhanced biosynthesis of phenylalanine, tyrosine, and tryptophan. Inhibition of fatty acid, amino acid, energy and carbohydrate metabolism and disturbance of the antioxidant system contribute to the persistence of toxicity. These findings highlight the phenomena and mechanisms of the persistence of phytotoxicity and are critical to the accurate assessment of NPs.

Toxicity interaction of polystyrene nanoplastics with sulfamethoxazole on the microalgae Chlamydomonas reinhardtii: A closer look at effect of light availability

The coexistence of nanoplastics and antibiotics in the aquatic environment has raised a complicated risk for ecosystems and human health. How the environmental factors e.g., light, regulate the interaction between nanoplastics and antibiotics and the resulting combined toxicity is poorly understood. Here, we investigated the individual and combined toxicity of polystyrene nanoplastics (nPS, 100 mg L¹) and sulfamethoxazole (SMX, 2.5 and 10 mg L^-1) toward the microalgae Chlamydomonas reinhardtii under low (LL, 16 μmol m^-2·s^-1), normal (NL, 40 μmol m^-2·s^-1), and high light (HL, 150 μmol m^-2·s^-1) in terms of cellular responses. Results indicated that the joint toxicity of nPS and SMX commonly exhibited a strong antagonistic/mitigative effect under LL/NL at 24 h, and under NL at 72 h. nPS could adsorb more SMX under LL/NL at 24 h (1.90/1.33 mg g^-1) and under NL at 72 h (1.01 mg g^-1), thereby alleviating SMX toxicity to C. reinhardtii. However, the self-toxicity of nPS had a negative influence on the degree of antagonism between nPS and SMX. The experimental results coupled with computational chemistry further revealed that the adsorption capacity of SMX on nPS was stimulated by low pH under LL/NL at 24 h (∼7.5), while by less co-existing saline ions (0.83 ppt) and algae-derived dissolved organic matter (9.04 mg L^-1) under NL at 72 h. nPS toxicity that was responsible for the toxic action modes was mainly attributed to the shading effect induced by hetero-aggregation and hindrance of light transmittance (>60%), as well as being regulated by additives leaching (0.49-1.07 mg L^-1) and oxidative stress. Overall, these findings provided a critical basis for the risk assessment and management of multiple pollutants in the complex natural environment.

Habitual feeding patterns impact polystyrene microplastic abundance and potential toxicity in edible benthic mollusks

That increasing microplastics (MPs, <5 mm) eventually end up in the sediment which may become a growing menace to diverse benthic lives is worthy of attention. In this experiment, three edible mollusks including one deposit-feeding gastropod (Bullacta exarate) and two filter-feeding bivalves (Cyclina sinensis and Mactra veneriformis) were exposed to polystyrene microplastic (PS-MP) for 7 days and depurated for 3 days. PS-MP numbers in the digestive system and non-digestive system, digestive enzymes, oxidative stress indexes, and a neurotoxicity index of three mollusks were determined at day 0, 3, 7, 8 and 10. After seven-day exposure, the PS-MP were found in all three mollusks' digestive and non-digestive systems. And PS-MP in M. veneriformis (9.57 ± 2.19 items/individual) was significantly higher than those in C. sinensis (3.00 ± 2.16 items/individual) and B. exarate (0.83 ± 1.07 items/individual) at day 7. Three-day depuration could remove most of the PS-MP in the mollusks, and higher PS-MP clearance rates were found in filter-feeding C. sinensis (77.78 %) and M. veneriformis (82.59 %) compared to surface deposit-feeding B. exarate (50.00 %). The digestive enzymes of B. exarate significantly reacted to PS-MP exposure, while oxidative responses were found in C. sinensis. After three-day depuration, the changes of digestive enzymes and the oxidative states were fixed, but neurotoxicity induced by PS-MP was not recoverable. Besides, it is noteworthy that changes of digestive enzymes and acetylcholinesterase are related to feeding patterns.

On the emergence of a health-pollutant-climate nexus in the wake of a global pandemic

COVID-19 has wreaked havoc throughout the planet within a short time frame, inducing substantial morbidity and mortality in the global population. The primary procedures commonly used to manage the pandemic can produce various environmental pollutants, primarily contaminants of emerging concern such as plastics, chemical disinfectants, and pharmaceutical waste. There is a huge influx of various environmental pollutants due to the pandemic effect. We, therefore, introduce the term "envirodemics" depicting the exacerbated surge in the amount of pandemic-induced pollutants. The general toxicity pattern of common chemical ingredients in widely used disinfectants shows negative impacts on the environment. We have identified some of the significant imprints of the pandemic on localizing the Sustainable Development Goals-environment interaction and their implications on achieving the goals in terms of environmental benefits. Climate change impacts are now widespread and have a profound effect on pollutant fluxes and distribution. The climate change signatures will impact the pandemic-induced enhanced fluxes of pollutants in the global waters, such as their transport and transformation. In this study, possible interactions and emerging pathways involving an emerging climate-health-pollutant nexus are discussed. The nexus is further elaborated by considering plastic as an example of an emerging pollutant that is produced in huge quantities as a by-product of COVID management and disaster risk reduction. Additionally, regulatory implications and future perspectives concerning the unleashed nexus are also discussed. We hope that this communication shall call for incisive investigations in the less explored realm concerning the health-pollutant-climate nexus.

Marine litter and climate change: Inextricably connected threats to the world's oceans

The global issues of climate change and marine litter are interlinked and understanding these connections is key to managing their combined risks to marine biodiversity and ultimately society. For example, fossil fuel-based plastics cause direct emissions of greenhouse gases and therefore are an important contributing factor to climate change, while other impacts of plastics can manifest as alterations in key species and habitats in coastal and marine environments. Marine litter is acknowledged as a threat multiplier that acts with other stressors such as climate change to cause far greater damage than if they occurred in isolation. On the other hand, while climate change can lead to increased inputs of litter into the marine environment, the presence of marine litter can also undermine the climate resilience of marine ecosystems. There is increasing evidence that that climate change and marine litter are inextricably linked, although these interactions and the resulting effects vary widely across oceanic regions and depend on the particular characteristics of specific marine environments. Ecosystem resilience approaches, that integrate climate change with other local stressors, offer a suitable framework to incorporate the consideration of marine litter where that is deemed to be a risk, and to steer, coordinate and prioritise research and monitoring, as well as management, policy, planning and action to effectively tackle the combined risks and impacts from climate change and marine litter.

Light availability modulates the responses of the microalgae Desmodesmus sp. to micron-sized polyvinyl chloride microplastics

The vertical movement of large-size and high-density MPs in the water column is usually along with dynamic changes in light intensity. However, whether the change in light availability affects the bioeffects of MPs on surrounding microalgae is currently unknown. This study investigated the effects of micron-sized polyvinyl chloride (mPVC, 143.5 μm) microplastics, alone and in combination with light intensity (from 7.5 to 162.5 μmol·m^-2·s^-1) on the growth and physiology of Desmodesmus sp. Although mPVC did not impact microalgal growth under optimal light (40 and 93.8 μmol·m^-2·s^-1), it could induce a no-contact shading effect, thereby significantly affecting the physiology of Desmodesmus sp. The growth of Desmodesmus sp. exposed to mPVC was enhanced under a high light intensity of 162.5 μmol·m^-2·s^-1 which can induce growth inhibition but was retarded when under a light inadequacy condition (20 μmol·m^-2·s^-1), along with a dose-dependent effect. Significantly, the photosynthesis of Desmodesmus sp. was a highly sensitive metabolic pathway to mPVC stress and largely influenced by the plastic particles under different light conditions. Additionally, mPVC modulated the energy metabolism strategy of Desmodesmus sp., depending on exposure dose and external light availability. Our findings provided a critical basis for the risk assessment of MPs in fluctuating light conditions.

Impact of climatic and non-climatic stressors on ocean life and human health: A review

Ocean life forms are fundamentally well adapted to natural environmental variations, and they can even tolerate extreme conditions for a short time. However, several anthropogenic stressors are causing such drastic changes in the ocean ecosystem. First, the review attempts to outline the impact of climatic and non-climatic stressors on ocean life, and it also outlines the synergistic impact of both stressors. Then the impact on human health caused by the damage of the marine ecosystem has been discussed. Furthermore, the type of prior studies and current mitigation adaptation programs have been presented. Finally, some perspectives about future research and mitigation adaptation are offered.

A microwave-based technique as a feasible method to detect plastic pollutants in experimental samples

Plastic-derived pollutants are hazardous and pervasive in the environment, and their detection is a challenge due to observational constraints of various dimensions. Physical, chemical, thermal, and spectroscopic methods are extensively used to identify microplastics in environmental systems, but fundamental challenges exist in the isolation and analysis of nanoplastics from environmental samples. The promising practices are often destructive, rendering the samples inutile for further investigations. In this paper, a technique based on the measurement of the dielectric properties of the samples, carried out using the rectangular cavity perturbation technique at the S-band of microwave frequency of 2-4 GHz is proposed. The ability of this method to identify some of the most abundant types of plastics found in the environment, polypropylene, low-density polyethylene, high-density polyethylene, and cross-linked polyethylene, is demonstrated. Electrical characteristics at microwave frequencies such as absorption factor, dielectric constant, and dielectric loss tangent are found useful in the identification of various polymers in the samples. Further, this method can be applied to identify other environmentally stable performance and engineering polymers, which are not often investigated in the environmental matrices for their hazardous effects. This non-destructive measurement method is quick and straightforward and can be further developed to identify a wide range of plastic materials present in various environmental compartments.

Litter and plastic monitoring in the Indian marine environment: A review of current research, policies, waste management, and a roadmap for multidisciplinary action

Environmental contamination due to plastic waste mismanagement is a growing global concern. Plastic problem is of particular concern to the Indian Ocean nations as Asia currently contributes to the highest share of mismanaged plastic waste. Consequently, there is a worldwide interest to understand the distribution and transboundary movement of plastic from this region, which is crucial for implementing management measures. This review article focuses on current knowledge of plastic research, policies, waste management, socio-economics, challenges, and research opportunities. To date, marine plastic studies have focused on a few locations, providing an analysis of distribution and plastic-organism interactions in the Indian marine system. Along with scientific investigation, enforcement, improvisation, and, if necessary, framing new policies, integrated technologies to manage plastic waste, and behavioural changes are essential to mitigate plastic pollution. Such measures will be effective through a combination of actions among national and international researchers, industries, environmental managers, and the public.

Impacts of Plastic Pollution on Ecosystem Services, Sustainable Development Goals, and Need to Focus on Circular Economy and Policy Interventions

Plastic pollution is ubiquitous in terrestrial and aquatic ecosystems. Plastic waste exposed to the environment creates problems and is of significant concern for all life forms. Plastic production and accumulation in the natural environment are occurring at an unprecedented rate due to indiscriminate use, inadequate recycling, and deposits in landfills. In 2019, the global production of plastic was at 370 million tons, with only 9% of it being recycled, 12% being incinerated, and the remaining left in the environment or landfills. The leakage of plastic wastes into terrestrial and aquatic ecosystems is occurring at an unprecedented rate. The management of plastic waste is a challenging problem for researchers, policymakers, citizens, and other stakeholders. Therefore, here, we summarize the current understanding and concerns of plastics pollution (microplastics or nanoplastics) on natural ecosystems. The overall goal of this review is to provide background assessment on the adverse effects of plastic pollution on natural ecosystems; interlink the management of plastic pollution with sustainable development goals; address the policy initiatives under transdisciplinary approaches through life cycle assessment, circular economy, and sustainability; identify the knowledge gaps; and provide current policy recommendations. Plastic waste management through community involvement and socio-economic inputs in different countries are presented and discussed. Plastic ban policies and public awareness are likely the major mitigation interventions. The need for life cycle assessment and circularity to assess the potential environmental impacts and resources used throughout a plastic product’s life span is emphasized. Innovations are needed to reduce, reuse, recycle, and recover plastics and find eco-friendly replacements for plastics. Empowering and educating communities and citizens to act collectively to minimize plastic pollution and use alternative options for plastics must be promoted and enforced. Plastic pollution is a global concern that must be addressed collectively with the utmost priority.

An examination of the occurrence and potential risks of microplastics across various shellfish

The ingestion of microplastics by shellfish pose a potential health risk for human via seafood consumption. This study investigated and compared the contamination levels and potential human health risks of microplastics in the digestive system of commercial shellfish from North (Qingdao) and South (Xiamen) China. Microplastics were detected in 70%-100% of shellfish samples from Qingdao and 70%-90% of shellfish samples from Xiamen, with abundances ranging from 1.2 to 4.1 items/individual (or 0.8-4.4 items/g, wet weight of digestive system) in shellfish from Qingdao and 1.3-6.0 items/individual (or 2.1-4.0 items/g) in shellfish from Xiamen. The microplastic composition was dominated by rayon and tended to be fibrous in shape, and white, black, and transparent in color. Microplastics <500 μm were the dominant size range, in which the size range of 100-200 μm was the most abundant size. Features of microplastics in the water-dwelling shellfish were different from those of the sediment-dwelling shellfish, and the microplastic features in the shellfish correlated with the sampling region, shellfish length, total wet body weight, and wet weight of the digestive system. Risk assessment results revealed that the potential human health risk posed by microplastics from the digestive system of commercial shellfish was higher in Qingdao than Xiamen.