Recent progress on the toxic effects of microplastics on Chlorella sp. in aquatic environments

Microplastics enhance the denitrification of glycogen-accumulating organisms by regulating electronic transport in carbon-nitrogen coupling

The increasing presence of microplastics (MPs) in wastewater treatment systems profoundly impacts microbial metabolism and process performance. However, the effects of MPs on the denitrification process of glycogen-accumulating organisms (GAOs) remain unclear. Herein, various types and concentrations of MPs were introduced into the activate sludge of GAOs to assess their impact on denitrification processes and to investigate the underlying mechanisms. Our findings revealed that adding 100 μm PVC increased the denitrification efficiency of GAOs by 14.6 %, whereas adding 100 nm PVC decreased efficiency by 8.4 %. Additionally, 100 nm PVC inhibited polyhydroxybutyrate (PHB) degradation, while 100 μm PVC promoted it. Furthermore, 100 nm and 100 μm PVC differently influenced metabolic functions, including reactive oxygen species (ROS) levels, electron transport chain (ETC) activity, and intracellular nicotinamide adenine dinucleotide (NADH) content. Metatranscriptome analyses revealed differential expression of genes such as phaC, CS, nuoL, CYC1, and nisK, which are involved in carbon-nitrogen metabolism and oxidative phosphorylation. Consequently, 100 μm PVC enhanced the denitrification rate in GAOs by promoting PHB decomposition, increasing NADH electron-donating capacity, and ultimately enhancing the denitrification rate of GAOs. Our findings reveal a novel mechanism on regulating the carbon-nitrogen coupling in activated sludge under the different particle size of MPs.

Combined toxicity of microplastic fibers and dibutyl phthalate on algae: Synergistic or antagonistic?

Plastics, combined with plasticizers, have been widely utilized worldwide. Microplastic fibers (MPFs) and dibutyl phthalate (DBP) account for the most predominant microplastics and plasticizers detected in freshwater ecosystem, with their joint toxicity being limited studied. In this study, we employed freshwater algae (Chlorella vulgaris) as toxicity test model organism to assess their growth, photosynthesis, metabolism, and oxidative response when exposing to different concentrations of polypropylene MPFs and the co-exposure of DBP. In addition, the toxic interaction between MPFs and DBP was assessed by combining the integrated toxicity value (Integrated Biomarker Response version 2, IBRv2) and the mixture toxicity index (Effect Addition Index, EAI). Our results demonstrated significant toxic effects of MPFs and DBP on C. vulgaris, and highlighted their dynamic interactions with C. vulgaris. Specifically, when combining with DBP, MPFs with high concentrations exhibited significantly increase in algae growth inhibition, photosynthetic pigment contents (Chl-a, Chl-b, and carotenoids), protein contents, and oxidative enzymes (SOD, CAT, and MDA). In terms of integrated toxicity values, higher IBRv2 values were recorded by the combined exposure of MPFs and DBP in contrast with the sole exposure groups, indicating that the combined exposure caused more severe damage to photosynthesis, oxidation and metabolism. In addition, our study recorded synergistic combined toxicity when MPFs were in high concentrations, whereas antagonistic combined toxicity when MPFs were in low concentrations. Our study highlights the MPFs concentration-dependent combined toxicity (synergistic or antagonistic) when exposing to microplastics and plasticizers in freshwater ecosystems.

Investigating the sorption of Zinc-Oxide nanoparticles on Tire-wear particles and their toxic effects on Chlorella vulgaris: Insights from toxicological models and physiological analysis

This study investigated the interaction of Tire-wear particles (TWPs) with Zinc-Oxide nanoparticles (ZNPs) and studied their individual and combined toxic effects on Chlorella vulgaris in the co-presence of Humics. Physiological parameters, including growth, photosynthetic pigments, oxidative stress, and membrane damage, were analysed using Flow cytometry. Adsorption experiments exhibited that ZNPs were significantly absorbed by TWPs (qmax= 312.49 mg/g). A positive dose-response relation concerning inhibition in growth was observed in all treatment groups, and it was associated with reduced chlorophyll levels and damaged cell membranes. A negative impact of increased concentrations of TWPs and ZNPs was observed on anti-oxidant enzymes CAT and SOD; however, the impact was more severe when combined with exposure to both contaminants. Elevated concentrations of ZNPs and TWPs led to increased ROS production, lipid peroxidation and membrane damage, which could be contributing to the observed inhibition in growth. In the combined exposure groups, the Independent Action and the Abbott toxicity models revealed a synergistic effect on growth rates, which agreed with the Integrated Biomarker model results. The current study could enhance our understanding of the interaction between TWPs and metal nanoparticles in aquatic systems and offer novel understandings of the mechanisms underlying their combined toxic effects on microalgae.

Removal of microplastics by algal biomass from aqueous solutions: performance, optimization, and modeling

Microplastics (MPs) are emerging pollutants that pose significant risks to ecosystems due to their inherent toxicity, capacity to accumulate various pollutants, and potential for synergistic impacts. Given these concerns, the focus of this research is on the critical need for effective MPs removal from aquatic environments. Using BBD method, this study aimed to identify the key parameters affecting the removal of MPs by algal biomass from aqueous solutions. The investigation specifically analyzed the effects of varying initial PS concentrations (100 to 900 mg/L), pH values (4 to 10), reaction durations (20 to 40 min), and C. vulgaris dosages (50 to 400 mg/L). Data analysis indicated that QM best described the experimental findings, leading to the identification of optimal conditions for PS removal: a pH of 7.5, a reaction time of 31.90 min, a C. vulgaris dosage of 274.05 mg/L, and a PS level of 789.37 mg/L. Under these conditions, the study achieved a maximum removal efficiency of 73.01% for PS. These outcomes demonstrate the significant potential of C. vulgaris in efficiently removing PS from water. Furthermore, using algae as a green, eco-friendly alternative to conventional chemical coagulants offers a practical and sustainable approach to addressing MPs pollution in our water systems.

Micro-nano bubbles enhanced immobilized Chlorella vulgaris to remove ofloxacin from groundwater

The phenomenon of antibiotic pollution has emerged as a significant global environmental concern. However, there is a lack of technical research on the effective removal of antibiotics based on the characteristics of the groundwater environment. This paper used micro-nano bubbles (MNBs) enhanced immobilized Chlorella technology to remove ofloxacin (OFLX) from groundwater. The study discussed the impact of initial antibiotic concentration (5-30 mg/mL), algae concentration (0.25-4 bead/mL), aeration time (5-30 min), and coexisting ions on the antibiotic removal rate and analyzed the removal mechanism by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The results showed that MNBs increased Chlorella vulgaris biomass by 2.48 times and significantly improved OFLX removal efficiency. The removal rate of OFLX exhibited a significant positive correlation with the algal concentration and coexisting ions and a significant negative correlation with the aeration time and the initial concentration of antibiotics. Enhanced immobilization of Chlorella vulgaris by MNBs for OFLX removal may involve -NH, -OH, -C=O, -CH2, and -C-O-C groups. Degradation (including biodegradation and non-biodegradation) is the primary mechanism of antibiotic removal. Overall, intensive immobilization of Chlorella by MNBs promises to be a technically feasible method for removing antibiotics from groundwater.

Microplastic pollution along the coastal island shorelines of Bangladesh: Distribution, patterns, and abundance

Microplastics (MPs), less than 5 mm in length, have become a major environmental issue due to their hazardous physical and chemical properties. The research investigated 54 sediment samples collected from three different zones of the beaches, namely the wrack line, beach face, and swash zone. This study aims to enumerate the number and polymeric variety of microplastics found in beach sediments from coastal islands of Bangladesh, including Sandwip, Kutubdia, and Saint Martin's Island in the northeastern Bay of Bengal. NaCl solution with the density of 1.2 g/cm3 was used as a density-separating solvent. Microplastics were extracted using conventional protocols, yielding an average of 193 ± 68.9, 175.5 ± 63.1, and 266.3 ± 232 particles per kg from the collected samples of Sandwip, Kutubdia, and Saint Martin's Island respectively, with five morphotypes: fiber, film, fragment, foam, and pellet, where fiber dominated each island. White microplastics were most spread in both Sandwip and Saint Martin's Island, whereas translucent and blue were most abundant in Kutubdia. Moreover, polypropylene (PP) was shown to be the greatest number of polymer groups among those analyzed microplastic particles using ATR-FTIR (Attenuated total reflectance-Fourier transform infrared) spectrometer. Using scanning electron microscopy (SEM), it was also possible to detect surface degradation, rupture, or fracture that was probably caused by the environment. The study emphasizes the critical need for continued research and monitoring to better understand the dynamics of microplastic pollution and its long-term impacts. By tackling the underlying causes and implementing effective management practices, we can achieve a cleaner and more sustainable future for coastal communities and marine ecosystems.

Fabric structure and polymer composition as key contributors to micro(nano)plastic contamination in face masks

The surge in face mask use due to COVID-19 has raised concerns about micro(nano)plastics (MNPs) from masks. Herein, focusing on fabric structure and polymer composition, we investigated MNP generation characteristics, mechanisms, and potential risks of surgical polypropylene (PP) and fashionable polyurethane (PU) masks during their wearing and photoaging based on stereomicroscope, μ-Fourier transform infrared spectroscopy (μ-FTIR), and scanning electron microscope (SEM) techniques. Compared with new PP and PU masks (66 ± 16 MPs/PP-mask, 163 ± 83 MPs/PU-mask), single- and multiple-used masks exhibited remarkably increased MP type and abundance (600-1867 MPs/PP-mask, 607-2167 MPs/PU-mask). Disinfection exacerbated endogenous MP generation in masks, with washing (416 MPs/PP-mask, 30,708 MPs/PU-mask) being the most prominent compared to autoclaving (219 MPs/PP-mask, 553 MPs/PU-mask) and alcohol spray (162 MPs/PP-mask, 18,333 MPs/PU-mask). Photoaging led to massive generation of MPs (8.8 × 104-3.7 × 105 MPs/PP-layer, 1.0 × 105 MPs/PU-layer) and NPs (5.2 × 109-3.6 × 1013 NPs/PP-layer, 3.5 × 1012 NPs/PU-layer) from masks, presenting highly fabric structure-dependent aging modes as "fragmentation" for fine fiber-structure PP mask and "erosion" for 3D mesh-structure PU mask. The MNPs derived from PP/PU mask caused significant deformities of Zebrafish (Danio rerio) larvae. These findings underscore the potential adverse effects of masks on humans and aquatic organisms, advocating to enhance proper use and rational disposal for masks.