Enhanced microalgal toxicity due to polystyrene nanoplastics and cadmium co-exposure: From the perspective of physiological and metabolomic profiles.

As important emerging contaminants, nanoplastics can act as vectors for other environmental pollutants, resulting in their migration throughout ecosystems and altering their toxicity. In this study, the fluorescent dye label aggravated the toxicity of polystyrene (PS) nanoplastics (100 nm diameter particles) to microalgae Euglena gracilis. Therefore, the toxicity of non-fluorescent labelled PS alone and in combination with divalent cadmium (Cd2+) on Euglena gracilis in the environmentally relevant concentrations was investigated. Results revealed that co-exposure to 50 µg/L (1.1 × 1010 particles/L) PS and 50 µg/L Cd2+ resulted in synergistic effects, significantly inhibiting microalgal growth by 28.76%. Superoxide dismutase, peroxidase and extracellular polymeric substances were distinctly enhanced in co-exposure treatments compared to the control, indicating that cellular antioxidant defense responses were activated. LC-MS-based metabolomic analysis suggested that PS and Cd2+ exposure alone or in combination induced significant disruption to carbohydrate and purine metabolism-related pathways, as compared to controls. As part of the PS and Cd2+ stress response, differential metabolites involved in lipid metabolism and amino acid metabolism provide antioxidants and cell membrane protective molecules. Overall, this combined physiological and metabolomic analysis approach provides a better understanding of the potential risks posed by nanoplastics and heavy metal pollution in aquatic ecosystems.

Exposure of microalgae Euglena gracilis to polystyrene microbeads and cadmium: Perspective from the physiological and transcriptional responses.

Micro(nano)plastics (MPs/NPs) are already present as contaminants in the natural environment globally and have been shown to be difficult to degrade, resulting in the potential for ecological damage and public health concerns. However, the adverse effects of exposure to MPs/NPs by aquatic organisms, especially freshwater microalgae, remains unclear. In the present study, the growth, physiology and transcriptome of the freshwater microalgae Euglena gracilis were comprehensively analyzed following exposure to 1 mg/L of polystyrene (PS) microbeads (5 µm PS-MPs and 100 nm PS-NPs), 0.5 mg/L cadmium (Cd), or a mixture of PS microbeads and Cd for 96 h. Results showed that the toxicity of PS-MPs to microalgae was greater than PS-NPs, inducing increased growth inhibition, oxidative damage and decreased photosynthesis pigment concentrations. PS-MPs alone or in combination with Cd caused cavitation within microalgal cells, as well as increasing the number and volume of vacuoles. The combined exposure toxicity test showed that a combination of Cd + PS-NPs was more toxic than Cd + PS-MPs, which may be explained by the transcriptomic analysis results. Differentially expressed genes (DEGs) in the Cd + PS-NPs group were mainly enriched in metabolism-related pathways, suggesting that algal metabolism was hindered, resulting in aggravation of toxicity. The reduced toxicity induced by Cd + PS-MPs may indicate a response to resist external stress processes. In addition, no adsorption of 0.5 mg/L Cd to 1 mg/L PS microbeads was observed, suggesting that adsorption of MPs/NPs and Cd was not the key factor determining the combined toxicity effects in this study.

Adverse physiological and molecular level effects of polystyrene microplastics on freshwater microalgae.

Microplastics have aroused widespread concern because of their adverse effects on aquatic organisms. However, the underlying toxicity mechanisms have not been examined in detail. This study investigated the interactions between polystyrene microplastics (PS-MPs) and the model freshwater microalgae Euglena gracilis. The results of transmission electron microscopy showed that the vacuoles of microalgae were induced after 24 h exposure to 1 mg/L PS-MPs (5 µm and 0.1 µm). Furthermore, PS-MPs significantly (p < 0.05) reduced pigment contents. Moreover, superoxide dismutase activities were significantly (p < 0.05) induced in all PS-MPs treated groups. Peroxidase activities were also significantly (p < 0.05) affected by two sizes of PS-MPs (5 µm and 0.1 µm), indicating that oxidative stress was induced after exposure to PS-MPs. At the molecular level, PS-MPs dysregulated the expression of genes involved in cellular processes, genetic information processing, organismal systems, and metabolisms. The KCS gene and the CTR1 gene may be key pathways to induce adverse effects on the E. gracilis after exposure to 5 µm PS-MPs. These findings will help to elucidate the underlying molecular mechanism of microplastics toxicity on freshwater organisms.

Ecotoxicity and genotoxicity of polystyrene microplastics on higher plant Vicia faba.

Nano- and microplastics have been widely spread in environmental matrices, especially in marine and terrestrial systems. In this study, higher plant Vicia faba root tips were exposed to 5 µm and 100 nm with 10, 50 and 100 mg/L polystyrene fluorescent microplastics (PS-MPs) for 48 h. Root length, weight, oxidative stress and genotoxicity of V. faba were assessed to investigate toxic effects of PS-MPs. The results showed that the biomass and catalase (CAT) enzymes activity of V. faba roots decreased under 5 µm PS-MPs whereas superoxide dismutase (SOD) and peroxidase (POD) enzymes activity significantly increased. Under the 100 nm PS-MPs exposure a significant decrease of growth was observed only at the highest concentration (100 mg/L). However, micronucleus (MN) test and antioxidative enzymes activities showed that 100 nm PS-MPs induce higher genotoxic and oxidative damage to V. faba than 5 µm PS-MPs. Furthermore, the laser confocal scanning microscopy (LCSM) demonstrated that 100 nm PS-MPs can accumulate in V. faba root and most probably block cell connections or cell wall pores for transport of nutrients. These findings provide a new insight into the toxic effects of microplastics on V. faba, and further apply to the ecological risk assessment of microplastics on higher plants.

[Effects of Microplastics on the Growth, Physiology, and Biochemical Characteristics of Wheat (Triticum aestivum)].

The toxicological effects of microplastics in the soil environment have gradually attracted widespread attention, while less is known about the influence of microplastics on plants. The growth of wheat, photosynthetic pigment content, soluble protein content, and the antioxidant enzyme activities of leaves were investigated to explore the toxic effects of microplastics on wheat (Triticum aestivum). In this study, 100 nm and 5 µm polystyrene microplastics (PS-MPs) were used for soil culture treatment combined with hydroponic growth. The results showed that in hydroponic experiment, high concentrations (200 mg·L-1) of PS-MPs significantly inhibited the elongation of wheat roots and stems, and 5 µm PS-MPs showed a greater toxicity effect than 100 nm PS-MPs. Roots and stem length inhibition rates were 67.15% and 56.45%, respectively. In the soil culture tests, 10 mg·kg-1 PS-MPs had the most significant effect on wheat growth. Within the test content range (0-100 mg·kg-1), with an increase in PS-MPs exposure, the content of photosynthetic pigment and soluble protein in wheat leaves increased first and then decreased. This indicated that PS-MPs damaged the photosynthetic pathway of wheat leaves and inhibited protein synthesis. SOD activity decreased, and CAT decreased first and then increased, indicating that the possible mechanism of toxicity to wheat involves oxidative stress. The results provide a basis for the ecological risk assessment of microplastics in the soil environment.