Microplastics with different functional groups modulate cellular and molecular mechanisms of reduced graphene oxide toxicity on the green microalga, Scenedesmus obliquus.

Even though microplastics (MPs) and graphene nanomaterials (GNMs) have demonstrated individual toxicity towards aquatic organisms, the knowledge gap lies in the lack of understanding regarding their combined toxicity. The difference between the combined toxicity of MPs and GNMs, in contrast to their individual toxicities, and furthermore, the elucidation of the mechanism of this combined toxicity are scientific questions that remain to be addressed. In this study, we examined the individual and combined toxicity of three polystyrene microplastics (MPs) with different functional groups-unmodified, carboxyl-modified (COOH-), and amino-modified (NH2-) MPs-in combination with reduced graphene oxide (RGO) on the freshwater microalga Scenedesmus obliquus. More importantly, we explored the cellular and molecular mechanisms responsible for the observed toxicity. The results indicated that the growth inhibition toxicity of RGO, either alone or in combination with the three MPs, against S. obliquus increased gradually with higher particle concentrations. The mitigating effect of MPs-NH2 on RGO-induced toxicity was most significant at a higher concentration, surpassing the effect of unmodified MPs. However, the MPs-COOH did not exhibit a substantial impact on the toxicity of RGO. Unmodified MPs and MPs-COOH aggravated the inhibition effects of RGO on the cell membrane integrity and oxidative stress-related biomarkers. Additionally, MPs-COOH exhibited a stronger inhibition effect on RGO-induced biomarkers compared to unmodified MPs. In contrast, the MPs-NH2 alleviated the inhibition effect of RGO on the biomarkers. Furthermore, the presence of differently functionalized MPs did not significantly affect RGO-induced oxidative stress and photosynthesis-related gene expression in S. obliquus, indicating a limited ability to modulate RGO genotoxicity at the molecular level. These findings can offer a more accurate understanding of the combined risks posed by these micro- and nano-materials and assist in designing more effective mitigation strategies.

Molecular mechanism for combined toxicity of micro(nano)plastics and carbon nanofibers to freshwater microalgae Chlorella pyrenoidosa.

The understanding of the environmental consequences resulting from the presence of micro(nano)plastics and carbon nanofibers (CNFs) in aquatic ecosystems is currently limited. This research endeavor sought to investigate the underlying molecular mechanisms by which engineered polystyrene-based microplastics (MPs)/nanoplastics (NPs) and CNFs, both individually and in combination, elicit toxic effects on an algal species Chlorella pyrenoidosa. The findings revealed that the combined toxicity of MPs/NPs and CNFs depended on the concentration of the mixture. As the concentration increased, the combined toxicity of MPs/NPs and CNFs was significantly greater than the toxicity of each component on its own. Furthermore, the combined toxicity of NPs and CNFs was higher than that of MPs and CNFs. The study integrated data on cell membrane integrity, oxidative stress, and antioxidant modulation to create an Integrated Biomarker Response index, which demonstrated that the co-exposure of algae to NPs and CNFs resulted in more severe cellular stress compared to exposure to NPs alone. Similarly, the combination of NPs and CNFs caused greater cellular stress than the combination of MPs and CNFs. Additionally, significant changes in the expression of stress-related genes caused by MPs/NPs alone and in combination with CNFs indicated that oxidative stress response, glucose metabolism, and energy metabolism played critical roles in particle-induced toxicity. Overall, this study provides the first insight into the toxicological mechanism of MPs/NPs and CNFs mixtures at the molecular level in freshwater microalgae.

Individual and binary exposure of embryonic zebrafish (Danio rerio) to single-walled and multi-walled carbon nanotubes in the absence and presence of dissolved organic matter.

The available toxicological information was inadequate to assess the potential ecological risk of a mixture of different nanostructured carbon nanotubes (CNTs) to aquatic organisms, especially for the co-existence of mixed CNTs with dissolved organic matter (DOM). Herein, we investigated individual and binary exposure of zebrafish (Danio rerio) embryos to single-walled (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) in the absence and presence of DOM. Results indicated that embryonic chorions were more resistant to mixed-type CNTs than to single-type CNTs, yet the addition of DOM decreased this resistance. The mixed-type CNTs increased the antioxidant capacity of zebrafish embryos by increasing superoxide dismutase activity in comparison to the single-type CNTs. Furthermore, the mixed-type CNTs caused oxidative damage to the zebrafish embryos, characterized by an increase in malondialdehyde level. Nevertheless, the activation of the antioxidant defense system was modulated by the presence of DOM. Transcriptome sequencing analysis showed that the number of unique genes (UGs) and differentially expressed genes (DEGs) between the mixed-type CNTs and control groups was significantly enhanced compared to the single-type CNTs. DOM increased the number of UGs and up-regulated DEGs, but decreased the number of down-regulated DEGs. GO classification analysis revealed that the mixed-type CNTs mainly altered the cellular component process of single-type CNTs to induce joint effects. DOM generally enhanced the GO enrichment of DEGs in D. rerio embryos exposed to the mixed-type CNTs during the biological process. KEGG pathway enrichment analysis for the mixed-type CNTs showed enrichment of DEGs encoding ether lipid metabolism, glycerophospholipid metabolism, glycerolipid metabolism, citrate cycle, and biosynthesis of nucleotide sugars. However, DOM allowed more specific KEGG pathways towards the mixed-type CNTs to be identified. Despite the mixed-type CNTs exhibiting differential expression of functional genes compared to the control and single-type CNTs, DOM could regulate the expression of these functional genes associated with oxidative stress response, carbohydrate metabolism, endoplasmic reticulum stress, neuroendocrine, osmotic stress, and DNA damage and repair. Our study thus paves a solid way for exploring the molecular mechanism of aquatic toxicity of multiple nanomaterials under field-relevant conditions.