We systematically investigated the toxicity mechanism of three graphene-family materials (GFMs), graphene oxide (GO), reduced graphene oxide (rGO) and multi-layer graphene (MG), to algae (Chlorella pyrenoidosa). GFMs exhibited much higher toxicity than other carbon materials (carbon nanotube and graphite), with the 96 h median effective concentration (EC) values of 37.3 (GO), 34.0 (rGO), and 62.2 (MG) mg/L. Shading effect contributed approximately 16.4% of growth inhibition by GO due to its higher dispersibility and transformation while the other GFMs did not show any shading effect. Hydrophobic rGO and MG more readily heteroagglomerated with algae than GO, thus likely leading to more direct contacts with algae. Flow cytometry results showed significant decrease of membrane integrity after GFM exposure, and rGO caused the highest membrane damage, which was confirmed by the increased DNA and K efflux. The observed membrane damage was caused by a combination of oxidative stress and physical penetration/extraction. Moreover, all the three GFMs could adsorb macronutrients (N, P, Mg, and Ca) from the algal medium, thus leading to nutrient depletion-induced indirect toxicity. GO showed the highest nutrient depletion (53% of total toxicity) due to its abundant functional groups. The information provided in this work will be useful for understanding toxicity mechanism and environmental risk of different GFMs in aquatic environments.

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BackgroundGiven the tremendous potential for graphene quantum dots (QDs) in biomedical applications, a thorough understanding of the interaction of these materials with macrophages is essential because macrophages are one of the most important barriers against exogenous particles. Although the cytotoxicity and cellular uptake of graphene QDs were reported in previous studies, the interaction between nuclei and the internalized graphene QDs is not well understood. We thus systematically studied the nuclear uptake and related nuclear response associated with aminated graphene QDs (AG-QDs) exposure.ResultsAG-QDs showed modest 24-h inhibition to rat alveolar macrophages (NR8383), with a minimum inhibitory concentration (MIC) of 200 μg/mL. Early apoptosis was significantly increased by AG-QDs (100 and 200 μg/mL) exposure and played a major role in cell death. The internalization of AG-QDs was mainly via energy-dependent endocytosis, phagocytosis and caveolae-mediated endocytosis. After a 48-h clearance period, more than half of the internalized AG-QDs remained in the cellular cytoplasm and nucleus. Moreover, AG-QDs were effectively accumulated in nucleus and were likely regulated by two nuclear pore complexes genes (Kapβ2 and Nup98). AG-QDs were shown to alter the morphology, area, viability and nuclear components of exposed cells. Significant cleavage and cross-linking of DNA chains after AG-QDs exposure were confirmed by atomic force microscopy investigation. Molecular docking simulations showed that H-bonding and π-π stacking were the dominant forces mediating the interactions between AG-QDs and DNA, and were the important mechanisms resulting in DNA chain cleavage. In addition, the generation of reactive oxygen species (ROS) (e.g., •OH), and the up-regulation of caspase genes also contributed to DNA cleavage.ConclusionsAG-QDs were internalized by macrophages and accumulated in nuclei, which further resulted in nuclear damage and DNA cleavage. It is demonstrated that oxidative damage, direct contact via H-bonding and π-π stacking, and the up-regulation of caspase genes are the primary mechanisms for the observed DNA cleavage by AG-QDs.Electronic supplementary materialThe online version of this article (10.1186/s12989-018-0279-8) contains supplementary material, which is available to authorized users.

Engineered nanoparticles (NPs) are being released into aquatic environments with their increasing applications. In this work, we investigated the interaction of CuO NPs with a floating plant, water hyacinth (Eichhornia crassipes). CuO NPs (50 mg/L) showed significant growth inhibition on both roots and shoots of E. crassipes after 8-day exposure, much higher than that of the bulk CuO particles (50 mg/L) and their corresponding dissolved Cu ions (0.30 mg/L). Scanning electron and light microscopic observations showed that the root caps and meristematic zone of E. Crassipes were severely damaged after CuO NP exposure, with disordered cell arrangement and a destroyed elongation zone of root tips. It is confirmed that CuO NPs could be translocated to shoot from both roots and submerged leaves. As detected by X-ray absorption near-edge spectroscopy analysis (XANES), CuO NPs were observed in roots, submerged leaves, and emerged leaves. CuS and other Cu species were also detected in these tissues, providing solid evidence of the transformation of CuO NPs. In addition, stomatal closure was observed during CuO NPs-leaf contact, which was induced by the production of HO and increased Ca level in leaf guard cells. These findings are helpful for better understanding the fate of NPs in aquatic plants and related biological responses.

This study investigated the toxicity of CuO nanoparticles (NPs) to Nicotiana tabacum L. cv. Bright Yellow-2 (BY-2) cells.

Many studies demonstrated that CeO2 nanoparticles (NPs) could protect plant from stress and improve plant growth, with a great application potential in agriculture. However, our knowledge of their fate particularly in asexual plants and their effect on the rhizosphere microbiome is limited. In this study, the transport and transformation of CeO2 NPs in an asexual plantstrawberry (Fragaria × ananassa Duch.)were investigated. The effects of root-exuded/newly formed Ce species on rhizosphere bacterial community were also examined. Strawberries were exposed to CeO2 NPs at 0–2000 mg/L for 45 days via a split-root system in the field. CeO2 NPs were taken up by the exposed mother ramet roots and then translocated to all the mother and daughter ramet tissues. As indicated by the analysis from high-resolution transmission electron microscopy and X-ray absorption near-edge structures, in addition to CeO2 NPs, CePO4, Ce­(III) acetate, and Ce­(III)-cysteine were found in the roots, and CePO4 was present in the rhizosphere soil. The Ce species in the rhizosphere soil decreased the rhizosphere microbial diversity, but stimulated the relative abundance of specific plant growth promoting rhizobacteria. These results provide new insights for understanding the benefits and sustainable applications of NPs.

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