Bioaccumulation, Depuration, and Transfer to Offspring of 13C-Labeled Fullerenols by Daphnia magna

Unraveling the Distribution, Metabolization, and Catabolism of Foliar Sprayed Carbon Dots in Maize and Effect on Soil Environment

The enormous potential of carbon dots (CDs) in agriculture has been widely reported, whereas their accurate distribution, transformation, and metabolic fate and potential soil health effects are not clearly understood. Herein, 13C-labeled CDs (13C-CDs) were sprayed on maize leaf, accumulated in all tissues, and promoted photosynthesis. Specifically, 13C-CDs were internalized to participate in the synthesis of glucose, sucrose, citric acid, glyoxylate, and chlorogenic acid, promoting tricarboxylic acid cycle (TCA) and phenylalanine metabolism. Additionally, the catabolism of 13C-CDs in vivo was mainly mediated by O2•- produced by oxidative stress. 13C-CDs did not have an obvious impact on the soil environment at the overall level. The detection of 13C signals in soil fauna suggested 13C-CDs in soil food chain transmission. This study systematically described the exact fate of CDs in plants and potential soil ecological risks and provided a more comprehensive analysis and support for the potential advantages of CDs in agricultural application.

Mechanistic Insights into the Biodegradation of Carbon Dots by Fungal Laccase

While carbon dots (CDs) have the potential to support the agricultural revolution, it remains obscure about their environmental fate and bioavailability by plants. Fungal laccase-mediated biotransformation of carbon nanomaterials has received little attention despite its known capacity to eliminate recalcitrant contaminants. Herein, we presented the initial investigation into the transformation of CDs by fungal laccase. The degradation rates of CDs were determined to be first-order in both substrate and enzyme. Computational docking studies showed that CDs preferentially bonded to the pocket of laccase on the basal plane rather than the edge through hydrogen bonds and hydrophobic interactions. Electrospray ionization-Fourier transform-ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS) and other characterizations revealed that the phenolic/amino lignins and tannins portions in CDs are susceptible to laccase transformation, resulting in graphitic structure damage and smaller-sized fragments. By using the 13C stable isotope labeling technique, we quantified the uptake and translocation of 13C-CDs by mung bean plants. 13C-CDs (10 mg L-1) accumulated in the root, stem, and leaf were estimated to be 291, 239, and 152 μg g-1 at day 5. We also evidenced that laccase treatment alters the particle size and surface chemistry of CDs, which could facilitate the uptake of CDs by plants and reduce their nanotoxicity to plants.

Mechanistic Understanding toward the Maternal Transfer of Nanoplastics in Daphnia magna

Nanoplastics induce transgenerational toxicity to aquatic organisms, but the specific pathways for the maternal transfer of nanoplastics remain unclear. Herein, laser scanning confocal microscopy (LSCM) observations identified the specific pathways on the maternal transfer of polystyrene (PS) nanoplastics (25 nm) in Daphnia magna. In vivo and in vitro experiments showed that PS nanoplastics could enter the brood chamber through its opening and then be internalized to eggs and embryos using LSCM imaging (pathway I). In addition, PS nanoplastics were observed in the oocytes of the ovary, demonstrating gut-ovary-oocyte transfer (pathway II). Furthermore, label-free hyperspectral imaging was used to detect the distribution of nanoplastics in the embryos and ovary of Daphnia, again confirming the maternal transfer of nanoplastics through the two pathways mentioned above. The contribution from pathway I (88%) was much higher than pathway II (12%) based on nanoflow cytometry quantification. In addition, maternal transfer in Daphnia depended on the particle size of PS nanoplastics, as demonstrated by using LSCM and hyperspectral imaging. Unlike 25 nm nanoplastics, 50 nm PS nanoplastics could enter the brood chamber and the eggs/embryos (pathway I), but were not detected in the ovary (pathway II); 100 nm PS nanoplastics were difficult to be internalized by eggs/embryos and could not enter the ovary either. These findings provide insight into the maternal transfer mechanisms of nanoplastics in Daphnia, and are critical for better understanding the transgenerational toxicity of aquatic organisms.

Nanotoxicity of Graphene Oxide - Gold Nanohybrid to Daphnia magna

The expanding use of hybrid nanomaterials in many applications necessitates evaluation of their environmental risks. This study investigates the acute toxicity and bioaccumulation of graphene oxide - gold (GO-Au) nanohybrid in neonates (<24 hrs old) of Daphnia magna after exposure to a wide range of concentrations (1-100 mg/L). No significant mortality or immobilisation was observed after the exposure period. Microscopic observation showed an uptake of the nanohybrid and internal damage in the gut of the exposed organisms. Bioaccumulation of the GO-Au nanohybrid also occurred in a concentration-dependant manner. Continuous evaluation of the environmental risks from exposure to this nanohybrid and other advanced materials is imperative to avert disruption to the ecosystem.

Evaluation of bioaccumulation of nanoplastics, carbon nanotubes, fullerenes, and graphene family materials

Bioaccumulation is a key factor in understanding the potential ecotoxicity of substances. While there are well-developed models and methods to evaluate bioaccumulation of dissolved organic and inorganic substances, it is substantially more challenging to assess bioaccumulation of particulate contaminants such as engineered carbon nanomaterials (CNMs; carbon nanotubes (CNTs), graphene family nanomaterials (GFNs), and fullerenes) and nanoplastics. In this study, the methods used to evaluate bioaccumulation of different CNMs and nanoplastics are critically reviewed. In plant studies, uptake of CNMs and nanoplastics into the roots and stems was observed. For multicellular organisms other than plants, absorbance across epithelial surfaces was typically limited. Biomagnification was not observed for CNTs and GFNs but were observed for nanoplastics in some studies. However, the reported absorption in many nanoplastic studies may be a consequence of an experimental artifact, namely release of the fluorescent probe from the plastic particles and subsequent uptake. We identify that additional work is needed to develop analytical methods to provide robust, orthogonal methods that can measure unlabeled (e.g., without isotopic or fluorescent labels) CNMs and nanoplastics.

Visualization of fullerenol nanoparticles distribution in Daphnia magna using Laser Ablation-isotope Ratio Mass (LA-IRMS) and Matrix-assisted Laser Desorption/Ionization Imaging Mass Spectrometry (MALDI-IMS)

Laser ablation-isotope ratio mass spectrometry (LA-IRMS) allows the mapping analysis of carbon isotope (δ¹³C) signature in organism samples.Matrix assisted laser desorption ionization time-of-flightimaging mass spectrometry (MALDI-TOF-IMS) enables image of target directly. In this study, the distribution of δ¹³C and fullerenol nanoparticles in Daphnia magna (D. magna) exposed to different fullerenol solution are mapped using the LA-IRSM and MALDI-TOF-IMS for comparison. We visualize thedistribution of fullerenol nanoparticles mainly in the intestine, also in other parts of the body as well. This is the first time that fullerenol nanoparticles was found outside the intestine of D. magna, which has been confirmed by the two imaging methods individually. Although the both imaging methods are applicable to in-situ visualize the localization and spatial distribution of fullerenol nanoparticles in organisms, MALDI-TOF-IMS is more suitable, in terms of sample preparation and image resolution. The results of our study will also provide a new idea and method for the research of environmental toxicology.

Visualization of the tissue distribution of fullerenols in zebrafish (Danio rerio) using imaging mass spectrometry

With the wide application of fullerenols in biomedicine, their environmental exposure risks and toxicity to organisms have been extensively studied. However, there is still a lack of knowledge about the distribution of fullerenols in organisms as an important aspect of their mechanism of toxicity. High-resolution matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) is an emerging technology for researching the distribution of molecules in biological tissue samples. Using this high-resolution technique, we map the distribution of fullerenols in zebrafish tissues, and the results suggest that fullerenols enter the gill, intestine, and muscle tissues and even permeate the blood-brain barrier, reaching the brain of zebrafish after aquatic exposure. Moreover, from the MS images of fullerenols, the distribution amount of fullerenols is highest in the gill, followed by that in the intestine and the small amount in muscle and brain tissues. As an emerging environmental pollutant, the establishment of this research method will provide a new method for the study of the environmental toxicity of carbon nanomaterials. Our results also indicated that this high-resolution imaging method could be applied to explore the mechanism of interaction between carbon nanomaterials and biological systems at the cellular level in the future.

Bioaccumulation, biodistribution，and depuration of 13C-labelled fullerenols in zebrafish through dietary exposure

In aquatic organisms, dietary exposure to nanomaterials is not only one of the important uptake pathways, but it is also one method to assess the transmission risk of the food chain. To address this concern, we quantitatively investigated the accumulation and depuration of fullerenols in the tissues of zebrafish after exposure to fullerenols-contaminated Daphnia magna. After exposure to ¹³C-labelled fullerenol solution at a concentration of 2.5 mg/L for 72 h, the steady state concentration of fullerenols in D. magna was 31.20 ± 1.59 mg/g dry weight. During the 28 d uptake period for zebrafish, fullerenols in the tissues increased in a tissue- and day-dependent manner, and the major target tissues of fullerenols were the intestines and liver, followed by the gill, muscle, and brain. The kinetic parameters of uptake and depuration were also quantitatively analyzed. After depuration for 15 d, a certain amount of residual fullerenols remained in the tissues, especially the brain, where approximately 64 d may be needed to achieve 90% of the cumulative concentration depuration. The calculated distribution-based trophic transfer factors (TTF_d values) (from 0.26 to 0.49) indicated that the tissue biomagnification of fullerenols by zebrafish through dietary exposure may not occur. Transmission electron microscopy (TEM) confirmed the presence of fullerenols in D. magna and the tissues of zebrafish. Our research data are essential for thoroughly understanding of the fate of nanoparticles through the dietary exposure pathway and directing future tissue bioeffect studies regarding target tissues for further research.

Bioconcentration and bioaccumulation of C60 fullerene and C60 epoxide in biofilms and freshwater snails (Radix sp.)

Fullerenes are carbon nanomaterials that have awaken a strong interest due to their adsorption properties and potential applications in many fields. However, there are some gaps of information about their effects and bioconcentration potential in the aquatic biota. In the present work, freshwater biofilms and snails (Radix sp.) were exposed to fullerene C₆₀ aggregates, at concentrations in the low μg/L order, in mesocosms specifically designed to mimic the conditions of a natural stream. The bioconcentration factors of C₆₀ fullerene and its main transformation product, [6,6]C₆₀O epoxide, were studied to the mentioned organisms employing analyses by liquid chromatography coupled to high-resolution mass spectrometry. Our results show that C₆₀ fullerene and its [6,6]C₆₀O present a low bioconcentration factor (BCF) to biofilms: BCF_C60 = 1.34 ± 0.95 L/kg_dw and BCF_C60O = 1.43 ± 0.72 L/kg_dw. This suggests that the sorption of these aggregates to biota may be less favoured than it would be suggested by its hydrophobic character. According to our model, the surface of fullerene aggregates is saturated with [6,6]C₆₀O molecules, which exposes the polar epoxide moieties in the surface of the aggregates and decreases their affinity to biofilms. In contrast, freshwater snails showed a moderate capacity to actively retain C₆₀ fullerenes in their organism (BAF_C60 = 2670 ± 3070 L/kg_dw; BAF_C60O = 1330 ± 1680 L/kg_dw), probably through ingestion. Our results indicate that the bioaccumulation of these carbon nanomaterials can be hardly estimated using their respective octanol-water partition coefficients, and that their colloidal properties, as well as the feeding strategies of the tested organism, play fundamental roles.

Uptake and Transfer of 13C-Fullerenols from Scenedesmus obliquus to Daphnia magna in an Aquatic Environment

Fullerenol, a water-soluble polyhydroxylated fullerene nanomaterial, enters aquatic organisms and ecosystems through different ingestion exposures and may pose environmental risks. The study of their uptake routes and transfer in aquatic systems is scarce. Herein, we quantitatively investigated the aquatic uptake and transfer of ¹³C-fullerenols from Scenedesmus obliquus to Daphnia magna using ¹³C-skeleton-labeling techniques. The bioaccumulation and depuration of fullerenol in Daphnia magna increased with exposure doses and time, reaching steady state within 16 h in aqueous and feeding-affected aqueous routes. The capacity of Daphnia magna to ingest fullerenol via the aqueous route was much higher than that via the dietary route. From the aqueous to feeding-affected aqueous, the kinetic analysis demonstrated the bioaccumulation factors decreases, which revealed that algae suppressed Daphnia magna uptake of fullerenols. The aqueous route was the primary fullerenols ingestion pathway for Daphnia magna. Kinetic analysis of the accumulation and transfer in Daphnia magna via the dietary route indicated low transfer efficiency of fullerenol along the Scenedesmus obliquus-Daphnia magna food chain. Using stable isotope labeling techniques, these quantitative data revealed that carbon nanomaterials underwent complex aquatic accumulation and transfer from primary producers to secondary consumers and algae inhibited their transfer in food chains.

A mechanism study on toxicity of graphene oxide to Daphnia magna: Direct link between bioaccumulation and oxidative stress

Graphene oxide (GO) possesses versatile applicability and high hydrophilicity, thus may have frequent contact with aquatic organisms. However, the ecological risks of GO in aquatic ecosystems remain largely unexplored currently. This study evaluated the comprehensive toxicological effects of GO on Daphnia magna, a key species in fresh water ecosystem. The results revealed nonsevere acute toxicities, including immobility (72 h EC₅₀: 44.3 mg/L) and mortality (72 h LC₅₀: 45.4 mg/L), of GO on D. magna. To understand the underlying mechanism of GO exposure, changes in superoxide dismutase (SOD) and lipid peroxidation (LPO) of D. magna exposed to GO were correlated, which revealed elevated GO-mediated oxidative stress and damages, especially in the long-time and high-dose exposure groups. The observations of in vivo fluorescence labeled with 2', 7'-dichlorofluorescin further demonstrated that reactive oxygen species were concentrated in daphnia guts, which corresponded with the high bioaccumulation level (5 mg/L, 24 h body burden: 107.9 g/kg) of GO in daphnia guts. However, depuration of GO from daphnia was not difficult. Daphnia almost released all GO within 24 h after it was transferred to clean water. These results hence suggest that GO could accumulate and induce significant oxidative stress in the gut of D. magna, while D. daphnia can also relieve the acute toxicity by depurating GO.

Time-gated luminescence imaging of singlet oxygen photoinduced by fluoroquinolones and functionalized graphenes in Daphnia magna

Singlet oxygen (¹O₂) can be photogenerated by photoactive xenobiotics and is capable of causing adverse effects due to its electrophilicity and its high reactivity with biological molecules. Detection of the production and distribution of ¹O₂ in living organisms is therefore of great importance. In this study, a luminescent probe ATTA-Eu³⁺ combined with time-gated luminescence imaging was adopted to detect the distribution and temporal variation of ¹O₂ photoinduced by fluoroquinolone antibiotics and carboxylated/aminated graphenes in Daphnia magna. Results show that the xenobiotics generate ¹O₂ in living daphnids under simulated sunlight irradiation (SSR). The photogeneration of ¹O₂ by carboxylated/aminated graphenes was also confirmed by electron paramagnetic resonance spectroscopy. The strongest luminescence signals of ¹O₂ were observed in the hindgut of daphnids, and the signals in different areas of the daphnids (gut, thoracic legs and post-abdominal claw) displayed a similar trend of enhancement over irradiation time. Mean ¹O₂ concentrations at different regions of daphnids within one hour of SSR irradiation were estimated to be in the range of 0.5∼4.8μM. This study presented an efficient method for visualizing and quantifying the temporal and spatial distribution of ¹O₂ photogenerated by xenobiotics in living organisms, which can be employed for phototoxicity evaluation of xenobiotics.

Bioaccumulation and Toxicity of 13C-Skeleton Labeled Graphene Oxide in Wheat

Graphene nanomaterials have many diverse applications, but are considered to be emerging environmental pollutants. Thus, their potential environmental risks and biosafety are receiving increased attention. Bioaccumulation and toxicity evaluations in plants are essential for biosafety assessment. In this study, ¹³C-stable isotope labeling of the carbon skeleton of graphene oxide (GO) was applied to investigate the bioaccumulation and toxicity of GO in wheat. Bioaccumulation of GO was accurately quantified according to the ¹³C/¹²C ratio. Wheat seedlings were exposed to ¹³C-labeled GO at 1.0 mg/mL in nutrient solution for 15 d. ¹³C-GO accumulated predominantly in the root with a content of 112 μg/g at day 15, hindered the development and growth of wheat plants, disrupted root structure and cellular ultrastructure, and promoted oxidative stress. The GO that accumulated in the root showed extremely limited translocation to the stem and leaves. During the experimental period, GO was excreted slowly from the root. GO inhibited the germination of wheat seeds at high concentrations (≥0.4 mg/mL). The mechanism of GO toxicity to wheat may be associated with oxidative stress induced by GO bioaccumulation, reflected by the changes of malondialdehyde concentration, catalase activity, and peroxidase activity. The results demonstrate that ¹³C labeling is a promising method to investigate environmental impacts and fates of carbon nanomaterials in biological systems.