Metabolomics and transcriptomics reveal the toxic mechanism of Cd and nano TiO2 coexposure on rice (Oryza sativa L.).

Engineered nanoparticles (ENPs) can resist heavy metal toxicity in plants, but their coexposure still exhibits toxicity to plants compared to plants without exposure to ENPs and heavy metals. There have been few studies on the toxic mechanism of nano TiO2-heavy metal coexposure and the effect mechanism of nano TiO2 in plants. Thus, transcriptomics and metabolomics were used to study the toxic mechanism of rutile nano TiO2 or TiO2-Cd (rutile nano TiO2 and CdCl2 mixture) on rice (Oryza sativa L.). After 40 days of exposure, the plant height and root dry weight of rice were significantly decreased in the nano TiO2-Cd group compared to the blank group (nano TiO2 and CdCl2 free). After Cd treatment, 423 differentially expressed genes (DEGs) and 16 differential metabolites were identified. Nano TiO2 exposure induced significant regulation of 299 DEGs and 6 metabolites. After nano TiO2-Cd coexposure, 1660 DEGs and 181 differential metabolites were identified. Notably, the EDGs (e.g., chalcone isomerase and hydroxycinnamoyl transferase) and differential metabolites (e.g., chrysin and galangin) demonstrated the disruption of flavonoid biosynthesis in Cd-treated rice. After rice was exposed to nano TiO2, the DEGs were related to ribosome, whereas the differential metabolites were associated with pyruvate metabolism and valine, leucine, and isoleucine biosynthesis. Furthermore, 14 DEGs (e.g., asparaginyl-tRNA synthetase and methionyl-tRNA formyltransferase) involved in aminoacyl-tRNA biosynthetic pathways were significantly upregulated in rice treated with nano TiO2-Cd, in line with the changes in related metabolites (e.g., L-asparagine and 10-formyltetrahydrofolate). Our results show that it is necessary to pay close attention to the toxicity of nano TiO2-Cd coexposure in paddy ecosystems and use ENPs with caution to combat the phytotoxicity of heavy metals.

Toxicokinetics and bioaccumulation characteristics of bisphenol analogues in common carp (Cyprinus carpio).

Toxicokinetics and bioconcentration of eight common bisphenol analogues, including bisphenol A (BPA), -B, -C, -E, -S, -Z, -AF, and -AP in common carp (Cyprinus carpio) were investigated. Both free (BPfree) and total forms (BPtotal) of the bisphenols were measured in various fish tissues. The conjugated forms of bisphenols were calculated based on BPfree and BPtotal. The calculated bioconcentration factors (BCFs) based on the total bisphenols (BPtotal) in the carp whole body were in the range of 0.3-320, agreeing with previous field results from Taihu Lake, China. The elimination rate constant (ke) positively correlated with the fraction of conjugated form (fconjugated), which displayed negative correlation with their log Kow (r = -0.861, p < 0.05), indicating that conjugation facilitated their elimination and those with higher hydrophobicity were more difficult to be eliminated. Except BPA, the concentrations of all bisphenols in the carp tissues were in the order of kidney > liver â‰« muscle. The uptake rate constants (ku) in kidney (r = 0.836, p < 0.05) and in liver (r = 0.863, p < 0.05) displayed significantly positive correlations with BCFs, and ku in kidney was greater than in liver except BPA. These results indicated that kidney and liver played important roles in accumulating bisphenols in carp, and kidney made more contribution than liver for most bisphenols. Biliary excretion predominated for elimination of most bisphenols while BPA and BPS were mainly through urinary excretion.

Impacts of Morphology, Natural Organic Matter, Cations, and Ionic Strength on Sulfidation of Silver Nanowires.

Silver nanowires (AgNWs) are being widely utilized in an increasing number of consumer products, which could release silver to aquatic environments during the use or washing process, and have received growing concerns on their potential risks to bio-organisms and humans. The present study demonstrated that AgNWs mainly experienced direct oxysulfidation by reacting with dissolved sulfide species (initial S2- concentration at 1.6 mg/L) to produce silver sulfide nanostructures under environmentally relevant conditions. Granular Ag2S nanoparticles were formed on the surface of the nanowires. The sulfidation rate constant (kAg) of AgNWs was compared with those of silver nanoparticles (AgNPs) at different particle sizes. It was found that the kAg positively correlated with the specific surface areas of the silver nanomaterials. Natural organic matter (NOM) suppressed the sulfidation of AgNWs to different extents depending on its concentration. Divalent cations (Mg2+ and Ca2+ ions) substantially accelerated the sulfidation rates of AgNWs compared to monovalent cations (Na+ and K+ ions). At the same ionic strengths, Ca2+ ions displayed the highest promoting effect among the four metallic ions.

Facilitated Bioaccumulation of Perfluorooctanesulfonate in Common Carp (Cyprinus carpio) by Graphene Oxide and Remission Mechanism of Fulvic Acid.

As one of the most popular carbon-based nanomaterials, graphene oxide (GO) has the potential to be released in aquatic environment and interact with some coexistent organic pollutants, such as perfluorooctanesulfonate (PFOS), which is an emerging persistent organic pollutant. In this study, the adsorption of PFOS on GO in the presence of fulvic acid (FA), the impacts of GO and FA on PFOS toxicokinetics in carp (Cyprinus carpio), and in vitro digestion behaviors were examined. The results indicated that PFOS could be strongly adsorbed on GO with a Freundlich affinity coefficient KF of 580 ± 205 (mg/g)/(mg/L)n, while the adsorption was suppressed by FA due to competitive adsorption. GO significantly enhanced the bioaccumulation of PFOS in blood, kidney, liver, gill, intestine, and muscle of carp, and the corresponding bioaccumulation factor (BAF) was in the range of 2026-53513 L/kg. The enhancement was greatest for liver and intestine, which was 10.3 and 9.33 times of that without GO, respectively. In vivo toxicokinetic and in vitro digestion-absorption experiments indicated that GO could carry PFOS to penetrate the intestine cells. There herein, PFOS absorption, especially via intestine, and the uptake rate coefficient (ku) were greatly enhanced, leading to distinctly promoted bioaccumulation of PFOS in fish. However, FA could facilitate the flocculation of GO in the intestine and also accelerate excretion of GO-PFOS complex. Thus, in the presence of FA, PFOS absorption was reduced and the promotion effect of GO on PFOS accumulation was remitted.

Bioaccumulation of perfluoroalkyl acids including the isomers of perfluorooctane sulfonate in carp (Cyprinus carpio) in a sediment/water microcosm.

Carp (Cyprinus carpio) were exposed to perfluoroalkyl acids (PFAAs) including perfluorooctane sulfonate (PFOS) isomers in an artificially contaminated sediment/water microcosm. The uptake constant of PFAAs increased with increasing carbon chain length, whereas the elimination coefficient displayed the opposite trend, suggesting that carbon chain length plays an important role in the bioaccumulation of PFAAs. When the contribution of suspended particulate matter was taken into account, the bioaccumulation factors (BAFs) became lower (3.61-600 L/kg) compared with BAFs derived from only considering the absorption from free PFAAs in water (3.85-97000 L/kg). The results indicate that suspended particulate matter in water constitutes an important source of exposure for aquatic organisms to long-chain PFAAs. Linear (n-)PFOS was preferentially accumulated compared with branched isomers in carp. Among the branched isomers, 1m-PFOS displayed the greatest bioaccumulation, whereas m2 -PFOS had the lowest. Linear PFOS displayed greater partitioning ability from blood to other tissues over branched PFOS (br-PFOS) isomers, leading to a relatively lower n-PFOS proportion in blood. In summary, suspended particulate matter made a contribution to the accumulation of long-chain PFAAs in aquatic organisms, and n-PFOS was preferentially accumulated compared with br-PFOS isomers. Environ Toxicol Chem 2016;35:3005-3013. © 2016 SETAC.

Effects of nano-TiO2 on perfluorooctanesulfonate bioaccumulation in fishes living in different water layers: Implications for enhanced risk of perfluorooctanesulfonate.

Nano-titanium dioxide (nano-TiO2) is one of the most universal engineered nano-materials while perfluorooctanesulfonate (PFOS) is a typical new persistent organic pollutant. They are widely used and present in aquatic environment. In this study, a novel semi-static multilayer microcosm was setup to investigate the impacts of nano-TiO2 on PFOS bioaccumulation in fish species [Danio rerio (D. rerio), Ctenopharyngodon idella (C. idella), Hypostomus plecostomus (H. plecostomus)] living in different vertical layers. As a result of aggregation and deposition, the concentration of TiO2 increased from upper to bottom layers in the water column. Concomitantly, due to adsorption of PFOS on the nano-TiO2 particles, PFOS also displayed an increasing trend from upper to bottom layer. Owing to ingestion of the TiO2-PFOS complexes, more PFOS was taken-up by fish. With the aid of intestinal fluid, PFOS was readily released from TiO2 particles and absorbed by fish. As a result, accumulation of PFOS in whole fish was facilitated and the bioaccumulation factors of PFOS in D. rerio, C. idella and H. plecostomus were 3.01, 2.42 and 1.11 times of that in the groups without TiO2. However, TiO2 aggregates were too large to penetrate biological membranes to participate body circulation, and no significant accumulation of TiO2 was observed in fish muscle. The results suggested that the ecological risk of PFOS could be enhanced due to the presence of nano-TiO2 in water.

Facilitated bioaccumulation of perfluorooctanesulfonate in zebrafish by nano-TiO2 in two crystalline phases.

Zebrafish were placed in the upper layer of aquariums to investigate the impacts of anatase and rutile nano-TiO2 on perfluorooctanesulfonate (PFOS) bioaccumulation in zebrafish. Both variations of particle hydrodynamic size and concentration in water column suggest that anatase was better dispersed than rutile. PFOS could be significantly adsorbed on nano-TiO2 to form TiO2-PFOS complexes, leading to reduced concentration of PFOS in upper layer. Due to enhanced exposure to PFOS by ingestion and adhesion of TiO2-PFOS complexes, the whole-body PFOS concentration in zebrafish was enhanced by 59.0% (95% CI: 55.9%, 61.9%) and 25.4% (95% CI: 24.8%, 25.6%) in the presence of anatase and rutile nano-TiO2 after equilibrium compared with the control with PFOS alone. The bioaccumulation of PFOS was much more promoted by anatase, which was attributed by greater adsorption capacity of PFOS to anatase, slower migration of their complex in water column, and slower elimination rate of anatase from fish.

In Vivo and in Vitro Isomer-Specific Biotransformation of Perfluorooctane Sulfonamide in Common Carp (Cyprinus carpio).

Biotransformation of PFOS-precursors (PreFOS) may contribute significantly to the level of perfluorooctanesulfonate (PFOS) in the environment. Perfluorooctane sulfonamide (PFOSA) is one of the major intermediates of higher molecular weight PreFOS. Its further degradation to PFOS could be isomer specific and thereby explain unexpected high percentages of branched (Br-) PFOS isomers observed in wildlife. In this study, isomeric degradation of PFOSA was concomitantly investigated by in vivo and in vitro tests using common carp as an animal model. In the in vivo tests branched isomers of PFOSA and PFOS were eliminated faster than the corresponding linear (n-) isomers, leading to enrichment of n-PFOSA in the fish. In contrast, Br-PFOS was enriched in the fish, suggesting that Br-PFOSA isomers were preferentially metabolized to Br-PFOS over n-PFOSA. This was confirmed by the in vitro test. The exception was 1m-PFOSA, which could be the most difficult to be metabolized due to its α-branched structure, resulting in the deficiency of 1m-PFOS in the fish. The in vitro tests indicated that the metabolism mainly took place in the fish liver instead of its kidney, and it was mainly a Phase I reaction. The results may help to explain the special PFOS isomer profile observed in wildlife.