Preferred Lung Accumulation of Polystyrene Nanoplastics with Negative Charges.

With the increasing presence of nanoplastics (NPs) in the human bloodstream, it is urgent to investigate their tissue accumulation and potential health risks. This study examines the effects of the size and surface charges of polystyrene (PS) NPs on lung accumulation. Using magnetic separation, we identified the protein corona composition on iron-core PS NPs, revealing the enrichment of vitronectin and fibrinogen. The corona promotes integrin αIIbß3 receptor-mediated uptake by lung endothelial cells, explaining that both the corona composition and protein structure determine preferred localization of negatively charged PS NPs in the lung. This study uncovers the role of protein corona in NP uptake and the way NPs enter the lung, emphasizing the need to consider interactions between nanoplastics with varying surface characteristics and biological molecules in the nanotoxicological field.

Effects of combined antibiotics on nitrification, bacteria and antibiotic resistance genes in activated sludge: Insights from legacy effect of antibiotics.

The effect of combined antibiotics exposure on nitrogen removal, microbial community assembly and proliferation of antibiotics resistance genes (ARGs) is a hotspot in activated sludge system. However, it is unclear that how the historical antibiotic stress affects the subsequent responses of microbes and ARGs to combined antibiotics. In this study, the effects of combined sulfamethoxazole (SMX) and trimethoprim (TMP) pollution on activated sludge under legacy of SMX or TMP stress with different doses (0.005-30 mg/L) were investigated to clarify antibiotic legacy effects. Nitrification activity was inhibited under higher level of combined exposure but a high total nitrogen removal (∼70%) occurred. Based on the full-scale classification, the legacy effect of past antibiotic stress had a marked effect on community composition of conditionally abundant taxa (CAT) and conditionally rare or abundant taxa (CRAT). Rare taxa (RT) were the keystone taxa in the microbial network, and the responses of hub genera were also affected by the legacy of antibiotic stress. Nitrifying bacteria and genes were inhibited by the antibiotics and aerobic denitrifying bacteria (Pseudomonas, Thaurea and Hydrogenophaga) were enriched under legacy of high dose, as were the key denitrifying genes (napA, nirK and norB). Furthermore, the occurrences and co-selection relationship of 94 ARGs were affected by legacy effect. While, some shared hosts (eg., Citrobacter) and hub ARGs (eg., mdtD, mdtE and acrD) were identified. Overall, antibiotic legacy could affect responses of activated sludge to combined antibiotic and the legacy effect was stronger at higher exposure levels.

Mercury Reduction, Uptake, and Species Transformation by Freshwater Alga Chlorella vulgaris under Sunlit and Dark Conditions.

As a major entry point of mercury (Hg) to aquatic food webs, algae play an important role in taking up and transforming Hg species in aquatic ecosystems. However, little is known how and to what extent Hg reduction, uptake, and species transformations are mediated by algal cells and their exudates, algal organic matter (AOM), under either sunlit or dark conditions. Here, using Chlorella vulgaris (CV) as one of the most prevalent freshwater model algal species, we show that solar irradiation could enhance the reduction of mercuric Hg(II) to elemental Hg(0) by both CV cells and AOM. AOM reduced more Hg(II) than algal cells themselves due to cell surface adsorption and uptake of Hg(II) inside the cells under solar irradiation. Synchrotron radiation X-ray absorption near-edge spectroscopy (SR-XANES) analyses indicate that sunlight facilitated the transformation of Hg to less bioavailable species, such as ß-HgS and Hg-phytochelatins, compared to Hg(Cysteine)2-like species formed in algal cells in the dark. These findings highlight important functional roles and potential mechanisms of algae in Hg reduction and immobilization under varying lighting conditions and how these processes may modulate Hg cycling and bioavailability in the aquatic environment.

Phytoavailability and transfer of mercury in soil-pepper system: Influencing factors, fate, and predictive approach for effective management of metal-impacted spiked soils.

Mercury (Hg) contamination and accumulation in food crops is a global threat posing potential health risk to humans. However, Hg phytoavailability in soil-pepper system and its influencing factors largely remain unknown. In this study, a greenhouse pot experiment was conducted to grow peppers using 21 Chinese agricultural soils with varied soil properties and aged Hg levels. Mercury concentration in pepper leaves and fruits ranged from 0.021 to 0.057 mg kg-1 and 0.005-0.022 mg kg-1 respectively, while fruit Hg content in three soils (Anhui, Hubei, Beijing) exceeded the safety limit. Fruit Hg concentration was better positively correlated with soil Mg(NO3)2-extractable Hg content (r = 0.7, P < 0.0001) than soil total Hg content (r = 0.45, P < 0.0001). Highest bioconcentration factor (BCF, ratio of Hg plant to Hg soil) yielded in acidic soils, while the lowest BCF occurred in alkaline soils. Path analysis indicated available-Hg (R2 = 0.40) and total-Hg (R2 = 0.40) had direct positive effects on the pepper fruit Hg concentration, while direct negative effects including pH (R2 = -0.86), organic matter (R2 = -0.7), crystalline-Fe (R2 = -0.68). Those agreed with the stepwise multiple linear regression analysis which yielded a regression predictive model (R2 = 0.73, P < 0.0001). Soil available-Hg, total-Hg, pH, organic matter and crystalline-Fe & Mn were the most influencing factors of Hg phytoavailability. These results provide new insights into the phytoavailability of Hg in soil-pepper system, thus facilitating the management of pepper cultivation in Hg-enriched soils.

Assessment of the Bioavailability of Mercury Sulfides in Paddy Soils Using Sodium Thiosulfate Extraction - Results from Microcosm Experiments.

Mercury sulfides (HgS), one of the largest Hg sinks in the lithosphere, has long been considered to be highly inert. Recently, several HgS speciation (e.g., nano- or micro-sized HgS particles) in paddy soils have been found to be reactive and bioavailable, increasing the possibility of methylation and bioaccumulation and posing a potential risk to humans. However, a simple and uniform method for investigating HgS bioavailability is still lacking. To address this issue, we extracted dissolved Hg from HgS particles by sodium thiosulfate (Na2S2O3) in paddy soils and analyzed the correlation between extracted Hg and soil methylmercury (MeHg). Results showed that the amounts of Hg extracted by Na2S2O3 had a strong positive correlation with the levels of soil MeHg (R 2 adj = 0.893, p < 0.05). It is suggested that Na2S2O3 extraction may be a good method of predicting Hg bioavailability in paddy soils. Our results would help to give clues in better predicting Hg risk in natural environments.

Protein-bound calcium phosphate in uremic rat serum: a quantitative study.

Protein-bound calcium (prCa) constitutes about 40% of serum total calcium, in which albumin is the most dominant protein. Given the chemical interaction between calcium and phosphate (Pi), the increased serum Pi in chronic kidney disease may cause changes in the composition and structure of the prCa fraction. Here, we report the phosphate binding on the protein-bound calcium in uremic rat serum. Using adenine-fed rats as a uremic model, we separated the calcium and phosphate fractions in rat serum by ultrafiltration, and found that the level of protein-bound phosphate (prPi) in the uremic serum was markedly higher than in control. The elevated prPi level was comparable to the prCa level, consistent with the presence of protein-bound calcium phosphate pr(Ca)j-m(CaPi)m. We then confirmed its presence by ex vivo X-ray absorption near-edge structure spectroscopy, revealing the discrete state of the calcium phosphate clusters associated with protein. Finally, in a quantitative investigation using Ca- and Pi-boosted serum, we discovered the threshold concentration for the Pi binding on prCa, and determined the binding constant. The threshold, while preventing Pi from binding to prCa in normal condition, allows the reaction to take place in hyperphosphatemia conditions. The protein-bound calcium phosphate could act as a link between the metabolism of serum proteins and the homeostasis of phosphate and calcium, and it deserves further investigation whether the molar ratio of (prPi/prCa)⋅100% may serve as a serum index of the vascular calcification status in chronic kidney disease.

Correction to: Protein-bound calcium phosphate in uremic rat serum: a quantitative study.

In the original article, few equations and units were published incorrectly.

Comparative study of the effects of different chelating ligands on the absorption and transport of mercury in maize (Zea mays L.).

Mercury (Hg) pollution seriously threatens food safety and has attracted global attention. Phytoextraction, due to its low cost, applicability, and environmental friendliness, is considered a new technology for clean-up of heavy metal contamination in the environment. However, the low bioavailability of Hg in polluted areas greatly limits the applicability of phytoextraction. Here, we compared the effects of six common chelating ligands on the absorption and transport of Hg in maize (Zea mays L.), which has a high biomass and short growth cycle. The results showed that the root length and biomass of maize seedlings of the groups treated with the six chelating ligands (EDTA, iodide, ammonium, thiosulfate, thiocyanate, and thiocarbamide) did not change compared with those of the non-treated groups. Co-exposure to Hg and each chelating ligand markedly alleviated the inhibitory effect induced by Hg. Iodide treatment resulted in the lowest root Hg content and highest translocation factor (TF) value, while ammonium treatment gave rise to the highest shoot Hg concentration and lowest TF. Compared with other chelating ligands, thiosulfate exhibited the maximum alleviation of Hg toxicity and achieved the highest concentration of Hg in the roots and aerial parts. Moreover, the TF and Hg accumulation in the thiosulfate and Hg co-exposed group were much higher than those in the group exposed to Hg alone. This finding suggests that, among these common chelating ligands, thiosulfate compounds have great potential for Hg phytoextraction, while the others can immobilize Hg in polluted areas.

A comparative study on the accumulation, translocation and transformation of selenite, selenate, and SeNPs in a hydroponic-plant system.

Plants can play important roles in overcoming selenium (Se) deficiency and Se toxicity in various regions of the world. Selenite (SeIV), selenate (SeVI), as well as Se nanoparticles (SeNPs) naturally formed through reduction of SeIV, are the three main Se species in the environment. The bioaccumulation and transformation of these Se species in plants still need more understanding. The aims of this study are to investigate the phytotoxicity, accumulation, and transformation of SeIV, SeVI and SeNPs in garlic, a relatively Se accumulative plant. The spatial distribution of Se in the roots were imaged using synchrotron radiation micro-focused X-ray fluorescence (SR-µXRF). The chemical forms of Se in different plant tissues were analyzed using synchrotron radiation X-ray absorption spectroscopy (SR-XAS). The results demonstrate that 1) SeNPs which has the lowest phytotoxicity is stable in water, but prone to be converted to organic Se species, such as C-Se-C (MeSeCys) upon uptake by root. 2) SeIV is prone to concentrate in the root and incorporated into C-Se-C (MeSeCys) and C-Se-R (SeCys) bonding forms; 3) SeVI with the lowest transformation probability to organic Se species has the highest phytotoxicity to plant, and is much easier to translocate from root to leaf than SeNPs and SeIV. The present work provides insights into potential impact of SeNPs, selenite and selenate on aquatic-plant ecosystems, and is beneficial for systematically understanding the Se accumulation and transformation in food chain.

Acute oral methylmercury exposure perturbs the gut microbiome and alters gut-brain axis related metabolites in rats.

Environmental pollutants like methylmercury (MeHg) can bring devastating neurotoxicity to animals and human beings. Gut microbiota has been found to demethylate MeHg and promote the excretion of Hg through feces. However, the impacts of MeHg on gut microbiota and metabolites related to gut-brain interactions were less studied in mammals. The object of this study was to investigate the impacts of acute MeHg exposure on gut microbiome and metabolites together with its impact on gut integrity and related biological responses in rats. Rats were exposed to MeHg through oral administration and were sacrificed after 24 h 16 S rRNA gene sequencing was used to study the perturbance to gut microbiome and liquid chromatography mass spectrometry (LC-MS) was used for metabolomics profiling. It was found that gut was one of the target tissues of MeHg. MeHg induce the changes of intestinal microbial community structure and induce the regulating neuron activity change of intestinal neurotransmitters and metabolites on intestinal neurotransmitters and metabolites regulating the neuron activity. This was supported by the increased BDNF level. These findings may suggest a potential new mechanism regarding the neurotoxicity of MeHg. The protocols used in this study may also be applied to understand the neurotoxicity of other environmental neurotoxins like Pb, Mn, polychlorinated biphenyls, and pesticides, etc and to screen the neurotoxicity of emerging environmental contaminants.

Ex vivo detection of calcium phosphate and calcium carbonate in rat blood serum.

The total calcium (tCa) in blood serum comprises free Ca2+ ions (fCa), protein-bound calcium (prCa), and complexed calcium by small anions (cCa). The cCa fraction, in addition to fCa, has been indicated to have some physiological activity. However, there is little evidence for the structure of its constituents. Here we report an ex vivo detection of the cCa constituents by synchrotron X-ray absorption near-edge structure spectroscopy. We collected the data directly on rat blood serum and, by making use of the reference samples, derived a spectrum that exhibits the features of cCa constituents. Among the features are those of the complexes of calcium phosphate and calcium carbonate. The detected complexes in the cCa fraction are mainly Ca(η2-HPO4)(H2O)4 and Ca(η1-HCO3)(H2O)5+, in which HPO42- and HCO3- serve as bidentate and unidentate ligands, respectively. The remained H2O molecules on the coordination sphere of Ca2+ enable these complexes to behave partially like aquated Ca2+ ions in protein-binding. Besides, as the dominant part of prCa, albumin-bound calcium (albCa) exhibits a spectrum that closely resembles that of fCa, indicating weak interactions between the protein carboxyl groups and calcium. The weak-bound cCa and albCa, along with fCa and the relevant anions, compose a local chemical system that could play a role in maintaining the calcium level in blood.

Increased Methylmercury Accumulation in Rice after Straw Amendment.

Consumption of rice has been shown to be an important route of dietary exposure to methylmercury (MeHg, a neurotoxin) for Asians having a low fish but high rice diet. Therefore, factors that increase MeHg production and bioaccumulation in soil-rice systems, could enhance the risk of MeHg exposure. On the basis of a national-scale survey in China (64 sites in 12 provinces) and rice cultivation experiments, we report that straw amendment, a globally prevalent farming practice, could increase MeHg concentrations in paddy soils (11-1043%) and rice grains (95%). By carrying out a series of batch incubation, seedling uptake and sand culture experiments, we demonstrate that these increases could be attributed to (1) enhanced abundances/activities of microbial methylators and the transformation of refractory HgS to organic matter-complexed Hg, facilitating microbial Hg methylation in soils; (2) enhanced MeHg mobility, and increased root lengths (35-41%) and tip numbers (60-105%), increasing MeHg uptake by rice roots; and (3) enhanced MeHg translocation to rice grains from other tissues. Results of this study emphasize fresh organic matter-enhanced MeHg production and bioaccumulation, and highlight the increased risk of MeHg after straw amendment and thus the need for new policies concerning straw management.

Understanding Enhanced Microbial MeHg Production in Mining-Contaminated Paddy Soils under Sulfate Amendment: Changes in Hg Mobility or Microbial Methylators?

Elevated methylmercury (MeHg) production in mining-contaminated paddy soils, despite the high fraction of refractory HgS(s), has been frequently reported, while the underlying mechanisms are not fully understood. Here, we hypothesized that sulfate input, via fertilization, rainfall, and irrigation, is critical in mobilizing refractory HgS(s) and thus enhancing Hg methylation in mining-contaminated paddy soils. To test this hypothesis, the effects of sulfate amendment on Hg methylation and MeHg bioaccumulation in mining-contaminated soil-rice systems were examined. The results indicated 28-61% higher net MeHg production in soils under sulfate amendment (50-1000 mg kg-1), which in turn increased grain MeHg levels by 22-55%. The enhancement of Hg methylation by Hg mobilization in sulfate-amended soils was supported by two observations: (1) the increased Hg(aq) release from HgS(s), the dominant Hg species in the paddy soils, in the presence of sulfide produced following sulfate reduction and (2) the decreases of refractory HgS(s) in soils under sulfate amendment. By contrast, changes in the abundances/activities of potential microbial Hg methylators in different Hg-contaminated soils were not significant following sulfate amendment. Our results highlight the importance to consider enhanced Hg mobility and thus methylation in soils under sulfate amendment.

Pseudo-equilibrium equation of calcium phosphate precipitation from aqueous solution.

An X-ray amorphous phase is frequently present at the early stage of calcium phosphate crystallization, and the relevant solution chemistry is essential for understanding the mechanism of reaction. Here, we report a quantitative study of a series of reaction systems at pseudo-equilibrium states. We determined the composition of solutions and the quantities of the precipitate samples, and characterized the long- and short-range order of the precipitate using X-ray diffraction and synchrotron X-ray absorption near-edge structure spectroscopy, respectively. We found that, in a particle with multiple structural units, only a fraction of the units was able to reach pseudo-equilibrium with the solution composition, which represents the average number of surficial clusters per unit. These findings enabled us to propose a general form of the equilibrium constant equation. The equation fits the pseudo-equilibrium data well, and it converts to the "solubility product (Ksp)" and the conventional "reaction quotient" in two limit cases, respectively. Further, using a cube model, we derived a "particle equation" that reveals the connection between the particle structure and the form of equilibrium constant equation. The dependency of the form of pseudo-equilibrium equation on the structure and size of the precipitate reveals a fundamental relation in chemistry, and its applicability remains to be examined in other reaction systems, such as those involving nanocrystals and porous materials.

Nanoelemental selenium alleviated the mercury load and promoted the formation of high-molecular-weight mercury- and selenium-containing proteins in serum samples from methylmercury-poisoned rats.

Selenite (Se4+) has been found to counteract the neurotoxicity of methylmercury (MeHg) in MeHg-poisoned rats. However, Se4+ has narrow range between its toxic and beneficial effects. Nanoelemental selenium (SeNPs) was found to be less toxic than other forms of Se such as Se4+. In this study, the effects of SeNPs on the load of mercury (Hg) in rats were investigated. Hyphenated technique based on size-exclusion chromatography coupled with UV and inductively coupled plasma mass spectrometry (SEC-ICP-MS) detection and synchrotron radiation X-ray fluorescence spectroscopy (SR-XRF) were used to analyze the Hg-Se-containing proteins in the serum from MeHg-poisoned rats. The Hg-Se-containing fractions monitored by UV and ICP-MS were further characterized by MALDI-TOF-MS. Elevated serum Hg and Se levels were found in MeHg-poisoned rats after SeNPs treatment. Three main Hg-containing bands with molecular weights (MWs) of 25, 62 and 140 kDa were detected in the control samples. Treatment with SeNPs increased the Hg content in proteins at 62 and 170 kDa and decreased the Hg content at 25 kDa. The fraction with 25 kDa was assigned to metallothioneins (MTs), and fractions with 40 and 75 kDa were assigned to albumin. This study showed that the low-toxicity SeNPs could reduce the Hg load in the tissues and promote the formation of high molecular weight Hg- and Se-containing proteins in MeHg-poisoned rats.

Human Biological Monitoring of Mercury Through Hair Samples in China.

Mercury (Hg) is a global pollutant that affects environmental and human health. Considering the high toxicity of Hg, it is required to assess the exposure of Hg in human body for appropriate risk management. In this review paper, we summarized data obtained through regional and small-scaled human biomonitoring (HBM) program for Hg in hair samples in China, which can deliver scientific data to make decisions on environmental health policy. Besides, the major conclusions got from this study and perspectives for future works through these HBM program in China were presented. To better understand the current situation of hair Hg levels in China, a well-coordinated and designed national HBM program is urgently needed considering the requirements of the Minamata Convention on Mercury for effectiveness evaluation.

Effects of Farming Activities on the Biogeochemistry of Mercury in Rice-Paddy Soil Systems.

The biogeochemistry of mercury (Hg) in rice-paddy soil systems raises concerns, given that (1) the redox potential in paddy soil favors Hg methylation and (2) rice plants have a strong ability to accumulate methylmercury (MeHg), making rice an important source for MeHg exposure to humans. Therefore, all factors affecting the behavior of Hg in rice-paddy soils might impact Hg accumulation in rice, with its subsequent potential risks. As a typical wetland, paddy soils are managed by humans and affected by anthropogenic activities, such as agronomic measures, which would impact soil properties and thus Hg biogeochemistry. In this paper, we reviewed recent advances in the effects of farming activities including water management, fertilizer application and rotation on Hg biogeochemistry, trying to elucidate the factors controlling Hg behavior and thus the ecological risks in rice-paddy soil systems. This review might provide new thoughts on Hg remediation and suggest avenues for further studies.

Botanic Metallomics of Mercury and Selenium: Current Understanding of Mercury-Selenium Antagonism in Plant with the Traditional and Advanced Technology.

The antagonistic effect between mercury (Hg) and selenium (Se) is conclusively established in animals and human beings in the past decades. However, the underlying mechanisms of the interactions between Hg and Se in plants, as well as the metabolism of Hg-Se compounds in crops are still far from being understood. The botanic metallomics of Hg and Se mainly focuses on the translocation, transformation, and metabolism of Hg and Se in the environmental and botanic systems employing metallomics methods. An adequate understanding of the biological behavior of Hg and Se in plant is beneficial for sequestration of Hg and Se in soil-plant systems with high Hg and Se contamination. It can also provide a molecular mechanistic basis for Se supplementation in Se-deficient areas. Here, the key developments in current understanding of Hg and Se interactions in plants are reviewed. The metabolism and antagonism of Hg and Se in various plants, as well as the advanced analytical methods commonly used in this field, are summarized and discussed. As suggested, plant Hg and Se uptake, metabolism, and antagonism can be taken into account for detoxification and remediation strategies for the reduction of Hg and Se in the food chain.

Intestinal Methylation and Demethylation of Mercury.

Mercury (Hg) is a global pollutant, which is linked with different diseases. The methylation of Hg and demethylation of methylmercury (MeHg) in the environment were extensively studied and summarized; however, the transformation of Hg in the intestine is less presented. In this review, the research progress and the perspectives on the intestinal transformation of Hg were discussed. Studies found that MeHg could be formed when exposed to inorganic Hg by the gut microbiota in aquatic organisms, terrestrial invertebrates, and mammals, etc. hgcAB genes could be used as indicators for predicting Hg methylation potential. In vitro studies using fecal specimen, intestinal contents, and the isolated intestinal microbes confirmed the intestinal demethylation of MeHg. The investigation on the effects of Hg exposure to the abundance and diversity of intestinal microbes and their metabolites could shed light on the mechanism of the toxicity of Hg, especially the neurotoxicity of MeHg, which deserves further study.