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Silver nanoparticles (AgNPs) are one of the most widely used NPs. Their adverse effects on either the host or its gut microbiota (GM) have been examined. Nevertheless, whether the GM plays any role in AgNP toxicity to the host remains unclear. In the present study, AgNPs were administered to mice by oral gavage once a day for 120 days. A significant dose-dependent accumulation of Ag in the liver was observed, with a steady state reached within 21 days. The AgNPs changed the structure of the GM, mainly with respect to microorganisms involved in the metabolism of energy, amino acids, organic acids, and lipids, as predicted in a PICRUST analysis. Effects of the AgNPs on liver metabolism were also demonstrated, as a KEGG pathway analysis showed the enrichment of pathways responsible for the metabolism of amino acids, purines and pyrimidine, lipids, and energy. More interestingly, the changes in GM structure and liver metabolism were highly correlated, evidenced by the correlation between ∼23% of the differential microorganisms at the genus level and ∼60% of the differential metabolites. This implies that the metabolic variations in liver as affected by AgNPs were partly attributable to NP-induced changes of GM structure. Therefore, our results demonstrate the importance of considering the roles of GM in the toxicity of NPs to the host in evaluations of the health risks of NPs.

Humic substances (HS) are the most abundant forms of natural organic matter on the earth surface. Comprised of decomposed plant and animal materials rich in carbon, oxygen, hydrogen, nitrogen, and sulfur complexes, HS facilitate global carbon and nitrogen cycling and the transport of anthropogenic contaminants. While it is known that HS also interact with organisms at different trophic levels to produce beneficial and harmful effects whether HS exert these biological effects through accumulation remains unknown. Current radiolabeling techniques, which only detect the amount of accumulated radiolabels, cannot visualize the transport and accumulation behavior of HS. Here, using a label-free method based on pump-probe microscopy, we show HS entered the protozoan

The release of silver ions (Ag+) is an important process in determining the environmental fate and toxic effects of silver nanoparticles (AgNPs), but the released Ag+ can be reduced to form new AgNPs in environments. Here the reduction of Ag+ by redox-active organic molecules to form AgNPs under different lighting and oxygen conditions was investigated using anthraquinonoe-2,6-disulphonate (AQDS) and nicotinamide adenine dinucleotide (NAD+) as representatives. In anaerobic environments, oxidized AQDS (AQDSox) and NAD+ failed to reduce Ag+ to form AgNPs, whereas reduced AQDS (AQDSred) and NAD+ (NADH) produced a concentration-dependent AgNP production pattern, underlining a key role of the redox state in Ag+ reduction by organics. The presence of O2 diminished the reducing capacity of NADH and AQDSred, probably due to their oxidation by O2. However, under UV light, the AgNP formation rate was dramatically enhanced in AQDS, independent of O2. Our results revealed that the Ag+ photoreduction was mainly attributed to the photoexcited AQDS, not the radical intermediates. For the complex organic humic acid (HA), and consistent with the phenomena in AQDS, the reduced HA (HAred) reduced Ag+ at a much faster rate than the native HA (HAox) in anaerobic and dark environments, and the amounts of AgNPs produced by HAred decreased in oxic environments. UV illumination enabled significant Ag+ reduction in both HAox and HAred, and O2 promoted the AgNP formation. Our study systematically revealed different Ag+-reduction pathways to form AgNPs, with an organic's redox state and environmental factors having a combined effect.

Despite their wide bioapplications, potential health risks of gold nanoparticles (AuNPs) remain unclear. As a determinant of their risks, AuNP accumulation within a cell population is subject to cell-to-cell heterogeneity. Methods to simultaneously quantify and visualize intracellular AuNPs at the single-cell level are, however, lacking. Here we developed a novel label-free technique, based on hyperspectral imaging with enhanced darkfield microscopy (HSI-DFM), to visualize and quantify AuNP accumulation at the single-cell level. The identification ability of the hyperspectral libraries derived from extra- and intracellular AuNPs was compared. The spectral number in the libraries was optimized to maximize their identification ability while minimizing the identification time. In addition, a filtration method was established to merge spectral libraries from different cell lines based on their similarity. The intracellularly accumulated AuNPs as determined by HSI-DFM well correlated with those detected by inductively coupled plasma mass spectrometry. This validation allowed us to calculate the intracellular concentration of AuNPs at the single-cell level and to monitor the accumulation kinetics of AuNPs in living cells. The label-free method developed herein can be applied to other types of AuNPs differing in their physicochemical properties as well as other NPs, as long as they are detectable by HSI-DFM.

Arsenic has been used for various purposes throughout human history, such as medicinal and industrial applications, while its health risks have only been gradually recognized in the 20th century and have raised global concerns since the 1990s. Reviewing the progress of arsenic research from a scientometric viewpoint is of great value and importance to predict future trends in arsenic studies. Unfortunately, such review is lacking, which could possibly lead to a biased understanding of the role of arsenic in human health. In this study, we collected 61,988 published literatures on arsenic research in the past 120 years from Web of Science, on which scientometric analysis using CiteSpace and subsequent review were conducted. Our scientometric-based review demonstrated the progress in the past 120 years of arsenic research and identified emerging trends in recent years, emphasizing the health risks posed by arsenic, arsenic applications, and their interaction. The information summarized in this study will shed light on the wise and extensive use of arsenic, which could be a double-edged sword in human health.

Microplastics (MPs) and nanoplastics (NPs) in the environment pose significant risks to organisms of different trophic levels. While the toxicity of MPs and NPs have been extensively investigated, it remains unknown whether these particles affect microbial transformation of organic pollutants. Here, we show that 20 and 100 nm polystyrene NPs (PS-NPs) can inhibit the transformation of tetrabromobisphenol A (TBBPA) by Gram-positive bacteriumiRhodococcus jostii/iin a concentration-dependent manner. We found that smaller PS-NPs were more inhibitory than larger ones and that both PS-NPs affected biotransformation in several ways. PS-NPs adsorbed TBBPA on their surface and reduced the bioavailable concentration of TBBPA for transformation byiR. jostii/i. Furthermore, PS-NPs induced oxidative stress, increased membrane permeability, and downregulatediO/i-methyltransferase enzymes that transform TBBPA into their methylated derivatives. Our results demonstrate that PS-NPs can impact microbial transformation of organic pollutants, and these effects should be accounted for in future environmental risk assessments.

Arsenic exists universally in freshwater and marine environments, threatening the survival of aquatic organisms and human health. To elucidate arsenic bioaccumulation and biotransformation processes in aquatic organisms, this review evaluates the dissolved uptake, dietary assimilation, biotransformation, and elimination of arsenic in aquatic organisms and discusses the major factors influencing these processes. Environmental factors such as phosphorus concentration, pH, salinity, and dissolved organic matter influence arsenic absorption from aquatic systems, whereas ingestion rate, gut passage time, and gut environment affect the assimilation of arsenic from foodstuffs. Arsenic bioaccumulation and biotransformation mechanisms differ depending on specific arsenic species and the involved aquatic organism. Although some enzymes engaged in arsenic biotransformation are known, deciphering the complicated synthesis and degradation pathway of arsenobetaine remains a challenge. The elimination of arsenic involves many processes, such as fecal excretion, renal elimination, molting, and reproductive processes. This review facilitates our understanding of the environmental behavior and biological fate of arsenic and contributes to regulation of the environmental risk posed by arsenic pollution.

The bioaccumulation of nanoplastics (NPs) has been intensively examined using the fluorescence-labeling technique. As the fluorescence intensity per particle is different for NPs with different physicochemical properties, it's hard to directly compare their bioaccumulation based on fluorescence. Therefore, how physicochemical properties may affect NPs' bioaccumulation remains unclear. In the present study, we chose polystyrene NPs (PSNPs) with the primary particle size of 70 nm (PS

The potential effects of engineered nanoparticles (NPs) on metal bioaccumulation in aquatic organisms have been the focus of increasing research attention. However, while NPs typically aggregate, the role of aggregation in NP-mediated metal bioaccumulation is largely unknown. The present study investigated the effects of polyacrylate-coated TiO

Carbon dots (CDs) are photoluminescent nanomaterials with wide-ranging applications. Despite their photoactivity, it remains unknown whether CDs degrade under illumination and whether such photodegradation poses any cytotoxic effects. Here, we show laboratory-synthesized CDs irradiated with light degrade into molecules that are toxic to both normal (HEK-293) and cancerous (HeLa and HepG2) human cells. Eight days of irradiation photolyzes 28.6-59.8% of the CDs to, Carbon dots have attracted much attention for biomedical applications but potential degradation and associated toxicity are still poorly understood. Here, the authors report on a study into the photo-degradation of carbon dots, the products produced and associated cytotoxicity.

Although nanoparticles' (NPs) toxicity has been intensively studied, their effects on bacterial ingestion by protozoans (as an important component of the microbial loop) is unknown. This study investigated the effects of NPs of different chemical composition [hematite (HemNPs), anatase (AnaNPs), and silica (SiNPs) NPs] and size [SiNPs with particle size of 20 (Si-20), 100 (Si-100), and 500 (Si-500) nm] on the ingestion of Escherichia coli by the protozoan Tetrahymena thermophila. Potential differences between pre- vs. co-exposure were also assessed. Pre-exposure to HemNPs had no effects on bacterial ingestion but the other NPs caused a significant inhibition, due to their inhibition of ATP synthesis and the down-regulation of phagocytosis-related genes (ACT1 and CTHB). Contrastively, co-exposure to HemNPs and Si-20 didn't affect bacterial ingestion while co-exposure to AnaNPs (Si-100 and Si-500) induced (inhibited) ingestion. The stimulatory effect of AnaNPs was due to their induction of an increase in the intracellular Ca concentration of T. thermophila whereas the inhibitory effects of Si-100 and Si-500 were attributable to ATP synthesis reduction, enhanced bacterial cell aggregation, and competition between the bacterial cells and the NPs. These findings provide insights into the mechanisms underlying the environmental risks of NPs.

Natural organic matter (NOM) that forms coronas on the surface of engineered nanoparticles (NPs) affects their stability, bio-uptake, and toxicity. After corona formation, a large amount of unbound NOM remains in the environment and their effects on organismal uptake of NPs remain unknown. Here, the effects of unbound NOM on the uptake of polyacrylate-coated hematite NPs (HemNPs) by the protozoan Tetrahymena thermophila were examined. HemNPs were well-dispersed without any detectable NOM adsorption. Kinetics experiments showed that unbound NOM decreased the uptake of HemNPs with greater inhibition at lower concentrations of the particles in the presence of NOM of higher molecular weight. The unbound NOM suppressed clathrin-mediated endocytosis but not the phagocytosis of HemNPs. Confirmation of these events was obtained using label-free hyperspectral stimulated Raman spectroscopy imaging and dissipative particle dynamics simulation. Overall, the present study demonstrates that unbound NOM can compete with HemNPs for internalization receptors on the surface of T. thermophila and inhibit particle uptake, highlighting the need to consider the direct effects of unbound NOM in bioapplication studies and in safety evaluations of NPs.

Bacterial accumulation of engineered nanoparticles (NPs) result in their transfer along the food chain. However, there are a lot of NPs not associated with bacteria. Whether bacteria, as representative biotic particles, influence the biological uptake of these non-associated NPs in aquatic ecosystems is unclear. In the present study, we examined the effects of four bacterial species on the uptake kinetics of polyacrylate-coated hematite nanoparticles (HemNPs) by the ciliate Tetrahymena thermophila. The HemNPs were well dispersed. Their adsorption on the bacteria was low with negligible uptake by T. thermophila through bacterial ingestion. This result demonstrated the feasibility of examining the effects of bacteria on the uptake of non-associated HemNPs. Our study further showed that all four bacterial species inhibited the uptake of HemNPs by T. thermophila; however, the effects of the bacterial cells on the physiological activities of the ciliate with respect to its uptake of HemNPs were negligible. In the absence of phagocytosis by T. thermophila, none of the bacteria inhibited HemNP uptake. This observation suggested that bacterial cells competed with the HemNPs for uptake via phagocytosis. Therefore, in evaluations of the environmental risks of NPs, their competition with biotic particles should be taken into account.

Certain engineered nanoparticles (NPs) have unique properties that have exhibited significant potential for promoting photosynthesis and enhancing crop productivity. Understanding the fundamental interactions between NPs and plants is crucial for the sustainable development of nanoenabled agriculture. Leaf mesophyll protoplasts, which maintain similar physiological response and cellular activity as intact plants, were selected as a model system to study the impact of NPs on photosynthesis. The mesophyll protoplasts isolated from spinach were cultivated with different NMs (Fe, Mn3O4, SiO2, Ag, and MoS2) dosing at 50 mg/L for 2 h under illumination. The potential maximum quantum yield and adenosine triphosphate (ATP) production of mesophyll protoplasts were significantly increased by Mn3O4 and Fe NPs (23% and 43%, respectively), and were decreased by Ag and MoS2 NPs. The mechanism for the photosynthetic enhancement by Mn3O4 and Fe is to increase the photocurrent and electron transfer rate, as revealed by photoelectrochemical measurement. GC-MS based single cell type metabolomics reveal that NPs (Fe and MoS2) altered the metabolic profiles of mesophyll cells during 2 h of illumination period. Separately, the effect of NPs exposure on photosynthesis and biomass were also conducted at the whole plant level. A strong correlation was observed with protoplast data; plant biomass was significantly increased by Mn3O4 exposure (57%) but was decreased (24%) by treatment of Ag NPs. The use of mesophyll protoplasts can be a fast and reliable tool for screening NPs to enhance photosynthesis for potential nanofertilizer use. Importantly, inclusion of a metabolic analysis can provide mechanistic toxicity data to ensure the development "safer-by-design" nanoenabled platforms.

Waterborne and dietborne exposure are both important sources for the accumulation of inorganic arsenic (iAs) in aquatic organisms. Although the waterborne toxicity of iAs has been extensively investigated, its dietborne toxicity has received little attention. The present study examined the acute and chronic toxicity of arsenate (iAsV) and arsenite (iAsIII) to the freshwater zooplankton species Daphnia magna under both waterborne and dietborne exposure scenarios. The bioaccumulation, speciation, and tissue and subcellular distributions of arsenic were analyzed to understand the mechanisms accounting for differences in toxicity related to different arsenic species, exposure scenarios, and exposure duration. The toxicity of iAs increased with exposure time, and iAsIII was more toxic than iAsV. Moreover, although dietborne iAs had no acute effect on D. magna, it incurred significant toxicity in the chronic-exposure experiment. Nevertheless, the toxicity of dietborne iAs was still lower than that of waterborne iAs regardless of the exposure duration. This difference was found to be caused by the lower bioaccumulation of dietborne iAs, its higher distribution in the gut and in the biologically detoxified subcellular fraction, and greater transformation to the less toxic dimethylarsinic acid. Overall, the dietborne toxicity of iAs should be considered when evaluating the environmental risks posed by arsenic.

Amorphous silica nanoparticles (AmSiNPs) are one of the most extensively produced NPs in the world. Nevertheless, the bioaccumulation kinetics of AmSiNPs, as an indicator of their toxicity, have rarely been examined, due to the lack of convenient methods of quantification. In this study, AmSiNPs of different sizes embedded with CdSeTe@ZnS–SiO2 quantum dots (QDs) were synthesized and the kinetics of their bioaccumulation in A549 human lung carcinoma cells were examined using the Cd in the QD core as the tracer. The toxicity of the embedded AmSiNPs was comparable to that of their coreless counterparts. In the bioaccumulation kinetics experiment, the internalization of AmSiNPs of two different size classes (20 and 100 nm) in A549 cells was significant. The Cd-based estimation of NP bioaccumulation was similar to that determined by direct Si-based quantification of both QD-embedded AmSiNPs and to their coreless counterparts. The uptake kinetics of the 20 and 100 nm AmSiNPs at different ambient concentrations were then investigated. Considering the uncertainty regarding the dose metric of NPs, their mass-, particle-number-, and surface-area-based uptake was determined. The difference in the uptake of NPs of different sizes was better explained by the surface-area-based metric. Overall, we developed a facile method to investigate the bioaccumulation kinetics of AmSiNPs. This method allows the environmental and biological behaviors of not only a single type but also a mixture of AmSiNPs to be examined if different Cd isotopes are applied in the core. The resulting information is essential in real applications and toxicity evaluation of AmSiNPs.

Microbial polyphosphate (polyP) production is vital to the removal of phosphate from wastewater. However, to date, engineered polyP synthesis using genetically accessible environmental bacteria remains a challenge. This study develops a simple solo medium-copy plasmid-based polyphosphate kinase (PPK1) overexpression strategy for achieving maximum intracellular polyphosphate accumulation by environmental bacteria. The polyP content of the subsequently engineered Citrobacter freundii (CPP) could reach as high as 12.7% of its dry weight. The biomass yield of CPP was also guaranteed because of negligible metabolic burden effects resulting from the medium plasmid copy number. Consequently, substantial removal of phosphate (Pi) from the ambient environment was achieved simultaneously. Because of the need for exogenous Pi for in vivo ATP regeneration, CPP could thoroughly remove Pi from synthetic municipal wastewater when it was applied for the “one-step” removal of Pi with a bench-scale sequence batch membrane ...

In aquatic ecosystems, the calcium (Ca) concentration varies greatly. It is well known that Ca affects the aggregation of nanoparticles (NPs) and thus their bioaccumulation. Nevertheless, Ca also plays critical roles in various biological processes, whose effects on NP accumulation in aquatic organisms remain unclear. In this study, the effects of Ca on the uptake of polyacrylate-coated hematite NPs (HemNPs) by the aquatic ciliate Tetrahymena thermophila were investigated. At all of the tested Ca concentrations, HemNPs were well dispersed in the experimental medium, excluding the possibility of Ca to influence HemNP bioaccumulation by aggregating the NPs. Instead, Ca was shown to induce the clathrin-mediated endocytosis and phagocytosis of HemNPs. Manipulation of the Ca speciation in the experimental medium as well as the influx and intracellular availability of Ca in T. thermophila indicated that HemNP uptake was regulated by the intracellular Ca level. The results of the proteomics analyses further showed that the binding of intracellular Ca to calmodulin altered the activity of proteins involved in clathrin-mediated endocytosis (calcineurin and dynamin) and phagocytosis (actin). Overall, the biologically inductive effects of Ca on NP accumulation in aquatic organisms should be considered when evaluating the environmental risks of NPs.

The potential effects of engineered nanoparticles (NPs) on metal bioaccumulation in aquatic organisms have been the focus of increasing research attention. However, while NPs typically aggregate, the role of aggregation in NP-mediated metal bioaccumulation is largely unknown. The present study investigated the effects of polyacrylate-coated TiO2 (anatase) NPs (AnaNPs) on Cd bioaccumulation in zebrafish. The Ca concentration in the experimental medium was manipulated to regulate AnaNP aggregation. At the low Ca concentration, the AnaNPs were well-dispersed and there was little bioaccumulation. Under this condition, Cd bioaccumulation was mainly via the uptake of free ions (Route 1), with only a minor contribution from NP-Cd complexes (Route 2). Therefore, AnaNPs decreased Cd bioaccumulation, as their inductive carrier effect could not offset the inhibition induced by the decrease in the free Cd ion concentration as a result of NP adsorption. At the high Ca concentration, the AnaNPs aggregated and their bioaccumulation increased. Accordingly, Cd bioaccumulation was equally accounted for by Routes 1 and 2 but the overall amount of Cd remained unchanged because the inductive effect of the AnaNPs offset their inhibitory effect. Thus, during risk evaluations of NPs, the contribution of aggregation to metal bioaccumulation should be considered.

Although the toxic effects of nanoparticles on aquatic organisms have been intensively investigated, less is known about the bioaccumulation kinetics of the particles as an indicator of toxicity. In the present study, we used a radiotracer-based method to examine the bioaccumulation kinetics of well-dispersible hematite nanoparticles (HemNPs) in the freshwater mixotrophic alga Euglena intermedia. Because nitrogen limitation of phytoplankton growth is common in aquatic ecosystems, we also compared the difference in nanoparticle accumulation by nutrient-enriched and nitrogen-depleted cells. HemNP accumulation in E. intermedia increased linearly with exposure time. More interestingly, nitrogen limitation induced the cell-surface adsorption and subsequent internalization of HemNPs. Both processes increased with increasing starvation time and with decreasing ambient nitrogen concentrations in the experimental medium. These inductive effects could be attributed to the increased irregularity/roughness of the E. intermedia cell surface and to an increase in cell-surface-attached polysaccharides of the nitrogen-depleted algal cells. Considering the ubiquity of phytoplankton nutrient limitation in many aquatic ecosystems, its impacts on the environmental behavior, effects, and fates of nanoparticles must be taken into account in ecosystem studies of nanoparticles.

Our previous study reported that the Ca-dependent aggregation of polyacrylate-coated TiO2 nanoparticles (PAA-TiO2–NPs) determines their routes of uptake by the waterflea Daphnia magna. Besides the effects of aggregation on NP bioaccumulation, how this process may influence the bioavailability of NP-adsorbed pollutants remains obscure. In the present study, the aggregation of PAA-TiO2–NPs was also adjusted through Ca. Then the accumulation and toxicity of Cd in D. magna were investigated in the presence and absence of the NPs. Although PAA-TiO2–NPs ameliorated Cd toxicity at both low and high Ca concentrations, the underlying mechanisms differed completely. At low Ca, the metal–NP complexes were accumulated by endocytosis and passive drinking, with both pollutants distributed throughout the daphnid. Nevertheless, Cd accumulation was reduced due to its rapid dissociation from the NPs during the endocytosis of the metal–NP complexes. At high Ca, the metal–NP complexes were actively ingested, Cd accumulation ...

The widespread use of nanoparticles (NPs) has drawn considerable attention because of their potential toxicity and the environmental consequences thereof. However, the effects of the exposure route and life stage of an organism on the bioaccumulation and toxicity of NPs are largely unknown. In the present study, we investigated the accumulation kinetics (uptake, assimilation, and efflux) and tissue distribution of waterborne and dietary hematite NPs (HemNPs) during three life stages (embryo, larva, and adult) of the zebrafish Danio rerio. For all zebrafish life stages, the waterborne accumulation of well-dispersed HemNPs increased linearly with exposure time but decreased after reaching a maximum. The increase in HemNPs accumulation followed the order embryo > larva > adult. Compared with the waterborne route, the dietary accumulation of HemNPs in larval and adult zebrafish fluctuated, reaching a maximum after each food refreshment and then decreasing until the next food addition. Similar to waterborne exposure, adult fish accumulated less dietary HemNPs than did larvae. Nevertheless, dietary HemNPs mostly accumulated in the intestinal tract, with smaller amounts in the truncus, head, and gills, as compared with their waterborne counterparts. Moreover, in the gonad no dietary HemNPs were detected whereas accumulation via waterborne HemNPs was significant. Despite the low assimilation efficiency of dietary HemNPs, biodynamic modeling showed that the diet was the main source of particle accumulation in zebrafish. Thus, both the life stage and the exposure route should be considered in evaluations of the environmental risks of NPs.

Microplastics, whether originating directly from industrial and household products or from the degradation of larger plastics, are currently of intense global concern. These particles are present in aquatic environments in high concentrations and may adversely affect aquatic organisms. An additional concern is the ability of microplastics to adsorb inorganic and organic pollutants and subsequently liberate them into marine and freshwater systems. In this review, we report on the occurrence and abundance of microplastics in the global aquatic environment. We then consider the accumulation (uptake, distribution, and elimination) of microplastics in aquatic organisms and the important factors that lead to bioaccumulation. The effects of microplastics on aquatic organisms of different trophic levels are also discussed. Several studies have shown that the size, shape, and surface physicochemical characteristics of microplastics are essential determinants of their biological effects. Finally, we examine the combined effects of microplastics and other pollutants, including persistent organic pollutants and heavy metals. Our review concludes by suggesting future lines of research based on the remaining knowledge gaps in microplastic research.

Rapid developments in nanotechnology have led to the release of substantial amounts of nanoparticles (NPs) into aquatic environments, where many types of biotic particles are present and could potentially interact with the NPs. Nevertheless, how biotic particles may affect the bioaccumulation and toxicity of NPs remains largely unknown. In the present study, we investigated the effects of the green alga Chlamydomonas reinhardtii on the accumulation kinetics (uptake, assimilation, efflux) and toxicity of polyacrylate-coated hematite NPs (HemNPs), using Daphnia magna as the test organism. As a biotic particle and daphnid food, C. reinhardtii reduced the accumulation and toxicity of HemNPs in D. magna. The HemNPs were well-dispersed with little adsorption to the alga. Their decreased accumulation could thus be partly explained by their low trophic transfer from the alga to the daphnid and by the inductive effects of the alga on HemNP efflux. However, the main cause was the direct inhibition of HemNP uptake from the water phase as a result of the reduced water-filtration activity of D. magna in the presence of C. reinhardtii. Overall, in bioaccumulation studies, the inhibitory effects of biotic particles on NP uptake from the water phase should be paid attention.

In the natural environment, the interactions of different types of nanoparticles (NPs) may alter their toxicity, thus masking their true environmental effects. This study investigated the toxicity of silver NPs (AgNPs) combined with hematite (HemNPs) or polystyrene (PsNPs) NPs toward the freshwater algae Chlamydomonas reinhardtii and Ochromonas danica. The former has a cell wall and cannot internalize these NPs, while the latter without a cell wall can. Therefore, the toxicity of AgNPs toward C. reinhardtii was attributed to the released Ag ions, while AgNPs had direct toxic effects on O. danica. Moreover, nontoxic HemNPs ameliorated AgNP toxicity toward C. reinhardtii, by decreasing the bioavailability of Ag ions through adsorption. Despite their role as Ag-ion carriers, HemNPs still reduced the toxicity of AgNPs toward O. danica by competitively inhibiting AgNP uptake. In both algae, Ag accumulation fully accounted for the combined toxicity of AgNPs and HemNPs. However, the combined toxicity of AgNPs and PsNPs was complicated by their significant individual toxicities and the synergistic interactions of these particles with the algae, regardless of differences in Ag accumulation. Overall, in environmental assessments, considerations of the combined toxicity of dissimilar NPs will allow more accurate assessments of their environmental risks.

To remove nitrate in wastewater treatment plant effluent, an aerobic denitrifier was newly isolated from the surface flow constructed wetland and identified as Pseudomonas mendocina strain GL6. It exhibited efficient aerobic denitrification ability, with the nitrate removal rate of 6.61 mg (N)&middot, L&minus, 1&middot, h&minus, 1. Sequence amplification indicated that the denitrification genes napA, nirK, norB, and nosZ were present in strain GL6. Nitrogen balance analysis revealed that approximately 74.5% of the initial nitrogen was removed as gas products. In addition, the response surface methodology experiments showed that the maximum removal of total nitrogen occurred at pH 7.76, C/N ratio of 11.2, temperature of 27.8 &deg, C, and with shaking at 133 rpm. Furthermore, under the optimized cultivation condition, strain GL6 was added into wastewater treatment plant effluent and the removal rates of nitrate nitrogen and total nitrogen reached 95.6% and 73.6%, respectively. Thus, P. mendocina strain GL6 has high denitrification potential for deep improvement of effluent quality.

Microplastics (MPs) are an environmental hazard of growing concern, including their potential toxic effects on the biota of different trophic levels. Nevertheless, the molecular mechanisms underlying MP-induced toxicity remain largely unknown. In the present study, Tetrahymena thermophila was exposed to polystyrene nanoplastics (PS-NPs) and the responses of this relatively sensitive ciliate were then followed using transcriptome analysis together with several other verification methods. The results showed that PS-NPs perturbed calcium (Ca) homeostasis, by inducing the inositol-1,4,5-trisphosphate-dependent liberation of Ca from the endoplasmic reticulum into the cytosol. The high cytosolic concentration of Ca induced Ca accumulation in mitochondria, which increased mitochondrial permeability and the generation of reactive oxygen species, finally leading to growth inhibition. Such toxicity is the so-called direct effects of PS-NPs. By contrast, PS-NPs also inhibited the activity of multixenobiotic resistance transporter, by down-regulating the ATP-binding cassette transporter genes Abcb15 and Abcc52. This additional effect may alter cellular responses to other pollutants and implicates PS-NPs in the risks to the organism posed by subsequent toxic exposures, which was named as the indirect effects of PS-NPs. Our study highlights the importance of considering both direct and indirect biological effects of MPs in evaluations of their environmental and health risks.

A new design of a pilot-scale constructed wetland managed with a membraneless microbial fuel cell (CW-MFC) was tested here to assess its potential to generate electricity and remove pollutants under different operating conditions. In the CW-MFC, the cathode was half vertically inserted into the matrixes of constructed wetland (CW) and half exposed to the air to benefit from both surrounding wetland plant growth and the atmosphere thereby ensured its demand for oxygen as well. A series of periodic and regular voltages were obtained after four cycles of wastewater treatment in the batch flow experiment with influent chemical oxygen demand (COD) 228 mg/L. The maximum voltage output (0.588 ± 0.01 V) for these four cycles lasted for 34, 35, 37 and 42 h, respectively. A steady set of maximum voltage (0.529 V) outputted over a wetland operation period of 15 days in the continuous flow experiment with the hydraulic retention time of 10 h. The maximum power density was 9.6 mW/m 2 and the maximum current density was 55 mA/m 2 according to the cathode area. Under batch flow mode, the COD removal rate was 91.2% and the outstanding removal rates of total nitrogen, ammonium nitrogen and total phosphorus appeared ranging between 95% and 99% while electricity generated from the CW-MFC. The influence of temperature on electricity generation was investigated and the result showed that the maximum voltage output values were inversely relative to the lasting duration of the voltage. Influent COD concentrations also affected the highest voltage output and continuous electricity generation of CW-MFC, and the higher initial COD concentration elevated the electricity generation. Thus, the new CW-MFC has high potentials not only of bioelectricity generation but also of the high pollutant removal rates.

We studied arsenite (iAs(III)) accumulation, oxidation, and toxicity in the freshwater green alga Chlamydomonas reinhardtii under nutrient-enriched (+NP), phosphorus-limited (-P), and nitrogen-limited (-N) conditions. The -P alga (55.1 μM) had a Michaelis constant (Kd) for uptake approximately one tenth of the +NP (419 μM) and -N (501 μM) cells, indicating iAs(III) uptake inhibition by extracellular phosphate. This conclusion was supported by the hyperbolic reduction in iAs(III) uptake rate (V) from 9.2 to 0.8 μmol/g-dw/h when the extracellular phosphate concentration went up from 0 to 250 μM. The maximal iAs(III) uptake rate (Vmax) of the -N alga (24.3 μmol/g-dw/h) was twice as much as that of the +NP (12 μmol/g-dw/h) and -P (8.1 μmol/g-dw/h) cells. It implies that more arsenic transporters were synthesized under the -N condition. Once accumulated, iAs(III) was oxidized and a higher proportion of arsenate (iAs(V)) was observed at lower [As]dis or under nutrient-limited conditions. Nevertheless, iAs(III) oxidation mainly occurred outside the cells with the extent of oxidation reciprocal to [As]dis. Based on the logistic modeling of the concentration-response curves in the +NP, -P, and -N toxicity tests, iAs(III) had an [As]dis-based EC50 of 1763, 13.1, and 1208 μM and an intracellular arsenic concentration based EC50 of 35.6, 28.8, and 195 μmol/g-dw, respectively. Higher iAs(III) toxicity to the -P cells occured because of their increased iAs(III) accumulation, whereas the underlying mechanisms why the -N alga was more tolerant need to be further revealed. Overall, both N and P had remarkable effects on the behavior and effects of iAs(III), which cannot be disregarded in the biogeochemical cycling research of arsenic.

Electrolysis combined with biochar (BC) was used in a constructed wetland to intensify nitrogen (N) and phosphorus (P) removal from wastewater simultaneously. A pilot study was conducted using an electrolysis-integrated, BC-amended, horizontal, subsurface-flow, constructed wetland (E-BHFCW). The research results showed that both electrolysis and BC substrate played important roles in the intensified, constructed wetland. The electrolysis combined BC substrate greatly enhanced the removal rates of nitrate (49.54%) and P (74.25%) when the E-BHFCW operated under the lower current density of 0.02 mA/cm2 and an electrolysis time of 24 h. Improved N removal was accomplished with the electrochemical denitrification of iron cathodes; the autotrophic denitrification bacteria appeared to remove nitrate which was adsorbed on the BC substrate because hydrogen gas was produced by cathodes in the E-BHFCW. Less nitrate was taken directly by wetland plants and microbes. The in-situ formation of ferric ions from a sacrificial iron anode, causing P chemical sedimentation and physical adsorption, improved P removal. BC, modified by iron ions from an iron anode to adsorb the nitrate and P, was a good material to improve effluent water quality. It can also serve as a favorable microbial carrier to bio-transform nitrate to N gas. This is because there were abundant and diverse bacterial communities in the biofilm on the BC substrate in the E-BHFCW. Thus, electrolysis integrated with BC in a constructed wetland is a novel, feasible and effective technique for enhancing wastewater N and P removal.

Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardants in the world but it is also a pollutant of global concern. In the present study, we studied the transformation of 14C-labeled TBBPA by a polychlorinated-biphenyl-degrading bacterium, Rhodococcus jostii RHA1 (RHA1), under oxic conditions. During the 5-day incubation, TBBPA was biotransformed rapidly first to its monomethyl ether MeO-TBBPA and then to its more hydrophobic but less toxic dimethyl ether diMeO-TBBPA. The biotransformation followed pseudo-first-order decay kinetics, with a half-life of TBBPA of 0.32 days and only 0.6% of the initially added amount being mineralized. Considering the frequent co-occurrence of TBBPA with heavy metals in the natural environment, we also investigated the effects of three heavy metals (Cd, Cu, and Fe) on the transformation of TBBPA by strain RHA1. While TBBPA transformation was not significantly altered by Cd, it was accelerated by Cu and Fe, presumably due to the effects of these two essential metals on O-methyltransferase activity. Overall, the present study showed that RHA1 is an effective transformer of TBBPA and that certain essential metals, including Cu and Fe, promote the transformation.

Imaging and quantification of nanoparticles in single cells in their most natural condition are expected to facilitate the biotechnological applications of nanoparticles and allow for better assessment of their biosafety risks. However, current imaging modalities either require tedious sample preparation or only apply to nanoparticles with specific physicochemical characteristics. Here, the emerging hyperspectral stimulated Raman scattering (SRS) microscopy, as a label-free and nondestructive imaging method, is used for the first time to investigate the subcellular distribution of nanoparticles in the protozoan Tetrahymena thermophila. The two frequently studied nanoparticles, polyacrylate-coated α-Fe2 O3 and TiO2 , are found to have different subcellular distribution pattern as a result of their dissimilar uptake routes. Significant uptake competition between these two types of nanoparticles is further discovered, which should be paid attention to in future bioapplications of nanoparticles. Overall, this study illustrates the great promise of hyperspectral SRS as an analytical imaging tool in nanobiotechnology and nanotoxicology.

Recent studies have revealed that not only fish but also rice consumption may significantly contribute to human exposure to mercury (Hg) in Asian countries. It is therefore essential to assess dietary exposure to Hg in rice and its associated health risk. However, risk assessments of Hg in rice in non-contaminated areas are generally lacking in Asian countries. In the present study, Hg concentrations were measured in rice samples collected from markets and supermarkets in Suzhou, a typical city in Eastern China. In addition, the rice ingestion rates (IR) were assessed via a questionnaire-based survey of Suzhou residents. The data were then used to assess the risk of Hg exposure associated with rice consumption, by calculating the hazard quotient (HQ). Hg contents in rice samples were well below the national standard (20 μg/kg), ranging from 1.46 to 8.48 ng/g. They were also significantly (p > 0.05) independent of the area of production and place of purchase (markets vs. supermarkets in the different districts). Our results indicate a low risk of Hg exposure from rice in Suzhou (HQ: 0.005–0.05), despite the generally high personal IR (0.05–0.4 kg/day). The risk of Hg associated with rice consumption for Suzhou residents was not significantly affected by the age or sex of the consumer (p > 0.05). Overall, our results provide a study of human exposure to Hg in rice in Chinese cities not known to be contaminated with Hg. Future studies should examine Hg exposure in different areas in China and in potentially vulnerable major food types.

When nanoparticles can enter a unicellular organism directly, how may they affect the bioaccumulation and toxicity of other pollutants already present in the environment? To answer this question, we conducted experiments with a protozoan Tetrahymena thermophila. The well-dispersed polyacrylate-coated TiO2 nanoparticles (PAA-TiO2-NPs) were used as a representative nanomaterial, and Cd as a conventional pollutant. We found that PAA-TiO2-NPs could get into Tetrahymena cells directly. Such internalization was first induced by low concentrations of Cd, but later suppressed when Cd concentrations were higher than 1 μg/L. Considering its significant adsorption on PAA-TiO2-NPs, Cd could be taken up by T. thermophila in the form of free ion or metal-nanoparticle complexes. The latter route accounted for 46.3% of Cd internalization. During the 5 h depuration period, 4.34-22.1% of Cd was excreted out, which was independent of the concentrations of intracellular Cd and PAA-TiO2-NPs. On the other hand, both free and intracellular Cd concentrations only partly predicted its toxicity at different levels of PAA-TiO2-NPs. This may have resulted from PAA-TiO2-NPs' synergistic effects and the distinct subcellular distribution of Cd taken up via the two routes above. Overall, we should pay attention to the carrier effects of nanoparticles when assessing their environmental risks.

Our previous study reported that the Ca-dependent aggregation of polyacrylate-coated TiO

The bioaccumulation kinetics of thioglycolic acid stabilized CdTe quantum dots (TGA-CdTe-QDs) in a freshwater alga Ochromonas danica was comprehensively investigated. Their photoluminescence (PL) was determined by flow cytometry. Its cellular intensity increased hyperbolically with exposure time suggesting real internalization of TGA-CdTe-QDs. This hypothesis was evidenced by the nanoparticle uptake experiment with heat-killed or cold-treated cells and by their localization in the vacuoles. TGA-CdTe-QD accumulation could further be well simulated by a biokinetic model used previously for conventional pollutants. Moreover, macropinocytosis was the main route for their internalization. As limited by their diffusion from the bulk medium to the cell surface, TGA-CdTe-QD uptake rate increased proportionally with their ambient concentration. Quick elimination in the PL of cellular TGA-CdTe-QDs was also observed. Such diminishment resulted mainly from their surface modification by vacuolar biomolecules, considering that these nanoparticles remained mostly undissolved and their expulsion out of the cells was slow. Despite the significant uptake of TGA-CdTe-QDs, they had no direct acute effects on O. danica. Overall, the above research shed new light on nanoparticle bioaccumulation study and would further improve our understanding about their environmental behavior, effects and fate.

Lake Taihu is the third largest freshwater lake in China with severe eutrophication issues. However, it remains ambiguous how its phytoplankton growth is limited by various nutrients in different seasons. A series of bottle-enrichment assays in Meiliang Bay was thus performed once a month from July, 2011 to June, 2012 in the present study. The initial chlorophyll a concentration and phytoplankton cell density ranged from 4.70 to 34.6 μg/l and from 1.25×10 6 to 6.72×10 8 cells/l with three peaks in July, November, and March. Although Cyanophyta was dominant (30.9–99.2 percent) in most cases, other phyla like Chlorophyta , Bacillariophyta , and Cryptophyta could account for as much as 69.1 percent of total phytoplankton in cold seasons. The microcystin-LR content in the particulate phase followed a similar seasonal pattern as Cyanophyta . It further went up exponentially with the proportion of cyanobacteria in phytoplankton suggesting more toxigenic species and (or) upregulated microcystin synthesis when the contribution of Cyanophyta was enhanced. On the other hand, the dissolved concentrations of various nitrogen and phosphorus species reached their maxima in late spring and autumn, respectively. According to its growth response to nutrient addition, phytoplankton in Meiliang Bay was restricted by nitrogen in August, October, and November. No nutrient limitation occurred in July, September, and April, whereas phosphorus deficiency prevailed in the other months. Overall, nutrient limitation in Lake Taihu and possibly other aquatic ecosystems worldwide may be more dynamic than what we thought before, which should be considered to eliminate eutrophication.

The aim of this work was to evaluate the utilization potential of a newly isolated indigenous aerobic denitrifier, Pseudomonas stutzeri strain T1, for nitrogen removal from the eutrophic Lake Taihu in China. The strain was capable of conducting heterotrophic nitrification-aerobic denitrification and had both excellent nitrate and ammonium removal without nitrite build-up. The characteristics of P. stutzeri strain T1 were studied under different cultural conditions. Furthermore, under the optimized cultivation conditions, strain T1 was added into the water samples from Lake Taihu, the ammonium and nitrate removal rates of the strain reached to 60% and 75%, respectively. Via adding this strain, the water qualities of the sample ameliorated from Grade V to Grade II. Thus, the strain T1 should be an useful biological tool to remediate eutrophic lakes and do not meet acclimation problems.

In order to assess the overall risk posed by engineered nanoparticles (ENPs), the biological effects of this emergent pollutant to aquatic ecosystems must be evaluated. We present findings from studies conducted with a diversity of ENPs (metallic, quantum dots) on a variety of freshwater and marine algae (phytoplankton) illustrating both their direct and indirect effects. We show that in general, while the surface properties of ENPs govern their aggregation behavior and ionic strength controls their dissolution, exopolymeric substances (EPS) produced by algae determine their potential to be toxic and thereby movement through the water column and food web. The production of EPS reduces the impact of ENPs (bioavailability and toxicity) and/or their ions on cellular activities of algae. It does not however directly reduce the aggregation and/or solubility of ENPs but rather affects their stability. Complicating understanding of these interactions is the great assortment of surface coatings for ENPs. This per...