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The quantitative analysis of nanoparticles (NPs) in the environment is significantly important for the exploration of the occurrence, fate, and toxicological behaviors of NPs and their subsequent environmental risks. Some protocols have been recommended for the separation and extraction of NPs that are potentially dispersed in complex environmental matrixes, e.g. sediments and soils, but they remain limited. However, certain factors that may significantly affect extraction efficiency have not been comprehensively explored. In this study, on the basis of the single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) technique, a simple standardized protocol for separating and analyzing metal-containing NPs in sediment samples was developed. On consideration of the extraction efficiencies of indigenous NPs (Ti- and Zn-NPs) and spiked NPs (Ag- and Au-NPs) in sediments, sedimentation with a settling time of 6 h is recommended for the separation of NPs and large particles, and the optimal sediment to water ratio, ultrasonication power, time, and temperature are 0.4 mg/mL, 285 W, 20 min, and 15-25 °C, respectively. On the basis of the optimized method, the recoveries of spiked Ag and Au-NPs were 71.4% and 81.1%, respectively. The applicability of the optimal protocols was verified, and TOC was proved to be an important factor controlling the separation and extraction of NPs in environmental samples. The separation and extraction of NPs in elevated TOC samples can be improved by increasing the ultrasonication power, time, and temperature.

The presence of sulfate-reducing bacteria (SRB) can reduce the bioavailability of toxic metal ions (e.g., Ag+) to plants via mediating the formation of metal sulfide precipitates; however, it remains largely elusive if SRB can also affect the phyto-uptake of metal nanoparticles (e.g., Ag0-NPs). In the current study, the bioavailability of Ag0-NPs to a model wetland plant, Scirpus triqueter, was investigated in the presence/absence of SRB. Comparative experiments were conducted using 0.01–10 mg L−1 Ag0-NPs and silver ions. In addition to quantifying the total dissolved Ag concentrations, we analyzed the average sizes and particle concentrations of Ag-containing NPs (Ag-NPs) in plant tissues, including both roots and stems, after the designated treatments. The results show that although the presence of SRB can reduce the uptake of total Ag by 37% during the exposure of the plant to Ag ions, it can significantly enhance the uptake of total Ag during exposure of the plant to Ag0-NPs, likely by transforming Ag0-NPs into Ag-sulfide NPs with smaller particle sizes. Transmission electron microscopy data revealed that biogenic secondary Ag-sulfide particles smaller than 10 nm in size form in the vicinity of pristine Ag0-NPs. These NPs are likely generated from the parent Ag0-NPs via a dissolution–diffusion–sulfidation process. Moreover, the phyto-uptake of Ag0-NPs of various sizes (i.e., 20, 40 and 80 nm) in the presence/absence of SRB also confirmed a size dependent pattern, with more silver identified in the plant exposed to smaller Ag-NPs. The combined results suggest that the enhanced bioavailability of Ag-NPs to Scirpus triqueter in the presence of SRB is mainly attributed to the formation of secondary biogenic NPs with minute size. This result points to the importance of complex, coupled interactions between aqueous solutions, bacteria, plants, and labile NPs.

Quantitative characterization of nanoparticles (NPs) in marine shellfish is critical to understanding the risks of bio-accumulation. Based on single particle (sp)ICP-MS and electron microscopy, a standardized protocol was developed to extract Ag, Au, and indigenous Ti-containing NPs from mussels. The optimal parameters are: dry sample extraction with tetramethylammonium hydroxide (TMAH), 5% (v/v) final concentration of TMAH, extraction at 25 ℃ for 12 h, and separation by centrifugation (3000 rpm for 5 min). The particle number recoveries of spiked Ag and Au NPs were 88 ± 0.9% and 95 ± 1.1%, respectively, while Ti-containing NPs had a particle number concentration of 8.2 × 106 particles/mg and an average size of 70 nm in tested mussels. Furthermore, titanium oxide NPs, including rutile, anatase, and Magneli phases (TixO2x-1) were found ubiquitously in 10 shellfish based on the optimal method. The particle number concentrations and average sizes of the Ti-containing NPs were 2.1 × 106–8.4 × 106 particles/mg and 70–80 nm, respectively. These Ti-containing NPs, such as TiO2, accounted for about half of the Ti mass in shellfish, indicating that marine shellfish may be a significant sink for Ti-containing NPs.

Nanoparticles (NPs) promote the horizontal gene transfer (HGT) of plasmid-borne antibiotic resistance genes (ARGs) in pure bacterial culture, but the impact of NPs on ARG dissemination in the natural environment remains unknown. This study focused on the impact of ZnO NPs on the variation in ARGs and the association among ARGs, mobile genetic elements (MGEs) and microbial communities in an estuarine aquatic environment by taking the Yangtze Estuary as a representative area. The present study showed that the abundances of total ARGs increased after exposure to ZnO NPs, particularly at low doses (0.2 and 1 mg L−1). Relatively low and environmentally relevant concentrations of ZnO NPs likely induced the selection of sul1, tetA, ermB and qnrS, whereas a high concentration (10 mg L−1) of ZnO NPs was more selective for sul2 and tetW. After normalization of the abundances of ARGs exposed to NPs to those of the corresponding blanks, the ARGs in the DH samples with relatively high salinity and relatively low NP doses showed the highest normalized values by the end of the exposure period, which indicated the high dissemination potential of ARGs in relatively brackish water. A significant positive correlation was found between ARGs and MGEs (Tn916/1545 and intI1), which indicated the high potential of ARG dissemination via HGT in estuarine waters after exposure to ZnO NPs. The response of the microbial community to ZnO exposure was dose- and time-dependent at both the phylum and genus levels. Although the absolute abundance of microbes showed a decreasing trend after exposure to ZnO NPs, the absolute abundance values normalized to the corresponding blanks generally showed a trend consisting of an initial inhibition followed by a rebound. A redundancy analysis showed that the microbial community contributed more to the variation in ARGs in estuarine waters after exposure to ZnO NPs than MGEs and dissolved Zn2+. A network analysis evaluated the possible host bacteria for the detected ARGs, and the results revealed that some of these bacteria were associated with multiple ARGs and might pose a high risk for the dissemination of ARGs in estuarine environments.

Sulfate-reducing bacteria (SRB), which are ubiquitous in intertidal sediments, play an important role in global sulfur and carbon cycles, and in the bioremediation of toxic metalloids/metals. Pollution from human activities is now a major challenge to the sustainable development of the intertidal zone, but little is known about how and to what extent various anthropic and/or natural factors affect the SRB community. In the current study, based on the dsrB gene, we investigated the SRB community in intertidal sediment along China's coastline. The results showed that dsrB gene abundances varied among different sampling sites, with the highest average abundance of SRB at XHR (near the Bohai Sea). The SRB community structures showed obvious spatial distribution patterns with latitude along the coastal areas of China, with Desulfobulbus generally being the dominant genus. Correlation analysis and redundancy discriminant analysis revealed that total organic carbon (TOC) and pH were significantly correlated with the richness of the SRB community, and salinity, pH, sulfate and climatic parameters could be the important natural factors influencing the composition of the SRB community. Moreover, metals, especially bioavailable metals, could regulate the diversity and composition of the SRB communities. Importantly, according to structural equation model (SEM) analysis, anthropic factors (e.g., population, economy and industrial activities) could drive SRB community diversity directly or by significantly affecting the concentrations of metals. This study provides the first comprehensive investigation of the direct and indirect anthropic factors on the SRB community in intertidal sediments on a continental scale.

The occurrence of antibiotic resistance genes (ARGs) and their associated environmental factors in estuaries are poorly understood. In this study, we comprehensively analyzed ARGs in both water and sediments from inlet to outlet of the Yangtze Estuary, China. The relative abundances of ARGs were higher in the turbidity maximum zone (TMZ) than other sites, implying that suspended particulate matter (SPM) was the major reservoir for ARGs in water. ARGs showed an increasing trend from inlet to outlet in sediments. Positively correlation between intI1 and sul1 in both water and sediments indicated that sul1 may be regulated by intI1. Correlation analysis and redundancy analysis showed that the spatial variations of estuarine ARGs were positively correlated with sample properties (e.g., temperature, SPM, pH) and chemical pollutants (e.g., heavy metals and antibiotic residues), among which chemical pollutants were the major drivers for the ARG distribution in both water and sediments.

This study was designed to investigate the characteristics of bacterial communities in intertidal sediments along the Yangtze Estuary and their responses to environmental factors. The results showed that bacterial abundance was significantly correlated with salinity, SO42 − and total organic carbon, while bacterial diversity was significantly correlated with SO42 − and total nitrogen. At different taxonomic levels, both the dominant taxa and their abundances varied among the eight samples, with Proteobacteria being the most dominant phylum in general. Cluster analysis revealed that the bacterial community structure was influenced by river runoff and sewerage discharge. Moreover, SO42 −, salinity and total phosphorus were the vital environmental factors that influenced the bacterial community structure. Quantitative PCR and sequencing of sulphate-reducing bacteria indicated that the sulphate reduction process occurs frequently in intertidal sediments. These findings are important to understand the microbial ecology and biogeochemical cycles in estuarine environments.

Nanoparticle (NP) assessment in sludge materials, although of growing importance in eco- and biotoxicity studies, is commonly overlooked and, at best, understudied. In the present study, sewage sludge samples from across the mega-city of Shanghai, China were investigated for the first time using a sequential extraction method coupled with single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) to quantify the abundance of metal-containing NPs in the extraction fractions and transmission electron microscopy to specifically identify the nanophases present. In general, most sludges observed showed high concentrations of Cr, Cu, Cd, Ni, Zn, and Pb, exceeding the maximum permitted values in the national application standard of acid soil in China. NPs in these sludges contribute little to the volume and mass but account for about half of the total particle number. Based on electron microscopy techniques, various NPs were further identified, including Ti-, Fe-, Zn-, Sn-, and Pb-containing NPs. All NPs, ignored by traditional metal risk evaluation methods, were observed at a concentration of 10

Understanding the behavior and risk of nanoparticles (NPs) in the aquatic environment is currently limited by the lack of quantitative characterization of NPs in the environmental matrices, such as sediments. In this study, based on the single particle (SP)-ICP-MS technique, metal-containing NPs, including Ti- and Zn-containing NPs, were analyzed in sediments taken along the Yangtze Estuary. Combined with the traditional sequential extraction method that has been widely used for metal risk assessment, different single extraction methods were used to understand the association of NPs with different chemical fractions in sediments and their potential environmental implications. Ti-containing NPs, with an average size of 81 nm, ranged from 3.02 × 107 parts/mg to 9.61 × 107 parts/mg, and Zn-containing NPs, with an average size of 41 nm, ranged from 2.47 × 106 parts/mg to 1.21 × 107 parts/mg. Both correlation and redundancy analyses showed that particle concentrations of Ti-containing NPs in sediment were significantly correlated to the Ti-containing NPs in the residual fraction and salinity, indicating that Ti-containing NPs in sediments may be dominated by Ti-containing NPs in the residue fractions of sediments. Large amounts of these NPs may be released from the residual fraction that has been considered to be not bioavailable and “environmentally safe” in the traditional environmental risk assessment of metals in sediments. Zn-containing NPs, mostly associated with carbonates, were positively correlated to all the bioavailable fractions of Zn in sediments, suggesting that these NPs may be largely presented in the bioavailable fraction. This study showed that, vast numbers of NPs with minute sizes were present in estuarine sediments, and that they were associated with different chemical fractions with different potential environmental risks. The study findings call for further research to update the traditional risk assessment method.

Many studies have examined the acute toxicity of nanoparticles (NPs) towards model bacteria. In this study, we report the time-dependent effects of ZnO NPs on native, selected Zn-resistant and dominant bacteria in estuarine waters. An initial inhibition of bacterial growth followed by a recovery at 24 h was observed, and this rebound phenomenon was particularly notable when the raw water samples were treated with relatively high ZnO NP concentrations (1 and 10 mg/L).By comparing the groups treated with Zn2+, Zn2+ was shown to largely explain the acute cytotoxic effect of ZnO NPs on bacteria in raw waters. Furthermore, similar to the native bacteria, especially the dominant bacteria, the viability of Escherichia coli (E. coli) decreased with the increasing treatments time and the concentrations of ZnO NPs in water with different salinities. Moreover, the expression of Zn-resistance genes including zntA and zntR in E. coli suggested that the Zn-resistance system in E. coli can be activated to defend against the stress of Zn2+ released from ZnO NPs, and salinity may promote this process in estuarine aquatic systems. Thus, the effect of ZnO NPs on bacteria in estuarine water bodies is likely determined by the synergistic effect of environmental salinity and dissolved Zn ions. As such, our findings are of high relevance and importance for understanding the ecological disturbances caused by anthropogenic NPs in estuarine environments.

In the contaminated coastal sediments, variations of microbial community can reflect the impact of anthropogenic activities. The identification, evaluation and monitoring of the potential bio-indicator species and biomarker communities are vital for the ecological studies in sedimentary environments. Based on the high-throughput sequencing, the microbial communities were characterized in the sediments along the Yangtze Estuary and its coastal area. The results showed that the structure and composition of microbial communities varied greatly among different sampling sites at the phyla level, especially for Euryarchaeota. Metabolic pathway and quantitative PCR analyses suggested that the methane metabolism-related microbes were mainly included in the phylum of Euryarchaeota. Elevated abundances of methane metabolism-related microbes were found at Shidongkou (SDK) and Wusongkou (WSK), where microbes were seriously impacted by the wastewater treatment plant (WWTP) effluent and urban runoff. By comparing with the Euryarchaeota in WWTP sludge, the relatively high abundance of Euryarchaeota in sediment at SDK may be mainly related to the massive growth of indigenous species, promoted by anthropogenic nutrients. Moreover, redundancy discriminant analysis and correlation analysis revealed that methanogens and methanotrophs mainly respond to the nutrients and metals, such as total organic carbon, total phosphorus, total nitrogen, SO42-, NO2-, NH4+, Cr, and Zn, which were often related to human activities. Network analyses showed that the species related to the metabolism of methane may play a vital role in the interassociation among different microbial communities. Therefore, methanogens, methanotrophs and their community compositions could be considered as potential bio-indicator species and biomarker communities, indicating anthropogenic activities in the sediments along the Yangtze Estuary and its coastal area.

Antibiotics resistance genes (ARGs) are considered as an emerging pollutant among various environments. As a sink of ARGs, a comprehensive study on the spatial and temporal distribution of ARGs in the estuarine sediments is needed. In the present study, six ARGs were determined in sediments taken along the Yangtze Estuary temporally and spatially. The sulfonamides, tetracyclines and fluoroquinolones resistance genes including sul1, sul2, tetA, tetW, aac(6')-Ib, and qnrS, were ubiquitous, and the average abundances of most ARGs showed significant seasonal differences, with relative low abundances in winter and high abundances in summer. Moreover, the relative high abundances of ARGs were found at Shidongkou (SDK) and Wusongkou (WSK), which indicated that the effluents from the wastewater treatment plant upstream and inland river discharge could influence the abundance of ARGs in sediments. The positive correlation between intI1 and sul1 implied intI1 may be related to the occurrence and propagation of sulfonamides resistance genes. Correlation analysis and redundancy discriminant analysis showed that antibiotic concentrations had no significant correlation to their corresponding ARGs, while the total extractable metal, especially the bioavailable metals, as well as other environmental factors including temperature, clay, total organic carbon and total nitrogen, could regulate the occurrence and distribution of ARGs temporally and spatially. Our findings suggested the comprehensive effects of multiple pressures on the distribution of ARGs in the sediments, providing new insight into the distribution and dissemination of ARGs in estuarine sediments, spatially and temporally.

Ubiquitous in the aquatic environment, sulphate-reducing bacteria (SRB) are considered one of the dominant microorganisms involved in the degradation of sulphate. This study focused on the spatial and temporal distributions of SRB in the Scirpus triquter rhizosphere sediments with a comparison to non-rhizosphere sediments and evaluated the implication of SRB to the bioavailability of metals in the Yangtze Estuary. The results showed that taking dsrB as the target gene, SRB abundances in rhizosphere sediments were significantly higher than those in non-rhizosphere sediments (P

Biofilms are ubiquitous throughout aquatic environments and they are thought to promote the acquisition and dissemination of antibiotic resistant genes (ARGs). This study focused on the occurrence and distribution of five types of ARG in naturally-occurring biofilms, in comparison to associated sediment and water samples, from the Yangtze Estuary, which borders the meta-city of Shanghai, China. The detection frequency and abundances of most ARGs showed the following order: biofilm > sediment > water, which can be attributed to a high level of antibiotics and metals that can accelerate the generation and propagation of ARGs in biofilms. Most of ARG abundances were contributed by extracellular DNA (eDNA) in biofilm and sediment samples. ARGs (sul1, sul2, tetA and tetW) in eDNA were significantly correlated with TOC in both biofilm and sediment samples. Furthermore, both intracellular DNA-associated ARGs per gram of microbial biomass carbon (MBC) and eDNA-associated ARGs per gram of non-MBC and were higher in biofilms than sediments, and the partitioning coefficients of ARGs in eDNA between biofilm and water were higher than those between sediment and water. Our results provide new insight for evaluating the occurrence and abundance of ARGs in aquatic environments, confirming that biofilms are a significant sink for ARGs in the estuarine environment.