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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.

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.

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