Aquatic ecosystems are ubiquitously polluted and deteriorated by micro/nanoplastics (MPs/NPs) and their associated hydrophobic organic contaminants (HOCs). However, the bioavailability of MPs/NPs and their associated HOCs remains largely unknown. This study employs passive dosing systems to study the bioavailability of differently-sized MPs (3 and 20 μm)/NPs (80 nm) and their associated polycyclic aromatic hydrocarbons (PAHs) to Daphnia magna, a model species in aquatic ecosystem. At constant concentrations of freely dissolved PAHs, the presence of MPs/NPs raises the immobilization of D. magna to 71.1-80.0%, far higher than their counterparts caused by PAHs (24.4%) or MPs (20.0-24.4%)/NPs (15.5%). It demonstrates that the MPs/NPs-associated PAHs are bioavailable, acting as a key contributor (37.1-50.0%) for the overall immobilization. Interestingly, although the immobilization of D. magna caused by MPs is higher than NPs, the bioavailability of MPs/NPs-associated PAHs declines with plastic size. Such a trend is due to the fact that MPs are actively ingested but hardly egested; while NPs are passively ingested and rapidly egested, leading to a continuous and higher accessibility of NPs-associated PAHs to D. magna. These findings clarify an integrated role of ingestion and egestion in controlling the bioavailability of MPs/NPs and their associated HOCs. Further, this study suggests that MPs/NPs-associated HOCs should be primarily concerned in chemical risk assessment in aquatic ecosystem.
The rapid developments of quantum dots (QDs)-based nanoagents for imaging tumor and tracking drug delivery have been proven to be reliable nanodiagnostic techniques. Although abundant types of QD nanoagents have been developed for fighting against cancer, it still is a challenge to control their quality and achieve prefect repetition due to the complicated synthetic steps. The precise intermolecular self-assembly (SA) may afford a facile and low-cost strategy for this challenge. Herein, a pH and H2O2 dual-sensitive Sb–cyclodextrin (CD)–doxorubicin (DOX) molecule was designed to construct a QD-based theranostic prodrug (named as Sb–CD–DOX–ZAISe/ZnS) via host–guest strategy (1st SA strategy), in which QDs water-transfer and drug-uploading were integrated well. That is, the nano-prodrug (NPD) inherited highly luminescent properties from "host" QDs for bioimaging, as well as environment sensitivities from "guest" Sb–CD–DOX for drug release. Experimental results indicate that the Sb–CD–DOX–ZAISe/ZnS exhibited effectively passive tumor-targeting and could provide clear imaging for malignant tumors in metaphase or advanced stages; meanwhile, after coating with folic acid (FA) through electric attraction (2nd SA strategy), the final Sb–CD–DOX–ZAISe/ZnS@FA NPD showed expected pH-controlled negative-to-positive charge reversal ability and a better curative effect compared with free DOX. Hence, fabricating nanocomposites by highly efficient self-assembly strategies is favorable toward inorganic nanoparticles-based prodrug delivery system for tumor-targeting theranostic.
CdS hollow spheres of about 25 nm average diameter and about 5 nm shell thickness can be easily synthesized in an aqueous solution of polyglycol. It was found that the polyglycol had a significant influence on the formation of the CdS hollow spheres, because when the experiments were carried out in the absence of polyglycol, only solid particles were formed. High-resolution transmission electron microscopy (HRTEM) shows the shell of the CdS hollow spheres is formed by a layer of primary CdS particles. The Brunauer–Emmett–Teller (BET) surface area of the CdS hollow spheres calculated from the N2 adsorption isotherm is 98.2 m2 g−1, which is much larger than the value of about 49.8 m2 g−1 calculated for the surface area of solid spheres. Compared with previous reports, the prepared hollow spheres have a small diameter, a large surface area and a thin shell. The photoluminescence (PL) spectrum of the CdS hollow spheres at 220 nm excitation shows two sharp emission peaks centered ∼493 nm and ∼530 nm which may be ascribed to the near band edge emission arising from the recombination of excitons and/or shallow trapped electron–hole pairs. Electrogenerated chemiluminescence (ECL) from the CdS hollow spheres and its first application to sensing H2O2 were studied. The H2O2 sensor based on ECL from the CdS hollow spheres had much better responses than those from CdS solid nanoparticles and had good stability.
A series of ZnSe nanocrystals was synthesized in the range of pH 6.5−11.5 in aqueous solution by using glutathione (γ-glutamyl-cysteinyl-glycine, GSH) as ligand. The photoluminescence quantum yields (PLQYs) of the ZnSe nanocrystals were dependent on the pH of the reaction solutions, which increased from 0.5 to 23% as the pH increased from 6.5 to 11.5. It is identified that Zn2+ primarily coordinates with thiol group of the cysteine residual at low pH (6.5−8.3); then, the deprotonated amino group of the glutamyl residue also contributed to the coordination at medium pH (8.3−10.3). With increasing pH to >10.3, N atom of the amide bond further took part in the coordination after its deprotonation. As a result, the growth rate of the ZnSe nanocrystals increased with increasing pH, indicating the improved activity of the Zn2+ precursors with increased pH. At pH <10.3, the products were identified to be ZnSe nanocrystals with low PLQY (<2%). At pH >10.3, the as-prepared nanocrystals were identified to have ZnSe/ZnS core/shell structure with higher PLQY (>8%). It is likely that coordination of Zn2+ with the N atom of the amide bond not only affects the activity of the Zn2+ precursor but also promotes the release of sulfur from GSH, thus resulting in the formation of ZnSe/ZnS core/shell nanocrystals with higher PLQY.
In order to investigate the community structure of ammonia oxidizing bacteria (AOB) in wastewater treatment plants and the influence of treatment process and system scale on AOB community. We investigated AOB communities in activated sludges collected from 9 wastewater treatment systems, using specific PCR followed by terminal restriction fragment length polymorphism (T-RFLP), cloning, and sequencing of amoA genes. The T-RFLP fingerprints analysis shows that there are some differences among the AOB community structures from different wastewater treatment systems, and the dominant terminal restriction fragments (T-RFs) are 354, 491 and 291 bp. The T-RFLP profiles and cluster analysis may also indicate the AOB structures are slightly affected by the treatment process, while they are influenced by the system scale to some extent. Phylogenetic analysis of cloned amoA gene shows clearly that all the dominant AOB in the systems were Nitrosomonas spp., not Nitrosospira spp.. The reason may be explained as that Nitrosomonas spp. have higher micromax, than Nitrosomonas spp.. This growth advantage may favor the Nitrosomonas spp. rather than Nitrosomonas spp. being prevail in activated sludge.
In recent years, the partial nitritation and anaerobic ammonium oxidation (PN/A) process has been widely appreciated by many countries around the world. As an autotrophic nitrogen removal process, this process can save more than 60% of the aeration energy consumption, reduce 80% of the residual sludge yield, and do not need to add additional carbon sources. However, this process is faced with several kinds of problems. This paper summarizes several effects of operating parameters on the inhibition of NOB in municipal wastewater treatment, implications of the reactor configuration and operation, and fixed film processes vs. suspended growth systems. The fixed film processes based on Anammox granular sludge and AOB flocculent sludge are alternative. Finally, a new strategy of continuous flow PN/A process with partial nitrification flocculent sludge and Anammox granular sludge was proposed.
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