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Background Osteosarcoma (OS) is the most common aggressive bone tumor in children and teenagers. Doxorubicin (DOX) is a chemotherapeutic drug for OS. This study aims to reveal the effects and underneath mechanism of DOX treatment in OS progression. Methods The expression of circular_0000006 (circ_0000006), microRNA-646 (miR-646) and brain-derived neurotrophic factor (BDNF) was detected by quantitative real-time polymerase chain reaction (qRT-PCR). BDNF protein expression was determined by western blot. Cell proliferation was illustrated by cell counting kit-8 (CCK-8) and cell colony formation assays. Cell migration and invasion were revealed by transwell migration and wound-healing assays and transwell invasion assay, respectively. Cell apoptosis was demonstrated by flow cytometry analysis. The binding relationship of miR-646 and circ_0000006 or BDNF was predicted by circRNA interactome and targetscan online database, respectively, and verified by dual-luciferase reporter assay. The effects of circ_0000006 knockdown on tumor growth in vivo were manifested by in vivo tumor formation assay. Results Circ_0000006 expression and the mRNA and protein levels of BDNF were dramatically upregulated, and miR-646 expression was effectively downregulated in OS tissues or cells compared with control groups. Circ_0000006 expression and BDNF protein expression were lower, and miR-646 expression was higher in DOX treatment groups than in control groups in OS cells. Circ_0000006 knockdown repressed cell proliferation, migration and invasion, whereas promoted cell apoptosis under DOX treatment in OS cells; however, these effects were attenuated by miR-646 inhibitor. Additionally, circ_0000006 sponged miR-646 to bind to BDNF. Circ_0000006 silencing suppressed tumor growth in vivo. Conclusion Circ_0000006 knockdown promoted DOX-mediated effects on OS development by miR-646/BDNF pathway, which provided a theoretical basis in treating OS with DOX.

As a typical alternative to perfluorooctanoic acid (PFOA), perfluoro-2-propoxypropanoic acid (GenX) has been detected worldwide in aquatic environment and attracted great concerns recently, but their adsorptive removal from water is not clear. In this study, the adsorption behavior and mechanism of GenX on granular activated carbon (GAC), powdered activated carbon (PAC), anion-exchange resins (IRA400 and IRA67) were compared. The particle size of activated carbon (AC) affected the initial adsorption rate but exhibited little influence on the adsorption capacity for GenX. The initial adsorption kinetics of GenX on the three granular adsorbents (GAC, IRA67 and IRA400) followed the intraparticle diffusion-controlled adsorption. IRA67 had the highest adsorption capacity of 3.22 mmol/g for GenX, higher than IRA400 (2.78 mmol/g) and much higher than the two ACs (0.79 mmol/g). When GenX was co-removed with perfluorooctanoic acid (PFOA) in competitive system, the adsorbed amounts of GenX on the four adsorbents decreased significantly, and adsorbed GenX was replaced by PFOA with increasing time. The small adsorbent size could speed up the replacement process, and the polyamine group on the resins was more prone to producing this effect than the quaternary ammonium group. PAC was more suitable for GenX removal at low pH, while IRA400 was better used at high solution pH. The spent AC and resins were successfully regenerated in the ethanol and NaCl solution, respectively, and their regeneration efficiency was significantly enhanced in hot water. The adsorption mechanisms including anion exchange, electrostatic interaction and hydrophobic interaction were involved in the GenX adsorption.

The historical use of aqueous film forming foams (AFFF) containing perfluoroalkyl substances (PFASs) for firefighting and training activities has resulted in groundwater contamination. The competitive adsorption of PFASs and the effect of co-existing compounds on the removal of PFASs by anion-exchange resins were studied in this study. Perfluorohexane sulfonate (PFHxS) was selected as the representative PFAS, and resin IRA910 was found to be effective for PFHxS removal. When PFHxS was co-removed with other PFASs in bisolute system, it replaced the adsorbed PFASs with shorter C-F chains on the IRA910, while perfluorooctanesulfonate (PFOS) was not replaced by PFHxS. The competitive adsorption among PFASs decreased in the order of PFOS > PFHxS > PFOA > PFBS>PFHxA > PFBA, closely related to the hydrophobicity and functional groups of PFASs. The nonionic organic compounds could not interfere with the PFHxS removal, while ionic ones can reduce the sorption amount and their influence to the sorption of PFHxS was concentration dependent. The presence of inorganic anions slightly decreased the removal efficiency of PFHxS and the influence of different inorganic anions was similar due to multiple effects including competitive anion, screening effect, and salting-out effect in the adsorption process.

Regeneration and reuse of spent activated carbon (AC) as well as recovery of the desorbed pollutants are challenging in the application of adsorption technology. In this study, the regeneration of perfluorooctanesulfonate (PFOS)-saturated coal-based granular AC by hot water and subsequent aeration method to enrich PFOS from eluent were investigated. The regeneration time, water temperature and solid-liquid ratio affected the regeneration efficiency of PFOS treated AC. PFOS was desorbed quickly from the AC within 30 min by hot water. High water temperature (92 °C) and low solid-liquid ratio (0.5) led to the highest desorption of 36.7% in one cycle (6 h). Over 90% PFOS on the spent AC was desorbed by 92 °C hot water with the solid-liquid ratio of 0.5 after six cycles. Subsequent experiments were conducted to enrich PFOS, and aeration of the regeneration eluent achieved the enrichment factors of 50.6–62.0 for PFOS at initial PFOS concentrations of 10–100 μg/L. The concentration of PFOS in the concentrated solution was 2.2 g/L following sequential sorption, regeneration and aeration treatments when the influent PFOS concentration was 2.7 μg/L.

Novel hydrated zirconium oxide (ZrO(OH)2) coated carbon nanotubes (CNTs) were prepared via a filtration-steam hydrolysis method, and were used to remove As(III) and As(V) from drinking water. This adsorbent was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The ZrO(OH)2 coated on the surface of CNTs was amorphous, and the coating thickness was in the range of 1–8 nm. The ZrO(OH)2/CNTs nanocomposite showed high adsorption for both As(III) and As(V) with the maximum adsorption capacities of 78.2 and 124.6 mg/g, respectively, according to the Langmuir fitting. The adsorption capacities of ZrO(OH)2/CNTs at the equilibrium concentration of 10 μg/L were 2.0 mg/g for As(III) and 7.2 mg/g for As(V) at pH 7, much higher than those of ZrO(OH)2 nanoparticles. Meanwhile, the adsorption rates of As(III) and As(V) on the ZrO(OH)2/CNTs were higher than the ZrO(OH)2 nanoparticles. The spent adsorbent can be regenerated by re-coating ZrO(OH)2 as the preparation method, and the adsorbed amounts of As(III) and As(V) on the ZrO(OH)2/CNTs changed little within six cycles. This ZrO(OH)2/CNTs nanocomposite shows a promising application potential for the removal of As(III) and As(V) from drinking water.

Adsorption by powder activated carbon (PAC) is recognized as an efficient method for the removal of perfluorinated compounds (PFCs) in water, while the poor separation of spent PAC makes it difficult for further regeneration, increasing the treatment cost significantly. In this study, an ultrafine magnetic activated carbon (MAC) consisting of Fe3O4 and PAC was prepared by ball milling to remove PFCs from water efficiently. Increasing the percentage of Fe3O4 and balling milling time decreased its adsorption capacity for perfluoroctane sulfonate (PFOS), whereas increased the magnetic separation property to some degree. The optimized MAC was prepared with a Fe3O4 to PAC mass ratio of 1:3 after ball milling for 2 h, and the adsorption equilibriums of all the four PFCs on the optimal MAC were reached within less than 2 h, with the adsorption capacities of 1.63, 0.90, 0.33 and 0.21 mmol/g for PFOS, perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS) and perfluorobutane sulfonate (PFBS), respectively. Increasing the solution pH hindered the adsorption of PFOS significantly when the pH was less than the zero potential point (around 6) of the MAC, due to the decreased electrostatic attraction. The spent MAC could be easily separated with a magnet and regenerated by a small volume of methanol, and the regenerated MAC could be reused for more than 5 time and remain stable adsorption capacity for PFOS after 3 cycles. This study provides useful insights into the removal of PFCs by separable magnetic PAC in wastewater.

Aqueous film-forming foams (AFFFs) used in fire-fighting are one of the main contamination sources of perfluorooctane sulfonate (PFOS) to the subterranean environment, requiring high costs for remediation. In this study, a method that combined aeration and foam collection was presented to remove PFOS from a commercially available AFFF solution. The method utilized the strong surfactant properties of PFOS that cause it to be highly enriched at air-water interfaces. With an aeration flow rate of 75 mL/min, PFOS removal percent reached 96% after 2 h, and the PFOS concentration in the collected foam was up to 6.5 mmol/L, beneficial for PFOS recovery and reuse. Increasing the aeration flow rate, ionic strength and concentration of co-existing surfactant, as well as decreasing the initial PFOS concentration, increased the removal percents of PFOS by increasing the foam volume, but reduced the enrichment of PFOS in the foams. With the assistance of a co-existing hydrocarbon surfactant, PFOS removal percent was above 99.9% after aeration-foam collection for 2 h and the enrichment factor exceeded 8400. Aeration-foam collection was less effective for short-chain perfluoroalkyl substances due to their relatively lower surface activity. Aeration-foam collection was found to be effective for the removal of high concentrations of PFOS from AFFF-contaminated wastewater, and the concentrated PFOS in the collected foam can be reused.