Influence of organic matters on the adsorption-desorption of 1,2-dichloroethane on soil in water and model saturated aquifer.

1,2-Dichloroethane (1,2-DCA) is a typical organic chlorinated compound largely utilized in chemical manufacturing and industrial production and also a common pollutant in organically contaminated sites. The adsorption of 1,2-DCA on soil grains significantly influences its environmental fate and removal process. This study investigated the influence of fulvic acid (FA) and humic acid (HA) on the adsorption-desorption of 1,2-DCA in solid-liquid interfaces in water or constructed porous media. Experimental findings demonstrated the influence of organic matter on the adsorption of 1,2-DCA at the solid-water interface. 1,2-DCA adsorption increased in the FA or HA-treated soils when organic matter was present on the solid surfaces. The 1,2-DCA adsorption in the mixture of FA and HA was slightly lower than that in single organic acids, depending on the binding of FA and HA to the soil grains/colloids. Basic conditions reduced the adsorption of 1,2-DCA on soils, whereas acidic conditions enhanced adsorption due to the increased interactions via adsorption sites and hydrogen bonds. Conversely, the presence of organic matter in solutions (liquid phase in constructed porous media) will reduce the adsorption of 1,2-DCA on solid surfaces and increase the transport in the model aquifer. The combination of FA, HA, and rhamnolipids is helpful for the removal of 1,2-DCA from solid surfaces. Additionally, because of the enhanced desorption, the risk of 1,2-DCA contamination in groundwater can be increased when the organic matter or surfactant is present in the liquid phase if the eluent is not collected. This study helps to better understand the cooperative interaction of soil organic matter and chlorinated hydrocarbons at solid-water interfaces and the environmental fate and potential removal strategies of chlorinated hydrocarbons in contaminated sites.

Investigating the use of Aspergillus niger fermentation broth as a washing treatment for arsenic and antimony co-contaminated soil.

High concentrations of arsenic and antimony contamination in soil are a potential risk to the ecological environment and human health. Soil washing can effectively and permanently reduce the soil contamination. This study used Aspergillus niger fermentation broth as a washing agent to remove As and Sb from contaminated soil. Characterization of organic acids in the fermentation broth by high-performance liquid chromatographic (HPLC) and chemically simulated leaching experiments revealed that oxalic acid played a significant role in removing As and Sb from the soil. The effect of washing conditions on the metal removal rate of Aspergillus niger fermentation broth was investigated by batch experiments, and the optimal conditions were determined: no dilution, pH 1, L/S ratio 15:1, and leaching at 25 °C for 3 h. The soils were washed three times under optimal conditions, with 73.78%, 80.84%, and 85.83% removal of arsenic and 65.11%, 76.39%, and 82.06% removal of antimony, respectively. The results of metal speciation distribution in the soil showed that the fermentation broth could effectively remove As and Sb on amorphous Fe/Al hydrous oxides in soil. The analysis of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) of soils before and after washing showed that the washing of Aspergillus niger fermentation broth had a minor effect on the structural changes of soils. After washing, soil organic matter and soil enzyme activity were increased. Thus, Aspergillus niger fermentation broth shows excellent potential as a washing agent for removing As and Sb from soils.

Effects of foliar applications of Brassinolide and Selenium on the accumulation of Arsenic and Cadmium in rice grains and an assessment of their health risk.

Arsenic and cadmium pose a potential health risk to human beings via rice grain consumption. In the current study, a pot experiment was conducted to evaluate the effect of Br (5 mM and 20 mM) and Se (1 mM) at rice tillering and filling stages on Cd and As accumulation in rice grain and their health risk indices. The results showed that Br or Se applications at different stages of rice improved the photosynthesis, reduce MDA content in flag leaves by 17.41%-38.65%, increased rice biomass and grain yield by 10.50%-29.94% and 10.50%-36.56%, and enhanced grain N and P uptake by 3.25%-34.90%, and 22.98%-72.05%, respectively. Applications of Br and Se effectively decreased Cd and As concentration in rice grain by 31.74%-86.97% and 16.42%-81.13% respectively. Compared to the individual treatment, combined 20 mM Br and 1 mM Se at the filling stage showed the lowest accumulation of As (0.149 mg·kg-1) and Cd (0.105 mg·kg-1) in grain, and its health risk index was below the acceptable limits (HRI < 1). This implies that application of Br and Se at the filling stage is a promising strategy for the safe production of rice in As and Cd co-contaminated regions.

In this study, foliar applications of Br and Se at the grain filling and tillering stage demonstrate their effect on As and Cd accumulation. The findings showed that Br and Se resulted in the Se concentration in grains reaching the Se-enriched level, and the accumulation of As and Cd was the lowest. Furthermore, the application of Br and Se decreased lipid peroxidation, promoted N and P uptake, and increased the rate of photosynthesis in the rice plants, which resulted in increasing rice growth and grain yield. The HRI of heavy metals was below the acceptable limits after application of Br and Se.

Application of Exogenous Iron Alters the Microbial Community Structure and Reduces the Accumulation of Cadmium and Arsenic in Rice (Oryza sativa L.).

Cadmium (Cd) and arsenic (As) contamination of soil has been a public concern due to their potential accumulation risk through the food chain. This study was conducted to investigate the performance of ferrous sulfate (FeSO4) and ferric oxide (Fe2O3) nanoparticle (Nano-Fe) to stabilize the concentrations of Cd and As in paddy soil. Both Fe treatments led to low extractable Cd and the contents of specifically sorbed As contents, increased (p < 0.05) the Shannon index and decreased (p < 0.05) the Simpson diversity indices compared with the control. Nano-Fe increased the relative abundances of Firmicutes and Proteobacteria and decreased the abundances of Acidobacteria and Chloroflexi. Moreover, the addition of both forms of Fe promoted the formation of Fe plaque and decreased the translocation factor index (TFs) root/soil, TFs shoot/root, and TFs grain/shoot of Cd and As. These results suggest that exogenous Fe may modify the microbial community and decrease the soil available Cd and As contents, inhibit the absorption of Cd and As by the roots and decrease the transport of Cd and As in rice grains and the risk intake in humans. These findings demonstrate that soil amendment with exogenous Fe, particularly Nano-Fe, is a potential approach to simultaneously remediate the accumulation of Cd and As from the soil to rice grain systems.

Hydrophobic features of EPS extracted from anaerobic granular sludge: an investigation based on DAX-8 resin fractionation and size exclusion chromatography.

The hydrophobic fractionation of extracellular polymeric substances (EPS) extracted from anaerobic granular sludge was performed on the DAX-8 resin (two elution pH conditions, i.e., pH 2 and pH 5 were tested). The impact of seven different EPS extraction methods on EPS hydrophobicity features was assessed. The results showed that the extraction methods and bulk solution pH influenced dramatically the biochemical composition of the EPS, and in turn, the hydrophobicity determined. Besides, EPS extracting reagents i.e., formaldehyde, ethanol, sodium dodecyl sulfate (SDS), and Tween 20 not only introduced extra carbon content in the total organic carbon (TOC) measurement but also interacted with the DAX-8 resin. By comparing the apparent molecular weight (aMW) distribution of untreated and pH-adjusted EPS samples, more complete EPS aMW information was preserved at pH 5. Thus, elution at pH 5 was preferred in this study for the qualitative analysis of EPS hydrophobic features. The hydrophobic fraction of EPS retained by the resin at pH 5 was ascribed to a wide aMW range, ranging from >440 to 0.3 kDa. Within this range, EPS molecules ranging from 175 to 31 kDa were mostly retained by the DAX-8 resin, which indicates that these EPS molecules are highly hydrophobic.

Structural characterization and biosorption of exopolysaccharides from Anoxybacillus sp. R4-33 isolated from radioactive radon hot spring.

The structure characteristics and biosorption behaviors of heavy metals on a novel exopolysaccharide, which was secreted by the thermophilic Anoxybacillus sp. R4-33 isolated from a radon hot spring in China, were investigated. We purified the EPS-II from the culture medium of strain Anoxybacillus sp. R4-33 using a DEAE Sepharose and Sephadex G-200 column. The results of partial acid hydrolysis, gas chromatography, infrared spectrum, and nuclear magnetic resonance analysis showed that EPS-II was a heteropolysaccharide, composed of D-mannose and D-glucose as its principal monosaccharide composition in the relative proportions 1:0.45. Batch adsorption processes were conducted to characterize the kinetics, equilibrium, and mechanisms of the biosorption process of Zn(II) and Cd(II) from aqueous solution. Sorption experiments confirmed that 1.9783 mg Zn(II) and 1.4095 mg Cd(II) were adsorbed per gram EPS-II at pH 6.0, respectively. The equilibrium data was described by two isotherm models (Langmuir and Freundlich) and two kinetics models (pseudo-first order and pseudo-second order). Freundlich model provided the better correlation of Zn(II) biosorption data, while Langmuir model did to Cd(II). Pseudo-second-order kinetic equation could depict the biosorption kinetics of tested heavy metals. The EPS-II would be a potential candidate in the exopolysaccharide bioresource.