Molecular characterization on the fractionation of organic phosphorus induced by iron oxide adsorption using ESI-FT-ICR MS.

The interaction between organic phosphorus (OP) and iron oxide significantly influences the phosphorus cycle in the natural environment. In shallow lakes, intense oxidation-reduction fluctuations constantly alter the existing form of iron oxides, but little is known about their impact on the adsorption and fractionation of OP molecules. In this study, electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS) was used to investigate the fractionation of OP from alkali-extracted sediment induced by crystalline goethite and amorphous ferrihydrite adsorption at a molecular scale. The results showed that ferrihydrite and goethite both exhibited high OP adsorption, and the adsorption amount decreased as the pH increased. The adsorption kinetics matched the pseudo-second-order equation. The ESI-FT-ICR MS analysis showed that 91 P-containing formulas were detected in the alkaline-extracted sediment solution. Ferrihydrite and goethite adsorbed 51 and 24 P-containing formulas, respectively, with adsorption rates of 56.0 % and 26.4 %. Ferrihydrite could adsorb more OP compounds than goethite, but no obvious molecular species selectivity was observed during the adsorption. The P-containing compounds, including unsaturated hydrocarbons-, lignin/carboxyl-rich alicyclic molecule (CRAM)-, tannin-, and carbohydrate-like molecular compounds, were more suitable for iron oxide adsorption. The double bond equivalence (DBE) is a valuable parameter that indicates OP fractionation during adsorption, and P-containing compounds with lower DBE values such as lipid- and protein-like molecular were prone to remain in the solution after adsorption. These research results provide insights into the biogeochemical cycling process of P in the natural environment.

Sources and hydrogeochemical processes of groundwater under multiple water source recharge condition.

Ecological water replenishment (EWR) is an essential approach for improving the quantity and quality of regional water. The Chaobai River is a major river in Beijing that is replenished with water from multiple sources, including reclaimed water (RW), the South-North Water Transfer Project (SNTP), reservoir discharge (RD). The effects of multiple water source recharge (MWSR) on groundwater quality remain unclear. In this study, hydrochemical ions, isotopes (δ2H-H2O, δ18O-H2O, δ15N-NO3-, and δ18O-NO3-), mixing stable isotope analysis in R (MixSIAR), and hydrogeochemical modeling were used to quantify the contributions and impacts of different water sources on groundwater and to propose a conceptual model. The results showed that during the period before reservoir discharge, RW and SNTP accounted for 38 %-41 % and 54 % of the groundwater in their corresponding recharge areas, respectively. The groundwater in the RW recharge area contained high levels of Na+ and Cl- leading to the precipitation of halite, and was the main factor for the spatial variation in groundwater hydrochemical components. The surface water changed from Na·K - Cl·SO4 type to Ca·Mg - HCO3 type which was similar to groundwater after reservoir discharge. RD accounted for 30 % of the groundwater; however, it did not change the hydrochemical type of groundwater. Dual nitrate stable isotopes and MixSIAR demonstrated that RW was the primary source of NO3- in groundwater, contributing up to 76-89 %, and reservoir discharge effectively reduced the contribution of RW. δ15N-NO3- or δ18O-NO3- in relation to NO3-N suggests that denitrification is the main biogeochemical process of nitrogen in groundwater, whereas water recharge from the SNTP and RD reduces denitrification and dilutes NO3-. This study provides insights into the impact of anthropogenically controlled ecological water replenishment from different water sources on groundwater and guides the reasonable allocation of water resources.

New insights into the mechanism of phosphate release during particulate organic matter photodegradation based on optical and molecular signatures.

Phosphate release from particulate organic matter (POM) dominates phosphorus (P) cycling in aquatic ecosystems. However, the mechanisms underlying P release from POM remain poorly understood because of complex fractionation and analytical challenges. In this study, the release of dissolved inorganic phosphate (DIP) during POM photodegradation was assessed using excitation-emission matrix (EEM) fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). POM in suspension was significantly photodegraded under light irradiation, concomitantly with the production and release of DIP in the aqueous solution. Chemical sequential extraction revealed that organic phosphorus (OP) in POM participated in photochemical reactions. Moreover, FT-ICR MS analysis revealed that the average molecular weight of P-containing formulas decreased from 374.2 to 340.1 Da. Formulas containing P with a lower oxidation degree and unsaturation were preferentially photodegraded, generating oxygen-enriched and saturated formula compounds, such as protein- and carbohydrate-like P-containing formulas, benefiting further utilization of P by organisms. Reactive oxygen species played an important role in the photodegradation of POM, and excited triplet state chromophoric dissolved organic matter (3CDOM*) was mainly responsible for POM photodegradation. These results provide new insights into the P biogeochemical cycle and POM photodegradation in aquatic ecosystems.

Hydrochemical evolution characteristics and genesis of groundwater under long-term infiltration (2007-2018) of reclaimed water in Chaobai River, Beijing.

The reuse of reclaimed water (RW) for river ecological restoration in global water-shortage regions has inevitably brought some potential risks for groundwater. However, little is known about the effects of reclaimed water on the hydrochemical evolution of groundwater especially under long-term infiltration conditions. Herein, 11-years monitoring data (2007-2018) of reclaimed water and groundwater were adopted to analyze the characteristics and genesis of groundwater hydrochemical evolution under long-term infiltration of reclaimed water from Jian River to Chaobai River in Beijing. The results showed that the hydrochemical components in groundwater totally performed a significant increase in Na+, Cl-, and K+and decrease in Ca2+, Mg2+, and HCO3- concentration after long-term infiltration of reclaimed water. Meanwhile, a significant hydrochemical evolution difference between the groundwater of Jian River and Chaobai River was observed. In Jian River, the hydrochemical type in groundwater shifted gradually from HCO3-Ca·Mg to the type of HCO3·Cl-Na·Ca approaching reclaimed water. In contrast, the hydrochemical evolution in the Chaobai River shows an obvious opposite trend from HCO3-Ca·Mg to HCO3·Cl-Na·Mg and finally deviating reclaimed water type of Cl·HCO3·SO4-Na. PHREEQC simulation indicated that the differences in hydrochemical evolution were mediated synergically by sediment thickness and geochemical processes (e.g. mixing and sulfate reduction). In such mediators, thinner sediment and strong mixing in the Jian River were confirmed to be the genesis of groundwater hydrochemical evolution progressively approaching reclaimed water. Different from the Jian River, multiple regression analyses revealed that the genesis of groundwater hydrochemical evolution in the Chaobai River was divided into two stages according to the increase of sediment thickness. Reclaimed water quality and infiltration amount are the leading proposed cause in the initial stage (2007-2008) due to thinner sediment formation, contributing 53.5% and 29.8% within the 95% confidence interval, respectively. Subsequently, the rise in sediment thickness is proved to play a crucial role in groundwater hydrochemical evolution trend away from reclaimed water (2009-2018), with a contribution of 41.6% within the 95% confidence interval. It is mainly attributed to the reduced reclaimed water infiltration rate and favorable sulfate reduction conditions. These findings advance our understanding on groundwater hydrochemical evolution under long-term infiltration of reclaimed water and also guide future prediction of evolution trends.

Molecular insight into the release of phosphate from dissolved organic phosphorus photo-mineralization in shallow lakes based on FT-ICR MS analysis.

Dissolved organic phosphorus (DOP) is a key factor in the water eutrophication process because of its high potential bioavailability and inorganic phosphate (Pi) compensation ability through bio- and photo-mineralization. However, the research on the characterization and transformation of DOP is insufficient owing to their complex composition. This study investigates the release of dissolved Pi from DOP photo-mineralization in Lake Dong based on Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. The results showed that the photo-release of dissolved Pi is spatially heterogeneous in Lake Dong and is consistent with the distribution of DOP concentration. The FT-ICR MS results showed that the simulated irradiation decreased the relative abundance (RA) of the DOP molecular formulae with higher molecular weight (MW) and higher double bond equivalence values (DBE), while the RA of DOP molecular formulae with lower MW and lower DBE value increased or remained. Besides, the total RA of lipid-like formulae increased from 49.09% to 55.90%, while the oxy-aromatic-like formulae decreased from 50.91% to 44.10%, suggesting that simulated irradiation would influence the potential bioavailability of DOP. As the main photolysis medium during DOP photo-mineralization, the hydroxyl radicals (∙OH) are mainly derived from dissolved organic matter (DOM) compared to the nitrate (NO3-) and iron ion (Fe3+) in Lake Dong. These results are important in understanding the ability and mechanism of DOP photo-mineralization and provide suggestions for cycling phosphorus in eutrophic shallow lakes.

Multiple optimizations of recombinant plasmid for improving expression of Hepatitis B core antigen in Escherichia coli.

Hepatitis B core antigen (HBcAg) can self-assemble into virus-like particles (VLPs) when expressed in Escherichia coli. We optimized the different of the expression plasmid pBV220, including the ribosome bind site (RBS), spacer region, promoter and replication origin (ori), as well as the hbc gene dosage, to enhance HBcAg transcription and translation in E. coli. The optimized construct with a customized RBS6, 6 nt spacer, T7 promoter and pUCori significantly increased the levels of HBc36GFP fusion protein to 3.4-folds compared to the control. Thereafter, we substituted hbc36gfp gene with different copies of the hbc gene and tested the effects of gene dosage on HBcAg expression. The HBcAg-VLPs yield obtained using an engineered strain with three copies of hbc was 842.1 ± 46.8 µg/mL, which was 2.2-folds higher compared to that in the control strain. Thus, our study provides a simple and effective strategy for improving HBcAg expression in E. coli. Since the HBcAg-VLPs are promising carriers for presenting foreign antigen epitopes, an in vitro expression system that can generate high levels of HBcAg-VLPs can serve as a promising tool for developing novel HBV vaccines and drugs.

Photo-induced phosphate release during sediment resuspension in shallow lakes: A potential positive feedback mechanism of eutrophication.

Dissolved phosphate (Pi) can be released during resuspended sediments exposed to sunlight. However, the significance of this phenomenon in the process of eutrophication is not clear. In this study, the behavior of photo-induced Pi release during sediment resuspension in shallow lakes with the different trophic states was investigated. The amount of photo-induced Pi release in the sediment resuspension from Lake Liangzi, Lake Dong, Lake Tangxun and Lake Longyang in China was 0.013, 0.019, 0.032, and 0.048 mg/L, respectively, and increased as the trophic states of the lakes increased. The results of phosphorus speciation analysis showed that the phosphate monoester in the particulate phosphorus is the organic phosphorus species participated in the photochemical reaction. The steady-state concentration of hydroxyl radical (OH) in the sediment resuspension also increased along with the trophic states of lakes increased and dissolved organic matter (DOM), nitrate, and Fe3+ presented in sediment resuspension were the main photosensitizers for OH production. All these results indicate that the increase of trophic states of lakes leads to the accumulation of organic phosphorus and OH, resulting in more dissolved phosphate photo-released, which accelerate the eutrophication process in a form of positive feedback.

Distribution of organic phosphorus species in sediment profiles of shallow lakes and its effect on photo-release of phosphate during sediment resuspension.

In this work, the distribution of organic phosphorus (Po) species in sediment profiles of five shallow lakes was analyzed and its effect on the photo-release of dissolved phosphate (Pi) was investigated during sediment resuspension under simulated sunlight irradiation. The results show that Po was highly enriched in the surface sediment and gradually decreased as sediment depths increased: 33.10 ±â€¯2.55-96.71 ±â€¯7.60 mg/kg, 33.55 ±â€¯2.34-142.86 ±â€¯5.73 mg/kg, 57.50 ±â€¯3.46-149.68 ±â€¯7.67 mg/kg, 55.18 ±â€¯4.67-168.73 ±â€¯8.31 mg/kg, 98.75 ±â€¯7.56-275.74 ±â€¯10.70 mg/kg for Lake Hou, Lake Tuan, Lake Tangling, Lake Guozheng and Lake Miao, respectively. The photo-release amount of dissolved Pi in the resuspension composed of surface sediments was also higher than that of deep sediment during sediment resuspension under the simulated sunlight irradiation for 9 h. The potential reasons for these results are: (1) difference in morphology and composition of sediments at different depths: the mean particle size of sediment decreased first and then increased as sediment depths increased; (2) difference in composition of Po species with depths in the sediment profiles: more photolytic Po species existed in surface sediments confirmed by sequential extraction and 31P NMR analysis; and (3) more OH production in the resuspension composed of surface sediment under simulated sunlight irradiation, which directly influence the photo-release of dissolved Pi from photodegradation of organic phosphorus. All of these results indicate that the distribution of organic phosphorus species in the sediment profiles plays an important role in P cycle and its photodegradation during sediment resuspension may be one of the potential pathways for phosphate supplement in shallow lakes.

[Comparison of migration characteristic of 3H and 99Tc in loess].

3H and 99Tc are important nuclides in low and intermediate level radioactive wastes, and in safety assessment of near surface repository their migration characteristic usually determines the computing result. The medium of loess appears to possess the characteristic of weak adsorption ability to 3H and 99Tc when they are migrating in it, so the adsorption ability are often neglected, and 3H are used to identify groundwater velocity. But in the field test it was showed that in the aerated zone loess possesses stronger adsorption ability to 99Tc than to 3H, and in the aquifer the stronger adsorption ability to 3H than to 99Tc. In this paper the migration tests of 3H and 99Tc were simulated by NESOR program of non-equilibrium adsorption model. The results show: 99Tc distribution coefficient ranges 0.05-0.055 mL/g in the aerated zone, 3H distribution coefficient is 0.116 mL/g in the aquifer, and the parameter reflects integrated impact of loess on 3H and 99Tc, and the mechanism of them being retarded still need proving.