Study of the Seasonal Water Environmental Capacity of the Central Shaanxi Reach of the Wei River

AbstractDue to local economic development, the Central Shaanxi reach of the Wei River suffers from serious water contamination, which is restricting sustainable development in this area. Therefore, it is desirous to study the water environmental capacity here in order to improve water quality. In this paper we chose chemical oxygen demand (COD) as the index, which reflects the organic contamination. After the unit division and parameter design, we used one-dimensional steady-state model to calculate the water environmental capacity of the Central Shaanxi reach of the Wei River. The results show that the water environmental capacity of the Central Shaanxi reach of the Wei River varies with different conditions, for instance, with the months, as well as with the seasons. We have determined that seasonal pollutant load distribution and total quantity control could help us utilize the water resource more effectively

Mechanisms of Sb(III) Photooxidation by the Excitation of Organic Fe(III) Complexes

Organic Fe­(III) complexes are widely distributed in the aqueous environment, which can efficiently generate free radicals under light illumination, playing a significant role in heavy metal speciation. However, the potential importance of the photooxidation of Sb­(III) by organic Fe­(III) complexes remains unclear. Therefore, the photooxidation mechanisms of Sb­(III) were comprehensively investigated in Fe­(III)–oxalate, Fe­(III)–citrate and Fe­(III)–fulvic acid (FA) solutions by kinetic measurements and modeling. Rapid photooxidation of Sb­(III) was observed in an Fe­(III)–oxalate solution over the pH range of 3 to 7. The addition of <i>tert</i>-butyl alcohol (TBA) as an ·OH scavenger quenched the Sb­(III) oxidation, suggesting that ·OH is an important oxidant for Sb­(III). However, the incomplete quenching of Sb­(III) oxidation indicated the existence of other oxidants, presumably an Fe­(IV) species in irradiated Fe­(III)–oxalate solution. In acidic solutions, ·OH may be formed by the reaction of Fe^II(C₂O₄) with H₂O₂, but a hypothetical Fe­(IV) species may be generated by the reaction of Fe^II(C₂O₄)₂^2– with H₂O₂ at higher pH. Kinetic modeling provides a quantitative explanation of the results. Evidence for the existence of ·OH and hypothetical Fe­(IV) was also observed in an irradiated Fe­(III)–citrate and Fe­(III)–FA system. This study demonstrated an important pathway of Sb­(III) oxidation in surface waters

Mechanisms of Sb(III) Oxidation by Pyrite-Induced Hydroxyl Radicals and Hydrogen Peroxide

Antimony (Sb) is an element of growing interest, and its toxicity and mobility are strongly influenced by redox processes. Sb­(III) oxidation mechanisms in pyrite suspensions were comprehensively investigated by kinetic measurements in oxic and anoxic conditions and simulated sunlight. Sb­(III) was oxidized to Sb­(V) in both solution and on pyrite surfaces in oxic conditions; the oxidation efficiency of Sb­(III) was gradually enhanced with the increase of pH. The pyrite-induced hydroxyl radical (·OH) and hydrogen peroxide (H₂O₂) are the oxidants for Sb­(III) oxidation. ·OH is the oxidant for Sb­(III) oxidation in acidic solutions, and H₂O₂ becomes the main oxidant in neutral and alkaline solutions. ·OH and H₂O₂ can be generated by the reaction of previously existing Fe^III_(pyrite) and H₂O on pyrite in anoxic conditions. The oxygen molecule is the crucial factor in continuously producing ·OH and H₂O₂ for Sb­(III) oxidation. The efficiency of Sb­(III) oxidation was enhanced in surface-oxidized pyrite (SOP) suspension, more ·OH formed through Fenton reaction in acidic solutions, but Fe­(IV) and H₂O₂ were formed in neutral and alkaline solutions. Under the illumination of simulated sunlight, more ·OH and H₂O₂ were produced in the pyrite suspension, and the oxidation efficiency of Sb­(III) was remarkably enhanced. In conclusion, Sb­(III) can be oxidized to Sb­(V) in the presence of pyrite, which will greatly influence the fate of Sb­(III) in the environment

Kinetics and Mechanism of Photopromoted Oxidative Dissolution of Antimony Trioxide

Light (sunlight, ultraviolet, simulated sunlight) irradiation was used to initiate the dissolution of antimony trioxide (Sb₂O₃). Dissolution rate of Sb₂O₃ was accelerated and dissolved trivalent antimony (Sb­(III)) was oxidized in the irradiation of light. The photopromoted oxidative dissolution mechanism of Sb₂O₃ was studied through experiments investigating the effects of pH, free radicals scavengers, dissolved oxygen removal and Sb₂O₃ dosage on the release rate of antimony from Sb₂O₃ under simulated sunlight irradiation. The key oxidative components were hydroxyl free radicals, photogenerated holes and superoxide free radicals; their contribution ratios were roughly estimated. In addition, a conceptual model of the photocatalytic oxidation dissolution of Sb₂O₃ was proposed. The overall pH-dependent dissolution rate of Sb₂O₃ and the oxidation of Sb­(III) under light irradiation were expressed by <i>r</i> = 0.08·[OH^–]^0.63 and <i>r</i>_ox = 0.10·[OH^–]^0.79. The present study on the mechanism of the photo-oxidation dissolution of Sb₂O₃ could help clarify the geochemical cycle and fate of Sb in the environment

Toxicity and bioavailability of antimony to the earthworm (Eisenia fetida) in different agricultural soils

Laboratory experiments in which earthworms were exposed to four different Sb spiked agricultural soils (acidic, neutral, alkaline and calcareous alkaline soil) were conducted in a climate-controlled room. The study surveyed the toxicity of Sb to the Eisenia fetida at the individual (mortality, growth inhibition, Sb accumulation), physiological (enzymatic activities), subcellular and tissue levels (histological damage), and for the induction of an avoidance response of Sb. The results showed that earthworms clearly avoided Sb spiked soil, and the avoidance response tended to be correlated to the exposure dose. The EC50 values of the net avoidance response in the four soils were as followed: S1 (acidic soil, 135 +/- 37 mg kg(-1)) < S3 (alkaline soil, 430 +/- 114 mg kg(-1)) < S4 (calcareous alkaline soil, 455 +/- 29 mg kg(-1)) < S2 (neutral soil, 946 +/- 151 mg kg(-1)). Different toxic effects of Sb to earthworms cultivated in the four types of soils were observed. Antimony was more toxic in a sandy alkaline soil than that in the other three soils tested. The LC50 of the 28 d mortality ranged as follows: S3 (22.2 +/- 0.1 mg kg(-1)) < S2 (372 +/- 177 mg kg(-1)) < S4 (491 +/- 140 mg kg(-1)) < S1 (497 +/- 29 mg kg(-1)). Changes in oxidative stress and the subcellular distribution of Sb in earthworms induced by Sb exposure differed between soil types. Additionally, histological damage in earthworm's epidermis and intestine were observed under Sb stress. Mortality, growth inhibition and Sb accumulation in the earthworms tended to increase with Sb exposure regardless of soil type and were all significantly correlated with the exposure dose. The growth inhibition and Sb concentration in tissues of earthworms were sensitive indicators of Sb bioavailability. The relatively comprehensive toxicological data provided herein can contribute to the toxicity threshold and assessment of bioavailability of Sb contaminated agricultural soil, and then to the ecological risk assessments

Monte Carlo simulation and delayed geochemical hazard revealed the contamination and risk of arsenic in natural water sources

Due to its ubiquity and carcinogenicity, the geochemical behavior and health risks of arsenic (As) have been a research focus worldwide. A comprehensive investigation was conducted on the contamination and ecological and health risks of As in the Zijiang River (ZR)-a natural water source. The concentration ranges of As were separately 1.36–6.23 μg/L, 11.42–74.53 mg/kg, and 1.26–130.68 μg/L in surface waters (dissolved), sediments, and pore waters. The concentrations of As in the midstream pore waters and sediments were relatively high, which was related to mining, dam interception, and sediment resuspension. The Monte Carlo simulation results showed that the occurrence probability of As contamination and static risk in sediments was low, however, in the midstream, the secondary risk caused by the release of As should be given more consideration. In the sediments, the transformation paths and the dynamic risk of As were explored based on the delayed geochemical hazard model, showing that there was a probability of a potential burst of 26.47% − 55.88% in the sediments of the ZR. Although at the detected surface waters, the total risk of the noncarcinogenicity and carcinogenicity of As were low, overall adults have lower health risks than children, and As exposure in children should be of concern. This study complements the further understanding of the geochemical behavior of arsenic, which can be extended to other toxic metal(loid)s

Transcriptomic Profiles in Zebrafish Liver Permit the Discrimination of Surface Water with Pollution Gradient and Different Discharges

The present study aims to evaluate the potential of transcriptomic profiles in evaluating the impacts of complex mixtures of pollutants at environmentally relevant concentrations on aquatic vertebrates. The changes in gene expression were determined using microarray in the liver of male zebrafish (Danio rerio) exposed to surface water collected from selected locations on the Hun River, China. The numbers of differentially expressed genes (DEGs) in each treatment ranged from 728 to 3292, which were positively correlated with chemical oxygen demand (COD). Predominant transcriptomic responses included peroxisome proliferator-activated receptors (PPAR) signaling and steroid biosynthesis. Key pathways in immune system were also affected. Notably, two human diseases related pathways, insulin resistance and Salmonella infection were enriched. Clustering analysis and principle component analysis with DEGs differentiated the upstream and downstream site of Shenyang City, and the mainstream and the tributary sites near the junction. Comparison the gene expression profiles of zebrafish exposed to river surface water with those to individual chemicals found higher similarity of the river water with estradiol than several other organic pollutants and metals. Results suggested that the transcriptomic profiles of zebrafish is promising in differentiating surface water with pollution gradient and different discharges and in providing valuable information to support discharge management