The risks of sulfur addition on cadmium accumulation in paddy rice under different water-management conditions

Recently, the application of sulfur (S) has been recommended to control the accumulation of cadmium (Cd) in rice in contaminated paddy soil. However, the effects of exogenous S on Cd transfer in paddy rice systems under different water-management practices have not been systematically investigated. Pot experiments were performed to monitor the composition of soil pore water and the Cd accumulation in iron plaque and rice tissue were compared under different S (0 and 200 mg/kg Na₂SO₄) and water (continuous and discontinuous flooding) treatments. Sulfur application significantly increased Cd concentrations in soil pore water under discontinuous flooding conditions, but slightly reduced them under continuous flooding. Moreover, the oxidation/reduction potential (Eh) was the most critical factor that affected the Cd levels. When the Eh exceeded −42.5 mV, S became the second critical factor, and excessive S application promoted Cd dissolution. In addition, S addition elevated the Cd levels in iron plaque and reduced the Cd transfer from the iron plaque to rice roots. In rice, S addition inhibited Cd transfer from the rice roots to the straw; thus, more Cd was stored in the rice roots. Nevertheless, additional S application increased the Cd content in the rice grains by 72% under discontinuous flooding, although this effect was mitigated by continued flooding. Under simulated practical water management conditions, S addition increased the risk of Cd contamination in rice, suggesting that S application should be reconsidered as a paddy fertilization strategy.     

Modeling iron release from cast iron pipes in an urban water distribution system caused by source water switch

Significant iron release from cast iron pipes in water distribution systems (WDSs), which usually occurs during the source water switch period, is a great concern of water utilities because of the potential occurrence of “red water” and customer complaints. This study developed a new method which combined in-situ water stagnation experiments with mathematical models and numerical simulations to predict the iron release caused by source water switch. In-situ water stagnation experiments were conducted to determine the total iron accumulation in nine cast iron pipes in-service in Beijing when switching the local water to treated Danjiangkou Reservior water. Results showed that the difference in the concentration increment of total iron in 24 hr (ΔCI_TI,24), i.e. short-term iron release, caused by source water switch was mainly dependent on the difference in the key quality parameters (pH, hardness, nitrate, Larson Ratio and dissolved oxygen (DO)) between the two source waters. The iron release rate (R_Fe) after switch, i.e. long-term iron release, was closely related to the pipe properties as well as the DO and total residual chlorine (TRC) concentrations. Mathematical models of ΔCI_TI,24 and R_Fe were developed to quantitatively reveal the relationship between iron release and the key quality parameters. The R_Fe model could successfully combine with EPANET-MSX, a numerical simulator of water quality for WDSs to extend the iron release modeling from pipe level to network level. The new method is applicable to predicting iron release during source water switch, thus facilitating water utilities to take preventive actions to avoid “red water”.     

Information source and valence: How information credibility influences earthquake risk perception

The present research aims at the relationship between information credibility and perception of seismic risk in a group of people living in severe disaster areas. 243 adult residents exposed to seismic hazard participated in a questionnaire study. With respect to four types of information which are generated by information sources and valence, participants were instructed to recall one type of the information they obtained respectively and rate the recalled information in terms of its credibility. After that, they were asked to report their seismic risk perception and all socio-demographic data were also collected. Regression analyses suggested that information credibility significantly influenced risk perception. Furthermore, the credibility of word-of-mouth and negative information were positively associated with risk perception. Meanwhile, risk perception was also affected greatly by the credibility of negative public information but not positive word-of-mouth information. It was clear that both information source and valence moderated the process and the latter exerted a stronger influence on it. The results were interpreted in relation to the elaboration likelihood model, accessibility-diagnosticity model, and other cognitive theories. The findings were discussed in terms of their general implications for the improvement of risk communication about earthquake related messages.     

Utilising of the oiled rolling mills scale in iron ore sintering process

Up to 5% of steel is lost with the scale at hot rolling operation. This waste contains 69-72% of iron in the form of oxides. However, its recycling is confronted with presence of up to 20% of oil and 10% of water. E.g. when the oiled scale is introduced as an additive to the iron ore sintering mixture, incomplete combustion of liberated oil at heating during sintering process creates problems for gas cleaning and may even lead to damage of the equipment. A possibility to improve combustion of the scale's oil at the sintering process by preparation of a mixture with peat was shown in the laboratory experiments. Industrial trials demonstrate possibility to increase the oil combustion degree at sintering 2.7 times as much. Consumption of the oiled scale was increased from zero to 12.8 kg (in a form of scale-peat blend) per ton of sinter, which allows for closing the loop of this waste at the integrated steelmaking factory.     

Efficient degradation of drug ibuprofen through catalytic activation of peroxymonosulfate by Fe3C embedded on carbon

Ibuprofen(IBU),a nonsteroidal anti-inflammatory drug,is becoming an important member of pharmaceuticals and personal care products(PPCPs)as emerging pollutants.To degrade IBU,magnetic Fe_3C nanoparticles embedded on N-doped carbon(Fe_3C/NC)were prepared as a catalyst by a sol–gel combustion method.As characterized,the Fe_3C/NC nanoparticles were composed of a NC nano-sheet and capsulated Fe_3C particles on the sheet.The Fe_3C/NC nanoparticles were confirmed an efficient catalyst for peroxymonosulfate(PMS)activation to generate sulfate radicals(SO_4~(·-)),single oxygen(~1O_2)and hydroxyl radicals(·OH)toward the degradation of IBU.The added IBU(10 mg/L)was almost completely removed in 30 min by using 0.1 g/L Fe_3C/NC and 2 g/L PMS.The catalyst was confirmed to have good ability and excellent reusability through leaching measurements and cycle experiments.A catalytic mechanism was proposed for the catalytic activation of PMS on Fe_3C/NC,which involves both Fe_3C reactive sites and N-doped carbon matrix as reactive sites in Fe_3C/NC.Moreover,the degradation pathway of IBU in the Fe_3C/NC-PMS system was proposed according to the detections of degradation intermediates.     

Ciprofloxacin degradation in photo-Fenton and photo-catalytic processes: Degradation mechanisms and iron chelation

Ciprofloxacin(CIP)is a broad spectrum synthetic antibiotic drug of fluoroquinolones class.CIP can act as a bidentate ligand forming iron complexes during its degradation in the photoFenton process(PFP).This work investigates on PFP for the degradation of CIP to understand the formation mechanism and stability of iron complexes under ultraviolet(UV)-light illumination.A comparison was made with the UV-photocatalysis(UV/TiO_2)process where CIP doesn't form a complex.In PFP,the optimal dose of Fe~(2+)and H_2O_2were found to be 1.25 and10 mmol/L with pH of 3.5.An optimal TiO_2dose of 1.25 g/L was determined in the UV/TiO_2process.Maximum CIP removal and mineralization efficiency of 93.1%and 47.3%were obtained in PFP against 69.7%and 27.6%in the UV/TiO_2process.The mass spectra could identify seventeen intermediate products including iron-CIP complexes in PFP,and only seven intermediate products were found in the UV/TiO_2process with a majority of common products in both the processes.The proposed mechanism supported by the mass spectra bridged the routes of CIP cleavage in the PFP and UV/TiO_2process,and the decomposition pathway of Fe~(3+)-CIP chelate complexes in PFP was also elucidated.Both in PFP and UV/TiO_2processes,the target site of HO~·radical attack was the secondary-N atom present in the piperazine ring of the CIP molecule.The death of Escherichia coli bacteria was 55.7%and 66.8%in comparison to the control media after 45 min of treatment in PFP and UV/TiO_2process,respectively.     

Phosphorus mobility in dam reservoir affected by redox oscillations: An experimental study

The internal sedimentary phosphorus(P) load of aquatic systems is able to support eutrophication, especially in dam–reservoir systems where sedimentary P stock is high and where temporary anaerobic conditions occur. The aim of this study therefore is to examine the response of sedimentary P exposed to redox oscillations. Surface sediments collected in the Champsanglard dam–reservoir(on the Creuse River, France) were subjected to two aerobic phases(10 and 12 days) alternated with two anaerobic periods(21 and 27 days)through batch incubations. The studied sediment contained 77 ± 3 μmol/g DW of P, mainly associated with the ascorbate fraction(amorphous Fe/Mn oxyhydroxides). The used sediment was rich in organic matter(OM)(21% ± 1%) with primarily allochthone signature.Our results showed that redox oscillations enhance dissolved inorganic phosphorus release at sediment/water interface. During the first anaerobic stage, the P release was mainly controlled by the dissolution/precipitation of iron minerals. The more pronounced increase of P release during the second anaerobic stage(44%) was due to various mechanisms related to the change in quality of dissolved organic matter(DOM), namely a higher SUVA254 and humification indices. The release of more refractory DOM(rDOM) served to lower the microbial metabolism activity, possibly favored iron oxyhydroxide aggregation and thus limiting iron reduction. In addition, rDOM is able to compete for mineral P sorption sites,leading to a greater P release. In reservoir with predominant allochthone OM input, the release of more aromatic DOM therefore plays an important role in P mobility.     

Effect of environmental factors on the complexation of iron and humic acid

A method of size exclusion chromatography coupled with ultraviolet spectrophotometry and off-line graphite furnace atomic absorption spectrometry was developed to assess the complexation properties of iron (Fe) and humic acid (HA) in a water environment. The factors affecting the complexation of Fe and HA, such as ionic strength, pH, temperature and UV radiation, were investigated. The Fe-HA complex residence time was also studied. Experimental results showed that pH could influence the deprotonation of HA and hydrolysis of Fe, and thus affected the complexation of Fe and HA. The complexation was greatly disrupted by the presence of NaCl. Temperature had some influence on the complexation. The yield of Fe-HA complexes showed a small decrease at high levels of UV radiation, but the effect of UV radiation on Fe-HA complex formation at natural levels could be neglected. It took about 10 hr for the complexation to reach equilibrium, and the Fe-HA complex residence time was about 20 hr. Complexation of Fe and HA reached a maximum level under the conditions of pH 6, very low ionic strength, in the dark and at a water temperature of about 25°C, for 10 hr. It was suggested that the Fe-HA complex could form mainly in freshwater bodies and reach high levels in the warm season with mild sunlight radiation. With changing environmental parameters, such as at lower temperature in winter or higher pH and ionic strength in an estuary, the concentration of the Fe-HA complex would decrease.     

Accumulation and elimination of iron oxide nanomaterials in zebrafish (Danio rerio) upon chronic aqueous exposure

A 52-day continuous semi-static waterborne exposure (test media renewed daily) regimen was employed to investigate the accumulation and elimination profiles of two iron oxide nanomaterials (nano-Fe₂O₃ and nano-Fe₃O₄) in zebrafish (Danio rerio). Adult zebrafish were exposed to nanomaterial suspensions with initial concentrations of 4.0 and 10.0 mg/L for 28 days and then were moved to clean water for 24 days to perform the elimination experiment. Fe content was measured in fish body and feces to provide data on accumulation and elimination of the two iron oxide nanomaterials in zebrafish. The experiment revealed that: (1) high accumulation of nano-Fe₂O₃ and nano-Fe₃O₄ were found in zebrafish, with maximum Fe contents, respectively, of 1.32 and 1.25 mg/g for 4.0 mg/L treatment groups and 1.15 and 0.90 mg/g for 10.0 mg/L treatment groups; (2) accumulated nanoparticles in zebrafish can be eliminated efficiently (the decrease of body burden of Fe conforms to a first-order decay equation) when fish were moved to nanoparticle-free water, and the elimination rates ranged from 86% to 100% by 24 days post-exposure; and (3) according to analysis of Fe content in fish excrement in the elimination phase, iron oxide nanomaterials may be adsorbed via the gastrointestinal tract, and stored for more than 12 days.     

Kinetics of nitrobenzene degradation coupled to indigenous microorganism dissimilatory iron reduction stimulated by emulsified vegetable oil

Widespread contamination by nitrobenzene(NB) in sediments and groundwater requires better understanding of the biogeochemical removal process of the pollutant. NB degradation, coupled with dissimilatory iron reduction, is one of the most efficient pollutant removal methods. However, research on NB degradation coupled to indigenous microorganism dissimilatory iron reduction stimulated by electron donors is still experimental. A model for remediation in an actual polluted site does not currently exist.Therefore, in this study, the dynamics was derived from the Michaelis–Menten model(when the mass ratio of emulsified vegetable oil and NB reached the critical value 91:1). The effect of SO_4~(2-), NO_3~-, Ca~(2+)/Mg~(2+), and the grain size of aquifer media on the dynamics were studied, and the NB degradation dynamic model was then modified based on the most significant factors. Utilizing the model, the remediation time could be calculated in a contaminated site.