Xiyuan Xiao

Heavy metal pollution of soils and vegetables in the midstream and downstream of the Xiangjiang River, Hunan Province

A total of 219 agricultural soil and 48 vegetable samples were collected from the midstream and downstream of the Xiangjiang River (the Hengyang-Changsha section) in Hunan Province. The accumulation characteristics, spatial distribution and potential risk of heavy metals in the agricultural soils and vegetables were depicted. There are higher accumulations of heavy metals such as As, Cd, Cu, Ni, Pb and Zn in agricultural soils, and the contents of Cd (2.44 mg kg−1), Pb (65.00 mg kg−1) and Zn (144.13 mg kg−1) are 7.97, 3.69 and 1.63 times the corresponding background contents in soils of Hunan Province, respectively. 13.2% of As, 68.5% of Cd, 2.7% of Cu, 2.7% of Ni, 8.7% of Pb and 15.1% of Zn in soil samples from the investigated sites exceeded the maximum allowable heavy metal contents in the China Environmental Quality Standard for Soils (GB15618-1995, Grade II). The pollution characteristics of multi-metals in soils are mainly due to Cd. The contents of As, Cd, Cu, Pb and Zn in vegetable soils are significantly higher than the contents in paddy soils. 95.8%, 68.8%, 10.4% and 95.8% of vegetable samples exceeded the Maximum Levels of Contaminants in Foods (GB2762-2005) for As, Cd, Ni and Pb concentrations, respectively. There are significantly positive correlations between the concentrations of Cd, Pb and Zn in vegetables and the concentrations in the corresponding vegetable soils (p<0.01). It is very necessary to focus on the potential risk of heavy metals for food safety and human health in agricultural soils and vegetables in the midstream and downstream of the Xiangjiang River, Hunan Province of China.

Effect of amendments on growth and metal uptake of giant reed (Arundo donax L.) grown on soil contaminated by arsenic, cadmium and lead

The effects of five amendments such as acetic acid(AA), citric acid (CA), ethylenediamine tetraacetic acid (EDTA), sepiolite and phosphogypsum on growth and metal uptake of giant reed (Arundo donax L.) grown on soil contaminated by arsenic (As), cadmium (Cd) and lead (Pb) were studied. The results showed that the shoot biomass of giant reed was enhanced by 24.8% and 15.0%, while superoxide mutase and catalase activities slightly varied when adding 5.0 mmol/kg CA and 2.5 mol/kg EDTA to soil as compared to the control, respectively. The concentrations of As, Cd and Pb in shoots were remarkably increased by the addition of 2.5 mmol/kg AA and CA, 5.0 mmol/kg EDTA, and 4.0 g/kg sepiolite as compared to the control. The accumulations of As and Cd were also significantly enhanced in the above condition, while the shoot Pb accumulation was noticeably enhanced by amending with 4.0 g/kg sepiolite and 8.0 g/kg phosphogysum, respectively. The results suggested that AA, CA and sepiolite could be used as optimum soil amendments for giant reed remediation system.

Optimization of brine leaching of metals from hydrometallurgical residue

An orthogonal array, L16(4^5), was used to examine the effects of four parameters, including NaCl concentration, H2SO4 concentration, temperature and pulp density, on the recovery of Cu, In, Pb and Zn from a hydrometallurgical residue via brine leaching. The results show that temperature of leaching solution has a significant effect on the recovery of Cu, In and Zn, while H2S04 concentration has an obvious influence on these metals extraction. Both pulp density and NaCl concentration significantly affect Pb extraction. Based on the orthogonal array experiments, the optimum conditions for the extraction of Cu, In, Pb and Zn from hydrometallurgical residue are NaCl concentration of 250 g/L, H2S04 concentration of 1.00 mol/L, temperature of 85℃, and pulp density of 100 g/L. After 1 h of treatment at these optimum conditions, over 91% of the metals are extracted from the residue. Brine leaching is therefore suitable for the recovery of metals from hydrometallurgical residues.

Soil vanadium pollution and microbial response characteristics from stone coal smelting district

Abstract A field investigation was performed to study the content, speciation and mobility of vanadium, as well as microbial response in soil from a stone coal smelting district in Hunan province of China. The results showed that the contents of soil V ranged from 168 to 1538 mg/kg, which exceeded the maximum permissible value of Canadian soil quality for V. The mean soil V content from wasteland area reached 1421 mg/kg, and those from the areas related with slag heap, ore pile and smelting center were 380, 260 and 225 mg/kg, respectively. Based on the results of the modified BCR sequential extraction procedure, V contents in the mobile fractions varied from 19.2 to 637 mg/kg accounting for 7.4%–42.3% of total V, and those of V(+5) species were between 21.9 and 534.0 mg/kg. Soil enzyme activity and microbial basal respiration were adversely affected by high level of soil V. More attention should be paid to soil V pollution and potential hazardous surrounding the stone coal smelting district.

Environmental availability and profile characteristics of arsenic, cadmium, lead and zinc in metal-contaminated vegetable soils

Abstract Environmental availability and profile characteristics of arsenic (As), cadmium (Cd), lead (Pb) and zinc (Zn) were studied in contaminated vegetable soils from the Pb/Zn mining and smelting areas in Hunan Province of China, and the potential environmental risks of these metals were also assessed. The results show that the concentrations of As, Cd, Pb and Zn in vegetable soils are higher than the levels of Soil Environmental Quality of China (GB15618—1995). The mobility of metals in soil profiles is mainly characterized by the low pH and organic matter content of soil. The major part of As, Cd, Pb and Zn is restricted to the upper soils and the contamination of these metals in soils is significantly influenced by the long-term Pb/Zn mining and smelting activities. Based on the results from the BCR sequential extraction, the fraction of Cd in the soil profiles is predominantly existed in the acid-extractable form and the large amount of Pb is closely associated with reducible fraction. The environmental availability of Cd and Pb is predominantly higher than that of As and Zn in the soil profiles, suggesting Cd and Pb have more huge potential risk for human health and surrounding environment.

Phytostabilisation potential of giant reed for metals contaminated soil modified with complex organic fertiliser and fly ash: A field experiment.

An orthogonal field experiment of giant reed (Arundo donax) modified with organic complex fertiliser (OCF), and OCF and fly ash (O&F), at different planting densities was carried out in metal-contaminated soil. The available percentage of arsenic (As) and lead (Pb) in soil decreased from 8.45% to 2.19% and from 29.6% to 13.5% by OCF, respectively, and that of cadmium (Cd) was reduced from 25.3% to 6.49% by O&F. The total biomass of giant reed was 631g per individual following application of O&F in contaminated soil. The accumulation of As, Cd, and Pb in giant reed was 1.57, 4.06, and 11.25mg per individual. Urease and sucrase activity were 87.4NH4-Nμg/gd and 63.1glucosemg/gd in response to the treatments modified using OCF, while the highest dehydrogenase activity was 101 TPF (triphenyltetrazolium formazan) μg/gd in the treatments modified using O&F. Dominant bacteria (frequency>50%) were enriched with increasing planting density of giant reed. These results indicate that the phytostabilisation of metal-contaminated soil by giant reed could be improved by the application of O&F or OCF.

Stabilization of heavy metals in biochar pyrolyzed from phytoremediated giant reed (Arundo donax) biomass

The pyrolysis of phytoremediated giant reed (Arundo donax) biomass could cause secondary pollution of heavy metals. The stabilization of heavy metals in the pyrolysis process with external materials such as Al2O3, CaCO3, FeCl3 and NaOH, was studied. The results showed that 37% As and 97% Cd in biochar were stabilized when giant reed powder was pyrolyzed at 250 °C with 5% Al2O3 for 2 h. Furthermore, 59% Pb in biochar was stabilized at 400 °C with 5% CaCO3 for 1 h. Under biochar produced in optimized pyrolysis conditions, Cd mainly existed in a residual fraction, while Pb and As mainly existed in oxidizable fraction in BCR analysis. In XRD analysis, As was only found in Ca2As2O7; Cd in biochar mainly existed in Cd (AlCl4)2, CdPbO3 or CdSO3; and Pb mainly existed as Pb3O2SO4.

Phytostabilization potential of ornamental plants grown in soil contaminated with cadmium

ABSTRACT In a greenhouse experiment, five ornamental plants, Osmanthus fragrans (OF), Ligustrum vicaryi L. (LV), Cinnamomum camphora (CC), Loropetalum chinense var. rubrum (LC), and Euonymus japonicas cv. Aureo-mar (EJ), were studied for the ability to phytostabilization for Cd-contaminated soil. The results showed that these five ornamental plants can grow normally when the soil Cd content is less than 24.6 mg·kg−1. Cd was mainly deposited in the roots of OF, LV, LC and EJ which have grown in Cd-contaminated soils, and the maximum Cd contents reached 15.76, 19.09, 20.59 and 32.91 mg·kg−1, respectively. For CC, Cd was mainly distributed in the shoots and the maximum Cd content in stems and leaves were 12.5 and 10.71 mg·kg−1, however, the total amount of Cd in stems and leaves was similar with the other ornamental plants. The enzymatic activities in Cd-contaminated soil were benefited from the five tested ornamental plants remediation. Soil urease and sucrase activities were improved, while dehydrogenase activity was depressed. Meanwhile, the soil microbial community was slightly influenced when soil Cd content is less than 24.6 mg·kg−1 under five ornamental plants remediation. The results further suggested that ornamental plants could be promising candidates for phytostabilization of Cd-contaminated soil.

Effect of moderately thermophilic bacteria on metal extraction and electrochemical characteristics for zinc smelting slag in bioleaching system

Abstract The effects of moderately thermophilic bacteria on the extraction of metals from zinc smelting slag and electrochemical characteristics of zinc smelting slag carbon paste electrode in bioleaching process were studied. The results show that the extraction rates of Fe, Cu and Zn from the slag reach 86.7%, 90.3% and 66.7% after adsorbed bacteria sterilize, while those with adsorbed bacteria are 91.9%, 96.0% and 84.5% in conditions of pulp density 2%, pH 1.0, temperature 65 °C and stirring rate 120 r/min, respectively. Some stretching peaks of functional groups from bacterial secretes on the bioleached residue surface, such as 1007 cm −1 and 1193 cm −1 , turn up through FI-IR analysis and indirectly reveal the presence of the adsorbed bacteria on the slag particles surface. Besides, the corrosion of zinc smelting slag is enhanced by bacteria according to the characteristics of cyclic voltametry and Tafel curves in bioleaching system.

Release of cadmium in contaminated paddy soil amended with NPK fertilizer and lime under water management

Agricultural soils contaminated with cadmium (Cd) pose a risk to receiving surface water via drainage or runoff. A 90-day laboratory incubation experiment was conducted to investigate the release characteristics and transformation of Cd from contaminated paddy soil amended with agrochemical (NPK fertilizer) and lime (L) under water management regimes of continuous flooding (F) and drying-wetting cycles (DW). The result showed that the dissolved Cd concentrations in overlying water of the fertilizer treatment under flooding (NPK+F) and drying-wetting (NPK+DW) reached up to 81.0 μg/L and 276 μg/L, and were much higher than that from the corresponding controls without NPK fertilizer addition at the end of experiment. The Cd concentration showed significantly negative correlation with overlying water pH, but positive correlation with soil redox potential and concentrations of dissolved total nitrogen, sulfate and manganese in overlying water (P < 0.05), indicating that drying-wetting cycles and N fertilizer addition may enhance soil Cd release. The Cd concentrations in overlying water from all treatments except NPK+L+F treatment exceeded the Cd threshold limit of Chinese Environmental Quality Standards for Surface Water (10 μg/L Grade V) and poses potential risk to surface water quality. Meanwhile, the proportion of Cd in the acid-soluble fraction from all incubated soil except NPK+L+F treatment increased compared to before incubation. The results indicated that continuous flooding was a reasonable water management candidate coupled with lime addition for immobilizing soil Cd.