Xiaoqin Chen

Risk assessment of potentially toxic element pollution in soils and rice (Oryza sativa) in a typical area of the Yangtze River Delta

Soil pollution with potentially toxic elements (PTEs) resulting from rapid industrial development has caused major concerns. Selected PTEs and their accumulation and distribution in soils and rice (Oryza sativa) collected from Changshu, east China, were analyzed to evaluate the potential health risk to the local population. The soils were primarily contaminated with Hg, followed by Cu, Cd, Pb, and Zn. The concentrations of Pb, Hg, and Cd of 46, 32, and 1 rice samples exceeded their national maximum allowable levels in foods, respectively. Spatial distributions of total Cr, Cu, Pb, Zn, and Cd in soils shared similar geographical trends. The risk assessment of PTEs through rice consumption suggests that the concentrations of Cu, Pb, and Cd in some rice samples exceed their reference oral dose for adults and children. In general, there was no target hazard quotient value of any individual element that was greater than 1, but hazard index values for adults and children were 1.726 and 1.523, respectively.

Removal of phosphate from aqueous solution by thermally treated natural palygorskite.

The potential of activated palygorskite was assessed for sorption of phosphate from aqueous solution. The natural palygorskite used was treated by thermal activation over 100-1000 degrees C for 2h. The thermal activation increased the phosphate sorption capacity and the highest phosphate sorption capacity occurred at 700 degrees C. H700 (palygorskite heated at 700 degrees C) showed higher sorption rate than natural palygorskite (NPAL), and the removal was favorable in acidic media. The sorption data were described using Freundlich isotherm equation over the concentration range (5-1000mg/L) (25 degrees C). Calcium bound phosphorus was the main fraction of the adsorbed phosphorus, about 98.0% in NPAL and 58.2% in H700, but the extractive Ca-P species varied greatly, Ca(2)-P was 87.7% in NPAL and 3.0% in H700, Ca(8)-P was 10.1% in NPAL and 54.5% in H700, and metal bound phosphorus was less than 2% in NPAL but more than 41.4% in H700, respectively. The dependence of the phosphate sorption capacity in the heating samples on thermal activation appears to be related to major changes in the crystal structure of palygorskite, and more calcium, iron and aluminum were released from the crystal matrix at 700 degrees C, which promoted phosphorus sorption.

Characteristics and accumulation of heavy metals in sediments originated from an electroplating plant.

Heavy metals in river water and sediments originated from an electroplating plant in Jiangsu Province of China were studied and analyzed for their environmental impact. The results indicated that the wastewater from the plant degraded the quality of the aquatic environment downstream from the plant. In surface water, considerable concentrations of Cu, Ni, Zn, Mn and Cr were present at the sites near the plant. Unsafe levels of Cu were observed at all sites, and unsafe levels of Ni, Zn, and Cr were present at some sites. Significant accumulation of Ni, Cu, Zn and Cr was identified, and heavy metal longitudinal distribution in sediments was similar to that in water. The contents of Ni, Cu and Cr at all sites and Zn at some sites were likely to result in harmful effects on the environment. The risks posed by Ni, Cu, Zn and Cr in water and sediments decreased with increasing downstream distance. Moreover, a modified sequential extraction procedure was employed to determine exchangeable, carbonate-bound, iron-manganese oxide bound, organic matter bound and residual fractions of metals in sediments. The results showed that Ni was distributed in every fraction except for iron-manganese oxide bound, significant Mn exhibited in exchangeable fractions, and high percentage of Cu was in the organic matter and residual fractions. Residual fraction was the dominant fractions for Pb and Zn. According to RACs, Ni and Mn posed a high risk to the environment, Zn exhibited medium to high risk, Cu had low to high risk, and Pb possessed a low to medium risk.

Effect of Long-Term Rice Straw Return on Soil Glomalin, Carbon and Nitrogen

A long-term experiment was conducted to investigate how long-term fertilization and rice straw incorporation into soil affect soil glomalin, C and N. The combined application of chemical fertilizer and straw resulted in a significant increase in both soil easily extractable glomalin (EEG) and total glomalin (TG) concentrations, as compared with application of only chemical fertilizer or no fertilizer application. The EEG and TG concentrations of the NPKS (nitrogen, phosphorus, and potassium fertilizer application + rice straw return) plot were 4.68% and 5.67% higher than those of the CK (unfertilized control) plot, and 9.87% and 6.23% higher than those of the NPK (nitrogen, phosphorus, and potassium fertilizer applied annually) plot, respectively. Application of only chemical fertilizer did not cause a statistically significant change of soil glomalin compared with no fertilizer application. The changes of soil organic C (SOC) and total N (TN) contents demonstrated a similar trend to soil glomalin in these plots. The SOC and TN contents of NPKS plot were 15.01% and 9.18% higher than those of the CK plot, and 8.85% and 14.76% higher than those of the NPK plot, respectively. Rice straw return also enhanced the contents of microbial biomass C (MBC) and microbial biomass N (MBN) in the NPKS plot by 7.76% for MBC and 31.42% for MBN compared with the CK plot, and 12.66% for MBC and 15.07% for MBN compared with the NPK plots, respectively. Application of only chemical fertilizer, however, increased MBN concentration, but decreased MBC concentration in soil.

Effect of Nitrogen on the Degradation of Cypermethrin and Its Metabolite 3-Phenoxybenzoic Acid in Soil

Abstract Increasing use of pyrethroid insecticides has resulted in concerns regarding potential effects on human health and ecosystems. Cypermethrin and its metabolite 3-phenoxybenzoic acid (PBA) have exerted adverse biological impacts on the environment; therefore, it is critically important to develop different methods to enhance their degradation. In this study, incubation experiments were conducted using samples of an Aquic Inceptisol supplied with nitrogen (N) in the form of NH 4 NO 3 at different levels to investigate the effect of nitrogen on the degradation of cypermethrin and PBA in soil. The results indicated that appropriate N application can promote the degradation of cypermethrin and PBA in soil. The maximum degradation rates were 80.0% for cypermethrin after 14 days of incubation in the treatment with N at a rate of 122.1 kg ha −1 and 41.0% for PBA after 60 days of incubation in the treatment with N at a rate of 182.7 kg ha −1 . The corresponding rates in the treatments without nitrogen were 62.7% for cypermethrin and 27.8% for PBA. However, oversupplying N significantly reduced degradation of these compounds. Enhancement of degradation could be explained by the stimulation of microbial activity after the addition of N. In particular, dehydrogenase activities in the soil generally increased with the addition of N, except in the soil where N was applied at the highest level. The lower degradation rate measured in the treatment with an oversupply of N may be attributed to the microbial metabolism shifts induced by high N.

Enhancement of Phosphorus Solubility by Humic Substances in Ferrosols

Abstract An investigation was conducted to study the effect of humic substance (HS) on the phosphorus (P) solubility in acidic soil. The soil (2.5 g), HS (0, 0.5, and 2.5 g), and P as monocalcium phosphate (0.31 and 1.25 g P kg−1 soil) were mixed with 50 mL distilled water and two different sequences of adding HS and P were used. The results indicated that the P concentration in water and 0.01 mol L−1 CaCl2 solution increased with increasing amounts of humic substance. The concentrations of Fe and Al were also increased. However, Olsen P decreased with increasing amount of humic substance. Water-soluble P concentrations from P rates at 0.31 and 1.25 g P kg−1 soil in the treatment with 0.5 g (2.5 g) humic substance addition were 360% and 70% (500% and 90%) higher, respectively, than those in the treatment with no humic substance addition. P extracted by 0.01 mol L−1 CaCl2 in the treatments with 0.5 and 2.5 g humic substance addition was increased by 400% and 540%, respectively, compared with that in the treatment without humic substance at the rate of 0.31 g P kg−1 soil, while the corresponding P concentrations were increased by 80% and 90% at the rate of 1.25 g P kg−1 soil. The order of mixing humic substance and phosphate did not significantly affect desorbed P and labile P extracted with CaCl2.

Minimum Data Set for Assessing Soil Quality in Farmland of Northeast China

Soil quality assessment provides a tool for agriculture managers and policy makers to gain a better understanding of how various agricultural systems affect soil resources. Soil quality of Hailun County, a typical soybean (Glycine max L. Merill) growing area located in Northeast China, was evaluated using soil quality index (SQI) methods. Each SQI was computed using a minimum data set (MDS) selected using principal components analysis (PCA) as a data reduction technique. Eight MDS indicators were selected from 20 physical and chemical soil measurements. The MDS accounted for 74.9% of the total variance in the total data set (TDS). The SQI values for 88 soil samples were evaluated with linear scoring techniques and various weight methods. The results showed that SQI values correlated well with soybean yield (r = 0.658**) when indicators in MDS were weighted by the regression coefficient computed for each yield and index. Stepwise regression between yield and principal components (PCs) indicated that available boron (AvB), available phosphorus (AvP), available potassium (AvK), available iron (AvFe) and texture were the main factors limiting soybean yield. The method used to select an MDS could not only appropriately assess soil quality but also be used as a powerful tool for soil nutrient diagnosis at the regional level.

Potassium Fractions in Soils as Affected by Monocalcium Phosphate, Ammonium Sulfate, and Potassium Chloride Application

Abstract Soil potassium (K) deficiency has been increasing over recent decades as a result of higher inputs of N and P fertilizers concomitant with lower inputs of K fertilizers in China; however, the effects of interactions between N, P, and K of fertilizers on K status in soils have not been thoroughly investigated for optimizing N, P, and K fertilizer use efficiency. The influence of ammonium sulfate (AS), monocalcium phosphate (MCP), and potassium chloride application on K fractions in three typical soils of China was evaluated during 90-d laboratory soil incubation. The presence of AS significantly altered the distribution of native and added K in soils, while addition of MCP did not significantly affected K equilibrium in most cases. Addition of AS significantly increased water-soluble K (WSK), decreased exchangeable K (EK) in almost all the soils except the paddy soil that contained considerable amounts of 2:1 type clay minerals with K added, retarded the formation of fixed K in the soils with K added, and suppressed the release of fixed K in the three soils without K added. These interactions might be expected to influence the K availability to plants when the soil was fertilized with AS. To improve K fertilizer use efficiency, whether combined application of AS and K was to be recommended or avoided should depend on K status of the soil, soil properties, and cropping systems.

Evaluating plant-available potassium in different soils using a modified sodium tetraphenylboron method.

Finding a uniform method to evaluate plant-available potassium (K) in a variety of soils has been a challenge. In this study, the sodium tetraphenylboron (NaBPh4) method was modified and compared with the conventional ammonium acetate (NH4OAc) method to evaluate K availability to perennial ryegrass (Lolium perenne L.) in soils with different K fertilities. The amount of K extracted using NaBPh4 was influenced by extraction time and concentrations of NaCl and NaBPh4. Without NaCl, the NaBPh4 method with low concentrations of NaBPh4 (0.001 and 0.003 mol L−1) could only extract soluble and exchangeable soil K, equivalent to three sequential extractions using the NH4OAc method, whereas the NaBPh4 method with a high NaBPh4 concentration (0.2 mol L−1) could extract all the NH4OAc-extractable K and some easily released nonexchangeable K (NEK) in soils. Easily released NEK contributed significantly to K uptake by ryegrass. Soil K availability estimated using the 60-min (r2 = 0.83-0.92) and 120-min (r2 = 0.84-0.94) modified NaBPh4 methods correlated well to the K removed by one to eight crops of ryegrass. The 60-min modified NaBPh4 method without NaCl (0.2 mol L−1 NaBPh4 + 0.01 mol L−1 EDTA) was suitable for evaluating K availability to plants in a variety of soils, whereas the NH4OAc method was only suitable for evaluating K availability in soils of the same type or with similar K-buffering capacities, but not in soils with variable K buffer capacities or in which the NEK contribution to plant K uptake varied.

Influence of Humic Acid on Interaction of Ammonium and Potassium Ions on Clay Minerals

Abstract Interaction of ammonium (NH+4) and potassium (K+) is typical in field soils. However, the effects of organic matter on interaction of NH+ and K+ have not been thoroughly investigated. In this study, we examined the changes in major physicochemical properties of three clay minerals (kaolinite, illite, and montmorillonite) after humic acid (HA) coating and evaluated the influences of these changes on the interaction of NH+4 and K+ on clay minerals using batch experiments. After HA coating, the cation exchange capacity (CEC) and specific surface area (SSA) of montmorillonite decreased significantly, while little decrease in CEC and SSA occurred in illite and only a slight increase in CEC was found in kaolinite. Humic acid coating significantly increased cation adsorption and preference for NH+4, and this effect was more obvious on clay minerals with a lower CEC. Results of Fourier transform infrared spectrometry analysis showed that HA coating promoted the formation of H-bonds between the adsorbed NH+ and the organo-mineral complexes. HA coating increased cation fixation capacity on montmorillonite and kaolinite, but the opposite occurred on illite. In addition, HA coating increased the competitiveness of NH+ on fixation sites. These results showed that HA coating affected both the nature of clay mineral surfaces and the reactions of NH+4 and K+ with clay minerals, which might influence the availability of nutrient cations to plants in field soils amended with organic matter.