Changwen Du

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.

Plants use alternative strategies to utilize nonexchangeable potassium in minerals

Plant species differ in their capacity to use nonexchangeable potassium (NEK) in soils. In this study two typical plants with high K use efficiency, ryegrass and grain amaranth, were compared with regard to their capacity to use K from five K-bearing minerals. Biomass relative yield and K uptake data indicated that ryegrass was much more efficient than grain amaranth at using NEK in minerals. Root exudates of grain amaranth collected under hydroponic culture contained considerable amounts of oxalic and citric acids, while these acids were not detected in ryegrass root exudates. Compared with grain amaranth, the kinetic parameters of K uptake by ryegrass roots were characterized by a significantly higher K uptake rate (Vmax) and a significantly lower Cmin, the minimum external K concentration at which K is taken up. The dynamic release of NEK from minerals in various solutions showed that the release rate of NEK was largely K-concentration dependent and some thresholds of K concentration prevented further NEK release from minerals. The K thresholds were related to mineral type and increased in the presence of Ca2+ or Na+ in solutions. The positive effect of H+ (20xa0mmol L−1) on NEK release was also mainly attributed to elevating the thresholds of K concentration, rather than to the effects of weathering. The results indicated that the main mechanism by which plant species efficiently use NEK in minerals was to the capacity of plants to absorb K at low concentrations. The lower the Cmin for the root K uptake, the higher the expected NEK use efficiency of the plant.

Application of Infrared Photoacoustic Spectroscopy in Soil Analysis

Abstract Soil analysis has become routine work for soil management and crop production. However, laboratory analysis–based determination of soil properties is expensive and time consuming, which is not suitable for precision agriculture. Infrared spectroscopy (IR) appears as an alternative and fast technique to measure soil properties and has had wide application; in particular, a new method called infrared photoacoustic spectroscopy (FTIR-PAS) has been applied in soil analysis. The soil infrared photoacoustic spectrum is more convenient to record; the spectra contain more useful information versus conventional reflectance spectroscopy, and it appears promising for identification of soil types and measure soil properties. The step-scan function of FTIR-PAS makes it possible to explore the soil microstructure in situ; furthermore, more sensible photoacoustic cells (PA), such as a quartz-enhanced PA cell, will make FTIR-PAS a strong tool for the study of soil science. The application of infrared photoacoutic spectroscopy in soil analysis is largely dependent on spectra pretreatment and chemometrics methods due to strong interferences, and more mathematical tools models will benefit or optimize the prediction performance. To make full use of soil infrared spectra, soil spectra library construction is required in the future, which will play an important role in the application of soil analysis.

Biodegradation of a biochar-modified waterborne polyacrylate membrane coating for controlled-release fertilizer and its effects on soil bacterial community profiles

Biochar-modified polyacrylate-like polymers are promising waterborne polymer-based membrane coatings for controlled-release fertilizers. However, the effect of these membrane polymers on paddy soil is unknown. A soil incubation experiment was conducted using Fourier transform infrared photoacoustic spectroscopy to monitor the changes in the polymer-coated membranes in paddy soil, and Biolog EcoPlates and polymerase chain reaction-denaturing gradient gel electrophoresis were used to detect the effects of the membranes on soil bacterial community profiles. Compared to unmodified membranes, the biodegradation rate of the biochar-modified membrane was slower, and the membrane was more intact, which improved and guaranteed the controlled release of nutrients. Compared to the soil without membranes, the biochar-modified membranes, as well as unmodified ones, showed no significant impacts on the composition diversity of soil dominant bacterial community. The activity and functional diversity of soil culturable microbial community during the early stage of incubation were reduced by biochar-modified membranes due to the release of small amount of soluble organic materials but were both recovered in the 12th month of the incubation period. Therefore, the biochar-modified waterborne polyacrylate was environmentally friendly, demonstrating its potential both in the development of coated controlled-release fertilizers and in the utilization of crop residue.

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.

Effects of Boron and Calcium Supply on Calcium Fractionation in Plants and Suspension Cells of Rape Cultivars with Different Boron Efficiency

Abstract In this study, the effects of boron (B) and calcium (Ca) supply on Ca fractionation in suspension cells and different tissues of rape (Brassica napus L.) plants of two cultivars with different B efficiency were studied, with a purpose to elucidate the mechanism by which B affects Ca concentration in plants. As Ca supply increased in nutrient solution or culture medium, the relatively easily extractable Ca fractions, that is H2O and 80% ethanol extractable Ca in leaves, 1 mol L−1 NaCl extractable Ca in upper leaves, roots and suspension‐cell were significantly increased. While the recalcitrant Ca fractions extracted by 2% acetic acid, 0.6 mol L−1 HCl and Ca in the residue were not affected by Ca supply. Increasing B supply in nutrient solution or culture media significantly reduced 1 mol L−1NaCl extracted Ca in suspension cell and roots of both cultivars, which were most likely related to the alteration of cell wall metabolism. Calcium extracted by 2% acetic acid, 0.6 mol L−1 HCl and Ca in residue in suspension‐cell and roots of B inefficient cultivar Bakow were easily improved by B deficiency as compared to that of B efficient cultivar Tezao16. Increasing of these relative recalcitrant Ca fractions was related to the different response of cultivars to the B deficiency, which may reflected different extent that Ca deposited in the two cultivars due to impaired membrane integrity under B deficiency. The effects of B on Ca concentration in lower and upper leaves of the two cultivars were quite different and were the integrated effects of B on Ca metabolism, Ca transport in plants and growth of certain organ. Increasing B supply increased total Ca concentration in upper leaves of Bakow and reduced that of Tezao16, which might relate to the different adaptability of the two cultivars to comparatively higher B supply.

Application of Nano FeIII–Tannic Acid Complexes in Modifying Aqueous Acrylic Latex for Controlled-Release Coated Urea

Acrylic latexes are valuable waterborne materials used in controlled-release fertilizers. Controlled-release urea coated with these latexes releases a large amount of nutrients, making it difficult to meet the requirement of plants. Herein, FeIII-tannic acid (TA) complexes were blended with acrylic latex and subsequently reassembled on a surface of polyacrylate particles. These complexes remarkably retarded the release of urea (the preliminary solubility was decreased from 22.3 to 0.8%) via decreasing the coating tackiness (Tg was increased from 4.17 to 6.42 °C), increasing the coating strength (tensile stress was improved from 3.88 to 4.45 MPa), and promoting the formation of denser structures (surface tension was decreased from 37.37 to 35.94 mN/m). Overall, our findings showed that a simple blending of FeIII-TA complexes with acrylic latex produces excellent coatings that delay the release of urea, which demonstrates great potential for use in controlled-release fertilizers coated with waterborne polymers.

Application of FTIR-PAS and Raman spectroscopies for the determination of organic matter in farmland soils

In soil analysis, Raman spectroscopy is not as widely used as infrared spectroscopy mainly owing to fluorescence interferences. This paper investigated the feasibility of Fourier-transform infrared photoacoustic (FTIR-PAS) and Raman spectroscopies for predicting soil organic matter (SOM) using partial least squares regression (PLSR) analysis. 194 farmland soil samples were collected and scanned with FTIR and Raman spectrometers in the spectral range of 4000-400cm(-1) and 180-3200cm(-1), respectively. For the PLSR models, the combined dataset was split into 146 samples as the calibration set (75%) and 48 samples as the validation set (25%). The optimal number of analytical factors was determined using a leave-one-out cross-validation. The results showed that SOM could be predicted using FTIR-PAS and Raman spectroscopies independently, with R(2)>0.70 and RPD>1.8 for the validation sets. In comparison to the single applications of FTIR-PAS and Raman spectroscopies, accurate prediction of SOM was made by combining FTIR-PAS and Raman spectroscopies, with R(2)=0.81 and RPD=2.18 for the validation sets. By statistically assessing large amounts of PLS models, model-population analysis confirmed that the accuracy of the PLS model can be increased by combining FTIR-PAS and Raman spectroscopies. In conclusion, the combination of FTIR-PAS and Raman spectroscopies is a promising alternative for soil characterization, especially for the prediction of SOM, owing to the availability of complementary information from both FTIR-PAS (polar vibrations) and Raman spectroscopy (non-polar vibrations).