Mei Lei

Spatial distribution of soil heavy metal pollution estimated by different interpolation methods: Accuracy and uncertainty analysis

Mapping the spatial distribution of contaminants in soils is the basis of pollution evaluation and risk control. Interpolation methods are extensively applied in the mapping processes to estimate the heavy metal concentrations at unsampled sites. The performances of interpolation methods (inverse distance weighting, local polynomial, ordinary kriging and radial basis functions) were assessed and compared using the root mean square error for cross validation. The results indicated that all interpolation methods provided a high prediction accuracy of the mean concentration of soil heavy metals. However, the classic method based on percentages of polluted samples, gave a pollution area 23.54-41.92% larger than that estimated by interpolation methods. The difference in contaminated area estimation among the four methods reached 6.14%. According to the interpolation results, the spatial uncertainty of polluted areas was mainly located in three types of region: (a) the local maxima concentration region surrounded by low concentration (clean) sites, (b) the local minima concentration region surrounded with highly polluted samples; and (c) the boundaries of the contaminated areas.

Cost-benefit calculation of phytoremediation technology for heavy-metal-contaminated soil.

Heavy-metal pollution of soil is a serious issue worldwide, particularly in China. Soil remediation is one of the most difficult management issues for municipal and state agencies because of its high cost. A two-year phytoremediation project for soil contaminated with arsenic, cadmium, and lead was implemented to determine the essential parameters for soil remediation. Results showed highly efficient heavy metal removal. Costs and benefits of this project were calculated. The total cost of phytoremediation was US

First evidence on different transportation modes of arsenic and phosphorus in arsenic hyperaccumulator Pteris vittata

75,375.2/hm(2) or US

Potential of Pteris vittata L. for phytoremediation of sites co-contaminated with cadmium and arsenic: The tolerance and accumulation

37.7/m(3), with initial capital and operational costs accounting for 46.02% and 53.98%, respectively. The costs of infrastructures (i.e., roads, bridges, and culverts) and fertilizer were the highest, mainly because of slow economic development and serious contamination. The cost of phytoremediation was lower than the reported values of other remediation technologies. Improving the mechanization level of phytoremediation and accurately predicting or preventing unforeseen situations were suggested for further cost reduction. Considering the loss caused by environmental pollution, the benefits of phytoremediation will offset the project costs in less than seven years.

Arsenic uptake and transport of Pteris vittata L. as influenced by phosphate and inorganic arsenic species under sand culture.

Arsenic (As) reduction and translocation are key processes for As hyperaccumulation by the hyperaccumulator Pteris vittata L. Micro-X-ray adsorption spectroscopy of P. vittatas rhizoid tissues revealed that As reduction mainly occurred in endodermis during translocation from epidermis to vascular bundle. Prior to reduction, arsenate (As (V)) translocation was an active process requiring energy and employing a phosphate (P) transporter. Use of a synchrotron X-ray microprobe showed that As (V) and P were cotransported and that this process could be enhanced by As (V) exposure or P deficiency but restrained by energy release inhibition caused by 2,4-dinitrophenol or sodium orthovanadate. In contrast, after As reduction, As(III) translocation differed from P translocation and was more efficient, appearing free from the apparent endodermal blockage. The results here revealed the role of the P transporter on As translocation as well as the key role of As reduction in As hyperaccumulation by P. vittata.

Simultaneous compartmentalization of lead and arsenic in co-hyperaccumulator Viola principis H. de Boiss : An application of SRXRF microprobe

Field investigation and greenhouse experiments were conducted to study the tolerance of Pteris vittata L. (Chinese brake) to cadmium (Cd) and its feasibility for remediating sites co-contaminated with Cd and arsenic (As). The results showed that P. vittata could survive in pot soils spiked with 80 mg/kg of Cd and tolerated as great as 301 mg/kg of total Cd and 26.8 mg/kg of diethyltriaminepenta acetic acid (DTPA)-extractable Cd under field conditions. The highest concentration of Cd in fronds was 186 mg/kg under a total soil concentration of 920 mg As/kg and 98.6 mg Cd/kg in the field, whereas just 2.6 mg/kg under greenhouse conditions. Ecotypes of P. vittata were differentiated in tolerance and accumulation of Cd, and some of them could not only tolerate high concentrations of soil Cd, but also accumulated high concentrations of Cd in their fronds. Arsenic uptake and transportation by P. vittata was not inhibited at lower levels (< or = 20 mg/kg) of Cd addition. Compared to the treatment without addition of Cd, the frond As concentration was increased by 103.8% at 20 mg Cd/kg, with the highest level of 6434 mg/kg. The results suggested that the Cd-tolerant ecotype of P. vittata extracted effectively As and Cd from the site co-contaminated with Cd and As, and might be used to remediate and revegetate this type of site.

Reducing H2S production by O2 feedback control during large-scale sewage sludge composting

In order to understand the similarity or difference of inorganic As species uptake and transport related to phosphorus in As-hyperaccumulator, uptake and transport of arsenate (As(V)) and arsenite (As(III)) were studied using Pteris vittata L. under sand culture. Higher concentrations of phosphate were found to inhibit accumulation of arsenate and arsenite in the fronds of P. vittata. The reduction in As accumulation was greater in old fronds than in young fronds, and relatively weak in root and rhizome. Moderate increases, from 0.05 to 0.3 mmol/L, in phosphate reduced uptake of As(III) more than As(V), while the reverse was observed at high concentrations of phosphate (> or = 1.0 mmol/L). Phosphate apparently reduced As transport and the proportion of As accumulated in fronds of P. vittata when As was supplied as As(V). It may in part be due to competition between phosphorus and As(V) during transport. In contrast, phosphate had a much smaller effect on As transport when the As was supplied as As(III). Therefore, the results from present experiments indicates that a higher concentration of phosphate suppressed As accumulation and transport in P. vittata, especially in the fronds, when exposed to As(V); but the suppression of phosphate to As transport may be insignificant when P. vittata exposed to As(III) under sand culture conditions. The finding will help to understand the interaction of P and As during their uptake process in P.

Arsenic Adsorption and its Fractions on Aquifer Sediment: Effect of pH, Arsenic Species, and Iron/Manganese Minerals

The cellular distributions of Pb and As in the leaves of co-hyperaccumulator Viola principis H. de Boiss. were inspected by synchrotron X-ray fluorescence spectroscopy (SRXRF). The results revealed that Pb and As had similar compartmentalization patterns in the leaves. Both elements were enriched in the bundle sheath and the palisade mesophyll. In comparison with the sheath and the mesophyll, the vascular bundle and the epidermis contained lower levels of Pb and As. The palisade enrichment of Pb and As indicated that V. principis H. de Boiss. may have a special mechanism on detoxification of toxic metals within the mesophyll cells. Relative concentrations of both Pb and As in trichome bases were higher than those in trichome rays. The results of hierarchical cluster analysis and correlation analysis confirmed that the distribution of Pb was similar to that of As in the leaves, and their distribution patterns were different from the nutrient elements, such as K, Ca, Mn, Fe, Ni, Cu and Zn. In vivo cellular localization of Pb and As in the leaves provides insight into the physiological mechanisms of metal tolerance and hyperaccumulation in the hyperaccumulators.

A comparison of arsenic accumulation and tolerance among four populations of Pteris vittata from habitats with a gradient of arsenic concentration

Hydrogen sulfide (H(2)S) production patterns and the influence of oxygen (O(2)) concentration were studied based on a well operated composting plant. A real-time, online multi-gas detection system was applied to monitor the concentrations of H(2)S and O(2) in the pile during composting. The results indicate that H(2)S was mainly produced during the early stage of composting, especially during the first 40 h. Lack of available O(2) was the main reason for H(2)S production. Maintaining the O(2) concentration higher than 14% in the pile could reduce H(2)S production. This study suggests that shortening the interval between aeration or aerating continuously to maintain a high O(2) concentration in the pile was an effective strategy for restraining H(2)S production in sewage sludge composting.

EXAFS study on arsenic species and transformation in arsenic hyperaccumulator

Effects of pH, As species, and Fe/Mn minerals on the fractions of adsorbed As in aquifer sediments were evaluated. Kinetic data showed that As adsorption was controlled by diffusion through the external film. Isothermal data of both As(III) and As(V) fitted the Langmuir isotherm well, revealing a monolayer adsorption process. Sequential extraction demonstrated that water-soluble As and non-specifically sorbed As were the major fractions of adsorbed As. Assessing the relationship between the Freundlich KF and the increases in the amounts of As fractions showed that the pH played a key role in weakly adsorbed As, especially water-soluble As. Although inorganic As species converted each other during the adsorption processes, more non-specifically sorbed As was adsorbed in As(V)-treated sediment than in As(III)-treated sediment, showing that the electrostatic selectivity controlled the non-specific adsorption. Additionally, specifically sorbed As and As associated with the amorphous phases were predominated by Fe/Mn minerals, especially Fe(III) (hydr)oxides. These results suggested that pH, As species, and Fe/Mn minerals would regulate the As fractions in aquifer sediments, and therefore control As cycling in aquifer systems.