Long Cang

Roles of abiotic losses, microbes, plant roots, and root exudates on phytoremediation of PAHs in a barren soil

Phytoremediation is an emerging technology for the remediation of polycyclic aromatic hydrocarbons (PAHs). In this study, pot experiments were conducted to evaluate the efficacy of phytoremediation of phenanthrene and pyrene in a typical low organic matter soil (3.75 g kg(-1)), and the contribution proportions of abiotic losses, microbes, plant roots, and root exudates were ascertained during the PAHs dissipation. The results indicated that contribution of abiotic losses from this soil was high both for phenanthrene (83.4%) and pyrene (57.2%). The contributions of root-exudates-enhanced biodegradation of phenanthrene (15.5%) and pyrene (21.3%) were higher than those of indigenous microbial degradation. The role of root exudates on dissipation of phenanthrene and pyrene was evident in this experiment. By the way, with the increasing of ring numbers in PAHs structures, the root-exudates-enhanced degradation became more and more important. BIOLOG-ECO plate analysis indicated that microbial community structure of the soil receiving root exudates had changed. The removal efficiency and substrate utilization rate in the treatment with plant roots were lower than the treatment only with root exudates, which suggested that possible competition between roots and microbes for nutrients had occurred in a low organic matter soil.

Humic Acid Facilitates the Transport of ARS-Labeled Hydroxyapatite Nanoparticles in Iron Oxyhydroxide-Coated Sand

Hydroxyapatite nanoparticles (nHAP) have been widely used to remediate soil and wastewater contaminated with metals and radionuclides. However, our understanding of nHAP transport and fate is limited in natural environments that exhibit significant variability in solid and solution chemistry. The transport and retention kinetics of Alizarin red S (ARS)-labeled nHAP were investigated in water-saturated packed columns that encompassed a range of humic acid concentrations (HA, 0-10 mg L(-1)), fractional surface coverage of iron oxyhydroxide coatings on sand grains (λ, 0-0.75), and pH (6.0-10.5). HA was found to have a marked effect on the electrokinetic properties of ARS-nHAP, and on the transport and retention of ARS-nHAP in granular media. The transport of ARS-nHAP was found to increase with increasing HA concentration because of enhanced colloidal stability and the reduced aggregate size. When HA = 10 mg L(-1), greater ARS-nHAP attachment occurred with increasing λ because of increased electrostatic attraction between negatively charged nanoparticles and positively charged iron oxyhydroxides, although alkaline conditions (pH 8.0 and 10.5) reversed the surface charge of the iron oxyhydroxides and therefore decreased deposition. The retention profiles of ARS-nHAP exhibited a hyperexponential shape for all test conditions, suggesting some unfavorable attachment conditions. Retarded breakthrough curves occurred in sands with iron oxyhydroxide coatings because of time-dependent occupation of favorable deposition sites. Consideration of the above effects is necessary to improve remediation efficiency of nHAP for metals and actinides in soils and subsurface environments.

Source identification and apportionment of heavy metals in urban soil profiles

Because heavy metals (HMs) occurring naturally in soils accumulate continuously due to human activities, identifying and apportioning their sources becomes a challenging task for pollution prevention in urban environments. Besides the enrichment factors (EFs) and principal component analysis (PCA) for source classification, the receptor model (Absolute Principal Component Scores-Multiple Linear Regression, APCS-MLR) and Pb isotopic mixing model were also developed to quantify the source contribution for typical HMs (Cd, Co, Cr, Cu, Mn, Ni, Pb, Zn) in urban park soils of Xiamen, a representative megacity in southeast China. Furthermore, distribution patterns of their concentrations and sources in 13 soil profiles (top 20 cm) were investigated by different depths (0-5, 5-10, 10-20 cm). Currently the principal anthropogenic source for HMs in urban soil of China is atmospheric deposition from coal combustion rather than vehicle exhaust. Specifically for Pb source by isotopic model ((206)Pb/(207)Pb and (208)Pb/(207)Pb), the average contributions were natural (49%)>coal combustion (45%)≫traffic emissions (6%). Although the urban surface soils are usually more contaminated owing to recent and current human sources, leaching effects and historic vehicle emissions can also make deep soil layer contaminated by HMs.

Heavy Metal Transfer from Soil to Vegetable in Southern Jiangsu Province, China

Vegetable fields in peri-urban areas receive large amounts of extraneous heavy metals because of rapid urbanization and industrialization in China. The concentrations of Cu, Zn, and Pb in 30 soil samples and 32 vegetable samples, collected from 30 different sites in southern Jiangsu Province of China, were measured and their transfer from soil to vegetable was determined. The results showed that the soil samples had wide ranges of pH (4.25–7.85) and electrical conductivity (EC) (0.24–3.42 dS m −1 ). Among the soil samples, there were four soil samples containing higher Cu and two soil samples containing higher Zn concentrations than those specified in the Chinese Soil Environmental Quality Standard II. However, no vegetable sample was found to contain a high level of Cu or Zn. In contrast, one vegetable sample contained 0.243 mg Pb kg −1 FW, which was above the Chinese Food Hygiene Standard, whereas the corresponding soil Pb concentration was lower than the Chinese Soil Environmental Quality Standard II. The transfer coefficients of Cu of all vegetable samples exceeded the suggested coefficient range, implying that extraneous Cu had high mobility and bioavailability to vegetables. There was no significant correlation between extractable soil heavy metal concentrations with four kinds of extractants and soil pH, EC, heavy metal concentrations in vegetables and soils, except that soil pH correlated well with the extractable soil Cu, Zn, and Pb concentrations with 1.0 mol L −1 NH4NO3. Moreover, diethylenetriamine pentaacetic acid (DTPA) extraction method was a more efficient method of extracting heavy metals from the soils independent of soil pH and EC than other three methods used.

Effects of electrokinetic treatment of a heavy metal contaminated soil on soil enzyme activities

There is a growing concern on the potential application of a direct current (DC) electric field to soil for removing contaminants, but little is known about its impact on soil enzyme activities. This study investigated the change of enzyme activities of a heavy metal contaminated soil before and after electrokinetic (EK) treatments at lab-scale and the mechanisms of EK treatment to affect soil enzyme activities were explored. After treatments with 1-3 V cm(-1) of voltage gradient for 420 h, soil pH, electrical conductivity (EC), soil organic carbon, dissolved organic carbon (DOC), soil heavy metal concentration and enzyme activities were analyzed. The results showed that the average removal efficiencies of soil copper were about 65% and 83% without and with pH control of catholyte, respectively, and all the removal efficiencies of cadmium were above 90%. The soil invertase and catalase activities increased and the highest invertase activity was as 170 times as the initial one. The activities of soil urease and acidic phosphatase were lower than the initial ones. Bivariate correlation analyses indicated that the soil invertase and acidic phosphatase activities were significantly correlated with soil pH, EC, and DOC at P<0.05, but the soil urease activities had no correlation with the soil properties. On the other hand, the effects of DC electric current on solution invertase and catalase enzyme protein activities indicated that it had negative effect on solution catalase activity and little effect on solution invertase activity. From the change of invertase and catalase activities in soil and solution, the conclusion can be drawn that the dominant effect mechanism is the change of soil properties by EK treatments.

Enhanced-electrokinetic remediation of copper–pyrene co-contaminated soil with different oxidants and pH control

Electrokinetic (EK) remediation has potential to simultaneously remove heavy metals and organic compounds from soil, but the removal percent of these pollutants is very low in general if no enhancing treatment is applied. This study developed a new enhanced-EK remediation technology to decontaminate a heavy metal-organic compound co-contaminated soil by applying different oxidants and pH control. A red soil was used as a model clayed soil, and was spiked with pyrene and Cu at about 500 mg kg(-1) for both to simulate real situation. Bench-scale EK experiments were performed using four oxidants (H(2)O(2), NaClO, KMnO(4), and Na(2)S(2)O(8)) and controlling electrolyte pH at 3.5 or 10. After the treatments with 1.0 V cm(-1) of voltage gradient for 335 h, soil pH, electrical conductivity, and the concentrations and chemical fractionations of soil pyrene and Cu were analyzed. The results showed that there was significant migration of pyrene and Cu from the soil, and the removal percent of soil pyrene and Cu varied in the range of 30-52% and 8-94%, respectively. Low pH favoured the migration of soil Cu, while KMnO(4) was the best one for the degradation of pyrene among the tested oxidants, although it unfortunately prevented the migration of soil Cu by forming Cu oxide. Application of Na(2)S(2)O(8) and to control the catholyte pH at 3.5 were found to be the best operation conditions for decontaminating the Cu-pyrene co-contaminated soil.

Application of bioassays to evaluate a copper contaminated soil before and after a pilot-scale electrokinetic remediation

Remediation programmes are considered to be complete when human risk-based criteria are met. However, these targets are often unsatisfied with the ecological parameters that may be important with regard to future soil use. Five soil subsamples, collecting along a pilot-scale soil column after electrokinetic treatment, were studied, from which about 42.0%-93.3% soil Cu had been successfully removed. A series of biological assays including soil microbial biomass carbon, basal soil respiration, soil urease activity, earthworm assays, and seed assays were used to evaluate their ecological risks. The results showed that the bioassay data from the treatment variants did not supposedly reflecting the decreased soil Cu concentrations after the electrokinetic treatment, but were highly correlated with some soil physicochemical characteristics. It suggests that bioassays are necessary to assess the ecotoxicity of soil after electrokinetic treatment.

TiO2 photocatalytic degradation of 4-chlorobiphenyl as affected by solvents and surfactants

PurposeTiO2 photocatalytic degradation of 4-chlorobiphenyl (PCB3) in aqueous solution under UV irradiation was investigated as affected by different environmental factors, including initial PCB3 concentration, TiO2 content, UV intensity, H2O2 concentration, cosolvents, and surfactants.Materials and methodsThe solution of PCB3 with TiO2 was irradiated by medium mercury lamp. The concentration of PCB3 and intermediates was analyzed by GC-μECD and GC–MS. The values of point charge and bond length were also calculated with ChemOffice 2004 (Mopac unit).Results and discussionPhotocatalysis was very effective for PCB3 removal, and the degradation kinetics were fitted with a pseudo-first order reaction model. PCB3 was efficiently degraded in the presence of acetone and acetonitrile, but was completely inhibited with other examined cosolvents. HPCD and Tween80 also inhibited the degradation rate of PCB3, while Brij35 slightly decreased the degradation rate of PCB3 at first, and then increased. The reaction mechanism occurred principally by hydroxyl radicals involving the participation of holes and superoxide anion oxidation. A possible photocatalytic degradation pathway of PCB3 was proposed based on the identified reaction intermediates as well as computer simulation.ConclusionsThe photocatalytic approach could be successfully applied to degrade PCB3, and cosolvents and surfactants significantly influenced its degradation kinetics.

Electrokinetic delivery of persulfate to remediate PCBs polluted soils: Effect of different activation methods.

Persulfate-based in-situ chemical oxidation (ISCO) for the remediation of organic polluted soils has gained much interest in last decade. However, the transportation of persulfate in low-permeability soil is very low, which limits its efficiency in degrading soil pollutants. Additionally, the oxidation-reduction process of persulfate with organic contaminants takes place slowly, while, the reaction will be greatly accelerated by the production of more powerful radicals once it is activated. Electrokinetic remediation (EK) is a good way for transporting persulfate in low-permeability soil. In this study, different activation methods, using zero-valent iron, citric acid chelated Fe(2+), iron electrode, alkaline pH and peroxide, were evaluated to enhance the activity of persulfate delivered by EK. All the activators and the persulfate were added in the anolyte. The results indicated that zero-valent iron, alkaline, and peroxide enhanced the transportation of persulfate at the first stage of EK test, and the longest delivery distance reached sections S4 or S5 (near the cathode) on the 6th day. The addition of activators accelerated decomposition of persulfate, which resulted in the decreasing soil pH. The mass of persulfate delivered into the soil declined with the continuous decomposition of persulfate by activation. The removal efficiency of PCBs in soil followed the order of alkaline activation > peroxide activation > citric acid chelated Fe(2+) activation > zero-valent iron activation > without activation > iron electrode activation, and the values were 40.5%, 35.6%, 34.1%, 32.4%, 30.8% and 30.5%, respectively. The activation effect was highly dependent on the ratio of activator and persulfate.

Reducing the bioavailability of PCBs in soil to plant by biochars assessed with triolein-embedded cellulose acetate membrane technique.

Coupling with triolein-embedded cellulose acetate membrane (TECAM) technique, hydroxypropyl β-cyclodextrins (HPCD) extraction method, and the greenhouse pot experiments, the influences of biochars on polychlorinated biphenyls (PCBs) bioavailability in soil to plant (Brassica chinensis L. and Daucus carota) were investigated. Addition of 2% biochars to soils significantly reduced the uptake of PCBs in plant, especially for di-, tri- and tetra-chlorobiphenyls. PCBs concentrations in the roots of B. chinensis and D. carota were reduced for 61.5-93.7%, and 12.7-62.4%, respectively in the presence of biochars. The kinetic study showed that in the soils amended with/without biochars, PCBs concentrations accumulated in TECAM, as well as in the HPCD extraction solution, followed significant linear relationships with those in plant roots. Application of biochars to soil is a potentially promising method to reduce PCBs bioavailability whereas TECAM technique can be a useful tool to predict the bioavailability of PCBs in soil.