Quan-Ying Wang

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.

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.

Solid/solution Cu fractionations/speciation of a Cu contaminated soil after pilot-scale electrokinetic remediation and their relationships with soil microbial and enzyme activities.

The aim of this study was to investigate the detailed metal speciation/fractionations of a Cu contaminated soil before and after electrokinetic remediation as well as their relationships with the soil microbial and enzyme activities. Significant changes in the exchangeable and adsorbed-Cu fractionations occurred after electrokinetic treatment, while labile soil Cu in the solution had a tendency to decrease from the anode to the cathode, and the soil free Cu(2+) ions were mainly accumulated in the sections close to the cathode. The results of regression analyses revealed that both the soil Cu speciation in solution phase and the Cu fractionations in solid phase could play important roles in the changes of the soil microbial and enzyme activities. Our findings suggest that the bioavailability of soil heavy metals and their ecotoxicological effects on the soil biota before and after electroremediation can be better understood in terms of their chemical speciation and fractionations.

Free Cu2+ Ions, Cu Fractionation and Microbial Parameters in Soils from Apple Orchards Following Long-Term Application of Copper Fungicides

Abstract Soil samples were collected from apple orchards 5, 15, 20, 30, and 45 years old, and one adjacent forest soil was used as reference to investigate the free Cu 2+ ion activity in soil solution and the soil Cu fractionation in the solid phase following long-term application of copper fungicide, Bordeaux mixture, in apple orchards and to investigate the relationships among soil free Cu 2+ ions, Cu fractionation and soil microbial parameters. The total Cu concentration in the orchard soils varied from 21.8 to 141 mg kg −1 , increasing with the orchard age, and the value for the reference soil was 12.5 mg kg −1 . The free Cu 2+ ion concentrations in the soil solutions extracted by 0.01 mol L −1 KNO 3 ranged from 3.13 × 10 −8 (reference) to 4.08 × 10 −6 mol L −1 (45 years-old orchard). The concentration of Cu complexed in the fulvic fraction increased with orchard age from 5.16 to 52.5 mg kg −1 . This was also the case for other soil Cu fractions except the residual one. The residual soil Cu remained practically constant, ranging from 4.28 to 5.66 mg kg −1 , suggesting that anthropogenic soil Cu mainly existed in the more labile active fractions. Regression analyses revealed that both the free Cu 2+ ions in the soil solution and the humic acid-complexed Cu fraction in the solid phase were strongly related with soil microbial parameters.

High performance and prospective application of xanthate-modified thiourea chitosan sponge-combined Pseudomonas putida and Talaromyces amestolkiae biomass for Pb(II) removal from wastewater

Biosorption using microbes has been proved to be an efficient technology to remove heavy metals from wastewater, whereas the imperfections in mechanical property and separation limit their practical application. In this study, Pseudomonas putida I3 and Talaromyces amestolkiae Pb respectively combined with xanthate-modified thiourea chitosan sponge (PXTCS and TXTCS) were synthesized to investigate the Pb(II) removal ability from solutions. The prepared biosorbents possessed a three-dimensional macroporous structure convenient for separation. Experimental data indicated their biosorption behaviors well followed the pseudo-second-order kinetics and Langmuir isotherm model. The maximum biosorption capacities of PXTCS and TXTCS were 232.03 and 241.61mgg-1 with 40% P. putida I3 and 15% T. amestolkiae Pb, respectively. For the effects of co-existing metal ions on Pb(II) biosorption, the promoting degree followed the sequence: Zn(II)>Na(I)≈K(I)>Ca(II)>Mg(II)≈Al(III)≫Cd(II)>Fe(III). Both prepared biosorbents were effective in removing heavy metals from simulated industrial effluents containing various trace-level heavy metals or high concentration Pb(II).

Bioavailability of Soil Copper from Different Sources： Integrating Chemical Approaches with Biological Indicators

Abstract Bioavailability is a key parameter in assessing contaminant transfer to biota. However, the input patterns and soil use types may impact the metal bioavailability. Several soil parameters were measured including chemical properties, such as pH, organic C, and Cu solution/solid speciation, and biological properties, such as soil microbial biomass C (SMBC), seed germination, and root elongation, to evaluate the bioavailability of Cu contaminated soils from three different sources, i.e., non-ferrous metal mining, Cu-based fungicides, and Cu-smelting. The results revealed that free Cu2+ ion in soil solution and the ratios of Cu fractions to total Cu content in the solid phase could not be used to predict total Cu content in soils. The indexes of seed germination and root elongation appeared not to be good biomonitors of Cu contamination in soils, which were more sensitive to soil pH and soil organic carbon (SOC). Relationships between SMBC and soil Cu forms or the ratio of SMBC/SOC and soil Cu forms showed that free Cu2+ ion and humic acid-complexed Cu could significantly inhibit soil microbial activities. Our findings suggested that both metal chemical forms and biological bioassays should be considered as a complementary technique rather than an alternative to evaluate the metal bioavailability from different pollution sources.

Integration of chemical and toxicological tools to assess the bioavailability of copper derived from different copper-based fungicides in soil

Because the extensive use of Cu-based fungicides, the accumulation of Cu in agricultural soil has been widely reported. However, little information is known about the bioavailability of Cu deriving from different fungicides in soil. This paper investigated both the distribution behaviors of Cu from two commonly used fungicides (Bordeaux mixture and copper oxychloride) during the aging process and the toxicological effects of Cu on earthworms. Copper nitrate was selected as a comparison during the aging process. The distribution process of exogenous Cu into different soil fractions involved an initial rapid retention (the first 8 weeks) and a following slow continuous retention. Moreover, Cu mainly moved from exchangeable and carbonate fractions to Fe-Mn oxides-combined fraction during the aging process. The Elovich model fit well with the available Cu aging process, and the transformation rate was in the order of Cu(NO3)2 > Bordeaux mixture > copper oxychloride. On the other hand, the biological responses of earthworms showed that catalase activities and malondialdehyde contents of the copper oxychloride treated earthworms were significantly higher than those of Bordeaux mixture treated earthworms. Also, body Cu loads of earthworms from different Cu compounds spiked soils were in the following order: copper oxychloride > Bordeaux mixture. Thus, the bioavailability of Cu from copper oxychloride in soil was significantly higher than that of Bordeaux mixture, and different Cu compounds should be taken into consideration when studying the bioavailability of Cu-based fungicides in the soil.

A facile approach for surface alteration of Pseudomonas putida I3 by supplying K2SO4 into growth medium: Enhanced removal of Pb(II) from aqueous solution

A new sight of obtaining a high efficient biosorbent by supplying specific salts into bacterial growth medium was investigated in this study for Pb(II). Among a series of salts including Na2SO4, Na2S2O3, KCl, and K2SO4, the highest Pb(II) removal efficiency was observed by psychrotrophilic Pseudomonas putida I3 grown in the presence of 30g/L K2SO4 (KSI3-30) with biosorption capacity of 62.89mg/g under cold condition (15°C), which was increased by 42.35% as compared to control (without any additive, RI3). This stimulation effect was ascribed to the increase of potassium and sulfur containing groups on KSI3-30 surface via metabolic dependent ways. The probable mechanism for Pb(II) adsorption was ion-exchange and chemical complexation. The thermal and kinetic data well fitted to Langmuir adsorption model and pseudo-second order and intraparticle diffusion kinetic model. Good recyclability and effectively dealing with real wastewater suggested KSI3-30 was a promising biosorbent for Pb-contaminated wastewater treatment.