The Evaluation on the Cadmium Net Concentration for Soil Ecosystems.

Yixing, known as the "City of Ceramics", is facing a new dilemma: a raw material crisis. Cadmium (Cd) exists in extremely high concentrations in soil due to the considerable input of industrial wastewater into the soil ecosystem. The in situ technique of diffusive gradients in thin film (DGT), the ex situ static equilibrium approach (HAc, EDTA and CaCl2), and the dissolved concentration in soil solution, as well as microwave digestion, were applied to predict the Cd bioavailability of soil, aiming to provide a robust and accurate method for Cd bioavailability evaluation in Yixing. Moreover, the typical local cash crops-paddy and zizania aquatica-were selected for Cd accumulation, aiming to select the ideal plants with tolerance to the soil Cd contamination. The results indicated that the biomasses of the two applied plants were sufficiently sensitive to reflect the stark regional differences of different sampling sites. The zizania aquatica could effectively reduce the total Cd concentration, as indicated by the high accumulation coefficients. However, the fact that the zizania aquatica has extremely high transfer coefficients, and its stem, as the edible part, might accumulate large amounts of Cd, led to the conclusion that zizania aquatica was not an ideal cash crop in Yixing. Furthermore, the labile Cd concentrations which were obtained by the DGT technique and dissolved in the soil solution showed a significant correlation with the Cd concentrations of the biota accumulation. However, the ex situ methods and the microwave digestion-obtained Cd concentrations showed a poor correlation with the accumulated Cd concentration in plant tissue. Correspondingly, the multiple linear regression models were built for fundamental analysis of the performance of different methods available for Cd bioavailability evaluation. The correlation coefficients of DGT obtained by the improved multiple linear regression model have not significantly improved compared to the coefficients obtained by the simple linear regression model. The results revealed that DGT was a robust measurement, which could obtain the labile Cd concentrations independent of the physicochemical features' variation in the soil ecosystem. Consequently, these findings provide stronger evidence that DGT is an effective and ideal tool for labile Cd evaluation in Yixing.

Photocatalytic degradation of polycyclic aromatic hydrocarbon benzo[a]pyrene by iron oxides and identification of degradation products.

Photocatalytic decay profiles of polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (B[a]P) have been investigated on various synthesized iron oxides and on soil surfaces under a set of diverse conditions. Samples were analysed using the developed HPLC procedure. Results of the present study demonstrate fastest photodisintegration of B[a]P on goethite followed by haematite, magnetite, akaganeite and maghemite, respectively. The effect of soil pH, irradiation wavelength and iron oxide and oxalic acid dose on the degradation of B[a]P was evaluated. The studies revealed enhancement in photodegradation in the presence of oxalic acid due to the occurrence of fenton like reaction. The results showed faster B[a]P degradation under short wavelength UV radiation. Rate constants in acidic, neutral and alkaline soils under optimum dissipation conditions were 1.11×10(-2), 7.69×10(-3) and 9.97×10(-3) h(-1), respectively. The study indicates that iron oxides along with oxalic acid are effective photocatalyst for the remediation of benzo[a]pyrene contaminated soil surfaces. The degradation products of B[a]P in the soils of different pH in presence of goethite were identified and degradation pathways proposed. Peaks due to toxic metabolites such as diones, diols and epoxides disappear after 120 h in all the three soils.

Application of microwave-irradiated manganese dioxide in the removal of polychlorinated biphenyls from soil contaminated by capacitor oil.

The removal of polychlorinated biphenyls (PCBs) from soil contaminated with capacitor oil, using microwave (MW)-irradiated manganese dioxide (MnO2), was examined under different conditions. The effects of different types of MnO2 added as oxidant, as well as the initial amount of water, MnO2, and sulphuric acid solution, were also investigated. The removal efficiencies for dichlorobiphenyls, trichlorobiphenyls, tetrachlorobiphenyls, pentachlorobiphenyls, hexachloro-biphenyls, heptachlorobiphenyls, and octachlorobiphenyls were approximately 95.9%, 82.5%, 52.0%, 71.6%, 62.5%, 28.6%, and 16.1%, respectively, by 800 W MW irradiation for 45 min with the assistance of 0.1 g delta-MnO2 and 0.2 mL water in 1.0 g severely PCB-contaminated soil (sigma PCB = 1560.82 mg/kg); meanwhile, the concentrations of Mn2+ ions detected were from 10.6 +/- 1.9 mg/kg at 0 min to 108.2 +/- 7.8 mg/kg after 45 min MW irradiation, indicating that MnO2 acted as not only a MW absorber but also an oxidizer. Removal efficiencies of PCBs from contaminated soil increased with increasing the amounts of water and MnO2 added. The type of MnO2 also affected the removal of PCBs, following an order of delta-MnO2 > alpha-MnO2 > beta-MnO2. The addition of low concentration of sulphuric acid (such as 1.0 mol/L) solution was favourable for the removal of low chloro-substituted PCBs, but the addition of more than 1.0 mol/L sulphuric acid reduced the removal of all PCBs. The pronounced removal of PCBs from contaminated soil in a short treatment time indicates that MW irradiation with the assistance of MnO2 is an efficient and promising technology for the remediation of PCB-contaminated soil.

Adsorption and desorption behavior of selected pesticides as influenced by decomposition of maize mulch.

Assessing pesticide fate in conservation agricultural systems requires a detailed understanding of their interaction with decomposing surface crop residues (mulch). Adsorption and desorption behavior of glyphosate, s-metolachlor and epoxiconazole was investigated on maize mulch residues decomposed under laboratory and field conditions. Our conceptual approach included characterization of chemical composition and hydrophobicity of mulch residues in order to generate parameters to predict sorption behavior. Adsorption of s-metolachlor and epoxiconazole greatly increased with mulch decomposition, whereas glyphosate adsorption was less affected but its desorption was increased. Mulch characteristics including aromaticity, hydrophobicity and polarity indices were strongly correlated to Koc of the non-ionic pesticides. A predictive model based on compositional data (CoDa) analysis revealed that the sorption capacity of decomposing mulch can be predicted from descriptors such as aromatic and alkyl C corresponding respectively to lignin and NDF biochemical fractions. The decomposition degree of mulch residues should be taken into account while predicting the fate of pesticides.

Influence of humidity and of the electric and magnetic microwave radiation fields on the remediation of TCE-contaminated natural sandy soils.

The influence of moisture content (15% w/w) on the remediation (vaporization) of trichloroethylene (TCE) present in natural sands, chosen as a TCE-polluted model system for soils, was investigated with regard to applied microwave power levels, the depth of the sand sample, and the dielectric factors. The heating process occurring in the sand samples arises through the microwave conduction loss heating and dielectric loss heating mechanisms. The characteristic relevance of the electric and magnetic microwave radiation fields to the heating mechanisms was also examined. Heating by the magnetic microwave radiation field was considerable when magnetite was added to the dry and wet sand samples as the microwave absorber. Optimal microwave conditions are reported for a single-mode microwave applicator. Near-quantitative elimination of the TCE contaminant was achieved for sandy soils within a very short time.

[Microwave thermal remediation of soil contaminated with crude oil enhanced by granular activated carbon].

The advantage of rapid, selective and simultaneous heating of microwave heating technology was taken to remediate the crude oil-contaminated soil rapidly and to recover the oil contaminant efficiently. The contaminated soil was processed in the microwave field with addition of granular activated carbon (GAC), which was used as strong microwave absorber to enhance microwave heating of the soil mixture to remove the oil contaminant and recover it by a condensation system. The influences of some process parameters on the removal of the oil contaminant and the oil recovery in the remediation process were investigated. The results revealed that, under the condition of 10.0% GAC, 800 W microwave power, 0.08 MPa absolute pressure and 150 mL x min(-1) carrier gas (N2) flow-rate, more than 99% oil removal could be obtained within 15 min using this microwave thermal remediation enhanced by GAC; at the same time, about 91% of the oil contaminant could be recovered without significant changes in chemical composition. In addition, the experiment results showed that GAC can be reused in enhancing microwave heating of soil without changing its enhancement efficiency obviously.

Basic studies on the treatment of volatile organic pollutant in sand by microwave radiation.

The heating characteristics of water and sand were investigated to understand the basic features of a microwave soil pollution treatment system and the reasonableness of this method was examined. The evaporation and temperature change of water by microwave irradiation were dependent on its volume and sand showed a three-fold temperature change compared with water. When microwave energy was applied, water showed an even variation in temperature on the whole, however, there was approximately 30 square difference according to the location inside the sand. Sand temperature was observed to show a larger difference as it was horizontally and vertically closer to the microwave irradiation point and horizontal temperature variations were more evenly distributed than vertical variations. Heating characteristics according to the particle size of sand showed that the temperature change was larger when the particle size became smaller and the moisture content of sand was found to influence its heating behavior. In the conditions of experiment, about 50% of the benzene in sand was volatized after 23 minutes of heating and 85% of the total benzene was removed from the sand after 60 minutes of microwave irradiation. For real soil test, more than 70% of BTEX was successfully removed from the soil after 120 minutes of heating.

Ah receptor agonists in UV-exposed toluene solutions of decabromodiphenyl ether (decaBDE) and in soils contaminated with polybrominated diphenyl ethers (PBDEs).

GOAL, SCOPE AND BACKGROUND: The use of polybrominated diphenyl ethers (PBDEs) as flame retardants increases the risk for emissions of other brominated compounds, such as polybrominated dibenzodioxins (PBDDs) and dibenzofurans (PBDFs). The large homology in structure of PBDD/Fs and mechanism of toxic action, i.e. the capacity to activate the Ah receptor (AhR) pathway, compared to their well-studied chlorinated analogues, justifies a raised concern to study the environmental levels and fate of these compounds. Decabromodiphenyl ether (decaBDE) is the most widely used PBDE today. Studies on photolytic debromination of decaBDE in organic solvents have shown debromination of decaBDE, as well as formation of PBDFs. However, little is known about the transformation mechanisms and there are only scarce data on photoproducts and PBDE transformation in environmentally relevant matrices. In this study, mechanism-specific dioxin bioassays were used to study photolytic formation of AhR agonists in toluene solutions of decaBDE. In addition, the influence of irradiation time and UV-light wavelength on the formation was studied. PBDE congener patterns and presence of PBDD/Fs were analysed. Further, AhR agonists were analysed in agricultural soils contaminated with PBDEs. Soils were also exposed to UV-light to study changes in AhR agonist levels. METHODS: Toluene solutions of decaBDE were irradiated using three different spectra of UV-light, simulating UV-A (320-400 nm), UV-AB (280-400 nm), and UV-ABC (250-400 nm). Additionally, decaBDE solutions were exposed to narrow wavelength intervals (10 nm bandwidth) with the central wavelengths 280, 290, 300, 310, 320, 330, 340, 350, 360 nm. AhR agonists in decaBDE solutions were analysed with two different bioassays, the chick embryo liver-cell assay for dioxins (Celcad) and the dioxin responsive, chemically activated luciferase expression assay (DR-Calux). Also, the decaBDE solutions were analysed with LRGC-LRMS to obtain PBDE congener patterns for breakdown of decaBDE, and with HRGC-HRMS, for presence of PBDD/Fs. Four soils were exposed to UV-AB light, under both dry and moist conditions. Levels of AhR agonists in soil extract fractions, before and after UV-exposure, were analysed with the DR-Calux. RESULTS AND DISCUSSION: Significant levels of photoproducts able to activate the AhR pathway, up to 31 ng bio-TEQ/ml, were formed in UV-exposed decaBDE solutions. The transformation yield of decaBDE into AhR agonists was estimated to be at the 0.1%-level, on a molar basis. The net formation was highly dependent on wavelength, with the sample irradiated at 330 nm showing the highest level of dioxin-like activity. No activity was detected in controls. PBDE analysis confirmed decaBDE degradation and a clear time-dependent pattern for debromination of PBDE congeners. AhR agonist effect in the recalcitrant fractions of the soils corresponded to the levels of chemically derived TEQs, based only on chlorinated dioxin-like compounds in an earlier study. It was concluded that no significant levels of other AhR agonists, e.g. PBDFs, were accumulated in the soil. UV-light caused changes in AhR-mediated activity in the more polar and less persistent fractions of the soils, but it is not known which compounds are responsible for this. RECOMMENDATIONS AND PERSPECTIVES: The laboratory experiments in this study show that high levels of AhR agonists can be formed as photoproducts of decaBDE and it is important to elucidate if and under which conditions this might occur in nature. However, soil analysis indicates that photoproducts of PBDE do not contribute to the accumulated levels of persistent dioxin-like compounds in agricultural soil. Still, more data is needed to fully estimate the environmental importance of PBDE photolysis and occurrence of its photoproducts in other environmental compartments. Analysis with dioxin bioassays enabled us to gather information about photoproducts formed from decaBDE even though the exact identities of these compounds were not known. CONCLUSION: Bioassays are valuable for studying environmental transformation processes like this, where chemical analysis and subsequent toxicological evaluation requires available standard compounds and information on toxicological potency. The use of bioassays allows a rapid evaluation of toxicological relevance.

An efficient technology to treat heavy metal--lead--contaminated soil by microwave radiation.

Microwave (MW) technology can be used to vitrify contaminated soil wastes and immobilize heavy metal ions in soils. More than 93% of the Pb(II)-contaminated soil was vitrified to a glass/ceramic formation after 30 min of MW radiation. In a 6-year study, the Pb(II) concentration of the vitrified soil in the leaching test was less than 1.0 mg/l, which is substantially below the USEPA regulatory limit of 5.0 mg/l.

Immobilization of chromium-contaminated soil by means of microwave energy.

To reduce the amount of hazardous wastes contaminated by heavy metals, a new technology to immobilize heavy metal ions is desired. Microwave (MW) technology which can be used to vitrify the contaminated soil wastes and immobilize the heavy metal ions for this purpose to satisfy the leachate test standard. We found that 90%+ of the chromium-contaminated soil went through the glass/ceramic transformation and was thus vitrified after being radiated with MW for 60 min. The chromium ion (Cr6+) concentration in the leaching test of all the vitrified soil samples is less than 1 mg/l, below the USEPA regulatory limit of 5.0 mg/l. This technology may become a major treatment method for hazardous wastes if the large-scale field test proves to be successful. In this paper, we will present the experimental conditions, the results and the future projects.