[Reduction and Oxidation of Mercury by Dissolved Organic Matter Under Anaerobic Conditions].

In sediments, wetlands, and flooded paddy soils, natural organic matter (DOM), such as humic acid (HA) and fulvic acid (FA), exist in a reduced state and mediate the reduction of Hg(Ⅱ) and affect the transformation of mercury and geochemical cycles. This study simulated a dark anaerobic environment to study the reduction of Hg(Ⅱ) by reduced HA and FA. Compared to oxidized HA and FA, the reduction capacity of the reduced HA and FA for Hg(Ⅱ) were higher. The optimal concentrations of reduced HA and FA to reduce Hg(Ⅱ) to Hg(0) were 0.2 mg·L-1 and 1.5 mg·L-1, respectively. The reduction quantity of Hg(Ⅱ) was enhanced with the increased concentration of reduced HA and FA at a lower than optimal concentration, whereas the reduction quantity of Hg(Ⅱ) decreased with increasing concentration of reduced HA and FA at a higher than optimal concentration due to the occurrence of thiol-competitive complexation. Hg(Ⅱ) was not reduced at a reduced HA concentration of 5 mg·L-1. The kinetics results of Hg(Ⅱ) reduction demonstrated that the reduction rates were IHSS-HA > FRC-HA > FRC-FA at a low molar ratio (dissolved organic carbon (DOC):Hg(Ⅱ)=400:1). The reduction of Hg(Ⅱ) by the reduced HA stopped or processed in the opposite direction at a high molar ratio (DOC:Hg(Ⅱ)=10000:1). The quantity of Hg(0) decreased with increasing HA concentration. Furthermore, as the concentrations of reduced HA and FA were increased to 5 mg·L-1 and 10 mg·L-1, respectively, no Hg(0) was detected in the samples. The experiment of the recovery confirmed that reduced HA and FA reacted with Hg(0). Additionally, reduced HA, FA, and Hg(0) induced oxidative complexation with sulfhydryl or disulfide bonds. Reduced DOM played a dual role in Hg redox reactions, affecting the availability of active Hg, which, in turn, affected the methylation of microbial Hg.

[Prediction of PAHs Bioavailability in Spiked Soil by Composite Extraction with Hydroxypropyl-ß-cyclodextrin and Rhamnolipid].

In this study, composite extraction of hydroxypropyl-ß-cyclodextrin (HPCD) with rhamnolipid (RL) was selected to assess the bioavailability of polycyclic aromatic hydrocarbons (PAHs) to earthworms in red soil from Hainan, China, spiked with phenanthrene (Phe), pyrene (Pyr) and benzo (a) pyrene (BaP). The results showed that when RL was more than the critical micelle concentration, apparent solubility of PAHs increased due to micellar solubilization of RL. So more PAHs were desorbed from solid phase of soil. Real biological experiments showed that there was a good linear relationship between earthworm-accumulated PAHs and HPCD/RL-extracted PAHs (R2=0.98, n=15). However, earthworm-accumulated PAHs was 2.04 times higher than HPCD-extracted PAHs, but only 1.15 times higher than HPCD/RL-extracted PAHs. This indicated that HPCD/RL was more actual and reliable than HPCD in the assessment of PAHs bioavailability to earthworms. Therefore, the addition of RL, to some extent, enhanced the prediction ability of HPCD in PAHs bioavailability, which might provide a new direction and implications in risk assessment and bioremediation of organic contaminants.

[Aging Law of PAHs in Contaminated Soil and Their Enrichment in Earthworms Characterized by Chemical Extraction Techniques].

To evaluate the effect of aging on the availability of PAHs, chemical extraction by exhaustive ( ASE extraction) and nonexhaustive techniques (Tenax-TA extraction, hydroxypropyl-p-cyclodextrin ( HPCD ) extraction, n-butyl alcohol ( BuOH) extraction) as well as PAHs accumulation in earthworms (Eisenia fetida) were conducted in yellow soil from Baguazhou, Nanjing, China, and red soil from Hainan, China, spiked with phenanthrene, pryene and benzo(a) pyrene and aged 0, 7, 15, 30 and 60 days. The results showed that the concentration of PAHs extracted by ASE and three nonexhaustive techniques and accumulated by earthworms significantly decreased with aging time, except the ASE extracted concentration between 30-and 60-day aging time. Furthermore, the relationships were studied in this experiment between chemical extracted PAHs concentration and accumulated concentration in earthworms. PAHs accumulated concentration in earthworms was not significantly correlated with the exhaustive extracted concentration of PAHs in soil (R² 0.44-0.56), which indicated that ASE extraction techniques could not predict PAHs bioavailability to earthworms because it overestimated the risk of PAHs. However, the PAHs accumulated concentration in earthworms was significantly correlated with the three nonexhaustive extracted concentrations of PAHs in soil, which indicated that all the three nonexhaustive techniques could predict PAHs bioavailability to earthworm to some extent, among which, HPCD extraction (R² 0.94-0.99) was better than Tenax-TA extraction (R² 0.62-0.87) and BuOH extraction (R² 0.69-0.94). So HPCD extraction was a more appropriate and reliable technique to predict bioavailability of PAHs in soil.

[Influence and assessment of biochar on the bioavailability of chlorobenzenes in soil].

A laboratory experiment was conducted to study the influence of biochar on the residues of chlorobenzenes (CBs) in soil. Two treatments as the control and the addition of 1% wheat straw biochar were designed. Three chemical extractions as butanol, HPCD and Tenax extractions and earthworm accumulation were used to assess the changes of the bioavailability of CBs in soil. The results showed that the residues of HCB, PeCB and 1,2,4,5-TeCB in the control were 29.87%, 18.02% and 5.16% after 4 months incubation, however, the residues of HCB, PeCB and 1,2,4,5-TeCB in biochar amended soil were 68.25%, 61.32% and 58.02%, respectively, indicating that biochar amendment would inhibit the dissipation of CBs in soil. Butanol, HPCD and Tenax extraction as well as earthworm accumulation results demonstrated that the bioavailability of CBs in soil was significantly affected by biochar amendment (P < 0.05). With aging time increase, the biochar amendment significantly lowered the bioavailability of CBs. The extraction ratios differed among different chemical extraction methods. The extraction ratio was HCB > PeCB > 1,2,4,5-TeCB for butanol and Tenax extraction, while 1,2,4,5-TeCB > PeCB > HCB for HPCD extraction. The bioaccumulation factor of CBs by earthworm was significantly lower in biochar amended soil compared to the control (P < 0.05). This study showed that the biochar could reduce the bioavailability of organic pollutants, however, the high residues of the pollutants in soil showed potential environmental risk.

[Enrichment characteristics and source apportionment of polycyclic aromatic hydrocarbons (PAHs) in pine (Pinus massoniana lamb) needles from parks in Nanjing City, China].

The concentrations of 15 polycyclic aromatic hydrocarbons (PAHs) in pine (Pinus massoniana Lamb) needles from 8 urban parks in Nanjing City (China) were determined using High Performance Liquid Chromatography, and the source apportionment of PAHs in pine needles was studied using diagnostic ratios. The results show that the total PAHs concentrations (sigma PAHs) accumulated in needles from different parks ranged from 909.8 (Linggu Temple) to 2 129.6 ng x g(-1) (Mochou Lake), with an average of 1438.0 ng x g(-1). The PAHs in pine needles mainly associates with 2,3-ring PAHs and 4-ring PAHs, accounting for 66.4% and 29.6% of the sigma PAHs, respectively, while 5,6-ring PAHs only accounts for 4% of the sigma PAHs. Phenanthrene is the dominant PAH with an average concentration of 591.4 ng x g(-1). The average concentration of Benzo (a) pyrene, the most carcinogenic PAH, is 5.1 ng x g(-1). The source apportionment indicates that vehicle emission is the predominant source for PAHs in the pine needles.

[Effect of long-term fertilization on dissipation of pentachlorophenol in red paddy field].

Dissipation of pentachlorophenol (PCP) with initial concentration of 85 mg/kg in red paddy field with rice cultivation and non-rice cultivation were investigated under the conditions of four long-term fertilization treatments, including the ones without fertilizer (CK), application of urea (N), application of organic fertilizer (OM), and N + OM. The results showed that the extractable PCP residues in surface soil in the treatments CK, N, OM and N + OM under non-rice cultivation condition were 28.3, 34.2, 19.3, 18.7 mg/kg after harvesting rice plant, and the extractable PCP residues in subsurface soil were 6.3, 9.1, 5.1, 4.1 mg/kg,respectively. Under rice cultivation condition, the extractable PCP residues in surface soil were 19.4, 30.9, 16.7, 8.7 mg/kg, and the extractable PCP residues in subsurface soil were 3.7, 6.1, 2.6, 2.8 mg/kg, respectively. The results indicated that the long-term application of organic fertilizer or inorganic plus organic fertilizer significantly accelerated the dissipation of PCP in surface soil, and decreased the transportation of PCP down the soil profile. However, long-term application of urea inhibited the dissipation of PCP in surface soil, and increased the transportation of PCP down the soil profile. When compared with non-rice cultivation, rice cultivation significantly accelerated the dissipation of PCP in surface soil other than the treatment N. In addition,the rice cultivation significantly decreased the transportation of PCP down the soil profile. No matter rice was cultivated or not, the dechlorinated metabolites of PCP detected in paddy soil were 2,3,4,5-TeCP and 3,4,5-TCP. 2,3,4,5-TeCP was the major dechlorinated metabolite of PCP under non-rice cultivation condition,whereas 3,4,5-TCP was the major dechlorinated metabolite of PCP under rice cultivation condition.

[Simulating methidathion transport in soil chromatographic column].

With a liquid chromatographic column, methidathion transport behaviors in red soil and gray fluvo-aquic soil columns were studied, respectively. Three types of simulated soil solutions(0.01 mol x L(-1) CaCl2, 0.01 mol x L(-1) CaCl2 + 0.001 mol x L(-1) citric acid, and 0.01 mol x L(-1) CaCl2 + 0.001 mol x L(-1) malic acid) and two pore water velocities (11.46 and 22.92 cm x h(-1)) were applied. The breakthrough curves (BTCs) of Cl- and methidathion were obtained in these soil column experiments. With Software CXTFIT2.1, the local equilibrium assumption (LEA) model and nonequilibrium two-site model (TSM) were used to simulate the observed BTCs of methidathion. Consequently, the physical and hydrodynamic parameters from the fitting results were obtained. This study suggests that the TSM based on nonequilibrium theory can be used as a useful approach to better quantifying methidathion transport, which provide guides for predicating and controlling the methidathion fate in environment.

[Influence of aging on the extractability and bioavailability of hexachlorocyclohexane (HCH) in soil].

Influence of aging on the extractability and bioavailability of HCHs (alpha-, beta, gamma- and delta- isomers) in paddy soil were investigated in the lab under simulated circumstances. Results indicate that extractable HCHs decreased as their contact time with soil increased. The aging rate of HCHs in soil was rather high at the initial stage, and then slowed down in the rest of the time. During the first 60 days aging period, alpha-HCH, beta-HCH, gamma-HCH and delta-HCH dropped off 57.2%, 50%, 52.2% and 43.2% of the initial concentrations, about 90.5%, 87.4%, 72.4% and 84.4% of the total quantity of HCHs decreased in 180 d respectively due to high aging rate. Bioaccumulation of HCHs in earthworm displayed the same rule as aging, that is, the contents of HCHs in earthworm decreased as the incubation time extended, and so did bioaccumulation factors (BAF). The contents of HCHs accumulated in earthworm showing the order of alpha-HCH > beta-HCH > delta-HCH > gamma-HCH, while the accumulative ability expressing the rule of gamma-HCH > alpha-HCH > beta-HCH > delta-HCH in the first 15 d, and then alpha-HCH > beta-HCH > gamma-HCH > delta-HCH in the rest incubation time. Though the extractable HCHs decreased with aging, they still can be accumulated in earthworms, thus posing potential risk to soil environment.

Polycyclic aromatic hydrocarbons in soils in the vicinity of Nanjing, China.

The occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) in vegetable soils from five vegetable fields (including: Liuhe, Xixia, Pukou, Jianye and Yuhua districts) in Nanjing outskirt were investigated with high performance liquid chromatography (HPLC) equipped with fluorescence detector. The total concentrations of 15 priority PAHs in 126 soil samples ranged from 21.91 to 533.84ng g(-1) dry weight, and the sum of seven carcinogenic PAHs concentrations varied from 1.48 to 236.19ng g(-1) dry weight. Statistical analysis of the PAHs concentrations showed that the highest PAHs concentration was observed in Liuhe, and the lowest PAHs concentrations were found in Xixia among the five districts. The ratios of fluoranthene to sum of fluoranthene and pyrene concentrations (Flt/(Flt+Pyr)) were more than 0.5 in 99% of vegetable soil samples, showing that the PAHs in soils were generally derived from straw and coal combustion sources. The results from principal component analysis (PCA) further indicated that extensive combustion activities affected the PAHs distribution in Nanjing vegetable soils.

[QSPR study on the lipid-water partition coefficients of dioxins based on DFT].

With computational method of density functional theory (DFT), quantified model study of equilibrium partitioning properties of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) between lipid phase of organism (Poecilia reticulata) and water phase was carried out based on quantum chemical and further calculated parameters, namely frontier orbital energies, entropies, traceless quadrupole moments as well as molecular absolute hardness, electronegativities and electrophilicity indices, which all were derived from full geometry optimization of PCDD/Fs. Through multiple linear regression (MLR) analyses, quantitative structure-property relationship (QSPR) was successfully proposed in the form of multi-parameter quadratic function: lgK(hw) = 5.343 - 0.001(S - 125.480)(2) - 0.355(omega - 3.239)(2) + 0.006( Q = - 2.950)(2) - 22.728(eta - 2.365)(2). It was shown that the obtained QSPR had higher goodness of fitting and robustness, determination coefficient and cross-validated correlation coefficient being 0.943 and 0.908 respectively, and it was also provided with ideal interior and exterior predictive abilities so that it could be used for prediction of unknown lipid-water partitioning properties. By comparison, QSPR in this research was superior to that from previous SOFA (solubility parameter for fate analysis) method on the whole. Lipid-water partitioning properties (coefficients) of PCDD/Fs should be mainly related to molecular volume and aryl hydrocarbon molecular interactions determined by charge distribution. To a certain degree, they also might be influenced by potential biotransformation and molecular reactivity.

[Characters of soil-vegetable transfer and accumulation of polycyclic aromatic hydrocarbons].

The transfer and accumulation of polycyclic aromatic hydrocarbons (PAHs) from aged contaminated agricultural soil to vegetable was studied. The results show that the positive correlation between the PAHs concentrations in tested vegetables and those in the corresponding soils is present. The PAHs concentrations in contaminated soils are significantly (p < 0.05) higher than that in roots, stems and leaves of vegetables, and the PAHs concentrations in roots are also significantly (p < 0.05) higher than that in stems and leaves. The ratio of sum of low molecular weight PAHs to total PAHs concentrations (Sigma LMW-PAHs/Sigma PAHs) in polluted vegetable roots is higher than that in corresponding soils (p < 0.05), and LMW-PAHs are more easily accumulated in vegetable roots than HMW-PAHs (high molecular weitht PAHs). The distinction of PAHs concentrations among the four selected leafy vegetables in the same tested soils does not achieve the significant level.

Organochlorine pesticides in soils under different land usage in the Taihu Lake region, China.

A field study was conducted in the Taihu Lake region, China in 2004 to reveal the organochlorine pesticide concentrations in soils after the ban of these substances in the year 1983. Thirteen organochlorine pesticides (OCPs) were analyzed in soils from paddy field, tree land and fallow land. Total organochlorine pesticide residues were higher in agricultural soils than in uncultivated fallow land soils. Among all the pesticides, sigmaDDX (DDD, DDE and DDT) had the highest concentration for all the soil samples, ranging from 3.10 ng/g to 166.55 ng/g with a mean value of 57.04 ng/g and followed by sigmaHCH, ranging from 0.73 ng/g to 60.97 ng/g with a mean value of 24.06 ng/g. Dieldrin, endrin, HCB and alpha-endosulfan were also found in soils with less than 15 ng/g. Ratios of p,p'-(DDD+DDE)/DDT in soils under three land usages were: paddy field > tree land > fallow land, indicating that land usage influenced the degradation of DDT in soils. Ratios of p,p'-(DDD+DDE)/DDT > 1, showing aged residues of DDTs in soils of the Taihu Lake region. The results were discussed with data from a former study that showed very low actual concentrations of HCH and DDT in soils in the Taihu Lake region, but according to the chemical half-lives and their concentrations in soils in 1980s, the concentration of DDT in soils seemed to be underestimated. In any case our data show that the ban on the use of HCH and DDT resulted in a tremendous reduction of these pesticide residues in soils, but there are still high amounts of pesticide residues in soils, which need more remediation processes.

[DFT study on the relationship between the structure and water solubility of dioxin compounds].

With DFT method of quantum chemistry, the electronic structures of all polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were fully optimized at the level of B3LYP/6-311G**, and the corresponding quantum parameters, viz. the mean polarizability(alpha), entropy(S) as well as the tensor components of polarizability and quadrupole moment (alpha(xx), alpha(yy), alpha(zz) and Q(xx), Q(yy), Q(zz)) and so on were used to the study on quantitative structure-property relationship (QSPR) of water solubility. And three QSPRs were successfully proposed on the basis of the internally consistent experimental values. The determination coefficients are 0.977, 0.968 and 0.961 respectively and the cross-validated correlation coefficients are 0.968, 0.959 and 0.946 respectively. It is indicated that water solubility of PCDD/Fs should mainly be related to the molecular volume, but much less influenced by the molecular interactions. And the differences of predicted values of QSPRs for the whole dioxins are probably related to the limited available experimental values and the characteristics of introduced variables. In comparison with the newly developed QSPR, the performance of QSPRs in this study is improved, which may attribute to both the precise calculations of electronic properties of PCDD/Fs by B3LYP/6-311G** and the introduction of tensor components of quadrupole moment into models.

[Effect of chlorpyrifos residue in red soil on crops].

The pot cultivation experiment method, integrating with laboratory analysis, was employed for exploring the influence of chlorpyrifos residue in red soil on growth of wheat and oil-seed rape seedlings, and the uptake of crops to chlorpyrifos residue. The results show that, wheat seedlings and oil-seed rape seedlings can absorb chlorpyrifos residue from soil to reach the concentration of 0.257 to approximately 4.50 microg/g and 0.249 to approximately 2.021 microg/g, respectively, 20 days later since chlorpyrifos was introduced into the pots, on condition that the initial concentration of chlorpyrifos residue in red soil was 1 to approximately 10 microg/g. The initial concentration of chlorpyrifos residue in red soil equivalent to or below 10 micro/g has not significant influence on growth of wheat seedlings. Similarly, the concentration equivalent to or below 5 microg/g has not significant influence on growth of oil-seed rape seedlings. The degradation rate in oil-seed rape rhizosphere soil is 1.4 to approximately 4.2 times more than in that in unvegetated soil. The amount of bacterium and fungus in oil-seed rape rhizosphere is 3.18 times and 1.84 times as much as these in unvegetated soil, respectively. However, there is no substantial difference of actinomyces between in rhizosphere soil and in unvegetated soil. Compared with unvegetated soil, pH in rhizosphere soil is lowered by 0. 19 to approximately 0.23.

[Hysteretic characteristics of atrazine desorption from fluvo-aquic soil].

Kinetic batch experiments are carried out in order to investigate the effects of a wide range of atrazine initial concentrations and consecutive desorption time on the desorption characteristics of atrazine from fluvo-aquic soil. The results reveal that, atrazine concentrations in soil solution gradually decreased with desorption time increasing, whose relationship can be expressed with empirically exponential functions. After consecutive five steps (or 5 days), when atrazine initial concentrations increased from 50 microg x L(-1) to 2000 microg x L(-1), the average desorption percentages were 23.1%, 30.4%, 33.0%, 36.4% and 38.5%, respectively. The relationships between the amount of atrazine adsorbed by soil colloids and corresponding atrazine concentrations in soil solutions may be described through the traditional and time-dependent desorption isotherms. The obvious discrepancies in two families of both traditional and time-dependent desorption isotherms from adsorption isotherm, which retention time last for 168 hours before commencement of desorption, were indicative of hysteresis. Two sets of Freundlich parameters derived from both desorption isotherms can quantify the hysteresis between desorption and adsorption isotherms. However, hysteresis coefficient, omega, was applicable only for the traditional desorption isotherms, H and lamda applicable for both.

[Kinetic characteristics of Cd2+ desorption in minerals and soils under simulated acid rain].

The kinetic characteristics of Cd2+ desorption in minerals and soils under simulated acid rain were studied by using the flow-stirred method. It showed that Cd2+ desorption could be described by first-order kinetics. Percents of desorption amounts of Cd2+ calculated were 70%-100% in red soil and goethite, and 25%-50% in latosols and kaolinite. Parabolic diffusion could describe Cd2+ desorption kinetics in latosols and not suitable for red soil and goethite and kaolinite. Cd2+ desorption, regarded as a heterogeneous diffusion in minerals and soils, could be fitted by Elovich equation more than Parabolic diffusion and two-constant equation. Cd2+ desorption could be divided into fast reaction and slow reaction. Except for latosols, fast reaction would be over during 60 min and be close to quasi-equilibrium. Adsorption forms of Cd2+ in soil surface could be exchangeable and specific. Fast reaction was relative to easily desorbed Cd2+. The affinity of edge hydroxyl to Cd2+ would lead to the difference of Cd2+ desorption rate and amounts. Increase of pH value in effluent indicated H+ consumption in the processes of Cd2+ desorption.

Separation of chlorinated hydrocarbons and organophosphorus, pyrethroid pesticides by silicagel fractionation chromatography and their simultaneous determination by GC-MS.

A silicagel fractionation procedure for environmental sample extracts, which separates chlorinated hydrocarbons (CHCs) and organophosphorus, pyrethroid pesticides into two groups for subsequent instrumental analysis, was developed in this study. This method was achieved by optimizing the fraction cut-off volume of elution and different solvents. Using fully activated silica gel and cut-off CHCs collection after 10 ml 10% dichloromethane (DCM) in n-hexane passing through the column resulted in satisfactory separation of CHCs and organophosphorus, pyrethroid pesticides. This procedure had a higher reliability for CHCs than for organophosphorus, pyrethroid pesticides, because there is a relatively reliable recovery for CHCs. This approach is less expensive due to reducing sample pre-treatment time and solvent consumption.