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.

Aging activity of DDE in dissimilar rice soils in a greenhouse experiment.

A green-house study was conducted in late 2005 to investigate the aging behavior of p,p'-DDE in two types of soil, Hydragric Anthrosols (An) and Hydragric Acrisols (Ac), according to the World Reference Base (WRB) [FAO/ISRIC/ISSS. 1998. World reference base for soil resources. World soil resources reports, Rome. p. 87]. Paddy rice and dry rice were grown in submerged paddy soils and non-submerged upland soils, respectively. The concentration of extractable p,p'-DDE in fresh DDE-spiked soils was 746.2ngg(-1). During the first few weeks of the experiment, the extractability of p,p'-DDE became increasingly low as the aging period prolonged. However, certain amount of p,p'-DDE that had been captured by soil minerals and organic matter (OM) could be released and became extractable in the later period. The extractability of p,p'-DDE in submerged soils was significantly lower than that in non-submerged soil, because flooding could increase the binding of pollutants to soil particles. The plantation of both dry rice and paddy rice slowed down the aging process of p,p'-DDE. After one month's growth of rice, p,p'-DDE bound to soil particles was released and became extractable. The OM and silt content of An are higher than that of Ac, resulting in more bound residues and relative lower extractability of p,p'-DDE in An. In addition, the extractability of p,p'-DDE could be reduced by the addition of rice straw to soils.

[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.

[Mild solvent extraction technique for the evaluation of PAHs bioavailability].

n-butanol and hydroxypropyl-beta-cyclodextrin (HPCD) were used to extract polyclic aromatic hydrocarbons from 9 aged agricultural fields and to assess the PAHs bioavailability to earthworm (Eisenia fetida). It was demonstrated that the high molecular weight (HMW) PAHs (> or = 4 rings) contribute the largest proportions (4-ring PAHs: 34.06%, 5-6 rings: 34.09%) to the contaminants in long-term aged field soils. Moreover, the light molecular weight PAHs were easily accumulated in the earthworm,while the high molecular weight PAHs were hard to accumulate. The extraction by mild solvent correlated well with the 3 ring PAHs (r2 0.77-0.79) but not for the other rings PAHs (r2 <0.35), indicating that mild extraction may not serve as a good predictor of PAHs bioavailability to earthworm.

[Degradation of highly-chlorinated benzenes by nanoscale iron and palladized iron in aqueous system].

Adsorption and degradation of three typical chlorinated benzenes (CBs) were evaluated using commercial nanoscale Fe (nFe) and synthesized palladized Fe (Pd/nFe) via batch experiments. The results showed that the adsorption capacity exhibited significant difference between various conditions, of which its maximum adsorption amount reached with Tris-buffered solution of pH = 6. 8. 1, 2, 4, 5-TeCB can be dechlorinated by Pd/nFe efficiently within 20 hours. The degradation rates were 75% and 92% in pure water system and Tris-buffered solution, respectively. However, nFe seemed to be inactive to 1, 2, 4, 5-TeCB with final degradation rate of about 25%. Meanwhile, Pd/nFe also only had slight degradation capacities to HCB and PeCB when compared to 1, 2, 4, 5-TeCB. 1, 2, 3, 4-TeCB, 1, 2, 3-TCB and 1, 2-DCB are the only products that were detected during the whole experiments, indicating that chlorine atoms of CBs with less steric effect were preferred to be dechlorinated. The degradation can be fitted by pseudo first order equations. The observed rate constants were ranged from 0. 14 4 h(-1) to 0.115 2 h(-1).

[Evaluation of bioavailability of hexachlorobenzene and pentachlorobenzene to rice roots in soils by accelerated solvent extraction].

A pot experiment was conducted in greenhouse in two types of soils, Hydragric Acrisols (Ac) and Gleyi-Stagnic Anthrosols (An). Three treatments as control and the additions of 1% and 2% organic fertilizer were designed in each type of soil. The objective of this study was to evaluate the accumulation abilities of hexachlorobenzene (HCB) and its predominant metabolite of pentachlorobenzene (PeCB) by rice roots, and to compare the correlation between HCB or PeCB concentrations in rice roots and in soils extracted by four extraction solvents (hexane/acetone = 3/1(V/V), ethanol, hexane, water) to evaluate the bioavailability of HCB and PeCB to rice roots. The results showed that the mean concentrations of HCB in rice roots for Ac and An were 364.1 and 306.0 ng/g, respectively, while PeCB were 12.7 and 28.7 ng/g, respectively, which was due to the higher degradation rates of HCB in An than in Ac. Both the applications of 1% and 2% organic fertilizer inhibited HCB degradation, so as to decrease PeCB concentrations in rice roots either in Ac or An. The orders of correlation coefficient of both HCB and PeCB concentrations in rice roots and in soils extracted by four extraction solvents were ethanol > hexane/acetone > hexane > water, which indicated that ethanol was the best extraction solvent of soils to evaluate the bioavailability of HCB and PeCB to rice roots. Only the HCB concentrations in soils extracted by ethanol were significantly positive correlated with the HCB concentrations in rice roots. And the PeCB concentrations in soils extracted by all solvents except for water were significantly positive correlated with the PeCB concentrations in rice roots. Our results suggested that it was feasible to evaluate the bioavailability of HCB and PeCB to rice roots using accelerated solvent extraction by choosing proper extraction solvent.

[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.

[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.