Xinglun Yang

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.

PAHs biodegradation potential of indigenous consortia from agricultural soil and contaminated soil in two-liquid-phase bioreactor (TLPB)

Estimation of PAHs degradation potential of indigenous consortia is essential for remediation of polluted soils. In this study, the biodegradation of a mixture of 11 PAHs was compared using a long-term PAH-contaminated soil (CS) and an unpolluted agricultural soil (AS) as inocula in a two-liquid-phase bioreactor (TLPB). In the TLPB, silicone oil was used as the organic phase to increase the PAHs bioavailability. The microbial numbers were also determined during the biodegradation. The results demonstrated that naphthalene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene could be completely biodegraded in both soils within 4-50 days. With the exception of dibenzo(a,h)anthrancene, the other PAHs including benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene and benzo(k)fluoranthene were degraded to different extents in both soils at the end of 170 days. Complete biodegradation of benzo(a)anthracene and benzo(b)fluoranthene only occurred in CS. During the process, microbial growth was highly correlated to the biodegradation of PAHs. Sequential utilization of PAHs showed a competitive-inhibition in the multi-substrate system. The half-life times of PAHs obtained here were much shorter than those reported previously in soils, indicating that indigenous microbes in both soils had high PAHs degradation potential, facilitated by TLPB.

Immobilization of Chlorobenzenes in Soil Using Wheat Straw Biochar

Biochar has shown great potential for immobilizing organic contaminants in soil. In this study, pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), and 1,2,4-trichlorobenzene (1,2,4-TCB) artificially spiked soil was amended with wheat straw biochar at 0.1%, 0.5%, 1%, and 2% application rates, respectively. The sorption, dissipation, and bioavailability of chlorobenzenes (CBs) in soil were investigated. The sorption of PeCB by biochar was significantly higher than that of its sorption by both biochar-amended and unamended soil (p < 0.05). The dissipation and volatilization of CBs from biochar-amended soil significantly decreased relative to unamended soil (p < 0.05). Bioavailability of CBs, expressed as butanol extraction efficiency and earthworm (Eisenia fetida) bioaccumulation factor, significantly decreased with increasing aging time and biochar application rate. The effect of biochar content in soil on the bioavailability of CBs was more pronounced for 1,2,4-TCB relative to other CBs. This study suggested that wheat straw biochar, even at low application rates, could effectively immobilize the semivolatile CBs in soil and thus reduce their volatilization and bioavailability.

Tenax TA extraction to assess the bioavailability of DDTs in cotton field soils.

The rapid-desorbing fraction plays an important role in the bioavailability of organic pollutants in soil. In the present study, DDTs desorption from the cotton field soils was investigated by Tenax extraction. The results of the Tenax consecutive extraction (400 h) indicated that the rate constants were in the order of 10(-1), 10(-2), and 10(-4) h(-1) for the rapid, slow and very-slow desorption, respectively. The rapid-desorbing fraction was about 0.3 times the total soil DDTs, and about 2 times the Tenax 6 h-extracted fraction (single-point extraction). The rapid-desorbing fraction correlated well with the 6 h-extracted fraction (p<0.05), implying the feasibility of measuring the rapid-desorbing fraction with Tenax 6 h-extration. The strong correlation with the carrot accumulation suggested that Tenax 6 h-extrated fraction could serve as a good predictor of DDTs bioavailability to carrot roots. Risk assessment demonstrated that when based on the rapid-desorbing concentration and 6 h-extracted concentration, about 60.7% and 17.9% of the soil samples were moderately polluted, however, up to 78.5% were moderately polluted when based on the total soil DDTs concentration. The risk assessment might be more representative when based on Tenax extraction because of the strong correlation with the carrot accumulation. Our results provided implications for site risk assessment and cleanup strategies.

Extracellular polymeric substances enhanced mass transfer of polycyclic aromatic hydrocarbons in the two-liquid-phase system for biodegradation

The objective was to elucidate the role of extracellular polymeric substances (EPS) in biodegradation of polycyclic aromatic hydrocarbons in two-liquid-phase system (TLPs). Therefore, biodegradation of phenanthrene (PHE) was conducted in a typical TLPs—silicone oil–water—with PHE-degrading bacteria capable of producing EPS, Sphingobium sp. PHE3 and Micrococcus sp. PHE9. The results showed that the presence of both strains enhanced mass transfer of PHE from silicone oil to water, and that biodegradation of PHE mainly occurred at the interfaces. The ratios of tightly bound (TB) proteins to TB polysaccharides kept almost constant, whereas the ratios of loosely bound (LB) proteins to LB polysaccharides increased during the biodegradation. Furthermore, polysaccharides led to increased PHE solubility in the bulk water, which resulted in an increased PHE mass transfer. Both LB-EPS and TB-EPS (proteins and polysaccharides) correlated with PHE mass transfer in silicone oil, indicating that both proteins and polysaccharides favored bacterial uptake of PHE at the interfaces. It could be concluded that EPS could facilitate microbial degradation of PHE in the TLPs.

Hexachlorobenzene dechlorination as affected by nitrogen application in acidic paddy soil.

Batch incubation experiments were conducted to study the effects of different nitrogen (N) fertilizers (NH(4)HCO(3), CO(NH(2))(2), and NaNO(3)) on hexachlorobenzene (HCB) dechlorination in an acidic paddy soil. Results showed that NH(4)HCO(3) and CO(NH(2))(2) had similar effects on HCB dechlorination, and their application amount was a crucial factor on reductive dechlorination. The addition of a proper amount of 0.14 g NH(4)HCO(3)- or CO(NH(2))(2)-N to 500 g soil promoted HCB dechlorination, however, the application of a high amount (0.84 g) of NH(4)HCO(3)- or CO(NH(2))(2)-N inhibited HCB dechlorination. Additional NaNO(3) served as an electron acceptor and led to lower soil pH, thus inhibited HCB dechlorination. Detected dechlorinated products showed that the dominant pathway of HCB dechlorination was HCB-->pentachlorobenzene (PeCB)-->1,2,3,5-tetrachlorobenzene (TeCB)-->1,3,5-trichlorobenzene (TCB), and PeCB was the main metabolite. The role of methanogenic bacteria in HCB dechlorination was uncertain and conditions-dependent.

Evaluation of soil washing process with carboxymethyl-β-cyclodextrin and carboxymethyl chitosan for recovery of PAHs/heavy metals/fluorine from metallurgic plant site.

Polycyclic aromatic hydrocarbons (PAHs)/heavy metals/fluorine (F) mixed-contaminated sites caused by abandoned metallurgic plants are receiving wide attention. To address the associated environmental problems, this study was initiated to investigate the feasibility of using carboxymethyl-β-cyclodextrin (CMCD) and carboxymethyl chitosan (CMC) solution to enhance ex situ soil washing for extracting mixed contaminants. Further, Tenax extraction method was combined with a first-three-compartment model to evaluate the environmental risk of residual PAHs in washed soil. In addition, the redistribution of heavy metals/F after decontamination was also estimated using a sequential extraction procedure. Three successive washing cycles using 50 g/L CMCD and 5 g/L CMC solution were effective to remove 94.3% of total PAHs, 93.2% of Pb, 85.8% of Cd, 93.4% of Cr, 83.2% of Ni and 97.3% of F simultaneously. After the 3rd washing, the residual PAHs mainly existed as very slowly desorbing fractions, which were in the form of well-aged, well-sequestered compounds; while the remaining Pb, Cd, Cr, Ni and F mainly existed as Fe-Mn oxide and residual fractions, which were always present in stable mineral forms or bound to non-labile soil fractions. Therefore, this combined cleanup strategy proved to be effective and environmentally friendly.

Use of Organic Solvents to Extract Organochlorine Pesticides (OCPs) from Aged Contaminated Soils

Abstract Problems associated with organochlorine pesticide (OCP)-contaminated sites in China have received wide attention. To solve such problems, innovative ex-situ methods of site remediation are urgently needed. We investigated the feasibility of the extraction method with different organic solvents, ethanol, 1-propanol, and three fractions of petroleum ether, using a soil collected from Wujiang (WJ), China, a region with long-term contamination of dichlorodiphenyltrichloroethanes (DDTs). We evaluated different influential factors, including organic solvent concentration, washing time, mixing speed, solution-to-soil ratio, and washing temperature, on the removal of DDTs from the WJ soil. A set of relatively better parameters were selected for extraction with 100 mL L −1 petroleum ether (60–90 °C): washing time of 180 min, mixing speed of 100 r min −1 , solution-to-soil ratio of 10:1, and washing temperature of 50 °C. These selected parameters were also applied on three other seriously OCP-polluted soils. Results demonstrated their broad-spectrum effectiveness and excellent OCP extraction performance on the contaminated soils with different characteristics.

Improved Biodegradation of 1,2,4-Trichlorobenzene by Adapted Microorganisms in Agricultural Soil and in Soil Suspension Cultures

Abstract Inoculating soil with an adapted microbial community is a more effective bioaugmentation approach than inoculation with pure strains in bioremediation. However, information on the potential of different inocula from sites with varying contamination levels and pollution histories in soil remediation is lacking. The objective of the study was to investigate the potential of adapted microorganisms in soil inocula, with different contamination levels and pollution histories, to degrade 1,2,4-trichlorobenzene (1,2,4-TCB). Three different soils from chlorobenzene-contaminated sites were inoculated into agricultural soils and soil suspension cultures spiked with 1,2,4-TCB. The results showed that 36.52% of the initially applied 1,2,4-TCB was present in the non-inoculated soil, whereas about 19.00% of 1,2,4-TCB was present in the agricultural soils inoculated with contaminated soils after 28 days of incubation. The soils inoculated with adapted microbial biomass (in the soil inocula) showed higher respiration and lower 1,2,4-TCB volatilization than the non-inoculated soils, suggesting the existence of 1,2,4-TCB adapted degraders in the contaminated soils used for inoculation. It was further confirmed in the contaminated soil suspension cultures that the concentration of inorganic chloride ions increased continuously over the entire experimental period. Higher contamination of the inocula led not only to higher degradation potential but also to higher residue formation. However, even inocula of low-level contamination were effective in enhancing the degradation of 1,2,4-TCB. Therefore, applying adapted microorganisms in the form of soil inocula, especially with lower contamination levels, could be an effective and environment-friendly strategy for soil remediation.

Effects of Autoclaving and Mercuric Chloride Sterilization on PAHs Dissipation in a Two-Liquid-Phase Soil Slurry

Abstract A two-liquid-phase (TLP) soil slurry system was employed to quantify the efficiencies of autoclaving and mercuric chloride sterilization in the dissipation of polycyclic aromatic hydrocarbons (PAHs). The fates of 11 PAHs (naphthalene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, dibenzo(a, h)anth-racene) were recorded over 113 days of incubation. No microorganisms were detected in the HgCl2-sterilized soil slurries during the whole incubation period, indicating very effective sterilization. However, about 2%–36% losses of PAHs were observed in the HgCl2-sterilized slurry. In contrast to the HgCl2-sterilized soil slurry, some microorganisms survived in the autoclaved soil slurries. Moreover, significant biodegradation of 6 PAHs (naphthalene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene) was observed in the autoclaved soil slurries. This indicated that biodegradation results of PAHs in the soil slurries, calculated on basis of the autoclaved control, would be underestimated. It could be concluded that the sterilization efficiency and effectiveness of HgCl2 on soil slurry was much higher than those of autoclaving at 121 °C for 45 min.