Amending soil with biochar is an effective soil remediation strategy for organic contaminants. This study investigated the dynamic effects of wheat straw biochar on the bacterial community structure during remediation by high-throughput sequencing. The wheat straw biochar amended into the soil significantly reduced the bioavailability and toxicity of polycyclic aromatic hydrocarbons (PAHs). Biochar amendment helped to maintain the bacterial diversity in the PAH-contaminated soil. The relationship between the immobilization of PAHs and the soil bacterial diversity fit a quadratic model. Before week 12 of the incubation, the incubation time was the main factor contributing to the changes in the soil bacterial community structure. However, biochar greatly affected the bacterial community structure after 12 weeks of amendment, and the effects were dependent upon the biochar type. Amendment with biochar mainly facilitated the growth of rare bacterial genera (relative abundance of 0.01–1%) in the studied soil. Therefore, the application of wheat straw biochar into PAH-contaminated soil can reduce the environmental risks of PAHs and benefit the soil microbial ecology.Keywords: bacterial community structure; biochar; immobilization; PAHs;

•The effect of concentration on OTC photolysis was pH dependent.•PH was the key factor controlling the direct photolysis rate of OTC.•The photolysis rate increased as temperature increased at neutral pH.•The photolysis quantum yields were derived with the order L2－ > H2L± > HL－ > H3L＋.•A mathematical approach was proposed for calculating the photolysis quantum yield.Oxytetracycline (OTC) commonly undergoes direct photolysis as the main elimination pathway in surface waters. The photolysis of OTC was studied as a function of initial concentration, pH and temperature. The experiments were performed in the absence of oxygen to avoid oxygen induced indirect photolysis. The photolysis rate decreased when increasing the initial OTC concentration, and was accelerated as raising the temperature. pH was the key factor controlling the photolysis rate. By measuring the UV–vis absorption spectra of OTC under various pH conditions and fitting them with global analysis, four OTC species H3L＋, H2L±, HL−, and L2− (L represents OTC) were decomposed, meanwhile, the acid dissociation constant of OTC and the molar absorption coefficient of each species were resolved. Because apparent photolysis rate constants under varied light source conditions are often incomparable, therefore the direct photolysis quantum yield of OTC species were calculated by a mathematical approach which based on the molar absorption coefficients, the species composition and apparent kinetic rates of OTC under experimental pH conditions. The result shows the photolysis quantum yield of OTC followed the order L2－ > H2L± > HL－ > H3L＋. The direct photolysis rates of OTC were tightly correlated to the energy dissipation processes at the excited states, e.g., the excited states inter-/intramolecular proton transfer (ESIPT), and the molecular conformation transfer induced internal energy transmission between ground state and excited state. Fluorescence emission was not an important energy dissipation process. The results of this study provide the useful parameters for predicting the environmental fate of OTC in surface waters. And the approach for calculating the photolysis quantum yield is also available for other antibiotics with multiple pKa values.

•HCB dechlorination in biochar-amended paddy soil was investigated.•Biochar initially stimulated the HCB dechlorination due to its redox activity.•The bioavailability of HCB in biochar-amended soil decreased.•The dissipation of HCB was correlated with the abundance of Dehalococcoidaceae.•Biochar did not significantly affect the bacterial community diversity in the soil.Anaerobic reductive dechlorination is an important degradation pathway for chlorinated organic contaminants in paddy soil. This study investigated the effects of amending paddy soil with wheat straw biochar on both the dechlorination of hexachlorobenzene (HCB), a typical highly chlorinated contaminant, and on the structure of soil bacteria communities. Soil amendment of 0.1% biochar did not significantly affect the dechlorination of HCB in the soil. However, biochar amendment at higher application levels (5%) stimulated the dechlorination of HCB in the first month of anaerobic incubation and inhibited the dechlorination of HCB after that period. The stimulation effect may be ascribed to the graphite carbon and carbon-centered persistent radicals, which are redox active, in biochar. The inhibiting effect could be partly ascribed to the reduced bioavailability of HCB in biochar-amended soils. High-throughput sequencing revealed that the amendment of biochar changed the soil bacterial community structure but not the bacterial abundances and diversities. The relative abundance of Dehalococcoidaceae in the tested soils showed a significant relationship with the dechlorination percentages of HCB, indicating that Dehalococcoidaceae may be the main HCB-dechlorinating bacteria in the studied paddy soil. The results indicated that low application levels of biochar did not affect the dechlorination of HCB in the paddy soil, while high application levels of biochar mainly inhibited the dechlorination of HCB due to the reduced bioavailability of HCB and the reduced abundances of certain dechlorinating bacteria in the biochar-amended paddy soil.Download high-res image (287KB)Download full-size image

Mixed contaminated brownfield sites have brought serious risks to human health and environmental safety. With the purpose of removing polycyclic aromatic hydrocarbons (PAHs) and heavy metals from a coking plant site, an innovative technology for ex-situ washing was developed in the present work. The combination of 15.0 mL L−1 soybean oil and 7.5 g L−1 tea saponin proved an effective method to extract co-pollutants from soil. After two consecutive washing cycles, the efficiency rates of removal for 3-, 4-, 5(+6)-ring, and total PAHs, Cd, and Ni were approximately 98.2%, 96.4%, 92.3%, 96.3%, 94.1%, and 89.4%, respectively. Meanwhile, as evaluated by Tenax extraction method and metal stability indices, the residual PAHs and heavy metals after consecutive washing mainly existed in the form with extremely low bioaccessibility in the soil. Thus, in the soil after two washing cycles, there appeared limited environmental transfer risk of co-pollutants. Moreover, a subsequent precipitation method with alkaline solution and PAH-degrading strain Sphingobium sp. PHE9 inoculation effectively removed 84.6%–100% of Cd, 82.5%–91.7% of Ni, and 92.6%–98.4% of PAHs from the first and second washing solvents. The recovered solvents also exhibited a high recycling effectiveness. Therefore, the combined cleanup strategy proposed in this study proved environmentally friendly, which also played a major role in risk assessment and management in mixed polluted sites.

Traditional exhaustive extraction methods often overestimate the risk of polycyclic aromatic hydrocarbon (PAH) bioaccessibility to biota. Therefore, reliable assessment methods need to be established. In this study, a composite extraction with hydroxypropyl-β-cyclodextrin (HPCD) and three low-molecular-weight organic acids, oxalic acid (OA), malic acid (MA), and citric acid (CA), was used to predict the PAH bioaccessibility to earthworms, subjecting to two soils (red soil and yellow soil) spiked with selected PAHs, phenanthrene, pyrene, chrysene, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, and benzo(a)pyrene. For both soils, concentrations of PAHs by composite extraction using HPCD-OA (R2 = 0.89–0.92, slope = 1.89–2.03; n = 35), HPCD-MA (R2 = 0.92–0.96, slope = 1.43–1.67; n = 35), and HPCD-CA (R2 = 0.92–0.96, slope = 1.26–1.56; n = 35) were significantly correlated with PAH accumulation in the Eisenia fetida earthworms. Moreover, the HPCD-CA- and HPCD-MA-extracted PAH concentrations were closer to the earthworm-accumulated PAH concentration than the extraction using just HPCD. The results indicated that the composite extraction could improve the prediction of PAH bioaccessibility, and therefore can serve as a reliable chemical method to predict PAH bioaccessibility to earthworms in contaminated soils.

A solvent free method of analysis for rapid simultaneous determination of ten medium and low brominated diphenyl ethers at trace levels in soil pore water by headspace solid phase microextraction coupled with gas chromatography equipped with an electron capture detector was developed. Extraction conditions such as desorption time, polydimethylsiloxane thickness, ionic strength, temperature, stirring and extraction time were carefully studied and optimized. In addition, the effects of pH and dissolved organic matter on headspace solid phase microextraction were thoroughly studied. For the ten medium and low brominated diphenyl ethers in this study, the limits of detection ranged from 0.04 to 1.20 ng L−1, and the relative standard deviations were lower than 10.00%. Soil pore water from red soil, yellow-brown soil and black soil was quantitatively analyzed with recoveries ranging from 80.40% to 108.90%, and from 85.9% to 108.45% at 50 ng L−1 and 200 ng L−1, respectively.

Several bacteria have been isolated to degrade 4-chloronitrobenzene. Degradation of 4-chloronitrobenzene by Cupriavidus sp. D4 produces 5-chloro-2-picolinic acid as a dead-end by-product, a potential pollutant. To date, no bacterium that degrades 5-chloro-2-picolinic acid has been reported. Strain f1, isolated from a soil polluted by 4-chloronitrobenzene, was able to co-metabolize 5-chloro-2-picolinic acid in the presence of ethanol or other appropriate carbon sources. The strain was identified as Achromobacter sp. based on its physiological, biochemical characteristics, and 16S rRNA gene sequence analysis. The organism completely degraded 50, 100 and 200 mg L−1 of 5-chloro-2-picolinic acid within 48, 60, and 72 h, respectively. During the degradation of 5-chloro-2-picolinic acid, Cl− was released. The initial metabolic product of 5-chloro-2-picolinic acid was identified as 6-hydroxy-5-chloro-2-picolinic acid by LC–MS and NMR. Using a mixed culture of Achromobacter sp. f1 and Cupriavidus sp. D4 for degradation of 4-chloronitrobenzen, 5-chloro-2-picolinic acid did not accumulate. Results infer that Achromobacter sp. f1 can be used for complete biodegradation of 4-chloronitrobenzene in remedial applications.

•Eggshell adsorption of E. coil and gmrA gene was quite effective.•Sulfate-calcined-modified eggshells demonstrated the highest removal.•Eggshells can remove pathogenic bacteria and ARGs from landfill leachates.•Modified eggshell adsorption is a promising strategy to reduce ARG transfer risk.High abundance of human pathogen and antibiotic resistance genes (ARGs) in landfill leachate has become an emerging threat against human health. Therefore, sulfate- and calcination-modified eggshells as green agricultural bioresource were applied to test the feasibility of removing pathogenic bacteria and ARGs from leachate. The highest removal of Escherichia coli (E. coil) and gentamycin resistant gene (gmrA) from artificial contaminated landfill leachate was achieved by the application of eggshell with combined treatment of sulfate and calcination. The 16S and gmrA gene copies of E. coil declined significantly from 1.78E8 ± 8.7E6 and 4.12E8 ± 5.9E6 copies mL−1 to 1.32E7 ± 2.6E6 and 2.69E7 ± 7.2E6 copies mL−1, respectively, within 24 h dynamic adsorption equilibrium process (p < 0.05). Moreover, according to the Langmuir kinetic model, the greatest adsorption amount (1.56 × 109 CFU E. coil per gram of modified eggshells) could be obtained at neutral pH of 7.5. The optimal adsorption eggshells were then screened to the further application in three typical landfill leachates in Nanjing, eastern China. Significant decrease in species and abundance of pathogenic bacteria and ARGs (tet, sul, erm, qnr, and ampC) indicated its great efficiency to purify landfill leachates. This study demonstrated that sulfate-calcined eggshells can be an environmentally-friendly and highly efficient bioadsorbent to the management of reducing dissemination risk of pathogen and ARGs in landfill leachate.Download high-res image (203KB)Download full-size image

The combined accumulation of antibiotics, heavy metals, antibiotic-resistant bacteria (ARB)/antibiotic resistance genes (ARGs) in vegetables has become a new threat to human health. This is the first study to investigate the feasibility of calcined eggshells modified by aluminum sulfate as novel agricultural wastes to impede mixed contaminants from transferring to bell pepper (Capsicum annuum L.). In this work, calcined eggshell amendment mitigated mixed pollutant accumulation in bell pepper significantly, enhanced the dissipation of soil tetracycline, sulfadiazine, roxithromycin, and chloramphenicol, decreased the water-soluble fractions of antibiotics, and declined the diversity of ARB/ARGs inside the vegetable. Moreover, quantitative polymerase chain reaction analysis detected that ARG levels in the bell pepper fruits significantly decreased to 10–10 copies/16S copies, indicating limited risk of ARGs transferring along the food chain. Furthermore, the restoration of soil microbial biological function suggests that calcined eggshell is an environmentally friendly amendment to control the dissemination of soil ARB/ARGs in the soil–vegetable system.

Volatilization of semi/volatile persistent organic pollutants (POPs) from soils is a major source of global POPs emission. This proof-of-concept study investigated a novel biochar-plant tandem approach to effectively immobilize and then degrade POPs in soils using hexachlorobenzene (HCB) as a model POP and ryegrass (Lolium perenne L.) as a model plant growing in soils amended with wheat straw biochar. HCB dissipation was significantly enhanced in the rhizosphere and near rhizosphere soils, with the greatest dissipation in the 2 mm near rhizosphere. This enhanced HCB dissipation likely resulted from (i) increased bioavailability of immobilized HCB and (ii) enhanced microbial activities, both of which were induced by ryegrass root exudates. As a major component of ryegrass root exudates, oxalic acid suppressed HCB sorption to biochar and stimulated HCB desorption from biochar and biochar-amended soils, thus increasing the bioavailability of HCB. High-throughput sequencing results revealed that the 2 mm near rhizosphere soil showed the lowest bacterial diversity due to the increased abundance of some genera (e.g., Azohydromonas, Pseudomonas, Fluviicola, and Sporocytophaga). These bacteria were likely responsible for the enhanced degradation of HCB as their abundance was exponentially correlated with HCB dissipation. The results from this study suggest that the biochar-plant tandem approach could be an effective strategy for remediating soils contaminated with semi/volatile organic contaminants.

A high performance liquid chromatographic (HPLC) method was established for the determination of the content of seven polycyclic aromatic hydrocarbons (PAHs) in soil and earthworm samples based on accelerated solvent extraction (ASE) for sample extraction and solid phase extraction (SPE) for sample purification. The samples were firstly extracted by the mixed solution of n-hexane and acetone (4:1, V/V), and purified by SPE column (silica gel column for soil sample purification and Al2O3-silica gel column for earthworm sample purification). Then the extract was eluted from the SPE column by 10 mL of n-hexane/dichloromethane (9:1, V/V), and evaporated to dryness with a rotary evaporator. After that, the extract was re-dissolved in acetonitrile to a constant volume and filtrated by a 0.22-μm organic filter membrane for the quantification of the seven PAHs by HPLC. The recoveries of this method for the seven PAHs were 83.5%–110.2% in soil samples and 81.2%–97.1% in earthworm samples. The detection limits of the method for the seven PAHs were 0.15–0.85 μg kg−1. The method had good reproducibility and could meet the quality control requirements of sample analysis.An accelerated solvent extraction (ASE)-solid phase extraction (SPE)-high performance liquid chromatographic (HPLC) method was developed for the determination of polycyclic aromatic hydrocarbons in soil and earthworm samples.

The objective of this study is to compare the efficacies of powder activated carbon (PAC) and granular activated carbon (GAC) as amendments for the immobilization of volatile compounds in soil. Soil artificially-spiked with chlorobenzenes (CBs) was amended with either PAC or GAC to obtain an application rate of 1%. The results showed that the dissipation and volatilization of CBs from the amended soil significantly decreased compared to the unamended soil. The bioavailabilities of CBs, which is expressed as butanol extraction and earthworm accumulation, were significantly reduced in PAC and GAC amended soils. The lower chlorinated and hence more volatile CBs experienced higher reductions in both dissipation and bioavailability in the amended soils. The GAC and PAC equally immobilized more volatile CBs in soil. Therefore, it could be concluded that along with environmental implication, applying GAC was the more promising approach for the effective immobilization of volatile compounds in soil.

The present study was conducted to investigate the anaerobic biodegradation potential of biostimulation by nitrate (KNO3) and methyl-β-cyclodextrin (MCD) addition on an aged organochlorine pesticide (OCP)-contaminated paddy soil. After 180 days of incubation, total OCP biodegradation was highest in soil receiving the addition of nitrate and MCD simultaneously and then followed by nitrate addition, MCD addition, and control. The highest biodegradation of chlordanes, hexachlorocyclohexanes, endosulfans, and total OCPs was 74.3, 63.5, 51.2, and 65.1 %, respectively. Meanwhile, MCD addition significantly increased OCP bioaccessibility (p < 0.05) evaluated by Tenax TA extraction and a three-compartment model method. Moreover, the addition of nitrate and MCD also obtained the highest values of soil microbial activities, including soil microbial biomass carbon and nitrogen, ATP production, denitrifying bacteria count, and nitrate reductase activity. Such similar trend between OCP biodegradation and soil-denitrifying activities suggests a close relationship between OCP biodegradation and N cycling and the indirect/direct involvement of soil microorganisms, especially denitrifying microorganisms in the anaerobic biodegradation of OCPs.

A Gram-negative, aerobic, non-motile bacterial strain hun6T isolated from the polluted soil near a chemical factory in northern Nanjing, China was investigated to clarify its taxonomic position. Growth of strain hun6T occurred between 10 and 45 °C (optimum, 30 °C) and between pH 6.0 and 8.0 (optimum, pH 7.0). No growth occurred at NaCl concentrations greater than 5 % (w/v). The 16S rRNA gene sequence analysis indicated that strain hun6T belongs to the genus Aquamicrobium. The sequence similarities of strain hun6T to other type strains of Aquamicrobium genus were all below 98.5 %. The presence of ubiquinone-10, the predominant fatty acid summed feature 8 (C18:1ω7c and/or C18:1ω6c) and C19:0 cyclo ω8c, a polar lipid pattern with phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol, phosphatidylethanolamine and phophatidylmonomethylethanoamine were in accord with the characteristics of the genus Aquamicrobium. The G+C content of the genomic DNA was determined to be 63.5 mol%. The results of DNA–DNA hybridization, physiological and biochemical tests and chemotaxonomic properties allowed genotypic and phenotypic differentiation of strain hun6T from all known Aquamicrobium species. Therefore, strain hun6T can be assigned to a new species of this genus for which the name Aquamicrobium terrae sp. nov. is proposed. The type strain is hun6T (= CICC 10733T = DSM 27865T).

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.

Problems associated with organochlorine pesticides (OCPs)-contaminated sites have received wide attention. To address the associated environmental concerns, innovative ex situ techniques are urgently needed.As regards long-term contamination by OCPs in Wujiang region, China, we investigated the feasibility of a cleanup strategy that employed hydroxypropyl-β-cyclodextrin (HPCD) and peanut oil to enhance ex situ soil washing for extracting OCPs, followed by the addition of supplemental nutrients to the residual soil.Elevated temperature (50 °C) in combination with ultrasonication (35 kHz, 30 min) at 50 g L−1 HPCD and 10 % peanut oil were effective in extracting, and therefore washing, the OCPs in soil. Ninety-three percent of total OCPs, 98 % of dichlorodiphenyltrichloroethanes, 93 % of chlordane as well as 85 % of Mirex were removed from soil after three successive washing cycles. Treating the residual soil with nutrients addition for 12 weeks led to significant increases (p < 0.05) in the average well color development obtained by the BIOLOG Eco plate assay, Shannon–Weaver index, Simpson index, and EC50 ecotoxicological evaluation compared with the controls. This implied that this cleanup strategy at least partially restored the microbiological functioning of the OCPs-contaminated soil and has the advantage of being an environmental-friendly technology.The ex situ cleanup strategy through HPCD and peanut oil enhanced soil washing followed by nutrients addition could be effective in remediation of OCPs-contaminated soil.

Bioavailability is mainly influenced by aging and desorption of contaminants in soil. The purpose of this study was to investigate the desorption kinetics of chlorobenzenes (CBs) in soil and to investigate whether chemical extractions are suitable for the bioavailability assessment of CBs in soil.A soil spiked with CBs and aged for different periods was extracted with Tenax, hydroxypropyl-β-cyclodextrin (HPCD), and butanol to assess the bioavailability of CBs in soil, respectively. Earthworm (Eisenia foetida) accumulation was used as bioassay in parallel experiments to evaluate the chemical extractions.The results showed that desorption of CBs from soil with consecutive Tenax extraction fitted into triphasic kinetics model. Different chemical methods extracted different amounts of CBs over different aging periods. For hexachlorobenzene (HCB), the extraction efficiency was in the order of butanol > Tenax-6h > HPCD extraction, while the order of butanol > HPCD > Tenax-6h extraction for pentachlorobenzene (PeCB). The bioaccumulation by earthworm decreased with increasing aging period and was significantly higher for HCB than for PeCB (p < 0.05). Earthworm accumulated CBs correlated well with all the three chemical extracted CBs. However, HPCD extraction showed the converse extraction tendency with earthworm uptake of CBs.Chemical extraction could be used to assess the bioavailability of contaminants in soil; however, they were method and compound specific. Tenax and butanol extractions were more reliable than HPCD extraction for bioavailability assessment of the tested CBs and the soil used since they showed the consistent extraction tendency with earthworm uptake of CBs.

A method to effectively remove pigments in fresh vegetables using activated carbon followed cleanup through solid phase extraction (SPE) cartridge to further reduce matrix interference and contamination, was established to determine eight organophosphorous pesticides (OPPs) by gas chromatography (GC) with nitrogen–phosphorus detection (NPD) in this study, and it has been successfully applied for the determination of eight OPPs in various fresh vegetables with the recoveries ranging from 61.8% to 107%. To evaluate eight OPPs residue level, some fresh vegetables retailed at three agricultural product markets (APM) of Nanjing in China were detected, the results showed that phorate in Shanghai green (0.0257 μg g−1) and Chinese cabbage (0.0398 μg g−1), dimethoate in Shanghai green (0.0466–0.0810 μg g−1), Chinese cabbage (0.077 μg g−1), and spinach (0.118–0.124 μg g−1), methyl-parathion in Shanghai green (0.0903 μg g−1), Chinese cabbage (0.157 μg g−1), and spinach (0.0924 μg g−1), malathion in Shanghai green (0.0342–0.0526 μg g−1), chorpyrifos in spinach (0.106–0.204 μg g−1), and Chinese cabbage (0.149 μg g−1), chlorfenvinfos in carrot (0.094–0.131 μg g−1), were found. However, fonofos and fenthion were not detected in all the collected vegetable samples.

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 533.84 ng g−1 dry weight, and the sum of seven carcinogenic PAHs concentrations varied from 1.48 to 236.19 ng 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.

A bacterial strain, BP3, capable of degrading biphenyl, was isolated from petroleum-contaminated soil. Strain BP3 was identified preliminarily as Achromobacter sp. based on its physiological and biochemical characteristics and 16S rRNA gene sequence analysis. Strain BP3 was able to degrade 50 mg l−1 of biphenyl within 12 h. A 16.7-kb DNA fragment consisting of the entire bph cluster (bphRA1A2XA3A4BCKHJID) was obtained by normal PCR amplification and chromosome walking. Genes encoding integrase and transposon related genes were detected upstream and downstream of the bph cluster, respectively, which indicated that the bph cluster might locate on a big mobile genetic element (MGE).

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.

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.

The total concentration of organic contaminants in soil often overestimates their environmental risk, it is thus important to establish time- and cost-efficient chemical techniques for predicting their bioavailability. In the present study, three chemical extractions, namely: Tenax extraction, butanol extraction and HPCD extraction, were conducted to predict PAHs bioavailability in soil for earthworms. The results showed that earthworm accumulations had less correlation with total concentrations except for PAHs of low molecular weight (R2–3 PAHs). Fractions extracted by butanol/HPCD correlated to earthworm accumulated PAHs of low molecular weight (R2–3 PAHs), but not to earthworm accumulated PAHs of high molecular weight (R5–6 PAHs). Tenax 6 h-extracted PAHs had significantly linear correlations with earthworm accumulated R2–3 PAHs, R4 PAHs as well as R5–6 PAHs (associated R2 were 0.96, 0.98 and 0.97, respectively). Furthermore, Tenax 6 h-extracted concentrations were comparable to earthworm accumulations for R2–3, R4 as well as R5–6 PAHs. These observations verified that Tenax 6 h extraction is better than butanol and HPCD extractions to predict earthworm accumulation of PAHs in soil. Tenax 6 h extraction can serve as a good technique to assess PAHs bioavailability for earthworms.

A batch experiment was performed to investigate nonequilibrium adsorption behavior of atrazine (2-chloro-4-ethylami-no-6-isopropylamino-1,3,5-triazine) on a fluvo-aquic soil. The amount of atrazine sorbed increased with increasing adsorption contact periods. For a range of initial atrazine concentrations, the percentage of atrazine sorbed within 24 h ranged from 24% to 77% of the observed total amount sorbed for the longest contact period; when adsorption contact periods were more than 72 h, the deviations in curves fitted using a nonlinear Freundlich equation gradually became less. The op- posite trend was observed for the atrazine concentrations in solution. The effect of adsorption contact periods on atrazine adsorption behavior was evaluated by interpreting the temporal variations in linear and nonlinear Freundlich equation parameters obtained from the phase-distribution relationships. As the adsorption contact period increased, the nonlinear Freundlich capacity coeffcient kf showed a significant linear increase (r2 = 0:9063, P < 0:001). However, a significant negative linear correlation was observed for the nonlinear coeffcient n, a dimensionless parameter (r2 = 0:5666, P < 0:05). Furthermore, the linear distribution coeffcient kd ranged from 0.38 to 1.44 and exhibited a significant linear correlation to the adsorption contact period (r2 = 0:72, P < 0:01). The parameters kf and n obtained from a time-dependent isotherm rather than the distribution coeffcient kd estimated using the linear Freundlich equation were more appropriate to predict the herbicide residue in the field and thus more meaningful for environmental assessment.

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.

Due to easy volatilization of volatile organic compounds from water, it is difficult to monitor their aerobic biodegradation in the traditional single water system. Whether a two-liquid-phase system (TLPS) could overcome this obstacle and enhance the degradation of volatile contaminants? In this study, a TLPS composed of silicone oil and water was employed to investigate the biodegradation of volatile compounds, trichlorobenzenes (TCBs), by the adapted microorganisms in an activated soil. The degradation and volatilization of TCBs in TLPS and in a single water system were compared. The results showed that due to volatilization losses of TCBs, the mass balance of TCBs in a single water system was very low. In contrast, using TLPS could effectively inhibit the volatilization losses of TCBs and achieved a very good mass balance during the biodegradation process. Meanwhile, the TLPS could increase microbial activity and microbial growth during the degradation process. With TLPS, the TCB degradation was in descending order of 1,2,4-TCB > 1,2,3-TCB ≫ 1,3,5-TCB, which was related to the exposed concentration of the contaminants in soil. This study showed that TLPS could be employed as an effective tool to evaluate the biodegradation of volatile hydrophobic organic compounds, which could not be achieved with the traditional single water system.

Rapeseed cake (RC), the residue of rapeseed oil extraction, is effective for improving tea (Camellia sinensis) quality, especially taste and aroma, but it has limited ability to ameliorate strongly acidic soil. In order to improve the liming potential of RC, alkaline slag (AS), the by-product of recovery of sodium carbonate, was incorporated. Combined effects of different levels of RC and AS on ameliorating acidic soil from a tea garden were investigated. Laboratory incubations showed that combined use of AS and RC was an effective method to reduce soil exchangeable acidity and Al saturation and increase base saturation, but not necessarily for soil pH adjustment. The release of alkalinity from the combined amendments and the mineralization of organic nitrogen increased soil pH initially, but then soil pH decreased due to nitrifications. Various degrees of nitrification were correlated with the interaction of different Ca levels, pH and N contents. When RC was applied at low levels, high Ca levels from AS repressed soil nitrification, resulting in smaller pH fluctuations. In contrast, high AS stimulated soil nitrification, when RC was applied at high levels, and resulted in a large pH decrease. Based on the optimum pH for tea production and quality, high ratios of AS to RC were indicated for soil acidity amelioration, and 8.0 g kg−1 and less than 2.5 g kg−1 were indicated for AS and RC, respectively. Further, field studies are needed to investigate the variables of combined amendments.

Polybrominated diphenyl ethers (PBDEs) are experimentally indicated to be capable of binding to the cytosolic aryl hydrocarbon receptor (AhR) and show a weak or moderate toxicity. However, little is yet known about the AhR-mediated toxicology. To fully evaluate the structural effects of PBDE ligand on AhR binding affinity and toxicity, quantitative structure–activity relationships (QSARs) were developed by PLS analysis. In this study, a simple but potent QSAR that was qualified with much better or comparable performance of prediction was optimally established for PBDE toxicity. With QSAR analysis, the AhR binding property was carefully described to reflect the origin of AhR binding affinity. Besides the effects from topological characters, the dispersion and electrostatic interactions were of indispensability for AhR binding affinity whereas the dispersion was further suggested to be dominant. The structural requirement for AhR binding affinity and toxicity was also investigated. As was similarly observed for polychlorinated biphenyls (PCBs), the preferential bromination at para- and meta (particularly 3,3′-)-sites was confirmed as a key determinant to improve the AhR binding affinity and the toxicity of PBDEs.Highlights► A simple but potent QSAR was successfully developed for PBDE toxicity. ► Dispersion and electrostatic interactions were reflective of AhR binding property. ► Dispersion interaction was suggested to be dominant in AhR binding affinity. ► Bromination at para- and meta (particularly 3,3′-)-sites was favorable for toxicity. ► Relationship between AhR binding property and toxicity was reasonably explained.

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, ZDDX (DDD DDE and DDT) had the Wghest concentration for all the soil samples, ranging from 310 ng/g to 166.55 ng/g with a mean value of 57.04 ng/g and fol lowed by ZHCH, ranging from 0.73 ng/g to 60.97 ng/g with a mean value of 24.06 ng/g. Dieldrin, endrin, HCB and a-endosulfan were also found in soils with less than 15 ng/g. Ratios ofp, p′-(DDD+DDE)/DDT in soils under three land usages were: paddy field > tree land > fallow land, indicating that land usage inlfuenced 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.

The objective of this study is to compare the efficacies of powder activated carbon (PAC) and granular activated carbon (GAC) as amendments for the immobilization of volatile compounds in soil. Soil artificially-spiked with chlorobenzenes (CBs) was amended with either PAC or GAC to obtain an application rate of 1%. The results showed that the dissipation and volatilization of CBs from the amended soil significantly decreased compared to the unamended soil. The bioavailabilities of CBs, which is expressed as butanol extraction and earthworm accumulation, were significantly reduced in PAC and GAC amended soils. The lower chlorinated and hence more volatile CBs experienced higher reductions in both dissipation and bioavailability in the amended soils. The GAC and PAC equally immobilized more volatile CBs in soil. Therefore, it could be concluded that along with environmental implication, applying GAC was the more promising approach for the effective immobilization of volatile compounds in soil.