Mingming Sun

Effect of bioaugmentation by Paracoccus sp. strain HPD-2 on the soil microbial community and removal of polycyclic aromatic hydrocarbons from an aged contaminated soil

A microcosm study was conducted to test the bioremediation potential of Paracoccus sp. strain HPD-2 on an aged PAH-contaminated soil. Bioaugmented microcosms showed a 23.2% decrease in soil total PAH concentrations after 28days, with a decline in average concentration from 9942 to 7638microg kg(-1) dry soil. The percentage degradation of 3-, 4- and 5(+6)-ring PAHs was 35.1%, 20.7% and 24.3%, respectively. Higher counts of culturable PAH-degrading bacteria, microbial biomass and enzyme activities were observed in bioaugmented soil. The bioaugmented microcosms showed significant increases (p<0.05) in the average well-color development (AWCD) obtained by the BIOLOG ecoplate assay and Shannon-Weaver index (H) compared to the controls. Principal component analysis of BIOLOG data clearly differentiated between the bioaugmented and control microcosms, implying that bioaugmentation restored the microbiological functioning of the PAH-contaminated soil. The results suggest that bioaugmentation by Paracoccus sp. strain HPD-2 may be a promising bioremediation strategy for aged PAH-contaminated soils.

Influence of Rhizobium meliloti on phytoremediation of polycyclic aromatic hydrocarbons by alfalfa in an aged contaminated soil.

Microbe-assisted phytoremediation is emerging as one of the most effective means by which plants and their associated rhizosphere microbes degrade organic contaminants in soils. A pot study was conducted to examine the effects of inoculation with Rhizobium meliloti on phytoremediation by alfalfa grown for 90 days in an agricultural soil contaminated with weathered polycyclic aromatic hydrocarbons (PAHs). Planting with uninoculated alfalfa (P) and alfalfa inoculated with R. meliloti (PR) significantly lowered the initial soil PAH concentrations by 37.2 and 51.4% respectively compared with unplanted control soil. Inoculation with R. meliloti significantly increased the counts of culturable PAH-degrading bacteria, soil microbial activity and the carbon utilization ability of the soil microbial community. The results suggest that the symbiotic association between alfalfa and Rhizobium can stimulate the rhizosphere microflora to degrade PAHs and its application may be a promising bioremediation strategy for aged PAH-contaminated soils.

Methyl-β-cyclodextrin enhanced biodegradation of polycyclic aromatic hydrocarbons and associated microbial activity in contaminated soil

The contamination of soils by polycyclic aromatic hydrocarbons (PAHs) is a widespread environmental problem and the remediation of PAHs from these areas has been a major concern. The effectiveness of many in situ bioremediation systems may be constrained by low contaminant bioavailability due to limited aqueous solubility or a large magnitude of sorption. The objective of this research was to evaluate the effect of methyl-beta-cyclodextrin (MCD) on bioaugmentation by Paracoccus sp. strain HPD-2 of an aged PAH-contaminated soil. When 10% (W/W) MCD amendment was combined with bioaugmentation by the PAH-degrading bacterium Paracoccus sp. strain HPD-2, the percentage degradation of total PAHs was significantly enhanced up to 34.8%. Higher counts of culturable PAH-degrading bacteria and higher soil dehydrogenase and soil polyphenol oxidase activities were observed in 10% (W/W) MCD-assisted bioaugmentation soil. This MCD-assisted bioaugmentation strategy showed significant increases (p < 0.05) in the average well color development (AWCD) obtained by the BIOLOG Eco plate assay, Shannon-Weaver index (H) and Simpson index (lambda) compared with the controls, implying that this strategy at least partially restored the microbiological functioning of the PAH-contaminated soil. The results suggest that MCD-aided bioaugmentation by Paracoccus sp. strain HPD-2 may be a promising practical bioremediation strategy for aged PAH-contaminated soils.

Remediation of polycyclic aromatic hydrocarbon and metal-contaminated soil by successive methyl-β-cyclodextrin-enhanced soil washing–microbial augmentation: a laboratory evaluation

Polycyclic aromatic hydrocarbon (PAH) and metal-polluted sites caused by abandoned coking plants are receiving wide attention. To address the associated environmental concerns, innovative remediation technologies are urgently needed. This study was initiated to investigate the feasibility of a cleanup strategy that employed an initial phase, using methyl-β-cyclodextrin (MCD) solution to enhance ex situ soil washing for extracting PAHs and metals simultaneously, followed by the addition of PAH-degrading bacteria (Paracoccus sp. strain HPD-2) and supplemental nutrients to treat the residual soil-bound PAHs. Elevated temperature (50xa0°C) in combination with ultrasonication (35xa0kHz, 30xa0min) at 100xa0g MCD L−1 was effective in extracting PAHs and metals to assist soil washing; 93xa0% of total PAHs, 72xa0% of Cd, 78xa0% of Ni, 93xa0% of Zn, 84xa0% of Cr, and 68xa0% of Pb were removed from soil after three successive washing cycles. Treating the residual soil-bound PAHs for 20xa0weeks led to maximum biodegradation rates of 34, 45, 36, and 32xa0% of the remaining total PAHs, 3-ring PAHs, 4-ring PAHs, and 5(+6)-ring PAHs after washing procedure, respectively. Based on BIOLOG Ecoplate assay, the combined treatment at least partially restored microbiological functions in the contaminated soil. The ex situ cleanup strategy through MCD-enhanced soil washing followed by microbial augmentation can be effective in remediating PAH and metal-contaminated soil.

Tenax extraction for exploring rate-limiting factors in methyl-β-cyclodextrin enhanced anaerobic biodegradation of PAHs under denitrifying conditions in a red paddy soil.

The effectiveness of anaerobic bioremediation systems for PAH-contaminated soil may be constrained by low contaminants bioaccessibility due to limited aqueous solubility and lack of suitable electron acceptors. Information on what is the rate-limiting factor in bioremediation process is of vital importance in the decision in what measures can be taken to assist the biodegradation efficacy. In the present study, four different microcosms were set to study the effect of methyl-β-cyclodextrin (MCD) and nitrate addition (N) on PAHs biodegradation under anaerobic conditions in a red paddy soil. Meanwhile, sequential Tenax extraction combined with a first-three-compartment model was employed to evaluate the rate-limiting factors in MCD enhanced anaerobic biodegradation of PAHs. Microcosms with both 1% (w/w) MCD and 20mM N addition produced maximum biodegradation of total PAHs of up to 61.7%. It appears rate-limiting factors vary with microcosms: low activity of degrading microorganisms is the vital rate-limiting factor for control and MCD addition treatments (CK and M treatments); and lack of bioaccessible PAHs is the main rate-limiting factor for nitrate addition treatments (N and MN treatments). These results have practical implications for site risk assessment and cleanup strategies.

Positive relationship detected between soil bioaccessible organic pollutants and antibiotic resistance genes at dairy farms in Nanjing, Eastern China.

Co-contaminated soils by organic pollutants (OPs), antibiotics and antibiotic resistance genes (ARGs) have been becoming an emerging problem. However, it is unclear if an interaction exists between mixed pollutants and ARG abundance. Therefore, the potential relationship between OP contents and ARG and class 1 integron-integrase gene (intI1) abundance was investigated from seven dairy farms in Nanjing, Eastern China. Phenanthrene, pentachlorophenol, sulfadiazine, roxithromycin, associated ARG genes, and intI1 had the highest detection frequencies. Correlation analysis suggested a stronger positive relationship between the ARG abundance and the bioaccessible OP content than the total OP content. Additionally, the significant correlation between the bioaccessible mixed pollutant contents and ARG/intI1 abundance suggested a direct/indirect impact of the bioaccessible mixed pollutants on soil ARG dissemination. This study provided a preliminary understanding of the interaction between mixed pollutants and ARGs in co-contaminated soils.

Evaluation of enhanced soil washing process and phytoremediation with maize oil, carboxymethyl-β-cyclodextrin, and vetiver grass for the recovery of organochlorine pesticides and heavy metals from a pesticide factory site

An innovative ex situ soil washing technology was developed in this study to remediate organochlorine pesticides (OCPs) and heavy metals in a mixed contaminated site. Elevated temperature (60xa0°C) combined with ultrasonication (40xa0kHz, 20xa0min) at 50xa0mLxa0L(-1) maize oil and 45xa0gxa0L(-1) carboxylmethyl-β-cyclodextrin were effective in extracting pollutants from the soil. After two successive washing cycles, the removal efficiency rates for total OCPs, mirex, endosulfans, chlordanes, Cd, and Pb were approximately 94.7%, 87.2%, 98.5%, 92.3%, 91.6%, and 87.3%, respectively. Cultivation of vetiver grass and addition of nutrients for 3 months further degraded 34.7% of the residual total OCPs and partially restored the microbiological functions of the soil. This result was indicated by the significant increase in the number, biomass C, N, and functioning diversity of soil microorganisms (pxa0<xa00.05). After the treatment, the residual OCPs and heavy metals existed as very slowly desorbing fraction and residual fraction, as evaluated by Tenax extraction combined with a first-three-compartment model and sequential extraction. Moreover, the secondary environmental risk of residual pollutants in the remediated soil was at an acceptable level. The proposed combined cleanup strategy proved to be effective and environmentally friendly.

Tenax TA extraction to understand the rate-limiting factors in methyl-β-cyclodextrin-enhanced bioremediation of PAH-contaminated soil

The effectiveness of many bioremediation systems for PAH-contaminated soil may be constrained by low contaminant bioaccessibility due to limited aqueous solubility or large sorption capacity. Information on the extent to which PAHs can be readily biodegraded is of vital importance in the decision whether or not to remediate a contaminated soil. In the present study the rate-limiting factors in methyl-β-cyclodextrin (MCD)-enhanced bioremediation of PAH-contaminated soil were evaluated. MCD amendment at 10xa0% (w/w) combined with inoculation with the PAH-degrading bacterium Paracoccus sp. strain HPD-2 produced maximum removal of total PAHs of up to 35xa0%. The desorption of PAHs from contaminated soil was determined before and after 32xa0weeks of bioremediation. 10xa0% (w/w) MCD amendment (M2) increased the Tenax extraction of total PAHs from 12 to 30xa0% and promoted degradation by up to 26xa0% compared to 6xa0% in the control. However, the percentage of Tenax extraction for total PAHs was much larger than that of degradation. Thus, in the control and M2 treatment it is likely that during the initial phase the bioaccessibility of PAHs is high and biodegradation rates may be limited by microbial processes. On the other hand, when the soil was inoculated with the PAH-degrading bacterium (CKB and MB2), the slowly and very slowly desorbing fractions (Fsl and Fvl) became larger and the rate constants of slow and very slow desorption (ksl and kvl) became extremely small after bioremediation, suggesting that desorption is likely rate limiting during the second, slow phase of biotransformation. These results have practical implications for site risk assessment and cleanup strategies.

Effect of biochar amendment on the control of soil sulfonamides, antibiotic-resistant bacteria, and gene enrichment in lettuce tissues.

Considering the potential threat of vegetables growing in antibiotic-polluted soil with high abundance of antibiotic-resistant genes (ARGs) against human health through the food chain, it is thus urgent to develop novel control technology to ensure vegetable safety. In the present work, pot experiments were conducted in lettuce cultivation to assess the impedance effect of biochar amendment on soil sulfonamides (SAs), antibiotic-resistant bacteria (ARB), and ARG enrichment in lettuce tissues. After 100 days of cultivation, lettuce cultivation with biochar amendment exhibited the greatest soil SA dissipation as well as the significant improvement of lettuce growth indices, with residual soil SAs mainly existing as the tightly bound fraction. Moreover, the SA contents in roots and new/old leaves were reduced by one to two orders of magnitude compared to those without biochar amendment. In addition, isolate counts for SA-resistant bacterial endophytes in old leaves and sul gene abundances in roots and old leaves also decreased significantly after biochar application. However, neither SA resistant bacteria nor sul genes were detected in new leaves. It was the first study to demonstrate that biochar amendment can be a practical strategy to protect lettuce safety growing in SA-polluted soil with rich ARB and ARGs.

Remediation of organochlorine pesticides (OCPs) contaminated soil by successive hydroxypropyl-β-cyclodextrin and peanut oil enhanced soil washing–nutrient addition: a laboratory evaluation

PurposeProblems associated with organochlorine pesticides (OCPs)-contaminated sites have received wide attention. To address the associated environmental concerns, innovative ex situ techniques are urgently needed.Materials and methodsAs 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.Results and discussionElevated temperature (50xa0°C) in combination with ultrasonication (35xa0kHz, 30xa0min) at 50xa0gu2009L−1 HPCD and 10xa0% peanut oil were effective in extracting, and therefore washing, the OCPs in soil. Ninety-three percent of total OCPs, 98xa0% of dichlorodiphenyltrichloroethanes, 93xa0% of chlordane as well as 85xa0% of Mirex were removed from soil after three successive washing cycles. Treating the residual soil with nutrients addition for 12xa0weeks led to significant increases (pu2009<u20090.05) 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.ConclusionsThe 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.