Manyun Zhang

Occurrence and risk assessment of phthalate esters (PAEs) in vegetables and soils of suburban plastic film greenhouses

Phthalate esters (PAEs) are suspected of having adverse effects on human health and have been frequently detected in soils and vegetables. The present study investigated their occurrence and composition in plastic film greenhouse soil-vegetable systems and assessed their potential health risks to farmers exposed to these widespread pollutants. Six priority control phthalates, namely dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DnBP), butyl benzyl phthalate (BBP), di-(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DnOP), were determined in 44 plastic film greenhouse vegetables and corresponding soils. Total PAEs ranged from 0.51 to 7.16mgkg(-1) in vegetables and 0.40 to 6.20mgkg(-1) in soils with average concentrations of 2.56 and 2.23mgkg(-1), respectively. DnBP, DEHP and DnOP contributed more than 90% of the total PAEs in both vegetables and soils but the proportions of DnBP and DnOP in vegetables were significantly (p<0.05) higher than in soils. The average concentrations of PAEs in pot herb mustard, celery and lettuce were >3.00mgkg(-1) but were <2.50mgkg(-1) in the corresponding soils. Stem and leaf vegetables accumulated more PAEs. There were no clear relationships between vegetable and soil PAEs. Risk assessment indicates that DnBP, DEHP and DnOP exhibited elevated non-cancer risk with values of 0.039, 0.338 and 0.038, respectively. The carcinogenic risk of DEHP was about 3.94×10(-5) to farmers working in plastic film greenhouses. Health risks were mainly by exposure through vegetable consumption and soil ingestion.

Non-target effects of repeated chlorothalonil application on soil nitrogen cycling: The key functional gene study

The widespread and increasing application of chlorothalonil (CTN) raises concerns about its non-target impacts, but little information is available on the effect of CTN on the key functional genes related to soil nitrogen (N) cycling, especially in the case of repeated applications. In the present study, a microcosm incubation was conducted to determine CTN residues and the impacts on the abundances of key functional genes related to N cycling after repeated CTN applications. The results demonstrated that repeated CTN applications at the recommended application rate and five times the recommended rate led to the accumulation of CTN residue in soil at concentrations of 5.59 and 78.79 mg kg(-1), respectively, by the end of incubation. Real time PCR (RT-PCR) revealed that repeated CTN applications had negative effects on the chiA and aprA gene abundances. There were significantly negative correlations between CTN residues and abundances of AOA and AOB genes. In addition, the abundances of key functional genes involved in soil denitrification were declined by repeated CTN applications with the sole exception of the nosZ gene. This study suggests that repeated CTN applications could lead to the accumulation of CTN residue and generate somewhat inconsistent and erratic effects on the abundances of key functional genes related to soil N cycling.

Isolation and Identification of a Di-(2-Ethylhexyl)Phthalate-Degrading Bacterium and Its Role in the Bioremediation of a Contaminated Soil

Abstract Di-(2-ethylhexyl) phthalate (DEHP) is a high-molecular-weight phthalate ester (PAE) that has been widely used in the manufacture of polyvinylchloride and contributes to environmental pollution. The objectives of the present study were to isolate a DEHP degrader that can utilize DEHP as a carbon source and to investigate its capacity to biodegrade DEHP in both liquid culture and soil. A bacterial strain WJ4 was isolated from an intensively managed vegetable soil, which was contaminated with PAEs. The strain WJ4 was affiliated to the genus Rhodococcus and was able to remove DEHP from soil effectively. A period of only 7 d was required to degrade about 96.4% of DEHP (200 mg L −1 ) in the liquid culture, and more than 55% of DEHP (1.0 g kg −1 ) in the artificially contaminated soil was removed within 21 d. Furthermore, Rhodococcus sp. strain WJ4 had a strong ability to degrade DEHP without additional nutrients in liquid minimal medium culture and DEHP-contaminated soil and to degrade the homologue of DEHP in both liquid culture and soil. Strain WJ4 represents a novel tool for removing PAEs from contaminated soils and it may have great potential for application in the remediation of environmental pollution by PAEs.

Effects of fungicide iprodione and nitrification inhibitor 3, 4-dimethylpyrazole phosphate on soil enzyme and bacterial properties

Agrochemical applications may have unintended detrimental effects on soil microorganisms and soil health. However, limited studies have been conducted to evaluate the effects of repeated fungicide applications and interactive effects of different agrochemical applications on soil microorganisms. In this study, an incubation experiment was established to evaluate the potential influences of the fungicide iprodione and the nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) on soil enzyme activities and bacterial properties. Weekly iprodione applications decreased the activities of all enzymes tested, and DMPP application inhibited soil urease activity. Compared with the blank control, bacterial 16S rRNA gene abundance decreased following repeated iprodione applications, but increased after DMPP application. After 28days of incubation, the treatment receiving both iprodione and DMPP application had higher bacterial 16S rRNA gene abundance and Shannon diversity index than the treatment with iprodione applications alone. Repeated iprodione applications significantly increased the relative abundance of Proteobacteria, but decreased the relative abundances of Chloroflexi and Acidobacteria. Simultaneously, bacterial community structure was changed by repeated iprodione applications, alone or together with DMPP. These results showed that repeated iprodione applications exerted negative effects on soil enzyme activities, bacterial biomass and community diversity. Moreover, relative to iprodione applications alone, additional DMPP application could alleviate the toxic effects of iprodione applications on bacterial biomass and community diversity.

Isolation and Characterization of Chlorothalonil-Degrading Bacterial Strain H4 and Its Potential for Remediation of Contaminated Soil

A chlorothalonil (CTN)-degrading bacterial strain H4 was isolated in this study from a contaminated soil by continuous enrichment culture to identify its characteristics and to investigate its potential for remediation of CTN in contaminated soil. Based on the morphological, physiological and biochemical tests and 16S rDNA sequence analysis, the strain was identified as Stenotrophomonas sp. After liquid culture for 7 d, 82.2% of CTN was removed by strain H4. The isolate could degrade CTN over a broad range of temperatures and pH values, and the optimum conditions for H4 degradation were pH 7.0 and 30 °C. Reintroduction of the bacteria into artificially contaminated soil resulted in substantial removal of CTN (> 50%) after incubation for 14 d. Soil samples treated by H4 showed significant increases (P < 0.05) in soil dehydrogenase activity, soil polyphenol oxidase activity, average well-color development obtained by the Biolog Eco plateTM assay and Shannon-Weaver index, compared with the control. Strain H4 might be a promising candidate for application in the bioremediation of CTN-contaminated soils.

Isolation of the PCB-degrading bacteria Mesorhizobium sp. ZY1 and its combined remediation with Astragalus sinicus L. for contaminated soil

ABSTRACT A bacterial strain ZY1 capable of utilizing PCBs as its carbon source was isolated from the root nodules of Chinese milk vetch (Astragalus sinicus L.). The strain was identified as Mesorhizobium sp. according to its physiological-biochemical properties and the analysis of its 16S rRNA gene sequence. When the initial OD600 was 0.15, 62.7% of 15 mg L−1 3,3′,4,4′-TCB in a liquid culture was degraded by Mesorhizobium sp. ZY1 within 10 days. Mesorhizobium sp. ZY1 also greatly increased the biotransformation of soil PCBs. Pot experiments indicated that the soil PCB concentrations of a single incubation of strain ZY1 (R) and a single planting of A. sinicus (P) decreased by 20.5% and 23.0%, respectively, and the concentration of PCBs in soil treated with A. sinicus and strain ZY1 decreased by 53.1%. We also observed that A. sinicus-Mesorhizobium sp. ZY1 treatment (PR) improved plant biomass and the concentration of PCBs in plants compared with a single A. sinicus planting treatment (P). The results suggest that the synergistic association between A. sinicus and PCBs-degrading Mesorhizobium sp. ZY1 can stimulate the phytoextraction of PCBs and the rhizosphere microflora to degrade PCBs, and might be a promising bioremediation strategy for PCB-contaminated soil.

Linking potential nitrification rates, nitrogen cycling genes and soil properties after remediating the agricultural soil contaminated with heavy metal and fungicide

Apart from the contaminant removal, the remediation of agricultural soil should also pay more attention to soil nutrient retention and biogeochemical cycling. This study aimed to evaluate changes of soil properties, potential nitrification rates (PNRs), and functional gene abundances and link their relationships after remediating co-contaminated agricultural soil with Medicago sativa L. (alfalfa) planting, alone or together with biochar application. Compared with the control (CK), alfalfa planting, alone or together with biochar application, could significantly increase soil organic matter (SOM) contents and discrepantly affect soil pH values. The PNRs of the amended treatments were significantly higher than that of the CK. Moreover, alfalfa plantings also enhanced the abundances of functional genes related to soil nitrification and denitrification, with the sole exception of nosZ gene. Stepwise regression analysis revealed that the PNRs were best described by the gene abundance ratios of AOB amoA/nifH and nirS gene abundances. Compared with the CK, alfalfa planting, alone or with biochar application, could restore nitrogen cycling in the co-contaminated agricultural soil and enhance the PNRs via decreasing contaminant bio-availabilities and increasing SOM contents and gene abundance ratios of AOB amoA/nifH.

Evaluating the effects of phytoremediation with biochar additions on soil nitrogen mineralization enzymes and fungi

Phytoremediation with biochar addition might alleviate pollutant toxicity to soil microorganism. It is uncertain to what extent biochar addition rate could affect activities of enzymes related to soil nitrogen (N) mineralization and alter fungal community under the phytoremediation. This study aimed to reveal the effects of Medicago sativa L. (alfalfa) phytoremediation, alone or with biochar additions, on soil protease and chitinase and fungal community and link the responses of microbial parameters with biochar addition rates. The alfalfa phytoremediation enhanced soil protease activities, and relative to the phytoremediation alone, biochar additions had inconsistent impacts on the corresponding functional gene abundances. Compared with the blank control, alfalfa phytoremediation, alone or with biochar additions, increased fungal biomass and community richness estimators. Moreover, relative to the phytoremediation alone, the relative abundances of phylum Zygomycota were also increased by biochar additions. The whole soil fungal community was not significantly changed by the alfalfa phytoremediation alone, but was indeed changed by alfalfa phytoremediation with 3.0% (w/w) or 6.0% biochar addition. This study suggested that alfalfa phytoremediation could enhance N mineralization enzyme activities and that biochar addition rates affected the responses of fungal community to the alfalfa phytoremediation.

Effects of Silicon on the Growth, Physiology and Cadmium Translocation of Tobacco ( Nicotiana tabacum L.) in Cadmium Contaminated Soil

Silicon (Si) offers beneficial effect on plants under cadmium (Cd) stress such as promoting plant growth and increasing resistance to heavy metal toxicity. In this study, a pot experiment was performed to study the role of Si in alleviating Cd toxicity in tobacco (Nicotiana tabacum L.) plants on a yellow soil taken from Guiyang, China. Nine treatments consisting of three concentrations of Cd (0, 1, and 5 mg kg−1) together with three Si levels (0, 1, and 4 g kg−1) were established. Plant growth parameters, Cd concentration, and the malondialdehyde (MDA), chlorophyll, and carotenoid contents were determined 100 d after transplanting of tobacco seedlings. Application of exogenous Si enhanced the growth of tobacco plants under Cd stress. When 5 mg kg−1 Cd was added, Si addition at 1 and 4 g kg−1 increased root, stem, and leaf biomass by 26.1%–43.3%, 33.7%–43.8%, and 50.8%–69.9%, respectively, compared to Si addition at 0 g kg−1. With Si application, the transfer factor of Cd in tobacco from root to shoot under both 1 and 5 mg kg−1 Cd treatments decreased by 21%. The MDA contents in the Si-treated tobacco plants declined by 5.5%–17.1% compared to those in the non-Si-treated plants, indicating a higher Cd tolerance. Silicon application also increased the chlorophyll and carotenoid contents by 33.9%–41% and 25.8%–47.3% compared to the Cd only treatments. Therefore, it could be concluded that Si application can alleviate Cd toxicity to tobacco by decreasing Cd partitioning in the shoots and MDA levels and by increasing chlorophyll and carotenoid contents, thereby contributing to lowering the potential health risks of Cd contamination.