Mycorrhizal colonization and microbial community structure in the rhizosphere of annual ryegrass grown in pyrene‐amended soils

In an 182‐d lightroom experiment, annual ryegrass (Lolium multiflorum Lam.) was grown in two soils under conditions of high and low fertility to examine the effect of pyrene (500 mg kg^‐1) on plant shoot biomass, mycorrhizal colonization, and soil microbial community structure. Treatments were destructively sampled every 14 d. Plant shoot biomass remained relatively unaffected by pyrene in either soil. Mycorrhizal colonization was only briefly affected by pyrene in one soil, but was unaffected in the other. Changes in soil microbial community structure were measured with whole soil fatty acid methyl ester (FAME) profiles. Differences in soil microbial community structure were observed between planted and nonplanted treatments at both fertility levels, but these differences were unrelated to the presence of pyrene. The bulk soil was associated primarily with fatty acid biomarkers for Gram‐positive bacteria, while the rhizosphere was associated primarily with the fatty acid biomarkers associated with protozoa. Differences in microbial community structure were observed between the two soils. Methylene chloride‐extractable pyrene decreased in nonplanted and planted treatments of one soil, but decreased only in nonplanted treatments of the other soil. These results suggest the potential for phytoremediation to differ among soils.     

Plant Uptake and Enhanced Dissipation of Di(2-Ethylhexyl) Phthalate (DEHP) in Spiked Soils by Different Plant Species

This study was conducted to investigate the uptake, accumulation and the enhanced dissipation of di(2-ethylhexyl) phthalate (DEHP) spiked in soil (with a concentration of 117.4 ± 5.2 mg kg^?1) by eleven plants including eight maize ( Zea mays) cultivars and three forage species (alfalfa, ryegrass and teosinte). The results showed that, after 40 days of treatment, the removal rates of DEHP ranged from 66.8% (for the control) to 87.5% (for the maize cultivar of Huanong-1). Higher removal rate was observed during the first 10 days than the following days. Plants enhanced significantly the dissipation of DEHP in soil. Enhanced dissipation amount in planted soil was 13.3–122 mg pot^?1 for DEHP, and a net removal of 2.2%–20.7% of the initial DEHP was obtained compared with non-plant soil. The contribution of plant uptake to the total enhanced dissipation was <0.3%, and the enhanced dissipation of soil DEHP might be derived from plant-promoted biodegradation and sorption stronger to the soil. Nevertheless, the capability in accumulation and enhanced dissipation of DEHP from spiked soils varied within different species and cultivars.     

PAH Degradation Capacity of Soil Microbial Communities—Does It Depend on PAH Exposure?

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants of the environment. But is their microbial degradation equally wide in distribution? We estimated the PAH degradation capacity of 13 soils ranging from pristine locations (total PAHs ≈ 0.1 mg kg^?1) to heavily polluted industrial sites (total PAHs ≈ 400 mg kg^?1). The size of the pyrene- and phenanthrene-degrading bacterial populations was determined by most probable number (MPN) enumeration. Densities of phenanthrene degraders reflected previous PAH exposure, whereas pyrene degraders were detected only in the most polluted soils. The potentials for phenanthrene and pyrene degradation were measured as the mineralization of ¹⁴C-labeled spikes. The time to 10% mineralization of added ¹⁴C phenanthrene and ¹⁴C pyrene was inversely correlated with the PAH content of the soils. Substantial ¹⁴C phenanthrene mineralization in all soils tested, including seven unpolluted soils, demonstrated that phenanthrene is not a suitable model compound for predicting PAH degradation in soils. ¹⁴C pyrene was mineralized by all Danish soil samples tested, regardless of whether they were from contaminated sites or not, suggesting that in industrialized areas the background level of pyrene is sufficient to maintain pyrene degradation traits in the gene pool of soil microorganisms. In contrast, two pristine forest soils from northern Norway and Ghana mineralized little ¹⁴C pyrene within the 140-day test period. Mineralization of phenanthrene and pyrene by all Danish soils suggests that soil microbial communities of inhabited areas possess a sufficiently high PAH degradation capacity to question the value of bioaugmentation with specific PAH degraders for bioremediation.     

Long-Term Explosive Contamination in Soil: Effects on Soil Microbial Community and Bioremediation

Explosive contamination in soil is a great concern for environmental health. Following 50 years of munitions manufacturing and loading, soils from two different sites contained ≥ 6,435 mg 2,4,6-trinitrotoluene (TNT), 2,933 mg hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,135 mg octahydrol-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) kg^{? 1} soil. Extractable nitrate-N was as high as 315 and ammonium-N reached 150 mg N kg^{? 1} soil. Water leachates in the highly contaminated soils showed near saturation levels of TNT and RDX, suggesting great risk to water quality. The long-term contamination resulted in undetectable fungal populations and as low as 180 bacterial colony forming units (CFU) g^–1 soil. In the most severely contaminated soil, dehydrogenase activity was undetectable and microbial biomass carbon was very low (< 3.4 mg C _mic kg^–1 soil). The diminished biological activity was a consequence of long-term contamination because short-term (14 d) contamination of TNT at up to 5000 mg TNT kg^–1 soil did not cause a decline in the culturable bacterial population. Natural attenuation may not be a feasible remediation strategy in soils with long-term contamination by high concentrations of explosives.     

Characteristics of an endophytic pyrene-degrading bacterium of Enterobacter sp. 12J1 from Allium macrostemon Bunge

One pyrene-degrading endophytic bacterium was isolated from plants grown in polycyclic aromatic hydrocarbon-contaminated soils and identified as Enterobacter sp. 12J1 based on the 16S rDNA gene sequence analysis. Heavy metal and antibiotic resistance, degradation of pyrene, solubilization of inorganic phosphate and cell surface hydrophobicity characteristics of the isolate were further characterized. The isolate was also evaluated for promoting plant growth of wheat and maize and pyrene removal from pyrene-amended soil in pot experiments. High-performance liquid chromatograph (HPLC) analysis showed that the degradation rate of pyrene (5 mg l⁻¹) by the endophytic bacterial strain 12J1 was 83.8% under 28 °C for 7 days. The Enterobacter sp. 12J1 could produce indole acetic acid (IAA), siderophore and solubilize inorganic phosphate. The Enterobacter sp. 12J1 also has a cell surface hydrophobicity. In the live bacterial inoculation experiment, an increase in pyrene removal varying from 60% to 107% was observed in the planted soils treated with 100 mg kg⁻¹ of pyrene compared with the unplanted soils. The rate of pyrene removal increased by 43–65% in the live bacterium-inoculated planted soils compared with the dead bacterium-inoculated planted soils. Although there were no significant differences in the total culturable bacterial numbers between live and dead bacterial inoculation, the numbers of pyrene-degrading bacteria were significantly greater in the live bacterium-inoculated planted or unplanted soils. The isolate could colonize the tissue (root and stem) interiors and rhizosphere soils of wheat and maize after root inoculation.     

蚯蚓在植物修复芘污染土壤中的作用

采用盆栽试验法,研究了蚯蚓(Pheretima hupeiensis)在植物修复芘污染土壤中的作用。结果显示,试验浓度(20.24-321.42 mg/kg) 范围内,蚯蚓活动促进了芘污染土壤中修复植物黑麦草(Lolium multiforum)黑麦草的生长,其根冠比明显增大。添加蚯蚓72 d后,种植黑麦草的土壤中芘的去除率高达60.01%-86.26%,其平均去除率(74.66%)比无蚯蚓活动的土壤-植物系统(64.55%)提高10.11%,比无植物对照组(18.24%)提高56.42%。各种生物、非生物修复因子中,植物-微生物交互作用对芘去除的平均贡献率(51.75%)最为突出,比无蚯蚓活动时(44.94%)提高6.81%。说明蚯蚓活动可强化土壤-植物系统对土壤芘污染的修复作用。     

PYRENE EFFECTS ON RHIZOPLANE BACTERIAL COMMUNITIES

Certain plant species promote biodegradation of polycyclic aromatic hydrocarbons (PAHs), but few studies have examined the microbial populations that are associated with the rhizoplane of these plants. In this study, the bacterial composition of the rhizoplane were characterized for four plant species during in soils with different histories of exposure to PAH and in the presence or absence of a pyrene spike at 100 mg kg^?1 pyrene. Three of the plant species including Andropogon gerrardii, Panicum coloratum and Melilotus officinalis were known to stimulate PAH degradation. Wheat (Triticum aestivum) was used as a reference species. Results showed that after 90 days, approximately 45% of the pyrene spike disappeared from soil without plants. In contrast, cultivation of plants resulted in 95% disappearance of pyrene. There were no significant differences in the extent of pyrene disappearance for different plants. In all cases, 16S rRNA gene profiles of the rhizoplane were less complex in the pyrene-spiked soils, suggesting that richness and evenness of the predominant bacteria were reduced. Our results show that pyrene contamination results in significant shifts in the composition of rhizosphere bacterial communities that are still further influenced by the plant species and prior exposure history to PAH contamination.     

Electrokinetic-enhanced phytoremediation of uranium-contaminated soil using sunflower and Indian mustard

Abstract

Electrokinetic-enhanced phytoremediation is an effective technology to decontaminate heavy metal contaminated soil. In this study, we examined the effects of electrokinetic treatments on plant uptake and bioaccumulation of U from soils with various U sources. Redistribution of uranium in soils as affected by planting and electrokinetic treatments was investigated. The soil was spiked with 100?mg kg^–1 UO₂, UO₃, and UO₂(NO₃)₂. After sunflower and Indian mustard grew for 60 days, 1 voltage of direct-current was applied across the soils for 9 days. The results indicated that U uptake in both plants were significantly enhanced by electrokinetic treatments from soil with UO₃ and UO₂(NO₃)₂. U was more accumulated in roots than in shoots. Electrokinetic treatments were effective on lowering soil pH near the anode region. Overall, uranium (U) removal efficiency reached 3.4–4.3% from soils with UO₃ and uranyl with both plants while that from soil with UO₂ was 0.7–0.8%. Electrokinetic remediation treatment significantly enhanced the U removal efficiency (5–6%) from soils with UO₃ and uranyl but it was 0.8–1.3% from soil with UO₂, indicating significant effects of U species and electrokinetic enhancement on U bioaccumulation. This study implies the potential feasibility of electrokinetic-enhanced phytoremediation of U soils with sunflower and Indian mustard.     

Effects of soil amendment with different carbon sources and other factors on the bioremediation of an aged PAH-contaminated soil

Carbon supplementation, soil moisture and soil aeration are believed to enhance in situ bioremediation of PAH-contaminated soils by stimulating the growth of indigenous microorganisms. However, the effects of added carbon and nitrogen together with soil moisture and soil aeration on the dissipation of PAHs and on associated microbial counts have yet to be fully assessed. In this study the effects on bioremediation of carbon source, carbon-to-nitrogen ratio, soil moisture and aeration on an aged PAH-contaminated agricultural soil were studied in microcosms over a 90-day period. Additions of starch, glucose and sodium succinate increased soil bacterial and fungal counts and accelerated the dissipation of phenanthrene and benzo(a)pyrene in soil. Decreases in phenanthrene and benzo(a)pyrene concentrations were effective in soil supplemented with glucose and sodium succinate (both 0.2 g C kg⁻¹ dry soil) and starch (1.0 g C kg⁻¹ dry soil). The bioremediation effect at a C/N ratio of 10:1 was significantly higher (P < 0.05) than at a C/N of either 25:1 or 40:1. Soil microbial counts and PAH dissipation were lower in the submerged soil but soil aeration increased bacterial and fungal counts, enhanced indigenous microbial metabolic activities, and accelerated the natural degradation of phenanthrene and benzo(a)pyrene. The results suggest that optimizing carbon source, C/N ratio, soil moisture and aeration conditions may be a feasible remediation strategy in certain PAH contaminated soils with large active microbial populations.     

Greenhouse and field assessment of phytoremediation for petroleum contaminants in a riparian zone

Greenhouse and field studies were conducted to evaluate the feasibility of phytoremediation for clean-up of highly contaminated sediments from Indiana Harbor. In the greenhouse study, plant species evaluated were willow (Salix exigua), poplar (Populus spp.), eastern gamagrass (Tripsacum dactyloides), arrowhead (Sagitaria latifolia), switchgrass (Panicum virgatum), and sedge (Carex stricta). Sediments with sedge, switchgrass, and gamagrass had significantly less residual total petroleum hydrocarbons (TPH) after one year of growth (approximately 70% reduction) than sediments containing willow, poplar, or no plants (approximately 20% reduction). Although not all polycyclic aromatic hydrocarbons (PAH) had concentration differences due to the presence of plants, residual pyrene concentrations in the unvegetated pots were significantly higher than in pots containing sedge, switchgrass, arrowhead, and gamagrass. As evaluated by TPH dissipation in the upper section of the pots, the sedge, switchgrass, and gamagrass treatments had higher TPH degradation than the unvegetated, willow and poplar treatments. These trends were similar for soil at the bottom of the pots, with the exception that in the switchgrass treatment, degradation was not significantly different than in the unvegetated soil. Two target contaminants, pyrene and benzo[b]fluoranthene, showed differences in degradation between planted and unvegetated treatments. In the field study, phytoremediation plant species were eastern gamagrass (T. dactyloides), switchgrass (P. virgatum), and sedge (C. stricta). In addition, rhizosphere characteristics of arrowhead (S. latifolia) and sedge were assessed. Arrowhead- and sedge-impacted soils were found to contain significantly more PAH-degrading bacteria than unvegetated soils. However, over the 12-month field study, no significant differences in contamination were found between the planted and unplanted soils for TPH and PAH concentrations. TPH concentrations near the canal were greater than concentrations further from the canal, indicating that the canal may have served as a continuous source of contamination during the study.     

Soybean residues sequestration affected by different tillage practices and the impacts on soil microbial characteristics and enzymatic activities

A large quantity of leaf litter was left on soil surface after soybean (Glycine max) harvest in the black soil region, northeast of China, where soybean was planted with the largest area. This paper investigated the effects of different fall tillage practices on soybean leaf litter sequestration into soil, and the subsequently durative effects on soil biological and biochemical properties during the next growing season. Two practices were investigated, fall tillage (T) and no fall tillage (NT) after soybean harvest in autumn. Results showed that the residue biomass on soil surface and in subsoil profile (0–20 cm) after soybean harvest was about 1450 kg ha^?1 and 340 kg ha^?1, respectively in October 2006. The residue biomass on soil surface and in subsoil profile was about 84 kg ha^?1, 1581 kg ha^?1 for T, and 423 kg ha^?1, 340 kg ha^?1 for NT respectively in May 2007. It was obvious that T practice can more effectively sequester leaf litter into soil compared to NT. Results also showed that T practices after soybean harvest eminently improved soil microbial carbon biomass and nitrogen biomass contents, and significantly improved soil urease and acid phosphate activities than NT. No significant difference of dehydrogenase activity was found between N and NT. The positive effects of T treatment on Soil microbial properties and soil enzymes activities among the next growing season due to soybean residues sequestration performed durative profit.     

Effect of Exposure Time,Contamination Level,and Type of PAH Compound on Biodegradation Capacity of Mangrove Sediment

Mangrove sediment had high natural attenuation potential with more than 50% of total PAHs being removed within 15 days. The efficiency in degrading PAHs varied with the declining order of phenanthrene (Phe), fluoranthene (Fla), and pyrene (Pyr). The Most Probable Number (MPN) of PAH-degrading bacteria in the PAH-contaminated slurries was 2 to 4 orders of magnitude higher than that in the non-contaminated mangrove slurries. The biodegradation ability of the indigenous microbial community in mangrove sediment slurry was significantly increased after exposure to polycyclic aromatic hydrocarbons. Such enhancement effect was dependent on the level and time of exposure, as well as the types of PAH compounds. The lowest contamination level of 3 mg kg^?1 was effective in promoting the degradation of Phe and Fla after seven days, but the enhancement effect for Pyr degradation was only found in the slurries exposed to contamination levels of 9 mg kg^?1 for 30 days, suggesting a threshold concentration of PAHs to stimulate growth and activity of pyrene-degrading bacteria. The contamination level higher than the threshold concentration did not lead to more degradation. The present study provides insights into the natural attenuation of PAH-contaminated mangrove sediments.     

Enhanced Microbial Removal of Pyrene in Soils in the Presence of Earthworms

Microbial degradation of pyrene was studied in soils in the presence and absence of earthworms (Eisenia foetida) to demonstrate an integrated innovative strategy for bioremediation of sites lightly polluted by polycyclic aromatic hydrocarbons. Desorption of pyrene and soil microbial respiration were measured to elucidate the mechanism of enhanced microbial degradation. The results showed that both soil properties and contact time could influence pyrene biodegradation. The introduction of E. foetida enhanced pyrene removal significantly both in freshly spiked and aged soils. The percentage pyrene removal in the presence of E. foetida was 45.5–91.0% after 14 d of incubation, which were 2.1 to 2.8 times greater than those without the worms. The enhanced pyrene removal is attributed to both enhanced microbial degradation and uptake by the worms. Microbial degradation of pyrene increased by 1.2 to 1.6 times in the presence of the worms. Overall, the introduction of live worms could improve both pyrene bioavailability and microbial activity, which leads to enhanced microbial degradation of pyrene.     

Bacterial community evaluation during establishment of tall fescue (Festuca arundinacea) in soil contaminated with pyrene

A greenhouse study was conducted to monitor microbial community dynamics related to contaminant concentration and plant growth during the phytoremediation of pyrene. Soil microbial communities in both bulk and rhizosphere soils were assessed using a polymerase chain reaction--denaturing gradient gel electrophoresis (PCR-DGGE). However, no correlation between pyrene concentration and bacterial community shifts was observed. Even though plants significantly enhanced pyrene degradation (undetectable after 91 d for planted treatments compared with 82 mg/kg for unplanted treatments after 147 d with initial concentration of 758 mg/kg), biodegradation may have been accomplished by the pre-existing microbial community. It is also possible that the method was unable to pick up subtle community shifts, considering that the carbon source from pyrene was only 3.7% of the existing soil organic matter. This research suggests that plants significantly enhance degradation and mineralization of pyrene in soil, although there was no conclusive evidence supporting any specific bacterial activity responsible for this enhancement.     

玉米幼苗根际土壤微生物活性对芘污染的响应

用根际袋法土培试验研究了玉米幼苗根际与非根际土壤微生物量碳、微生物熵、代谢熵和土壤酶活性对不同芘污染水平(50、200、800mg·kg-1,记为T1、T2、T3)的响应差异。结果表明,较低浓度芘可适当的刺激玉米幼苗的生长,而较高浓度芘则抑制幼苗生长,其抑制作用随芘处理浓度的提高而增强;芘对玉米根系的影响要大于对茎叶的影响。玉米幼苗能够明显促进土壤中芘的去除。根际和非根际土壤中芘的去除率分别为56.67%-76.18%和32.64%-70.44%,根际土壤中芘的平均去除率比非根际土壤高16.06%。同处理中根际土壤芘含量显著低于非根际土壤,随着芘处理浓度的提高其差异更加显著。根际土壤微生物量碳、微生物熵、多酚氧化酶活性、脱氢酶活性和磷酸酶活性均高于非根际土壤,代谢熵低于非根际土壤,且其差异随芘处理浓度的提高而增大。在不同芘污染水平下,微生物量碳、微生物熵和脱氢酶活性根际和非根际土壤为T1T2T3,代谢熵为T3T2T1;多酚氧化酶活性根际土壤为T2T1T3,非根际土壤为T1T2T3;磷酸酶活性根际土壤为T3T1T2,非根际土壤为T1T2T3。土壤中残余芘含量与土壤微生物量碳、微生物熵、多酚氧化酶、脱氢酶和磷酸酶活性呈显著负相关,与代谢熵呈显著正相关。     

Rhizosphere microbial community and hexachlorocyclohexane degradative potential in contrasting plant species

The organochlorine 1,2,3,4,5,6 hexachlorocyclohexane (HCH) is a broad-spectrum insecticide that was used on a large-scale worldwide. The soil–plant–microbe system and its influence on HCH biodegradation are evaluated. A greenhouse experiment was designed to evaluate HCH dissipation and several microbial parameters among rhizosphere and bulk soil of two contrasting plants, Cytisus striatus (Hill) Rothm and Holcus lanatus L. Plants were grown for 180 days in three treatments: uncontaminated soil (control), uncontaminated soil inoculated with soil (3% w/w) from a HCH-contaminated site (INOC), and uncontaminated soil inoculated with soil (3% w/w) from the HCH-contaminated site and artificially contaminated to obtain 100 mg HCH kg⁻¹ dry soil (100HCH-INOC). At harvest, plant biomass, soil water-extractable organic C, pH and Cl concentration, rhizosphere microbial densities (total heterotrophs, ammonifiers, amylolytics) and C substrate utilization patterns, and degradation of α-, β-, δ- and γ-HCH isomers were determined in bulk and rhizosphere soils. Soil solution Cl concentration was determined every 30 days throughout the entire growth period. Results demonstrate that both Cytisus striatus and Holcus lanatus can grow in soils with up to 100 mg HCH kg⁻¹. An enhanced degradation of α-HCH, but not β- or δ-HCH, was observed in the rhizosphere. Significant changes in the microbial densities were observed between bulk and rhizosphere soils of Cytisus, and an increase in C source utilization indicated changes in community level physiological profiles (CLPP) in the rhizosphere of this species when grown in contaminated soils. HCH dissipation was also greater in soils planted with this species. In accordance, increases in soil extractable C, Cl concentration and acidity were greater at the rhizosphere of Cytisus. Concentration of Cl in soil solutions also indicates greater HCH dechlorination in soils planted with Cytisus than Holcus. Results suggest that phytostimulation of bacteria present or added to soil is a promising approach to cleaning HCH-contaminated sites, and especially for biodegradation of α-HCH.     

Effect of field limestone applications on cadmium content of sunflower (Helianthus annuus L.) leaves and kernels

Nonoilseed sunflower (Helianthus annuus L.) is naturally higher in cadmium (Cd) than many other grain crops. Because raising soil pH usually depresses Cd uptake by most species, a study was designed to determine if application of agricultural limestone to neutralize soil acidity would decrease Cd uptake by sunflower plants grown on different soils in the production area of North Dakota. The field experiments were conducted at 3 locations in 1991 and 2 locations in 1992. At each site, limestone was applied to bring soil pH to 6.5–7.0, or an additional 45 Mg ha^-1 more limestone was applied, and these two treatments were compared to no-lime control. Commercial nonoilseed hybrid 954 was planted in these experiments. The rapid short-term lime-soil reaction occurred in first 12 weeks following limestone application. Mean kernel Cd concentration for each treatment varied from 0.35 to 1.45 mg kg^-1 DW in the first year of the experiments, and from 0.37 to 1.23 mg kg^-1 DW in the experiments of 1992 across all locations. Large variations in kernel Cd levels between locations were obtained. There were no significant differences among control and limestone treatments for kernel Cd, seedling leaf Cd and diagnostic leaf Cd within each location, respectively. In regression analysis, we found that kernel Cd level correlated with diagnostic leaf Cd concentration in each treatment, but poor correlations were obtained among other variables. These results indicated that limestone application did not reduce Cd uptake and transfer to kernels of sunflower, in contrast with most species studied.     

Mycoremediation of PAH-contaminated soil

Out of a number of white-rot fungal cultures, strains ofIrpex lacteus andPleurotus ostreatus were selected for degradation of 7 three- and four-ring unsubstituted aromatic hydrocarbons (PAH) in two contaminated industrial soils. Respective data for removal of PAH in the two industrial soils byI. lacteus were: fluorene (41 and 67%), phenanthrene (20 and 56%), anthracene (29 and 49%), fluoranthene (29 and 57%), pyrene (24 and 42%), chrysene (16 and 32%) and benzo[a]anthracene (13 and 20%). In the same two industrial soilsP. ostreatus degraded the PAH with respective removal figures of fluorene (26 and 35%), phenanthrene (0 and 20%), anthracene (19 and 53%), fluoranthene (29 and 31%), pyrene (22 and 42%), chrysene (0 and 42%) and benzo[a]anthracene (0 and 13%). The degradation of PAH was determined against concentration of PAH in non-treated contaminated soils after 14 weeks of incubation. The fungal degradation of PAH in soil was studied simultaneously with ecotoxicity evaluation of fungal treated and non-treated contaminated soils. Compared to non-treated contaminated soil, fungus-treated soil samples indicated decrease in inhibition of bioluminescence in luminescent bacteria (Vibrio fischerii) and increase in germinated mustard (Brassica alba) seeds. An erratum to this article is available at .     

4种植物对133Cs和88Sr污染土壤的修复研究

以露地盆栽的苏丹草、向日葵、芥菜、萝卜4种植物为对象,研究它们对土壤中不同浓度(0、2.5、5.0、10.0、20.0、40.0mg/kg)133Cs、88Sr的吸收积累状况,并比较它们对133Cs、88Sr污染土壤的修复效率。结果显示:(1)4种植物单株生物量在各浓度处理下均表现为向日葵>萝卜>芥菜>苏丹草,但它们对133Cs的吸收能力为萝卜>苏丹草>向日葵>芥菜,单株133Cs累积量为向日葵>萝卜>苏丹草>芥菜,单株88Sr累积量表现为萝卜、向日葵>苏丹草>芥菜,而且4种植物对88Sr的吸收能力均强于133Cs。(2)萝卜在除10.0mg/kg133Cs外的各处理中富集系数均大于1,对土壤中133Cs的吸收能力较强;苏丹草在除5.0mg/kg133Cs处理外的转运系数均大于1,其余3种植物在各处理中的转运系数均低于1;88Sr在萝卜体内从根系向上转运到地上部分的能力明显高于其它3种植物,芥菜、向日葵次之。(3)4种植物对88Sr在体内向上的迁移转运能力均大于133Cs。研究表明,向日葵单株对133Cs、88Sr污染土壤的修复效率最高,萝卜次之,且向日葵和萝卜分别因其生物量和吸收能力优势而对被污染土壤中的133Cs和88Sr具有更强的提取能力。     

Optimization of soil physical and chemical conditions for the bioremediation of creosote-contaminated soil

Mispah type soil (FAO : Lithosol) contaminated with >250 000 mg kg^-1 creosote was collected from the yard of a creosote treatment plant. The soils carbon, nitrogen and phosphorus contents were determined. Due to creosote contamination, thecarbon content of the soil was found to be 130,000 mg C kg^-1. This concentration was found to greatly affect the nitrogen content (0.08%). The phosphorus content was less affected (4.5%). It was estimated that a nutrient amendment to bring the soil to a C : N 10 : 1 would be adequate to stimulate microbial growth and creosote degradation. The soil was amended with a range of C : N ratios below and above the estimated ratio. In one of the treatments, the phosphorus content was amended. Sterile and natural controls were also set up. The soil was incubated at 30 °C on a rotaryshaker at 150 rpm in the dark for six weeks. Water content was maintained at 70% field capacity. The lowest nitrogen supplementation (C : N = 25 : 1) was more effective in enhancing microbial growth (3.12E + 05) and creosote removal (68.7%) from the soil. Additional phosphorus was not very effective in enhancing the growth of microorganisms and removal of creosote. The highest nitrogen supplementation(C : N = 5 : 1) did not enhance microbial growth and creosote removal.A relationship between mass loss and creosote removal was also observed. Phenolics and lower molecular mass polycyclic aromatic hydrocarbons (PAHs) were observed to be more susceptible to microbial degradation than higher molecular mass compounds. Nutrient concentration, moisture content and pH were thus observed to play very significant roles in the utilization of creosote in soil. These results are being used for the development of a bioremediation technology for the remediation of creosote contaminated soils in a treatment plant in South Africa.