Release of Chemicals from Contaminated Soils

At sites that contain contaminated soils, there can be questions about the magnitude of risk posed by the chemicals in the soils and about the cleanup levels that should be achieved. Knowledge about the rate of release of chemicals is important to answers to such questions. This article: (1) describes a laboratory protocol to obtain rate of release information for chemicals in soils, and (2) provides estimates of the rate of release of individual polyaromatic hydrocarbon (PAH) compounds from several manufactured gas plant (MGP) site soils. The data were analyzed using an empirical two-site model. Different fractions of PAH were released rapidly from these soils. For one soil, this fraction was less than 20%, for others, the fraction ranged from 36 to 85%. The first-order rate constant (k2) of PAH released during the slow phase of chemical release ranged from 0.0001 to 0.01 per hour.     

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) by native microflora and combinations of white-rot fungi in a coal-tar contaminated soil

Four white-rot fungi (Phanerochaete chrysosporium IMI 232175, Pleurotus ostreatus from the University of Alberta Microfungus Collection IMI 341687, Coriolus versicolor IMI 210866 and Wye isolate #7) and all possible combinations of two or more of these fungi, were incubated in microcosms containing wheat straw and non-sterile coal-tar contaminated soil to determine their potential to degrade polycyclic aromatic hydrocarbons (PAHs). Biotic and abiotic controls were prepared similarly and PAH concentrations remaining in each microcosm were determined after 8, 16 and 32 weeks by GC-MS following extraction with dichloromethane. The greatest PAH losses were in the biotic control, compared to small or negligible differences in microcosms inoculated with one or more fungi. These results suggest that in the biotic control native microorganisms colonised the straw added as organic substrate and degraded PAH as an indirect consequence of their metabolism. By contrast, in other microcosms, colonisation of straw by the natural microflora was inhibited because the straw was previously inoculated with fungi. Soil cultures prepared at the end of the experiment showed that though introduced fungi were still alive, they were unable to thrive and degrade PAH in such a highly contaminated soil and remained in a metabolically inactive form.     

Degradation of polycyclic aromatic hydrocarbons with three to seven aromatic rings by higher fungi in sterile and unsterile soils

Seven commercial 3- to 7-ring (R) polycyclic aromatic hydrocarbons (PAH) as well as PAH derived from lignite tar were spiked into 3 soils (0.8 to 9.7% of organic carbon). The disappearance of the original PAH was determined for the freshly spiked soils, for soils incubated for up to 287 d with their indigenous microflora, and for autoclaved, unsterile and pasteurized soils inoculated with basidiomycetous and ascomycetous fungi. Three to 12 d after spiking, 22 to 38% of the PAH could no longer be recovered from the soils. At 287 d, 88.5 to 92.7%, 83.4 to 87.4%, and 22.0 to 42.1% of the 3-, 4-, and 5- to 7-R PAH, respectively, had disappeared from the unsterile, uninoculated soils. In 2 organic-rich sterile soils, the groups of wood- and straw-degrading, terricolous, and ectomycorrhizal fungi reduced the concentration of 5 PAH by 12.6, 37.9, and 9.4% in 287 d. Five- to 7-R PAH were degraded as efficiently as most of the 3- to 4-R PAH. In organic-rich unsterile soils inoculated with wood- and straw-degrading fungi, the degradation of 3- to 4-R PAH was not accelerated by the presence of fungi.The 5- to 7-R PAH, which were not attacked by bacteria, were degraded by fungi to 29 to 42% in optimum combinations of fungal species and soil type. In organic-poor unsterile soil, these same fungi delayed the net degradation of PAH possibly for 2 reasons. Mycelia of Pleurotus killed most of the indigenous soil bacteria expected to take part in the degradation of PAH, whereas those of Hypholoma and Stropharia promoted the development of opportunistic bacteria in the soil, which must not necessarily be PAH degraders. Contemporarily, the contribution of the fungi themselves to PAH degradation may be negligible in the absence of soil organic matter due to the lower production of ligninolytic enzymes. It is concluded that fungi degrade PAH irrespective of their molecular size in organic-rich and wood chip-amended soils which promote fungal oxidative enzyme production.     

Bioremediation of oil-polluted soil with an association including the fungus Pleurotus ostreatus and soil microflora

The possibility of application of the Pleurotus ostreatus D1-soil microflora to bioremediation of oil-polluted soils was studied. The fungus degraded mainly the aromatic fraction, whereas soil microflora intensely degraded paraffin and naphthene oil fractions. Introduction of the fungus Pleurotus ostreatus D to soil induces degradation of a wider range of oil hydrocarbons. It is reasonable to further investigate the discovered phenomenon in order to improve procedures of remediation of oil-polluted soils.     

Chemical characterization of humic substances extracted from organic-waste-amended soils

Humic substances were extracted from a soil treated, in a 4-year experiment, at different rates with a sludge from anaerobic treatment of combined civil and industrial wastes, and with agricultural manure. Elemental and chemical analyses, molecular weight (MW) distribution and infrared (IR) spectroscopy were performed on the purified humic acids (HA). Organic wastes significantly increased the HA content of the treated soils and improved CEC. The C/N, C/H and C/O ratios of HA extracted from the original wastes showed a higher degree of humification for sludge than for manure. This difference was also noticed for the C/N ratio of soil humic extracts, indicating a faster humification process for the sludges in soil. The content of oxygen-containing functional groups was lower than the ‘model’ HA reported in the literature, and even more so for HA from sludges, reflecting their anaerobic formation. MW distribution and E₄/E₆ ratios showed that the sludge material had a higher molecular complexity than manure, supporting the high degree of humification attributed to the former. HA extracted from sludge-treated soils revealed a molecular dimension increasing with the application doses of waste material. Infrared spectra showed that HA formed in soils after waste additions reflected the chemical composition of the original organic material, which was rich in aliphatic groups and peptides for sludge and in carbohydrates for manure. On the basis of this study, it is concluded that not only are organic waste additions able to build up the HA content in soils but the HA formed assume the chemical characteristics and the degree of humification of the original material.     

Pseudomonas, the dominant polycyclic aromatic hydrocarbon-degrading bacteria isolated from Antarctic soils and the role of large plasmids in horizontal gene transfer

Twenty-two polycyclic aromatic hydrocarbon (PAH)-degrading bacterial strains were isolated from Antarctic soils with naphthalene or phenanthrene as a sole carbon source, while no degrader was obtained from an unpolluted sampling site. Phylogenetic analysis showed that all belonged to the genus Pseudomonas except one that was identified as the genus of Rahnella. Some of them were closely related to previously reported cold-tolerant species, while some were separated in deeply rooted branches and represent new strains. All these strains showed a high efficiency to degrade naphthalene at 4 degrees C, and some additionally degraded phenanthrene. Using degenerate primers and polymerase chain reaction (PCR) amplification, ndo gene encoding naphthalene dioxygenase (NDO) was detected from all the isolates. Phylogenetic analysis grouped these genes into two clusters which shared 94% similarity to each other, and showed about 97% similarity within a cluster. However, no obvious difference was observed with mesophilic ndo genes; this indicates that the host cell is pivotal in cold adaptation. In addition, the mismatch between 16S rRNA and NDO phylogenetic trees strongly indicates horizontal gene transfer among these isolates and may have happened in situ. Further, Southern hybridization and plasmid curing confirmed that ndo genes were located on a large self-transmissible plasmid, which can be transferred to a mesophilic strains. The transconjugants acquired the ability to utilize naphthalene and phenanthrene. Results of this article imply that Pseudomonas plays an important role in PAH biodegradation in Antarctic soils, and the related genes might be originally transferred from outside Antarctica and spread among indigenous species.     

Local environmental correlates of variability in the organic soils of moorland and alpine vegetation,Mt Sprent,Tasmania

Abstract Data on soils, vegetation and environment were collected between 510 and 1050m a. s. l. on Mt Sprent, southwestern Tasmania, traversing the Gymnoschoenus sphaerocephalus sedgeland-alpine vegetation boundary. One or more of the following horizons were found in almost all soil pits (downwards from the surface to the bed rock) fibric peat, hemic peat, sapric peat, organic sand, sand and clay. Mean total soil depth, mean organic soil depth, mean humification of the soil surface horizon, pH and mean organic content of the surface horizon all decline with altitude, while the redness of the soil and the mean depth of the mineral and gravel layers increase. At four intensively studied sites at 620, 850, 930 and 1040 m the relationships between phytosociological, topographic and water-table variables, and soil characteristics were determined. The pH of the topsoil was significantly positively related to water-table depth at three sites, but there were no other relationships between local environmental variation and soil characteristics that were consistent between most of the four sites, despite a large number of locally significant relationships. The alpine and sedgeland soils differ most markedly in colour, number of horizons and degree of humification of the surface horizon. The vegetation at each site was separated into communities along a drainage gradient. The mesoscale differences in soils seem most likely to be attributable to a vegetation productivity gradient.     

酶修复土壤农药污染的研究进展

1　农药生物修复的重要性和紧迫性农药是人们主动投放于环境中数量最大、毒性最广的一类化学物质 [1] ,据统计 [2 ,5] ,1 960年世界农药的销售额仅为 8.5亿美元 ,1 994年增加到 2 78亿美元 ,增长 32 .71倍。在我国 ,农药至少占农业生产费用的 3% ,每年施用量 5.0× 1 0 5～ 6.0× 1 0 5t,其中约 80 %的农药直接进入环境 ,导致现有耕地的 1 /7受到不同程度污染 ,过量施用的农田约 1 .33×1 0 6ha,可见 ,农药已成为土壤主要污染源之一。同时由于土壤中农药 [4 ]的化学性质比较稳定 ,不易分解 ,如 DDT分解 95%需 4～ 30年 ,六六六 3～ 2 0年 …     

Extracellular oxidative enzyme production and PAH removal in soil by exploratory mycelium of white rot fungi

Selected strains of three species of white rot fungi, Pleurotus ostreatus, Phanerochaete chrysosporium and Trametes versicolor, were grown in sterilized soil from straw inocula. The respective colonization rates and mycelium density values decreased in the above mentioned order. Three- and four-ringed PAHs at 50 ppm inhibited growth of fungi in soil to some extent. The activities of fungal MnP and laccase (units per g dry weight of straw or soil), extracted with 50 mM succinate-lactate buffer (pH 4.5), were 5 to 20-fold higher in straw compared to soil. The enzyme activities per g dry soil in P. ostreatus and T. versicolor were similar, in contrast to P. chrysosporium, where they were extremely low. Compared to the aerated controls, P. ostreatus strains reduced the levels of anthracene, pyrene and phenanthrene by 81–87%, 84–93% and 41–64% within 2 months, respectively. During degradation of anthracene, all P. ostreatus strains accumulated anthraquinone. PAH removal rates in P. chrysosporium and T. versicolor soil cultures were much lower.     

Levels,Sources, and Toxic Potential of Polycyclic Aromatic Hydrocarbons in Urban Soil of Delhi,India

This study was done to determine the concentration of PAHs in urban soil of Delhi (India). Surface top soil (up to 10 cm depth) samples were collected from four different sampling sites including industrial, roadside, residential, and agricultural areas of Delhi and 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) were evaluated. Total PAH concentrations at industrial, roadside, residential, and agricultural sites were 11.46 ± 8.39, 6.96 ± 4.82, 2.12 ± 1.12, and 1.55 ± 1.07 mg/kg (dry weight), respectively, with 3–7 times greater concentrations in industrial and roadside soils than that in residential and agricultural soils. The PAH pattern was dominated by 4- and 5-ring PAHs (contributing >50% to the total PAHs) at industrial and roadside sites with greater concentration of fluoranthene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]anthracene, benzo[ghi]perylene, and pyrene, whereas, residential and agricultural sites showed a predominance of low molecular weight 2- and 3-ring PAHs (fluoranthene, acenaphthene, naphthalene, chrysene, and anthracene). Isomeric pair ratios suggested biomass combustion and fossil fuel emissions as the main sources of PAHs. The toxic equivalency factors (TEFs) showed that carcinogenic potency (benzo[a]pyrene-equivalent concentration (B[a]P_eq) of PAH load in industrial and roadside soils was ～10 and ～6 times greater than the agricultural soil.     

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.     

Basic examinations on chemical pre-oxidation by ozone for enhancing bioremediation of phenanthrene contaminated soils

Biological treatment of polycyclic aromatic hydrocarbons (PAH) has been demonstrated to be a feasible and common remediation technology which has been successfully applied to the clean-up of contaminated soils. Because bioavailability of the contaminants is of great importance for a successful bioremediation, a chemical pre-oxidation step by ozone was tested to enhance the subsequent biodegradation steps. Oxidation of PAH by ozone should result in reaction products that have a better solubility in water and thus a better bioavailability. A major part of this work was done by examinations of the model substance phenanthrene as a typical compound of PAH. After initial ozonation of phenanthrene, analysis by GC-MS showed at least seven identified conversion-products of phenanthrene. In comparison with phenanthrene these conversion products were more efficiently biodegraded by Sphingomonas yanoikuyae or mixed cultures when the ozonation process resulted in monoaromatic compounds. Primary ozonation products with biphenylic structures were found not to be biodegradable. Investigations into the toxicity of contaminated and ozonated soils were carried out by well-established toxicity assays using Bacillus subtilis and garden cress. The ozonated soils surprisingly showed higher toxic or inhibitory effects towards different organisms than the phenanthrene or PAH itself. The microbial degradation of phenanthrene in slurry reactors by S. yanoikuyae was not enhanced significantly by preozonation of the contaminated soil.     

Microbial Factors Rather Than Bioavailability Limit the Rate and Extent of PAH Biodegradation in Aged Crude Oil Contaminated Model Soils

The rate and extent of polynuclear aromatic hydrocarbons (PAH) biodegradation in a set of aged model soils that had been contaminated with crude oil at the high concentrations (i.e.,>20,000?mg/kg) normally found in the environment were measured in 90-week slurry bioremediation experiments. Soil properties such as organic matter content, mineral type, particle diameter, surface area, and porosity did not significantly influence the PAH biodegradation kinetics among the 10 different model soils. A comparison of aged and freshly spiked soils indicates that aging affects the biodegradation rate and extent only for higher-molecular-weight PAHs, while the effects of aging are insignificant for 4-ring PAHs and total PAHs. In all model soils with the exception of kaolinite clay, the rate of abiotic desorption was faster than the rate of biodegradation during the initial phase of bioremediation treatment, indicating that PAH biodegradation was limited by microbial factors. Similarly, any of the higher-molecular-weight PAHs that were still present after 90 weeks of treatment were released rapidly during abiotic desorption tests, which demonstrates that bioavailability limitations were not responsible for the recalcitrance of these hydrocarbons. Indeed, an analysis of microbial counts indicates that a severe reduction in hydrocarbon degrader populations may be responsible for the observed incomplete PAH biodegradation. Therefore, it can be concluded that the recalcitrance of PAHs during bioremediation is not necessarily due to bioavailability limitations and that these residual contaminants therefore might pose a greater risk to environmental receptors than previously thought.     

Mobilizing agents enhance fungal degradation of polycyclic aromatic hydrocarbons and affect diversity of indigenous bacteria in soil

The impact of several mobilizing agents (MAs) (i.e., soybean oil, Tween-20, Tween-80, olive-oil mill wastewaters, and randomly methylated beta-cyclodextrins) on the degradation performances of the white-rot fungi Irpex lacteus and Pleurotus ostreatus was comparatively assessed in a soil spiked with a mixture of seven polycyclic aromatic hydrocarbons (PAHs). Among the different MAs, soybean oil best supported the growth of both fungi that was twice that observed in soil in the absence of MAs. In addition, soybean oil positively affected PAH degradation by both fungi. In this case, the total weight of organic contaminants (TWOC) was lower than that in the absence of MAs (57.7 vs. 201.3 and 26.3 vs. 160.4 mg kg(-1) with I. lacteus and P. ostreatus, respectively). On the other hand, the number of cultivable heterotrophic bacteria was significantly lower in the soil with soybean oil augmented with either one of the two fungi (5.21 vs. 8.71 and 0.22 vs. 0.51 x 10(7) CFU g(-1) soil with I. lacteus and P. ostreatus, respectively). The effect of soybean oil was confirmed by denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA genes that showed a general decrease in biodiversity. The impact of the other MAs on bacterial diversity was either slightly negative or positive in incubation controls. Both richness and Shannon-Weaver index decreased upon treatment with P. ostreatus. Moreover, with this fungus the composition of the indigenous bacteria was not significantly affected by the type of MA used. By contrast, both indices increased in soil with I. lacteus in the presence of randomly methylated beta-cyclodextrins (39 vs. 33 and 1.43 vs. 1.26, respectively) and soybean oil (19 vs. 5 and 1.01 vs. 0.65, respectively).     

The mitochondrial genome of the Basidiomycete fungus Pleurotus ostreatus (oyster mushroom)

In this study, the full mitochondrial genome of a basidiomycete fungus, Pleurotus ostreatus, was sequenced and analyzed. It is a circular DNA molecule of 73 242 bp and contains 44 known genes encoding 18 proteins and 26 RNA genes. The protein-coding genes include 14 common mitochondrial genes, one ribosomal small subunit protein 3 gene, one RNA polymerase gene and two DNA polymerase genes. In addition, one RNA and one DNA polymerase genes were identified in a mitochondrial plasmid. These two genes show relatively low similarities to their homologs in the mitochondrial genome but they are nearly identical to the known mitochondrial plasmid genes from another Pleurotus ostreatus strain. This suggests that the plasmid may mediate the horizontal gene transfer of the DNA and RNA polymerase genes into mitochondrial genome, and such a transfer may be an ancient event. Phylogenetic analysis based on the cox1 ORFs verified the traditional classification of Pleurotus ostreatus among fungi. However, the discordances were observed in the phylogenetic trees based on the six cox1 intronic ORFs of Pleurotus ostreatus and their homologs in other species, suggesting that these intronic ORFs are foreign DNA sequences obtained through HGT. In summary, this analysis provides valuable information towards the understanding of the evolution of fungal mtDNA.     

Development of a catabolically significant genetic probe for polycyclic aromatic hydrocarbon-degrading <Emphasis Type="Italic">Mycobacteria</Emphasis> in soil

A gene probe for the detection of polycyclic aromatic hydrocarbon (PAH) induced nidB and nidA dioxygenase genes has been designed from Mycobacteria JLS, KMS, and MCS. The probe detects a catabolic gene involved in the initial steps of PAH biodegradation in mycobacteria. The gene probe is comprised of three PCR primer sets designed to detect the genes that code for two subunits of the PAH induced dioxygenase enzyme within PAH-degrading mycobacteria. The probe was built by combining three primer sets with a DNA extraction procedure that was designed to lyse the gram-positive mycobacteria cells while in the soil matrix and remove PCR inhibitors. The probe was tested on PAH contaminated soils undergoing bioremediation through landfarming and uncontaminated soils from the same site. The PAH gene probe results demonstrate that the dioxygenase genes can be detected in soils. Sequencing the nidA and nidBPCR products verified that the genes were detected in soil. Comparisons of the sequences obtained from the soil probe to seven known nid gene sequences from various PAH-degrading mycobacteria showed between 97 and 99% nucleotide matches with the nidB gene and 95 and 99% matches with the nidA gene.     

Effects of sewage sludge amendment on the properties of two Brazilian oxisols and their humic acids

The effect of sewage sludge (SS) amendment on the general properties of the top layers of a sandy and a clayey oxisols and on the nature of their humic acid (HA) fractions was evaluated by chemical and physico-chemical techniques. The amended soils, especially the sandy soil, benefited of SS amendment by increasing their pH to above neutrality and enhancing the contents of C, N, P, and Ca and cation exchange capacity. The SS-HA-like sample showed larger H and N contents and a greater aliphatic character and humification degree than the HAs isolated from non-amended soils. The composition and structure of amended soil HAs were affected by SS application as a function of soil type and layer. In particular, N-containing groups and aliphatic structures of SS-HA-like sample appears to be partially incorporated in the amended soil HAs, and these effects were more evident in the HAs from the sandy oxisol.     

Fate of phenanthrene, pyrene and benzo[a]pyrene during biodegradation of crude oil added to two soils

The release of 14CO2 from 9-[14C]phenanthrene, 4,5,9,10-[14C]pyrene and 7-[14C]benzo[a]pyrene, added to Brent/Fortes crude oil and mixed into a pristine sand soil (0.40% organic C) and a pristine organic soil (22.9% organic C), was determined. After 244 days at 25 degrees C, 11.1 +/- 3.5% (sand) and 17.1 +/- 0.30% (organic) phenanthrene-14C and 9.77 +/- 2.8% (sand) and 5.86 +/- 1.4% (organic) benzo[a]pyrene-14C was released. After 210 days, 3.65 +/- 0.5% (sand) and 4.43 +/- 0.33% (organic) pyrene-14C was released. Inoculation of these two soils with DC1 and PD2 (bacteria capable of accelerating the phenanthrene and pyrene mineralisation in soil in the absence of crude oil) either at day 0 or after release as 14CO2 by indigenous degraders had ceased, failed to increase or initiate further mineralisation. Thus, aged PAH residues were non-bioavailable to these metabolically competent degrading microorganisms. At the end of the first period of incubation (210 days or 244 days), the total aromatic hydrocarbons recovered using Soxhlet extraction was 0.18% (sand) and 42.8% (organic) compared with approximately 100% from bio-inhibited soils. This confirmed that the indigenous microbiological activity not only caused a limited amount of PAH mineralisation but also reduced the extractability of residues, possibly due to the generation of metabolites which were chemisorbed and bound (and non extractable) in 'aged' soils.     

Organic matter transformations in soil

Summary In an investigation on the biochemical changes of added C¹⁴-tagged oat roots incubated with soils under aerobic and anaerobic conditions, biosynthesis of polysaccharides of varying composition was noted during the humification process. Possible causes of persistence of carbohydrates in soils are indicated.     

糙皮侧耳(Pleurotus ostreatus)的AFLP指纹图谱分析

在对糙皮侧耳(Pleurotus ostreatus)的AFLP分析条件进行优化的基础上,利用该技术建立了14株产自不同地区的糙皮侧耳：DNA指纹图谱,并进行了数据分析。结果表明,在合成的14条引物的不同组合中,引物对E-3／M-3可以产生较多的DNA多态片段,E-AGC／M-CAT引物对的扩增效果最好,共获得184条DNA扩增带,其中多态性条带i101条,占54．89％。利用UPGMA法对所获数据进行聚类分析,计算得到糙皮侧耳菌株之间的遗传距离,发现不同品种间遗传距离差异较大,从0．192到0．754,说明糙皮侧耳的遗传多样性比较丰富。绘制的指纹分析树状图表明,14个糙皮侧耳菌株被分为6个组群,其中P17和杂3的相似性系数最高,达到了81．2％,而侧5与其他菌株的亲缘关系相对最远。