Heavy metal contamination affects the core microbiome and assembly processes in metal mine soils across Eastern China.

Mining activities in metal mine areas cause serious environmental pollution, thereby imposing stresses to soil ecosystems. Investigating the ecological pattern underlying contaminated soil microbial diversity is essential to understand ecosystem responses to environment changes. Here we collected 624 soil samples from 49 representative metal mines across eastern China and analyzed their soil microbial diversity and biogeographic patterns by using 16 S rRNA gene amplicons. The results showed that deterministic factors dominated in regulating the microbial community in non-contaminated and contaminated soils. Soil pH played a key role in climatic influences on the heavy metal-contaminated soil microbial community. A core microbiome consisting of 25 taxa, which could be employed for the restoration of contaminated soils, was identified. Unlike the non-contaminated soil, stochastic processes were important in shaping the heavy metal-contaminated soil microbial community. The largest source of variations in the soil microbial community was land use type. This result suggests that varied specific ecological remediation strategy ought to be developed for differed land use types. These findings will enhance our understanding of the microbial responses to anthropogenically induced environmental changes and will further help to improve the practices of soil heavy metal contamination remediation.

Insight into adsorption process and mechanisms of Cr(III) using carboxymethyl cellulose-g-poly(acrylic acid-co-acrylamide)/attapulgite composite hydrogel.

Cr(III) as one of the most concerned potentially toxic elements, is discharged from relevant industries and Cr(VI) reduction. Hydrogel-based adsorption could be one of the promising approaches for Cr(III) removal. Featured with environmental friendliness and low cost, carboxymethyl cellulose (CMC) was employed for the hydrogel synthesis, and attapulgite (APT) could be used to strengthen its stability. However, the adsorption performance and mechanisms need to be examined. In the present study, carboxymethyl cellulose-g-poly(acrylic acid-co-acrylamide)/ attapulgite (CMC-g-p(AA-co-AM)/APT) was synthesised via in situ copolymerisation. Its efficacy for removing Cr(III) from an aqueous solution was investigated using batch adsorption experiments. Results showed that the introduction of APT enhanced the thermal stability but decreased the swelling performance of the hydrogel. The prepared hydrogel could strongly adsorb Cr(III) at a wide pH range of 3.0-7.0. Cr(III) can be efficiently removed by the composite hydrogel within 1-2 h. At low concentration, CMC-g-p(AA-co-AM)/APT could slightly adsorbed more Cr(III) than CMC-g-p(AA-co-AM). The maximum absorption of CMC-g-p(AA-co-AM) and CMC-g-p(AA-co-AM)/APT were 74.8 and 47.7 mg/g at 298 K, respectively. The negative value of ΔHo and ΔGo indicated the adsorption of Cr(III) onto the two studied hydrogels is an exothermic and spontaneous process. Ion exchange and complexation, as implied by EDS, FT-IR and XPS, combining with electrostatic attraction are the possible adsorption mechanisms for Cr(III) onto the prepared hydrogels. All the results above suggests that the composite hydrogel CMC-g-p(AA-co-AM)/APT can be a promising candidate for the removal of Cr(III) from waste water.

Untangling microbial diversity and assembly patterns in rare earth element mine drainage in South China.

Ion-adsorption rare earth element (REE) deposits are the main reservoirs of REEs worldwide, and are widely exploited in South China. Microbial diversity is essential for maintaining the performance and function of mining ecosystems. Investigating the ecological patterns underlying the REE mine microbiome is essential to understand ecosystem responses to environmental changes and to improve the bioremediation of mining areas. We applied 16S rRNA and ITS gene sequence analyses to investigate the composition characteristics of prokaryotic (bacteria, archaea) and fungal communities in a river impacted by REE acid mine drainage (REE-AMD). The river formed a unique micro-ecosystem, including the main prokaryotic taxa of Proteobacteria, Acidobacteria, Crenarchaeota, and Euryarchaeota, as well as the main fungal taxa of Ascomycota, Basidiomycota, and Chytridiomycota. Analysis of microbial diversity showed that, unlike prokaryotic communities that responded drastically to pollution disturbances, fungal communities were less affected by REE-AMD, but fluctuated significantly in different seasons. Ecological network analysis revealed that fungal communities have lower connectivity and centrality, and higher modularity than prokaryotic networks, indicating that fungal communities have more stable network structures. The introduction of REE-AMD mainly reduced the complexity of the community network and the number of keystone species, while the proportion of negative prokaryotic-fungal associations in the network increased. Ecological process analysis revealed that, compared to the importance of environmental selection for prokaryotes, stochastic processes might have contributed primarily to fungal communities in REE mining areas. These findings confirm that the different assembly mechanisms of prokaryotic and fungal communities are key to the differences in their responses to environmental perturbations. The findings also provide the first insights into microbiota assembly patterns in REE-AMD and important ecological knowledge for the formation and development of microbial communities in REE mining areas.

Anoxic oxidation of As(III) during Fe(II)-induced goethite recrystallization: Evidence and importance of Fe(IV) intermediate.

Under anoxic conditions, aqueous Fe(II) (Fe(II)aq)-induced recrystallization of iron (oxyhydr)oxides changes the speciation and geochemical cycle of trace elements in environments. Oxidation of trace element, i.e., As(III), driven by Fe(II)aq-iron (oxyhydr)oxides interactions under anoxic condition was observed previously, but the oxidative species and involved mechanisms are remained unknown. In the present study, we explored the formed oxidative intermediates during Fe(II)aq-induced recrystallization of goethite under anoxic conditions. The methyl phenyl sulfoxide-based probe experiment suggested the featured oxidation by Fe(IV) species in Fe(II)aq-goethite system. Both the Mössbauer spectra and X-ray absorption near edge structure spectroscopic evidenced the generation and quenching of Fe(IV) intermediate. It was proved that the interfacial electron exchange between Fe(II)aq and Fe(III) of goethite initiated the generation of Fe(IV). After transferring electrons to goethite, Fe(II)aq was transformed to labile Fe(III), which was then transformed to Fe(IV) via a proton-coupled electron transfer process. This highly reactive transient Fe(IV) could quickly react with reductive species, i.e. Fe(II) or As(III). Considering the ubiquitous occurrence of Fe(II)-iron (oxyhydr)oxides reactions under anoxic conditions, our findings are expected to provide new insight into the anoxic oxidative transformation processes of matters in non-surface environments on earth.

Indicator species drive the key ecological functions of microbiota in a river impacted by acid mine drainage generated by rare earth elements mining in South China.

Acid mine drainage (AMD) generated by rare earth elements (REEs) deposits exploration contains high concentrations of REEs, ammonium and sulfates, which is quite different from typical metallic AMD. Currently, microbial responses and ecological functions in REEs-AMD impacted rivers are unknown. Here, 16S rRNA analysis and genome-resolved metagenomics were performed on microbial community collected from a REEs-AMD contaminated river. The results showed that REEs-AMD significantly changed river microbial diversity and shaped unique indicator species (e.g. Thaumarchaeota, Methylophilales, Rhodospirillales and Burkholderiales). The main environmental factors regulating community were pH, ammonium and REEs, among which high concentration of REEs increased REEs-dependent enzyme-encoding genes (XoxF and ExaF/PedH). Additionally, we reconstructed 566 metagenome-assembled genomes covering 70.4% of identifying indicators. Genome-centric analysis revealed that the abundant archaea Thaumarchaeota and Xanthomonadaceae were often involved in nitrification and denitrification, while family Burkholderiaceae were capable of sulfide oxidation coupled with dissimilatory nitrate reduction to ammonium. These indicators play crucial roles in nitrogen and sulfur cycling as well as REEs immobilization in REEs-AMD contaminated rivers. This study confirmed the potential dual effect of REEs on microbial community at the functional gene level. Our investigation on the ecological roles of indicators further provided new insights for the development of REEs-AMD bioremediation.

The pH-sensitive sorption governed reduction of Cr(VI) by sludge derived biochar and the accelerating effect of organic acids.

Reduction coupling immobilization is one of the most commonly adopted strategies for the remediation of Cr(VI) contamination. Biochar is a carbon-rich material with abundant active functional groups for sorption and reduction reactions. In previous reports, phytomass derived biochars and organic functional groups have been emphasized, while the performance of sludge derived biochar (SBC) has often been understated. In the present study, a 30 d kinetic study proved that the removal route involved the sorption of Cr(VI), reduction to Cr(III) and immobilization of Cr(III), and that the sorption process was the primary and rate determining step. As a result of the SBC alkalinity, the solution pH increased, and sorption was largely inhibited, which then governed the overall removal ratio. The FTIR spectra suggested the involvement of hydroxyls in these processes. Low molecular weight organic acids accelerated the removal process in the early phase and improved the reduction process.

Roles of soluble minerals in Cd sorption onto rice straw biochar.

Transforming to biochar provides an environmentally friendly approach for crop residue reutilization, which are usually applied as sorbent for heavy metal removal. As typical silicon-rich material, the specific sorptive mechanisms of rice straw derived biochar (RSBC) are concerned, especially at the low concentration range which is more environmentally relevant. In the present study, Cd sorption onto RSBCs at the concentration of ≤ 5 mg/L was investigated. The sorptive capacity was positively correlated with the pyrolytic temperature of the biochar and the environmental pH value. Water soluble minerals of the RSBCs played the dominant roles in Cd sorption, contributing 29.2%, 62.5% and 82.9% of the total sorption for RSBCs derived under 300°C, 500°C and 700°C, respectively. Increased number of cations, dominantly K+, were exchanged during the sorption. Coprecipitation with cations and carbonates may also be contributive to the sorption. The dissolution of silicon-containing minerals was found to be declined during sorption, suggesting its involvement in the sorption process, possibly through precipitation. Whilst, the sparingly soluble silicate crystals may impose ignorable role in the sorption. Complexation with organic groups is only a minor mechanism in Cd sorption, compared to the much more dominant roles of the inorganic ashes.

Genome- and community-level interaction insights into the ecological role of archaea in rare earth element mine drainage in South China.

Microbial communities play crucial roles in mine drainage generation and remediation. Despite the wide distribution of archaea in the mine ecosystem, their diversity and ecological roles remain less understood than bacteria. Here, we retrieved 56 archaeal metagenome-assembled genomes from a river impacted by rare earth element (REE) mining activities in South China. Genomic analysis showed that archaea represented four distinct lineages, including phyla of Thaumarchaeota, Micrarchaeota, Nanoarchaeota and Thermoplasmata. These archaea represented a considerable fraction (up to 40%) of the total prokaryote community, which might contribute to nitrogen and sulfur cycling in the REE mine drainage. Reconstructed metabolic potential among diverse archaea taxa revealed that archaea were involved in the network of ammonia oxidation, denitrification, sulfate redox reaction, and required substrates supplied by other community members. As the dominant driver of ammonia oxidation, Thaumarchaeota might provide substrates to support the survival of two nano-sized archaea belonging to Micrarchaeota and Nanoarchaeota. Despite the absence of biosynthesis pathways for amino acids and nucleotides, the potential capacity for nitrite reduction (nirD) was observed in Micrarchaeota, indicating that these nano-sized archaea encompassed diverse metabolisms. Moreover, Thermoplasmata, as keystone taxa in community, might be the main genetic donor for the other three archaeal phyla, transferring many environmental resistance related genes (e.g., V/A-type ATPase and Vitamin B12-transporting ATPase). The genetic interactions within archaeal community through horizontal gene transfer might be the key to the formation of archaeal resistance and functional partitioning. This study provides putative metabolic and genetic insights into the diverse archaea taxa from community-level perspectives, and highlights the ecological roles of archaea in REE contaminated aquatic environment.

Factors influencing heavy metal availability and risk assessment of soils at typical metal mines in Eastern China.

China exemplifies the serious and widespread soil heavy metal pollution generated by mining activities. A total of 420 soil samples from 58 metal mines was collected across Eastern China. Total and available heavy metal concentrations, soil physico-chemical properties and geological indices were determined and collected. Risk assessments were applied, and a successive multivariate statistical analysis was carried out to provide insights into the heavy metal contamination characteristics and environmental drivers of heavy metal availability. The results suggested that although the degrees of pollution varied between different mine types, in general they had similar contamination characteristics in different regions. The major pollutants for total concentrations were found to be Cd and As in south and northeast China. The availability of Zn and Cd is relatively higher in south China. Soil physico-chemical properties had major effect on metal availability where soil pH was the most important factor. On a continental scale, soil pH and EC were influenced by the local climate patterns which could further impact on heavy metal availability. Enlightened by this study, future remediation strategies should be focused on steadily increasing soil pH, and building adaptable and sustainable ecological system to maintain low metal availabilities in mine site soils.

Feasibility of sewage sludge derived hydrochars for agricultural application: Nutrients (N, P, K) and potentially toxic elements (Zn, Cu, Pb, Ni, Cd).

Hydrochars derived from municipal sewage sludge was analyzed for its feasibility for value-added recycling. Results of carbon content and elemental composition suggested that the hydrochars might not be comparable with pyrochars regarding to the carbon sequestration, long-term stability and fuel quality. Application as soil amendment would be a better approach for hydrochar utilization. To examine the potential benefits and risks of that, the total and available content of nutrients (i.e. N, P, and K) were measured, and the potentially toxic elements (PTEs, i.e. Zn, Cu, Pb, Ni and Cd) were analyzed for the total content, speciation, and leaching potential. Compared with pyrochars derived from the same feedstock, hydrochars had lower pH and higher cation exchange capacity. The available content of N (1.58-6.87 g/kg), P (0.270-0.901 g/kg), and K (0-0.873 g/kg) in the chars was less than the feedstock sludge (3.33 g/kg N, 3.02 g/kg P, 2.07 g/kg K), but still far higher than that of the agricultural soil (i.e. 0.014-0.488 g/kg N, 0.02 g/kg P, <0.1-0.272 g/kg). Remarkably, hydrochars showed better nutritional balance than pyrochars for its higher available K content. Risk of potentially toxic elements contamination by the sludge was efficiently reduced in either hydrochars or pyrochars, except the high leaching potential of Zn in pyrochars. Overall, in addition to the advantages of the hydrothermal carbonization process as energy saving and value-added liquid by-products, the hydrochars derived from sludge, with sufficient and balanced nutrients and limited PTEs pollution risk, can be a feasible and value-added material as soil amendment.

Phosphorous Retention and Release by Sludge-Derived Hydrochar for Potential Use as a Soil Amendment.

To solve both the problems of P deficiency in arable soil and excessive waste sludge disposal, we evaluated hydrothermal carbonization of sludge with the aim of recycling sludge P resources for soil amendment. In contrast with pyrochars obtained through pyrolysis, hydrochars generated from hydrothermal carbonization often feature variable properties and therefore require detailed characterization. In this study, sludge-derived hydrochars were evaluated to determine their P content and fractionation, release and availability of P, and P adsorption and desorption behavior. We also assessed changes in P availability after soil was amended with the hydrochars. Our results showed that the chars were rich in total P (up to 25,175 mg kg), but most of the free fractions were transformed to bound fractions, thereby reducing the available P concentrations. However, available P content was >417 mg kg, which was far higher than soil demand. The hydrochars shifted from releasing to adsorbing P adsorbent when the environmental P concentration increased above 20 mg L. The hydrochars showed a high phosphate adsorption capacity (up to 23,815 mg kg) and the adsorbed P could be readily released. The addition of 1% P-laden hydrochar significantly enhanced the soil available P content by 8.93 mg kg. These findings have important implications for further development of hydrochar-based P carriers as a slow-releasing fertilizer.

Biochar Addition Enhances Phenanthrene Fixation in Sediment.

Biochar is believed to be promising for soil contaminant stabilization due to its large adsorption capacity. However, study in sediment is rare, especially with the aging effect. In the present study, a plant biomass-derived biochar was added to phenanthrene polluted sediment, in order to investigate its performance in sediment remediation. During the incubation period of 60 days, it was observed that the partition coefficient of phenanthrene increased in sediment either with or without biochar addition, as a result of aging process. Whilst, the biochar-added sediments showed much higher partition coefficients, as well as more curved adsorption isotherms, suggesting larger retention of the contaminant. Under the extreme extraction by strong surfactant, the release ratio of phenanthrene from polluted sediment was significantly reduced from 60% to 5% by 0.5% (w/w) addition of biochar. These results suggested that biochar would be applicable for improving the adsorption of organic pollutant in sediment, and the adsorbed organic pollutant would be stably fixed during aging as a result of the increased affinity.

Cadmium accumulation in edible flowering cabbages in the Pearl River Delta, China: Critical soil factors and enrichment models.

Although many previous studies have reported the soil pH and organic matter to be the most critical factors that affect the transfer of Cd in soil-crop systems in temperate zones, the behavior of Cd transfer is different in the Pearl River Delta (PRD), which is located in a subtropical zone with different climate and soil conditions. Therefore, we must determine the critical environmental factors that influence the transfer of Cd in the soil-vegetable system in the PRD region. Such knowledge can improve the safety of vegetables. In this study, the soil geochemical properties are investigated to explore the key soil factors that control the uptake of Cd by flowering cabbage, a popular leaf vegetable in China, from soils in the PRD region. The Cd contents in vegetables were most positively correlated to soil oxalate-Cd (p < 0.01), which indicates that amorphous Cd is the most available form for uptake into the cabbages. With the characteristics of rich in Fe oxide and Al oxide in the PRD soils, soil Fe and Al oxides were found to be the most relevant to the transfer factors of Cd from the soils to the cabbages. Soil secondary minerals are the key factor that affects the transfer of Cd, thereby influencing the migration and fate of Cd in soil-cabbage systems, with DCB-Fe significantly decreasing the Cd accumulation in cabbages. Additionally, models were developed to predict the enrichment of Cd in flowering cabbages, in which oxalate-Cd, DCB-Fe, and NaOAc-Al in soils were determined to be the most important factors that affect the Cd enrichment in flowering cabbages. In this study, we determine the important role of soil secondary minerals in affecting the transfer of Cd in soil-cabbage systems in the PRD. These observations are important to evaluate the accumulation of Cd in vegetables in subtropical zones.

Adsorption of 17 α-ethyl estradiol with the competition of bisphenol A on the marine sediment of Hong Kong.

The present experimental study was to characterize the adsorption behavior of 17 α-ethyl estradiol (EE2) onto marine sediment in both the single and binary solute systems. Stepwise spiking was innovatively performed to better understand the competition effects. Adsorption of EE2 on the marine sediment can be well fitted by the Freundlich model with an affinity coefficient (KF) varying from 15.8 to 39.8L/kg. It was significantly influenced by SOM and the particle properties. Co-presence of BPA brought about a significant competition effect on the adsorption of EE2, leading to a reduced EE2 adsorption. The competitive effect imposed by EE2 to BPA, however, was even more serious owing probably to the large molecular structure and high hydrophobicity of EE2. The sediment sample with the highest SOM and SSA presented a mild competition effect, while the sediment with the lowest SOM and largest particle size exhibited the most serious competition effect.

Changes in the adsorption of bisphenol A, 17 α-ethinyl estradiol, and phenanthrene on marine sediment in Hong Kong in relation to the simulated sediment organic matter decomposition.

Marine sediment with an input of particulate organic matter was incubated to simulate the early aging process. On the sediment after various incubation periods, adsorption and desorption tests were conducted for three selected organic micropollutants: bisphenol A (BPA), 17α-ethinyl estradiol (EE2), and phenanthrene (Phe). The results showed significant sediment organic matter (SOM) decomposition during the incubation, and the SOM decay and transformation had a profound impact on the adsorption of organic compounds by the sediment. An increasing-delay-increasing pattern of change was observed for the SOM normalized partition coefficients of EE2 and Phe. This change was accordant to the transformation of SOM from labile organics into active biomass and its microbial products, and finally into more condensed and humic-like substances. Comparison between the 3 model micropollutants indicates that the chemical adsorption behaviors were mostly affected by their hydrophobic properties.

Adsorption and desorption behaviors of selected endocrine disrupting chemicals in simulated gastrointestinal fluids.

An in vitro technique using simulated gastrointestinal (GI) fluids was applied to investigate the desorption of selected endocrine disrupting chemicals (EDCs), i.e. bisphenol A (BPA) and 17 α-ethinylestradiol (EE2), from the marine sediment in the digestive environment. The results show that the GI fluids suppressed chemical adsorption and greatly increased the desorption of BPA and EE2 from the sediment. Pepsin in the gastric fluid would compete for the adsorption sites with the adsorbates, and bile salts in the intestinal fluid had a solubilization effect on the chemicals. The amount of chemical release from the sediment in different fluids followed intestinal (fed)>intestinal (fasted)>gastric>saline water. During the dynamic desorption tests, 62% and 21% of sediment-bound BPA and EE2, respectively, could be released into the simulated GI fluids. The enhanced desorption of EDCs from sediment in the digestive system would make the pollutants more bioavailable in the ecosystem.

Adsorption of tetracyclines on marine sediment during organic matter diagenesis.

The effect of decomposition and diagenesis of sediment organic matter (SOM) on the adsorption of emerging pollutants by the sediment has been seldom addressed. In the present experimental study, artificial sediment was incubated to simulate the natural organic diagenesis process and hence investigate the influence of organic diagenesis on the adsorption of tetracyclines (TCs) by marine sediment. During a period of 4 months of incubation, SOM initially added into the sediment underwent biodegradation and diagenesis. The results showed an early decrease in TC adsorption by the sediment, which was likely caused by the competition between the microbial organic products and TC molecules for the adsorption sites. Afterward, TC adsorption by the sediment increased significantly, which was mainly due to the accumulation of condensed SOM. The experimental results indicate the interactions between TCs and the sediment during the dynamic process of SOM diagenesis. Moreover, the remaining SOM is shown to have an increasing affinity with the antibiotics.

Organic diagenesis in sediment and its impact on the adsorption of bisphenol A and nonylphenol onto marine sediment.

Hydrophobic organic contaminants in marine water are mostly adsorbed onto (partitioned into) sediment organic matter (SOM). To study the impact of SOM diagenesis on sediment adsorption properties, artificial sediment with rich SOM content was incubated for more than 120 days. The sediment was sampled every week, and batch sediment adsorption tests were conducted with bisphenol A (BPA) and nonylphenol (NP) as the model pollutants. The results show that the amount of organic matter loaded in the sediment decreased by nearly 80% during incubation. For the incubated sediment, the BPA partition coefficient, Kd, decreased whereas the organic normalized partition coefficient, Koc, more than doubled. The experiments with NP show an even greater increase in Koc. Organic matter diagenesis shows a profound effect on the adsorption behavior of sediment, as the SOM residue has an increasing affinity and partition capacity for organic contaminants.

Soluble protein and acid phosphatase exuded by ectomycorrhizal fungi and seedlings in response to excessive Cu and Cd.

Fungi and their symbionts can alleviate heavy metal stress by exuding soluble proteins and enzymes. This study examined the role of soluble protein and acid phosphatase (APase) exuded by Xerocomus chrysenteron, an ectomycorrhizal fungus, and the seedlings of its symbiont, Chinese pine (Pinus tabulaeformis), under conditions of excessive Cu and Cd. The growth type showed that this poorly studied ectomycorrhizal fungus was capable of tolerating high concentrations of Cu, and may be useful in phytoremediation. X. chrysenteron grew well at 80 mg/L Cu, and the EC50 for Cd was 17.82 mg/L. X. chrysenteron also showed enhanced exudation of soluble protein in both isolated and inoculated cultivations under the influence of Cu and Cd. Soluble protein exudation, however, differed under Cu and Cd stress in isolates. In mediums containing Cu, soluble protein exudation increased with concentration, but in mediums containing Cd the content of soluble protein increased to a comparable level at all concentrations. This study demonstrated that soluble protein was related to heavy metal tolerance, although the different ions played different roles. While APase activity in exudates of fungi and seedlings decreased under Cu and Cd stress in comparison to the control, the APase activity in seedlings was maintained by inoculation. Thus, X. chrysenteron facilitated the ability of plant to maintain a normal nutrient uptake, and therefore to protect it from heavy metal toxicity.

[Tolerance and enzyme response of ectomycorrhizal fungi Xerocomus chrysenteron to DDT stress].

The growth effect, tolerance and oxidative enzymes activities of Xerocomus chrysenteron under different concentrations of DDT were studied at the condition of pure culture. The changes of biomass accumulation and laccase activity were also examined along with the liquid medium period under the DDT concentration of 80.0 mg L(-1). The results show that various DDT concentrations don't change the growth mode of the studied ectomycorrhizal fungi, which are all in the mode of classic Logistic growth. Xerocomus chrysenteron has a good tolerant ability to the DDT stress, whose hemi-inhibit concentration reaches 139.75 mg L(-1). Under the liquid medium of 80.0 mg L(-1) of DDT, Xerocomus chrysenteron grows normally and after 36 days and the residue of DDT in the liquid medium is only 3.5% of the original concentration. Under the high concentration of DDT, the laccase and peroxidase activities significantly increase. The laccase is detected since the 16th day. After 36 days' culture, the laccase activity and specific activity in liquid medium reach 107.24 U L(-1) and 61.77 U g(-1) respectively. The ectomycorrhizal fungi Xerocomus chrysenteron responses to the DDT stress in various ways, which suggests large potential of biodegradation or mineralization of DDT.