The reductive dechlorination and biodegradation of 2,2′4,5,5′-pentachlorobiphenyl (PCB#101) was investigated in a laboratory-scale. Palladium coated iron (Pd/Fe) was used as a catalytic reductant for the chemical degradation of 2,2′4,5,5′-pentachlorobiphenyl, and an aerobic bacteria was used for biodegradation following the chemical reaction in this study. Dechlorination was affected by several factors such as Pd loading, initial soil pH and the amount of Pd/Fe used. The results showed that higher Pd loading, higher dosage of Pd/Fe and slightly acid condition were beneficial to the catalytic dechlorination of 2,2′,4,5,5′-pentachlorobiphenyl. In laboratory batch experiments, 2,2′4,5,5′-pentachlorobiphenyl was reduced in the presence of Pd/Fe bimetal, which was not further degraded by aerobic bacteria. 2,2′,4-trichlorobiphenyl (PCB#17), a reduction product from 2,2′4,5,5′-pentachlorobiphenyl, was readily biodegraded in the presence of a aerobic bacterial strain. It is suggested that an integrated Pd/Fe catalytic reduction-aerobic biodegradation process may be a feasible option for treating PCB-contaminated soil.

A few researchers have reported on work concerning bioleaching of heavy-metal-contaminated soil using Acidithiobacillus ferrooxidans, since this acidophile is sensitive to dissolved low molecular weight (LMW) organic acids. Iron oxidation by A. ferrooxidans R2 as well as growth on ferrous iron was inhibited by a variety of dissolved LMW organic acids. Growth experiments with ferrous iron as an oxidant showed that the inhibition capability sequence was formic acid > acetic acid > propionic acid > oxalic acid > malic acid > citric acid. The concentrations that R2 might tolerate were formic acid 0.1 mmol L−1 (2 mmol kg−1 soil), acetic and propionic acids 0.4 mmol L−1 (8 mmol kg−1 soil), oxalic acid 2.0 mmol L−1 (40 mmol kg−1 soil), malic acid 20 mmol L−1 (400 mmol kg−1 soil), citric acid 40 mmol L−1 (800 mmol kg−1 soil), respectively. Although R2 was sensitive to organic acids, the concentrations of LMW organic acids in the contaminated soils were rather lower than the tolerable levels. Hence, it is feasible that R2 might be used for bioleaching of soils contaminated with metals or metals coupled with organic compounds because of the higher concentrations of LMW organic acids to which R2 is tolerant.

An Acidithiobacillus ferrooxidans strain R2 was isolated from the soil around Hongtoushan copper mine, Liaoning province in China through incubation in the modified Leathen-selected liquor medium followed by inoculation in solid plate. The cell of R2 strain was Gram negative and rod-shaped in (0.4±0.2)μm×(1.6±0.4)μm observed under SEM. The optimum growth pH was 2.0. The R2 strain can grow chemoautographically by using Fe2+, sulfur and Na2S2O3 as sole energy sources, but cannot grow with glucose and peptone. A phylogenetic tree was constructed by comparing with the published 16S rDNA sequences of the relative bacteria species. In the phylogenetic tree, the R2 strain was the closest relative to Acidithiobacillus ferrooxidans strain TGS and Acidithiobacillus ferrooxidans strain ATCC33020 with 100% and 99.3% sequence similarity. These results revealed that the R2 strain was a strain of Acidithiobacillus ferrooxidans. A batch experiment further demonstrated that as high as 30.6%, 16.3%, 58.4% and 72% of the removal efficiency of Cu, Cr, Zn and Cd could be obtained, respectively, in the period of 5 days bioleaching by using the isolated strain R2.

Pd/Fe bimetallic particles were synthesized by chemical deposition and used to dechlorinate 2,2′,4,5,5′-pentachlorobiphenyl in soil. Batch experiments demonstrated that the Pd/Fe bimetallic particles could effectively dechlorinate 2,2′,4,5,5′-pentachlorobiphenyl. Dechlorination was affected by several factors such as reaction time, Pd loading, the amount of Pd/Fe used, initial soil pH, and 2,2′,4,5,5′-pentachlorobiphenyl concentration. The results showed that higher Pd loading, higher dosage of Pd/Fe, lower initial concentration of 2,2′,4,5,5′-pentachlorobiphenyl and slightly acid condition were beneficial to the catalytic dechlorination of 2,2′,4,5,5′-pentachlorobiphenyl. The degradation of 2,2′,4,5,5′-pentachlorobiphenyl, catalyzed by Pd/Fe followed pseudo-first-order kinetics.

Dechlorination of 2, 2', 3, 4, 4', 5, 5'- heptachlorobiphenyl in soil was studied by using Pd/Fe bimetallic catalytic reduction. 2, 2', 3, 4, 4', 5, 5'- heptachlorobiphenyl can be dechlorinated effectively by Pd/Fe bimetal. It was found that the removal efficiency of 2, 2', 3, 4, 4', 5, 5'- heptachlorobiphenyl in soil could reach 54% after 5 days of reaction with 1 g of Pd/Fe (Pd loading 0.05%) and at an initial pH of 5.6. Several important experiment parameters involved in this process were also studied, including Pd loading, initial soil pH, the reaction time, the amount of Pd/Fe used and 2, 2', 3, 4, 4', 5, 5'- heptachlorobiphenyl initial concentration. The results showed that higher Pd loading, higher dosage of Pd/Fe, lower initial concentration of 2, 2', 3, 4, 4', 5, 5'- heptachlorobiphenyl and weak acid condition were beneficial to the catalytic dechlorination of 2, 2', 3, 4, 4', 5, 5'- heptachlorobiphenyl. The degradation of 2, 2', 3, 4, 4', 5, 5'- heptachlorobiphenyl, catalyzed by Pd/Fe, followed first-order kinetics, and the rate constant was 0.014 2/h, the half life was 49 h. In addition, two possible mechanisms of the dechlorination reaction were proposed and discussed.

A little work has been reported concerning bioleaching of heavy-metal contaminated soil using Acidithiobacillus ferrooxidans,since this acidophile is sensitive to low molecular weight(LMW) organic acids.Effects of LMW organic acids(formic,acetic,propionic,citric,malic and oxalic acids) on Fe2+ oxidation by A.ferrooxidans R2 were examined,and the concentrations of LMW organic acids in soils(from Shenyang Smeltery and Zhangshi irrigation area) were determined by high performance liquid chromatography(HPLC).Iron oxidation by R2 was inhibited by a variety of LMW organic acids.Growth experiments with ferrous iron as an oxidant showed that the inhibition capability sequence was formic acid>acetic acid>propionic acid>oxalic acid>malic acid>citric acid.Formic acid was the most toxic that the inhibition rate was up to 60% at the concentration of 0.064 mmol/L and the oxidation ability of R2 was entirely inhibited at the concentration of 0.254 mmol/L.HPLC analyses showed that the highest concentrations of LMW organic acids in the soils were 0.04 mmol/L and 0.149 mmol/L oxalic acid,respectively.Although R2 was sensitive to organic acids,the concentrations of LMW organic acids in the contaminated soils were rather lower than the tolerable levels.Hence,it is feasible that R2 might be used for bioleaching of heavy metal-contaminated soils.

Spatial distribution and sources of 16 priority polycyclic aromatic hydrocarbons (16 EPA-PAHs) in soils were studied in Shenfu Irrigation Area (SIA) located at northeast of China. SIA (1.3 x 10(4) ha) was an important agricultural farmland irrigated with oil-sewage since the 1960s. Soil profiles at 91 sites controlling all SIA were sampled. The results demonstrated that four- and five-ring PAHs accounted for 71.2% and 73.0% of the total PAHs in surface (0-20 cm) and subsurface (20-30 cm) soil, respectively. Phenanthrene (Phe), Fluoranthene (Fla), Pyrene (Pyr), Benzo(b)fluoranthene (BbF), benzo(a)pyrene (BaP) were identified as five dominant individual PAHs. Generally, there was a decreasing trend in concentrations of 16 EPA-PAHs from upper to lower reaches (by distance away from source) within 0.6-12.36 mg kg(-1) and 0.04-4.99 mg kg(-1) in surface and subsurface soil, respectively. The concentrations of 16 EPA-PAHs in the surface soil were threefold higher than those in the subsurface soil. A combination of grass, wood or coal combustion and petroleum combustion in surface soil and a combination of grass, wood or coal combustion and petroleum sources in subsurface soil might be the most significant contributors of 16 EPA-PAHs in SIA, indicating different pollution periods.

Polychlorinated biphenyls (PCBs) are the toxic organic compounds widely and massively distributed in the environment, and have great environmental impacts. Many scientists endeavored to devise remediation techniques to effectively treat the PCBs-contaminated matrices including water, oil, sediment, and soil. This paper summarized the research progress and development trend of reductive dechlorination of PCBs by zero-valent metal. Zero-valent metal can effectively promote the reductive dechlorination of PCBs under high temperature or the existence of Pd, Pt, Ni and Cu as catalyzers. There are three possible pathways of PCBs dehalogenation by zero-valent metal. The first pathway involves the metal directly, and the reduction occurs by electron transfer from Fe0 surface to the PCBs. The second pathway involves Fe2+, which is an immediate product of corrosion in aqueous systems. Dissolved Fe2+ is a reductant capable of causing PCBs dehalogenation. The third pathway for reductive dehalogenation by iron involves the hydrogen produced as a product of corrosion with water. In this paper, the effective, low-cost, and facile characteristics of PCBs reductive dechlorination by zero-valent metal were commented, and the further research areas were prospected.

Bioleaching is a technology mainly applied in the extraction of metals from low-grade ores,desulfurization of coal gas,recovery of metals from waste materials,and detoxification of metal ions in contaminated medium.As a principal part of microorganisms used in bioleaching technology,heterotrophic microorganisms have the potential in producing acidic metabolites that are able to extract or solubilize metals from non-sulfidic minerals,solid residues,sewage sludge,and soil via the mechanisms of reduction,acidolysis,and complexation.This technology is helpful to solve the problems of resources shortage and offer technique supports to the environmental management,with important theoretic meaning and practical worthiness.The major heterotrophic microorganisms applied in bioleaching include bacteria(mostly Pseudomonas sp.)and fungi(mainly Aspergillus sp.and Penicillium sp.),and bioleaching process involves acidolysis,complexation,reduction,and basification.At present,heterotrophic bioleaching is mostly used in bio-metallurgy,and disposal of solid wastes,sewage,and contaminated soil.The problems in metals recovery by bioleaching with heterotrophic micro-organisms were analyzed in this paper,with its development directions brought forward.

Pot experiment was conducted to evaluate the phytoremediation of pyrene-contaminated soil using alfalfa (Medicago sativa L.). Alfalfa biomasses, microbial viable counts, dehydrogenase activity, residual pyrene concentration and pyrene removal percentage were determined after 60 days of alfalfa growth. The results indicated that pyrene had an inhibitive effect on alfalfa growth, and higher pyrene concentration seriously affected alfalfa growth. In addition, the inhibitive effect on the root was more severe than that on the shoot. When pyrene concentration reached 492mgkg−1 in soil, the shoot and root biomasses were only 34% and 22% of those of alfalfa growing in non-spiked soil, respectively. The rhizospheric bacterial and fungi counts were 5.0–7.5 and 1.8–2.3 times higher than those in non-rhizosphere soil, respectively. The residual concentrations of pyrene in the rhizosphere soil were lower than those in the non-rhizosphere soil. After 60 days, 69–85% and 59–80% of spiked pyrene disappeared from the rhizosphere and non-rhizosphere soils, respectively. The removal percentage decreased with increasing pyrene concentration. However, the average removal of pyrene in the rhizosphere soil was 6% higher than that in the non-rhizosphere soil. Therefore, the presence of alfalfa roots was effective in promoting the phytoremediation of freshly added pyrene into the soil.

Pot experiment was used to investigate phytoremediation of phenanthrene-contaminated soil with alfalfa (Medicago sativa L.). Results indicated that phenanthrene had inhibitive effect on alfalfa growth, and higher phenanthrene concentration seriously prevent alfalfa growth. When the concentration was 445.22 mg/kg, the shoot and root biomasses were only 57.31% and 31.20% of control respectively. Alfalfa significantly promoted phenanthrene degradation in the soil. After 60 days, 85.68%-91.40% and 75.25%-86.61% of spiked phenanthrene disappeared from the rhizosphere and non-rhizosphere soils respectively. And the average removal ratio of phenanthrene in rhizosphere soils was 6.33% higher than that in non-rhizoshpere soils. The residual concentration of phenanthrene in the rhizosphere was lower than that in the non-rhizosphere but the dehydrogenase activity was on the contrary. With phenanthrene concentration increase the removal ratio and dehydrogenase activity decreased. A positive correlation was observed between the soil dehydrogenase activity and the removal ratio of phenanthrene in both the rhizosphere and non-rhizosphere soils. Therefore the presence of alfalfa roots was effective in promoting the phytoremediation of phenanthrene.

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds of persist organic pollutants (POPs) which are toxic to environment and pose hazard to human from food chain. Phytoremediation, the use of plants for the treatment of contaminated environment, has been developed during recent years, which is also a green technology with potential for effective and inexpensive cleanup of contaminated soil. Many researches have found that plants can enhance the removal of PAHs in soil. The mechanism of phytoremediation includes the direct effect of plants and the microbial degradation in the rhizosphere. And the efficiency of phytoremediation is affected by many environmental factors. This review generalizes the screening of plant species, remediation mechanism and influence factors, and summarizes the applications and research achievements of phytoremediation at home and abroad on contaminated soils by polycyclic aromatic hydrocarbons.

The problems caused by oil pollution in surface water have gradually become more serious.Traditional remediation technologies for oil pollution in surface water are difficult to implement because of its particularity.Microbe immobilization is a rising biotechnology.In contrast with traditional microbioremediation,it has the advantage of high biodensity and toxity-resistance.In accordance with oil pollution in surface water's character of large area and low concentration,microbe immobilization has special technical advantage and applied prospect.