Yong Bok Lee

Remediation approaches for polycyclic aromatic hydrocarbons (PAHs) contaminated soils: Technological constraints, emerging trends and future directions.

For more than a decade, the primary focus of environmental experts has been to adopt risk-based management approaches to cleanup PAH polluted sites that pose potentially destructive ecological consequences. This focus had led to the development of several physical, chemical, thermal and biological technologies that are widely implementable. Established remedial options available for treating PAH contaminated soils are incineration, thermal conduction, solvent extraction/soil washing, chemical oxidation, bioaugmentation, biostimulation, phytoremediation, composting/biopiles and bioreactors. Integrating physico-chemical and biological technologies is also widely practiced for better cleanup of PAH contaminated soils. Electrokinetic remediation, vermiremediation and biocatalyst assisted remediation are still at the development stage. Though several treatment methods to remediate PAH polluted soils currently exist, a comprehensive overview of all the available remediation technologies to date is necessary so that the right technology for field-level success is chosen. The objective of this review is to provide a critical overview in this respect, focusing only on the treatment options available for field soils and ignoring the spiked ones. The authors also propose the development of novel multifunctional green and sustainable systems like mixed cell culture system, biosurfactant flushing, transgenic approaches and nanoremediation in order to overcome the existing soil- contaminant- and microbial-associated technological limitations in tackling high molecular weight PAHs. The ultimate objective is to ensure the successful remediation of long-term PAH contaminated soils.

Microbial and biochemical basis of a Fusarium wilt-suppressive soil

Crops lack genetic resistance to most necrotrophic pathogens. To compensate for this disadvantage, plants recruit antagonistic members of the soil microbiome to defend their roots against pathogens and other pests. The best examples of this microbially based defense of roots are observed in disease-suppressive soils in which suppressiveness is induced by continuously growing crops that are susceptible to a pathogen, but the molecular basis of most is poorly understood. Here we report the microbial characterization of a Korean soil with specific suppressiveness to Fusarium wilt of strawberry. In this soil, an attack on strawberry roots by Fusarium oxysporum results in a response by microbial defenders, of which members of the Actinobacteria appear to have a key role. We also identify Streptomyces genes responsible for the ribosomal synthesis of a novel heat-stable antifungal thiopeptide antibiotic inhibitory to F. oxysporum and the antibiotic’s mode of action against fungal cell wall biosynthesis. Both classical- and community-oriented approaches were required to dissect this suppressive soil from the field to the molecular level, and the results highlight the role of natural antibiotics as weapons in the microbial warfare in the rhizosphere that is integral to plant health, vigor and development.

Pyrosequencing analysis of bacterial diversity in soils contaminated long-term with PAHs and heavy metals: Implications to bioremediation

Diversity, distribution and composition of bacterial community of soils contaminated long-term with both polycyclic aromatic hydrocarbons (PAHs) and heavy metals were explored for the first time following 454 pyrosequencing. Strikingly, the complete picture of the Gram positive (+ve) and Gram negative (-ve) bacterial profile obtained in our study illustrates novel postulates that include: (1) Metal-tolerant and PAH-degrading Gram -ves belonging to the class Alphaproteobacteria persist relatively more in the real contaminated sites compared to Gram +ves, (2) Gram +ves are not always resistant to heavy metal toxicity, (3) Stenotrophomonas followed by Burkholderia and Pseudomonas are the dominant genera of PAH degraders with high metabolic activity in long-term contaminated soils, (4) Actinobacteria is the predominant group among the Gram +ves in soils contaminated with high molecular weight PAHs that co-exist with toxic heavy metals like Pb, Cu and Zn, (5) Microbial communities are nutrient-driven in natural environments and (6) Catabolically potential Gram +/-ves with diverse applicability to remediate the real contaminated sites evolve eventually in the historically-polluted soils. Thus, the most promising indigenous Gram +/-ve strains from the long-term contaminated sites with increased catabolic potential, enzymatic activity and metal tolerance need to be harnessed for mixed contaminant cleanups.

Heavy Metal Contamination of Arable Soil and Corn Plant in the Vicinity of a Zinc Smelting Factory and Stabilization by Liming

The heavy metal contamination in soils and cultivated corn plants affected by zinc smelting activities in the vicinity of a zinc smelting factory in Korea was studied. Soils and corn plants were sampled at the harvesting stage and analyzed for cadmium (Cd) and zinc (Zn) concentration, as well as Cd and Zn fraction and other chemical properties of soils. Cd and Zn were highly accumulated in the surface soils (0–20 cm), at levels higher than the Korean warning criteria (Cd, 1.5; Zn, 300 mg kg−1), with corresponding mean values of 1.7 and 407 mg kg−1, respectively, but these metals decreased significantly with increasing soil depth and distance from the factory, implying that contaminants may come from the factory through aerosol dynamics (Hong et al., Kor J Environ Agr 26(3):204–209, 2007a; Environ Contam Toxicol 52:496–502, 2007b) and not from geological sources. The leaf part had higher Cd and Zn concentrations, with values of 9.5 and 1733 mg kg−1, compared to the stem (1.6 and 547 mg kg−1) and grain (0.18 and 61 mg kg−1) parts, respectively. Cd and Zn were higher in the oxidizable fraction, at 38.5% and 46.9% of the total Cd (2.6 mg kg−1) and Zn (407 mg kg−1), but the exchangeable + acidic fraction of Cd and Zn as the bioavailable phases was low, 0.2 and 50 mg kg−1, respectively. To study the reduction of plant Cd and Zn uptake by liming, radish (Raphanus sativa L.) was cultivated in one representative field among the sites investigated, and Ca(OH)2 was applied at rates of 0, 2, 4, and 8 mg ha−1. Plant Cd and Zn concentrations and NH4OAc extractable Cd and Zn concentrations of soil decreased significantly with increasing Ca(OH)2 rate, since it markedly increases the cation exchange capacity of soil induced by increased pH. As a result, liming in this kind of soil could be an effective countermeasure in reducing the phytoextractability of Cd and Zn.

Characteristics of boron accumulation by fly ash application in paddy soil

Fly ash has a high content of plant available silicate which is strongly needed for rice cultivation in Korea. One concern for plants grown on soils amended with fly ash is boron (B) toxicity because most of the fresh fly ash contains considerable B. This study was conducted in paddy soil to determine B uptake by rice and characteristics of B accumulation in soil after fly ash application (0, 40, 80, and 120 Mg fly ash ha(-1)). In all fly ash treatments, B content in rice leaves and available B in soil at all growing stage were higher than those of control, but were not exceeded a toxicity levels. Boron occluded in amorphous Fe and Al oxides comprised ca. 20-39% of total B and was not affected by fly ash application. Most of the B was accumulated by fly ash application as a residual B which is plant-unavailable form, comprised >60% of the total B in soil. Thus, fly ash can be a good soil amendment for rice production without B toxicity.

Influence of cold stress on contents of soluble sugars, vitamin C and free amino acids including gamma-aminobutyric acid (GABA) in spinach (Spinacia oleracea).

The contents of soluble sugars (sucrose, fructose, glucose, maltose and raffinose), vitamin C and free amino acids (34 compounds, essential and non-essential) were quantified in open-field and greenhouse-grown spinaches in response to cold stress using liquid chromatography. In general, greenhouse cultivation produced nutritionally high value spinach in a shorter growing period, where the soluble sugars, vitamin C and total amino acids concentrations, including essential were in larger amounts compared to those grown in open-field scenarios. Further, low temperature exposure of spinach during a shorter growth period resulted in the production of spinach with high sucrose, ascorbate, proline, gamma-aminobutyric acid, valine and leucine content, and these constitute the most important energy/nutrient sources. In conclusion, cultivation of spinach in greenhouse at a low temperature (4-7°C) and exposure for a shorter period (7-21days) before harvest is recommended. This strategy will produce a high quality product that people can eat.

Proteomic analysis of Rhizoctonia solani AG-1 sclerotia maturation

Rhizoctonia solani (R. solani), a soil-borne necrotrophic pathogen, causes various plant diseases. Rhizoctonia solani is a mitosporic fungus, the sclerotium of which is the primary inoculum and ensures survival of the fungus during the offseason of the host crop. Since the fungus does not produce any asexual or sexual spores, understanding the biology of sclerotia is important to examine pathogen ecology and develop more efficient methods for crop protection. Here, one- and two-dimensional gel electrophoresis (1-DE and 2-DE, respectively) were used to examine protein regulation during the maturation of fungal sclerotia. A total of 75 proteins (20 proteins from 1-DE using matrix-assisted laser desorption/ionization (MALDI)-time of flight (TOF) mass spectrometry (MS) and 55 proteins from 2-DE using MALDI-TOF MS or MALDI-TOF/TOF MS) were differentially expressed during sclerotial maturation. The identified proteins were classified into ten categories based on their biological functions, including genetic information processing, carbohydrate metabolism, cell defense, amino acid metabolism, nucleotide metabolism, cellular processes, pathogenicity and mycotoxin production, and hypothetical or unknown functions. Interestingly, two vacuole function-related proteins were highly up-regulated throughout sclerotial maturation, which was confirmed at the transcript level by reverse transcriptase polymerase chain reaction (RT-PCR) analysis. These findings contribute to our understanding of the biology of R. solani sclerotia.

Reduction of Phosphate Adsorption by Ion Competition with Silicate in Soil

To increase phosphate (P) availability in soils, the efficiency of silicate (Si) in reducing P adsorption was investigated by competitive adsorption tests under changing conditions of pH, ion concentrations, and order of anion addition along with single adsorption properties of each ion at 20°C. In the single ion adsorption study, P and Si ions showed the opposite reaction patterns: phosphate adsorption decreased with increasing pH and attained adsorption maximum however, silicate adsorption increased with increasing pH without attaining adsorption maximum. Phosphorus and Si adsorption were influenced by pH in the range of 5.0 - 9.0 and the type and amount of P and Si concentration. Silicate added to soil before P or in a mixture with P significantly reduced P adsorption above pH 7.0; however, there was no significant Si-induced decreased in P adsorption at pH 5.0 when anions were added as mixture. The efficiency of Si in reducing P adsorption increased with increasing Si concentration and pH. The effect of P on Si adsorption was relatively small at pH 5.0 and no effect of P on silicate adsorption was observed at pH 9.0. The presence of Si strongly depressed P adsorption when Si was added before P compared to P and Si added as a mixture. These results suggest that application of Si may decrease P adsorption and increase the availability of P in soils. Furthermore, a Si source would be better to add before P application to enhance the availability of P in soils.

Kinetics of PAH degradation by a new acid-metal-tolerant Trabulsiella isolated from the MGP site soil and identification of its potential to fix nitrogen and solubilize phosphorous

Development of an efficient bioinoculum is considered as an appropriate remedial approach to treat the PAHs-metal mixed contaminated sites. Therefore, we aimed to isolate a degrader able to exert an outstanding PAH catabolic potential with added traits of pH-metal-resistance, N-fix or P-solubilization from a manufactured gas plant site soil. The identified strain (MTS-6) was a first low and high molecular weight (LMW and HMW) PAHs degrading Trabulsiella sp. tolerant to pH 5. MTS-6 completely degraded the model 3 [150mgL(-1) phenanthrene (Phe)], 4 [150mgL(-1) pyrene (Pyr)] and 5 [50mgL(-1) benzo[a]pyrene (BaP)] ring PAHs in 6, 25 and 90 days, respectively. Presence of co-substrate (100mgL(-1) Phe) increased the biodegradation rate constant (k) and decreased the half-life time (t1/2) of HMW PAHs (100mgL(-1) Pyr or 50mgL(-1) BaP). The strain fixed 47μgmL(-1)N and solubilized 58μgmL(-1)P during PAH metabolism and exhibited an EC50 value of 3-4mgL(-1) for Cu, Cd, Pb and Zn. Over 6mgL(-1) metal levels was lethal for the microbe. The identified bacterium (MTS-6) with exceptional multi-functional traits opens the way for its exploitation in the bioremediation of manufactured gas plant sites in a sustainable way by employing bioaugmentation strategy.

Effect of a fly ash and gypsum mixture on rice cultivation

Abstrat Paddy soil in Korea generally required the addition of silicate to enhance rice productivity. Even though a silicate fertilizer has been applied at 4-year intervals by the Korean government, the quantity has not been sufficient, due to financial constraints, and an alternative source of cheaper silicate is required. Fly ash, which has a high silicate content, was selected as an alternative in the present study. To improve fly ash, which is highly alkaline and has a high boron content, the material was mixed with a by-product of gypsum (hereafter, described as gypsum) and the pH changes were monitored in water using an incubation test. The initial pH of the water suspension was compatible with the optimum range (ca. 6.5–7.0) for rice using a mixture of 75% fly ash and 25% gypsum. A field experiment was carried out to evaluate the productivity of rice (Oryza sativa) on silt loamy soil to which 0 (FG 0), 20 (FG 20), 40 (FG 40), or 60 (FG 60) Mg ha−1 of the mixture were added. Silicate and lime treatments were selected as a control. The highest rice yield was achieved following the addition of 40 Mg ha−1 of the mixture to the soil. The mixture of fly ash and gypsum increased the uptake of silicate and phosphate and the amount of exchangeable calcium in the soil. The plant elemental uptake revealed that the application of the fly ash and gypsum mixture did not result in an excessive uptake of heavy metals by the rice in the submerged paddy soil. The amount of available boron increased with the increase in the amount of fly ash up to 0.62 mg kg−1 following the application of 60 Mg ha−1 of the mixture, but did not reach toxicity levels for rice, probably due to the dilution and leaching effects under the submerged growing conditions. It is concluded that the fly ash and gypsum mixture could be a good alternative to inorganic soil amendments to restore the soil nutrient balance in paddy soil.