Sanghwa Oh

Diffusive gradients in thin films (DGT) for the prediction of bioavailability of heavy metals in contaminated soils to earthworm (Eisenia foetida) and oral bioavailable concentrations

The applicability of diffusive gradients in thin-films (DGT) as a biomimic surrogate was investigated to determine the bioavailable heavy metal concentrations to earthworm (Eisenia foetida). The relationships between the amount of DGT and earthworm uptake; DGT uptake and the bioavailable concentrations of heavy metals in soils were evaluated. The one-compartment model for the dynamic uptake of heavy metals in the soil fitted well to both the earthworm (R(2)=0.641-0.990) and DGT (R(2)=0.473-0.998) uptake data. DGT uptake was linearly correlated with the total heavy metal concentrations in the soil (aqua regia), the bioavailable heavy metal concentrations estimated by fractions I+II of the standard measurements and testing (SM&T) and physiologically based extraction test (PBET, stomach+intestine). The coefficients of determination (R(2)) of DGT uptake vs. aqua regia were 0.433, 0.929 and 0.723; vs. SM&T fractions (I+II) were 0.901, 0.882 and 0.713 and vs. PBET (stomach+intestine) were 0.913, 0.850 and 0.649 for Pb, Zn and Cu, respectively. These results imply that DGT can be used as a biomimic surrogate for the earthworm uptake of heavy metals in contaminated soils as well as predict bioavailable concentrations of heavy metals estimated by SM&T (I+II) and PBET as a human oral bioavailable concentrations of heavy metals.

Assessment of metal bioavailability in smelter-contaminated soil before and after lime amendment.

In this study, changes in bioavailable concentrations of Pb, Zn, Cu and As in former smelter site soils (J1 and J2) were investigated before and after lime amendment. The immobilization efficiencies of metal(loid)s were evaluated by Toxicity Characteristic Leaching Procedure (TCLP). Their bioavailable concentrations in the soils were evaluated by the acid-extractable and -reducible fractions in Standard Measurement and Testing Program (i.e., SM&T(I+II)), in vitro physiologically based extraction test (PBET) and diffusive gradients in thin-films (DGT). The results showed that the bioavailable concentrations remarkably decreased after lime amendment in both J1 and J2 soils. DGT uptake and resupply (R) of Zn, Cu and As from soil to soil solution increased but that of Pb decreased. This pattern was consistent with SM&T(I+II)- and PBET-extractable concentrations after lime amendment. This indicates that lime amendment is highly effective for the immobilization of Zn, Cu and As, but not for Pb. Our results implicate that DGT can be used to estimate bioavailability of metal(loid)s in soils and further extended to estimate risk reduction after soil remediation.

Adsorptive Removal of Co and Sr Ions from Aqueous Solution by Synthetic Hydroxyapatite Nanoparticles

Hydroxyapatite nanoparticles were synthesized by using the precipitation method with simulated body fluid solution and applied for adsorption of Co2+ and Sr2+ in aqueous solution. The single- and bi-solute adsorption experiments were performed to evaluate the maximum adsorption capacity of hydroxyapatite nanoparticles for Co2+ and Sr2+, the effect of temperature and pH, and the influence of simultaneous presence of other competing metal ion in a binary system. The synthesized hydroxyapatite nanoparticles had high adsorption capacity for Co2+ and Sr2+ due to a high specific surface area. The maximum adsorption capacity and binding energy of Co2+ were higher than those of Sr2+ in single-solute adsorption. The extended Langmuir model was fitted well for bi-solute competitive adsorption of Co2+ and Sr2+ onto the hydroxyapatite nanoparticles. Thermodynamic analysis showed that adsorption occurred spontaneously for both metals and was endothermic for Co2+, but exothermic for Sr2+.

Human Health Risk Assessment of Soils Contaminated with Metal(loid)s by Using DGT Uptake: A Case Study of a Former Korean Metal Refinery Site

ABSTRACT The human health risk of soils contaminated with As, Pb, Cu, and Zn was evaluated based on pseudo-total concentrations of metal(loid)s, the physiologically based extraction test (PBET), and diffusive gradients in thin films (DGT). Non-carcinogenic (NCR) and carcinogenic (CR) risks exceeded the U.S. Environmental Protection Agency criteria under both the residential and non-residential scenarios. Human bioavailable concentrations (PBET) were much lower than pseudo-total concentrations. The Hazardous Index of NCR (HI (NCR)) for the PBET in the studied soils was 67% and 94% less than that for pseudo-total concentration, respectively, under the non-residential and residential scenarios. Similarly, CR for the PBET was also 65% and 93% less for the two soils. The concentration of metal(loid)s accumulated in the DGT resin was highly correlated with the PBET-extractable concentration (R2 > 0.649). Therefore, for both the CR and HI (NCR), the DGT-calculated risk was linearly related to the PBET-calculated risk for the studied soils under both scenarios. The results suggest that DGT uptake and PBET-extracted concentrations are good surrogates for risk estimation and that both J1 and J2 soils require remediation before their use for residential or non-residential purposes.

Effect of ageing on desorption of lead and cadmium from sediments: Kinetics and desorption-resistance

In this study, the effect of ageing on sorption isotherms and desorption behaviors (kinetics and desorption-resistance) of lead (Pb) and cadmium (Cd) in natural sediments was investigated. Several sorption models such as Freundlich, Langmuir and Dubinin-Radushkevich models were fitted to the sorption data. The sorption affinity and sorption capacity of the heavy metals onto sediments increased with cation exchange capacity (CEC) and BET surface area (ABET). The sorption affinity of Pb was higher than that of Cd in all sediments at all ageing time scales (1, 30 and 100 d). Four different models: the one-site mass transfer model (OSMTM), the pseudo-first-order kinetic model (PFOKM), the pseudo-second-order kinetic model (PSOKM) and the two compartment first-order kinetic model (TCFOKM) were used to analyze desorption kinetics. All models predicted that the sorbed amount (q e,s ) at the apparent desorption equilibria increased as the cation exchange capacity (CEC) and BET surface area (ABET) of the sediments increased. However, the fast desorption fractions (f 1,d ) decreased with increasing CEC, ABET and organic carbon content (f oc ). Sequential desorption experiments were conducted to investigate the effect of ageing on desorption-resistance and a biphasic desorption model was fitted to the data. The biphasic desorption model parameters indicate that the maximum capacity of desorption resistant fraction (q max irr ) of Pb was higher than that of Cd and the q max irr increased with CEC, ABET and ageing time for both Pb and Cd. Sequential extraction analysis revealed that the transformation of heavy metals in more mobile fraction into less mobile fractions was the main reason for the increase in desorption-resistance.

Sorption and desorption kinetics of PAHs in coastal sediment

Sorption and desorption kinetics of PAHs (naphthalene, phenanthrene and pyrene) in coastal sediment were investigated. Several kinetic models were used to analyze the kinetics: one-site mass transfer model (OSMTM), pseudo-first-order kinetic model (PFOKM), pseudo-second-order kinetic model (PSOKM), two compartment firstorder kinetic model (TCFOKM) and modified two compartment first-order kinetic model (MTCFOKM). Among the models, the MTCFOKM was the best in fitting both sorption and desorption kinetic data, and therefore could predict the most accurately. In MTCFOKM, the fast sorption fraction (f′1, s) increased with the hydrophobicity (Kow) of the PAHs, whereas the fast desorption fraction (f′1, d) decreased. The fast sorption rate constant (k′1, s) was much greater than the slow sorption rate constant (k′2, s). Effect of aging on the desorption kinetics was also analyzed. The f′1, d in MTCFOKM decreased but the slow desorption fraction (f′2, d) increased with aging, indicating that slow desorption is directly related to aging.

Solidification/stabilization of heavy metals in tannery sludge char with various binders

AbstractThe leaching potential of heavy metals (Cr, Pb, Ni, Zn, and Cu) from the tannery sludge charred at above 350°C under oxygen-depleted conditions was evaluated for re-use as landfill cover materials. Solidification/stabilization (S/S) was employed for the immobilization of heavy metals in the tannery sludge chars (TSCs) to further reduce the leaching potential. The effects of charring temperatures, different types of binders (FeSO4, lime, cement, HAP, and ladle slag), and aging on the immobilization of heavy metals (Pb, Ni, Zn, Cu, and Cr) in the TSCs were investigated. The immobilization efficiencies were estimated using the toxicity characterization leaching procedure (TCLP). The results show that the extractable concentrations of heavy metals decreased with the charring temperature. The single binder (FeSO4 alone) was highly effective for Cr immobilization, but not for other heavy metals such as Ni and Zn. The binary binders, FeSO4 combined with lime, cement, or ladle slag, were highly effective ...

Sorption and Desorption Kinetics of Naphthalene and Phenanthrene on Black Carbon in Sediment

Black carbon (BC), a kind of high surface area carbonaceous material (HSACM), was isolated from Andong lake sediment. Sorption and desorption kinetics of naphthalene (Naph) and phenanthrene (Phen) in organic carbon (OC) and BC in the Andong lake sediment were investigated. Several kinetic models such as one-site mass transfer model (OSMTM), two-compartment first-order kinetic model (TCFOKM), and a newly proposed modified two-compartment first-order kinetic model (MTCFOKM) were used to describe the sorption and desorption kinetics. The MTCFOKM was the best fitting model. The MTCFOKM for sorption kinetics showed that i) the sorbed amounts of PAHs onto BC were higher than those onto OC, consistent with BET surface area; ii) the equilibration time for sorption onto BC was longer than those onto OC due to smaller size of micropore () of BC than OC (); iii) initial sorption velocity of BC was higher than OC; and iv) the slow sorption velocity in BC caused the later equilibrium time than OC even though the fast sorption velocity was early completed in both BC and OC. The MTCFOKM also described the desorption of PAHs from the OC and BC well. After desorption, the remaining fractions of PAHs in BC were higher than those in OC due to stronger PAHs-BC binding. The remaining fractions increased with aging for both BC and OC.

Sorption of antibiotics onto montmorillonite and kaolinite: Competition modeling

ABSTRACT Antibiotic contaminants, which are generally present in bi-solute systems, can be competitively adsorbed onto clays. Single- and bi-solute sorptions of sulfadiazine (SDZ) and ciprofloxacin (CIP) onto montmorillonite and kaolinite were investigated at pH values of 5 and 8. Freundlich and Langmuir models were used and fit the experimental data well for single-solute sorption. The sorption isotherms were nonlinear (NF = 0.265–0.730), and the maximum sorption capacities (qmL) of the SDZ and CIP onto montmorillonite were higher than those onto kaolinite. The octanol–water distribution ratio (Dow), cation exchange capacity (CEC), Brunauer–Emmett–Teller (BET) surface area (ABET), pore size, point of zero charge (pHPZC), and basal spacing predominantly affected the Freundlich constant (KF) and qmL of SDZ0 and CIP+ at pH 5 more than SDZ− and CIP± at pH 8. For bi-solute sorption, the presence of CIP inhibited the SDZ sorption onto montmorillonite and kaolinite. Competitive sorption models such as Sheindorf–Rebhun–Sheintuch (SRS), Murali–Aylmore (M–A) and the modified extended Langmuir model (MELM) were used; of these, the MELM provided the best prediction with SDZ sorption onto montmorillonite at pH 8 and CIP onto kaolinite at pH 5 and 8 in SDZ/CIP system occurring synergistically, whereas others occurred antagonistically. The distribution coefficient (Kd) of the bi-solute sorption decreased with increasing pH in the order cationic > neutral > anionic for SDZ and cationic > zwitterionic > anionic for CIP, which resembled the Kd of single-solute sorption. Fourier transform infrared spectroscopy (FT-IR) spectra indicated that amine in SDZ and keto oxygen in CIP were responsible for the interactions with the montmorillonite and kaolinite. GRAPHICAL ABSTRACT

Separation of Heavy Metals from Metal-EDTA in Spent Soil Washing Solution by using Na 2 S

Soil washing with ethylenediaminetetraacetic acid (EDTA) is highly effective in the remediation of soils contaminated with heavy metals. The EDTA recycling process is a requisite for reducing the operating cost. The applicability of Na2S addition on the precipitation of heavy metals from the spent soil washing solution and thereby recycling of EDTA was investigated. Addition of Na2S into the single metal-EDTA and the mixed metal-EDTA solutions ([Na2S]/[metal-EDTA] ratio = 30, reaction time = 30 min and pH = 7~9) was highly effective in the separation of Cu and Pb from metal-EDTA complexes, but not for Ni. The Zn removal efficiency varied with pH and slightly increased upto 40% as the reaction time increased from 0 to 240 min which was longer than those for Cu and Pb. Ca(OH)2 was subsequently added to induce further precipitation of Zn and Ni and to reduce the Na2S dose. At the [Na2S]/[metal-EDTA] ratio of 10, the removal efficiencies of all heavy metals excluding Ni were above 98% with the dose of Ca(OH)2 at 0.002, 0.006 and 0.008 g into 100 mL of Cu-, Pb- and Zn-EDTA solutions, respectively. However, Ca(OH)2 addition was not effective for Ni-EDTA solution. A further research is needed to improve metal removal efficiency and subsequent EDTA recycling for the real application in field-contaminated soils.