Byung-Tae Lee

Ozonation of diesel fuel in unsaturated porous media

The objectives of this study were to determine the feasibility of ozonation in unsaturated porous media, and consequently to observe its features and to identify possible limiting factors. Diesel fuel was chosen to represent a complex organic contaminant that is widespread in the environment. In this experiment, the effects of several ozonation features were investigated. Sand was spiked with commercially available diesel fuel (17.024 g diesel/kg dry sand), and packed into a column. Ozone was supplied into the column in a downward direction. When the sand was treated for 7 h at 20 mg ozone/l of air, 40% of the diesel was removed. As the ozone concentration increased from 5 to 20 mg ozone/l, the removal efficiency increased. The removal rate varied significantly depending on the ozone concentration and the treatment duration. At higher ozone concentration, significant quantities of ozone were consumed by the intermediates produced by the ozonation process, and therefore, the removal efficiency and the apparent removal rate of diesel became lowered. The low removal efficiency of diesel results from the high concentrations of normal alkanes. Total hydrocarbon concentration (THC) in the effluent gas was measured using a total hydrocarbon analyzer. The THC decreased with the period of exposure and increasing ozone concentration. Ozonation decreased the gas-extractable fraction and accordingly, the THC decreased. Water-extractable fractions formed by the action of ozone were further oxidized by ozone. Due to the reduction of WEOC (water-extractable organic C) caused by ozone treatment, the potential spread of contamination can be reduced.

A novel combination of anaerobic bioleaching and electrokinetics for arsenic removal from mine tailing soil.

This study provides evidence that a hybrid method integrating anaerobic bioleaching and electrokinetics is superior to individual methods for arsenic (As) removal from mine tailing soil. Bioleaching was performed using static reactors in batch tests and flow conditions in column test, and each test was sequentially combined with electrokinetics. In the bioleaching, indigenous bacteria were stimulated by the injection of carbon sources into soil, leading to the mobilization of As with the concurrent release of Fe and Mn. Compared with the batch-type bioleaching process, the combined process showed enhanced removal efficiency in the equivalent time. Although the transport fluid bioleaching conditions were inadequate for As removal, despite long treatment duration, when followed by electrokinetics the combined process achieved 66.5% removal of As from the soil. The improvement of As removal after the combined process was not remarkable, compared with single electrokinetics, whereas a cost reduction of 26.4% was achieved by the reduced duration of electrokinetics. The As removal performance of electrokinetics was significantly dependent on the chemical species of As converted via microbial metal reduction in the anaerobic bioleaching. The synergistic effect of the combined process holds the promise of significant time and cost savings in As remediation.

Citrate coated silver nanoparticles change heavy metal toxicities and bioaccumulation of Daphnia magna.

Citrate-coated AgNPs (c-AgNPs) have negatively charged surfaces and their surface interactions with heavy metals can affect metal toxicity in aquatic environments. This study used Daphnia magna to compare the acute toxicities and bioaccumulation of As(V), Cd, and Cu when they interact with c-AgNPs. The 24-h acute toxicities of As(V) and Cu were not affected by the addition of c-AgNPs, while bioaccumulation significantly decreased in the presence of c-AgNPs. In contrast, both the 24-h acute toxicity and bioaccumulation of Cd increased in the presence of c-AgNPs. These toxicity and bioaccumulation trends can be attributed to the interactions between the AgNP surface and the heavy metals. As(V) and c-AgNPs compete by negative charge, decreasing As(V) toxicity. Copper adheres readily to c-AgNP citrate, decreasing Cu bioavailability, and thus reducing Cu toxicity and bioaccumulation. Citrate complexes with divalent cations such as Ca and Mg reduce the competition between divalent cations and Cd on biotic ligand, increasing toxicity and bioaccumulation of Cd. This study shows that surface properties determine the effect of c-AgNPs on heavy metal toxicities and bioaccumulations; hence, further studies on the effect of nanoparticle by it surface properties are warranted.

Arsenic accumulation and toxicity in the earthworm Eisenia fetida affected by chloride and phosphate

Chloride and phosphate (PO4) were added to field soils contaminated with arsenic and heavy metals, and Eisenia fetida were inoculated in these treated soils for 70 d. After 28 d, earthworm survival, body weight, and cocoon production were measured. During the exposure period, the accumulation of As and four metals (Cu, Zn, Cd, and Pb) in E. fetida was analyzed. Bulk soils and soil solutions were characterized for the contents of As, metals, organic matter, and major cations and anions; cation exchange capacity; and pH. Although addition of Cl to the soil did not impact As toxicity, it significantly reduced As uptake. The addition of PO4 induced changes in As toxicity and reduced As accumulation even though the As concentration in the soil pore water increased because of the substitution of As by P at soil sorption sites. These results imply that the addition of Cl induced the formation of an As-Cl complex, thereby resulting in decreased As bioavailability; they also imply that monovalent phosphate (H2PO4(-)) competes with As for uptake through transporter-mediated mechanisms in cells.

Comparative study of simultaneous removal of As, Cu, and Pb using different combinations of electrokinetics with bioleaching by Acidithiobacillus ferrooxidans

Different designs of electrokinetics were applied to simultaneously remove arsenic, copper, and lead from contaminated soils. Single electrokinetics (control) resulted in superior removal efficiencies for Cu (73.5%) and Pb (88.5%), though the removal of As (3.11%) was relatively little. Sequential bioelectrokinetics of bioleaching with Acidithiobacillus ferrooxidans and electrokinetics enhanced the removal of As (25%), while Pb exhibited a significant decrease in removal efficiency (10.6%), due to the formation of insoluble compounds. In order to improve the overall performance, integrated bioelectrokinetics was designed by inoculating A. ferrooxidans into the electrolyte after 5 or 15 days of electrokinetics. Lead (75.8%) and copper (72%) were effectively removed through electrokinetics, after which arsenic (35%) was more efficiently removed by bioleaching-enhanced electrokinetics. A pilot-scale experiment indicated that integrated bioelectrokinetics is an effective means of remediation of soils contaminated with multiple heavy metals and arsenic.

Lysosomal membrane response of earthworm, Eisenia fetida, to arsenic contamination in soils.

Earthworm (Eisenia fetida) were exposed to sandy soils contaminated with arsenate (0.01–0.3 μmol g−1) for 28 days. Lysosomal membrane stability was used as a biomarker to determine the applicability of neutral‐red retention times (NRRTs) for arsenic (As) toxicity to earthworm in soils. Total As and As speciation were analyzed to evaluate dose–response relationship between As accumulation and NRRTs and to observe the role of As metabolism in earthworms on a subcellular level toxicity. Significant decrease of NRRTs was found with the increasing As concentration in soils (ANOVA, P < 0.05). Adverse effects on earthworm survival and growth did not occur when exposed to 0.1 and 0.05 μmol g−1 at 14 and 28 days, respectively, whereas NRRTs showed significant reduction from the control, as was readily bioconcentrated in the reduced form of As(III) in earthworms and clear dose–response relationships were found for As body burden and NRRTs. Therefore, it is possible to conclude that As has an adverse effect on lysosomal membrane of coelomocytes, and NRRT assay is a potentially applicable method to assess As toxicity as an early warning tool. Also, sequestered As in the form of As(III)‐thiol complex can be expected to cause an adverse effect on lysosomal membrane stability.

Progress in Earthworm Ecotoxicology

Earthworms are regarded as one of the most suitable animals for testing the toxicity of chemicals in soils and have been adopted as standard organisms for ecotoxicological testing. In several guidelines concerning earthworm toxicity tests, Eisenia fetida/andrei (E. fetida/andrei) was chosen because it can be easily cultured in the laboratory and an extensive database on the effects of all classes of chemicals exists for this species. Acute and chronic toxicity tests have been used traditionally to assess the toxicity of contaminants, with mortality and changes in biomass, reproduction rates and behavioral responses representing endpoints. Moreover, the avoidance behavior test (AVT) using earthworm is under development and standardization, which records the ability of earthworms to choose or avoid a certain soil. Recent studies have shown that neutral red retention time (NRRT) has the potential for a rapid assessment of the toxic effects for earthworms of soils contaminated with heavy metals and metalloids. Toxicity is the apparent expression of the metal accumulation in earthworm body. The uptake, accumulation and elimination properties of metals by earthworm are the major part of toxicology, which is called toxicokinetics. Geochemical factors may have signifi cant effects on metal transport or bioavailability. Prediction models for metal accumulation and toxicity in soils are being developed based on metal bioavailability. In this study, methodologies and research trends in earthworm toxicity are reviewed for understanding metal bioavailability. Toxicity prediction models are introduced for terrestrial environment and several studies are referred to understand the role of geochemistry in toxicology.

Comparative toxicity of silver nanoparticles and silver ions to Escherichia coli

With the increase in silver (Ag)-based products in our lives, it is essential to test the potential toxicity of silver nanoparticles (AgNPs) and silver ions (Ag ions) on living organisms under various conditions. Here, we investigated the toxicity of AgNPs with Ag ions to Escherichia coli K-12 strain under various conditions. We observed that both AgNPs and Ag ions display antibacterial activities, and that Ag ions had higher toxicity to E. coli K-12 strain than AgNPs under the same concentrations. To understand the toxicity of AgNPs at a cellular level, reactive oxygen species (ROS) enzymes were detected for use as antioxidant enzymatic biomarkers. We have also studied the toxicity of AgNPs and Ag ions under various coexistence conditions including: fixed total concentration, with a varied the ratio of AgNPs to Ag ions; fixed the AgNPs concentration and then increased the Ag ions concentration; fixed Ag ions concentration and then increasing the AgNPs concentration. Exposure to AgNPs and Ag ions clearly had synergistic toxicity; however, decreased toxicity (for a fixed AgNPs concentration of 5mg/L, after increasing the Ag ions concentration) to E. coli K-12 strain. AgNPs and Ag ions in the presence of L-cysteine accelerated the bacterial cell growth rate, thereby reducing the bioavailability of Ag ions released from AgNPs under the single and coexistence conditions. Further works are needed to consider this potential for AgNPs and Ag ions toxicity across a range of environmental conditions. ENVIRONMENTAL SIGNIFICANCE STATEMENT As silver nanoparticles (AgNPs)-based products are being broadly used in commercial industries, an ecotoxicological understanding of the AgNPs being released into the environment should be further considered. Here, we investigate the comparative toxicity of AgNPs and silver ions (Ag ions) to Escherichia coli K-12 strain, a representative ecotoxicological bioreporter. This study showed that toxicities of AgNPs and Ag ions to E. coli K-12 strain display different relationships when existing individually or when coexisting, and in the presence of L-cysteine materials. These findings suggest that the toxicology research of nanomaterials should consider conditions when NPs coexist with and without their bioavailable ions.

Nanoparticles in the environment: stability and toxicity.

Abstract With the increasing use and application of engineered nanoparticles (ENPs) in a number industries, ENPs, through their unique properties, have made their way into the environment. However, the environmental fate and behavior of ENPs are largely unknown. Laboratory studies have shown that some ENPs have the potential for toxicity, suggesting they may affect organisms in the environment. To fully assess the risk of ENPs, a better estimation of exposure concentrations is needed. This requires an understanding of the stability and toxicity of nanoparticles (NPs) in the environment. This review presents a brief overview of the fate, behavior, and ecotoxicity of NPs in the environment. The fate and transport of NPs, which can be affected by various environmental conditions like light, pH, ionic strength, and type and concentration of cations, are important for the examination of the life cycle of NPs.

Equilibria, kinetics, and spectroscopic analyses on the uptake of aqueous arsenite by two-line ferrihydrite

Arsenite sorption from aqueous solutions was investigated using two-line ferrihydrite at room temperature, as a function of solution pH and arsenite loading. The isotherms, pH envelopes, and kinetics of arsenite sorption were characterized and its mechanism was elucidated via X-ray absorption spectroscopic studies. Arsenite sorption showed only slight pH dependence with a sorption maximum centered around pH 8.0. The Langmuir isotherm is most appropriate for arsenite sorption over the wide range of pH, indicating the homogenous and monolayer sorption of arsenite. The kinetic study demonstrated that arsenite sorption onto two-line ferrihydrite is considerably fast and the equilibrium is achieved within the reaction time of 3 h. X-ray absorption near-edge structure spectroscopy elucidated a slight change in oxidation state of arsenite for the initial concentration of 13.35 mM at pH 4. The extended X-ray absorption fine structure (EXAFS) spectroscopy results indicate that types of surface complexes of arsenite appeared to be very similar to those proposed by the previous studies in that the bidentate binuclear corner-sharing (2C) complex is predominant at all the surface loadings. However, our EXAFS results suggest that regardless of pH, the mixed complexes of 2C and bidentate mononuclear edge-sharing surface complex (2E) as well as the 2C complex are favoured at low and intermediate surface loadings, but only the 2C complex is dominant at high surface loading. Overall, the EXAFS results support the efficient removal of arsenite by the two-line ferrihydrite through the formation of highly stable inner-sphere surface complexes, such as 2C complex.