Zn speciation and fate in soils and sediments along the ground transportation route of Zn ore to a smelter.

Assessment of Zn toxicity/mobility based on its speciation and transformations in soils is critical for maintaining human and ecosystem health. Zn-concentrate (56 % Zn as ZnS, sphalerite) has been imported through a seaport and transported to a Zn-smelter for several decades, and smelting processes resulted in aerial deposition of Zn and sulfuric acids in two geochemically distinct territories around the smelter (mountain-slope and riverside). XAFS analysis showed that the mountain-slope soils contained franklinite (ZnFe2O4) and amorphous (e.g., sorbed) species of Zn(II), whereas the riverside sediments contained predominantly hydrozincite [Zn5(OH)6(CO3)2], sphalerite, and franklinite. The mountain-slope soils had low pH and moderate levels of total Zn (~ 1514 ppm), whereas the riverside sediments had neutral pH and higher total Zn (12,363 ppm). The absence of sphalerite and the predominance of franklinite in the mountain-slope soils are attributed to the susceptibility of sphalerite and the resistance of franklinite to dissolution at acidic pH. These results are compared to previous Zn analyses along the transportation routes, which showed that Zn-concentrate spilled along the roadside in dust and soils underwent transformation to various O-coordinated Zn species. Overall, Zn-concentrate dispersed in soils and sediments during transportation and smelting transforms into Zn phases of diverse stability and bioavailability during long-term weathering.

Identification of weathered multiple petroleum products in contaminated soils by characterizing unresolved complex mixture hump in gas chromatograph data.

A new method for identifying the petroleum products in contaminated soils is presented, which characterizes the unresolved complex mixture (UCM) hump in the baseline of gas chromatograph (GC) data. The UCM hump identified in soil data was fitted to the Gaussian function, and characterized according to the time for the maximum point (TUCM) and the width of the hump (w). Experimental results showed that a UCM hump should be clearly observed in soils when contaminated with petroleum, and that soils contaminated with kerosene, diesel, or some lubricating oils estimated herein should present different characteristic values of TUCM and w. Even though the environmental weathering of contaminated soils under evaporative conditions might cause variations in these characteristic values, they converged to specific constants depending on the product. The method could also differentiate between multiple petroleum contaminants in soil. Feasibility was evaluated using soils from a military oil storage site that was closed in 1970. The soil contaminants identified by the proposed method corresponded to the historical storage records, suggesting that the UCM hump characterization method could have strong potential in environmental forensics for differentiating products in petroleum-contaminated soils.

Identifying the source of Zn in soils around a Zn smelter using Pb isotope ratios and mineralogical analysis.

The contribution by anthropogenic sources to abnormally high Zn concentrations in soils with naturally abundant Zn was investigated at a contaminated site surrounding a Zn smelter in eastern Korea. Nineteen soil samples were collected within a 2km radius of the smelter, and analyzed for metal concentrations and Pb isotope ratios using an inductively coupled plasma-optical emission spectrometer and -mass spectrometer, respectively. Higher Zn concentrations in locations closer to the smelter implied that the smelter was the source of the Zn pollution. Lead isotope ratios (206/207Pb) from soil samples assumed to be unaffected by the smelter were higher than those found in the contaminated area, suggesting that the raw materials of Zn concentrates (ZnS, sphalerites) and smelting by-products from the smelter with low 206/207Pb ratios were the anthropogenic Zn source impacting the area. To verify this finding, the mineralogical forms of Zn found in the different soil fractions were investigated by X-ray diffraction analysis, scanning-electron-microscope energy-dispersive spectrometer analysis, and sulfur element analysis. Since approximately 50% of Zn concentrates have particle sizes less than 0.044 mm, the observation of sphalerites and elevated sulfur concentrations in the finer soil fraction (<0.044mm) provide substantial support to the hypothesis that the deposition of airborne Zn-containing dust from the smelter is responsible for the high Zn concentration in the area.

Potential risks of TiO2 and ZnO nanoparticles released from sunscreens into outdoor swimming pools.

The potential risks of nanoparticles (NPs) in sunscreens being released into swimming water were evaluated by a series of laboratory experiments simulating the fate and transport of NPs in outdoor swimming pools. NPs released from sunscreen-applied skin were estimated using pig skins covered with five different commercial sunscreens containing TiO2, ZnO, or both at various concentrations. Assuming that the swimming water treatment processes consisted of filtration, UV irradiation, heating, and chlorination, possible removal of the released NPs by each process was estimated. Generation of hydrogen peroxide (H2O2) by the NPs under sunlight and after UV photochemical treatment were measured, and the H2O2 concentration possibly present in the swimming pool was calculated based on some specific scenarios of operating an outdoor swimming pool. It was found that a significant amount of the NPs in sunscreens could be released into the swimming water, and accumulate during circulation through the treatment system. However, the concentration of H2O2 possibly present in the swimming pool should be below the level at which an adverse effect to bathers is concerned.

Semi-quantitative estimation of cellular SiO2 nanoparticles using flow cytometry combined with X-ray fluorescence measurements.

In this study, we have demonstrated feasibility of a semi-quantitative approach for the estimation of cellular SiO2 nanoparticles (NPs), which is based on the flow cytometry measurements of their normalized side scattering intensity. In order to improve our understanding on the quantitative aspects of cell-nanoparticle interactions, flow cytometry, transmission electron microscopy, and X-ray fluorescence experiments were carefully performed for the HeLa cells exposed to SiO2 NPs with different core diameters, hydrodynamic sizes, and surface charges. Based on the observed relationships among the experimental data, a semi-quantitative cellular SiO2 NPs estimation method from their normalized side scattering and core diameters was proposed, which can be applied for the determination of cellular SiO2 NPs within their size-dependent linear ranges.

Impact of agglomeration on the bioaccumulation of sub-100 nm sized TiO2.

To improve our understanding on the impact of extrinsic properties of NPs on their bioaccumulation and toxicity, we have investigated the bioaccumulation of sub 100 nm sized P25 TiO2 nanoparticles (NPs) by Daphnia magna (D. magna) in toxicity testing media. Based on our quantitative ICP-MS measurements as well as spectromicroscopic observations, we found that the bioaccumulation by D. magna were strongly influenced by the extrinsic properties of NPs as well as the biological uptake characteristics of D. magna. New sets of effective dosimetry parameters well correlated with the amount of NPs bioaccumulated within D. magna were also proposed. Based on these findings, we suggested that the extrinsic physicochemical properties of NPs (e.g., interfacial and colloidal properties of NPs) and biological characteristics for NPs (e.g., uptake cutoff sizes of testing organisms) should be considered and included when developing alternative dosimetry of NPs.

The effects of sedimentation and dissolution on the cytotoxicity of Ag nanoparticles.

Nanoparticles (NPs) are being employed for various industrial purposes with increasing frequency, yet the adverse health effects associated with the prolonged exposure of humans and the environment to NPs has not been well-established. Particularly, the effects of the extrinsic (or dynamic) physicochemical properties of NPs in aqueous cell culture media (e.g., hydrodynamic size, aggregation, agglomeration, sedimentation, and dissolution of nanoparticles) on the cytotoxicities of the NPs are barely understood. In this study, to investigate the effects of two important extrinsic properties of Ag NPs, namely the sedimentation and dissolution of Ag NPs, we performed MTT cell viability tests for HeLa cells exposed to Ag NPs with varying extrinsic properties. Ag NPs with different hydrodynamic sizes, sedimentation rates, and dissolution rates were prepared via exposure to NaCl and FBS. Sedimentation of aggregated/agglomerated Ag NPs was found to contribute more significantly to the cytotoxicity of Ag NPs during early periods of exposure, whereas the cytotoxicity was more greatly enhanced later during the exposure period due to the increase in silver ions. Therefore, it is offered that any assessment of NP cytotoxicity should consider the extrinsic properties of NPs, and their time-dependent properties, because the dominant processes affecting NP cytotoxicity may change over time and lead to a misunderstanding or poor prediction of NP cytotoxicity.

Synaptic vesicle protein 2b is expressed temporospatially in (pre)odontoblasts in developing molars.

The formation of dentin and enamel is initiated by the differentiation of odontogenic precursor cells into odontoblasts and ameloblasts, respectively. This study was performed to identify new molecules involved in the differentiation of odontogenic cells. The genes expressed differentially between the root stage (after the differentiation of odontogenic cells and dental hard-tissue formation) and the cap stage (before the differentiation of odontogenic cells and dental hard-tissue formation) were searched using differential display PCR. For the first time, synaptic vesicle protein (SV) 2b, an important transmembrane transporter of Ca(2+) -stimulated vesicle exocytosis, was identified as a differentially expressed molecule. Real-time PCR and western blotting revealed an increase in the transcriptional and translational levels of SV2b during or after the differentiation of odontogenic cells. Immunofluorescence revealed this molecule to be localized in not only fully differentiated odontoblasts but also in pre-odontoblasts before dentin matrix secretion. The expression pattern of the SV2a isoform was similar to that of the SV2b isoform, whereas the SV2c isoform showed a contrasting pattern of expression. After treatment with alendronate, an inhibitor of protein isoprenylation for the transport of secretory vesicles, the expression of SV2a and SV2b decreased, whereas that of SV2c increased. These results suggest that the SV2 isoforms are functional molecules of (pre)odontoblasts which may be involved in vesicle transport.