Effects of Natural Organic Matter Properties on the Dissolution Kinetics of Zinc Oxide Nanoparticles

The dissolution of zinc oxide (ZnO) nanoparticles (NPs) is a key step of controlling their environmental fate, bioavailability, and toxicity. Rates of dissolution often depend upon factors such as interactions of NPs with natural organic matter (NOM). We examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs in buffered potassium chloride solution using anodic stripping voltammetry to directly measure dissolved zinc concentrations. The observed dissolution rate constants (<i>k</i>_obs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg C L^–1) for Suwannee River humic and fulvic acids and Pony Lake fulvic acid. When dissolution rates were compared for the 16 NOM isolates, <i>k</i>_obs was positively correlated with certain properties of NOM, including specific ultraviolet absorbance (SUVA), aromatic and carbonyl carbon contents, and molecular weight. Dissolution rate constants were negatively correlated to hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. The findings of this study facilitate a better understanding of the fate of ZnO NPs in organic-rich aquatic environments and highlight SUVA as a facile and useful indicator of NOM interactions with metal-based nanoparticles

Trends in the Rare Earth Element Content of U.S.-Based Coal Combustion Fly Ashes

Rare earth elements (REEs) are critical and strategic materials in the defense, energy, electronics, and automotive industries. The reclamation of REEs from coal combustion fly ash has been proposed as a way to supplement REE mining. However, the typical REE contents in coal fly ash, particularly in the United States, have not been comprehensively documented or compared among the major types of coal feedstocks that determine fly ash composition. The objective of this study was to characterize a broad selection of U.S. fly ashes of varied geological origin in order to rank their potential for REE recovery. The total and nitric acid-extractable REE content for more than 100 ash samples were correlated with characteristics such as the major element content and coal basin to elucidate trends in REE enrichment. Average total REE content (defined as the sum of the lanthanides, yttrium, and scandium) for ashes derived from Appalachian sources was 591 mg kg^–1 and significantly greater than in ashes from Illinois and Powder River basin coals (403 and 337 mg kg^–1, respectively). The fraction of critical REEs (Nd, Eu, Tb, Dy, Y, and Er) in the fly ashes was 34–38% of the total and considerably higher than in conventional ores (typically less than 15%). Powder River Basin ashes had the highest extractable REE content, with 70% of the total REE recovered by heated nitric acid digestion. This is likely due to the higher calcium content of Powder River Basin ashes, which enhances their solubility in nitric acid. Sc, Nd, and Dy were the major contributors to the total REE value in fly ash, based on their contents and recent market prices. Overall, this study shows that coal fly ash production could provide a substantial domestic supply of REEs, but the feasibility of recovery depends on the development of extraction technologies that could be tailored to the major mineral content and origins of the feed coal for the ash

ASV-labile Znin filtered vent fluid samples collected from the ELSC and in filtered samples amended with 0

5 μM Cu(II) prior to analysis for ASV-labile Zn.<p><b>Copyright information:</b></p><p>Taken from "Formation of Zn- and Fe-sulfides near hydrothermal vents at the Eastern Lau Spreading Center: implications for sulfide bioavailability to chemoautotrophs"</p><p>http://www.geochemicaltransactions.com/content/9/1/6</p><p>Geochemical Transactions 2008;9():6-6.</p><p>Published online 19 May 2008</p><p>PMCID:PMC2396607.</p><p></p

Naturally Occurring Radioactive Materials in Coals and Coal Combustion Residuals in the United States

The distribution and enrichment of naturally occurring radioactive materials (NORM) in coal combustion residuals (CCRs) from different coal source basins have not been fully characterized in the United States. Here we provide a systematic analysis of the occurrence of NORM (²³²Th, ²²⁸Ra, ²³⁸U, ²²⁶Ra, and ²¹⁰Pb) in coals and associated CCRs from the Illinois, Appalachian, and Powder River Basins. Illinois CCRs had the highest total Ra (²²⁸Ra + ²²⁶Ra = 297 ± 46 Bq/kg) and the lowest ²²⁸Ra/²²⁶Ra activity ratio (0.31 ± 0.09), followed by Appalachian CCRs (283 ± 34 Bq/kg; 0.67 ± 0.09), and Powder River CCRs (213 ± 21 Bq/kg; 0.79 ± 0.10). Total Ra and ²²⁸Ra/²²⁶Ra variations in CCRs correspond to the U and Th concentrations and ash contents of their feed coals, and we show that these relationships can be used to predict total NORM concentrations in CCRs. We observed differential NORM volatility during combustion that results in ²¹⁰Pb enrichment and ²¹⁰Pb/²²⁶Ra ratios greater than 1 in most fly-ash samples. Overall, total NORM activities in CCRs are 7–10- and 3–5-fold higher than NORM activities in parent coals and average U.S. soil, respectively. This study lays the groundwork for future research related to the environmental and human health implications of CCR disposal and accidental release to the environment in the context of this elevated radioactivity

Relative Contributions of Copper Oxide Nanoparticles and Dissolved Copper to Cu Uptake Kinetics of Gulf Killifish (<i>Fundulus grandis</i>) Embryos

The toxicity of soluble metal-based nanomaterials may be due to the uptake of metals in both dissolved and nanoparticulate forms, but the relative contributions of these different forms to overall metal uptake rates under environmental conditions are not quantitatively defined. Here, we investigated the linkage between the dissolution rates of copper­(II) oxide (CuO) nanoparticles (NPs) and their bioavailability to Gulf killifish (<i>Fundulus grandis</i>) embryos, with the aim of quantitatively delineating the relative contributions of nanoparticulate and dissolved species for Cu uptake. Gulf killifish embryos were exposed to dissolved Cu and CuO NP mixtures comprising a range of pH values (6.3–7.5) and three types of natural organic matter (NOM) isolates at various concentrations (0.1–10 mg-C L^–1), resulting in a wide range of CuO NP dissolution rates that subsequently influenced Cu uptake. First-order dissolution rate constants of CuO NPs increased with increasing NOM concentration and for NOM isolates with higher aromaticity, as indicated by specific ultraviolet absorbance (SUVA), while Cu uptake rate constants of both dissolved Cu and CuO NP decreased with NOM concentration and aromaticity. As a result, the relative contribution of dissolved Cu and nanoparticulate CuO species for the overall Cu uptake rate was insensitive to NOM type or concentration but largely determined by the percentage of CuO that dissolved. These findings highlight SUVA and aromaticity as key NOM properties affecting the dissolution kinetics and bioavailability of soluble metal-based nanomaterials in organic-rich waters. These properties could be used in the incorporation of dissolution kinetics into predictive models for environmental risks of nanomaterials

Total acid-volatile sulfide (AVS), total Fe and total Zn concentrations in high temperature ( 250°C) vent fluid samples collected along the north-to-south ELSC ridge axis

The bars represent average ± one standard deviation (n = 2 to 5). The average [Fe]:[Zn]ratio is also noted for each site.<p><b>Copyright information:</b></p><p>Taken from "Formation of Zn- and Fe-sulfides near hydrothermal vents at the Eastern Lau Spreading Center: implications for sulfide bioavailability to chemoautotrophs"</p><p>http://www.geochemicaltransactions.com/content/9/1/6</p><p>Geochemical Transactions 2008;9():6-6.</p><p>Published online 19 May 2008</p><p>PMCID:PMC2396607.</p><p></p

A) Temperature, b) acid-volatile sulfide (AVS), c) total Fe(II) Fe(III), and d) total Zn as a function of pH in unfiltered and filtered vent fluids collected from ELSC vent fields located in basalt-hosted and andesite-hosted sites

<p><b>Copyright information:</b></p><p>Taken from "Formation of Zn- and Fe-sulfides near hydrothermal vents at the Eastern Lau Spreading Center: implications for sulfide bioavailability to chemoautotrophs"</p><p>http://www.geochemicaltransactions.com/content/9/1/6</p><p>Geochemical Transactions 2008;9():6-6.</p><p>Published online 19 May 2008</p><p>PMCID:PMC2396607.</p><p></p

Boron and Strontium Isotopic Characterization of Coal Combustion Residuals: Validation of New Environmental Tracers

In the U.S., coal fired power plants produce over 136 million tons of coal combustion residuals (CCRs) annually. CCRs are enriched in toxic elements, and their leachates can have significant impacts on water quality. Here we report the boron and strontium isotopic ratios of leaching experiments on CCRs from a variety of coal sources (Appalachian, Illinois, and Powder River Basins). CCR leachates had a mostly negative δ¹¹B, ranging from −17.6 to +6.3‰, and ⁸⁷Sr/⁸⁶Sr ranging from 0.70975 to 0.71251. Additionally, we utilized these isotopic ratios for tracing CCR contaminants in different environments: (1) the 2008 Tennessee Valley Authority (TVA) coal ash spill affected waters; (2) CCR effluents from power plants in Tennessee and North Carolina; (3) lakes and rivers affected by CCR effluents in North Carolina; and (4) porewater extracted from sediments in lakes affected by CCRs. The boron isotopes measured in these environments had a distinctive negative δ¹¹B signature relative to background waters. In contrast ⁸⁷Sr/⁸⁶Sr ratios in CCRs were not always exclusively different from background, limiting their use as a CCR tracer. This investigation demonstrates the validity of the combined geochemical and isotopic approach as a unique and practical identification method for delineating and evaluating the environmental impact of CCRs

Anodic stripping square wave voltammograms of Ar-purged sample in the absence and presence of 0

5 μM Cu(II). a) 2.0 μM ZnS model solution (0.1 M KCl, pH 7.6). The deposition step occurred for 10 s at -1.3 V. b) Filtered diffuse-flow vent fluid from Tow Cam (TC-159-2), which contained approximately 0.1 μM labile Znprior to Cu(II) addition. The deposition step occurred for 120 s at -1.3 V. The half-wave potentials (vs. SCE) for the metal analytes are -1.0 V for Znand -0.18 V for Cu.<p><b>Copyright information:</b></p><p>Taken from "Formation of Zn- and Fe-sulfides near hydrothermal vents at the Eastern Lau Spreading Center: implications for sulfide bioavailability to chemoautotrophs"</p><p>http://www.geochemicaltransactions.com/content/9/1/6</p><p>Geochemical Transactions 2008;9():6-6.</p><p>Published online 19 May 2008</p><p>PMCID:PMC2396607.</p><p></p

Zn concentration as determined by anodic stripping voltammetry in model Zn-sulfide solutions containing 2 μM ZnS, 2 μM ZnS 2

5 μM cysteine (CYS), and 2 μM Zn + 2.5 μM CYS (all model solutions prepared in 0.1 M KCl, 4 mM HEPES buffer, pH 7.6). (a) ASV-labile Zn in unfiltered solutions before and after addition of 0.5 μM Cu(II). Addition of Cu(II) caused oxidative dissolution of ZnS; (b) ASV-labile and total Zn quantified in filtered (< 0.2 μm) solutions.<p><b>Copyright information:</b></p><p>Taken from "Formation of Zn- and Fe-sulfides near hydrothermal vents at the Eastern Lau Spreading Center: implications for sulfide bioavailability to chemoautotrophs"</p><p>http://www.geochemicaltransactions.com/content/9/1/6</p><p>Geochemical Transactions 2008;9():6-6.</p><p>Published online 19 May 2008</p><p>PMCID:PMC2396607.</p><p></p