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The chemical and physical characteristics of humic acids (HA) may differ depending on their source, and the ideal extraction method should not modify the characteristics of HA. Hydrofluoric acid (HF) is often used in HA extraction methods to remove inorganic substances that are often present in the sample in addition to the organic molecules of interest. Organic soils contain up to 90% of organic matter and some may think that the necessity of the HF treatment is not crucial when extracting HA from organic soils. In this study, HA were extracted from turkey litter compost (TLC), an agricultural organic soil (AOS) and a riparian soil (RS), and the impact of HF on the properties of the extracted HA was assessed. HF decreased the ash content and the concentration of inorganic components in extracted materials, especially in the HA from RS, which had higher concentrations of aluminosilicates and amorphous Si. For TLC, no significant difference in either the total charge or charge distribution was observed with HF treated samples compared to untreated samples, while the HF treatment decreased the proton binding capacity at alkaline pH (.7) in the HA from the two soils. We assume that aluminosilicates, amorphous Si and iron oxides left in the samples interacted with protons at alkaline pH, thus increasing the proton binding capacity. Therefore, HF treatment should be included when samples containing these mineral constituents even for materials rich in organic matter.

High resolution fluorescence and fluorescence excitation spectra of all-trans-2,4,6,8,10,12,14-hexadecaheptaene have been obtained in n pentadecane at 10 K. The most prominent vibronic features, like those in spectra of shorter polyene hydrocarbons, are due to combinations of symmetric carbon–carbon stretching vibrations. These in turn are dominated by a double bond mode whose frequency increases from 1555 to 1782 cm-1 upon electronic excitation (1 1Ag→2 1Ag). This 227 cm-1 increase, the largest yet observed in polyene spectroscopy, can be explained by vibronic coupling between the ground and first excited singlets. The possible role of vibrational mixing due to mutual polarizibilities between carbon–carbon bonds also is discussed. [ABSTRACT FROM AUTHOR]

Speciation of copper in marine systems strongly influences the ability of copper to cause toxicity. Natural organic matter (NOM) contains many binding sites which provides a protective effect on copper toxicity. The purpose of this study was to characterize copper binding with NOM using fluorescence quenching techniques. Fluorescence quenching of NOM with copper was performed on nine sea water samples. The resulting stability constants and binding capacities were consistent with literature values of marine NOM, showing strong binding with $$\log K$$ values from 7.64 to 10.2 and binding capacities ranging from 15 to 3110 nmol mg $${\text {C}}^{-1}.$$ Free copper concentrations estimated at total dissolved copper concentrations corresponding to previously published rotifer effect concentrations, in the same nine samples, were statistically the same as the range of free copper calculated for the effect concentration in NOM-free artificial seawater. These data confirms the applicability of fluorescence spectroscopy techniques for NOM and copper speciation characterization in sea water and demonstrates that such measured speciation is consistent with the chemical principles underlying the biotic ligand model approach for bioavailability-based metals risk assessment. [ABSTRACT FROM AUTHOR]

We conducted a survey of 1707 children in 141 impoverished rural areas of Guizhou and Sichuan Provinces in Southwest China. Kato-Katz smear testing of stool samples elucidated the prevalence of ascariasis, trichuriasis and hookworm infections in pre-school and school aged children. Demographic, hygiene, household and anthropometric data were collected to better understand risks for infection in this population. 21.2 percent of pre-school children and 22.9 percent of school aged children were infected with at least one of the three types of STH. In Guizhou, 33.9 percent of pre-school children were infected, as were 40.1 percent of school aged children. In Sichuan, these numbers were 9.7 percent and 6.6 percent, respectively. Number of siblings, maternal education, consumption of uncooked meat, consumption of unboiled water, and livestock ownership all correlated significantly with STH infection. Through decomposition analysis, we determined that these correlates made up 26.7 percent of the difference in STH infection between the two provinces. Multivariate analysis showed that STH infection is associated with significantly lower weight-for-age and height-for-age z- scores; moreover, older children infected with STHs lag further behind on the international growth scales than younger children. [ABSTRACT FROM AUTHOR]

The copper sensitivity of four saltwater invertebrates (the mussel Mytilus galloprovincialis, the oyster Crassostrea virginica, the sand dollar Dendraster excentricus, and the sea urchin Strongylocentrotus purpuratus) was determined experimentally using chronic-estimator embryo-larval test procedures. The effect of sample dissolved organic matter (DOM) content on Cu bioavailability was determined for these species using commonly prescribed test procedures. Comparisons were made among these test results and test results reported previously for two other invertebrate species: the mussel Mytilus edulis and the copepod Eurytemora affinis. All six species exhibited a direct and significant relationship between the sample dissolved organic carbon (DOC; a surrogate measure of DOM) and either the dissolved Cu median lethal concentration (LC50) values or median effect concentration (EC50) values. This relationship is significant even when the DOM has different quality as evidenced by molecular fluorescence spectroscopy. Once normalized for the effects of DOM, the Cu sensitivity of these species from least to most sensitive were E. affinis < D. excitricus < C. virginica ≈ S. purpuratus ≈ M. edulis ≈ M. galloprovincialis. This ranking of species sensitivity differs from the saltwater species sensitivity distribution proposed in 2003 by the U.S. Environmental Protection Agency. These results support the need to account for factors that modify Cu bioavailability in future saltwater Cu criteria development efforts. More specifically, Cu saltwater species sensitivity distribution data will need to be normalized by factors affecting Cu bioavailability to assure that accurate and protective criteria are subsequently developed for saltwater species and their uses. Environ. Toxicol. Chem. 2010;29:311–319. © 2009 SETAC [ABSTRACT FROM AUTHOR]

The surface binding site characteristics and Ni sorptive capacities of synthesized hydrous Mn oxyhydroxides experimentally conditioned to represent three hydrological conditions—MnOXW, freshly precipitated; MnOXD, dried at 37°C for 8 d; and MnOXC, cyclically hydrated and dehydrated (at 37°C) over a 24-h cycle for 7 d—were examined through particle size analysis, surface acid-base titrations and subsequent modelling of the pKa spectrum, and batch Ni sorption experiments at two pH values (2 and 5). Mineralogical bulk analyses by XRD indicate that all three treatments resulted in amorphous Mn oxyhydroxides; i.e., no substantial bulk crystalline phases were produced through drying. However, drying and repeated wetting and drying resulted in a non-reversible decrease in particle size. In contrast, total proton binding capacities determined by acid-base titrations were reversibly altered with drying and cyclically re-wetting and drying from 82 ± 5 μmol/m2 for the MnOXW to 21 ± 1 μmol/m2 for the MnOXD and 37 ± 5 μmol/m2 for the MnOXC. Total proton binding sites measured decreased by &ap;75% with drying from the MnOXW and then increased to &ap;50% of the MnOXW value in the MnOXC. Thus, despite a trend of higher surface area for the MnOXD, a lower total number of sites was observed, suggesting a coordinational change in the hydroxyl sites. Surface site characterization identified that changes also occurred in the types and densities of surface sites for each hydrologically conditioned Mn oxyhydroxide treatment (pH titration range of 2–10). Drying decreased the total number of sites as well as shifted the remaining sites to more acidic pKa values. Experimentally determined apparent pHzpc values decreased with drying, from 6.82 ± 0.06 for the MnOXW to 3.2 ± 0.3 for the MnOXD and increased again with rewetting to 5.05 ± 0.05 for the MnOXC. Higher Ni sorption was observed at pH 5 for all three Mn oxyhydroxide treatments compared to pH 2. However, changes in relative sorptive capacities among the three treatments were observed for pH 2 that are not explainable simply as a function of total binding site density or apparent pHzpc values. These results are the first to our knowledge, to quantitatively link the changes induced by hydrologic variability for surface acid base characteristics and metal sorption patterns. Further, these results likely extend to other amorphous minerals, such as Fe oxyhydroxides, which are commonly important geochemical solids for metal scavenging in natural environments. [Copyright &y& Elsevier]

A modified regularized least squares pKa spectrum approach is applied to determine disassociation constants and proton binding site concentrations on bacteria, hydrous ferric oxide (HFO), and bacteria/HFO composite surfaces. This involves fitting experimental acid–base titration data to a continuous binding site model for a chemically heterogeneous surface with a variety of reactive groups yielding a pKa spectrum. The modified parameter fitting method optimizes simultaneously for both smoothness of the pKa spectrum and goodness of fit, whereas other methods optimize for goodness of fit given a fixed smoothness factor. Uncertainty estimates in pKa spectra were made by taking the mean and standard deviation of the spectra from replicate titration data. Titration of Shewanella putrefaciens strain CN32, a facultative iron-reducing bacterial species, demonstrate five types of binding sites consistent with known cell surface groups on bacteria, with mean pKa values of 3.62, 4.97, 6.92, 8.22, and 9.97. Composite surfaces formed by precipitation of HFO onto bacteria surfaces were also titrated. These surfaces no longer yielded low pKa sites in pKa spectra, indicating that ferric iron interacts with the bacteria via carboxylic (low pKa) sites during precipitation. In addition, mechanically mixed HFO bacterial samples also showed removal of carboxylic binding sites, suggesting that solid phase HFO interacts directly with carboxylic sites on bacterial cells. Moreover, the pKa spectra for HFO bacterial composites were not dependent on how the composite was formed; the mechanically mixed or surface-precipitated samples exhibited very similar binding site distributions. The determined pKa spectra imply that the overall binding mechanism for bacteria interactions with HFO involve carboxylic groups on the bacteria binding to the most basic sites on the HFO surface in approximately 1:1 stoichiometry. [Copyright &y& Elsevier]