Effects of Soil Composition on Zn Speciation in Drainage Waters from Agricultural Soils

The influence of Zn speciation on Zn transport by drainage from different soils to surface water is examined in a stream catchment in an agricultural area. Drainage waters were collected from two types of soils, a mineral soil (MS) and a soil rich in organic matter (OS) by means of artificial drainage pipes. The speciation of dissolved Zn in the stream and the drainage waters was determined using ligand-exchange and voltammetry. About 50-95% of dissolved Zn is bound in strong complexes, and the free Zn2+ ion concentration is in the range of 1-16% of dissolved Zn. A substantial part of Zn is present in weaker organic or inorganic complexes. The simulated Zn speciation using the WHAM VI model is compared to the determined speciation. Free Zn2+ concentrations predicted by the WHAM VI model are generally higher than the analytically determined free Zn2+, but are mostly within the same order of magnitude. Effects of different soil organic matter content on Zn speciation and transport are discussed. Zn speciation in the drainage at the OS site is influenced by the distribution of organic matter between the solid and solution phase. The abundant organic Zn complexes in solution contribute to facilitate Zn transport from soil into surface waters, through the drainage at the OS site. Drainage from the OS site contributes about twice as much Zn input to the receiving water as the MS soil, as related to specific area. The mineral soil contains much lower organic matter, and a part of Zn bound with inorganic phases can hardly be released by dissolved organic ligands, leading to much higher Zn retention at the MS sit

A Ligand Exchange Model for the Adsorption of Inorganic and Organic Ligands at Hydrous Oxide Interfaces

Specific adsorption of organic and inorganic weak acids and of anions on hydrous oxide surfaces and the concomitant influences upon surface charge can be interpreted as ligand exchange reactions at the reactive surface sites. Direct (inner sphere) binding of the ligands to the surface is postulated. The extent of adsorption and its pH dependence can be explained by considering the affinity of the surface sites and those of the ligands. Surface equilibrium constants have been determined experimentally for various surface reactions; they can be used to predict extent of adsorption and resulting surface charge. The adsorption of simple weak acids or their anions is largest around the pH value of pH = pK. The surface complex formation constants show the same trend in stability as the corresponding solute complex formation constants; thus surface coordination equilibrium constants can be estimated from the corresponding complex formation constants in solution

Effects of pH and Ca competition on complexation of cadmium by fulvic acids and by natural organic ligands from a river and a lake

The technique of competitive ligand-exchange/anodic stripping voltammetry (CLE-SV) was used to investigate effects of pH and Ca concentration on cadmium complexation by fulvic acid (FA), as well as Cd speciation in two different freshwaters, a hardwater Lake Greifen and a softwater River Wyre. Binding of Cd to Suwannee river FA (10mg/l) was determined at different pH (7-8.5) and in the presence of various concentration of Ca2+ (0-2mmol/l). The results from one-ligand discrete models were compared to simulations by the WHAM VI model. In Lake Greifen, the determined dissolved [Cd2+] ranged from 10−13 to 10−12mol/l, and the conditional stability constant with natural ligands was log K CdL about 9.5-10.5 (pH8.6-8.8) with ligand concentrations of 1.2-7.8×10−6mol/g C. In the softwater River Wyre, dissolved [Cd2+] ranged from 4×10−12 to 1×10−11mol/l, and the ligands were weaker (log K CdL 8.9-9.8, pH8.0) with lower ligand concentrations (0.9-2.3×10−6mol/g C). The titration curves of FA samples were close to the simulated curves by the WHAM VI model at pH8.0-8.5, but deviated more from the model at lower pH, indicating that the results determined with CLE-SV for Cd-FA complexation are relevant to the data base in the model. Calculation of the Ca competition for Cd binding by FA showed a competition effect of similar strength as the measured one, but indicated a systematic difference between measured and modeled data at pH7.5. Using the WHAM model for comparison with FA, the complexation of Cd by the River Wyre ligands was close to that of FA, whereas stronger complexation was observed in the Lake Greifen water. These differences may originate from different ligand composition in the lake and the rive

Adsorption of Copper, Nickel, and Cadmium on Goethite in the Presence of Organic Ligands

Adsorption of copper, cadmium and nickel at low concentrations on goethite was studied in the presence of the simple organic ligands oxalate, salicylate, and pyromellitate. The experimental metal adsorption behavior was compared to calculations with a surface complexation model to evaluate the most important interactions. Oxalate mostly decreased Cu and Ni adsorption at high pH-values by competition between solution and surface complexation but had no effect on Cd adsorption. Cu adsorption in the presence of oxalate below pH 6 could best be described by defining a ternary complex of type A (surface-metal-ligand). Salicylate had only minor effects on metal adsorption. The adsorption of Cu in the presence of salicylate above pH 5 could be explained by a ternary complex of type A. Pyromellitate increased the adsorption of Cu and Cd in the acidic pH-range, likely by formation of ternary surface complexes of type B (surface-ligand-metal

Characterization of extracellular polymeric substances (EPS) from periphyton using liquid chromatography-organic carbon detection-organic nitrogen detection (LC-OCD-OND)

A protocol was developed to extract, fractionate, and quantitatively analyze periphyton extracellular polymeric substances (EPS), which obtains both information on the molecular weight (M r) distribution and protein and polysaccharide content. The EPS were extracted from freshwater periphyton between July and December 2011. Organic carbon (OC) compounds from different EPS extracts were analyzed using liquid chromatography-organic carbon detection-organic nitrogen detection (LC-OCD-OND), and total protein and polysaccharide content were quantified. Four distinct OC fractions, on the basis of M r, were identified in all extracts, corresponding to high M r biopolymers (≥80-4kDa), degradation products of humic substances (M r not available), low M r acids (10-0.7kDa), and small amphiphilic/neutral compounds (3-0.5kDa). Low C/N ratios (4.3 ± 0.8) were calculated for the biopolymer fractions, which represented 16-38% of the measured dissolved organic carbon (DOC), indicating a significant presence of high M r proteins in the EPS. Protein and polysaccharide represented the two major components of EPS and, when combined, accounted for the measured DOC in extracts. Differences in specific OC fractions of EPS extracts over the course of the study could be quantified using this method. This study suggests that LC-OCD-OND is a new valuable tool in EPS characterization of periphyto

The Fate of Trace Pollutants in Natural Waters – Lakes as 'Real-World Test Tubes'

Lakes play an important role as ecosystems and drinking-water supplies, but they are also ideal 'real-world test tubes' for studying the fate and behavior of trace pollutants in natural waters. The trace metals Cu, Zn, and Cd and the organic herbicide atrazine are used to illustrate the combined approach of field measurements and mathematical modeling to assess the behavior of pollutants in natural waters. In contrast to fast flowing waters (i.e., rivers), lakes act as integrators of pollutant inputs from surface waters of the respective catchment area, thus being regional indicators of human activities

Sorption Phenomena at Environmental Solid Surfaces

Sorption phenomena from the aqueous and from the gaseous phase to solid surfaces play an important role for the fate of inorganic and organic compounds and of bacteria in the environment. Case studies illustrating the role of different sorption mechanisms for various classes of compounds and for bacteria are presented. They show that sorption at solid surfaces ranges from weak unspecific interactions to very specific and strong complexation. Strong surface complexation in particular affects the surface reactivity. Studies of model systems provide a conceptual framework to understand and predict the behavior of substances and of bacteria in complex environmental systems, such as aquifers and sediments

Original biographies from the Dictionary of African Christian Biography

A publication of the Dictionary of African Christian Biography with U.S. offices located at the Center for Global Christianity and Mission at Boston University. The editors are pleased to offer the first annual cumulative volume of the Journal of African Christian Biography, the monthly scholarly publication that was launched in June of 2016. Since then, the life stories of twelve individuals who played vital roles in and through their faith communities have been published online as free downloads. But it is important that a selection of DACB stories be more readily available to those without access to the internet. As I mentioned in the fall 2016 newsletter of the DACB, each issue of the journal is available in its e-journal, on-line version, where it is configured either as A4 or 8.5 x 11 format printable as booklets, ready for local printing and binding or stapling. Our intention is to make it easy for academics and church leaders in various parts of Africa to make print copies of the journal available to their students, colleagues or church members. And so it is with this cumulative volume.This issue focuses on: 1. "Walatta Petros and Hakalla Amale, Pious Women of Ethiopia," with commentary by Dr. Jonathan Bonk, Project Director. 2. Walatta Petros. 3. Hakalla Amale. 4. Bishop Josiah Kibira of Tanzania, Ecumenical Statesman. 5. Josiah Mutabuzi Isaya Kibira. 6. Josiah Kibira. 7. David Lonkibiri Windibiziri. 8. Abiodun Babatunde Lawrence. 9. Dominic Ignatius Ekandem. 10. William Wadé Harris, Prophet-Evangelist of West Africa: His Life, Message, Praxis, Heritage, and Legacy. 11. William Wadé Harris. 12. Michael Timneng and Jeremiah Chi Kangsen: Christianity Beyond the Missionary Presence in Cameroon. 13. Michael Timneng. 14. Jeremiah Chi Kangsen. 15. Rainisoalambo, Ravelonjanahary, and Volahavana Germaine (Nenilava): Revival Leaders of Madagascar. 16. Rainisoalambo. 17. Ravelonjanahary. 18. Volahavana Germaine (Nenilava). 19. Recent Print and Digital Resourcews Related to Christianity in Africa

Environmental behavior and ecotoxicity of engineered nanoparticles to algae, plants, and fungi

Developments in nanotechnology are leading to a rapid proliferation of new materials that are likely to become a source of engineered nanoparticles (ENPs) to the environment, where their possible ecotoxicological impacts remain unknown. The surface properties of ENPs are of essential importance for their aggregation behavior, and thus for their mobility in aquatic and terrestrial systems and for their interactions with algae, plants and, fungi. Interactions of ENPs with natural organic matter have to be considered as well, as those will alter the ENPs aggregation behavior in surface waters or in soils. Cells of plants, algae, and fungi possess cell walls that constitute a primary site for interaction and a barrier for the entrance of ENPs. Mechanisms allowing ENPs to pass through cell walls and membranes are as yet poorly understood. Inside cells, ENPs might directly provoke alterations of membranes and other cell structures and molecules, as well as protective mechanisms. Indirect effects of ENPs depend on their chemical and physical properties and may include physical restraints (clogging effects), solubilization of toxic ENP compounds, or production of reactive oxygen species. Many questions regarding the bioavailability of ENPs, their uptake by algae, plants, and fungi and the toxicity mechanisms remain to be elucidate