Es wurde eine Arsenkontamination von Boden und Grundwasser im Bereich einer Zellstofffabrik untersucht, die auf Ablagerungen von Eisenoxidschlacken (Rückstände aus der Pyritröstung) mit hohem Gehalt an verschiedenen Spurenelementen zurückzuführen ist. Der Standort ist dadurch gekennzeichnet, dass über viele Jahre Lösungen aus der Celluloseproduktion („Sulfitablauge“) versickerten. Hierdurch gelangten größere Mengen an Sulfat und organischen Stoffen in den Untergrund. Infolgedessen weist das Grundwasser einen stark reduzierten, sulfidischen Chemismus auf. Ein Großteil der Spurenelemente wurde aus der Schlacke im Oberboden in den darunter liegenden wassergesättigten Bereich transportiert und dort in Form von sulfidischen Niederschlägen festgelegt. Eine Ausnahme bildet Arsen, das unter den spezifischen Milieubedingungen im Schadenzentrum lösliche schwefelhaltige Verbindungen bildet (max. 4 mg As/L). Diese Arsen-Schwefel-Spezies wurden erstmals mit einer neu entwickelten IC-ICP/MS- Methode in einem Grundwasser nachgewiesen. Die Grundwasser- und Bodenuntersuchungen sowie begleitende hydrogeologische Messungen ergaben, dass die Arsen-Schwefel-Spezies innerhalb einer Fließstrecke von 30-80 m im Abstrom des Schadenzentrums vollständig immobilisiert werden. Bei der Festlegung von Arsen spielt die biologische Sulfatreduktion, die durch versickerte Sulfitablauge ermöglicht wurde, eine entscheidende Rolle. Anhand dieser Erkenntnisse wurde im Jahr 2000 ein natural attenuation-Konzept zur Sicherung des Standortes ausgearbeitet. Nach Auswertung der Ergebnisse der Standortuntersuchungen aus den Jahren 1999-2005 sowie einer Literaturrecherche zur Arsen-Schwefel-Chemie wurden die Struktur und das Verhalten der unbekannten Arsen-Schwefel-Spezies sowie die Vorgänge bei der Festlegung von Arsen im Boden genauer untersucht. Das wesentlichste Ergebnis der Arbeiten ist, dass in sulfidischen Systemen, z.B. in Grundwässern unter Sulfat reduzierenden Bedingungen, Thioarsenate gebildet werden. In Lehrbüchern und Fachpublikationen aus den vergangenen Jahrzehnten wurde bislang ausschließlich die Existenz von Thioarseniten vermutet. Ursache für die Bildung von Thioarsenaten ist eine hohe Affinität zwischen Arsen und Schwefel, die eine Oxidation von As(III) durch Anlagerung eines Schwefelatoms an dessen freiem Elektronenpaar „erzwingt“. In sulfidhaltigen Lösungen wird hierzu ein Teil des As(III) zu elementarem Arsen reduziert. Das zunächst gebildete Monothioarsenat wird weiter zu den schwefelhaltigeren Thioarsenaten sulfidiert. In sulfidischen Grundwässern bestimmen deshalb die Anionen von Oxomonothioarsenat, Oxodithioarsenat, Oxotrithioarsenat und Tetrathioarsenat das Verhalten von Arsen. Wesentlich für das Verständnis der Arsen-Schwefel-Chemie ist auch die Instabilität der As-SH-Gruppen, die entsprechend dem Dissoziationsverhalten der jeweiligen Arsen-Schwefel-Spezies gebildet werden. Dies erfolgt bei pH-Werten im Bereich von ca. 7-8,5, wobei die monomeren Anionen unter Abspaltung von Schwefelwasserstoff kondensieren. Infolgedessen muss in Grundwässern auch mit polymeren Thioarsenaten gerechnet werden. In saurer Lösung zerfallen die Thioarsenate in arsenige Säure und Schwefel bzw. fallen als Arsenpentasulfid aus. Arsen wird in sulfidischen Aquiferen als Sulfid (z.B. As4S4), als Arsenpyrit (FeAsS) oder durch Einbau von Arsen als Schwefelsubstituent in das Kristallgitter von Mackinawite bzw. Pyrit (FeS, FeS2) festgelegt. Die ermittelten Prozesse können ggf. zur Sanierung bzw. Sicherung von Standorten mit arsenhaltigen Rückständen im Boden bzw. von arsenbelasteten Grundwässern eingesetzt werden. Dabei ist auch von Bedeutung, dass Thioarsenate nach derzeitigem Kenntnisstand relativ gering toxisch sind. Im Umgang mit Thioarsenaten, z.B. auch bei der Analyse von Arsen in sulfidischen Proben, ist jedoch deren Umwandlung in arsenige Säure bei einer pH-Absenkung und auch bei Sauerstoffzutritt zu berücksichtigen. Die biologische Sulfatreduktion spielt eine wesentlich größere Rolle für die Mobilität von Arsen in Grundwässern als bisher angenommen. Im Hinblick auf die weltweit große gesundheitliche Relevanz von Arsen im Trinkwasser und auf mögliche Sanierungsverfahren sollten die Umsetzungen von Arsen unter Sulfat reduzierenden Bedingungen eingehender untersucht werden. / The motivation for the thesis was a project at an industrial site conducted in 1999 to define a remediation concept for soil and groundwater contaminated with arsenic. The contamination resulted from the deposition of residuals from pyrite burning (iron oxides containing different trace elements) in the upper soil many years ago. Because of long-term pollution with process waters rich in organic substances and sulfate, the aquifer is strongly reduced (sulfidic). Most of the arsenic was transferred out of the contaminated soil into the saturated zone in a depth of 7-10 m. There it is partly immobilized as sulfide precipitations, but part of it is solved in the groundwater in form of arsenic-sulfur-complexes (up to 4 ppm). These complexes were detected for the first time in a groundwater by means of an improved IC-ICP-MS method. It was also found that approx. 80 m downstream of the contaminated spot the concentrations of arsenic in soil and groundwater were not increased. On this basis a natural attenuation concept was proposed in 2000. The data from the investigated site was evaluated and specific laboratory tests were carried out in order to identify the unknown arsenic species as well as the processes which lead to their immobilization in the aquifer. The key role of the soluble arsenic-sulfur complexes for the mobility and toxicity of arsenic in sulfate-reducing environments is commonly accepted. In the past, thioarsenites were assumed to be the existing species in sulfidic systems. In this study, however, thioarsenates were identified in solutions spiked with in arsenite and hydrogen sulfide as well as in the contaminated groundwater. The unexpected finding of an oxidation of arsenite to thioarsenates in strongly reducing systems can be explained by the high affinity between As(III) and sulfur. In sulfide containing solutions without any oxidant, arsenite therefore undergoes disproportionation to thioarsenates and elemental arsenic. This was already found out in the 19th century, but has been neglected in publications from the last decades. According to the results of this study the anions of oxomonothioarsenate, oxodithioarsenate, oxotrithioarsenate und tetrathioarsenate are the dominating arsenic species in sulfidic waters. The partitioning of the four species is governed mainly by the sulfide concentration. Beside the high affinity between arsenic and sulfur, the instability of the As-SH group is essential to understand the reactions in the arsenic-sulfur system. As soon as the arsenic-sulfur complexes form As-SH groups (according to their dissociation characteristics) they condensate in separating hydrogen sulfide. Thioarsenates form polymers in the pH range of approx. 7-8.5. Therefore beside the mentioned monomers, thioarsenate polymers can also be important in natural environments. In more acidic solutions they decay into arsenite and sulfur or precipitate as arsenic-pentasulfide. When analyzing arsenic in sulfide containing solutions, it has always to be taken into account that thioarsenates are highly sensitive to oxygen and pH. Therefore, e.g. arsenic speciation by means of HG-AAS is not suitable for sulfidic waters and can wrongly indicate a mixture of arsenite and arsenate. It has previously been supposed that the mobility as well as the toxicity of arsenic increase if the redox state decreases. For sulfidic waters the opposite is probably the case owing to the formation of thioarsenates. The toxicity of arsenite is due to the high reactivity of the As(III) towards sulfohydroxyl groups in proteins. Without a free electron pair and sulfur already incorporated, thioarsenates should be less toxic compared to arsenite. Arsenic can be mobilized out of contaminated soils in form of thioarsenates via infiltration of sulfide solutions or by input of sulfate and biodegradable organic matter. In the presence of iron, thioarsenates can be fixated in sulfidic aquifers as a minor substitute in mackinawite and biogenic pyrite or as arsenic pyrite. Bacterial sulfate reduction is a crucial factor for the mobilization and immobilization of arsenic in reduced aquifers. Considering the negative health impacts of arsenic for millions of people worldwide, as well as the implementation of the mentioned remediation strategies the arsenic-sulfur chemistry deserves closer attention.

Elevated arsenic content in food crops pose a serious human health risk. Apart from rice wheat being another main food crop is possibly cultivated on contaminated sites. But for wheat uptake mechanisms are not entirely understood especially with regard to nutrient fertilization and different moisture regimes taking into account heavy rainfall events due to climate change. Here we show that especially higher P-fertilization under changing redox conditions may enhance arsenic uptake. This counteracts with higher N-fertilization reducing arsenic transfer and translocation into aboveground plant parts for both higher P-fertilization and reducing soil conditions. Arsenic speciation did not change in grain but for leaves P-fertilization together with reducing conditions increased the As(V) content compared to other arsenic species. Our results indicate important dependencies of nutrient fertilization, moisture conditions and substrate type on As accumulation of wheat as one of the most important crop plants worldwide with implications for agricultural practices.

Hair is an excellent matrix for monitoring trace elements and minerals in the body. To long-term changes in concentration of elements in the body are reflected in their value in her hair, so the assessment of the organism from the mineral analysis of hair is a very suitable method. This method is widely used in toxicological testing and forensics. This work deals with the analysis of Mg, K, Fe, Zn, Mn, Se, As, Cd and Pb in 100 samples by ICP-MS. It is a male hair samples with the age range 19 – 74 years. Analysis of hair revealed that concentrations of individual elements are moving in a narrow range of values. Values of older age category are in some case significantly deflective.

This thesis describes the optimization of the method for determination of arsenic by the chemical hydride generation coupled with AAS detection in beer samples and raw materials for its preparation. The beer usually contain arsenic at ultratrace level, however, it is necessary to monitor the concentration of this element in the beer. The routinely used method for determination of arsenic is determination by electrothermal atomization. This approach is time consuming, expensive and less sensitive. It has been developer suitable determination of arsenic as a faster and less expensive method. For this method there was optimized the flow rate of argon to 75 ml·min-1, the optimum flow rate for the reagents was 4.0 ml·min-1 and for the sample 5.0 ml·min-1 . 3 % NaBH4 in 0.5 % NaOH was used as the reducing agent for the determination of arsenic, and HCl diluted 1:1 with distilled water was used to acidify the sample. With this parameter LOD was 0.32 μg·l-1 and LOQ 1.05 μg·l-1 . It has been tested the arsenic determination in samples of barley, malt and potable water as beer raw materials. It has been found that the beer matrix is unsuitable for the hydride generation technique due to a stormy reaction in the gas/liquid phase separator. The effect of pretreatment, which is likely to enhance the effect of...

Heavy metal contamination significantly reduces crop yields, causing serious problems in agriculture and having a major impact on human health if these contaminants enter the food chain. Understanding the mechanisms of plant responses could help to increase their resistance to heavy metals as well as their potential use in phytoremediation. Carbohydrates play an important role in plant growth and development as well as in defense reactions. This work summarizes the results of four publications focused on the effects of arsenic and thorium on antioxidant mechanisms in tobacco plants and horseradish root crops. Attention is paid, among other things, to the dynamics of sugar contents, which are potentially important molecules involved in the fight against oxidative stress. The first publication summarizes arsenic effects on plant physiological parameters, focusing on arsenic tolerance-enhancing mechanisms as well as summarizing the ability of plants to cope with arsenic-induced oxidative and nitrosative stress. Emphasis was placed on, among other things, a topic that was unjustly neglected in previous publications - i.e. carbohydrate metabolism. Further work was already experimental and dealt with the study of arsenic as a trigger of oxidative stress in the root culture of horseradish and...

The objective of the work described in this thesis was to understand sorption reactions of uranium occurring at the water-clay mineral interfaces in the presence and absence of arsenic and other inorganic ligands. Uranium(VI) removal by clay minerals is influenced by a large number of factors including: type of clay mineral, pH, ionic strength, partial pressure of CO2, load of the sorbent, total amount of U present, and the presence of arsenate and other inorganic ligands such as sulfate, carbonate, and phosphate. Both sulfate and carbonate reduced uranium sorption onto IBECO bentonite due to the competition between SO42- or CO32- ions and the uranyl ion for sorption sites, or the formation of uranyl-sulfate or uranyl-carbonate complexes. Phosphate is a successful ligand to promote U(VI) removal from the aqueous solution through formation of ternary surface complexes with a surface site of bentonite. In terms of the type of clay mineral used, KGa-1b and KGa-2 kaolinites showed much greater uranium sorption than the other clay minerals (STx-1b, SWy-2, and IBECO montmorillonites) due to more aluminol sites available, which have higher affinity toward uranium than silanol sites. Sorption of uranium on montmorillonites showed a distinct dependency on sodium concentrations because of the effective competition between uranyl and sodium ions, whereas less significant differences in sorption were found for kaolinite. A multisite layer surface complexation model was able to account for U uptake on different clay minerals under a wide range of experimental conditions. The model involved eight surface reactions binding to aluminol and silanol edge sites of montmorillonite and to aluminol and titanol surface sites of kaolinite, respectively. The sorption constants were determined from the experimental data by using the parameter estimation code PEST together with PHREEQC. The PEST- PHREEQC approach indicated an extremely powerful tool compared to FITEQL. In column experiments, U(VI) was also significantly retarded due to adsorptive interaction with the porous media, requiring hundreds of pore volumes to achieve breakthrough. Concerning the U(VI) desorption, columns packed with STx-1b and SWy-2 exhibited irreversible sorption, whereas columns packed with KGa-1b and KGa-2 demonstrated slow, but complete desorption. Furthermore, most phenomena observed in batch experiments were recognized in the column experiments, too. The affinity of uranium to clay minerals was higher than that of arsenate. In systems containing uranium and arsenate, the period required to achieve the breakthrough in all columns was significantly longer when the solution was adjusted to pH 6, due to the formation of the uranyl-arsenate complex. In contrast, when pH was adjusted to 3, competitive sorption for U(VI) and As(V) accelerated the breakthrough for both elements. Finally, experiments without sorbing material conducted for higher concentrations of uranium and arsenic showed no loss of total arsenic and uranium in non-filtered samples. In contrast, significant loss was observed after filtration probably indicating the precipitation of a U/As 1:1 phase.

<p>Prisusutvo&nbsp; arsena&nbsp; u&nbsp; podzemnim&nbsp; vodama,&nbsp; koje&nbsp; se&nbsp; primenjuju&nbsp; za vodosnabdevanje stanovni&scaron;tva je globalan problem. Različiti&nbsp; konvencionalni<br />procesi&nbsp; se primenjuju&nbsp; za&nbsp; uklanjanje&nbsp; arsena iz vode, uključujući koagulaciju i<br />flokulaciju,&nbsp; sorpciju,&nbsp; membransku&nbsp; filtraciju&nbsp; i&nbsp; jonsku&nbsp; izmenu.&nbsp; Uzimajući&nbsp; u<br />obzir relativnu nisku cenu, jednostavnu kontrolu procesa i održavanje, visok<br />stepen uklanjanja arsena, sorpcija se smatra jednom od najpodobnijih tehnika<br />za uklanjanje arsena u tretmanu vode za piće. Premda su na trži&scaron;tu dostupni<br />različiti&nbsp; sorbenti&nbsp; za&nbsp; uklanjanje&nbsp; arsena,&nbsp; postoji&nbsp; potreba&nbsp; za&nbsp; iznalaženjem&nbsp; i<br />razvojem&nbsp; novih&nbsp;<em> low-cost&nbsp;</em> sorbenata,&nbsp; a&nbsp; kojima&nbsp; bi&nbsp; se&nbsp; pak&nbsp; mogao&nbsp; obezbediti<br />visok stepen uklanjanja oba oksidaciona oblika&nbsp; arsena,&nbsp; i&nbsp; As(III) i As(V). Cilj<br />ovog rada bio je usmeren na sintezu i karakterizaciju novih sorbenata na bazi<br />gvožđa&nbsp; i&nbsp; mangana&nbsp; odnosno&nbsp; Fe-Mn&nbsp; binarnog&nbsp; oksida,&nbsp; ispitivanje&nbsp; njihovog<br />potencijala&nbsp; za&nbsp; uklanjanje&nbsp; arsena&nbsp; iz&nbsp; vode&nbsp; i&nbsp; utvrđivanje&nbsp; da&nbsp; li&nbsp; novosintetisani<br />sorbenti po pitanju efikasnosti, mogu konkurisati postojećim komercijalnim i<br />&scaron;iroko kori&scaron;ćenim sorbentima u tretmanima voda.<br />Metodom&nbsp; precipitacije,&nbsp; sintetisani&nbsp; su&nbsp; Fe-Mn&nbsp; binarni&nbsp; oksidi&nbsp; sa&nbsp; različitim Fe:Mn&nbsp; molskim&nbsp; odnosima&nbsp; 1:1,&nbsp; 3:1,&nbsp; 6:1&nbsp; i&nbsp; 9:1,&nbsp; dok&nbsp; su&nbsp; kombinacijom heterogene&nbsp; nukleacione&nbsp; tehnike&nbsp; i&nbsp; precipitacije,&nbsp; sintetisana&nbsp; i&nbsp; četiri&nbsp; sorbenta magnetnih&nbsp; svojstava&nbsp; (Mag,&nbsp; Mag-Fe,&nbsp; Mag-Mn,&nbsp; Mag-FeMn).&nbsp; Modifikacijom biopolimera&nbsp; Chitosana&nbsp; i&nbsp; GAC,&nbsp; sa&nbsp; Fe-Mn&nbsp; binarnim&nbsp; oksidom,&nbsp; razvijena&nbsp; su preostala&nbsp; dva&nbsp; materijala&nbsp; Chit-FeMn,&nbsp; odnosno&nbsp; GAC-FeMn.&nbsp; Sintetisani sorbenti su karakterisani različitim tehnikama i metodama (SEM/EDS, XRD,FTIR, BET).Fizičko-hemijskom karakterizacijom sintetisanih sorbenata ustanovljeno je da se Fe-Mn binarni oksidi i magnetni materijali, karakteri&scaron;u relativno velikim specifičnim&nbsp; povr&scaron;inama&nbsp; (109-300&nbsp; m²/g)&nbsp; i&nbsp; zapreminama&nbsp; mezopora (0,144-0,403&nbsp; cm ³ /g).&nbsp; Velika&nbsp; specifična&nbsp; povr&scaron;ina&nbsp; i&nbsp; razvijena&nbsp; mikroporozna struktura uočena je kod GAC-FeMn (996 m<br />² /g; 0,394 cm^{3 /}g). U poređenju sa ostalim&nbsp; sintetisanim&nbsp; sorbentima,&nbsp; Chit-FeMn&nbsp; je&nbsp; karakterisala&nbsp; najmanja specifična&nbsp; povr&scaron;ina&nbsp; i&nbsp; zapremina&nbsp; mezopora&nbsp; (1,99&nbsp; m<br />²/g;&nbsp; 0,014&nbsp; cm ³ /g).&nbsp; XRD analiza&nbsp; Fe-Mn&nbsp; binarnih&nbsp; oksida&nbsp; ukazala&nbsp; je&nbsp; da&nbsp; je&nbsp; fazna&nbsp; struktura&nbsp; sintetisanih Fe-Mn&nbsp; binarnih&nbsp; oksida&nbsp; slična&nbsp; ferihidratu&nbsp; dok&nbsp; je&nbsp; fazna&nbsp; struktura&nbsp; magnetnih materijala ukazala na prisustvo magemita.<br />Ispitivanja kinetike sorpcionog procesa ukazala su da je mehanizam sorpcije<br />As(III)&nbsp; i&nbsp; As(V)&nbsp; na&nbsp; sintetisanim&nbsp; sorbentima&nbsp; sloţena&nbsp; kombinacija&nbsp; povr&scaron;inske<br />hemisorpcije,&nbsp; koja&nbsp; se&nbsp; odvija&nbsp; kroz&nbsp; granični&nbsp; sloj&nbsp; čestica&nbsp; sorbenata&nbsp; i unutarčestične difuzije. Tome u prilog i&scaron;li su i rezultati FTIR analize kojima<br />je potvrđeno da se sorpcija arsena na sintetisanim sorbentima ostvaruje kroz<br />interakcije hidroksilnih grupa gvožđa prisutnih na povr&scaron;ini sorbenata i arsena.<br />Dodatno, pokazano je da se za razliku od sorpcije As(V), sorpcija As(III) na sorbentima&nbsp; koji&nbsp; pored&nbsp; oksida&nbsp; gvožđa&nbsp; sadrže&nbsp; i&nbsp; okside&nbsp; mangana&nbsp; (Fe-Mn binarni oksidi, Mag-FeMn, Mag-Mn,Chit-FeMn i GAC-FeMn) odvija u dva koraka. U prvom koraku As(III) se oksiduje do As(V), dok u drugom koraku, oksidovani&nbsp; As(V)&nbsp; mehanizmom&nbsp; ligandne&nbsp; izmene&nbsp; formira&nbsp; komplekse&nbsp; na povr&scaron;ini ovih sorbenata.<br />Afiniteti sorpcije Fe-Mn binarnih oksida (na osnovu K_d vrednosti)&nbsp; za As(III) opadali su u nizu Fe-Mn 3:1 &gt; Fe-Mn 1:1 &gt; Fe-Mn 6:1 &gt; Fe-Mn 9:1 odnosno kod&nbsp; As(V):&nbsp; Fe-Mn&nbsp; 6:1&nbsp; &gt;&nbsp; Fe-Mn&nbsp; 3:1&nbsp; &gt;&nbsp; Fe-Mn&nbsp; 9:1&nbsp; &gt;&nbsp; Fe-Mn&nbsp; 1:1.&nbsp; Kod magnetnih kompozita,&nbsp; najveća K_d vrednost za As(III) i As(V) ustanovljena je kod&nbsp; Mag-FeMn.&nbsp; Uop&scaron;teno,&nbsp; Kd<br />vrednosti&nbsp; za&nbsp; As(III),&nbsp; kod&nbsp; magnetnih kompozita,&nbsp; opadale&nbsp; su&nbsp; u&nbsp; nizu:&nbsp; Mag-FeMn&nbsp; &gt;&nbsp; Mag-Mn&nbsp; &gt;&nbsp; Mag&nbsp; &gt;&nbsp; Mag-Fe, Slično, afinitet sorbenata za As(V), opadao je na sledeći način: Mag-FeMn &gt; Mag&nbsp; &gt;&nbsp; Mag-Fe&nbsp; &gt;&nbsp; Mag-Mn.&nbsp; U&nbsp; poređenju&nbsp; sa&nbsp; neimpregniranim,&nbsp; K_d vrednosti bile su daleko veće kod obloţenih materijala, Chit-FeMn i GAC-FeMn, &scaron;to je ukazalo&nbsp; na&nbsp; značajan&nbsp; doprinos&nbsp; Fe-Mn&nbsp; binarnog&nbsp; oksida&nbsp; adsorpcionom kapacitetu neimpregniranih medija za As(III) i As(V). U&nbsp; odnosu&nbsp; na&nbsp; ostale&nbsp; ispitivane&nbsp; anjone,&nbsp; najveći&nbsp; uticaj&nbsp; na&nbsp; sorpciju&nbsp; oba&nbsp; oblika arsena&nbsp; na&nbsp; svim&nbsp; sintetisanim&nbsp; sorbentima&nbsp; uočen&nbsp; je&nbsp; kod&nbsp; fosfata,&nbsp; dok&nbsp; je&nbsp; uticaj nitrata i hlorida, u svim slučajevima bio bez značaja. Uticaj ispitivanih anjona na&nbsp; sorpciju&nbsp; As(III)&nbsp; i&nbsp; As(V)&nbsp; na&nbsp; Fe-Mn&nbsp; binarnim&nbsp; oksidima,&nbsp; magnetnim materijalima, Chit-FeMn kao i na sorpciju As(V) na GAC-FeMn, opadao je u nizu: fosfati &gt; silikati &gt; karbonati &gt; sulfati &gt; nitrati &gt; hloridi. Slično, uticaj ispitivanih&nbsp; anjona&nbsp; na&nbsp; sorpciju&nbsp; As(III)&nbsp; na&nbsp; GAC-FeMn&nbsp; je&nbsp; opadao&nbsp; na&nbsp; sledeći način: fosfati &gt; silikati &gt; sulfati &gt; karbonati &gt; nitrati &gt; hloridi.Primenom&nbsp; sme&scaron;e&nbsp; NaCl-NaOH-NaOCl&nbsp; odnosno&nbsp; primenom&nbsp; 0,1&nbsp; M&nbsp; i&nbsp; 0,5&nbsp; M&nbsp; rastvora NaOH, ustanovljeno je da se sintetisani sorbenti mogu jednostavno i&nbsp; efikasno&nbsp; regenerisati&nbsp; i&nbsp; vi&scaron;estruko&nbsp; primeniti,&nbsp; &scaron;to&nbsp; je&nbsp; od&nbsp; izuzetnog&nbsp; značaja&nbsp; sa ekolo&scaron;kog i ekonomskog aspekta.&nbsp; Najmanje smanjenje sorpcionog kapaciteta&nbsp; i za As(III) i za As(V), nakon pet ciklusa sorpcije -desorpcije, ustanovljeno je kod binarnog oksida sa Fe:Mn molskim odnosom 3:1 i Mag-FeMn.&nbsp; Na osnovu rezultata prikazanih u ovom radu, može se zaključiti da sintetisani sorbenti,&nbsp; Fe-Mn&nbsp; binarni&nbsp; oksidi&nbsp; i&nbsp; magnetni&nbsp; kompoziti,&nbsp; posebno&nbsp; Mag-FeMn, mogu&nbsp; biti&nbsp; efikasna&nbsp; i&nbsp; ekonomična&nbsp; alternativa&nbsp; skupim&nbsp; komercijalnim sorbentima&nbsp; i&nbsp; drugim&nbsp; sofisticiranim&nbsp; tehnologijama.&nbsp; Visok&nbsp; oksidacioni&nbsp; i sorpcioni kapacitet ovih&nbsp; materijala, koji obezbeđuje istovremeno uklanjanje&nbsp; oba oksidaciona oblika arsena daje veliku prednost ovim sorbentima i čini ih veoma&nbsp; atraktivnim&nbsp; i&nbsp; obećavajućim&nbsp; u&nbsp; tretmanu&nbsp; voda.&nbsp; Dodatni&nbsp; benefit<br />magnetnih&nbsp; sorbenata,&nbsp; pre&nbsp; svega&nbsp; Mag-FeMn,&nbsp; ogleda&nbsp; se&nbsp; u&nbsp; njegovoj jednostavnoj separaciji iz vodenog medijuma i recirkulaciji u sistemu. Glavne prednosti&nbsp; sintetisanih&nbsp; Chit-FeMn&nbsp; i&nbsp; GAC-FeMn,&nbsp; ogledaju&nbsp; se&nbsp; u&nbsp; mogućnosti&nbsp; njihove primene kao efikasne filtracione ispune.</p> / <p>The&nbsp; presence&nbsp; of&nbsp; inorganic&nbsp; arsenic&nbsp; in&nbsp; groundwater&nbsp; used&nbsp; for&nbsp; drinking&nbsp; water supply&nbsp; is&nbsp; a&nbsp; global&nbsp; problem.&nbsp; Different&nbsp; techniques&nbsp; such&nbsp; as&nbsp; oxidation, coagulation,&nbsp; adsorption,&nbsp; ion&nbsp; exchange,&nbsp; and&nbsp; membrane&nbsp; filtration&nbsp; have&nbsp; been developed&nbsp; and&nbsp; applied&nbsp; for&nbsp; arsenic&nbsp; removal&nbsp; from&nbsp; aqueous&nbsp; media.&nbsp; Among these&nbsp; technologies,&nbsp;&nbsp; adsorption&nbsp; is&nbsp; regarded&nbsp; as&nbsp; one&nbsp; of&nbsp; the&nbsp; most&nbsp; promising approaches to remove arsenic from water because of its high efficiency, low cost, simplicity of operation. Although many sorbents for arsenic removal are available on the market, there is still a need to identify and develop new&nbsp; lowcost&nbsp; sorbents which are highly effective in removing both oxidation states of arsenic, As(III) and As(V). This dissertation therefore presents the synthesis and&nbsp; characterization&nbsp; of&nbsp; ten&nbsp; new&nbsp; iron&nbsp; and&nbsp; manganese&nbsp; based&nbsp; sorbents specifically developed for effective As removal. The Fe- Mn binary oxides were prepared with Fe:Mn molar ratios of 1:1, 3:1,6:1 and 9:1, while four heterogeneous magnetic composites (Mag, Mag-Fe,Mag-Mn,&nbsp; Mag-FeMn)&nbsp; were&nbsp; synthesized&nbsp; by&nbsp; combining&nbsp; the&nbsp; heterogeneous nucleation&nbsp; technique&nbsp; with&nbsp; precipitation.&nbsp; The&nbsp; remaining&nbsp; two&nbsp; materials, Chit-FeMn&nbsp; and&nbsp; GAC-FeMn,&nbsp; were&nbsp; created&nbsp; by&nbsp; modifying&nbsp; the&nbsp; Chitosan&nbsp; and GAC&nbsp; biopolymers&nbsp; with&nbsp; Fe-Mn&nbsp; binary&nbsp;&nbsp; oxide&nbsp; (Chit-FeMn&nbsp; and&nbsp; GAC-FeMn).Multiple&nbsp; techniques&nbsp; were&nbsp; applied&nbsp; to&nbsp; determine&nbsp; the&nbsp; physical&nbsp; and&nbsp; chemical characteristics&nbsp; of&nbsp; the&nbsp; resulting&nbsp; sorbents&nbsp; (including&nbsp; SEM/EDS,&nbsp; XRD,&nbsp; FTIR and BET analyses). In order to establish which sorbents show&nbsp; the greatest promise for application during&nbsp; drinking&nbsp; water&nbsp; treatment,&nbsp; the&nbsp; sorption&nbsp; capacity&nbsp; of&nbsp; the&nbsp; sorbents,&nbsp; theAs(III)&nbsp; and&nbsp; As(V)&nbsp; sorption&nbsp; mechanisms,&nbsp; and&nbsp; the&nbsp; impact&nbsp; of&nbsp; various&nbsp; factors relevant to arsenic sorption, including the regeneration potential and the reuse potential of the sorbents, were all investigated in&nbsp; batch experiments. During the physical characterisation, the Fe-Mn binary oxides and magnetic materials&nbsp; were&nbsp; found&nbsp; to&nbsp; have&nbsp; relatively&nbsp; large&nbsp; specific&nbsp; surface&nbsp; areas (109-300 m 2 /g) and mesopore volumes (0.144-0.403 cm 3 /g).&nbsp; A large specific surface&nbsp; area&nbsp; and&nbsp; microporous&nbsp; structure&nbsp; was&nbsp; observed&nbsp; for&nbsp; GAC-FeMn&nbsp; (996 m 2 /g;&nbsp; 0.394&nbsp; cm 3 /g).&nbsp; In&nbsp; comparison&nbsp; with&nbsp; the&nbsp; other&nbsp; synthesized&nbsp; sorbents,&nbsp; Chit-FeMn has the smallest specific surface area and pore volume (1.99 m 2 /g; 0.014&nbsp; cm 3 /g).&nbsp; XRD&nbsp; analyses&nbsp; of&nbsp; the&nbsp; Fe-Mn&nbsp; binary&nbsp; oxides&nbsp; indicated&nbsp; that&nbsp; the phase&nbsp; structure&nbsp; of&nbsp; the&nbsp; synthesized&nbsp; Fe-Mn&nbsp; binary&nbsp; oxides&nbsp; was&nbsp; similar&nbsp; to ferrihydrate,&nbsp; while&nbsp; the&nbsp; phase&nbsp; structure&nbsp; of&nbsp; the&nbsp; magnetic&nbsp; materials&nbsp; showed&nbsp; a good agreement with the XRD diffractogram of maghemite. Investigations into As sorption process kinetics have shown that the sorption mechanism&nbsp; for&nbsp; both&nbsp; As(III)&nbsp; and&nbsp; As(V)&nbsp; on&nbsp; the&nbsp; synthesized&nbsp; sorbents&nbsp; is&nbsp; a combination&nbsp; of&nbsp; surface&nbsp; hemisorption,&nbsp; which&nbsp; takes&nbsp; place&nbsp; through&nbsp; the boundary&nbsp; layer&nbsp; of&nbsp; sorbent&nbsp; particles,&nbsp; and&nbsp; intracellular&nbsp; diffusion.&nbsp; The&nbsp; FTIR analyses&nbsp; confirmed&nbsp; that&nbsp; arsenic&nbsp; sorption&nbsp; was&nbsp; accomplished&nbsp; through&nbsp; the interactions&nbsp; of&nbsp; the&nbsp; hydroxyl&nbsp; groups&nbsp; of&nbsp; iron&nbsp; present&nbsp; on&nbsp; the&nbsp; surface&nbsp; of&nbsp; the sorbents and arsenic. In contrast to the sorption of As(V), it was also shown that&nbsp; As(III)&nbsp; sorption&nbsp; onto&nbsp; sorbents&nbsp; containing&nbsp; manganese&nbsp; oxides&nbsp; (Fe-Mn binary&nbsp; oxides,&nbsp; Mag-FeMn,&nbsp; Mag-Mn,&nbsp; Chit-FeMn&nbsp; and&nbsp; GAC&nbsp; -FeMn)&nbsp; takes place in two steps. In the first step As(III) is oxidized to As(V), while in the second&nbsp; step,&nbsp; the&nbsp; oxidized&nbsp; As(V)&nbsp; forms&nbsp; complexes&nbsp; on&nbsp; the&nbsp; surface&nbsp; of&nbsp; the sorbents via ligand exchange. The&nbsp; Fe-Mn&nbsp; binary&nbsp; oxide&nbsp; sorption&nbsp; capacities&nbsp; (expressed&nbsp; as&nbsp; Kd values)&nbsp; for As(III)&nbsp;&nbsp; followed the trend Fe-Mn 3:1 &gt; Fe-Mn 1:1 &gt; Fe-Mn 6:1 &gt; Fe-Mn 9:1, whereas the&nbsp; As(V) trend was Fe-Mn 6:1 &gt; Fe-Mn 3:1 &gt; Fe-Mn 9:1 &gt; Fe-Mn 1:1. In the magnetic&nbsp; composites, the largest&nbsp; Kd value for As(III) and As(V) was&nbsp; obtained&nbsp; for&nbsp; Mag-FeMn.&nbsp; Generally,&nbsp; the&nbsp; Kd values&nbsp; for&nbsp; As(III)&nbsp; in&nbsp; the magnetic composites decreased in the series: Mag-FeMn &gt; Mag-Mn &gt; Mag &gt; Mag-Fe.&nbsp; Similarly,&nbsp; the&nbsp; affinity&nbsp; of&nbsp; the&nbsp; sorbents&nbsp; for&nbsp; As(V)&nbsp; was&nbsp; as&nbsp; follows: Mag-FeMn&nbsp; &gt;&nbsp; Mag&nbsp; &gt;&nbsp; Mag-Fe&nbsp; &gt;&nbsp; Mag- Mn.&nbsp; In&nbsp; comparison&nbsp; to&nbsp; the&nbsp; nonimpregnated&nbsp; materials,&nbsp; the&nbsp; Kd values&nbsp; were&nbsp; much&nbsp; higher&nbsp; for&nbsp; the&nbsp;&nbsp; boated materials,&nbsp; Chit-FeMn&nbsp; and&nbsp; GAC-FeMn,&nbsp; demonstrating&nbsp; the&nbsp; significant advantage&nbsp; Fe-Mn&nbsp; binary&nbsp; oxides&nbsp; provide&nbsp; in&nbsp; increasing&nbsp; As(III)&nbsp; and&nbsp; As(V)&nbsp; adsorption capacities. One&nbsp; of&nbsp; the&nbsp; most&nbsp; problematic&nbsp; limiting&nbsp; factors&nbsp; in&nbsp; applying&nbsp; adsorption technologies during drinking water treatment is the presence of other water constituents which interfere with the adsorption process.&nbsp; Investigations into the inhibitory effect of competive anions on the adsorption of both forms of arsenic&nbsp; revealed&nbsp; that&nbsp; phosphates&nbsp; were&nbsp; the&nbsp; worst&nbsp; offenders&nbsp; in&nbsp; terms&nbsp; ofreducing&nbsp; the&nbsp; arsenic&nbsp; removal&nbsp; efficacy&nbsp; of&nbsp; sorbents&nbsp; investigated.&nbsp; From&nbsp; the largest&nbsp; to&nbsp; the&nbsp; smallest&nbsp; negative&nbsp; influence&nbsp; of&nbsp; the&nbsp; anions&nbsp; investigated,&nbsp; for As(III)&nbsp; and&nbsp; As(V)&nbsp; adsorption&nbsp; on&nbsp; Fe-Mn&nbsp; binary&nbsp; oxides,&nbsp; magnetic&nbsp; materials and Chit-FeMn, as well as As(V) adsorption on GAC-FeMn, the order was: phosphates &gt; silicates &gt; carbonates &gt; sulfates &gt; nitrates &gt; chlorides, with the presence&nbsp; of&nbsp; the&nbsp; latter&nbsp; two&nbsp; anions&nbsp; proving&nbsp; almost&nbsp; irrelevant&nbsp; to&nbsp; the&nbsp; As adsorption&nbsp; process.&nbsp; Similarly,&nbsp; the&nbsp; negative&nbsp; influence&nbsp; of&nbsp; anions&nbsp; on&nbsp; As(III) sorption on GAC-FeMn was: phosphates &gt; silicates &gt; sulphates &gt; carbonates &gt; nitrates &gt; chlorides. Another&nbsp; issue&nbsp; with&nbsp; applying&nbsp; adsorption&nbsp; in&nbsp; real&nbsp; treatment&nbsp; conditions&nbsp; is&nbsp; the need to regularly&nbsp; regenerate and/or replace the spent sorbent. In this work, a simple&nbsp; and&nbsp; efficient&nbsp; process&nbsp; for&nbsp; sorbent&nbsp;&nbsp; rfegeneration&nbsp; is&nbsp; demonstrated.&nbsp; This regeneration&nbsp; process&nbsp; can&nbsp; be&nbsp; applied&nbsp; to&nbsp; the&nbsp; sorbents&nbsp; investigated&nbsp; multiple times, and uses an NaCl-NaOH-NaOCl mixture, or 0.1 M and 0.5 M NaOH solutions.&nbsp; This&nbsp; finding&nbsp; is&nbsp; of&nbsp; great&nbsp; importance&nbsp; from&nbsp; an&nbsp; ecological&nbsp; and economic point of view. The minimum reduction in the sorption capacity for both As(III) and As(V), after five sorption-regeneration cycles, was found in&nbsp; the&nbsp; binary&nbsp; oxide&nbsp; with&nbsp; a&nbsp; 3:1&nbsp; Fe:Mn&nbsp; molar&nbsp; ratio&nbsp; and&nbsp; Mag-FeMn.&nbsp; Arsenic sorption&nbsp; behaviour&nbsp; was&nbsp; also&nbsp; investigated&nbsp; using&nbsp; real&nbsp; groundwater&nbsp; samples, with the results demonstrating the great potential of 3:1 Fe-Mn binary oxide and Mag- FeMn. However, Chit-FeMn and GAC-FeMn were less effective at adsorbing As from the groundwater samples.Based on the results presented in this dissertation, it can&nbsp; be concluded that the synthesized&nbsp; sorbents,&nbsp; especially&nbsp; the&nbsp; Fe-Mn&nbsp; binary&nbsp; oxides&nbsp; and&nbsp; magnetic composites,&nbsp; and&nbsp; Mag-FeMn&nbsp; in&nbsp; particular,&nbsp; can&nbsp; be&nbsp; efficient&nbsp; and&nbsp; economical alternatives&nbsp; to&nbsp; expensive&nbsp; commercial&nbsp; sorbents&nbsp; and&nbsp; other&nbsp; sophisticated&nbsp; As removal&nbsp; technologies.&nbsp; The&nbsp; high&nbsp; oxidation&nbsp; and&nbsp; sorption&nbsp; capacity &nbsp; of&nbsp; these materials,&nbsp; which&nbsp; ensure&nbsp; the&nbsp; simultaneous&nbsp; removal&nbsp; of&nbsp; arsenic&nbsp; with&nbsp; both oxidation states, is a large advantage for these sorbents and makes them very attractive&nbsp; and&nbsp; promising&nbsp; for&nbsp; application&nbsp; in&nbsp; drinking&nbsp; water&nbsp; treatment.&nbsp; An additional&nbsp; benefit of the magnetic sorbents, primarily Mag-FeMn, is the ease with&nbsp; which&nbsp; they&nbsp; may&nbsp; be&nbsp; separated&nbsp; from&nbsp; the&nbsp; aqueous&nbsp; medium,&nbsp; allowing&nbsp; for simple&nbsp; recirculation within a system. Similarly,&nbsp; the main advantages of&nbsp; the synthesized Chit- FeMn and GAC-FeMn are reflected in their application as effective filtration media.</p>

The theme of this thesis is " Evaluation of water quality in water treatment plant Mokošín". The source of water supply are 4 artesian wells. The paper first describes the supply area and water treatment plant with individua water treatment technologies. In the practical section there is the specification of contaminating elements required to be separated at the water treatment plant. Since it is an underground source of water, there is an increased amount of iron and manganese. Increased attention is given to arsenic, which occurs in two water sources in recent years. There are also offered the possibilities of removing arsenic at water treatment plant and two filter materials tested in the laboratory. Monitoring of water quality takes place always in resources and after treatment in the time period of five years, the arsenic values are reported for ten years.

Es wurde eine Arsenkontamination von Boden und Grundwasser im Bereich einer Zellstofffabrik untersucht, die auf Ablagerungen von Eisenoxidschlacken (Rückstände aus der Pyritröstung) mit hohem Gehalt an verschiedenen Spurenelementen zurückzuführen ist. Der Standort ist dadurch gekennzeichnet, dass über viele Jahre Lösungen aus der Celluloseproduktion („Sulfitablauge“) versickerten. Hierdurch gelangten größere Mengen an Sulfat und organischen Stoffen in den Untergrund. Infolgedessen weist das Grundwasser einen stark reduzierten, sulfidischen Chemismus auf. Ein Großteil der Spurenelemente wurde aus der Schlacke im Oberboden in den darunter liegenden wassergesättigten Bereich transportiert und dort in Form von sulfidischen Niederschlägen festgelegt. Eine Ausnahme bildet Arsen, das unter den spezifischen Milieubedingungen im Schadenzentrum lösliche schwefelhaltige Verbindungen bildet (max. 4 mg As/L). Diese Arsen-Schwefel-Spezies wurden erstmals mit einer neu entwickelten IC-ICP/MS- Methode in einem Grundwasser nachgewiesen. Die Grundwasser- und Bodenuntersuchungen sowie begleitende hydrogeologische Messungen ergaben, dass die Arsen-Schwefel-Spezies innerhalb einer Fließstrecke von 30-80 m im Abstrom des Schadenzentrums vollständig immobilisiert werden. Bei der Festlegung von Arsen spielt die biologische Sulfatreduktion, die durch versickerte Sulfitablauge ermöglicht wurde, eine entscheidende Rolle. Anhand dieser Erkenntnisse wurde im Jahr 2000 ein natural attenuation-Konzept zur Sicherung des Standortes ausgearbeitet. Nach Auswertung der Ergebnisse der Standortuntersuchungen aus den Jahren 1999-2005 sowie einer Literaturrecherche zur Arsen-Schwefel-Chemie wurden die Struktur und das Verhalten der unbekannten Arsen-Schwefel-Spezies sowie die Vorgänge bei der Festlegung von Arsen im Boden genauer untersucht. Das wesentlichste Ergebnis der Arbeiten ist, dass in sulfidischen Systemen, z.B. in Grundwässern unter Sulfat reduzierenden Bedingungen, Thioarsenate gebildet werden. In Lehrbüchern und Fachpublikationen aus den vergangenen Jahrzehnten wurde bislang ausschließlich die Existenz von Thioarseniten vermutet. Ursache für die Bildung von Thioarsenaten ist eine hohe Affinität zwischen Arsen und Schwefel, die eine Oxidation von As(III) durch Anlagerung eines Schwefelatoms an dessen freiem Elektronenpaar „erzwingt“. In sulfidhaltigen Lösungen wird hierzu ein Teil des As(III) zu elementarem Arsen reduziert. Das zunächst gebildete Monothioarsenat wird weiter zu den schwefelhaltigeren Thioarsenaten sulfidiert. In sulfidischen Grundwässern bestimmen deshalb die Anionen von Oxomonothioarsenat, Oxodithioarsenat, Oxotrithioarsenat und Tetrathioarsenat das Verhalten von Arsen. Wesentlich für das Verständnis der Arsen-Schwefel-Chemie ist auch die Instabilität der As-SH-Gruppen, die entsprechend dem Dissoziationsverhalten der jeweiligen Arsen-Schwefel-Spezies gebildet werden. Dies erfolgt bei pH-Werten im Bereich von ca. 7-8,5, wobei die monomeren Anionen unter Abspaltung von Schwefelwasserstoff kondensieren. Infolgedessen muss in Grundwässern auch mit polymeren Thioarsenaten gerechnet werden. In saurer Lösung zerfallen die Thioarsenate in arsenige Säure und Schwefel bzw. fallen als Arsenpentasulfid aus. Arsen wird in sulfidischen Aquiferen als Sulfid (z.B. As4S4), als Arsenpyrit (FeAsS) oder durch Einbau von Arsen als Schwefelsubstituent in das Kristallgitter von Mackinawite bzw. Pyrit (FeS, FeS2) festgelegt. Die ermittelten Prozesse können ggf. zur Sanierung bzw. Sicherung von Standorten mit arsenhaltigen Rückständen im Boden bzw. von arsenbelasteten Grundwässern eingesetzt werden. Dabei ist auch von Bedeutung, dass Thioarsenate nach derzeitigem Kenntnisstand relativ gering toxisch sind. Im Umgang mit Thioarsenaten, z.B. auch bei der Analyse von Arsen in sulfidischen Proben, ist jedoch deren Umwandlung in arsenige Säure bei einer pH-Absenkung und auch bei Sauerstoffzutritt zu berücksichtigen. Die biologische Sulfatreduktion spielt eine wesentlich größere Rolle für die Mobilität von Arsen in Grundwässern als bisher angenommen. Im Hinblick auf die weltweit große gesundheitliche Relevanz von Arsen im Trinkwasser und auf mögliche Sanierungsverfahren sollten die Umsetzungen von Arsen unter Sulfat reduzierenden Bedingungen eingehender untersucht werden. / The motivation for the thesis was a project at an industrial site conducted in 1999 to define a remediation concept for soil and groundwater contaminated with arsenic. The contamination resulted from the deposition of residuals from pyrite burning (iron oxides containing different trace elements) in the upper soil many years ago. Because of long-term pollution with process waters rich in organic substances and sulfate, the aquifer is strongly reduced (sulfidic). Most of the arsenic was transferred out of the contaminated soil into the saturated zone in a depth of 7-10 m. There it is partly immobilized as sulfide precipitations, but part of it is solved in the groundwater in form of arsenic-sulfur-complexes (up to 4 ppm). These complexes were detected for the first time in a groundwater by means of an improved IC-ICP-MS method. It was also found that approx. 80 m downstream of the contaminated spot the concentrations of arsenic in soil and groundwater were not increased. On this basis a natural attenuation concept was proposed in 2000. The data from the investigated site was evaluated and specific laboratory tests were carried out in order to identify the unknown arsenic species as well as the processes which lead to their immobilization in the aquifer. The key role of the soluble arsenic-sulfur complexes for the mobility and toxicity of arsenic in sulfate-reducing environments is commonly accepted. In the past, thioarsenites were assumed to be the existing species in sulfidic systems. In this study, however, thioarsenates were identified in solutions spiked with in arsenite and hydrogen sulfide as well as in the contaminated groundwater. The unexpected finding of an oxidation of arsenite to thioarsenates in strongly reducing systems can be explained by the high affinity between As(III) and sulfur. In sulfide containing solutions without any oxidant, arsenite therefore undergoes disproportionation to thioarsenates and elemental arsenic. This was already found out in the 19th century, but has been neglected in publications from the last decades. According to the results of this study the anions of oxomonothioarsenate, oxodithioarsenate, oxotrithioarsenate und tetrathioarsenate are the dominating arsenic species in sulfidic waters. The partitioning of the four species is governed mainly by the sulfide concentration. Beside the high affinity between arsenic and sulfur, the instability of the As-SH group is essential to understand the reactions in the arsenic-sulfur system. As soon as the arsenic-sulfur complexes form As-SH groups (according to their dissociation characteristics) they condensate in separating hydrogen sulfide. Thioarsenates form polymers in the pH range of approx. 7-8.5. Therefore beside the mentioned monomers, thioarsenate polymers can also be important in natural environments. In more acidic solutions they decay into arsenite and sulfur or precipitate as arsenic-pentasulfide. When analyzing arsenic in sulfide containing solutions, it has always to be taken into account that thioarsenates are highly sensitive to oxygen and pH. Therefore, e.g. arsenic speciation by means of HG-AAS is not suitable for sulfidic waters and can wrongly indicate a mixture of arsenite and arsenate. It has previously been supposed that the mobility as well as the toxicity of arsenic increase if the redox state decreases. For sulfidic waters the opposite is probably the case owing to the formation of thioarsenates. The toxicity of arsenite is due to the high reactivity of the As(III) towards sulfohydroxyl groups in proteins. Without a free electron pair and sulfur already incorporated, thioarsenates should be less toxic compared to arsenite. Arsenic can be mobilized out of contaminated soils in form of thioarsenates via infiltration of sulfide solutions or by input of sulfate and biodegradable organic matter. In the presence of iron, thioarsenates can be fixated in sulfidic aquifers as a minor substitute in mackinawite and biogenic pyrite or as arsenic pyrite. Bacterial sulfate reduction is a crucial factor for the mobilization and immobilization of arsenic in reduced aquifers. Considering the negative health impacts of arsenic for millions of people worldwide, as well as the implementation of the mentioned remediation strategies the arsenic-sulfur chemistry deserves closer attention.

Groundwater is one of the main sources for water supply for domestic use, irrigation, aquaculture and industry in Mekong Delta. With rapidly increasing in human population, groundwater becomes more important for social and economic activities. This study evaluated the quality of groundwater using data from the eight monitoring wells over the period of 2009 - 2016. Human health risk was assessed for the population consuming groundwater contaminated with arsenic. The findings indicated that groundwater wells in An Giang province were contaminated with microorganisms. The total dissolved solids (TDS) and hardness in Phu Tan (PT) and Cho Moi (CM) wells were significant higher than the national technical regulations on groundwater quality (QCVN 09-MT:2015/BTNMT). In addition, groundwater wells in some small islands of An Giang were seriously contaminated with organic matters and arsenic. The mean arsenic concentration was up to 0.55 ± 1.21 mg/L. Estimation of carcinogenic risk for human population showed that the cancer risks ranged from medium (8.66 x 10-4) to high (8.26 x 10-2) for both children and adults. Alternative water supply sources should be offered for the population at risk. Besides, regular health check is essential for local people in the arsenic contaminated groundwater. / Nước ngầm là một trong những nguồn cung cấp nước chính cho sinh hoạt, tưới tiêu, nuôi trồng thủy sản và công nghiệp ở Đồng bằng sông Cửu Long. Cùng với sự gia tăng dân số, nước ngầm ngày càng đóng vai trò quan trọng hơn trong các hoạt động phát triển kinh tế - xã hội. Nghiên cứu đã tiến hành đánh giá diễn biến chất lượng nước ngầm thông qua số liệu của tám giếng quan trắc trong giai đoạn từ năm 2009 – 2016. Kết hợp với đánh giá rủi ro sức khỏe của người dân khi sử dụng nước ngầm chứa arsenic. Kết quả nghiên cứu cho thấy các giếng nước ngầm ở tỉnh An Giang đã bị nhiễm vi sinh. Tổng chất rắn hòa tan (TDS) và độ cứng ở trạm Phú Tân và Chợ Mới phân tích được cao hơn quy chuẩn cho phép (QCVN 09-MT:2015/BTNMT). Các giếng nước ngầm ở một số khu vực cù lao của tỉnh An Giang đã bị ô nhiễm hữu cơ và arsenic nghiêm trọng. Nồng độ arsenic trong nước ngầm có thể dao động lên đến 0.55 ± 1.21 mg/L. Rủi ro ung thư ở hai đối tượng người lớn và trẻ em khi sử dụng nước ngầm nhiễm arsenic dao động từ trung bình (8 người trong 1.000 người) tới cao (8 người trong 100 người). Cung cấp nguồn nước thay thế là giải pháp khả thi để giảm rủi ro sức khỏe cho con người trong trường hợp này. Ngoài ra, người dân địa phương cần được khám sức khỏe thường xuyên để kịp thời phát hiện và sớm điều trị bệnh.