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Item type:Publication, Access status: with files , Effects of redox processes on acid-producing potential and metal mobility in sedimentsRedox processes can significantly affect the acid-producing potential and metal bioavailability in sediments. Many oxidation reactions producing acid can occur in natural aquatic sediment systems and human-affected environments. S, Fe, and N are the most important elements involved in redox processes of sediment/water systems. The actual extent of acidification in a sediment/water system depends not only on APP, but also on the acid neutralizing capacity (ANC) of the system. Periodic redox processes leading to "ferrolysis", "split" of sulfate, and the volatilization of H2S can cause changes in APP, and then affect metal transformation and bioavailability. The effects of redox and pH variations on the mobility of metals has been successfully assessed by pore water chemistry, which reflects the interactions of metals in aqueous and solid systems under changing redox environments with depth of sediments. Redox reactions, especially reoxidation of anoxic sediments, can lead to metal release from contaminated sediments. The bioavailability of metals in sediments depends on metal species, especially metal sulfide species. A lack of understanding of the kinetic processes controlling acid production and about the accurate determination of ANC quantitatively limits our ability to predict apparent APP. Heavy sulfide (AVS) may control the toxicity of heavy metals in anoxic sediments, under changing redox conditions AVS is oxidized and dissolved metal sulfates are released. Furthermore, the acidity which follows sulfide oxidation may accelerate metal release. Thus, assessment of the relationship between metal sulfides and their bioavailability in periodic redox environments needs much more research.Publicationtype: Conference Paper303 225 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Effects of redox variations on metal speciation : implications on sediment quality criteria assessmentNew objectives regarding the improvement of water quality, as well as problems with the resuspension and land deposition of dredged materials, require a standardized assessment of sediment quality. Numerical criteria approaches, which are based on pore water concentrations, and the accumulation, solid/liquid partition, and elution properties of contaminants, usually do not imply variations of chemical interactions with solid matrices. Regarding the potential release of metals from sediments, changes in pH and redox conditions are of prime importance. To incorporate new experience with non-linear and time-delayed processes, special emphasis should be put on the characteristics of the mineral and organic solid matrices, e.g. to capacity controlling properties, and in particular, the buffer capacity against pH-depression.Publicationtype: Conference Paper318 175 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Mobilization and scavenging of heavy metals following resuspension of anoxic sediments from the Elbe River(1994); ; Resuspension of sediments from the Elbe River can significantly decrease pH values due to high acid-producting potential and low neutralizing capacity. Metals can be released into the dissolved phase, but may subsequently be readsorbed or precipitated in part to solid phases. To evaluate the potential for metal release and scavenging on a regional and long-term scale, experiments were undertaken at stable neutral-pH values. Rates of total metal release and metal scavenging were extrapolated from time series of netrelease values measured over 630 hours. The order of total release from the sediment was Cd (5%) > Zn (1.5%) > Cu (1%) > Pb (0.7%). The scavenging of released metals was in the reverse order: Pb (86%) > Cu (53%) > Zn (34%) > Cd (30%). Dominant processes are adsorption on organic substances, adsorption/coprecipitation by fresh Fe-Mn oxides and precipitation of metal phosphates originating from the decomposition of organic matter. Based on our experimental results and relevant published data, a four-stage interaction model is developed for metals in anoxic sediments. This model describes the behavior of heavy metals in the system subsequent to oxidation.Publicationtype: Conference Paper584 519 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Binding and mobilization of heavy metals in contaminated sediments affected by pH and redox potential(1993); ; In a contaminated sediment from Hamburg harbour, acid production, mobilization of Cu, Zn, Pb, and Cd at different redox- and pH-conditions, and the transfer and change of those particle bound metals are studied. During oxidation the pH value in the sediment suspension decreases from about 7 to 3.4 because of the low acid neutralization capacity (ANC). This leads to a mobilization of heavy metals whereby Cd and Zn as distinguished from Cu and Pb are strongly released. Also a change in particulate phase specific heavy metal binding forms is found. Generally the easily and moderately reducible fractions increase during oxidation while the sulfidic fraction decreases. Also great changes were found for the dissolved Zn- and Cd-concentrations which increased continuously. The results show that at identical pH values obviously more metals are mobilized in the oxidized sediment than in the reduced state. But although the pH value is the key factor - in particular if it sinks below 4.5 - the redox conditions may also control the mobilization of certain metals. Consequently, also in well buffered sediments a mobilization of metals during oxidation cannot be excluded.Publicationtype: Conference Paper1576 1883 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Sediment quality criteria - role of redox-sensitive componentsRegarding the potential release of contaminants from sediments changing of pH and redox conditions are of prime importance. In practice, therefore, characterization of sediment substrates with respect to their buffer capacity is a first step for the prognosis of middle- and long-term processes of mobilization, in particular, of toxic chemicals in a certain milieu.Publicationtype: Conference Paper196 160 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Einfluß von pH-Wert und Redoxpotential auf die Bindung und Mobilisierung von Schwermetallen in kontaminierten Sedimenten(1992); ; Generally, contaminated dredged sediments are deposited on spoiling areas on land or directly re-stored in water. As a result, anoxic sediments have contact with air oxygen or oxygenated water, and redox conditions change. The change in redox potential leads to changes in particulate heavy metal binding forms. In weakly buffered sediments this may lead to a distinct decrease in the pH value, which has consequences in increasing mobilities of most heavy metals. In a contaminated sediment from Hamburg harbour, acid production, mobilization of Cu, Zn, Pb, and Cd at different redox- and pH-conditions, and the tranfer and change in particle bound metals were studied. During oxidation the pH value in the sediment suspension decreases from about 7 to 3.4 because of the low acid neutralization capacity (ANC). This leads to a mobilization of heavy metals, whereby Cd and Zn are strongly released, as compared to Cu and Pb. A change in particulate heavy metal compounds is also found. Generally, the easily and moderately reducible fractions increase during oxidation while the sulfidic fraction decreases. The results show that at identical pH values significantly more metals are mobilized in the oxidized sediment than in the reduced state. But although the pH value is the key factor - in particular if it sinks below 4.5 - the redox conditions may also control the mobilization of certain metals. Consequently, even in well buffered sediments a mobilization of metals during oxidation cannot be excluded.Publicationtype: Journal Article1986 690 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Change in pH and release of heavy metals in the polluted sediments of Hamburg-Harbour and the downstream Elbe during oxidation(CEP Consultants, 1991-09); ; ; ; Change in pH in a sediment-water system and its influence on release of Cu, Zn, Pb and Cd during the suspension of polluted sediments collected from Hamburg-Harbour and the downstream Elbe have been investigated. Heavy metals were released significantly from the anoxic polluted sediment with changes in pH and redox state. During the resuspension at stable pH (7.5) heavy metals in bottom sediment of the river Elbe were released slowly into the solution.Publicationtype: Conference Paper612 205