Joachim Gerth

The relative affinities of Cd, Ni and Zn for different soil clay fractions and goethite

Cadmium, Ni and Zn ions in aqueous solution were allowed to react with clay fractions (< 2 μm) separated from soils with a wide range of mineralogical composition and properties. Sorbed metals were separated into two components, termed specifically and non-specifically bound, by a controlled washing procedure using 10−2M Ca(NO3)2. Sorption reactions were characterized by Δ pH50 values, by shapes of adsorption curves, and by measuring separation factors and distribution coefficients under prescribed conditions. Three reaction types were identified, viz., (i) those associated with soil adsorbing surfaces dominated by iron oxides; these appear to be controlled by mechanisms which involve metal-ion hydrolysis and result accordingly in relative sorption affinities of Zn > Ni > Cd; (ii) those associated with organic surfaces for which metal-ion hydrolysis was of little significance and little difference in metal-ion affinity was evident; at lower pH-values, Cd and Ni were somewhat preferred over Zn, with the converse at higher pH-values; (iii) those associated with 2:1 layer lattice silicates which exhibit greater preference for Zn, i.e., Zn >> Ni, Cd and higher affinities for each metal at lower pH-values (< 5) than is shown by clays dominated by iron oxides. There was also evidence of greater relative affinity for Ni shown by clay fractions dominated by fine kaolinites when compared with other clays. This investigation has shown that a range of sorption processes are involved in reactions of heavy metals with soils. We caution against undue emphasis on any particular sorption process in developing theoretical sorption models as a basis of understanding and solving problems connected with pollution and plant nutrition; we also stress the need for studies with colloids separated from soils in conjunction with those using synthetic adsorbents as models for soil constituents.

The sorption of Cd, Zn and Ni by soil clay fractions: Procedures for partition of bound forms and their interpretation

Abstract This work is the first of several projects concerned with the study of higher-affinity reactions of Cd, Zn and Ni ions with soil clay fractions. Procedures for the separation of sorbed metals into fractions of lower and higher affinity for soil surfaces are described and evaluated. Various concentrations of Cd, Zn and Ni were allowed to react in the presence of 0.01 M Ca(NO3)2 with soil clays for 1 week after stabilization of suspension pH. The adsorbed metals were partitioned by a brief extraction with 0.01 M Ca(NO3)2 and the resultant fractions, called specifically and non-specifically sorbed metals, were measured by radioisotopic procedures. Measured separation factors showed that the fraction of sorbed metals that was desorbed by a rapid Ca(NO3)2 extraction still had a preference, sometimes marked, over Ca on the soil clay fraction. Separation of fractions of sorbed metals on the basis of affinity was reproducible, but the boundary conditions defined by separation factors vary appreciably between adsorbents, with values in the range 3–20 for amounts sorbed equivalent to ≦ 0.05% of cation exchange capacity and for pH values The proportions of Cd, Zn and Ni bound at high-affinity sites were strongly dependent on experimental conditions of pH, equilibrium time and surface saturation in relation to each soil clay. Hence, comparisons of affinities of trace metals for soils by reliance on measures of total sorption only, without assessing the contribution of lower-affinity forms, may prejudice conclusions and predictions arising from studies of the possible retention of metal pollutants in soils and fixation of micronutrients from fertilizers.

Abschätzung und Beeinflussbarkeit der Arsenmobilität in kontaminierten Böden

Die Sickerwasserkonzentration in arsenkontaminierten Rieselfeldboden eines ehemaligen Gerbereistandortes wird durch Schuttel- und Saulenversuche abgeschatzt. Zusatzlich wird der Einfluss reduzierender Verhaltnisse, des pH-Wertes und der Ionenstarke berucksichtigt. Der eisenreiche Unterboden (C-Horizont) stellt die Hauptquelle fur eine Belastung des Grundwassers mit Arsen dar. Hier ist bei starkerer Durchfeuchtung zeitweise mit reduzierenden Verhaltnissen und einer erhohten Mobilisierung zu rechnen. Die potentiell freisetzbare Arsenfraktion wird daher durch Auflosen der leicht reduzierbaren Eisenoxidfraktion mit 0.1 M Ascorbinsaure naherungsweise erfasst. Die Arsenkonzentration in der Losung lasst sich durch Erhohung der Ionenstarke (z. B. mit 0.01 M CaCl2-Losung) von uber 100 μg/L auf unter 20 μg/L stabilisieren. Arsenkontaminierte Boden sollten mit CaCO3 behandelt werden, um eine moglichst hohe Calciumkonzentration in der Bodenlosung zu erzielen. Die Arsenkonzentration im Sickerwasser wird in erster Linie durch Sorptionsprozesse gesteuert und nicht durch Losungs- und Fallungsprozesse. Assessment and Modification of Arsenic Mobility in Contaminated Soil Arsenic concentration in the seepage of contaminated soils of an old tannery site is assessed using batch and column experiments. The effect of reducing conditions, pH, and ionic strength is also investigated. The iron oxide rich subsoil (C-horizon) is the main source of groundwater pollution with arsenic. In this horizon, mobilization can increase as a result of reducing conditions upon periodical water saturation. Therefore, the potentially mobile arsenic is determined by a reductive dissolution of the poorly crystalline iron oxide fraction using 0.1 M ascorbic acid. Arsenic concentration can be reduced from 100 μg/L to below 20 μg/L by an increase of ionic strength (e.g. by a 0.01 M CaCl2 solution). Arsenic contaminated soils should be limed regularly in order to maintain the highest possible calcium concentration in the soil solution.

Managing contaminated sediments: III. In-situ Sediment Treatment (Spittelwasser Case Study)

While remediation and storage of contaminated dredged materials is a key issue at harbour sites, there is another type of sediment pollution problem, which mainly originates from large-scale dispersion of contaminants in flood-plains, dike foreshores and polder areas. In recent years, catastrophic cases of sediment contaminations have occurred in connection with the failure of tailing dams from mines. Unlike problems related to conventional polluted sites, the risks here are primarily connected with the transporting and depositing of contaminated solids in a catchment area, especially in downstream regions.A special example demonstrating the dispersion of highly contaminated sediments in a large catchment area will be shown from the so-called Chemistry Triangle of the upper Elbe River system, Germany. The Spittelwasser area, situated there, was chosen by the organisers of the international conference ConSoil 2000 for a case comparison and four expert teams from Denmark, Germany, the Netherlands and the UK were invited to participate in this Case Study. Evaluation of the plan was done by members of the networks of NICOLE (Network for Industrially Contaminated Land) and CLARINET (Contaminated Land Rehabilition Network).In the study of the German team, five major groups of technical measures have been identified by the environmental authorities to be discussed in relation to the Spittelwasser case or for similar problem solutions in contaminated flood-plain areas. The team came to the conclusion that none of these techniques would be applicable as an individual measure. Instead, a stepwise approach combining different monitoring techniques and remediation measures was proposed. These would include point excavations of critical material, promotion of plant growth as an element for stabilising the soil and flood sediments, as well as the installation of sediment traps.At the Spittelwasser site, investigations are planned on the effects of natural attenuation processes of organic and inorganic contaminants in flood-plain sediments and soils. In the practice of this concept, non-destructive, ‘intrinsic’ bonding mechanisms and their temporal development have thus far found much less recognition compared to destructive processes such as biological degradation. Yet these so-called ‘diagenetic’ effects, which apart from chemical processes involve an enhanced mechanical consolidation of soil and sediment components by compaction, loss of water, and mineral precipitations in the pore space, may induce a quite essential reduction of the reactivity of solid matrices [see Part I ‘Improving Chemical and Biological Criteria’ (JSS - Journal of Soils and Sediments, Vol 1, No 1, pp 30-36)].

Interactions of organic pollutants with soil constituents in aqueous and oil-contaminated systems

Different soil samples and synthetic goethite were reacted with γ-HCH, anthracene, 2,4-D and atrazine in a solid/water and a solid/oil system. The non-polar compounds γ-HCH and anthracene were only sorbed from aqueous solution, in particular by soil samples with a high content of organic carbon. When dissolved in oil these non-polar compounds were not sorbed by any of the soil samples investigated. For atrazine, little sorption was observed whereas for 2,4-D, sorption from the oil phase was much higher than from aqueous solution. This effect is probably connected to modifications of the electric double layer on the particle surfaces.

Ingenieurgeochemie im Boden- und Gewässerschutz — Praxisbeispiele und rechtlicher Rahmen

Konzeptionelle und praktische Entwicklungen im Umweltschutz sind in vielen Fallen durch neue oder novellierte rechtliche Bestimmungen ausgelost worden. Dies gilt auch fur die Konzepte, Methoden und Verfahren, wie sie typisch fur die Ingenieurgeochemie sind. Hier waren es vor allem die neuen oder wesentlich erweiterten Gesetze im Bodenschutz, bei der Vermeidung, Verwertung und Beseitigung von Abfallen und fur den flussgebietsubergreifenden Gewasserschutz, die entweder direkt oder durch ihre untergesetzlichen Regelwerke ein verstarktes Interesse an naturnahen und relativ kostengunstigen Technologien hervorriefen.

Methoden zur Erkundung und Beschreibung des Untergrundes

Bei der Erkundung des Untergrundes von Deponien und Altlasten begegnet man komplexen Standortgegebenheiten mit individuellen topographischen, naturraumlichen, geologischen und stofflichen Eigenschaften, die eine Einzelfallbearbeitung erfordern. Knappes Budget, langwierige Verwaltungsvorgange und enge Termine bilden den ublichen Rahmen fur eine Tatigkeit, die durch hohe Qualitatsanspruche und hohe Verantwortung gekennzeichnet ist. Zusatzlich sind oft der Leistungsumfang schwer abgrenzbar die Anforderungsprofile an die Experten unklar Normen und Richtlinien teilweise nicht vorhanden der Untergrund heterogen das Gefahrdungspotential unbekannt und die Schadstoffausbreitung stark heterogen die Stofftransportvorgange vielfaltig und insbesondere fur die wasserungesattigte Zone wenig erforscht eine Schadstoffmobilisierung durch Aufschlustatigkeiten moglich Mes- und Analysenergebnisse insbesondere durch Probenahmefehler nicht reproduzierbar sowie das zu erkundende Gelande (teilweise) unzuganglich

Soil/Solution Distribution Equilibria of Lindane at Different Soil/Water Ratios and Under Non-Saturated Conditions

For the assessment of the binding and migration behaviour of organic pollutants in soils the soil/water distribution coefficient (Kd value) is an essential parameter which can easily be determined by batch experiments. Using this technique, e.g. according to the OECD-guideline 106 “Adsorption/Desorption”, a relatively small amount of soil material (S) is equilibrated with a big amount of solution (W) (S:W = 1:5 kg/kg) by shaking This high proportion of liquid is used for technical reasons only and does not refer to the mainly non-saturated conditions in soils. Therefore, the aim of this investigation was to find out if Kd values obtained from batch experiments with non-polar organic contaminants can be applied to the conditions in soils.

Wechselwirkungen Organischer Schadstoffe mit Bodenkomponenten in Wässrigen und Ölkontaminierten Systemen

Durch eine Kontamination mit ol werden Boden in ihren elementaren Funktionen gestort und zusatzlich mit zahlreichen organischen Spurenstoffen belastet. Vor allem Altol enthalt verschiedene schwer abbaubare organische Schadstoffe. Extrem hohe Konzentrationen an unterschiedlichen Schadstoffen wurden in olbecken von Mulldeponien gefunden, die zur Ablagerung von Ruckstanden aus der Pestizidproduktion genutzt wurden (Umweltbehorde Hamburg, 1988).