Extraktion von Schwermetallen aus Böden mit Ionenaustauscherharz

Extraction of Heavy Metals from Soils by Ion Exchangers The aim of this investigation was to optimize an extraction method for the analysis of available heavy metals (Cd, Cu, Pb, Zn) in soils. LEWATIT was used as an ion exchanger (IEX) which absorbs heavy metals specificly. A special extraction vessel with two chambers was developed to recover the IEX from the soil solution. Nitric acid was used for the desorption of heavy metals from the ion exchanger. The described method measures water soluble and exchangeable ions as well as acid soluble heavy metals. The amount of acid soluble heavy metals can be regulated by conditioning the IEX with K⁺. Using an IEX conditioned with 30% K⁺, the maximum change of pH in the soil solution was 2 units. This is the same range of acidity changes occuring in the rhizosphere of plants by nutrient uptake. The extract contains no organic compounds. Thus the co-determination of stabil organic complexes is excluded. Accordingly, this method is also feasible for the investigation of forest soils with humic layers.     

Verhalten von Schwermetallen in Böden 1. Untersuchungen zur Schwermetallmobilität

Behaviour of heavy metals in soils. 1. Heavy metal mobility 158 soil samples with widely varying composition were analysed for their total, EDTA, DTPA and CaCl₂ extractable contents of Cd, Zn, Mn, Cu and Pb. By means of single and multiple regressions the relations between the different heavy metal fractions and the pH, organic carbon and clay content were considered. The correlations between the total, EDTA and DTPA extractable contents are very close, whereas the CaCl₂ extractable contents are not or only weakly correlated with these fractions. According to these statistical results the former fractions are considered to be the total quantity (total content) and the reactive quantity (EDTA and DTPA extractable contents) of the heavy metals, whereas the CaCl₂ extractable fraction represents the mobile fraction of the heavy metals in soils. The multiple regressions show that the mobile content of heavy metals is closely correlated with each of the quantity fractions and with soil pH. In the same way the proportion of the mobile fraction (in %) of the total, EDTA and DTPA extractable heavy metal content of the soil samples is closely related to the soil pH. Hereby the proportion of the mobile content of the various elements increases in the pH range 6,5 - 3 below element-specific threshold pH values (in brackets) in the order Cd (6,5) > Mn (5,7) > Zn (5,3) > Cu (4,5) > Pb (3,5). In the pH range 6,5 - 7,5 mainly Cu and to a lesser degree also Pb show an increasing mobility due to the influence of soluble organic substances.     

Einflußgrößen der Schwermetallöslichkeit und -bindung in Böden

Solubility and retention of heavy metals in soils Model experiments were carried out under oxidizing conditions with soil samples from surface and subsurface horizons of different composition in order to investigate the solubility and retention of Cu, Zn, Cd, and Pb in soils. The solubility of heavy metals is mainly determined by ad- and desorption processes and complexation reactions of organic and inorganic ligands. Precipitation and dissolution of definite heavy metal compounds do not seem to govern the solution concentration in soils. An exception may probably be the formation of lead phosphate and zinc silicate under specific reaction conditions. The main factors which determine solubility and retention of heavy metals are total amount (except the proportion incorporated in the silicate structure) of the different metals, soil reaction, content of mobilizing and immobilizing organic substances, content of pedogenic oxides and clay minerals, and kind and concentration of salts and inorganic ligands. The results of the model experiments are used together with the results of other authors and general physico-chemical data to give an interpretation of the solubility behaviour of heavy metals in soils. The relations between heavy metal solubility, availability and mobility and possible procedures for melioration of soils contaminated with heavy metals are discussed.     

Bodenchemische Vertikalgradienten als charakteristische Zustandsgrößen von Waldökosystemen

Soil chemistry depth gradients as characteristic state variables of forest ecosystems Based on model concepts and on analyses of the soil solution and the soil solid phase we present a procedure to predict the cation composition of the soil solution from solid phase properties. For the intended prediction, the aluminum (or base) saturation (NH₄Cl extraction) of the soil exchange complex yields the best results. This parameter shows distinct gradients through a soil profile, and these gradients can be used to characterize the state of the ecosystem. We suggest to utilize this parameter as an additional criterion in the practice of forest site classification.     

Kurzfristige pH-Pufferung von Böden

Short-time pH buffering of soils Changes in pH of 60 soils after HCl addition were related to reaction time and soil characteristis. Between 80 and 100% of the added protons were taken up by the soils within a few seconds, resulting in the release of exchangeable Ca, Mg and Al in strongly acid soils. The decrease of proton activity between 0.25 and 30-70 h can be formally described as a diffusion process. pH buffering depended on soil pH and organic C content but not on clay content. Buffering decreased from pH 3.5 to about 6 and increased again up to pH 7. Increase of C_org increased buffering mainly from pH 6-7.     

Zur Anreicherung von Schwermetallen in Böden und Kulturpflanzen durch praktische Klärschlammdüngung

The accumulation of heavy metals in soils and crops by practical sewage sludge application An accumulation of cadmium, lead, zinc and copper was found in some soils and crops after sewage sludge application as compared with same soils and plants not fertilized with sewage sludge. In the soils the heavy metals mainly were accumulated in the Ap-horizons. The displacement into subsoils was small, in spite of the good permeability of the sandy soils investigated. Relatively the mobility of zinc and cadmium in soils was most distinct. Within the plants the accumulation of the heavy metals was strongest in the roots, however also evident in the shoots of rye, barley and oats. Zinc and copper was concentrated in the grains, too. On the meadow-land an accumulation of the elements investigated was found in the blades of rye grass (Lolium perenne L.).     

Regenwürmer als Bioindikatoren für Schwermetallbelastungen von Böden unter Freilandbedingungen

The use of earthworms in monitoring soil pollution by heavy metals Total heavy metal contents (HNO₃-soluble) and exchangeable fractions (Ca(NO₃)₂-soluble) of Pb, Zn and Cd were measured in soils, litter layers and earthworms (dry masses) from forest, arable and pasture sites in a transect of the main wind direction and varying distances (1.5, 5.4, 11.4, 15.6 km) to a lead smelter near Bad Ems, Germany. Additionally, cast materials of Lumbricus terrestris-individuals were collected from the surface of the pasture sites. In the observed area total soil contents of Pb and Cd exceeded the C-level and total contents of Zn the B-level of the “Netherland-list”. Heavy metal contents in soils and earthworms decreased with increasing distance to the smelter. Pb showed the best correlation. Correlation between total contents of Pb and Cd in soils and earthworms were significant (rs = 0.66; p < 0.05 and rs = 0.67; p < 0.01, respectively). The uptake of heavy metals by Lumbricus rubellus, L. terrestris and Aporrectodea caliginosa was metal specific rather than species specific with factors of accumulation being <1 (Pb), 2.7–7.6 (Zn) and 19.5–85.5 (Cd). The heavy metal contents of the observed cast materials signified the different transfer of elements from soil material via earthworm individuals to the faeces. In the cast materials the amounts of Pb were high and the amounts of Zn and Cd were low. This indicates a high accumulation rate for Zn and especially for Cd in the tissues of the observed earthworm individuals. The present data support the necessity of ecotoxicological threshold levels.     

Stickstoffdynamik von Böden mit Abwasserverrieselung

Nitrogen dynamic of soils with wastewater irrigation The nitrogen status of a Sandy Cambisol and a Loamy Luvisol of Berlin, which were flooded with wastewater over a period of 100 years were studied. The two-year examination of the water, redox and nitrogen dynamics showed great differences in nitrogen leaching and the intensity of nitrification and denitrification processes.     

PH-Verteilung und Pufferung von Böden

PH-distribution and buffering of soils A frequency distribution of the pH values of 927 soils clearly reflects the three soil buffer ranges (carbonate, pH-dependent charge and aluminium release) by higher frequencies within these ranges and lower frequencies between them.     

Methodenvergleich zur pH-Bestimmung von Böden

Comparison of methods for determining of soil-pH Comparative studies are being described of pH-determinations in suspensions with m-KCl, 0.1 m-KCl, 0.01 m-CaCl₂ and water of soils derived from loess and sand. For a standard the pH-values in 0.01 m-CaCl₂-suspensions were chosen, considering, that such CaCl₂-solution reflects best conditions in natural soil solution. Mean differences of pH(H₂O)-, m-KCl- and 0.1 m-KCl-values as compared to pH(CaCl₂)-values were + 0.56, — 0.27 and — 0.02 for the soils derived from loess, and + 0.63, — 0.11 and + 0.18 for those from sand. Taking into account the pH-dependence of the difference pH(CaCl₂)-values were + 0.56 – 0.11, — 0.27 – 0.26 and — 0.02 – 0.21, for the soils derived from loess, and + 0.63 – 0.21, — 0.11 – 0.14 and + 0.18 – 0.10 for those from sand. Taking into account the pH-dependence of the difference of pH(H₂O)-values of sandy soils, and its dependence on the present electrolyte content with all soils, further the unequal differences of the pH(KCl)-values with soils from loess as compared to sand, and their particular large variability with soils from loess, it is being argued that the CaCl₂-method may only insufficiently be substitued by any one of these methods. pH-values obtained at a soil-to-liquid-ratio of 1:2.5 were only slightly different from those with a ratio of 1:1. A suspension effect could not be observed with the application of a glasselectrode.     

Zur Bestimmung von Gips in Böden

On the determination of gypsum in soils The (020) X-ray reflection of gypsum at 7,56 Å is nearly specific and may be used for detection and quantitative measurement of the mineral in soil samples. By X-ray powder diffractometry gypsum can be detected as far down as 0,5% by weight. This limit may be extended down to 0,005% by concentration in the density fraction 2,1–2,5 g/cm³. For quantitative measurements references may be prepared from sample parts by dehydration of the original gypsum and adding known quantities of this mineral. So it is possible to compare samples of nearly identical grain size distribution, and mineral contents. This is important in the powder-diffractometrical quantitative measurement of a mineral with low hardness and good cleavage where mechanical stress during homogenisation lowers the intensities of X-ray reflections. Under comparable conditions for sample and reference, gypsum contents can be determined in the range of 0,5 to 20% by weight with an accuracy of ± 3% (relative).     

Abbau von Monolinuron in verschiedenen Böden

Degradation of monolinuron in different soil types The degradation of ¹⁴C-methyl, -ureido- and -phenyl-labelled monolinuron was studied in laboratory experiments with different soil types. Mineralization of the ureido-group was followed by two methods. It was found, that the mineralization rate depends on the soil. For the herbicide monolinuron there was a definite degradation characteristic. The release of ¹⁴CO₂ from the methyl- and ureido-group was faster than from the phenylring. In soil extracts monolinuron was found together with one or two radioactive substances not yet identified. Soil respiration was unchanged after the application of monolinuron. In a sterile soil no degradation occurred.     

Kolorimetrische Bestimmung von Dicyandiamid in Böden

A colorimetric method for the determination of dicyandiamide in soils A colorimetric method derived from the diacetyl reaction for the determination of creatine has been developed for the determination of dicyandiamide in soil extracts. Dicyandiamide reacts with 1-naphtol and diacetyl forming a red colour complex with maximum absorption between 535 and 540 nm. The detection limit ranges between 0.1 and 0.3 mg dicyanidiamide-N/100 g soil. In soil extracts neither naturally occurring substances nor metabolites of dicyandiamide influenced this colour reaction. After addition of 1, 5, 10, 20 mg dicyandiamide-N to 100 g soil and immediate extraction by water an average recovery rate of 95% was found. The relative standard deviation amounted to ± 1.60%.     

Kurzmitteilung Ein methodischer Beitrag zur Porengrößen-Messung bei Böden

A methodic contribution for the measuring of volume of pores in soils An apparatus for determination of the soil pores in the pF-range 0–2,5, partially produced in home-work, is described. Thereby are used ceramic plates 50 × 35 cm with a thickness of 5–8 mm. The ceramic plates are sticked on 63 × 50 cm gum plates with Teroson-Cement-BE and packed in correspondingly great wooden boxes. The soil samples are dehydrated in an over-pressure chamber.     

Die N-Mineralisierung von Böden im Laborbrutversuch

N mineralization in soils under laboratory incubation conditions The potential rate of release of nitrogen by the organic matter in agriculturally used soils was determined under laboratory conditions by means of incubation. Mineralization of the more resistant soil organic matter proceeded linearly with time during an incubation period of 2–3 weeks, when field-moist and air-dried samples were used and at the beginning of the incubation experiment sufficient water was added to bring them to saturation. Mineralization was taking an exponential course in soils with additions of easily decomposable organic matter or in soils with a higher proportion of organic residues from crops. For the 14 investigated arable and grassland soils great variations in the average daily rate of mineralization were found ranging from 5–60 μg N_min/10 g DM. The data correlated very well with the biomass (r = 0.96) and the cell-free protease activity (r = 0.98) of the soils. Different measures of soil management (preceding crops, application of sewage sludge, addition of heavy metals) had a more or less pronounced influence on the rate of mineralization. The optimum temperature was 50°C for N mineralization and 26°C for nitrification. Contrary to nitrification, the soil reaction had only little influence on mineralization and proved also independent of the N_min content of soils. The results indicate that ammonification of organic N compounds may largely proceed via the microbial biomass.     

Die Verwendung von Antimon-Elektroden zur pH-Messung in Böden

The application of antimony electrodes for soil pH measurements Glass electrodes are unsuitable for long-term, micro-volume pH measurements in soils because of their form, size and drying of the glass membrane. Sb-electrodes are suited for pH measurements in soils whose oxygen saturation does not vary excessively. pH values determined with Sb electrodes decrease with increasing water tension or decreasing moisture. Colour changes of pH indicators confirm this trend.