Metal soils

Extraction of the CARB fraction by the NaOAc-HOAc solution at various pHs resulted in the larger differences obtained in the subsequent fractions, i.e., ERO fraction, OM fraction, and to some extent, the RO fraction (Figs. 4.4 and 4.5). Extraction of the CARB fraction by NaOAc-HOAc solutions at pH 6.0 and 7.0 usually led to higher contents of major and trace elements in the ERO fraction than that by the buffer solutions at pH 4.0 and 5.0. This was especially obvious for Ca and Mg in calcareous soils. Metal extraction from the OM and RO fractions after extraction of the CARB fraction by the NaOAc-HOAc solutions at pH 7.0 and 6.0 were also higher than those extracted by the buffer solutions at pH 4.0 and 5.0, as shown in Figs. 4.4 and 4.5. 

Mercury has several other characteristics that make it of particular environmental concern and make it likely to be found as many different species. It is a natural constituent of soil, although it occurs at low concentrations. It is widely used both in industry and in the laboratory, making it a common contaminant of reference soils. Metallic mercury has a relatively high vapor pressure, which means that it can occur in measurable amounts in the soil atmosphere. It has a high affinity for reduced sulfur compounds in soil solids and soluble organic matter that allows species to be present in the soil solution above mercury s solubility limit. 

Two different objectives are common when extracting soil to determine its metal content. The first is to determine the amount of biologically active metal present. This is typically the goal for determining the levels of plant-required metals. In terms of total samples analyzed, this is the most common reason for extracting soil. Metals in soil that are essential to plants and that are most... 

Phosphate is widely used as a chemical stabilization agent for MSW combustion residues in Japan and North America and is under consideration for use in parts of Europe. The application of this technology to MSW ashes generally parallels its application to contaminated soils. Metal phosphates (notably Cd, Cu, Pb and Zn) frequently have wide pH distribution, pH-pE predominance, and redox stability within complex ash pore water systems. Stabilization mechanisms identified in other contaminated systems (e.g., soils), involving a combination of sorption, heterogeneous nucleation, and surface precipitation, or solution-phase precipitation are generally observed in ash systems. 

It is to be expected that a relationship exists between the metal content of soils and the metal content of the crop. Table 11.2 gives data on the maximum metal contents observed in soils (taken from Table 11.1) and the maximum metal contents determined for various crops, including corn, wheat and rice flours, apples, potatoes, broccoli and kale. A plot of maximum metal contents (mg/kg) in soil and crops respectively, shows the relationship between these parameters (Fig. 11.1). Metal contents in crops in the range 0.01 -1000 mg/kg increase with increasing soil metal content in the range 1-100 000 mg/kg. 

SHMBC methodology briefly consists of adding a given metal solution, at various concentrations, to the soil under investigation. The metal solution is also added to clean Ottawa sand, which serves as the control soil with no or little metal binding capacity. The soil-metal mixtures are shaken at room temperature for 4 hours. The mixtures are centrifuged, the supernatants are assayed by MetPLATE and an IC50 is determined for the metal. 

In the following discussion an example is given of the multivariate characterization of soil metal status to distinguish pollution of soil layers from geogenic enrichments from the background. Further case studies and a deeper description are given in detail in the literature [KRIEG and EINAX, 1994],... 

It is not clear what is the best model to describe the variability of soil metal concentrations. Ahrens (1954, 1966) has proposed that the distribution of elements in igneous rocks approximates to a log-normal distribution. This model does not necessarily apply to soils but the available evidence suggests it may. Its applicability underlies the interpretation of geochemical data in mineral exploration. 

Fig. 3-3. Relative available metal ion concentrations (top) and relative metal tolerances to the ions (bottom) for six populations of Silene vulgaris. In both graphs, for each metal the population with the highest tolerance or soil metal concentration has been given the value of 100 all the other populations have been expressed relative to this. Key to populations Am Amsterdam (normal, control) PI Plombieres Br Breinig Im Imsbach Bl Blankenrode Ma Marsberg Ha Harlingerode. Drawn from data in Schat and ten Bookum (1992b).

Fig. 8-2. Response of plants to increasing soil metal concentrations reflected by the metal concentrations in the aerial parts of the plants A, Accumulator B, Indicator C, Excluder. (Adapted from Baker, 1981).

Lubricant film between the moving parts generally provides an electrical insulation, and breakdown voltage ranges between 30 and 50 V. Electrical bridges may form due to soiling, metal particles, or insufficient lubricant. 

Metal bioavailability is the fraction of the total metal occurring in the soil matrix, which can be taken up by an organism and can react with its metabolic system (Campbell, 1995). Metals can be plant-bioavailable, if they come in contact with plants (physical accessibility) and have a form which can be uptaken by plant roots (chemical accessibility). Soil metals become accessible for humans by ingestion, inhalation and dermal contact. Available forms of PTMs are not necessarily associated with one particular chemical species or a specific soil component. Main soil PTMs pools of different mobility, target organisms and routes of transfer are sketched in Fig. 9.2. The most labile fraction, corresponding to the soluble metal pool, occurs as either free ions or soluble complexed ions and is considered the... 

Feng, M. H., Shan, X. Q., Zhang, S., andWen, B. (2005b). Comparison of rhizosphere-based method with other one-step extraction methods for assessing the bioavailabihty of soil metals to wheat. Chemosphere 59, 939—949. 

The method of soil suspensions extracts is based on metal desorption/dissolution processes, which primarily depend on the physico-chemical characteristics of the metals, selected soil properties and environmental conditions. Metal adsorption/ desorption and solubility studies are important in the characterization of metal mobility and availability in soils. Metals are, in fact, present within the soil system in different pools and can follow either adsorption and precipitation reactions or desorption and dissolution reactions (Selim and Sparks, 2001). The main factors affecting the relationship between the soluble/mobile and immobile metal pools are soil pH, redox potential, adsorption and exchange capacity, the ionic strength of soil pore water, competing ions and kinetic effects (e.g. contact time) (Evans, 1989 Impelhtteri et al., 2001 McBride, 1994 Sparks, 1995). 

Keywords organophosphorus compound nerve agent adsorption decomposition soil metal... 

Attempts to model soil-metal adsorption behavior using the double-layer model have not been adequate (Van Raij and Peeeh, 1972). The reason is that in the... 

In effect higher H30" concentration in surface waters may remove from soils metal ions, mainly Mn" ", which are solubilized in water. 

---