Contents of trace elements

FACTORS AFFECTING CONTENTS OF TRACE ELEMENTS IN ARID AND SEMI-ARID SOILS... 

The contents of trace elements extracted by the buffer solutions depend upon the solution s acid capacity in dissolving carbonate from soils. Trace elements dissolved by the buffer solution increased with decreasing pH of the buffer solution (Table 4.3). Release of trace elements by the buffer solutions at pH 6.0 was much smaller from calcareous soils with more than 30% of CaCC>3. The dissolution of trace elements by the buffers paralleled with the dissolution of Ca and Mg. The correlation coefficients between Ca and trace elements were as follows Cd (0.92), Pb (0.87), Zn (0.90), Ni (0.90), Cr (0.91), V (0.54) and Co (0.70) and between Mg and trace elements were Cd (0.88), Pb (0.80), Zn (0.79), Ni (0.87), Cr (0.58), V (0.69) and Co (0.80), (all with n = 32). 

PLANT UPTAKE, STORAGE, TRANSLOCATION, AND CONTENTS OF TRACE ELEMENTS... 

Table 3. Lung and stomach cancer distribution and average content of trace elements in soils and drinking waters of various bio geochemical provinces.

Average content of trace elements, ppm Rank of cancer... 

The content of trace elements in foods depends on their concentration in the raw materials and additives used in food production. In addition, trace elements may be transmitted to food from the equipment used during food processing and from the packaging material during storage. 

Kotz, L., Kaiser, G., Tschopel, P. and Tolg, G. (1972) Decomposition of biological materials for the determination of extremely low contents of trace elements in limited amounts with nitric acid under pressure in a Teflon tube. Fresenius Zeitschrift fur Analytische Chemie 2 60(3), 207-209. 

A comprehensive treatment of the properties and contents of trace elements in soils and plants is given by Kabata-Pendias (2000). 

Quevauviller, Ph., Rauret, G., Rubio, R., Lopez-Sanchez, J.-F., Ure, A., Bacon, J. and Muntau, H. (1997c) Certified reference materials for the quality control ofEDTA- and acetic acid-extractable contents of trace elements in sewage sludge amended soils (CRMs 483 and 484). Fresenius J. Anal. Chem., 357, 611. 

Mussels (Mytilus edulis) have a content of trace elements, both essential and toxic (As, Cd, Hg, Ni, and Pb), that is tightly correlated to the geographic zone, water salinity, and degree of sea contamination [15]. 

To shed further light on the actual content of trace elements in rice from various countries, an investigation was recently undertaken which reached completion at the moment of writing this chapter. The study is reported in detail in the following section. 

A special group of materials analyzed are crade and lubricating oils. Ni, V, and Fe act as poisons on cracking catalysts (see Catalysis), and the wear of mechanical parts of engines can be indicated by the content of trace elements (see Trace Element) in lubricating oils. Their determination is therefore an important task. To eliminate the tedious mineralizatiou of the samples, they can be analyzed directly after dilution with some nonpolar solvent, usually xylene, or methyl isobutyl ketone (MIBK). 

Contents of trace elements in some earth materials. 3... 

Contents of trace elements (values as (ig element of dry material)... 

The content of trace elements in Steppe soils is tightly connected with their contents in geological rocks. In soils of Desert ecosystems water soluble forms play the most important role. We can see an analogy between the increasing content of elements in soil dead organic matter as a function of decreasing water excess in Forest ecosystems and the increasing content of water-soluble species of chemical elements in the soils of Dry Steppe and Desert ecosystems as a function of enhanced aridity. The accumulation of water-soluble species occurs in the upper horizon for almost all elements, with exception of strontium. The main factor responsible for the accumulation of water-soluble forms is connected with evapotranspiration. 

Table 37 compares the contents of trace elements in the ash of various grass and tree species from the Savanna ecosystems of East Africa. We can see that nickel, barium, and strontium accumulate in the tree organs (twigs), whereas the accumulation of other metals is pronounced in grasses. 

It is possible to produce artificial matrix materials [12]. Such materials can be prepared on a mass basis by weighing all components both to mimic the matrix composition and the content of trace elements or trace organic substances. The materials could help to have matrix materials available for which the exact contents and composition are known. As a consequence it would be, in theory, possible to certify them on a mass basis and validate methods with highly traceable materials. In organic trace analysis this would circumvent the unknown extraction step. In reality, this is much more difficult to achieve than can be expected. The real matrix composition of many materials is unknown — in particular for environment samples. The physico-chemical status of the various substances depends on the history of the material. Therefore, various natural samples of expected similar composition are different in behaviour. In addition, when preparing mixtures of solid components, losses cannot be excluded and unfortunately are not quantifiable. Attempts have been made where losses were demonstrated but not quantified [12]. Therefore, materials certified for matrix composition and analyte content on a mass basis do not yet exist or are not of real use for method validation by routine laboratories. They may be of interest for laboratories active in the field of fundamental research in chemical metrology where smaller quantities of material are handled. 

CERTIFIED CONTENTS OF TRACE ELEMENTS IN SEA LETTUCE CRM 279 Element Certified value (mg kg ) Uncertainty (mg kg )... 

CERTIFIED CONTENTS OF TRACE ELEMENTS IN MUSSEL TISSUE CRM 278... 

Seawater and estuarine water CRMs certified for their contents of trace elements (see sections 8.7 and 8.8) were not analysed for mercury. Due to the high volatility of mercury, water to be analysed for Hg content can not be stored in polythene bottles and a higher acidification is necessary. So far, no CRM existed for this element, and hence a separate reference material had to be produced. 

Contents of trace elements in soil materials from natural as well as from contaminated sites show a high variability in both dimensions, horizontal and vertical. Soil is not homogenous, and the microscale heterogeneity creates a real problem in representative sampling. Thus, the reproducibility and comparability of analytical data for trace elements in soils have been a great concern. The procedure of soil sampling and storage has been broadly described in several publications (Mortvedt et al. 1991, Sparks etal. 1996, Tan 1995). 

Several methods were developed to calculate background (pristine) contents of trace elements in soils. There is a great demand for such data as reference values, as today... 

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