Trace and Toxic Elements in Soils

Among other methods for determining trace and toxic elements in the soil, there are also electro-chemical analytical methods, mainly polarogra-phy and in the case of nuclear analytical methods, activation analysis and radionuclide X-ray fluorescence analysis are employed. Mass spectrometry, laser emission spectral microanalysis and other instrumental methods can also be used. 

Abiotic toxic damage and accumulation of metals and nonmetals in wild and cultivated plants may result from natural geochemical loads in the soil (Kovalskij 1977) caused by macro, trace and ultratrace elements in water used for irrigation, in natural volcanoes and anthropogenic industrial pollution of the atmosphere. Water, aerosols, and dust contain a variety of aluminum, arsenic, cad-... 

Reduction-oxidation is one of the most important processes controlling solubility and speciation of trace elements in soils, especially for those elements with changeable values, such as Cr, As and Se. Within normal ranges of redox potentials and pH commonly found in soils, the two most important oxidation states for Cr are Cr(III) and Cr(VI). Cr(III) is the most stable form of chromium and less soluble and nontoxic, but Cr(VI) is mobile, soluble and toxic. The main aqueous species of Cr(III) are Cr3+, Cr(OH)2+, Cr(OH)3° and Cr(OH)4" and the major aqueous species of Cr(VI)... 

Chemical remediation refers to the application of various minerals or chemicals to adsorb, bind, precipitate or co-precipitate trace elements and heavy metals in soils and waters thereby reducing their bioavailability, toxicity, and mobility. In situ immobilization refers to the treatment of contaminants in place without having to excavate the soils or waste, often resulting in substantial cost savings. However, in situ immobilization or extraction by these physicochemical techniques can be expensive and are often only appropriate for small areas where rapid and complete decontamination is required. 

The total content of the major elements in soil is of little practical significance since only a tiny, soluble fraction is available for absorption by plant roots (West, 1981 Tinker, 1986). To some extent this is less true for trace elements and micronutrients where for example, analyses of total copper or zinc can be used to assess the likelihood of plant deficiencies or toxicities. Nonetheless, for an element to be bioavailable it has to be relatively soluble. 

Chemical elements that are either present naturally in the soil or introduced by pollution are more usefully estimated in terms of availability of the element, because this property can be related to mobility and uptake by plants. A good estimation of availability can be achieved by measuring the concentration of the element in soil pore water. Recent achievements in analytical techniques allowed to expand the range of interest to trace elements, which play a crucial role both in contaminated and uncontaminated soils and include those defined as potentially toxic elements (PTE) in environmental studies. A complete chemical analysis of soil pore water represents a powerful diagnostic tool for the interpretation of many soil chemical phenomena relating to soil fertility, mineralogy and environmental fate. This chapter describes some of the current methodologies... 

The varieties of rice examined in this study show only modest differences in trace element content between the Italian and Asian samples. The slight variations observed can be ascribed to specific characteristics of the botanical varieties, soil composition, and availability for each element, and local environmental contamination. The concentration of potentially toxic elements in rice ascertained in this study raise no specific concerns. On the other hand, the key role played by rice consumption in Asia diets calls for careful evaluation of the average daily intake for elements such as As, Cd, and Pb, which might exceed the established tolerance level. 

Danika, L. and LeDuc, N.T. 2005. Phytoremediation of toxic trace elements in soil and water. Journal of Industrial Microbiology and Biotechnology, 32 514-20. 

Many nonessential trace elements are found in the body. Depending on the local environment, at least 43 elements are normally incorporated into developing teeth another 25 elements are seen less frequently. The rest, notably the heavy metals, have never been detected in teeth. Many trace elements, particularly the heavy metals, are considered when testing for metal poisoning. Many plants concentrate essential and nonessential elements from soil and water, including aluminum (several species of subtropical plants), selenium (many plants), strontium (mesquite beans), and lithium (wolfberries, used by Native Americans in the southwestern United States for jam). Ingestion of these plants can cause toxicity for the element involved. 

To facilitate fundamental understanding of the linkage of trace elements in soils with plant—animal—human—environment systems and related geomedical problems and to provide practical solutions to their deficiency and toxicity problems, it is essential to promote research on the relationship between soil physicochemical-biological interactions and the impacts on the transformation, transport, bioavailability, toxicity, and fate of trace elements in the terrestrial environment. 

The transition and heavy metals, referred to hereafter as trace metals, are important to plants and animals as both micronutrients and toxic elements. Many of them occur in the soil environment in cation form. As naturally occurring elements, some of these cations are incorporated into primary and secondary mineral structures and may be very unavailable. Schemes for complete extraction of these metals from soils require extreme treatments, including dissolution of certain minerals. As pollutants, the metals may enter the soil in organically complexed form or as metal salts. In the latter case, the metal cations then adsorb on mineral and organic surfaces. 

The phytotoxic actions of rubidium mostly affect the transportation of substances in the xylan (Zornoza and Carpona 1996). In order to prevent excessive amounts of rubidium in plant tissues, these authors proposed an increase in the content of potassium, manganese and boron in the soil solution, because of the known antagonism of these elements towards rubidium. Young, growing plants or parts of plants are extremely rubidium-rich and accumulate this element like most other macro, trace and ultratrace elements (Angelow 1994, Wyttenbach et al. 1995). The toxicity of rubidium in plants is low, and essentially unknown. 

Cobalt, Co, is a metallic element. Cobalt 59 is the only stable isotope. Common isotopes are cobalt 57, cobalt 58, and the most common, cobalt 60. Cobalt is a steel-gray, shining, hard, ductile, and somewhat malleable metal. It has magnetic properties and corrodes readily in air. Cobalt dust is flammable and toxic by inhalation, with a TLV of 0.05 mg/m of air. It is an important trace element in soils and animal nutrition. Cobalt 57 is radioactive. It has a half-life of 267 days. It is a radioactive poison and is used in biological research. Cobalt 58 is also radioactive and has a half-life of 72 days. It is a radioactive poison, and it is used in biological and medical research. Cobalt 60 is one of the most common radioisotopes. It has a half-life of... 

The potentials of using activation analysis techniques for studies in botany and plant biochemistry are good. It offers a practical method to investigate and measure (a) the concentrations of trace elements, (b) the behavior of essential trace elements, (c) the nutritional rates and metabolic functions of the absorption of trace elements from soils, (d) the determination of toxic elements in plants and soils, and (e) the origin of specific flora and their relation to similar flora from other geographical regions. 

Seregin, 1. V., Ivanov, V. B. Physiological aspects of cadmium and lead toxic effects on higher plants. Russian journal of plant physiology. 2001, V. 48, 523-544. Kabata-Pendias, A., Pendias, El. Trace elements in soil and plants. CRC Press EEC, Boca Raton, FL, 1992, 453 p. 

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