Metal/metalloid bioavailability

Another key factor in the popularity of the technique is its increasingly widespread use in speciation chemistry. The current awareness of the importance of the chemical form in which an element is present in food (e.g., the oxidation state, the nature of the ligands, and the molecular structure), on its possible absorption and fate inside the body, has made elemental speciation a prominent topic of present research in the food science. If speciation critically influences the bioavailability, essentiality, or toxicity of an element, the analytical techniques that enable species discrimination and quantification gather prominence. ICP-MS has the capability for quantifying metal (metalloid)-containing species in a chromatographic or capillary electrophoresis effluent or, as recently demonstrated, in a gel spot after SDS-PAGE via electrothermal vaporization (ETV) or laser ablation (LA) [4, 5]. Hence, it has firmly established as a sensitive,... 

An overview of the distribution, bioavailability, biomagnification, fate and sources of chemical pollutants such as metals, metalloids, and radionuclides in different compartments (sediments, biota, suspended matter, water) for the whole Baltic Sea ecosystem was given by Szefer (2002). 

To predict the health effects of metal ions, the US EPA s Office of Chemical Safety and Pollution Prevention uses mechanism-based SAR. A metal ion s bioavailability, as it exists in inorganic and organic metal compounds, is estimated by considering the ion s solubility, oxidation state, dissociation, and reactivity. To predict potential carcinogenicity, the EPA developed the OncoLogic Cancer Expert system, which has a metals/metalloids subsystem that includes major carcinogenic metals (http //www. epa.gov/oppt/sf/pubs/oncologic.htm). 

Arsenic is another element with different bioavailability in its different redox states. Arsenic is not known to be an essential nutrient for eukaryotes, but arsenate (As(V)) and arsenite (As(III)) are toxic, with the latter being rather more so, at least to mammals. Nevertheless, some microorganisms grow at the expense of reducing arsenate to arsenite (81), while others are able to reduce these species to more reduced forms. In this case it is known that the element can be immobilized as an insoluble polymetallic sulfide by sulfate reducing bacteria, presumably adventitiously due to the production of hydrogen sulfide (82). Indeed many contaminant metal and metalloid ions can be immobilized as metal sulfides by sulfate reducing bacteria. 

The biohazard in soils attributable to heavy metals, and to metalloids such as arsenic, has often been assessed by determination of their total soil contents and national guidelines based on such total contents are currently in use (see for example, Appendices 3-6 in Alloway, 1995). Total soil contents, however, reflect the geological origins of soils as well as the anthropogenic inputs such as pollutants from industrial processes and are poor indicators of mobility or bioavailability. A more relevant assessment of the contents of elemental contamination can be made by measuring the pseudototal element contents of a soil by the... 

Bioavailable metals and metalloid species are either adsorbed or incorporated into the structure of proteins, lipids, nucleic acids, amino acids, sugars, vitamins and hormones to form complexes of varying degrees of thermodynamic stability and reactivity. These complexes could be classified as either metal-proteins or metalloproteins on the basis of their stability during isolation and purification (Vallee and Coleman, 1964). Whereas metal-proteins are relatively labile and the metal is easily lost during dialysis, metalloproteins are stable and inert. 

Wine is a very complex matrix and the accurate, selective determination of species constitutes a challenge for analytical chemists. Furthermore, the speciation analysis of metals bound to biological ligands is a subject of increasing interest since complexation may reduce their toxicity and bioavailability. There is a limited number of studies concerning the speciation analysis of metals or metalloids in wines. Arsenite, arsenate, MMA, and DMA were separated in less than 10 min by means of an anion-exchange column [88], Arsenic species detection was accomplished by the direct coupling of the column effluent to an HG system and AFS was used for detection. LoDs in white wine were 0.16, 0.33, 0.32, and 0.57 ng ml-1 for As(III), DMA, MMA, and As(V), respectively. In real samples... 

Human milk (or the substitute food, formula milk) is the only source of essential trace elements for newborns. To ensure the optimum development of the baby, mother s milk contains essential elements at the adequate levels. However, today it is well known that bioavailability, biological activity, nutritional value, as well as toxicity and metabolism of trace metals and metalloids strongly depend of their... 

Natural particles suspended in the air can be transported to regions far from their sources. This is important for transporting many metals and metalloids in the ecosystem. A few metals and metalloids, most notably Hg, As, and Se, can exist not only in the solid and liquid phases but also as gases in ambient environments. The loss of Hg from the aqueous phase can result from reduction of Hg " " to Hg and alkylation to form methyl- or dimethylmercury. Through microbial activity, the methylated forms can be converted to Hg, which is more volatile and less toxic. Microbial mediation can also transform several other trace elements (e.g., As, Se) to organometallic compounds (Gadd, 1993). These volatile organometallic compounds can dominate the transport of these trace elements in local environments. However, bacterial mediation of alkylation of metals such as Hg is influenced substantially by Hg speciation. Mineral colloids vary in their ability to affect the bioavailability and methylation of Hg(II) in aqueous systems... 

Soil is the most diverse ecosystem and Earth s most important resource in sustaining all life in the terrestrial environment. Physical, chemical, and biological processes are not independent but rather, interactive with each other. The interactions at physical-chemical-biological interfaces govern the mechanisms of transformations, speciation, dynamics, bioavailability, toxicity, and fate of metals and metalloids in soil and related environments. 

SPECIATION, MOBILITY, AND BIOAVAILABILITY OF METALS AND METALLOIDS AND RESTORATION OF CONTAMINATED SOILS... 

As a recognition of the importance of biophysico-chemical processes of metals and metalloids in soil environments, we initiated the first volume of the lUPAC—Wiley book series Biophysico-Chemical Processes in Environmental Systems. This volume, which consists of 15 chapters, is organized into three parts Fundamentals of Biotic and Abiotic Interactions of Trace Metals and Metalloids with Soil Components Transformations and Dynamics of Metals and Metalloids as Influenced by Soil—Root—Microbe Interactions and Speciation, Mobility, and Bioavailability of Metals and Metalloids and Restoration of Contaminated Soils. 

This chapter outlines current approaches for characterizing elements in settled dust and indoor air, factors influencing the geochemistry of household dust, potential indoor and outdoor sources, and the need for reliable bioavailability data to improve assessments of residential exposures to metals. The emphasis of this chapter is on studies that examine a variety of metals and metalloids in indoor environments. For information on individual elements, the reader is referred to the elemental chapters in Part III, and for information on other indoor sources and pathways (e.g., food and drinking water) and potential effects on human health, the appropriate chapters in Part I and II should be considered. 

In the rhizosphere, the presence of hiomolecules continuously released hy plants as root exudates or microorganisms play a crucial role in the dynamics and bioavailability of metals and metalloids for plants and biota. The influence of biomolecules as well as of biotic and abiotic components on trace elements transformation and mobility deserves to be studied with particular attention. 

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