Chromium occurrence in the environment and methods of its speciation.

Sequential selective extraction techniques are commonly used to fractionate the solid-phase forms of metals in soils. Many sequential extraction procedures have been developed, particularly for sediments or agricultural soils, and, despite numerous criticisms, they remain very useful. This article reviews the reagents used in the various schemes, with their advantages and disadvantages. The particular case of elements giving anionic species is also developed. Finally, there is discussion of the limits of sequential extraction procedures.

Fractionation studies of trace elements in contaminated soils and sediments: a review of sequential extraction procedures

Arsenic is a trace element found in the earth’s crust at an average concentration of ∼5 μg/g (ppm). Although its relative abundance in the earth’s crust is about 54th, arsenic can become concentrated in some parts of the world because of natural mineralization. Arsenic is a component of 245 minerals, associated most frequently with other metals such as copper, gold, lead, and zinc in sulfidic ores.1−3 When disturbed by natural processes, such as weathering, biological activity, and volcanic eruption, arsenic may be released into the environment. Anthropogenic activities, such as combustion of fossil fuels, mining, ore smelting, and well drilling, also mobilize and introduce arsenic into the environment.

Chronic exposure to arsenic from groundwater has been recognized to cause the largest environmental health disaster in the world, putting more than 100 million people at risk of cancer and other arsenic-related diseases.4,5 Because of its prevalence in the environment, potential for human exposure, and the magnitude and severity of health problems it causes, the United States Agency for Toxic Substances and Disease Registry (ATSDR) has ranked arsenic as No. 1 on its Priority List of Hazardous Substances for many years. The recent priority list, posted in 2011 (http://www.atsdr.cdc.gov/SPL/index.html), shows arsenic as No. 1, ahead of lead, mercury, and polychlorinated biphenyls (PCBs).

Epidemiological studies of populations exposed to high levels of arsenic due to ingestion from water, including those from Taiwan,6−8 Argentina,9,10 Chile,11,12 West Bengal, India,13,14 Bangladesh,15−17 and Inner Mongolia, China,18,19 have repeatedly shown strong associations between the exposure to high concentrations of arsenic and the prevalence of several cancers,20−23 most severely bladder, lung, and skin cancers. Arsenic is classified as a human carcinogen by the International Agency for Research on Cancer (IARC) and the U.S. Environmental Protection Agency (EPA). Chronic exposure to elevated concentrations of arsenic has also been associated with the increased risk of a number of noncancerous effects.24−27 Although the adverse health effects arising from exposure to arsenic have been well-recognized, the mechanism(s) of action responsible for the diverse range of health effects are complicated and poorly understood.26−30

It is believed that inorganic arsenate (HAsO42-), which is a molecular analogue of phosphate (HPO42-), can compete for phosphate anion transporters and replace phosphate in some biochemical reactions.28 For example, generation of adenosine-5′-triphosphate (ATP) during oxidative phosphorylation can be inhibited by the replacement of phosphate with arsenate. Depletion of ATP by arsenate has been observed in cellular systems.28 However, the replacement of phosphate in DNA by arsenic is not firmly established.31−35

The toxicity of trivalent arsenicals likely occurs through the interaction of trivalent arsenic species with sulfhydryl groups in proteins. Arsenic binding to a specific protein could alter the conformation and function of the protein as well as its recruitment of and interaction with other functional proteins. Therefore, there has been much emphasis on studies of arsenic binding to proteins, for the purpose of understanding arsenic toxicity and developing arsenic-based therapeutics.

This review summarizes various aspects of arsenic binding to proteins. It discusses the chemical basis and biological implications and consequences of arsenic binding to proteins. It also describes analytical techniques and the characterization of arsenic binding, including the binding affinity, kinetics, and speciation.

Arsenic binding to proteins.

Since their introduction in the late 1970s, sequential extraction procedures have experienced a rapid increase in use. They are now applied for a large number of potentially toxic elements in a wide range of sample types. This review uses evidence from the literature to consider the usefulness and limitations of sequential extraction and thereby to assess its future role in environmental chemical analysis. It is not the intention to provide a comprehensive survey of all applications of sequential extractions or to consider the merits and disadvantages of individual schemes. These aspects have been covered adequately in other, recent reviews. This review focuses in particular on various key issues surrounding sequential extractions such as nomenclature, methodologies, presentation of data and interpretation of data, and discusses typical applications from the recent literature for which sequential extraction can provide useful and meaningful information. Also covered are emerging developments such as accelerated procedures using ultrasound- or microwave energy-assisted extractions, dynamic extractions, the use of chemometrics, the combination of sequential extraction with isotope analysis, and the extension of the approach to non-traditional analytes such as arsenic, mercury, selenium and radionuclides.

Is there a future for sequential chemical extraction

http://projects.itn.pt/UCQR_QAA/Morrilo_et_al_%202004.pdf

Heavy metal distribution in marine sediments from the southwest coast of Spain

Metal speciation in solid matrices

A review on molybdenum determination in solid geological samples

The literature on the speciation of metal ions in biological fluids is comprehensively reviewed. Critical examination on this subject reveals that major work has been done in blood and urine. Speciation in materials like milk has not yet been widely studied. On the other hand, only few references could be found on sweat, saliva, cell lysate, cerebrospinal, seminal, tear and bronchoalveolar fluids. The topics studied for these fluids were mainly the speciation of arsenic, mercury, aluminium and selenium. Work on the speciation of other elements like zinc, chromium, cadmium, lead, copper, iron etc. have also been carried out in such matrices. The present literature survey includes also a critical comment about the sampling and storage of the fluids, general methodologies and analytical details of the developed methods for studying such metal ion speciation.

Metal speciation in biological fluids : a review

The literature on the use of solid-phase extraction (SPE) as a tool for trace-element speciation is highly significant. Among methods of pretreatment, SPE is unique because of its effectiveness, robustness, speed and, above all, its “greenness”. We illustrate the combination of SPE with highly sensitive detection methods for accurate measurements of chemical species at extremely low concentrations in environmental samples with special reference to aqueous solutions. We examine the analytical strategies for speciation of elements in terms of limits of detection.

Recent developments in solid phase extraction in elemental speciation of environmental samples with special reference to aqueous solutions

Bismuth is a trace element of the Earth’s crust, which is becoming environmentally significant. Although bismuth has relatively low toxicity, it can form characteristic intracytoplasmatic inclusions. This article illustrates the increasing need for fast pre-treatment techniques and highly sensitive detection methods for accurate measurements of bismuth at extremely low concentrations in solid environmental matrices.

Arabinda K. Das

Papers

Metal speciation in solid matrices

A review on molybdenum determination in solid geological samples

Metal speciation in biological fluids : a review

Recent developments in solid phase extraction in elemental speciation of environmental samples with special reference to aqueous solutions

Analytical techniques for the determination of bismuth in solid environmental samples