Speciation, chemical

From an environmental standpoint, there are two reasons to perform chemical speciation. One reason is that the toxicity of an element varies with its chemical form. For example, mercury and silver form an amalgam that is used to fill tooth cavities. Ninety per cent of dentists use amalgam to fill cavities, and mercury in this form can be in the body for years with no toxic effects. Elemental mercury has low toxicity and, although this is not recommended, can be touched and handled with Utde chance of ill effects. However, methyl mercury, caused by industrial pollution and sometimes found in sea food, is readily adsorbed into the body and once there is extremely toxic. Pollution incidents involving mercury have shown that total metal data are insufficient and often misleading in assessing the potential hazard of this metal. 

The other environmental reason for measuring the type and concentration of each chemical species in a sample is to help determine the technology needed for removal or cleanup. The chemical properties, and the technology needed to remove an element, will vary with chemical species formed from that element 

Ion Chromatography, 4th Ed. James S. Fritz and Douglas T. Gjerde Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32052-3 

Exposure to high levels of arsenic can cause cancers of the skin, bladder, kidney and lung, and diseases of the blood vessels of the legs and feet, as well as possibly diabetes, high blood pressure, and reproductive disorders. Monitoring the effectiveness of the cleanup technologies will require measurement of the various chemical forms of arsenic in the water. 

The general application of ion chromatography (IC) to environmental samples has been described in a review [1]. More laboratories are looking at speciation as methods are being developed. As well as the traditional ion chromatography companies, most of the inductively coupled plasma mass spectrometry (ICP-MS) companies (PE, Agilent, Thermo, Varian) have done applications or offer speciation columns and/or kits. A website on speciation called Evisa is sponsored by the EU and provides much information (www.spedation.net). There is a links tab that lists various elemental metals, with further Usts of references and certified methods on several different spedes of each particular element 

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Preventive Measures. The intake uptake biokinetic model (lUBK) projects the impact of lead in the environment on blood lead. This model assumes conservatively high levels of intake and cannot account for chemical speciation, thus over-predictions of blood lead levels often occur. Nonetheless, because of the allegations of the impact of blood lead and neurobehavioral development, blood lead levels in children are being reduced adrninistratively to below 10 //g/dL. In order to do so, soil leads are being reduced to a level of between 500—1000 ppm where remediation is required. 

SALI compares fiivorably with other major surface analytical techniques in terms of sensitivity and spatial resolution. Its major advantj e is the combination of analytical versatility, ease of quantification, and sensitivity. Table 1 compares the analytical characteristics of SALI to four major surfiice spectroscopic techniques.These techniques can also be categorized by the chemical information they provide. Both SALI and SIMS (static mode only) can provide molecular fingerprint information via mass spectra that give mass peaks corresponding to structural units of the molecule, while XPS provides only short-range chemical information. XPS and static SIMS are often used to complement each other since XPS chemical speciation information is semiquantitative however, SALI molecular information can potentially be quantified direedy without correlation with another surface spectroscopic technique. AES and Rutherford Backscattering (RBS) provide primarily elemental information, and therefore yield litde structural informadon. The common detection limit refers to the sensitivity for nearly all elements that these techniques enjoy. 

Prediction of the chemistry of plutonium in near-neutral aqueous media is highly dependent on understanding reactions that may be occurring in such media. One of the most important parameters is the stability and nature of complexes formed by plutonium in its four common oxidation states. Because Pu(III), Pu(IV), and Pu(VI) are readily hydrolysed, complexation reactions generally are studied in mildly to strongly acidic media. Data determined in acid media (and frequently at high concentrations of plutonium) then are used to predict the chemical speciation of plutonium at near-neutral pH and low concentrations of the metal ion. 

Fig. 15-11 Effects of strong complexation on metal ion toxicity, (a) Increasing concentration of NTA, a strong multi-dentate complexing agent, decreases the toxicity of Cd to grass shrimp. All systems have equal concentrations of total Cd. (b) When the results are replotted showing survival as a function of Cd concentration, the data for all concentrations of NTA collapse to a single curve. (Reprinted with permission from W. G. Sunda et al. (1978). Effect of chemical speciation on toxicity of cadmium to grass shrimp, Palaemonetes pugio importance of free cadmium ions. Environ. Sci. Technol. 12,409-413, American Chemical Society.)...

The chemical speciation of the metal is defined as its distribution among different phases and different dissolved forms. When heavy metals enter aquatic... 

R. Tauler, A.K. Smilde, J.M. Henshaw, L.W. Burgess and B.R. Kowalski, Multicomponent determination of chlorinated hydrocarbons using a reaction-based chemical sensor. 2 Chemical speciation using multivariate curve resolution. Anal. Chem., 66 (1994) 3337-3344. 

Fraser CA, Gardner GJ, Maxwell PS, Kubwabo C, Guevremont R, Siu KWM, Berman SS (1995) Preparation and certification of a biological reference material (CARP-i) for polychlorinated dibenzo-p-dioxin and dibenzofliran congeners. Fresenius J Anal Chem 352 143-147. Gardiner PE (1993) Consideration in the preparation of biological and environmental reference materials for use in the study of the chemical speciation of trace elements. Fresenius J Anal Chem 345 287-190. 

Today it has become clear that the effect of trace elements in living systems, in food, and in the environment depends on the chemical form in which the element enters the system and the final form in which it is present. The form, or species, clearly governs its biochemical and geochemical behaviour. lUPAC (the International Union for Pure and Applied Chemistry) has recently set guidelines for terms related to chemical speciation of trace elements (Templeton et al. 2000). Speciation, or the analytical activity of measuring the chemical species, is a relatively new scientific field. The procedures usually consist of two consecutive steps (i) the separation of the species, and (2) their measurement An evident handicap in speciation analysis is that the concentration of the individual species is far lower than the total elemental concentration so that an enrichment step is indispensable in many cases. Such a proliferation of steps in analytical procedure not only increases the danger of losses due to incomplete recovery, chemical instability of the species and adsorption to laboratory ware, but may also enhance the risk of contamination from reagents and equipment. 

Cornelis R (1996) Involvement of analytical chemistry in chemical speciation of metals in clinical samples. Ann Clin Lab Sd 26 252-263. 

Presently, the precise determination of the true dissolved Th fraction in water samples remains a challenge. Results from ultrafiltration experiments on organic-rich water samples from the Mengong river tend to demonstrate that Th concentration is less than 15 ng/L in absence of DOC (Table 2 and Viers et al. 1997), and that Th is still controlled by organic carbon in the final filtrate of the ultrafiltration experiments. The latter conclusion is also supported by the results obtained for the Kalix river (Porcelli et al. 2001). These results therefore not only raised the question of the determination of the amount of dissolved Th in water but also of the nature of Th chemical speciation. 

Webb LM, Taylor DM, Williams DR. 1998. Computer modeling of the chemical speciation of lanthanide and actinide elements in the human gastrointestinal tract Mouth and stomach. Radiat Prot Dosim 79(l/4) 219-222. 

For chemical speciation, X-ray absorption spectroscopy is another supreme tool taking advantage of its electronic and structural information power. Also, REMPI-MS is outstanding in its selectivity for molecular species. Radioanalytical methods have also been used for speciation analysis [548]. Microscopical speciation analysis requires SSIMS or LMMS [549]. 

Twiss, M., Errecalde, O., Fortin, C., Campbell, P., Jumarie, C., Denizeau, F., Berkelaar, E., Hale, B., and van Rees, K., Coupling the use of computer chemical speciation models and culture techniques in laboratory investigations of trace metal toxicity, Chem Spec Bioavailab, 13 (1), 9-24, 2001. 

Zirino, A. and Yamamoto, S., A pH-dependent model for the chemical speciation of copper, zinc, cadmium, and lead in seawater, Limnol Oceanogr, 17 (5), 661-671, 1972. 

A method for estimating the TSCF for equation 14.24 is given in Table 14.10. The root concentration factor is also defined in Table 14.10 as the ratio of the contaminant in the roots to the concentration dissolved in the soil water (pg/kg root per pg/L). This is important in estimating the mass of contaminant sorbed to roots in phytoremediation systems. The values of TSCF and RCF for metals depend on the metals redox states and chemical speciation in soil and groundwater. 

This paper discusses (1) soil and groundwater and (2) aquatic equilibrium and ranking models. The second category deals with the chemical speciation in soil and groundwater, and with the environmental rating of waste sites, in cases where detailed modeling is not desirable. 

Bolger PM, Carrington CD, Capar SG, et al. 1991. Reductions in dietary lead exposure in the United States. Chemical Speciation and Bioavailability 3(314) 31-36. 

Mushak P. 1991. Gastro-intestinal absorption of lead in children and adults Overview of biological and biophysico-chemical aspects. Chemical Speciation and Bioavailability 3 87-104. 

Nolan A.L., McLaughlin M. J., Mason S.D. Chemical speciation of Zn, Cd, Cu and Pb in pore waters of agricultural and contaminated soils using donnan dialysis. Environ Sci... 

Tauler R., Smilde A.K., Hemshaw J.M., Burgess L.W., Kowalski B.R., Multicomponent Determination of Chlorinated Hydrocarbons Using a Reaction-based Chemical Sensor. Part 2. Chemical Speciation Using Multivariate Curve Resolution, Anal. Chem. 1994 66 3337-3344. 

The term bioavailability has different meanings in different contexts and disciplines. Numerous definitions of bioavailability exist. Research on the relationship between bioavailability and chemical speciation (forms) originated in the field of soil fertility in the search for a good predictor for the bioavailability of essential plant nutrients (Traina and Laperche 1999). It is well accepted that dissolved nutrients are more labile and bioavailable to plants than solid-phase forms (including sorbed species). The same has been considered to be true for organic contaminants and their availability for microbial degradation. 

Kounaves and Zirino [ 145] studied cadmium-EDTA complex formation in seawater using computer-assisted stripping polarography. They showed that the method is capable of determining the chemical speciation of cadmium in seawater at concentrations down to 10 8 M. 

The experiments performed by Amdurer [847] were not intended to study chemical speciation or cycling of natural elements in the ecosystem. To do this, the tracers must be fully equilibrated with all of the reactive (i.e., nonmatrix) phases of the stable elements. This equilibration may require a time... 

Dyrssen D, Wedborg M (1980) Major and minor elements, chemical speciation in estuarine waters. In Olausson E, Cato I (eds) Chemistry and biogeochemistry of estuaries. Wiley, New York, pp 71-119... 

Muller, B., 2004, ChemEQL V3.0, A program to calculate chemical speciation equilibria, titrations, dissolution, precipitation, adsorption, kinetics, pX-pY diagrams, solubility diagrams. Limnological Research Center EAWAG/ETH, Kastanienbaum, Switzerland. 

Parker, D.R., W. A. Norvell and R. L. Chaney, 1995, GEOCHEM-PC, a chemical speciation program for IBM and compatible personal computers. In R. H. Loep-pert, A. P. Schwab and S. Goldberg (eds.), Chemical Equilibrium and Reaction Models. Soil Science Society of America Special Publication 42,253-269. 

Cadmium is a silver-white, blue-tinged, lustrous metal that melts at 321°C and boils at 767°C. This divalent element has an atomic weight of 112.4, an atomic number of 48, and a density of 8.642 g/cm3. It is insoluble in water, although its chloride and sulfate salts are freely soluble (Windholz et al. 1976 USPHS 1993). The availability of cadmium to living organisms from their immediate physical and chemical environs depends on numerous factors, including adsorption and desorption rates of cadmium from terrigenous materials, pH, Eh, chemical speciation, and many... 

Numerous and disparate copper criteria are proposed for protecting the health of agricultural crops, aquatic life, terrestrial invertebrates, poultry, laboratory white rats, and humans (Table 3.8) however, no copper criteria are now available for protection of avian and mammalian wildlife, and this needs to be rectified. Several of the proposed criteria do not adequately protect sensitive species of plants and animals and need to be reexamined. Other research areas that merit additional effort include biomarkers of early copper stress copper interactions with interrelated trace elements in cases of deficiency and excess copper status effects on disease resistance, cancer, mutagenicity, and birth defects mechanisms of copper tolerance or acclimatization and chemical speciation of copper, including measurement of flux rates of ionic copper from metallic copper. 

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