Speciation assessing

The term species generally refers to the molecular forms of an element or a cluster of atoms of different elements in a given (in this case solid) matrix (Bernhard et al., 1986a). The term form is also used to indicate uncertainty or lack of knowledge about the exact nature of the species one expects to find in an environmental sample. Conditional speciation assessment techniques like sequential extractions or leaching tests are not able to yield information at the true molecular level in solid phases thus the more general term form is used rather than species when referring to the results of such techniques commonly applied to date to soils and sediments. 

The chemistries of Ru, Os, Rh, and Ir in seawater are poorly understood. Available evidence suggests that the probable oxidation state of Ru is + IV OSO4 has a large field of stability on oxidation potential vs pH diagrams and can thereby be considered as an important species in seawater. Rh and Ir are expected to exist in lower oxidation states than Ru and Os. Available evidence (Baes and Mesmer, 1976) indicates that the most important oxidation state for Rh and Ir is + III. Rhm and Irm form strong chloride complexes and should, as well, hydrolyse extensively in solution at pH 7.4-8.2. This speciation assessment is consistent with the relative enrichment of Os in seawater compared to Ir. OSO4 should be substantially less reactive towards particles than is the case for Ir(Cl) - and Ir(OH) - species. 

While some elements, such as Fe, can be singled out for their special biogeo-chemical significance, the speciation of other elements can be highlighted due to an extreme paucity of quantitative assessments with respect to both speciation and distribution. Elements such as Nb, Ta, Ru, Os, Rh, Ir, Pt and Au are especially deserving of further distributional characterisations and speciation assessments. 

Resolution of taxonomy of probiotic species and development of user-friendly methods for conducting speciation assessments... 

The thermodynamic data compilations of Sillen and Martell catalyzed rapid advances in equilibrium models of seawater speciation. These works were followed by additional compilations that were critically important to modern sea-water speciation assessments. In view of these developments, and additional extensive experimental analyses appropriate to seawater. Principal Species assessments ten to fifteen years after the pioneering work of Sillen demonstrated a much improved awareness of the importance of hydrolysis in elemental speciation. 

An additional major speciation assessment provided a greatly improved, comprehensive view of inorganic complexation in seawater. Based on the analogous characteristics of metal complexation by carbonate and oxalate, Turner et al. concluded that rare earth element complexation in seawater is dominated by carbonate. Subsequently, as the result of approximately twenty years of progress in seawater speciation, the Principal Species assessment of Bruland listed seventeen elements with carbonate-dominated Principal Species. 

The proposed method can be applied to the speciation analysis of environmental solids for risk assessment of their contaminants as well as to design of effective leaching schemes. 

Mass spectrometry can be specific in certain cases, and would even allow on-line QA in the isotope dilution mode. MS of molecular ions is seldom used in speciation analysis. API-MS allows compound-specific information to be obtained. APCI-MS offers the unique possibility of having an element- and compound-specific detector. A drawback is the limited sensitivity of APCI-MS in the element-specific detection mode. This can be overcome by use of on-line sample enrichment, e.g. SPE-HPLC-MS. The capabilities of ESI-MS for metal speciation have been critically assessed [546], Use of ESI-MS in metal speciation is growing. Houk [547] has emphasised that neither ICP-MS (elemental information) nor ESI-MS (molecular information) alone are adequate for identification of unknown elemental species at trace levels in complex mixtures. Consequently, a plea was made for simultaneous use of these two types of ion source on the same liquid chromatographic effluent. 

Howari F. Heavy metal speciation and mobility assessment of arid soils in the vicinity of A1 Ain landfill, United Arab Emirates Int J Environ Pollut 2004 22 721-731. 

In aquatic environments, more research is needed on the chemical speciation of silver to evaluate risk to the organism and its consumers (USEPA 1987 Berthet etal. 1992). Most silver criteria formulated for the protection of aquatic life are now expressed as total recoverable silver per liter (Table 7.8), but total silver measurements do not provide an accurate assessment of potential hazard. Silver ion (Ag+), for example, is probably the most toxic of all silver chemical species and must... 

Delhi soils by studying its speciation in the soil profile and to assess if there was any spatial variability. Soils representing the Aravali Ridge and the alluvial floodplains of river Yamuna were collected as a single, undisturbed core up to a depth of lm and the profile differentiated into four layers- 0-17 cm, 17-37 cm, 37-57 cm, and 57-86 cm. Pseudo total Aluminum and Iron in the soils were speciated into the operationally defined species (weakly exchangeable, organic matter complexes, amorphous oxides and hydroxides, and crystalline or free oxides) by widely recommended selective extraction procedures. Both A1 and Fe in these soils are bound predominantly as Fe oxides and silicates and have only very low percentages in the easily mobilizable pools. 

The major part of the biosphere is aerobic and consequently priority has been given to the study and assessment of biodegradability under aerobic conditions. Nevertheless, there are environmental compartments that can be permanently (e.g. anaerobic digesters) or temporarily anaerobic (e.g. river sediments and soils) and surfactants do reach these. The majority of surfactants entering the environment is exposed to and degraded under aerobic conditions. This is the predominant mechanism of removal even in cases of absence of wastewater treatment practices (direct discharge) and it is estimated that less than 20% of the total surfactant mass will potentially reach anaerobic environmental compartments [1]. Only in a few cases, however, will the presence of surfactants in these compartments be permanent. The presence of surfactants in anaerobic zones is not exclusively due to the lack of anaerobic degradation. Physico-chemical factors such as adsorption or precipitation play an important role as well as the poor bioavailability of surfactant derivatives (chemical speciation) in these situations. 

Conditions prevailing in the environment, however, are extremely difficult to simulate in the laboratory, in particular those occurring under strict anaerobic zones. Chemical speciation of the test substance in such environments is difficult to assess and consequently to reproduce in laboratory tests. 

Conventional studies generally involve the collection of an assemblage of airborne particles followed by determinations of the average or bulk concentrations of pollutant species present (12). However, the results often lack the analytical specificity required to identify particle sources, to determine particle speciation and reactivity, or to assess particle toxicity. 

The Nickel Producers Environmental Research Association (NiPERA) is sponsoring research on the application of inductively coupled plasma-mass spectroscopy (ICP-MS) to isotopic analysis of nickel in biological samples, on the development of sampling instrumentation for assessing workers exposure to nickel in the nickel industry, and on methods for utilizing newly developed analytical methods, such as laser beam ionization mass spectrometry, for the identification and speciation of nickel compounds in powders and dusts with particular reference to nickel refining. 

Illustrative Example 8.1 Assessing the Speciation of Organic Acids and Bases in Natural Waters... 

In order to estimate how the bioavailability of benzo(a)pyrene (BP) is affected by DOM, you want to assess the speciation of this compound as a function of DOM quantity and quality. To this end, calculate the fw value of BP for aqueous solutions (pH 7, 25°C) containing (a) 10 mg DOC-L"1 and 100 mg DOC-L"1, respectively, and (b) assuming DOM qualities as reflected by the LFERs 1 and 7 in Fig. 9.16 (see figure caption for slopes and intercepts). Note that DOM 1 represents a humic acid that exhibits a high affinity for PAHs, whereas DOM 7 is a fulvic acid with a low affinity. Hence, the two DOMs may represent extreme cases with respect to sorption of apolar and weakly polar compounds in natural waters. 

P 9.7 Assessing the Speciation of a PCB-Congener in a Sediment-Pore Water... 

Ruiz-Chancho, M.J., Lopez-Sanchez, J.F. and Rubio, R. (2007) Analytical speciation as a tool to assess arsenic behaviour in soils polluted by mining. Analytical and Bioanalytical Chemistry, 387(2), 627-35. 

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