Heavy metals, definition

At X-ray fluorescence analysis (XRF) of samples of the limited weight is perspective to prepare for specimens as polymeric films on a basis of methylcellulose [1]. By the example of definition of heavy metals in film specimens have studied dependence of intensity of X-ray radiation from their chemical compound, surface density (P ) and the size (D) particles of the powder introduced to polymer. Have theoretically established, that the basic source of an error of results XRF is dependence of intensity (F) analytical lines of determined elements from a specimen. Thus the best account of variations P provides a method of the internal standard at change P from 2 up to 6 mg/sm the coefficient of variation describing an error of definition Mo, Zn, Cu, Co, Fe and Mn in a method of the direct external standard, reaches 40 %, and at use of a method of the internal standard (an element of comparison Ga) value does not exceed 2,2 %. Experiment within the limits of a casual error (V changes from 2,9 up to 7,4 %) has confirmed theoretical conclusions. 

For exposure of reasons of observable discrepancy of results of the analysis simulated experiment with application synthetic reference samples of aerosols [1]. The models have demonstrated absence of significant systematic errors in results XRF. While results AAA and FMA depend on sort of chemical combination of an elements, method of an ashing of a material and mass of silicic acid remaining after an ashing of samples. The investigations performed have shown that silicic acid adsorbs up to 40 % (rel.) ions of metals. The coefficient of a variation V, describing effect of the indicated factors on results of the analysis, varies %) for Mn and Fe from 5 up to 20, for Cu - from 10 up to 40, for Pb - from 10 up to 70, for Co the ambassador of a dry ashing of samples - exceeds 50. At definition Cr by a method AAA the value V reaches 70 %, if element presences an atmosphere in the form of Cr O. At photometric definition Cr (VI) the value V is equal 40%, when the element is present at aerosols in the form of chromates of heavy metals. 

Underpotential deposition of heavy metals on H2 evolving electrodes is a well known problem [133], The existence of a direct correlation between H2 evolution activity and metal work function, makes UPD very likely on high work function electrodes like Pt or Ni. Cathode poisoning for H2 evolution is aggravated by UPD for two reasons. First, deposition potentials of UPD metals are shifted to more anodic values (by definition), and second, UPD favors a monolayer by monolayer growth causing a complete coverage of the cathode [100]. Thus H2 evolution may be poisoned by one monolayer of cadmium for example, the reversible bulk deposition potential of which is cathodic to the H2 evolution potential. 

Some toxic effects of heavy metals pertain to a change of amino acid contents in urine. It is established that accumulation of metals in hair and nails and secretions through urine and saliva are definitely correlated. It was obviously due to enzyme features as well as the level of environmental pollution. 

Trace elements include heavy metals, some of which have recently received particular attention. Many definitions of heavy metals have been put forward. The simplest and most precise describes heavy metals as all metal compounds of atomic weight over 20. Other definitions are based on the specific weight, and give the lower limits for heavy metals as 4.5, 5, or even 6 g per cm. Due to toxicity of some heavy metals and the possibility of environmental contamination, the potential for high risk is linked to Hg, Cd, As, Pb, as well as Cu, Zn, Sn, Cr, Ni. 

The term heavy metal in environmental chemistry has traditionally been used to describe certain elements and compounds that are hazardous to the health of humans and other animals. Some elements included in this definition are arsenic, beryllium, cadmium, chromium, lead, and mercury. 

Most of them dissolve in solutions of the fixed alkalies, whether hot or cold, as also in ammonia, and form definite salts—re slnates—some of which are quite neutral, These resinates are soluble in water, and form a considerable portion of the cheaper kinds of soap, being themselves possessed of detergent qualities. RoBtnatcs of the alkaline earths, and of the heavy metallic oxides, may be prepared from those of the alkalies by double decomposition but they are insoluble, and generally strong acids liberate the resin from them unchanged. 

Salminen, R., and Gregorauskiene, V. (2000). Considerations regarding the definition of a geochemical baseline of heavy metals in the overburden in areas differing in basic geology. Appl. Geochem. 15, 647-653. 

Speciation encompasses both the chemical and physical form an element takes in a geochemical setting. A detailed definition of speciation includes the following components (1) the identity of the contaminant of concern or interest (2) the oxidation state of the contaminant (3) associations and complexes to solids and dissolved species (surface complexes, metal-ligand bonds, surface precipitates) and (4) the molecular geometry and coordination environment of the metal.5 The more of these parameters that can be identified the better one can predict the potential risk of toxicity to organisms by heavy metal contaminants. Prior to the application... 

It should be noted that the complexity and ill definition of carbonate salts in highly saline solutions is documented in literature by the complete absence of single salt osmotic and activity coefficient data. This situation requires the use of this less than satisfying technique to define heavy metal chemistry in brines. 

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