Metal concentrations in natural

Despite the difficulties, there have been many efforts in recent years to evaluate trace metal concentrations in natural systems and to compare trace metal release and transport rates from natural and anthropogenic sources. There is no single parameter that can summarize such comparisons. Frequently, a comparison is made between the composition of atmospheric particles and that of average crustal material to indicate whether certain elements are enriched in the atmospheric particulates. If so, some explanation is sought for the enrichment. Usually, the contribution of seaspray to the enrichment is estimated, and any enrichment unaccounted for is attributed to other natural inputs (volcanoes, low-temperature volatilization processes, etc.) or anthropogenic sources. 

Bordin, G., J. McCourt, and A. Rodriguez. 1994. Trace metals in the marine bivalve Macoma balthica in the Westerschelde estuary, the Netherlands. Part 2 intracellular partitioning of copper, cadmium, zinc and iron — variations of the cytoplasmic metal concentrations in natural and in vitro contaminated clams. Sci. Total Environ. 151 113-124. 

Schindler, P. W. The regulation of trace metal concentrations in natural water systems a chemical approach, in "Atmospheric Contribution to the Chemistry of Lake Waters." Proc. First Speciality Symposium, Internat l Assoc. Great Lakes Res. 1975. 

Scarponi et al. [93] concluded that filtration of seawater through uncleaned membrane filters shows positive contamination by cadmium, lead, and copper. In the first filtrate fractions, the trace metal concentration maybe increased by a factor of two or three. During filtration, the soluble impurities are leached from the filter, which is progressively cleaned, and the metal concentration in the filtrate, after passage of 0.8 -11 of seawater, reaches a stable minimum value. Thus it is recommended that at least one litre of seawater at natural pH be passed through uncleaned filters before aliquots for analysis are taken... 

Ruzic [278 ] considered the theoretical aspects of the direct titration of copper in seawaters and the information this technique provides regarding copper speciation. The method is based on a graph of the ratio between the free and bound metal concentration versus the free metal concentration. The application of this method, which is based on a 1 1 complex formation model, is discussed with respect to trace metal speciation in natural waters. Procedures for interpretation of experimental results are proposed for those cases in which two types of complexes with different conditional stability constants are formed, or om which the metal is adsorbed on colloidal particles. The advantages of the method in comparison with earlier methods are presented theoretically and illustrated with some experiments on copper (II) in seawater. The limitations of the method are also discussed. 

In many mountain-industrial areas there are 3 1 landscape-functional zones with different extents of the anthropogenic transformation of natural environments. As a rule, the first zone is the spatial complex joining mines, pits and tails site area with almost whole degradation of soil and vegetation cover and high metal concentrations in dust, technogenic depositions, waters and plants. 

Rubidium does not exist in its elemental metallic form in nature. However, in compound forms it is the 22nd most abundant element on Earth and, widespread over most land areas in mineral forms, is found in 310 ppm. Seawater contains only about 0.2 ppm of rubidium, which is a similar concentration to lithium. Rubidium is found in complex minerals and until recently was thought to be a rare metal. Rubidium is usually found combined with other Earth metals in several ores. The lepidolite (an ore of potassium-lithium-aluminum, with traces of rubidium) is treated with hydrochloric acid (HCl) at a high temperature, resulting in lithium chloride that is removed, leaving a residue containing about 25% rubidium. Another process uses thermochemical reductions of lithium and cesium ores that contain small amounts of rubidium chloride and then separate the metals by fractional distillation. 

Windom HE, Schropp SJ, Calder FD, et al. 1989. Natural trace metal concentrations in estuarine and coastal marine sediments of the southeastern United States. Enviromnental Science and Technology 23 314-320. 

Heavy metal toxicity in plants is infrequent (143). In many cases, metal concentrations in plant parts show poor correlation with soil concentrations of the element (147). Plants tend to exclude certain elements and readily accept or concentrate others. Lisk (148) reported natural plant soil concentration ratios of 0.05 or less for As, Be, Cr, Ga, Hg, Ni, and V. Cadmium appears to be actively concentrated and selenium appears to be easily exchangeable. Indicator plants are capable of markedly concentrating specific elements, e.g., Astragalus spp. for selenium (138) and Hybanthus floribundus for nickel (149). Plants growing on mine wastes have been shown to evolve populations which exhibit metal-specific tolerances (150). 

Most metals occur in nature as minerals, the crystalline, inorganic constituents of the rocks that make up the earth s crust. Silicates and aluminosilicates (Section 19.7) are the most abundant minerals, but they are difficult to concentrate and reduce and are therefore generally unimportant as commercial sources of metals. More important are oxides and sulfides, such as hematite (Fe203), rutile (Ti02), and cinnabar (HgS) (Figure 21.1), which yield iron, titanium, and... 

Anodic stripping voltammetry (ASV) is a very sensitive instrumental technique for the measurement of metals in solution. Of particular importance are determinations of reactive or ASV-labile metal concentrations. ASV-labile metal is defined as the fraction of the total metal concentration that is measured under a defined set of ASV and solution conditions. Labilities of metal species in natural water have been related to toxicities. Thus, one objective of speciation analysis carried out by ASV is to find conditions where the ASV-labile fraction is a close approximation to the toxic fraction of a metal. In experimental terms, the ASV-labile metal should be equal to the electroactive fraction of the metal. The latter... 

More recently plant analysis has been carried out to screen for the accumulation of metals indicative of pollution. Usually metal concentrations are reported in dry plant material. However, it has been suggested (Claussen, 1990) that the concentrations of pollutants are better related to the dry ash of a plant, than to the dry weight, since it eliminates the natural variations of organic matter. Heavy metal concentrations in ash of Populus nigra Italica were reported to correlate better with values in air and soil than those in dry plant material. 

These metals (i.e. typical metals) occur in nature as silicate minerals. Due to weathering we also find concentrated deposits of other compounds such as halides (e.g. NaCl, CaF2), carbonates (CaCo3) and... 

Fitzwater SE, Johnson KS, Gordon RM, Coale KH, Smith WO (2000) Trace metal concentrations in the Ross Sea and their relationship with nutrients and growth. Deep-Sea Res Part II 47 3159-3179 Gerringa LJA, de Baar HJW, Timmermans KR (2000) A comparison of iron limitation of phytoplankton in natural oceanic waters and laboratory media conditioned with EDTA. Mar Chem 68 335-346 Gibson JAE, Garrick RC, Burton HR, McTaggart AR (1990) Dimethylsulfide and the alga Phaeocystis pouchetii in Antarctic coastal waters. Mar Biol 104 339-346... 

Phosphoric acid, as pointed out previously, exhibits three pKa values, 2.23,7.2, and 12.3, and its titration plot is shown in Figure 1.10. As expected, it shows three pKa values and four equivalence points. The only pKa that is of environmental importance is that at slightly above 7.2 (marked with an X). However, phosphate is not a desirable environmental buffer because of its eutrophication potential and its strong tendency to precipitate in natural water systems as metal-phosphate (where metal denotes any divalent or bivalent cations) (Stumm and Morgan, 1981). In most cases, its concentration in natural waters is less than 1 ppm. 

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