Distribution in Soils and Sediments

The average amount of zinc in the earth s crust is a little over 100 mg kg. Average zinc concentration in soils and sediment is approximately 30 mg kg. In sediments, the reported concentrations are variable and have been found to range from 10 to over 200 mg kg . Anthropogenic activities seem to be an important factor in the increase of zinc in the environment. High concentrations of zinc in aquatic environment are detrimental to fish and aquatic life. 

Zinc is one of the most mobile of the heavy metals. The zinc compounds formed with the common anions found in surface waters are soluble in neutral and acidic conditions. In reducing environments, zinc sulfide (ZnS) is a relatively insoluble and stable compound, which may oxidize in the presence of dissolved oxygen. Zinc carbonate (ZnCOj) is assumed to be less stable than zinc sulfide, though still relatively insoluble. Zinc ions are dominant up to pH values of about 9 in simple aqueous systems. In basic solutions, zinc hydroxide (Zn(OH)2) precipitates if the concentration of zinc is 10.4 M. Zinc hydroxide shows minimal solubility at pH 9.5 and dissolves at higher pH values as the zincate anion, Zn(OH) . 

The cycling of sediment-bound Zn among various geochemical forms is strongly influenced by changes in pH and oxidation-reduction (redox) potential in sediment-water systems (Khalid et al., 

A study was conducted on Mississippi River sediment material under conditions of controlled pH (5.0, 6.5, and 8.0) and redox potential (-150, 50, 250, and 500 mV) to determine the effect of these parameters on chemical forms and distribution of added zinc. The results of this study indicate that adsorption by or coprecipitation with oxides and hydroxides of iron and manganese was the important regulatory process governing the availability of zinc in this sediment-water system. 

Retention of added zinc by sediment solids was 56-60% at pH 5.0, 97% at pH 6.5, and essentially 100% at pH 8.0. Most of the zinc was present in the exchangeable and reducible fractions. Only a small proportion of added zinc was associated with insoluble organic material, as evidenced by the low recovery in DTPA and residual organic fractions (Table 12.3). The reducible phase is believed to consist of Zn strongly adsorbed to or coprecipitated with oxides and hydroxides of iron 

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Camilion, C., Manassero, M., Hurtado, M. and Ronco, A. (2003) Copper, Lead and Zinc distribution in soils and sediments of the South Western coast of the Rio de la Plata estuary, Journal of Soils and Sediments 3, 213-220. 

Cave, M.R. and Wragg, J. (1997) Measurement of trace element distributions in soils and sediments using sequential leach data and a non-specific extraction system with chemo-metric data processing. Analyst, 122, 1211-1221. 

The oxide and oxyhydroxide minerals of Mn are widely distributed in soils and sediments (Jenne, 1968 McKenzie, 1989). In terrestrial and aquatic environments, Mn oxides and oxyhydroxides occur as coatings on other soil and sediment particles and as discrete particles they exist in close associa-... 

Carbonates, organic matter, Fe and Mn oxides, and clay minerals play important roles in controlling overall reactivity of trace elements in soils and sediments. This chapter addresses the interaction of trace elements with carbonates, organic matter, Fe and Mn oxides and clay minerals. Analytical techniques for trace element speciation in solid-phase and their distribution among various solid-phase components in arid and semi-arid soils are reviewed. Solubilities of trace elements in solid phases and their mineralogical characteristics in arid and semi-arid soils also are discussed. 

This technique is extremely useful for determining the surface concentration and distribution of elements e.g. chlorine, arsenic, etc. in soils and sediments. 

Schmidt, M. W. I., and Noack, A. G. (2000). Black carbon in soils and sediments Analysis, distribution, implications, and current challenges. Glob. Biogeochem. Cycles 14, 777-793. 

Species distribution studies have shown that trace element (e.g. metals) concentrations in soils and sediments vary with physical location (e.g. depth below bed surface) and with particle size. In these speciation studies the total element content of each fraction was determined using a suitable trace element procedure, for example, solid sample analysis by X-ray emission spectroscopy or neutron activation analysis, or alternatively by dissolution of sample and analysis by ICPOES, AAS or ASV. The type of sample fraction analysed can vary, and a few... 

There are many other indirect techniques for determining colloidal species size or size distribution. These include sedimentation/centrifugation, conductivity, x-ray diffraction, gas and solute adsorption, ultrafiltration, viscometric, diffusiometric, and ultrasonic methods [12,13,26,69,82], Two reasons for the large number of techniques are the range of properties that can be influenced by the size of dispersed species, and the wide range of sizes that may be encountered. The grains in soils and sediments can range from colloidal size up to the size of boulders. 

Extrapolation by Prediction of actual exposure semimechanistic model Organic toxicants in soil and sediment Organic toxicants in water Prospective distribution modeling... 

Arsenic is widely distributed on earth in the atmosphere, in the aquatic environment, in soils and sediments, and... 

Wauters, J., Elsen, A., Cremers, A., Konoplev, A. V., Bulgakov, A. A., and Comans, R. N. J. (1996). Prediction of solid/liquid distribution coefficients of radiocesium in soils and sediments, 1 A simplified procedure for the solid phase characterisation. Appl. Geochem. 11, 589-594. 

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