Trace element extractants

The determination of total amounts in soil is valid for finding whether there are toxic levels of certain metals (e.g. after repeated slurry applications), and comparisons can be made with published tables of maximum recommended levels. Some typical and maximum values are shown in Table 4.5 (ADAS, 1987 DOE/NWC, 1981). Dutch values differ from those developed in the UK in that the intention is to allow the return of contaminated land to any potential use, rather than tailoring the level of remediation to the intended use of the land. The most recent values include general targets and intervention values (httpy/www.athene.freeserve.co.uk/sanaterre/guidelines/dutch.htm). 

Metal Typical value In uncontaminated soil Maximum recommended level Earth/sediment (mg kg dry matter)  

The availability of the trace metals is easily determined without any of the above risks, and the results used to assess both deficiencies and toxici-ties. The metals need to be removed from the sites where they are bound to the soil particles by use of an even stronger binding agent than the soil. This is achieved with two possible complexing reagents EDTA and DTPA. They are a class of chemicals known as complexones, which form complex molecules with metals in a cage-like structure called a chelate. 

DTPA is diethylenetriaminepentaacetic acid, also known as diethylen-etrinitrilopentaacetic acid, mol. wt 393.36. It is octo-dentate, having eight active metal-complexing sites per molecule. A diagrammatic representation of the DTPA molecule is shown in Eig. 4.6. 

The amount of metal extracted from the soil by both EDTA and DTPA is dependent on the pH, the metal being extracted, the soiksolution ratio, the concentration of chelating agent, the shaking time, the temperature, and the sample preparation procedure. Clearly, the methodology used should be clearly described and closely followed if repeatable work is to be possible, and comparison of results is to be meaningful. 

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Table 4.3. Dissolution of some trace elements extracted by NaOAc-HOAc at various pHs after removing the exchangeable fraction (mg/kg)a... 

The contents of trace elements extracted by the buffer solutions depend upon the solution s acid capacity in dissolving carbonate from soils. Trace elements dissolved by the buffer solution increased with decreasing pH of the buffer solution (Table 4.3). Release of trace elements by the buffer solutions at pH 6.0 was much smaller from calcareous soils with more than 30% of CaCC>3. The dissolution of trace elements by the buffers paralleled with the dissolution of Ca and Mg. The correlation coefficients between Ca and trace elements were as follows Cd (0.92), Pb (0.87), Zn (0.90), Ni (0.90), Cr (0.91), V (0.54) and Co (0.70) and between Mg and trace elements were Cd (0.88), Pb (0.80), Zn (0.79), Ni (0.87), Cr (0.58), V (0.69) and Co (0.80), (all with n = 32). 

For a discussion on the nature of the extractants, see Chapter 4 Trace element extractants. ... 

Dreesen, D. R., Gladney, E. S., Owens, J. W., Perkins, B. L., Wienke, C. L. Wangen, L. E. 1977. Comparison of levels of trace elements extracted from fly ash and levels found in effluent waters from a coal fired power plant. Environmental Science and Technology, 10, 1017-1019. 

Griepink, B. (1993) Some considerations with regard to the quality of results of analysis of trace element extractable contents in soil and sediment. Int.f. Environ. Anal. Chem., 51, 123. 

Trace Element Removal During Physical Cleaning. Comnercial coal cleaning processes employ physical means for beneficiation and are aimed at removing ash forming minerals and sulfur, although removal of the mineral matter also results in reduced levels of some trace elements. Trace element extraction efficiencies for various physical cleaning processes have been reported. 

Trace element extraction efficiencies for a given cleaning process are highly variable between coals. 

Table 1 summarises the concentrations of trace elements extracted with chloroform from oil shale samples of the two... 

Dresser, D.R., Gladney, E.S., Owens, J.W. Perkins, B.L., Winke, C.L. and Wangen, L.E., Comparasion of trace elements extracted from fly ash levels found in efflunt waters from coal fired powerplant. Envion. Sci. Technol., 1977, 11, 1017. 

HM Crews, JA Burrell, DJ McWeeney. Preliminary enzymolysis studies on trace element extractability from food. J Sci Food Agric 34 997-1004, 1983. 

Table 2, Trace elements extracted by 1 M ammonium acetate and CO C respired from fumigated and non-fumigated soil (iig g -l dry soil).

BERROW M.L., DAVIDSON M.S. and BURRIDGE J.C. 1982. Trace elements extractable by 2-ketogluconic acid from soils and their relationship to plant contents. Plant and Soil, 66, 161-171. 

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