Standard Practices for Extraction of Trace Elements from Sediments

Importancia y uso:

5.1 Industrialized and urban areas have been found to deposit a number of toxic elements into environments where those elements were previously either not present or were found in trace amounts. Consequently, it is important to be able to measure the concentration of these pollution-deposited elements to properly study pollution effects.

5.2 This procedure is concerned with the pollution-related trace elements that are described in 4.1 rather than those elements incorporated in the silicate lattices of the minerals from which the sediments were derived. These pollution-related trace elements are released into the water and readsorbed by the sediments with changes in general water quality, pH in particular. These elements are a serious source of pollution. The elements locked in the silicate lattices are not readily available in the biosphere (1-8).

5.3 When comparing the trace element concentrations, it is important to consider the particle sizes to be analyzed (8, 9).

5.3.1 The finer the particle the greater the surface area. Consequently, a potentially greater amount of a given trace element can be adsorbed on the surface of fine, particulate samples (4). For particle sizes smaller than 80 mesh, metal content is no longer dependent on surface area. Therefore, if this portion of the sediment is used, the analysis with respect to sample type (that is, sand, salt, or clay) is normalized. It has also been observed that the greatest contrast between anomalous and background samples is obtained when less than 80-mesh portion of the sediment is used (4, 5).

5.3.2 After the samples have been dried, care must be taken not to grind the sample in such a way to alter the natural particle-size distribution (14.1). Fracturing a particle disrupts the silicate lattice and makes available those elements which otherwise are not easily digested (6). Normally, aggregates of dried, natural soils, sediments, and many clays dissociate once the reagents are added (14.3 and 15.2).

Subcomité:

D19.07

Referida por:

D5258-22, D8404-21, D5074-90R22, D5765-16

Volúmen:

11.02

Número ICS:

13.060.30 (Sewage water)

Palabras clave:

extraction; sediments; toxic; trace elements;