Assessment of selected sequential extraction and the toxicity characteristic leaching test as indices of metal mobility in serpentinite soils

Abstract

Serpentinite soils are characterised by high concentrations of chromium, nickel, and cobalt. The accumulation of heavy metals as non-degradable inorganic contaminants is of great concern. Under normal circumstances the form in which a metal exists governs its transport in the environment and thus, its hazards. In this study, a specific developed speciation analysis for tropical soils was applied to determine the mobility of Cr, Ni and Co in two serpentinitic soil outcrops in Malaysia. The combination of selective sequential extraction analysis (SEE) and X-ray diffraction of soil powders showed that Cr and Ni are primarily associated with the residual fraction of soil which is inherited from resistant silicates. The crystalline Fe-oxide fraction of soil is the second substanial scavenger of Cr and Ni, whilst the dynamics of Co are mostly controlled by Mn-oxide and the poor crystalline Fe-oxide. The more easily mobilised forms of the studied metals carried on soluble-exchangeable, surface adsorbed and organic matter fractions are of minimal compartments. Therefore these metals are basically not available in the environment. On the other hand, corroborating information on the mobility of the metals was gained by applying the toxicity characteristic leaching procedure test (TCLP). The consistent results of the TCLP with the SSE revealed the non-toxic effects of Cr, Ni and Co in the environment despite their overload accumulation in the analysed serpentinite soils.