Distribution and geochemical baselines of major, minor and trace elements in tropical topsoils of the Terengganu River basin, Malaysia

摘要

This study reports on the physico-chemical properties and concentrations of major, minor and trace elements (Si, Al, Fe, K, Na, Mg, Ca, Ti, Ba, Mn, Cr, Sr, Zr, Zn, Ni, Y, Li, Cu, Co, Nb, Ga, Th, Sc, Mo, W, Be, Ge, Ta, Bi, Se, Te, and Re) in tropical topsoils (0-10 cm) of the Terengganu River basin, Malaysia. Soils were observed to be mildly acidic (average pH_(1:5) ~5.4) with loam to sandy loam texture, and exhibited low CEC (average ~2.25cmol_((+))/kg) and low organic matter contents (average LOI ~3.0%). NE monsoonal heavy rains and annual flooding remove finer particles leaving soils with a high sand size fraction (average ~52.46%) rich in quartz. Under the humid tropical conditions most of the metals from the topsoil layer, especially alkali and alkali earth metals (e.g. Na, Ca, Mg, Sr, Ba), are significantly depleted by preferential leaching and/or plant uptake. The average concentrations of Si, Cr, Zn, Ni, Mo, W, Bi, Se and Te were measured to be higher in soils as compared to the upper continental crust. Mineral deposits associated with granite rock also contribute to the elevated levels of metals apart from cases where the soil geochemical processes enrich metals by fixation on the secondary Al-Fe-(hydro)oxides. Soils developed on granite rock registered higher concentrations of most of the elements investigated throughout the four main geological units in the Terengganu River basin. Principal component analysis (PC1, 91.9% and PC2, 5.90%) revealed that the element concentration and distribution are primarily influenced by the local geology and soil texture. Most of the metals investigated registered concentrations well below the guideline values with the exception of Mn, Cr, Ni and Ba which exceeded the permissible levels. Higher Cr concentrations (average -94.89 mg/kg) seemed to be introduced into soils by the use of pesticides (e.g. CCA) as a wood preservative at a few locations. Soils developed on metasedimentary rocks registered higher W concentration (average -2.3 mg/kg) as compared to other rock units, probably as a result of the presence of mineral scheelite (CaWO4) as revealed by SEM analysis. This work presents the local and regional geochemical baseline values of 32 major, minor and trace elements of tropical surface soils of the NE region of Peninsular Malaysia.