Geochemical assessment of metal transfer from rock and soil to water in serpentine areas of Sabah (Malaysia)

Tashakor, M, Hochwimmer, B and Brearley, FQ (2017) Geochemical assessment of metal transfer from rock and soil to water in serpentine areas of Sabah (Malaysia). Environmental Earth Sciences, 76 (7). pp. 281-293. ISSN 1866-6280

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Abstract

The mobility of metals in ultramafic rock–soil systems and metal contamination in serpentine soils were investigated from the Ranau area in Sabah, East Malaysia. Metal concentrations were analysed after division into seven operationally defined fractions by selective sequential extraction (SSE). Geochemical studies showed that the soils are exceptionally high in Cr (<19,000 mg kg−1), Ni (<4800 mg kg−1) and Co (<170 mg kg−1), about 140, 16 and 10 times higher than global soil averages, respectively. Thus, the soil can be categorized as unusually contaminated in comparison with relevant guidelines. Nevertheless, despite expectations, low concentrations of Cr, Ni and Co were found in surface waters flowing over the serpentine massifs (<14, 94 and 7 µg L−1, respectively), indicating mobile ingress into river waters is low or, alternatively, diluted in the tropical environment resulting in minimal decline in their quality ascribed to the regional ultramafic geology of the area. The main reason is revealed by the SSE finding of very low (<1%) mobile metal abundances in available fractions of Ranau soils. While this study is one of the first to use a comprehensive SSE in tropical serpentine soils, the major SSE finding highlights the majority of metals (>95%) residing in refractory residual fractions. Metal speciation studies will shed further light on toxicities in the Malaysian ultramafic tropical environment, reconciled against elemental metal tenure, adopted by common standards.