Distribution of Pb, As, Cd, Sn and Hg in soil, sediment and surface water of the tropical river watershed, Terengganu (Malaysia)

Hydrogeochemistry and distribution of Pb, As, Cd, Sn and Hg in soils (n = 53), sediments (n = 42) and surface waters (n = 51) of the tropical Terengganu River basin, northeast coast of Peninsular Malaysia, were investigated. The order of abundance of the elements in soils followed granite > metasedimentary > Quaternary deposit ≫ volcanic with slight enrichment as compared to the upper continental crust. Both soils and sediments registered the order of concentration of Pb > Sn > As ≫ Cd ≫ Hg with an enrichment factor (EF) < 6 for sediments indicating slight enrichment representing the regional background and less likely due to the anthropogenic activity related input. SEM analysis revealed the presence of Malayaite (CaSnOSiO4) explaining elevated Sn concentration (up to ∼34 mg/kg; 3 times the upper continental crust) in soils. Soil Pb distribution showed the geology as the primary control.Dissolved concentrations of As showed an increasing and Cd decreasing with distance from upstream to downstream along the river flow path. Lake surface waters registered 16 times higher Cd concentrations (average ∼ 14.21 μg/L) than the river waters, but lake sediments registered lower Cd concentration than the river sediments (average ∼ 0.45 mg/kg) revealing Eh, pH and TDS control. Dissolved average Hg concentration (∼0.04 μg/L) was measured to be lower than the tropical river waters from the Central Africa river, but higher than the Mekong and the Amazon Rivers.

► The geochemical baseline values of potentially toxic elements (Hg, Pb, As, Cd and Sn) in Asian tropical basins are reported to be higher than the tropical river basins in the Central Africa and the South America (Amazon basin).
► The order of abundance of the elements in Asian tropical soils derived from various rocks followed granite > metasedimentary > Quaternary deposit ≫ volcanic with slight enrichment as compared to the upper continental crust.
►  This study highlights the need for the local and global geochemical baselines of elements.