CADMIUM AND ZINC IN ACID TROPICAL SOILS - I - SOIL PHYSICOCHEMICAL PROPERTIES EFFECT ON THEIR ADSORPTION

Interactions of heavy metals, such as cadmium (Cd) and zinc (Zn) at th e soil particle surfaces play an important role in controlling their l eaching losses to the underground water and their availability to plan ts. Adsorption isotherms for eight soils [Apas (Rhodic Hapludox), Bata ng (Typic Plinthudult), Jarangan (Xanthic Hapludox), Katai (Typic Hapl udult), Koyah (Oxic Dystropept), Lumisir (Typic Plinthudult), Paliu (T ypic Hapludult), and Table (Typic Hapludox)] from major cocoa (Theobro ma cacao, L.), oil palm (Elaeis guineensis Jacq.), and rubber (Hevea b rasiliensis Muell Agr.) growing areas in Tawau, Sabah, Malaysia were d etermined at concentrations of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg Cd or Zn mL(-1) in a 0.025M calcium chloride (CaCl2. 2H(2)O ) solution. The adsorption of Cd and Zn by the soils can successfully be explained by the Freundlich equation (r = 0.832* - 0.977**) as com pared to the Langmuir equation (r = 0.130ns - 0.977*). The ability of the soils to adsorb Cd and Zn differed markedly with the highest obta ined in Table soil (18.4 mg Cd kg(-1) soil) for Cd and Koyah soil (29. 97 mg Zn kg(-1)) for Zn. The important soil parameters in controlling the adsorption of both Cd and Zn in acid tropical soils were cation ex change capacity (CEC) (r = 0.888*), total aluminium (Al) content (r = 0.675*), and extractable-Al (r = 0.875**).