Ecological Risk Assessment of Heavy Metal Pollution in Surface Sediment of Mahakam Delta, East Kalimantan☆

Abstract Spreading heavy metals in the water column may subsequently be accumulated in sediment because of low solubility then become sensitivity indicator for aquatic organism. Ecological risk is assessed through the heavy metals concentration in the surface sediment. Sediment samples were grabbed from 20 stations in Mahakam Delta. Hakanson method was used to identify ecological potential risk of heavy metals pollution. The results showed that Zn (70.63 mg/kg), Cr (4.93 mg/kg), Cd (0.11 mg/kg) and Ni (33.48 mg/kg) exceeded Threshold Effect Level. Furthermore Ni exceeded Probable Effect Level. Ecological potential risk of heavy metals sequence was Pb>As>Cd>Ni>Zn>Cr>Cu. The criteria of ecological risk on Pb and as were considerable risk ( E r i Pb: 52.18 and E r i As: 50.00 and the others were low risk. Moreover, the potential ecological risk sequence of study were ST18> ST3> ST8> ST1> ST7> ST6> ST11> ST20> ST19> ST4> ST16> ST5> ST9> ST15> ST2> ST13> ST14> ST17> ST10> ST12. The criteria of ST 18, ST 3, ST 8, ST 1 and ST 7 belonged to considerable risk, ST 12 was low risk and others location were medium risk. Heavy metals input in Mahakam Delta are possibly caused by human activities such as industrial, mining, household activities, and from natural process by erosion and natural water flow.