FRACTIONATION OF HEAVY METALS AND EVALUATION OF THEIR MOVILIZATION IN SEDIMENTS IN TITICACA LAKE, BOLIVIA

In the absence of anthropogenic influences, trace metals in sediments are mainly associated with silicates and primary minerals, therefore they have low mobility. The Titicaca Lake is large and deep with a volume of 930.106 million m³; its elevation is 3.810 m a.s.l., it is known as the highest among world’s great lakes. The activities (commerce, transport, food production and tourism) are increasing in the small riparian towns around the Titicaca Lake, and all of these have impacted over the water quality; the highest impact are the mining activities as these have generated a large amounts of wastes thrown away without treatment to river and lakes. The study is focusing in the determination of distribution of heavy metal in deep sediments samples in the Titicaca Lake using sequential extraction procedure (SEP).

The results depicted that Cd (0,3 – 1,5mg/kg), Cu (6,7 – 55,5 mg/kg) and Zn (14,9 – 940 mg/kg) can be considered to be very low to moderately contaminated. While Pb (29,7 – 45,8 mg/kg) has been considered to constitute moderate contamination. The Ni values show very high concentrations (6,1 – 20,6 mg/kg). The results have been evaluated by comparison with reference values for sediments of Swedish Environmental Protection Agency.

The results from SEP´s show that i) heavy metals associated to the fraction exchangeable and soluble, decrease in the order Fe > Mn > Zn > Pb > Co > Ni > Cu > Cd. ii) The reducible fraction-metals associated with oxides of Fe and Mn, decrease in the order Fe > Zn > Mn > Pb > Cu > Ni > Co > Cd. iii) The heavy metals associated to the oxidizable fraction-metals associated with OM and sulfides, decrease in the order Fe > Mn > Zn >Pb > Cu > Co > Ni > Cd and iv) The heavy metals associated to crystalline structure of minerals, decrease in the order Fe > Mn > Zn > Pb > Cu > Co > Ni > Cd. Manganese show high contents between Vilque Chico and Jakantaya (S1) and in Chaguaya (S4), while Zn and Pb concentrations are in S4 near to surface water inflow impacted by leaching from abandoned mines.

The Risk Assessment Code (RAC) has evaluated the risk from moderate to high to Cu, Zn, Pb, Cd, Fe, Mn, Co and Ni, the values shows risk of the presence of these metals impacts and its bioavailability in aquatic ecosystem.

The Geoacumulation index (Igeo) show that Cd, Pb and Zn have high values in S4 meaning highly polluted, and there sources is mining activities.