Studies on the Total and Exchangeable Concentrations of Zn, Pb, Co and Cd in Fine-Grained Sediments of Gavkhuni Playa Lake (Southeast of Isfahan)

The fine grained sediments of Gavkhoni Playa Lake have the potential for concentrations of heavy metals due to climatic conditions, petrology and the presence of lead and zinc ores in the drainage basin and the passage of Zayandehrud River through industrial and agricultural regions. In this research, muddy sediments from the delta and playa of Gavkhuni Playa Lake were sampled to determine the levels of concentration of heavy metals and the geochemical/sedimentological parameters. Calcium carbonate, pH and organic matter increase while clay and Eh decrease from North to South of the playa. Clay minerals of muddy sediments in their order of frequency include, respectively, illite, chlorite, kaolinite and montmorillonite and the amount of these minerals does not vary from the delta to the south of the playa. Average concentrations of the heavy metals in ppm in order of abundance are: Zn (46.96), Pb (39.25), Co (8.14) and Cd (3.53). Cd and Pb concentrations are greater than normal while the Co and Zn concentrations are almost equal to the usual concentrations of these elements in shale. The Geoaccumulation index shows that the sediments are highly polluted by Cd, slightly to unpolluted polluted by Pb and not polluted to the other heavy metals. Exchangeable cation contents are much lower than the total concentrations. Organic matters play a more important role in the exchangeable concentration of the heavy metals relative to the type and content of clay minerals and their increase has augmented the exchangeable concentrations.