The evaluation of heavy metals in relation to physicochemical parameters of mud sediments in a core sediment from the Gavkhuni playa lake

The Gavkhuni playa is located 130 km southeast of Isfahan. This playa consists of three mud, sand and salt flats. The mud flat mainly covers northern part of the playa (the Zayandehrud delta). A sediment core was drilled in order to study heavy metals pollution in the subsurface mud sediments of the Zayandehrud delta. Accordingly, 7 facies including black mass mud, brown mass mud, black mass sand mud, brown sand mud, light green mass mud, light green sand mud and brown gypsum bearing mud, and 5 sub-environments of branching canals, canal margin, lake and playa were identified. To determine role of the physicochemical factors in concentration changes and pollution of the heavy metals in the facies, granulometry of the sediments was carried out through wet sieving and hydrometric methods. Eh and pH, calcium carbonate and organic matter contents and heavy metals concentration in the sediments were measured asx well. Average concentrations of the heavy metals (in ppm) in order of their abundances are Mn (576.46), Zn (79.73), Cr (50.84), Cu (46.32), Ni (37.40), Pb (10.99), Co (09.09) and Cd (0.092). According to the correlation between the heavy metals and physicochemical parameters and also cluster analysis, the retention of Mn, Co, Ni and Cr has been affected by clay, Fe oxi-hydroxides and Eh whereas the contents of calcium carbonate and organic matter have been effective in the adsorption of Cd, Zn, Pb and Cu. The indices of sediment pollution to heavy metals including the Enrichment Index (EF), Geoaccumulation Index (Igeo) and Pollution Accumulation Index (PLI) indicate that despite changes in the sedimentation condition, sediments of the drilled core show no pollution. Based only on the Igeo index, the sediment samples show little pollution to Zn, Cu and Cd.