Study of total and exchangeable concentrations of Cu, Ag, Sr, Ni and Mn in mud flat of Gavkhoni playa lake (South east Isfahan)

Gavkhuni Playa Lake covers about 520 km2 and is located at the downstream of Zayandeh-roud River. This playa is composed of three main flats including mud, sand and salt flats. The muddy deposits mainly spread in Zayandeh-roud Delta and underly a saline sublayer. The fine grained sediments of Gavkhuni Playa Lake have potential for concentrations of heavy metals due to the climatic conditions, petrology and presence of lead and zinc ores in the drainage basin and the flowing of the river through the industrial and agricultural regions.Variations of characteristics are: calcium carbonate (35.5-73%), organic matters (2.53-17.12%), clay (6.45-60.88%), pH (6-8.53) and Eh (-334 -+ 47 mv). Calcium carbonate, pH and organic matters increase and clay and Eh decrease from north to south of the playa. Clay minerals of the muddy sediments in order of frequency include illite, chlorite, kaolinite and montmorionite, respectively and the amount of these minerals do not vary from north to south of the playa. Heavy metals concentrations in ppm are: Mn (395.5-1040), Sr (100.4-725.76), Ni (37-73.66), Cu (13.83-29.83) and Ag (3.03-4.76) in order of abundance. Ag, Ni and Sr concentrations are higher and Cu and Mn concentrations are lower than the mean concentrations of these elements in natural soils. Geoaccumulation index and enrichment factor show that the sediments are highly polluted only by Ag. Exchangable cation contents are much lower than the total concentrations. Organic matters have a more important role in the exchangeable concentration of the heavy metals relative to the type and content of clay minerals and their elevation leads to increase the exchangeable concentrations.