Selenium Speciation of Surface Sediments from Saline Lakes of the Soan-Sakesar Valley Salt-Range, Pakistan

Abstract

Abstract The chemical species of selenium from the surface sediments from three eutroph-ic lakes of the Soan-Sakesar Valley were examined. The major objectives of the study were to examine the oxidation states of selenium in the lake sediments. The following selenium concentrations were observed from lakes Uchhali, Khabbaki and Jahlar, respectively: total selenium: 4.03, 1.55 and 1.4 mg/kg; Se+VI: 0.86, 0.39 and 0.31 mg/kg; Se+IV: 0.95, 0.27 and 0.25 mg/kg; Se-II:1.15, 0.45 and 0.33; and Se0: 1.17, 0.48 and 0.53 mg/kg. Lake sediments have higher nitrogen (0.04—0.35% of dry weight) and phosphorus (0.04—0.29% of dry weight) levels due to agriculture drainage water and sewage waste from small villages. X-ray diffraction analysis has shown that albite, calcite, chlorite, illite and quartz minerals were present in the sediments of lakes Uchhali, Khabbaki and Jahlar. Kaolinite was present only in lakes Uchhali and Khabbaki and goethite only in Lake Uchhali. Linear relationships were observed between selenium fractions, and minerals present in these lakes point out the phenomena of adsorption on the surface of these minerals. The organic C contents of 2.2, 2.8 and 3.1% dry weight in lakes Uchhali, Khabbaki and Jahlar, respectively, show linear relationships with Se-II, Se0 and total selenium. It suggests that Se in the sediments is highly associated with the sediment organic fraction. The results indicate that nutrient loads and organic C are responsible for the high microbial activity, which reduces sele-nates to more insoluble Se species in the lake sediments.