Geo-accumulation indexes of trace elements in sediments from uranium environments (Central Portugal)

Abstract

Stream sediments are usually used as a tool for contamination evaluation. The studied area is an abandoned uranium mine located in Central Portugal, in a not steep area, with altitudes ranging from 360 to 380 m. Geoaccumulation index and contamination factor have been used in the as-sessment of the degree of contamination of stream sediments with toxic metals. The stream sediments are heavily to extremely contaminated in U and Th and moderately to heavily contaminated in As and W. The contami-nation factor is moderate for Al, Cu and Pb, considerably contaminated for As and W, and very highly contaminated for U and Th. The degree of con-tamination is very high. The contamination of stream sediments is mainly related to the erosion and leaching of the mine dumps located in the study area. Furthermore, the con-taminant concentrations tend to decrease downstream of the source, due to hydrodynamic and chemical processes in fluvial systems affected by the mine drainage.