Using Factor Analysis to Characterise Historical Trends of Trace Metal Contamination in a Sediment Core from the Tagus Prodelta, Portugal

A box-core 3576 (PO287-26-1B) collected from the Tagus Prodelta in 2002 was analysed for organic carbon, 210Pb, 226Ra, major (Al, Fe, Ca, Ti, Mg and Mn) and trace elements (Ba, Hg, Cr, Cu, Li, Ni, Pb, Sb, Sn, Sr, and Zn). Maximum concentrations of contaminants in 210Pb-dated samples were reached in the decades between 1960 and 1980, followed by a slightly decrease in up-core metal trends. Trace metal concentrations increased in the bottom of the core (210Pb dated as 1925) to maximum values during the 1970s. Factor analysis of geochemical data was used to reduce the 18 variables into four factors that reveal distinct origins or accumulation mechanisms controlling the chemical composition in the study area. Changes in the dominance of these factors through the time indicate not only changes in industrial activity, but also the increase of biological productivity towards the present.