Bioavailability of Fe and heavy metals in sediments from the Ria of Huelva (South-Western Spain)

Bioavailability of Fe, Cu, Zn, As, Cd and Pb has been studied in 17 samples of surface sediments of the Ria of Huelva. In all cases, total concentration of these elements is high, especially of Zn (1660,6 ppm), followed by Cu (1499,9 ppm), Pb (919,2 ppm), As (432,5 ppm) and Cd (2,7 ppm). The highest concentrations associated with bioavailable fractions are shown by Zn (86% of total concentration) followed by Cd (76,5%), Fe (59%), Cu (45%), As (32%) and Pb (31%). The main source of metal input are the Tinto and Odiel rivers, which acidic water (pH < 4) discharge coming from acid mine drainage (AMD) to the estuary. Acidic water inputs and mixing processes with sea water are the main control in the spatial distribution of metals and their association with the different target fraction