Spatial variation of metal(loid)s in sediments of an Atlantic mesotidal estuary (Sado estuary, Portugal)

Estuaries offer favorable conditions for human settlement. As a result, pollutants, such as metals, have been released to these systems. Those are adsorbed by particulate material that tend to settle at the bottom and sink in the sediment. This article analyses the results of metals in sediments of the Sado estuary (Portugal) on a large spatial scale, to differentiate areas according to their impacts and possible sources. The metals were analyzed by Atomic Absorption Spectroscopy and a Direct Mercury Analyser. Higher concentrations, particularly of As, Cr and Zn ([32, 40] mg/kg, [102, 115] mg/kg, [672, 896] mg/kg) were observed at upstream areas of the Alcácer and Marateca channels. Both anthropogenic and natural origins in the area were considered to understand the results, such as industrial activities and geological context. Overall, the concentrations registered do not reach levels of contamination, and the improvement in the quality of the estuary is reflected.