Heavy metals and As in surface sediments of the north coast of the Río de la Plata estuary: Spatial variations in pollution status and adverse biological risk

Abstract The concentration and pollution level of heavy metals and As in surface sediments from Montevideo coastal zone (Rio de la Plata estuary) were measured in 18 sites in March 2015, ranging from the western portion at the mouth of Santa Lucia river to the east at the mouth of Carrasco stream. The study area receives a continuous discharge of untreated domestic and industrial effluents through two streams and one submarine sewage pipe. Sediments were analysed for sediment fractions, organic matter content and heavy metal and As concentrations (As, Cd, Cr, Cu, Ni, Pb, Zn, Sc, Al, Fe and Mn). Results showed that in the study area the contribution of sand was low, with exception of the innermost region of Montevideo Bay at the mouth of Miguelete and Pantanoso streams. Total organic matter contents were in general high (ranged between 3.82 and 15.72%), and values are typical for estuarine, low energy and anthropized ecosystems. Concentrations in a descending order was Zn>Cr>Cu>Pb>Ni>As>Sc>Cd and highest concentrations were found in the innermost stations of the bay, while lower in the western portion of the study area. Pearson correlation and principal component analysis suggest the similar distinctiveness of Cr, Cu, Pb and Zn. The different indices applied suggest that the study area can be considered from low to mildly polluted by metals in general, and compared with previous results all the studied metals showed marked reductions, highlighting the importance of management measures. In this sense, efforts made by the government and industries some years ago apparently had positive results in terms of reclamation/reduction of particular metallic elements.