Influence of human-induced pressures on dissolved and particulate metal concentrations in a South American estuary.

Coastal areas are urbanized and industrialized environments, affected by dredging operations, discharges of untreated municipal wastewaters, and farming. Developing countries are in continuous growth and will deal, in a close future, with the highest rate of coastal transformation, posing serious risks for the ecological and environmental value of ecosystem assets. This research aims to study the dissolved and particulate Cr, Ni, Pb and Zn values within an argentinean estuarine environment which is currently under human-induced pressures. Concentrations of all the metals under analyses showed seasonal variability of both dissolved and particulate metals. An important outcome of this study was that dissolved Cr, Pb and Zn attained maximum values and overall increased concentrations with respect to previous records from the same area. Indeed, the highest concentrations were found during the dredging operations or in association with increases in the metal levels from wastewater discharges. The results also indicated that human activities contributed the least to the dissolved Ni concentrations. The particulate fraction of Cr, Ni and Zn showed an upward trend in the concentrations, particularly during the last two sampling dates, being also positively correlated between each other. Regarding their respective environmental quality standards, many samples achieved dissolved Cr and Zn concentrations above the maximum values recommended by international guidelines. Thus, this study highlights the possibility of stressors like dredging activities and municipal wastewaters to cause increases in the water column pollution levels.