Impact of the Red Mud Disposal on Several Floodplain Lagoons of the Lower Orinoco River

摘要

This paper identifies the effects of red mud spills on several lagoons of the Orinoco River located surrounding the red mud deposits. Chemical and mineralogical analyses of sediments indicate that the geochemical signature of red mud is evident in Los Caribes and Guadita lagoons, with elevated concentrations of Fe, Al, and Na and the presence of goethite and hematite as the major mineral phases. Water quality analyses indicate that these lagoons have elevated values of dissolved oxygen, pH, conductivity, and dissolved Ca, Na, Ni, and Al. Also, elevated concentrations of Ca, Mg, and Mn in sediments suggest the precipitation of calcite, brucite a Mn-oxyhydroxides due to high pH values. Although Los Cardonales lagoon also showed evidence of red mud deposition, the enrichment of Mn, Zn, Ni, and Cd in sediments from this lagoon could be associated with wastewaters coming from landfills. The absence of vascular plants and the low abundance of fish communities in several lagoons can be related with the high pH values and the elevated concentrations of dissolved Al. The high concentrations of Fe and Mn in sediments of these lagoons can have adverse effects on benthic organisms, according to International Guidelines. Even though this lagunar system is impacted by red mud spills, hyperalkaline conditions (pH>13) were not found in superficial waters. Thus, dissolved trace element concentrations (Fe, Zn, Mn, Cr, Cu, Cd, and Pb) in waters were not high, mainly due to trace elements are immobilized by sorption or coprecipitation at circum-neutral pH.