Trace element survey in Chilean agricultural resources. III. Soils from Malpo and Mapocho valleys, Metropolitan Region

Sergio González M.1

A top soil survey within the Maipo and Mapocho valleys to quantily total and 0,05 M EDTA extractable fractions of Cd, Cu, Mn, Mo, Pb and Zn, was carried out since October 1986. Additionally, some local areas suspicious of being submitted to pollution processes were included. Probably due to their alluvial sedimentary origin, the soits of both valleys reflectthe geochemical richness of thelr aquifers. Is was detected that the Mapocho soils contain higher richness of trace elements than those ones belonging to the Maipo valley. Cu was the most interesting trace element as it showed the largest difference between soils frem both valleys. Its higher total contents are restricted to a western area, where two Cu mines are lacatad. Because of this fact, a preferential natural origin for the soil cupricity was presumed. 0.05M EDTA extractable Cu fraction was directly associated to total content; this relationship is valid only if the EDTA-Cu is expressed in absolute terms and not in relative ones. According lo some researchers, higher EDTA extractable fractions should be defined as phytotoxic. Special surveys carried out in various sites within the Metropolitan Region, proved the existence of three areas affected by industrial pollution precesses. It was showed that Rungue dam was being polluted by continuous slurry discharges from a refinery piant, that an area in the neighborhood of Caren pond was receiving the discharges of refusals from a Cu mine, and that an area neld to Nos was polluted by the atmospheric emissions from a number of industrial chimneys. Impacts upon agricultural production must be assessed.

Keywords: total oopper, exchangeable copper, top soils, heavy metals, trace elements, slurry discharges, mining refusals.
1 Estación Experimental La Platina (INIA), Casilla 439, Correo 3, Santiago. Chile