Estimation of the concentrations of trace metals in natural systems: The application of codissolution and coprecipitation approaches to El Berrocal (Spain) and Poços de Caldas (Brazil)

Trace element concentrations in natural systems indicate that, in most cases, solubility controls are not exerted by pure solid phases. The cycling of trace metals in the environment is coupled to the chemistry of the major components. To model this behaviour we have developed a methodology based on codissolution and coprecipitation approaches. We have applied this methodology to the El Berrocal (Spain) and Poços de Caldas (Brazil) sites. Trace metals under investigation were: Ba, Cu, Mn, Ni, Sr, and U. The models took into account: (1) the observed association of copper and uranium with iron oxyhydroxides (both in El Berrocal and in Poços de Caldas), (2) the interaction of barium and manganese with calcite in El Berrocal, and (3) the association between strontium and fluorite in Poços de Caldas. In most cases, the results were in good agreement with field data, showing that application of these approaches can reproduce more accurately the measured concentration of trace metals in groundwater than the assumption of a pure solid phase controlling the concentration of trace metals in solution. However, some problems still remain, such as the description of nickel concentrations in groundwater.