Application of the Weng's ratio for the identification of Zn, Cu, and Pb contamination in soils and sediments

This work explores the application of the use of Zn, Cu, and Pb relative contents as a new type of normalization method for geochemical properties of soils and sediments in an Atlantic Basin (Anllns River, NW Spain). The method is based on the conservative behavior of these elements, which exhibit a certain concentration ratio that remains stable as long as there are no human disturbances. The average relative contents of Zn, Cu, and Pb were calculated by dividing the concentration of each metal in soils or sediments, in the < 63-mu m fraction, by the sum of Zn, Cu, and Pb, expressed as a percentage. The evaluation of the sum of the average relative concentrations of Zn, Cu, and Pb (Ri), together with three standard deviations for each element, namely, Ri +/- 3Si, allows a hexagon to be constructed, represented in ternary diagrams of Zn:Cu:Pb. Following the method proposed by Weng et al. (Environ Geol 45:79-85, 2003), those samples falling outside the hexagon must be considered outliers. Results obtained confimed the conservative behavior between the relative contents of Zn, Cu, and Pb in surficial samples (soils, bed, and suspended sediments). Only sediment cores displayed nonconservative behavior, showing a marked Pb enrichment, with respect to the surficial samples. When Zn, Cu, and Pb relative contents were plotted in ternary diagrams, outliers were best classified when the hexagon was drawn with standard deviations of samples from the study area. The hexagon drawn with an international database of soils and sediments showed a poorer classification of outliers. The results showed that total Zn, Cu, and Pb relative contents may be employed to investigate anthropogenic disturbances of these elements in soils and sediments of the Anllns River Basin, thus corroborating that this type of normalization may be employed as a tool to assess outliers in a contaminated area.