Assessment of Metal Enrichment Factors in Waters Draining a Mixed-Land-Use Catchment

Pollution assessment in a given area depends mostly on the precise determination of the so-called background values. In this work, enrichment factors (EFs) for iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in suspended solids (SS) of a stream draining a rural catchment (NW Spain) were determined to assess whether the observed concentrations of these metals represent natural or contaminated levels. Aluminum was used as a normalizer element. Four approaches were used for defining background values used in the EF analyses: a local background value for metals concentrations in SS, a local background value for metals concentrations in C-horizon soils, mean crust values, and mean shale values. The most satisfactory result was obtained when using local background values for metals concentrations of SS, suggesting that on average the Fe, Mn, Cu, and Zn concentrations measured represent natural levels. However, some signs of enrichment were observed (16–28 percent of the samples with EF > 1.5).