Heavy metals in stream sediments: Error versus concentration

Abstract

A regional geochemical mapping program in southern Norway carried out by the Geological Survey of Norway is based on sampling of stream sediments at road/stream intersections. At each site two individual subsamples have been taken. The subsamples were treated independently during the chemical analysis. This procedure enables an estimation of the reproducibility of the element concentration at each sample site. The paper gives results for the average relative total, sampling and laboratory errors at various levels of metal concentration using data for HNO 3 -soluble Mn, Pb and Cu as examples. For Mn and Pb the relative total error reaches a minimum near the median concentration and increases toward both the high and low concentrations. For Cu the relative total and laboratory errors decrease with increasing concentration throughout the whole concentration range, while the sampling error is fairly constant. The results suggest that the models which are commonly used for error determination in geochemical data, are too simple as far as relationships between error and concentration are concerned.