Evaluation of In Situ Heterogeneity of Elements in Solids: Implications for Analytical Geochemistry

A general method for the evaluation of in situ heterogeneity of geochemical materials is described and the significance of the results discussed, by using three case studies and earlier data sets. The heterogeneity of Pb in soil (expressed as RSD due to sampling, RSDsamp) varies from <5 to >100% between different sites, in a way that relates to the mode of deposition of the element. The heterogeneity of an element also varies systematically as a function of the distance scale at some sites. This variation can be modelled using linear regression, accounting for over 90% of the experimental variance, at seven scales over three orders of magnitude. Variation in heterogeneity between elements at the same site, seems to be somewhat diagnostic of the origin of the element, lithogenic being less than anthropogenic, although the later is also being modified by the mode of deposition. Where the heterogeneity is large (RSD >30%), it is proposed that it can be expressed more accurately as a heterogeneity factor (10(GSDsamp)), to reflect its frequency distribution, which is positively skewed towards higher concentration values.