Exploring the particle size effect on the geochemical composition using experimental soil mixtures

The impact of particle size on elemental content in soils is difficult to predict because the positive linearity between them does not apply equally to all elements. This assumption needs to be constantly examined and considered for fingerprinting studies. Overall, higher element enrichment in the fine fractions reflects the increasing adsorption potential of larger specific surface area (SSA), however, this relationship is often non-linear or more complex. Previous studies have been reported that the relationship between SSA and elemental geochemistry is different in terms of linearity, magnitude, and even direction for each element, and it could also depend on the type of sample. Fingerprinting approach is founded on the assumption that the properties of source and sediment mixtures are directly comparable, however, when a particle size correction (PSC) is needed because of the enrichment of sediment mixtures in fine particles, the use of a single PSC factor based on SSA could negatively affect unmixing results. Based on our previous study, in which we examined the behavioural characteristics of geochemical tracers in artificial mixtures with different grain size, we demonstrated that the source apportionment estimated with unmixing models was sensitive to particle size. In this contribution, we explore in detail, and tracer by tracer, the effect of the particle size variation on the correct estimation of source apportions. Artificial mixtures with known percentages contribution from three experimental sources have been used, comparing i) sources and mixtures at <63 μm, ii) sources at <63 μm and mixtures at <20 μm simulating fine enrichment and iii) sources at <63 μm and mixtures at <20 μm with particle size correction factor (PSC). These results support the need to develop alternatives to improve the use of correction factors in fingerprinting studies.