engleski

Differences between elemental association in two sediment fractions from Idrijca, Bača and Soča rivers, explained by principal component analysis (PCA)

Sediment samples were taken in August 2001, along Idrijca, Bača and Soča Rivers (Slovenia) at 12 sampling stations. The location was chosen, because Idrijca River is polluted from the second largest mercury mine in the world in Idrija. Although mercury investigation in this region is going on by numerous authors, detailed mineralogical and multielemental analyses are lacking. Mineralogical composition was determined only in f < 63 ľm, using X-ray diffraction (XRD). A total of 50 elements were determined in f < 63 ľm and in f 63 - 500 ľm in Actlabs, Canada, using program "Ultratrace 2" and program "1G" for total mercury. A Principle Component Analysis (PCA) demonstrates differences between the two grain size fractions. 3 PCA components explain 86% of the data variance in f < 63 ľm and 98% in f 63 - 500 ľm. In the fraction < 63 ľm, component 1 explains 45% of the variance. The factor loadings are explained by the detrital proportion of the sediment. Component 2 explains 28% of the variance and assembles havy metals Hg, Zn, Cr, Cu, As, Mo, W, Bi and Au. Component 3 explains 13% of the variance. Strong factor loadings of Fe, Cr, Cu and Sb indicate elemental association, which is related to basaltic rocks. In contrast to these findings, the component 1 of the fraction 63 - 500 ľm carries the detrital fraction and all heavy metals (56% of the variance). Component 2 (13% of the variance) can be explained by carbonates, whereas the factor loadings of K, Al and Th indicate component 3 as geochemical carrier of elements associated with clay minerals. The geochemical data can be interpreted as a result of weathering of a pollution source, in which heavy metals are dissipated in the downstream direction. In f 63 - 500 ľm the heavy metals are associated with the detritus. This is the result of physical weathering process. In contrast, the heavy metals in the fine fraction (f < 63 ľm) form a single elemental association. This can be explained by chemical weathering process. The fine fraction is more effective in respect to the elemental transport. These results present work in progress, because more data are necessary for exact PCA analysis.

elemental association; sediment fractions; polluted rivers; PCA

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