Distributions of elements in stream sediments in and around Seto City, Aichi Prefecture: An attempt to a geoenvironmental assessment by geochemical mapping

Abstract

Stream sediments in and around Seto City, Aichi Prefecture, were examined for geoenvironmental assessment of the area. New 157 samples were analysed for seventeen elements including Al, Ca, Ce, Co, Cr, Cu, Fe, K, Mn, Mg, Na, Ni, P, Sr, Ti, V and Zn. ICP atomic emission spectrometry and atomic absorption spectrometry were employed for the analyses. The representativeness of the analysed data for the sampling locality is examined by means of duplicate or triplicate samplings from the same place and by repeated analyses of the singly bottled sample. The data show ±100% variations in the abundance of Ti and ±50% or less variations for the other elements. This variation may have been caused by heterogeneous distribution of small accessory minerals bearing Ti. The stream sediments from the area where granitic rocks are exposed are rich in Al, Ca, Na, K and Sr. On the contrary, Co, Cr, Fe, Ni, V, Mn and Zn are enriched in the sediments from the area where the Tertiary sediments are dominant. Correlation coefficients higher than 0.6 are found between abundances of Ca-Na-Sr-Al, Ni-Co, P-Cu-Zn and Ti-Ce. The coefficients are remarkably higher for the samples took from the area of the Tertiary sediments than for the samples from granitic region. Although one sample shows a high Cr-abundance (785 ppm), which is 20 times the abundance of the average value for the Tertiary sediments, no clear evidence for artificial pollution of any elements examined here is found.