Waters from Rivers Yono, Ibaraki, Minoh in the low mountainous area of northern Osaka have been reported with high concentrations of harmful elements above the environmental standard limits. The rural to lightly urbanized environment allow to establish a relationship between the natural occurrence of trace elements in river waters and the surrounding geology. Previous studies have shown that the Palaeozoic-Mesozoic sedimentary rocks are the sources of trace metals (here Co, Cr, Ni, Cd, Pb and especially As) whereas the Ibaraki granitic complex is the source of rare earth elements (here Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Yb, Lu). Here results of the geochemical patterns of river waters and riverbed sediments, and insights into transportation of trace elements along the rivers course. High concentrations of As (>10ppb) and other trace metals were observed in river waters flowing across the trace elements enriched sediments from sandstone and quartz diorite. While sediments from adamellite contained low trace elements but river waters flowing across this formation had the highest concentrations of REEs. Unfiltered and filtered (0.45µm) river waters showed large differences (>50%) concentrations of REEs. Those elements are likely to be transported with Fe and Al-colloidal particles or other suspended particles, while most of the trace metals would remain mainly present in the dissolved fraction. Particulate organic matter (>0.45?m in size) was nearly absent from samples and dissolved organic matter didn't seem to have a major role in trace elements transport as no clear correlation could be observed with trace metals nor REEs. H/O isotopic ratio datas pointed at the meteoritic origin of waters that recharged from more or less remote areas, inducing a primary concentration in spring waters that later evolved via interactions with the river system; most of elements lower in the filtered fraction than in the unfiltered fraction exhibited high concentrations at spring that decreased afterwards due to absorption/precipitation along river course.
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