The distribution of trace elements, including toxic and harmful elements, in different aqueous fractions can be investigated via their determination in non filtered and filtered water samples. Concentrations determined in non filtered samples can be roughly regarded as total amounts. Filtration through 0.45 um pore-size filters is conventionally used to remove the matter in suspension, thus concentrations determined in the water fraction <0.45 um should be regarded as dissolved amounts. However, in this fraction inorganic contaminants may occur either as truly dissolved species or hosted in fine particles of <0.45 um size, such as clay and colloidal materials. Results of hydrogeochemical surveys carried out on river and stream waters from Sardinia (Italy) showed significant differences in concentrations of specific elements under different seasonal conditions. Variations in the dissolved amount of trace elements appear to depend on the composition of rocks drained, and the occurrence of mineral deposits, as well as on hydrological conditions, such as runoff, flow and turbulence. The elements B, Li, Rb, Sr, Ba, As, Sb, Mo, and U in the studied waters showed small differences in concentrations determined either in non filtered or filtered water samples. Dissolved concentrations were higher in summer, when the contribution of rainwater to the rivers was minimum; concentrations were often positively correlated with Total Dissolved Solids (TDS) and/or major ions. These elements occurred as truly dissolved species, which concentrations appeared related to the intensity of water-rock interaction processes. The elements Al, Fe, Pb, Zn, Cd, Co, Ni, Cs, Y, REE and Th were not related to TDS and/or major ions; they showed higher concentrations under high flow conditions; marked differences occurred between total and dissolved amounts; concentrations in the water filtered through 0.015 um were much lower than in the water filtered through 0.4 um, especially when sampling was carried out after storm events that enhanced the load of solid matter in the water, hence indicating an aqueous transport via sorption processes on very fine particles. Considering that seasonal variability in concentrations of inorganic contaminants may affect the water quality, results from this study can be useful to understand the human- and aquatic-life risk exposure to toxic and harmful elements.
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|Titolo:||Overview on the occurrence and seasonal variability of trace elements in different aqueous fractions in river and stream waters|
|Data di pubblicazione:||2011|
|Tipologia:||2.1 Contributo in volume (Capitolo o Saggio)|