Geochemistry distribution of heavy metals and other chemical elements in the groundwater of Sinos River Basin, RS

Abstract

The Sinos River Basin comprises 32 municipalities in the metropolitan region of Porto Alegre, at Rio Grande do Sul State, all of them showing an accentuated urban/ industrial growth with environmental impacts evidenced by disasters in surface water resources, however poorly described in regard to the groundwater. The hydrogeochemical analysis of aquifers in the basin was based on samples from 37 wells, bearing consistent stratigraphic profiles, and 2 springs, which were analyzed through an ICP-MS equipment for 70 elements. Throughout the SPSS software, the data collection was processed for factorial principal component and clusters analysis, allowing the identification of outliers. Five main groups were identified, two of those in porous aquifer with shales (clusters 1 and 4), two with mixed water with evidences of rising groundwater from underlying aquifers (clusters 3 and 6) and one in fractured aquifer (cluster 2). Among the outliers, emphasis should be given to the arsenic with maximal concentration around 43.8 ppb and showing close association with boron (920.0 ppb) and sulfur (195.0 ppb), which origin is considered to be geogenic. On the other hand, lead concentrations of 34.0 ppb in close association with copper (365.0 ppb) may reveal anthropogenic contamination events. Heavy metals such as chrome, nickel, cadmium and mercury bear concentrations very close to or below the detection limit. The results show that distinct aquifers occasionally reveal groundwater anomalous compositions, which should be monitored and detailed, ensuring more assertive and safe drinking water distribution.