Inorganic chemical characterization of the soil and sediment from Taiaçupeba Reservoir, São Paulo

Abstract

Taiaçupeba reservoir, located in the state of São Paulo, Brazil, belongs to Producer System of Alto Tietê (Sistema Produtor Alto Tietê –SPAT) and it is responsible for water supply for about 3.1 million of people. The water quality of a reservoir became very important in the last decades due to the increase of environmental degradation of the soil and its several uses. Trace and major elements can accumulate in high levels in soil and sediment, and the study of its concentration can indicate if the ecosystem is polluted. Therefore, the study of soil profiles and sediment cores are an important tool for the understanding of geophysical and geochemical aspects of aquatic ecosystems. The objective of this work was to present the elements As, Ba, Br, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, K, La, Lu, Na, Nd, Rb, Sb, Sc, Ta, Tb, Th, U, Yb and Zn concentrations using Instrumental Neutron Activation Analysis (INAA) in four soil profiles and four sediment cores collected in the influence area of Taiaçupeba reservoir. To verify if these elements could be enriched and the ecosystem polluted the Enrichment Factor and the Geoacumulation Index were also used. Soil profiles were collected in trenches up to 2m deep and sampled every 5 cm; in the laboratory the samples were dried at room temperature. The sediment samples were collected with a manual PVC sampler sliced every 2 cm or according to their textural characteristics, and dried in an oven at 50 C; the length of the sediment cores ranged from 42 cm to 61 cm. After drying, soil and sediment samples were sieved in a 2 mm mesh and packed in polyethylene bottles for INAA. The elements Na, As and Sb presented the highest values for both soil and sediment samples, implying in continuous, regular and spatial monitoring of the reservoir. One sediment core presented a very high concentration of the element Zn when compared to the values of the Upper Continental Crust, indicating a possible anthropic contribution from the region’s industries and classifying the reservoir as extremely polluted in relation to this element. In the evaluation of the enrichment factor it was concluded that the soil presented very high enrichment for the elements Na, As and Sb and the sediment presented very severe enrichment for the elements Na, As and Zn.