Trace element assessment in sediment cores from Graminha reservoir, São Paulo State, by INAA

Abstract

In the present study, sediment cores were collected in the Graminha (Caconde) water supply reservoir in Feb/2015 (points 1 and 3) and Aug/2015 (points 1 and 4) sampling campaigns. The four sediment cores with different depths were cut every 2.5 cm, yielding 36, 21, 33 and 37 slices of sediments, respectively, that were individually analyzed by INAA (Instrumental Neutron Activation Analysis). This analytical technique was used to quantify the elements: As, Ba, Br, Co, Cr, Cs, Fe, Hf, Rb, Sb, Sc, Ta, Zn, U and Th. The validation of precision of the methodolody was made by analyzing certified reference material. The concentration values obtained for As, Cr and Zn were compared with TEL and PEL oriented values established by the CCME (Canada) and adopted by CETESB for sediment quality evaluation. None of the sediment cores analyzed surpassed the PEL value for these elements. Sediment samples from points 2 and 3 presented the worst sediment quality but were still classified as good quality for sediments. The enrichment factor (EF) and Geoacumulation Index (IGeo) tools used for contamination level assessment were used for all sediment cores and mostly presented enrichment on As and U. The results from concentrations, EF and IGeo showed a significant increase mostly below 30 cm of depth in every core. Statistical analyses were applied to the elemental concentration values for better interpretation of the results.