Reference Values for Metals and Metalloids Concentrations in Bottom Sediments of Tietê River Basin, Southeast of Brazil

Abstract

This paper represents the first attempt in Brazil to propose and establish regional reference concentrations of metals and metalloids in bottom sediments of freshwater. The selected study site is the Tietê river basin (São Paulo State, Southeast region of Brazil), a system under significant environmental impact and degradation since the onset of the Brazilian economic revolution in the early mid-1950 s. In order to consolidate the analytical values, metal and metalloid determinations were performed on samples from 84 sites in 27 municipalities, from the upper reaches of the river down to its effluent into the Paraná River. Sediment samples were collected in small streams and rivers as close as possible to their upper reaches, as well as in rivers and reservoirs in locations minimally affected by human contamination. Samples were initially sieved to remove the particles > 63 μm, dried at 50°C, and submitted to extraction with a mixture of acids. Chemical analyses were performed by inductively coupled plasma atomic emission spectrometry for Co, Cr, Cu, Ni, Pb, Ti, Zn and V, and by atomic absorption spectrometry with a graphite furnace for Cd and Ag, hydride generation for As and Se, and cold vapor for Hg. Molecular absorption spectrophotometry, with Arsenazo III as colorimetric reagent, was used for U and Th determinations. The reference concentrations determined by this study showed significant deviations from the assumed global geological reference for some elements; differences were also detected among the concentrations of the same element from the different regions of the basin. Four different sets of reference concentrations values are being proposed for different regions of the studied basin as a consequence of lithological variations.

Keywords:

• Metals and metalloids
• reference values
• freshwater sediments

Notes

⁽¹⁾Number of accepted laboratory means used to calculate the recommended values and confidence intervals.

⁽²⁾Replicates used to calculate mean value and standard deviation.

⁽³⁾Not determined.

⁽¹⁾Values compiled by Turekian and Wedepohl (1961)

(1) Obtained from GGRL values compiled by Turekian and Wedepohl (1961)