Geochemical evaluation of potentially toxic elements determined in surface sediment collected in an area under the influence of gold mining

Abstract

In this present paper, the distribution of toxic metals and sediment quality were evaluated in five sampling points of the Itapicuru-Mirim River located in the city of Jacobina, Bahia, Brazil. The concentration of the elements arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) were determined from sediment samples collected from the superficial layer (0–10 cm) in November 2013. After the samples' total decomposition, the total concentration of metals was determined by inductively coupled plasma optical emission spectrometry (ICP OES), except for Hg, which was measured by inductively coupled plasma atomic emission spectrometry (ICP AES). A geochemical evaluation of sediment quality was performed using enrichment factor (EF), geoaccumulation index (Igeo), and pollution load index (PLIThe results of the total concentrations in the analyzed sediment samples were compared with the threshold effect levels (TELs) and probable (PELs) effect levels (PELs) in sediment quality guidelines (SQGs). For the fraction <75 μm, the decreasing order for the metal concentrations was (ppm): Fe (10.86%) > Mn (120.8) > Cr (122) > Zn (76.5) > Pb (49.6) > Cu (32.6) > Ni (28.6) > Hg (0.31) > Cd (0.13). Igeo suggested a moderate to seriously polluted category for Hg and moderately polluted for Cu. Generally, the results indicated probable risks to the biota caused by Cr, Ni, Pb, and Hg metals. However, only Hg, Cd, and Cu were of anthropogenic origin. Although the sediments are relatively preserved from pollution by these metals, there is a progressive deterioration of this compartment downstream of the Itapicuru-Mirim River in the city of Jacobina.