Evaluation of the chromium contamination at Ribeirão dos Bagres, Franca (SP), Brazil, by the ²¹⁰Pb method

This paper presents a chronological study focusing the use of ²¹⁰Pb in four sediment cores collected at Ribeirão dos Bagres in the region of Franca, São Paulo State, Brazil. When evaluating the sedimentation rate by using the ²¹⁰Pb method, it was possible to monitor historical changes occurring in the concentrations of chromium present in the sediments. In order to do so, several specific parameters were determined in sediments, as chromium concentration, major oxides, organic matter, grain size, and chemical and physical-chemical parameters of waters. The sediments possessed a Cr concentration range of 0.83-26.25mg/kg that is below the world's average of shales. The sedimentation rates obtained from the ²¹⁰Pb analysis were between 0.07 and 0.77 g cm⁻²year⁻¹, while the linear sedimentation rate was from 0.6 to 3.2 cm/year. The adoption of the CIC (Constant Initial Concentration) ²¹⁰Pb model allowed characterize older sediments, aged 177 years, and younger sediments, aged 4 years. The organic matter in the sediments was more abundant in the first few centimeters of practically all profiles, and the analysis of oxides showed that silica is the major constituent of the sediments, in which there is predominance of sand and silt. In addition, the analysis of the physical and chemical parameters of waters indicated that they are suitable for navigation and natural harmony landscape.