Estudo da presença de chumbo em solos em áreas de falhas geológicas for voltametria de redissolução anódica

In general, metals occur naturally in the soil at low concentrations, due to weathering and pedogenic processes that act on the rock. Changes in metal concentrations can occur over time, influenced by different ways. Lead has a longer residence time in the soil, compared to many other environmental pollutants[1] and the anthropogenic activities can result in higher concentrations of this metal in soils, for example the use of fertilizers and other treatments in agriculture. The emission of radon gas in regions of geological faults, during the radioactive decay of uranium, results in the formation of lead as the most stable element. This work investigates the relation between total lead concentrations in soils of regions with geological faults and soil outside the geological fault zone, both located in rural area. Sample collection in the region identified with geological faults (P1 - P6 points) and sample soil outside the geological fault (P7 – P8 points) were manually obtained at three different depths (15, 30, and 60 cm). The pretreatment of the soil samples was performed according to USEPA Method 3050 [2] and the analysis of all lead isotopes (total lead concentrations) was realized by anodic stripping voltammetry (Model 797 VA, Metrohm) using the hanging mercury drop electrode. This is a good method of analysis for a mixture of radioactive isotopes because it doesn´t require the forehand knowledge to add an inactive carrier to the unknown solution as it does in most other radiochemical procedures. The quantitative analysis of Pb in the soil samples obtained at different depths showed the Pb concentration increased with soil depth, with lower lead concentrations in the shallowest horizons, compared to the deepest horizons. This behavior can be explained by the fact that the source of the lead was radon emissions, with Pb being the most stable element in the decay series, which in turn also suggests the existence of a geological fault. The Pb concentrations at P7 and P8 points (outside the area of faults) were therefore far lower than in the fault areas, and at P1 to P6 the Pb concentrations in the range from 114.00 to 301.00 mg kg-1, which exceeded both the reference and prevention values, and were above the level at which intervention is required.