Estimativa das perdas de solo e do transporte de chumbo e zinco por erosão hídrica no entorno da cidade de Santo Amaro da Purificação, Bahia

Abstract

Several environmental problems have affected humanity and many of them had serious consequences for both human health and natural resources, as well as for animals. In this context is cited the city of Santo Amaro, in the Reconcavo of Bahia, where a lead smelter processed lead ore until the year 1993; the ore refining has generated many problems, such as the very large amount of slag, pollution of water by industrial sewage and diffuse soil pollution in the region by the chimney emissions of metal-enriched particulate matter. The present work aimed at identifying the soil loss and subsequent transport of metals in an area of 6 x 8 km around the plant affected by this diffuse contamination. Quantification was performed by using the universal equation of soil loss (USLE), through Geographic Information Systems. Mapping the soil loss may possible to check the areas that most contribute to soil erosion, and, crossing to the geochemical soil maps, to estimate the mass of lead and zinc transported to the Subaé river through soil erosion. It has been found a high rate of soil loss in the region, due to the strong wavy relief region (49.4% of the studied area), with soil loss higher than 100 t ha-1 year-1 (moderate to strong or higher) in 64% of the area. Regarding the metals, their transport was estimated to more than 1 kg ha-1 for Pb and more than 0.5 kg ha-1 year-1 for Zn, in a 2 km radius area around the smelter. Next to the plant, these values increased to more than 10 kg ha-1 year-1 of Pb and 2 kg ha-1 year-1 Zn. Within a 2 km-radius area, the total mass of metals transported annually to rivers by erosion was estimated at 4989 kg of lead and 418 kg of zinc, pointing out the current high contribution to the pollution of Subaé River and its estuary through the laminar erosion of diffuse contaminated soil.