Numerous socio-economic benefits are associated with the oil industry. However, problems cannot be neglected, resulting in many accidents that can occur at any production stage of this industry. A serious problem created by this industry is environmental contamination by hydrocarbons. Gasoline in contact with infiltration water, the aromatic constituents, in particular the BTEX group, partially dissolve being the first contaminants to reach the groundwater. Studies published in the literature indicate that biological degradation is the main mechanism responsible for reducing the concentration of these toxic pollutants. Laboratory studies of this kind have been conducted in small scale columns, where the biological field conditions are not well reproduced. However, studies conducted in a larger scale with structured soil, remaining closer to field conditions, evidenced biodegradation processes of BTEX. This paper presents the in situ construction, instrumentation and monitoring of a large rectangular block of undisturbed residual gneissic soil, subjected to a horizontal flow of a contaminant solution composed of water, benzene and toluene to evaluate the biodegradation of these compounds in different points of the block over time. During the period of 85 days, samples of the percolating solution were periodically collected from pre-established monitoring points and the concentrations of benzene and toluene were determined using a coupled technique of gas chromatography and mass spectrometry (GC-MS). Based on the monitoring results, decay in the concentrations of the compounds over time and along the length of the block was observed. These results indicated, consistently with the biological characterization of the soil that showed the existence of microbial degrading activity, the occurrence of biodegradation of benzene and toluene, and, by an extraction process, the retention of these compounds in soil was also verified.
Studies on heavy metal behavior in soil have received considerable attention and have helped to increase the understanding of their mobility and retention in the environment. Given the scarcity of information available in the literature on heavy metal transport parameters in Brazilian tropical soils, the main contribution of this paper is improving the knowledge about the mobility of some of these elements in compacted residual gneissic soil. Laboratory soil column tests together with chemical, physical and micromorphological analyses were performed on soil samples. The artificial contaminant solution used in the tests was prepared by addition of nitrate salts of Mn2+, Zn2+, Cd2+, Cu2+, Pb2+ and Cr3+. The main conclusions were as follows. Initial percolation of distilled water to saturate the soil without counter pressure influenced the column test results since the soil structure was altered, especially when a large pore volume was percolated. Hydraulic conductivity values decreased significantly in all soil columns with contaminant solution percolation. The metals Cu, Pb and Cr remained totally retained in the soil. Comparison of Mn transport parameters determined in the present study with those obtained in a previous one showed that for the tests performed Mn mobility was practically independent of soil hydraulic conductivity when all other factors were held constant.
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