Soil changes and effects on ionic mobility resulting from the application of oxidative methods for degradation of organic contaminants in gasoline-impacted soils

Abstract

Gasoline has more than 200 potentially toxic substances in its composition, including benzene, toluene, ethylbenzene and xylene (BTEX). These polluting agents, when leaked in gas stations, are initially found in the Unsaturated Zone in adsorbed and vapor forms. The BTEX compounds, in contact with the aqueous phase, partially dissolve and reach the groundwater, contaminating it. Among the remediation processes, the oxidative ones stand out: Fenton reagent, hydrogen peroxide, permanganate and persulfate, treated in this work. The application of these decontamination techniques promotes total degradation of a wide variety of dangerous substances, resulting in innocuous compounds such as carbon dioxide and water. However, in most cases, their application leads to undesirable side effects to the environment, such as the release of toxic metal ions. Aiming to study the changes in soil and water, laboratory experiments were carried out using a Latosol artificially impacted by gasoline and treated with oxidative agents (Fenton, hydrogen peroxide, sodium persulphate and potassium permanganate). It was verified that the oxidising treatments result in pH decrease, reduction of the exchangeable bases contents and, because they are not very selective processes, they may cause degradation of the natural organic matter of the soil. These alterations favour the desorption of metallic ions, which are released into the aqueous phase in concentrations that exceed hundreds of times the limit established by legislation, affecting the environment and altering the quality of the water, making it unsuitable for human consumption.