ABSTRACT

Any transformative human activity generates by-products that must be disposed of properly, especially those that can damage the environment in which we live. By-products, also known as wastes, derived from industrial activities and water and sewage treatment processes can be excellent sources of essential nutrients for plants and the correction of arable soils (Alvarenga et al., 2007). However, the presence of heavy metals in these wastes can create negative effects for the entire food chain. Heavy metals can only be considered essential for plant, animal, and human nutrition when they occur in low concentrations. In high concentrations, both groups are characterized as toxic elements and will have an adverse effect on exposed organisms. Their average concentration in the soil is relatively low and generally occurs as trace elements (Adriano, 2001). The anthropogenic contribution of metals that has occurred since antiquity contributes enormously to increased metal

CONTENTS

6.1 Introduction ................................................................................................ 171 6.2 Factors That Affect the Sorption of Heavy Metals in

Tropical Soils.........................................................................................172 6.2.1 Solid Phase Components .............................................................. 172

6.2.1.1 Organic Matter ................................................................ 173 6.2.1.2 Fe and Al Oxides ............................................................. 176

6.2.2 Liquid Phase ................................................................................... 178 6.2.2.1 pH ...................................................................................... 178 6.2.2.2 pH50 ................................................................................... 181 6.2.2.3 Kurbatov Plots and Protonic Coefcient (α) ................ 183 6.2.2.4 Ionic Strength (I) ............................................................. 186 6.2.2.5 Variation of the Gibbs Free Energy (∆G) ...................... 188

6.3 Adsorption and Desorption of Heavy Metals in Competitive Systems in Tropical Soils .......................................................................... 192

References ............................................................................................................. 204

levels in soils, sediments, water, and air (Nriagu, 1996; Claudio et al., 2003). Anthropogenic contamination of soils by metals is a constant concern in most industrialized (United States, Canada, and Eastern Europe) and emerging countries, such as Brazil, China, and India.