ABSTRACT Extensive pastures are commonly converted to sugarcane areas in Brazil. In soils cultivated with sugarcane, tillage and fertilization are management practices commonly carried out. Soil management practices alter the physical and chemical properties increasing or decreasing metal availability. The purpose of this study was to quantify soil metal concentrations during pasture-to-sugarcane conversion correlating these changes with physical and chemical properties. The results showed that the concentration of metals in soil samples occurred according to the following order Fe > Mn > Cr > Zn > Cu > Pb > Cd. Significant increases in soil metal concentrations due the sugarcane cultivation were observed to Cd and Cu. The soil physical and chemical properties presented correlations with soil metal concentrations. There was a strong relationship on inorganic fertilization to change in soil metal concentrations. The principal component analysis (PCA) explained 55.4% of the total data variance, separating factors in two groups that pointed to an influence of fertilization on metal grouping. Inorganic fertilizer application may input 1.06 g·ha–1·year–1 Cd. The Cd concentration ranged from 0.15 to 1.07 mg·kg–1, representing addictions of 9.54 mg·ha–1·year–1 Cd in soil. The metal concentrations observed after five years of pasture-to-sugarcane conversion did not represent environmental risks since the concentrations remained below the Brazilian official determinations.

The Mundaú-Manguaba lagoon estuary complex is the most important ecosystem in the state of Alagoas, and a source of sustenance for a large number of the state’s inhabitants. However, degradation by anthropic sources has been causing impacts on this ecosystem. Understanding the characteristics of the natural organic material of the waters of the mundaú-manguaba lagoon complex is extremely important to understand the interaction dynamics of the contaminants in these lagoons. Thus, the objective of this work was to extract and characterize aquatic humic substances from the Mundau-Manguaba lagoon complex and to evaluate the interaction of this organic material with mercury ions. The profile of the aquatic humic substances of the respective lagoons evidenced the greater influence of aliphatic groups in their structures. The interactions of aquatic humic substances and mercury ions are directly related to the oxygen groups in their structures, corroborated by Principal Component Analysis. Thus, understanding the water and organic matter characteristics present in the Mundaú-Manguaba estuarine lagoon complex is fundamental for establishing strategies, seeking the preservation of this ecosystem and remediation of environmental contamination.