Biogeoquímica de metais pesados em solos de manguezal do Rio Botafogo - PE, Brasil

Abstract

The Botafogo river basin is an important source for the population and industries of the northern coast of Pernambuco. However, the intense urban and industrial activity has generated a load of waste containing heavy metals that is directly deposited in the estuary. As a consequence, there is contamination of the mangrove soils to the environment by heavy metals, altering the ecosystem and compromising the role of the river as a natural resource for the communities. The objective of this study was to determine the heavy metals contents and to evaluate their distribution in the mineral and organic compartments along the profiles of mangrove soils of the Botafogo River, relating the dynamics of the metals to the soil function as a sink or source of heavy metals. For this, chemical and physical analyzes for soil characterization and determinations of the metals (total, environmentally available and associated with operationally defined geochemical compartments) were performed. Biological matrices were also evaluated for the accumulation of metals, aiding in the verification of their transfer to the biota. The results indicate the contamination of mangrove soils by Hg due to waste discarded by the soda alkali industry located in the region. Although ecological risk estimates were high for Hg, it was observed the majority association of the metal to the fractions of high stability in the soil, besides the low accumulation of Hg by plants and oysters, evidencing the soil function as sink, which limits the transfer of the contaminant to the biota. Clay and MOS are the main attributes of soil that govern the accumulation of metals, while pH and Eh condition the stability of the geochemical compartments to which the metals are associated. The oxyhydroxide and pyrite fractions represented important mineral phases for Cu, Fe and Zn, governing the availability of these elements. It is verified that even though the Hg contamination is identified, the soil plays a fundamental role as a contaminant filter. Changes in the geochemical conditions of this environment may increase the bioavailability and risks of intoxication of humans, especially to communities that depend on the natural resources of the Botafogo River and consumers of fish from the region.