Bioavailability of heavy metals in mangrove soil in Alagoas, Brazil

The mangrove forest is an important transitional ecosystem consisted of terrestrial and marine environment located in tropical and subtropical regions with average temperatures above 20 °C. In Alagoas, the mangrove forests are found on the entire coastline from Maragogi to Piaçabuçu. In the last 20 years, due to the pollution of water resources, studies of coastal aquatic ecosystems have been developed. The objective of this study was to analyze the physicochemical properties and determine the levels of heavy metals in mangrove sediments of the Mundaú-Manguaba estuary lagoon complex (MMELC) and Meirim River in Alagoas. Zinc, copper, lead, cadmium and chromium were chosen due to their relationship with sewer, agricultural, and industrial wastes. 22 soil samples were collected in the MMELC and in the Meirim River. The samples were submitted to soil routine analyses of Embrapa. The heavy metals were extracted by the Mehlich-1 method and analyzed by atomic absorption spectrometry. The mean concentrations of these metals in the sediment samples followed the order Mn > Zn >Pb > Cr> Cu >Cd in MMELC and Zn > Mn >Pb > Cr> Cu >Cd in Meirim River. All proposed heavy metals were found in sediments, however, the cadmium levels were above the normal levels proposed by Environment National Council (CONAMA) and Canadian Council of Ministers of the Environment. The study shows that the analysis of sediment can contribute to environmental monitoring actions and development of public policies aimed to controlling the sustainable use of natural resources of the studied areas.