Stable isotope characterization of humic acids and retention capacity for Pb and other heavy metals in the Cananeia-Iguape coastal system (São Paulo - Brazil)

Abstract

Humic acids are mixtures of organic matter formed during the decay of plants and microbial remains. Humic acids are capable of binding heavy metals through surface adsorption, which makes these organic compounds extremely interesting in environmental studies of estuarine systems impacted by mining activities. The Cananeia-Iguape estuarine system (São Paulo state, Brazil), today under environmental protection, presents moderate contamination by Pb. Recent studies pointed out that the relatively high concentration of Pb in the sediment, linked to past mining activities in the Ribeira River Basin, still constitutes a potential concern for the environment. It is likely that a significant amount of Pb and other heavy metals be bound to humic acids within the sediments. This project aims at (i) identifying the dominant source (marine or terrestrial) of humic acids in the Cananeia-Iguape estuarine system by carbon and nitrogen isotopic analysis; (ii) mapping the spatial abundance of marine and terrestrial humic acids; (iii) using elemental analysis to assess the retention capacity of marine and terrestrial humic acids with respect to Pb and other heavy metals. The results of this project are expected to give insights into the role of humic acids in controlling the dispersion of Pb in estuaries. The project is of potentially high societal relevance, given that the study area is a Biosphere Reserve recognized by UNESCO, hosting numerous traditional fishing communities. (AU)