Integrated evaluation of accumulated sediments in a buried channel of a subtropical estuary

Abstract

The Bay of Babitonga presents an environmental impasse, due to the closure of one of its connections with the Atlantic Ocean (the Linguado channel) in 1930, altering this environment and turning it into a deposition basin, making it more susceptible to chemical contamination. Nowadays, the possibility of reopening of the canal is discussed. This discussion is necessary for its evaluation, in view of possible impacts due to the presence of contaminants in the sediment. The present study therefore evaluates the quality of the sediments of the Linguado channel, based on their physical, chemical and ecotoxicological characterization. Surface sediments were collected to determine particle size, calcium carbonates, organic matter, metals and hydrocarbons, and an evaluation by the toxicity test was conducted, using Hyalella azteca and Monokalliapseudes schubartii as test organisms. The metals Hg and Ni showed levels above the Threshold Effect Level (TEL) but without a spatial and temporal pattern. The mean Sediment Quality Guideline Quotients (mean SQGQs) classified the sediments as having low contamination, which may occasionally induce low ecotoxicological responses of H. azteca, this being the only assay to present a relation with the presence of metals in the sediment. The results suggest that the surface sediments of the buried channel do not present problems of environmental contamination, contrary to findings of previous studies in the area. However, further analysis of contaminants in deep layers of the sediment and benthic community is required.