Assessment of potential ecological risk by metals in Ilha Grande Bay (Southeast Brazil)

This study evaluates contamination and potential ecological risk in Ilha Grande Bay (BIG) in southeastern Brazil. To achieve these objectives, we analyzed physicochemical, sediment textural, and geochemical data from 134 stations distributed throughout the bay. The results reveal significant environmental degradation in the coastal areas of Paraty, Saco do Mamanguá, Angra dos Reis City, and Abraão Cove (at Ilha Grande Island). These regions exhibit moderate to significant pollution from metals. High potential ecological risk was identified in approximately 87 stations (about 65 %), primarily due to Hg, Cd, and As, with additional contributions from Tl, Ni, and Cu. Evidence indicates that concentrations of these chemical elements have been increasing in recent years. Among these metals, Hg is particularly concerning because of its toxicity and persistence in the environment. The primary sources of contamination in BIG appear to be urban and industrial effluents, metalworks, the combustion of coal and oil, and the incineration of waste and sewage sludge, all of which have contributed to rising pollution levels over the past two decades. Sedimentary processes also facilitate the formation of pollution patches. It is crucial to address the recent escalation in contamination by effectively controlling pollution sources. This study recommends revising the methods and standards for metals established by national and international legislation to better assess sediment quality in marine environments. •Sediments in Ilha Grande Bay (BIG) in Southeast Brazil are experiencing moderate to extreme pollution due to metals, particularly in areas close to dense populations and river mouths.•Approximately 65% of the analyzed sampling stations throughout the bay show a high to very high potential ecological risk.•This risk is mainly associated with the presence of mercury (Hg), cadmium (Cd), arsenic (As), thallium (Tl), nickel (Ni), and copper (Cu).•This study recommends regular environmental monitoring of Ilha Grande Bay.•It suggests revising the methods and limits used to assess the quality of marine sediments in national and international legislation.