Metals and organic matter baselines in sediments in a cross-shelf gradient at Abrolhos Bank, SW Atlantic

The present study performed geochemical fractioning of major and minor elements in a cross-shelf gradient of the Abrolhos Bank, where the largest and most diverse coral reefs in the South Atlantic are concentrated. The fractioning was performed using sequential extractions to determine the degree of availability and toxicity of the elements. The mobility pattern of the elements investigated were in the following order: Ca > Mn > Pb > Cr > Zn > Fe > V > Cu > Ba>Al > Ni > Ti. For elements, such as (Ti, Ni, Al, Ba, Cu, V, Fe, Zn, Cr, Pb), the highest concentrations were in the residual phase at some sampling sites. As established by Environment Canada (Threshold Effect Level - TEL and Probable Effect Level - PEL), Ba, Cr, and Ni produced values higher than the limits, associated with higher concentrations of other elements. In addition, significant proportions of these elements were found in mobile phases in the same sites. Thus, more rigorous measures are critical to avoid alarming levels of chronic environmental pollution inside and outside protected areas of the region. To enhance the sustainability of the region, more effective enforcement is crucial to prevent anthropic contamination that may threaten its biodiversity. The results provide the baseline for future studies regarding the potential impacts of the breach of the tailings dam in the region of Mariana, Minas Gerais. [Display omitted] •Metals were evaluated in surface sediments before the impact of ore tailings dams.•Oxidizable phase elements were related with Corg indicating potential bioavailability.•Mobility levels of metals were in the order of Ca > Mn > Pb > Cr > Zn > Fe > V > Cu > Ba>Al > Ni > Ti.•The concentrations of Ba, Ni, and Cr were above the TEL in three conservation units.•Antropogenic sources increase metal concentration in Santa Barbara Island.