Trace metals distribution along sediment profiles from the Doce River Continental Shelf (DRCS) 3 years after the biggest environmental disaster in Brazil, the collapse of the Fundão Dam

Abstract

The Doce river adjacent continental Shelf (DRCS) was evaluated regarding sediment quality three years after the biggest environmental disaster in Brazil, the rupture of the Fundão Dam, that released 39 million cubic meters in the Doce river basin. Five sediment cores were sampled in the shelf, two at the south of the river mouth (T3, T4), two at the north (T6, T7) and one in front of it (T13). Analyses of sedimentary variables (grain size, organic matter and carbonates), trace and major metals occurred in the first 30 cm of each core. The presence of the tailings along the cores was investigated through an Iron Mineralogical Set (IMS). Results of the geoccumulation index (Igeo) revealed sediment enrichment with Fe, Mn, Zn, Cu, Pb, Ni, Cr reaching class 6 of contamination in every core. The contamination index (mCd) revealed high contamination levels by trace and major metals, for T3, T4, T6 and T13. Sediment Quality Guideline Quotient (SQG-Q), revealed moderate impact for all the cores, regarding the potential observation of adverse biological effects. The presence of the tailings along the cores T4, T6, T7 and T13 was confirmed through the IMS. Core T13 showed the presence of the tailings all along its extension, characterizing a depocenter of this material in front of the river mouth. IMS has proved to be a good proxy to identify presence of the tailings and revealed the trend of transport of this material towards north in DRCS. Despite the prevailing accumulation of the tailings in the north and in front of the river mouth, higher levels of metal contamination were registered in the south suggesting contamination originated from anthropogenic activities previous to the rupture of the dam.