Ecological risks of trace metals in Guanabara Bay, Rio de Janeiro, Brazil: An index analysis approach

• Ni, Cu, Cr, Pb and Zn were determinated at 30 sediment samples in Guanabara Bay.
• Enrichment and Contamination Indices showed elevated levels of Cu and Pb.
• Ecological Risk Indices indicated severe threat to local biota.
• Guanabara Bay stood out as a most contaminated coastal area by trace metals.

Total concentrations of Ni, Cr, Cu, Pb and Zn were determined in surface sediments from 30 stations in Guanabara Bay in 1999 and 2008. An approach using various environmental indices was used to assess contamination status of metals. This approach allowed the comparison with different coastal areas. Background Enrichment Index, Contamination index and Ecological Risk index (Pollution Load Index; Sediment Quality Guideline Quotient and Ecological Risk Index) were calculated for the metals. Results revealed a great load of organic matter and significant increases in Cu and Pb levels between 1999 and 2008. The concentrations of Cr and Zn were of great concern, surpassing the values of Probable Effect Level reference values. In spite of the differences of each index, results effectively revealed the striking contamination in Guanabara Bay concerning trace metals, and also suggested potential risk to local biota. The contamination of the northwest area was notably higher than the rest of the bay. In comparison with some other coastal bays around the world, Guanabara Bay stood out as a remarkably contaminated environment.