Distribution and Fractionation of Metals in Mangrove Sediment from the Tibiri River Estuary on Maranhão Island

Sediment quality guidelines and the sequential chemical extraction protocol of the European Commission were applied for the assessment of Cd, Cr, Cu, Ni, Pb and Zn in mangrove sediments from the Tibiri River on Maranhao Island. Metals concentrations were determined using the inductively coupled plasma optical emission spectrometry (ICP OES) technique. The results demonstrated that metal levels were below TEL (Threshold effect level) and ERL (effect range low), range associated with occasional adverse biological effects for the aquatic life. Metal mobility in decreasing order was: Ni (24%) > Zn (20.6%) > Cu (14.5%) > Pb (1.9%). Except by Ni and Zn, other metals were not found in the exchangeable/acid-soluble fraction (F1). Only Ni, Zn and Cu were present in the reducible fraction (F2). The major metal percentage was associated to oxidizable fraction (F3) and residual fraction (F4). In the latter, metal percentage ranged from 76 to 100%, which suggests an inexpressive impact of anthropogenic activities.