Sediment and tissue analysis for metals in a tropical estuary

Abstract

Metal concentrations were measured for Al, As, Cd, Cr, Hg, Sr, Ni, Pb and Zn in sediments throughout nine sites over two periods (dry and rainy), as well as within organism tissues for the dry period in the Mamanguape River estuary in Brazil. The potential metal bioaccumulation in tissues was evaluated using the bioaccumulation factor (BAF). The estuary suffers from great anthropogenic pressure, mainly due to sugarcane crops, which are distributed in the areas surrounding the river. The concentrations of metals in the sediment were different according to the periods (dry and rainy) with a significance value of α≤0.05, with the rainy period presenting the highest concentrations. Positive correlations between the metal concentrations and granulometry (silt and clay) were found for both experimental periods. Maximum concentrations of As (9 mg/kg), Cr (513 mg/kg) and Ni (33.8 mg/kg) during the dry period, were above the limits for values estimated by international agencies and As (9 mg/kg) and Hg (0.13 mg/kg) values, were also above the limits for rainy periods. Crassostrea rhizophorae had the highest concentrations of metals (868.1 mg/kg) when compared to the other species. In Anomalocardia flexuosa, C. rhizophorae, Litopenaeus schmitti and Mugil curema the concentrations of Al, As, Cd, Cr, Hg, Sr, Ni and Zn were above the limits, established by legislation, for human consumption. The BAF showed the bioaccumulation of As, Cd, Hg, Ni and Zn in A. flexuosa; As, Cd, Sr and Zn in C. rhizophorae; Cd, Hg and Zn in L. schmitti; and Cd, Hg and Zn in M. curema. We conclude that according to international agencies, some metal concentrations found in the sediment and tissues of organisms exceed the previously established limits, indicating that the Mamanguape River estuary is under the influence of anthropogenic pressure.