A 5-YEAR STUDY ON THE HEAVY-METAL POLLUTION OF GUANABARA BAY SEDIMENTS (RIO-DE-JANEIRO, BRAZIL) AND EVALUATION OF THE METAL BIOAVAILABILITYBY MEANS OF GEOCHEMICAL

Surface sediments of the Guanabara Bay (Rio de Janeiro, Brazil) were a nalyzed by a sequential extraction procedure for Cd, Cr, Cu, Pb, Zn, M n and Fe, determining their distribution among five geochemical phases and in the nitric acid extractable phase. Bioavailable phases and non -bioavailable phases have been determined in six transects in the bay to define the significant level of pollution due to sediment metal con tamination. A multiple correlation showed limited responsibility of Mn and Fe oxides and humic acids in the adsorption process, which allowe d discrimination among the different processes and suggested the stron g influence of the hydrogen sulfide present in the highly reduced bay bottom environment. The authors suggest the need to avoid disturbing b ottom sediment by dredging or by artificial bottom aeration which coul d result in a rapid worsening of the environment due to the accelerate d formation of more soluble oxygenated metal compounds making the toxi c metals much more available to the benthic fauna and to the bay biota in general. (C) 1997 Elsevier Science Ltd.