HEAVY-METAL DISTRIBUTION IN SEDIMENTS AND ECOLOGICAL RISK ASSESSMENT - THE ROLE OF DIAGENETIC PROCESSES IN REDUCING METAL TOXICITY IN BOTTOM SEDIMENTS

This paper describes the heavy metal distributions in river and lagoon al sediments of Jacarepagua Basin, Rio de Janeiro, Brazil. The occurre nce of metal phase translocation from the reducible to the oxidizable was observed for Fe, Mn and Ni, from the fluvial environment to the la goonal. Cu was mainly associated with the oxidizable phase while Zn an d Pb were mainly associated with the reducible phase in both environme nts. It has been demonstrated that metal sulfide formation and complex ation by organic complexes are very important aspects in terms of toxi city reduction. By means of a risk assessment methodology, based on av ailable sediment data, it was demonstrated that the lagoonal system is exposed to a low potential ecological risk and that Zn was the metal of greater concern with respect to the system pollution. (C) 1997 Else vier Science Ltd. All rights reserved.