The impact of human activities on sediments of San Francisco Bay, California: an overview

This note introduces a set of eight papers devoted to a detailed study of two sediment cores from San Francisco Bay with an overview of the region and a chronology of human activities. Data used in this study to constrain the range of sediment ages at different depths include Th-234,Pb-210, Cs-137, Pu-239,Pu-240 and Be-10 concentrations in the sediment and the C-14 age of shell fragments. In order of first detectable appearance in the record, the indicators of contamination that were analyzed include PAHs > Hg > Ag, Cu, Pb, Zn > DDT, PCB > foraminiferal Cd/Ca. This study also documents a large memory effect for estuarine contamination caused by sediment mixing and resuspension. Once an estuary such as San Francisco Bay has been contaminated, decades must pass before contaminant levels in surface sediment will return to background levels, even if external contaminant inputs have been entirely eliminated. (C) 1999 Elsevier Science B.V. All rights reserved.