Changes in the metal content of surficial sediments of Boston Harbor since the cessation of sludge discharge.

Temporal trends of metals in surficial sediments (1991-1998) at two sites in Boston Harbor were analyzed to evaluate the effect of stopping sludge dumping in December 1991. Metal contents of sediments from the old sludge disposal site were higher than those of a station in the central Harbor. Since 1991, carbon, copper, and lead contents have significantly decreased in sediments from the disposal site. Chromium and Zn have shown smaller decreases while Fe, and Mn, have remained relatively constant. Metal content in the central Harbor station, located in an area of sediment reworking, has been quite variable, but, with the exception of Zn which has shown a large decrease relative to iron, the changes seemed to be well correlated with changes in the organic carbon content at this site due to resuspension. Ratios of metals in the sediments are fairly similar at both sites and similar to those of sewage-derived particles, with the exception of Cr, which appears to be enriched in the sediments.