Abstract:
Concentrations of copper (Cu), silver (Ag), and cadmium (Cd) in eastern oysters (Crassostreu tirgkicu)
from the upper Patuxent River estuary analyzed since 1986 (Cd since 1991) were high relative to concentrations in other
sites in the United States analyzed by the National Oceanic and Atmospheric Administration National Status and Trends
program. Patuxent River oysters had above average concentrations of Ag and Cu, and unusually high concentrations of
Cd. Metal concentrations were highest in summer, a period in which oyster meat condition index was relatively low.
Copper values were highest in 1986-1987, likely elevated by erosion from Cu-Ni alloy condensers at a local power plant.
Silver and Cd values exhibited more year-to-year variation. A number of factors were examined as candidates to explain
the interannual differences, including river flow, salinity, and oyster condition, but none was able to explain the high and
low years. Samples collected in spring and late summer of 1996 at a number of oyster bars located along the length of
the Patuxent River showed that concentrations of ail three metals increased with distance up-river. For Cd, the upstream
increase was linear with distance, while for Ag and Cu, there was a secondary maximum near river km 16. A close
correlation was observed between Ag and Cu for individuals at each site, with a poorer correlation between Cd and
either Ag or Cu.
