Accumulation and depuration of mercury in the American oyster Crassostrea virginica

To study the kinetics of mercury uptake in oysters, adult Crassostrea virginica (Gmelin) were held in seawater containing 10 g mercury/l (ppb) or 100 g mercury/l (ppb), added in the form of mercuric acetate, for 60 days. Mercury concentration in tissues was determined by analysis of individually homogenized oyster meats, using wet digestion and flameless absorption spectrophotometry. After 45 days, average mercury tissue concentration was 140,000 g mercury/kg tissue (ppb) and 28,000 g mercury/kg tissue (ppb) in the 100 ppb and 10 ppb experimental groups, respectively. After this time, concentrations dropped sharply, probably due to spawning. Clearance of mercury from tissue was studied by exposing treated adults to estuarine water (with no additions) for 30 days (100 ppb group) and 160 days (10 ppb group). Tissue concentrations in the 100 ppb mercury environment group declined from 115,000 to 65,000 ppb, and those of the 10 ppb group declined from 18,000 to 15,000 ppb, in 18 days; there-after, no further decline occurred in either group. Oysters accumulated mercury 1,400 times and 2,800 times above the environmental concentrations of 100 and 10 ppb mercury, respectively. Total self-purification was not achieved over a 6 month cleansing period.