Effect of age and tissue weight on the cadmium concentration in Pacific oysters (Crassostrea gigas)

This study investigated the influence of age and tissue weight on cadmium (Cd) levels in Pacific oysters (Crassostrea gigas). Oysters from 4 different age groups (1, 2, 3, and 4 y) were collected at an oyster farm in Willapa Bay, Washington. To examine the effects of age, 60 oysters from each group were sorted into 3 composites of 20, and Cd analysis was carried out on all composite samples. To study the effects of tissue weights, 25 oysters from each of the 4 age groups were collected and analyzed individually for Cd. All oyster Cd concentrations were below the 3.7 ppm (mu g/g) wet wt Food and Drug Administration (FDA) level of concern and the 2 ppm wet wt Hong Kong limit. There was a moderate correlation between Cd concentration and age (R-2 = 0.60). The 1-y-old oysters had significantly lower Cd concentrations than the 2-4-y-old oysters. Tissue weight also influenced Cd concentration (R-2 = 0.31). The effect of tissue weight was found to vary with age, with a stronger correlation to Cd levels in the 1- and 2-y-olds and a weaker correlation among the 3- and 4-y-olds. The results indicate that oysters accumulate the majority of their Cd during the first two years of their lives, after which point they become saturated and show only incremental additions of Cd in later years.