Estimates for depuration periods of copper, cadmium and zinc in a pacific oyster [Crassostrea gigas] under field condition
1991
Ikuta, K. (Miyazaki Univ. (Japan). Faculty of Agriculture) | Morikawa, A.
Pacific oysters (Crassostrea gigas) containing high contents of copper, cadmium and zinc were collected from the intertidal zone of Akamizu, and transplanted to Urashiro Inlet where native oysters contain low metal contents. The oysters transplants were picked up at intervals over a year, and copper, cadmium and zinc contents in soft bodies were individually measured by an atomic absorption spectrophotometer. At each sampling time, more than 100 individuals were analysed. Contents of the three metals in the oyster transplants diminished exponentially toward those of Urashiro natives. Durations in days for the three metals to attain to the content levels of Urashiro natives were estimated by solutions of simultaneous equations; (1) diminution curves composed of five regression groups (mu + 3sigma, mu + 2sigma, mu + sigma, mu and mu - sigma) combined by means (mu) and standard deviations (sigma) of content data obtained at each sampling time and (2) the three content levels (mu + sigma, mu and mu - sigma) of Urashiro natives. The solutions by the combinations of T (mu + 3sigma) and U (mu + sigma) were 488 (Cu), 458 (Cd) and 370 (Zn) days. The solutions between T (mu + 3sigma) and U (mu) or U (mu -sigma) were 555 (Cu), 603 (Cd) and 470 (Zn) days, or 661 (Cu), 883 (Cd) and 612 (Zn) days, respectively. Taking the solutions described above and the content ratios of Akamizu / Urashiro (9.94 (Cu), 3.14 (Cd) and 1.74 (Zn)) into consideration, it can be inferred that copper is most easily liberated from the soft bodies, secondarily zinc, and tertiarily cadmium, and that this metal liberating strength is reversely related to the binding strength in the order of cadmium, zinc and copper
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