Rapid determination of silver in cultivated Japanese and South Korean oysters and Japanese rock oysters using the 24.6-s neutron activation product 110Ag and estimation of its average daily intake

Soft tissues of cultivated Japanese (Miyagi Prefecture) and South Korean (Koje-do and Kosong) oysters and Japanese rock oysters (Honshu Island) were analyzed to measure silver levels. The soft tissues, namely hepatopancreas, gill, muscle, and mantle were separated, freeze-dried, pulverized, and analyzed by an instrumental neutron activation analysis method in conjunction with compton suppression spectrometry (INAA-CSS). The method consisted of the irradiation of samples in a neutron flux of 5 x 10(11) cm(-2) s(-1) using the rapid transfer system in an inner pneumatic irradiation site of the Dalhousie University SLOWPOKE-2 reactor (DUSR) facility for 12-15 s, decay for 20 s, and counting for 60 s. The 657.8-keV gamma-ray of the 24.6-s nuclide Ag-110 was used for assaying silver. The method was validated using NIST, NRC and NIES certified reference materials. An absolute detection limit of 0.05 mu g silver using NIST SRM 1566b Oyster Tissue was achieved. About 10-50 times higher levels of silver were found in cultivated Japanese oysters compared to the South Korean ones. The silver concentrations in cultivated oysters in Miyagi Prefecture showed the following trend: gill > mantle > hepatopancreas > muscle as well as on the age. Rock oysters generally had higher silver content compared to cultivated oysters. A very preliminary value of about 0.466 mu g silver average intake per person per day was estimated from the consumption of oysters by the people living in the Sendai city of Miyagi Prefecture.