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

Abstract

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 × 1011 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 110Ag was used for assaying silver. The method was validated using NIST, NRC and NIES certified reference materials. An absolute detection limit of 0.05 μg 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 μg 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.