Public health aspects of the culture of the Japanese oyster Crassostrea gigas (Thunberg) in a waste recycling aquaculture system

A study of 24 weeks duration was carried out in which oysters (Crassostrea gigas) were grown in four regimes. These were: (i) on phytoplankton cultured in a mixture of secondary treated sewage effluent and seawater for a period of 12 weeks followed by a second 12-week period of feeding on phytoplankton cultured in a “clean”, inorganically enriched regime; (ii) as for (i) except that the secondary effluent was sand filtered prior to use; (iii) as for (ii) except that the effluent was charcoal filtered prior to use; and (iv) using “clean”, inorganically enriched phytoplankton food for the 24-week duration. At intervals of 2 weeks, populations of oysters were removed for assay for trace metals (Cd, Cr, Cu, Hg, Ni, Pb, Zn) and organic contaminants (hydrocarbons, polychlorinated biphenyls). No significant accumulation or depuration of any metal or organic contaminant was evident in any of the regimes. In terms of these contaminants all oysters are within acceptable edible standards as set by the U.S. Food and Drug Administration.