Precautions in the use of 110MAG as a tracer of silver metabolism in ecotoxicology:: Preferential bioconcentration of 109CD by trout gills after 110MAG exposure

An often overlooked problem in the use of radiotracers is the possibility of isotopic contamination. Commercially available silver Ag-110m was used to study silver uptake and deputation in rainbow trout and European eel. Quality control by means of comparative gamma and beta counting brought our attention to a contamination of the Ag-110m stock with Cd-109, which could be seen only because the Cd-109 was markedly bioconcentrated by trout gills. The contamination could not be detected in eel gills or in other tissues of both species. The difference between trout and eel gill structure and function is the probable explanation for the marked difference in Cd-109 accumulation. This contamination was identified as Cd-109 by gamma spectroscopy and its origin by transmutation of natural silver as a result of neutron activation is described. Failure to recognize this contamination problem would have resulted in serious misinterpretation of the data set. Guidance for avoiding this problem is given.