The distribution kinetics of waterborne silver-110m in juvenile rainbow trout

Juvenile rainbow trout (Oncorhynchus mykiss) were subjected to a 2-day radioactive pulse of 110mAg at 11.9 microg/l (as AgNO3), followed by a 19-day post-tracer exposure to non-radioactive Ag(I) (3.8 microg/l). The distribution of 110mAg in the gills, liver, intestine, kidney, brain and remaining carcass was investigated over a 19-day post-tracer period. Initially, the intestine contained the highest proportion of the 110mAg burden (34%), however, by day 8, less than 5% of the total radioactivity remained in this tissue. The majority of the 110mAg eliminated from the intestine appeared to distribute to the liver. Eventually, the 110mAg content in the liver accounted for as much as 65% of the total radioactivity in the fish. Apart from the liver and intestine, only the gills and carcass contained any appreciable amount (>5%) of the total body 110mAg content. Liver and gill samples were fractionated using differential centrifugation techniques to discern the subcellular distribution of 110mAg in these tissues. In the liver, the 110mAg levels in the cytosolic fraction increased from 35% to 72% of the total cellular burden between days 8 and 19, respectively. The radioactive pulse in the gills was predominantly found in a membrane compartment termed the nuclear fraction ( approximately 60% of the total). Little change was observed over time (day 8 to day 19) to the subcellular distribution of Ag in the gills. Using size-exclusion chromatography, most ( approximately 70%) of the 110mAg content in the liver cytosol eluted at a molecular weight characteristic of metallothionein. The cytosolic distribution of 110mAg in gills was quite diffuse, occurring primarily in the heavy molecular weight fractions.