Effects of chronic sublethal exposure to waterborne Cu, Cd or Zn in rainbow trout 2: tissue specific metal...

Tissue specific metal accumulations (gills, liver, kidney and whole body) in rainbow trout (Oncorhynchus mykiss) were compared during chronic exposure (up to 100 days) to sublethal levels of waterborne Cd (3 µg.l(-1)), Cu (75 µg.l(-1)) or Zn (250 µg.l(-1)) in moderately hard water (hardness of 140 mg.l(-1), pH 8.0). A general pattern of tissue metal increase and stabilization was evident for all three metals, although the degree and time course of accumulation varied. The exception to this general pattern was a lack of Zn accumulation in the liver and kidney although small amounts did accumulate in the gills and whole body. Accumulation of Cu occurred primarily in the liver while for Cd the kidney was the major organ of accumulation. Exponential modeling was employed to compare and contrast the saturation concentration and time to half saturation of various tissues. Accumulation of essential metals (Cu and Zn), if it occurred, was rapid and increases were relatively low. For example the time to half saturation during Cu exposures was always less than 2 weeks and the maximum level of accumulation was less than four times background levels. For non-essential Cd, time to half saturation for the liver and kidney was always longer than 5 weeks and modeled saturation concentrations were up to 80-fold higher than background. The response to Cu and Zn suggested an active regulation of tissue burdens while that of Cd appears to be more passive, resulting in continuous metal accumulation over an extended time course. While the initial patterns of accumulation for each metal were generally consistent with the damage, repair and acclimation pattern from concurrent physiological measurements it was clear that tissue metal accumulation was not a good indicator of either exposure of physiological impact.