Influence of metal (Cd and Zn) waterborne exposure on radionuclide (134Cs, 110Ag, and 57Co) bioaccumulation by rainbow trout (Oncorhynchus mykiss): a field and laboratory study.

Field and laboratory experiments were carried out to assess the influence of Cd and Zn on the contamination levels of 110Ag, 57Co, and 134Cs in rainbow trout. During a four-week prior exposure phase, two fish groups were held in tanks in the Lot River (France) at a reference (<0.05 microg Cd/L and 68 microg Zn/L) and at a polluted site (1.5 microg Cd/L and 152 microg Zn/L). During a subsequent phase, organisms were brought back to the laboratory, where the radionuclide accumulation and depuration were studied for 14 and 7 d, respectively. During this second phase, the water used in the experiments was brought back from the two sites on the Lot River in order to work under the same chemical conditions. The potential effect of chronic exposure to stable metals on several biomarkers has been explored: Plasma analysis indicated the disruption of certain variables linked to the energetic metabolism and to the maintenance of the ionic balance. In contrast, no significant disruption of the measured enzyme activities was observed. With regard to the bioaccumulation of radionuclides, concentrations in fish exposed to metals are much lower than those in fish from the control group. Various hypotheses are proposed to link fish metabolic profiles due to metal exposure to the radiocontamination of organisms.

Alterations of tissue glutathione levels and metallothionein mRNA in rainbow trout during single and combined exposure to cadmium and zinc.

The objective of this study was to assess the effects of Cd and Zn exposure of rainbow trout (Oncorhynchus mykiss) on (a) hepatic glutathione (GSH) levels; and (b) hepatic and branchial metallothionein (MT) mRNA expression. Juvenile rainbow trout were exposed to waterborne Cd (nominal concentrations: 1.5 or 10 microg Cd l(-1)), Zn (150 or 1000 microg Zn l(-1)) or Cd/Zn mixtures (1.5 microg Cd l(-1) with 200 microg Zn l(-1) or 10 microg Cd l(-1) with 1000 microg Zn l(-1)). After 14 and 28 days of treatment, hepatic concentrations of total glutathione, oxidized glutathione (GSSG) and cysteine were determined by means of fluorometric high performance liquid chromatography (HPLC). Branchial and hepatic expression of MT mRNA was measured by means of semi-quantitative RT-PCR. Exposure of trout to Zn did not result in significantly elevated tissue levels of Zn, whereas Cd accumulation factors changed significantly with time and concentration. Despite of the absence of Zn accumulation, hepatic GSH but not MT mRNA levels were significantly altered in Zn-exposed fish. Cd, on the contrary, affected mainly the MT response but not GSH. Also tissue specific differences in the regulation of the two thiol pools were expressed. The thiol response after exposure to metal mixtures could not be explained by simple addition of the effects of the individual metals. The results indicate that cellular thiol pools show different reaction patterns with respect to specific metals and metal mixtures. Under conditions of long-term, low dose metal exposure, the function of GSH appears to go beyond that of a transitory, first line defense.