Acute waterborne cadmium uptake in rainbow trout is reduced by dietary calcium carbonate

The effects of elevated dietary calcium (as CaCO sub(3)) and acute waterborne Cd exposure (50 mu g/l) on whole body uptake, tissue uptake, and internal distribution of newly accumulated Cd, Ca super(2+), and Na super(+) in juvenile rainbow trout were examined. Fish were fed with three diets (mg Ca super(2+)/g food): 20 (control), 30 and 60 for 7 days before fluxes were measured with radiotracers. The highest dietary Ca super(2+) elevation reduced waterborne whole body Ca super(2+) uptake, but did not protect against inhibition of waterborne Ca super(2+) uptake by waterborne Cd. Both Ca super(2+)-supplemented diets reduced newly accumulated Ca super(2+) in the gills in relation to the control treatment, but did not prevent the Cd-inhibiting effect against accumulation of new Ca super(2+) in most compartments. Fish fed with Ca super(2+)-supplemented diets showed markedly lower rates of whole body uptake and internalization (in some tissues) of waterborne Cd, illustrating that, while dietary Ca super(2+) supplementation did not protect against the impact of waterborne Cd on waterborne Ca super(2+) uptake, it did protect against the uptake of Cd. Waterborne Cd had no effect on Na super(+) fluxes, total Cl super(-), and in most body compartments, newly accumulated Na super(+) and total Na super(+) were also not affected. Dietary supplementation with CaCO sub(3) had the same protective effect as demonstrated by dietary supplementation with CaCl sub(2) in an earlier study. Thus, the reduction of waterborne Cd uptake and internalization by dietary Ca super(2+) was specifically due to Ca super(2+) and not to the anion.