Bodily variability of zinc natural isotope abundances in sheep

Evidence is growing that the range of zinc stable isotope compositions, represented by the deviation of Zn-66 in permil units relative to a standard and expressed as delta Zn-66, is larger in organic matter than in inorganic material. This study reports the variations of delta Zn-66 in various organs of sheep raised on a controlled diet. Zinc was purified by anion-exchange chromatography. The Zn concentrations and Zn stable isotope compositions were determined by quadrupole inductively coupled plasma mass spectrometry and multi-collector inductively coupled plasma mass spectrometry, respectively. The data show that delta Zn-66 variability exceeds 1 parts per thousand, with bone, muscle, serum and urine enriched in the heavy isotopes, and feces, red blood cells, kidney and liver enriched in light isotopes, all relative to the diet value. The Zn-66 enrichment of the circulating serum reservoir is likely to take place in the digestive tract, probably through the preferential binding of lighter isotopes with phytic acid, which is known to control the uptake of metallic elements. Mass balance calculations suggest that the Zn-66 depletion between diet and feces, which is not balanced by any other outward flux, leads to a secular isotopic drift in serum. A simple time-dependent two-box model, involving the gastrointestinal tract on the one hand and the muscle and bone on the other, predicts that the maximum Zn-66 enrichment, which equals the difference in delta Zn-66 between diet and bulk (similar to 0.25 parts per thousand), is reached after about ten years. Therefore, a better understanding of the variations of natural abundance of Zn isotopes in animals and humans will probably bring new perspectives for the assessment of their Zn status. Copyright (C) 2010 John Wiley & Sons, Ltd.