ISOTOPE GEOCHEMISTRY OF COPPER AND ZINC IN THE GEOSPHERE AND BIOSPHERE
Zinc homeostasis is disrupted during the formation of breast tumours. Malignant tumours contain elevated levels of Zn (mean = 14.93 ± 11.05 μg/g) and isotopically light d66Zn values (mean = -0.40 ± 0.15 ‰) compared to histologically normal tissue adjacent to malignant tumours (pvalue = 3.4 x 10-5 and pvalue = 0.04, respectively), indicating that the processes that govern Zn accumulation in malignant tumours are fundamentally different from those that control homeostasis in healthy cells and benign tumour cells. No statistically significant difference in bulk serum Zn concentration or d66Zn value was observed between healthy controls and patients. Serum zinc concentrations have been reported to fall by between about 10 and 25% three hours postprandial (i.e. after eating). I investigated whether this well-documented effect is accompanied by a zinc isotopic shift, with implications for study design and sampling protocols. No postprandial change in stable Zn isotope composition (mean Δ66Zn180-minute – Baseline = 0.01 ± 0.09‰, 2SD) was observed. I proposed that hemodilution and the rapid, efficient postprandial transfer of albumin-bound Zn from serum to the liver and pancreas is responsible for the lack of postprandial serum Zn isotopic response. These results indicate that studies examining solely the distribution of Zn isotopes in serum may obtain samples without considering timing of the most recent meal. However, future studies seeking to compare serum Zn concentrations with d66Zn values should draw blood samples in the morning after overnight fasting. With the goal of expanding the number and variety of geological and biological materials that can be precisely and accurately measured, I characterized the copper isotopic compositions of ten reference materials by multiple collector inductively coupled plasma mass spectrometry using a combined standard-sample bracketing and internal normalisation mass bias correction using agallium internal standard. The reference materials measured in this thesis possess complex and ii varied matrices with copper concentrations ranging from 1.2 μg g-1 to 497 μg g-1, and δ65Cu values ranging from -0.20‰ to 0.52‰ with an average expanded uncertainty of ± 0.07‰ (U, k = 2), covering much of the natural copper isotope variability observed in the environment.
URI for this recordhttp://hdl.handle.net/1974/28227
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