Distribution and speciation of bromine in mammalian tissue and fluids by X-ray fluorescence imaging and X-ray absorption spectroscopyElectronic supplementary information (ESI) available: Representative X-ray fluorescence integrated spectrum and Compton scatter maps; LC-MS/MS experimental and results. See DOI: 10.1039/c4mt00338a

Bromine is one of the most abundant and ubiquitous trace elements in the biosphere and until recently had not been shown to perform any essential biological function in animals. A recent study demonstrated that bromine is required as a cofactor for peroxidasin-catalysed formation of sulfilimine crosslinks in Drosophila . In addition, bromine dietary deficiency is lethal in Drosophila , whereas bromine replenishment restores viability. The aim of this study was to examine the distribution and speciation of bromine in mammalian tissues and fluids to provide further insights into the role and function of this element in biological systems. In this study we used X-ray fluorescence (XRF) imaging and inductively coupled plasma-mass spectrometry (ICP-MS) to examine the distribution of bromine in bovine ovarian tissue samples, follicular fluid and aortic serum, as well as human whole blood and serum and X-ray absorption spectroscopy (XAS) to identify the chemical species of bromine in a range of mammalian tissue (bovine, ovine, porcine and murine), whole blood and serum samples (bovine, ovine, porcine, murine and human), and marine samples (salmon ( Salmo salar ), kingfish ( Seriola lalandi ) and Scleractinian coral) . Bromine was found to be widely distributed across all tissues and fluids examined. In the bovine ovary in particular it was more concentrated in the sub-endothelial regions of arterioles. Statistical comparison of the near-edge region of the X-ray absorption spectra with a library of bromine standards led to the conclusion that the major form of bromine in all samples analysed was bromide. The first study of bromine speciation and distribution in mammalian tissues using X-rays shows bromine present predominantly as bromide.