Waterborne versus dietary zinc accumulation and toxicity in Daphnia magna: a synchrotron radiation based X-ray fluorescence imaging approach.

Recent studies have suggested that exposure of the freshwater invertebrate Daphnia magna to dietary Zn may selectively affect reproduction without an associated increase of whole body bioaccumulation of Zn. The aim of the current research was therefore to investigate the hypothesis that dietary Zn toxicity is the result of selective accumulation in tissues that are directly involved in reproduction. Since under field conditions simultaneous exposure to both waterborne and dietary Zn is likely to occur, it was also tested if accumulation and toxicity under combined waterborne and dietary Zn exposure is the result of interactive effects. To this purpose, D. magna was exposed during a 16-day reproduction assay to Zn following a 5 × 2 factorial design, comprising five waterborne concentrations (12, 65, 137, 207, and 281 µg Zn/L) and two dietary Zn levels (49.6 and 495.9 µg Zn/g dry wt.). Tissue-specific Zn distribution was quantified by synchrotron radiation based confocal X-ray fluorescence (XRF). It was observed that the occurrence of reproductive inhibition due to increasing waterborne Zn exposure (from 65 µg/L to 281 µg/L) was accompanied by a relative increase of the Zn burdens which was similar in all tissues considered (i.e., the carapax, eggs, thoracic appendages with gills and the cluster comprising gut epithelium, storage cells and ovaries). In contrast, the impairment of reproduction during dietary Zn exposure was accompanied by a clearly discernible Zn accumulation in the eggs only (at 65 µg/L of waterborne Zn). During simultaneous exposure, bioaccumulation and toxicity were the result of interaction, which implies that the tissue-specific bioaccumulation and toxicity following dietary Zn exposure are dependent on the Zn concentration in the water. Our findings emphasize that (i) effects of dietary Zn exposure should preferably not be investigated in isolation from waterborne Zn exposure, and that (ii) XRF enabled us to provide possible links between tissue-specific bioaccumulation and reproductive effects of Zn.

Application of the fundamental parameter method to the in vivo x-ray fluorescence analysis of Pt.

The application of the fundamental parameter method (FPM) to the in vivo x-ray fluorescence (XRF) analysis of Pt has been investigated. The FPM is conventionally used to carry out elemental analysis of samples in vitro without the need to use standard samples of accurately known composition for system calibration. The present work has involved the use of the FPM to calculate the concentration of Pt solutions in phantoms, with concentrations ranging from 25-1000 ppm. The phantoms simulate the measurement of Pt-based chemotherapy drugs in head and neck tumours. The radiation sources were a 150 kV tungsten-anode x-ray tube and the isotope 99mTc. The minimum detection limit measured for Pt was in the range 8-30 ppm (depending on radiation source and geometry), using a narrow (5 mm) diameter beam. Dose rates in the phantom were 0.1-5 mGy h(-1). Average differences between nominal and calculated values of Pt concentration were <8% using the phantoms in air to simulate measurement of Pt in superficial body sites. If the phantoms were placed in a water bath, to simulate measurement at greater depths of overlying tissue, higher systematic differences (15-20%) were observed. This effect is probably due to multiple scattering processes in the surrounding medium.