Synchrotron-Based X-ray Fluorescence Imaging Elucidates Uranium Toxicokinetics in Daphnia magna

Abstract

A combination of synchrotron-based elemental analysis and acute toxicity tests was used to investigate the biodistribution and adverse effects in Daphnia magna exposed to uranium nanoparticle (UNP, 3−5 nm) suspensions or to uranium reference (U ref ) solutions. Speciation analysis revealed similar size distributions between exposures, and toxicity tests showed comparable acute effects (UNP LC 50 :). However, the uranium body burden was 3to 5-fold greater in UNP-exposed daphnids, and analysis of survival as a function of body burden revealed a ∼5-fold higher specific toxicity from the U ref exposure. High-resolution X-ray fluorescence elemental maps of intact, whole daphnids from sublethal, acute exposures of both treatments revealed high uranium accumulation onto the gills (epipodites) as well as within the hepatic ceca and the intestinal lumen. Uranium uptake into the hemolymph circulatory system was inferred from signals observed in organs such as the heart and the maxillary gland. The substantial uptake in the maxillary gland and the associated nephridium suggests that these organs play a role in uranium removal from the hemolymph and subsequent excretion. Uranium was also observed associated with the embryos and the remnants of the chorion, suggesting uptake in the offspring. The identification of target organs and tissues is of major importance to the understanding of uranium and UNP toxicity and exposure characterization that should ultimately contribute to reducing uncertainties in related environmental impact and risk assessments.

Laboratory Liquid-Jet X-ray Microscopy and X-ray Fluorescence Imaging for Biomedical Applications

“…Both systems typically operate at synchrotron facilities because they provide high spectral brightness [27][28][29]. These techniques have successfully demonstrated a range of different imaging applications at the cellular level, imaging tissues, and small animals, such as visualizing membranes, determining the shape and size of organelles, detecting nanoparticles (NPs) inside the cell [30][31][32][33], tracking nutrient distribution in plant tissues [34], in vivo tracking of immune cells [35], and assessing the toxic effects of NPs in small animals [36]. However, a limited number of synchrotron facilities results in limited access to these methods by biological scientists.…”