Uranium accumulation and toxicokinetics in the crustacean Daphnia magna provide perspective to toxicodynamic responses

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

“…A previous toxicokinetic assessment showed that molting (ecdysis) is an important depuration pathway for D. magna exposed to U, 20 and the biodistribution mapping in the current study provided further insights and detail to specific areas where U is lost. For D. magna , molting is not limited to the general carapace but also includes the cuticle surrounding the epipodites and the intestinal foregut and hindgut.…”

“…These observations are in line with previous assessments of U toxicity in D. magna that indirectly reported accumulation in the intestine via observation of histological changes to epithelial cells 29 and on the carapace, as well as maternal transfer. 20 However, the biodistribution in the current study provides much more detailed information on whole body uptake and distributions. The following sections describe the identified areas of U accumulation of importance to toxicokinetic and toxicodynamic assessments.…”

“… 43 , 45 On the other hand, removal of excess U from the carapace and epipodites via molting represents a significant depuration pathway for daphnids. 20 , 43 …”

“… 3 , 15 Aquatic freshwater invertebrates, such as Daphnia magna , have a key function in nutrient cycling and constitute an essential part of the food web. 16 , 17 In ecotoxicological assessments, D. magna is an important sentinel test organism with high sensitivity to metals, including U, 18 − 20 but to date no toxicity studies have been published on UNP exposure. Traditional toxicity assessments have relied on measurements of total water concentration and whole body burden to provide overall uptake and depuration rates in D. magna .…”

Synchrotron XRF and Histological Analyses Identify Damage to Digestive Tract of Uranium NP-Exposed Daphnia magna

“…In the environment, U can be present in different physicochemical forms varying in size and charge properties. The speciation (i.e., low-molecular-mass (LMM) species, colloids, and particles) is known to influence the mobility and potential transfer of U in the environment, where LMM species (<1 nm) are assumed to be mobile and bioavailable and colloidal forms (1 nm to 0.45 μm) including nanoparticles (NPs) can be relatively mobile, while particles (>0.45 μm) are considered inert. ,,, Molecular growth processes or weathering of minerals and nuclear fuel material may give rise to nanoscale U particles with properties that may differ from those of ions and larger particles with respect to mobility, biological transfer, and toxicity. − Uranium concentrations in aquatic systems vary widely depending on the surrounding minerals and sedimentary rock formations as well as anthropogenic activities, in some cases exceeding the World Health Organization (WHO) guideline value (<30 μg U L –1 ) for drinking water by 2 orders of magnitude. , Uranium is especially problematic for aquatic ecosystems where it is known to be taken up into the food web and exhibits a chemotoxicity that can lead to acute effects. − The freshwater invertebrate Daphnia magna is a preferred model for aquatic toxicological studies due to their role as primary consumers of various algae and bacterial species as well as their functional role in nutrient cycling. , Daphnia magna are highly sensitive to waterborne U where chronic effects have been shown at concentrations > 10 μg L –1 , while the 48 h LC 50 (lethal concentration in 50% of the population) has been reported to occur at concentrations > 390 μg L –1 , depending on water conditions such as pH or the presence of U binding ligands . Traditionally, aquatic toxicology studies have relied on total water concentrations and body burden measurements that lack detailed information to identify underlying toxicokinetic mechanisms.…”