Effects of waterborne uranium on survival, growth, reproduction and physiological processes of the freshwater cladoceran Daphnia magna.
ABSTRACT Acute uranium toxicity (48 h immobilisation test) for Daphnia magna was determined in two different exposure media, differing in pH and alkalinity. LC(50) varied strongly between media, from 390+/-40 microgL(-1)U at pH 7 to 7.8+/-3.2 mgL(-1)U at pH 8. According to the free ion activity model uranium toxicity varies as a function of free uranyl concentration. This assumption was examined by calculating uranium speciation in our water conditions and in those reported in the literature. Predicted changes in free uranyl concentration could not solely explain observed differences in toxicity, which might be due to a competition or a non-competitive inhibition of H(+) for uranium transport and/or the involvement of other bioavailable chemical species of uranium. Chronic effects of uranium at pH 7 on mortality, ingestion and respiration, fecundity and dry mass of females, eggs and neonates were investigated during 21-day exposure experiments. A mortality of 10% was observed at 100 microgL(-1)U and EC(10) for reproduction was 14+/-7 microgL(-1)U. Scope for growth was affected through a reduction in feeding activity and an increase in oxygen consumption at 25 microgL(-1)U after 7 days of exposure. This had strong consequences for somatic growth and reproduction, which decreased, respectively, by 50% and 65% at 50 microgL(-1)U after 7 days and at 25 microgL(-1)U after 21 days. Uranium bioaccumulation was quantified and associated internal alpha dose rates from 2.1 to 13 microGyh(-1) were estimated. Compared to the toxicity of other alpha-emitting radionuclides and stable trace metals, our results confirmed the general assumption that uranium chemical toxicity predominates over its radiotoxicity.
Article: Relative importance of direct and trophic uranium exposures in the crayfish Orconectes limosus: Implication for predicting uranium bioaccumulation and its associated toxicity.[show abstract] [hide abstract]
ABSTRACT: Pollutants that occur at sublethal concentrations in the environment may lead to chronic exposure in aquatic organisms. If these pollutants bioaccumulate, then organisms higher in the food chain may also be at risk. Increased attention has thus been focused on the relative importance of dietary uptake, but additional knowledge of the cellular distribution of metals after dietary exposure is required to assess the potential toxicity. The authors address concerns relating to increasing uranium (U) concentrations (from 12 µg/L to 2 mg/L) in the freshwater ecosystem caused by anthropogenic activities. The objective of the present study is to compare uranium bioaccumulation levels in tissues and in the subcellular environment. The authors focused on the cytosol fraction and its microlocalization (TEM-EDX) in the gills and the hepatopancreas (HP) of the crayfish Orconectes limosus after 10 d of direct exposure (at concentrations of 20, 100, and 500 µg/L) and five trophic exposure treatments (at concentrations from 1 to 20 µg/g). Results indicated that adsorption of uranium on the cuticle represents the main contribution of total uranium accumulation to the animal. Accumulation in the gills should be considered only as a marker of waterborne uranium exposure. Accumulation in the HP after trophic environmental exposure conditions was higher (18.9 ± 3.8 µg/g) than after direct exposure. Moreover, no significant difference in the subcellular distribution of uranium (50%) in HP was observed between animals that had been exposed to both types of treatment. A potential toxic effect after uranium accumulation could therefore exist after trophic exposure. This confirms the need to focus further studies on the metal (uranium) risk assessment. Environ. Toxicol. Chem. 2012;XXX:xxx-xxx. Environ. Toxicol. Chem. © 2012 SETAC.Environmental Toxicology and Chemistry 11/2012; · 2.81 Impact Factor
Article: Population-level modeling to account for multigenerational effects of uranium in Daphnia magna.[show abstract] [hide abstract]
ABSTRACT: As part of the ecological risk assessment associated with radionuclides in freshwater ecosystems, toxicity of waterborne uranium was recently investigated in the microcrustacean Daphnia magna over a three-generation exposure (F0, F1, and F2). Toxic effects on daphnid life history and physiology, increasing over generations, were demonstrated at the organism level under controlled laboratory conditions. These effects were modeled using an approach based on the dynamic energy budget (DEB). For each of the three successive generations, DEBtox (dynamic energy budget applied to toxicity data) models were fitted to experimental data. Lethal and sublethal DEBtox outcomes and their uncertainty were projected to the population level using population matrix techniques. To do so, we compared two modeling approaches in which experimental results from F0, F1, and F2 generations were either considered separately (F0-, F1-, and F2-based simulations) or together in the actual succession of F0, F1, and F2 generations (multi-F-based simulation). The first approach showed that considering results from F0 only (equivalent to a standard toxicity test) would lead to a severe underestimation of uranium toxicity at the population level. Results from the second approach showed that combining effects in successive generations cannot generally be simplified to the worst case among F0-, F1-, and F2-based population dynamics.Environmental Science & Technology 11/2011; 46(2):1136-43. · 4.80 Impact Factor