Laboratory and field assessment of uranium trophic transfer efficiency in the crayfish Orconectes limosus fed the bivalve C. fluminea

Aquatic insect accumulation of uranium at spring outflows in the Grand Canyon region as influenced by aqueous and sediment geochemistry and biological factors: implications for monitoring

Potential adverse ecological effects of expanded uranium (U) mining within the Grand Canyon region motivated studies to better understand U exposure and risk to endemic species. This study documents U exposures and analyzes geochemical and biological factors affecting U bioaccumulation at spring-fed systems within the Grand Canyon region. The principal objective was to determine if aqueous U was broadly indicative of U accumulated by insect larvae, a dominate fauna. Analyses focused on three widely distributed taxa: Argia sp. (a predatory damselfly), Culicidae (suspension feeding mosquitos), and Limnephilus sp. (a detritivorous caddisfly). The study showed that U accumulated by aquatic insects (and periphyton) generally correlated positively with total dissolved U, although correlations were strongest when based on modeled concentrations of the U-dicarbonato complex, UO₂(CO₃)₂^-2, and UO₂(OH)₂. Sediment metal concentration was a redundant indicator of U bioaccumulation. Neither insect size or U in the gut content of Limnephilus sp. substantially affected correlations between aqueous U and whole-body U concentrations. However, in Limnephilus sp., the gut and its content contained large quantities of U. Estimates of the sediment burden in the gut indicated that sediment was a minor source of U mass but contributed substantially to the total insect weight. As a result, whole-body U concentration would tend to vary inversely with the sediment burden of the gut. The correlations between aqueous U and bioaccumulated U provide an initial relational baseline against which newly acquired data could be evaluated for changes in U exposure during and after mining operations.

In vivo appraisal of oxidative stress response, cell ultrastructural aberration and accumulation in Juvenile Scylla serrata exposed to uranium

In vivo studies were performed to evaluate the organ specific tissue accumulation and cellular toxicity of uranium to mud crab Scylla serrata. The specimens were acclimated in natural seawater and the exposure to 50-250 μg/L uranium was investigated up to 60 days. The present study examined the effects of concentration and duration of uranium exposure in the tissue of S. serrata at cellular and subcellular level using scanning electron microscopy and bright field transmission electron microscopy in addition to histological analysis. The results indicated that accumulation of U in S. serrata was organ specific and followed the order gills > hepatopancreas > muscle. The response of key antioxidant enzyme activities such as SOD, GPx and CAT in different organs of crabs indicated oxidative stress due to U in the ambient medium and tissue. At 50 and 100 μg/L of U exposure, individuals were able to acclimate the oxidative stress and withstand the uranium exposure. This acclimation could not be sustained at higher concentrations (250 μg/L), affecting the production of CAT in the tissues. Cellular and subcellular changes were observed in the hemocytes with reduction in their number in consonance with the antioxidant enzymes. Histological aberrations like lamellar disruption of gill, necrosis of hepatopancreas, disruption and rupture of muscle bundles were observed at different concentrations and were severe at higher concentration (250 μg/L). Necrosis was observed in the electron micrographs of tissues shortly after 15 days of exposure. SEM micrograph clearly shows disrupted lamellae, folding of marginal canal and reduction of inter lamellar spaces in the gills of crab exposed to high concentration of uranium. Mitochondrial anomalies are reported for the first time in the present study in addition to the subcellular changes and vacuoles on exposure uranium in the cells of gill and hepatopancreas.

Chronic toxicity of uranium to three benthic organisms in laboratory spiked sediment

Due to mining activities, concentration of uranium (U) in the environment nearby former and operating sites can be higher than in other areas. The derivation of quality criteria for U in freshwater ecosystems, rivers and lakes includes the consideration of contaminated sediments and the associated risk to the benthic life. Therefore, the derivation of a quality criteria for sediment has been viewed as a logical and necessary extension of the work already done to establish water quality criteria. In order to contribute to the determination of a Quality Standard for sediment (QS_sediment) according to the European recommendations, this study focuses on the acquisition of a new toxicity dataset, to enrich the few rare existing data, most often unsuitable. A basic set of organisms, including three complementary benthic organisms (Chironomus riparius, Hyalella azteca, Myriophyllum aquaticum), was chronically exposed to U spiked to a standard laboratory-formulated sediment, according to the related bioassay guidelines (ISO/FDIS16303, OECD 218/9, ISO/DIS 16191). We looked to determine when possible both NOEC and EC₁₀ values for each organism. For C. riparius, a NOEC (emergence rate) value was estimated at 62 mgU, kg^-1, dm and the EC₁₀ value reached 188 mgU, kg^-1, dm (CI_95% 40-885 mgU kg^-1, dm). For H. azteca, a NOEC (survival rate) value of 40 mgU kg^-1, dm was observed while the EC₁₀ value at 296 mgU kg^-1, dm (CI_95% = 155-436 mgU kg^-1, dm) was slightly higher than for growth at 199 mgU kg^-1, dm (CI_95% = 107-291 mgU kg^-1 dm). Finally, the less sensitive organism seemed to be the plant, M. aquaticum, for which we determined a NOEC value of 100 mgU kg^-1, dm. Results obtained regarding the toxicity of U made it possible to suggest a preliminary QS_sediment value of 4 mgU kg^-1, dry mass. This value was shown conservative compared to U sediment quality criteria derived by other jurisdictions.

Uranium Bioaccumulation Dynamics in the Mayfly Neocloeon triangulifer and Application to Site-Specific Prediction

Little is known about the underlying mechanisms governing the bioaccumulation of uranium (U) in aquatic insects. We experimentally parameterized conditional rate constants for aqueous U uptake, dietary U uptake, and U elimination for the aquatic baetid mayfly Neocloeon triangulifer. Results showed that this species accumulates U from both the surrounding water and diet, with waterborne uptake prevailing. Elevated dietary U concentrations decreased feeding rates, presumably by altering food palatability or impairing the mayfly's digestive processes, or both. Nearly 90% of the accumulated U was eliminated within 24 h after the waterborne exposure ceased, reflecting the desorption of weakly bound U from the insect's integument. To examine whether the experimentally derived rate constants for N. triangulifer could be generalized to baetid mayflies, mayfly U concentrations were predicted using the water chemistry and U measured in periphyton from springs in Grand Canyon (United States) and were compared to U concentrations in spring-dwelling mayflies. Predicted and observed mayfly U concentrations were in good agreement. Under the modeled site-specific conditions, waterborne U uptake accounted for 52-93% of the bioaccumulated U. U accumulation was limited in these wild populations due to a combination of factors including low concentrations of bioavailable dissolved U species, slow U uptake rates from food, and fast U elimination.

Tracking sources and transfer of contamination according to pollutants variety at the sediment-biota interface using a clam as bioindicator in peri-alpine lakes

Point pollution sources may differently impact lakes littoral, possibly leading to local ecological risks. The concomitant chemical analysis of littoral-benthic organisms and sediment can provide insights into the bioavailability and thus the ecological risk of contaminants. In this study, the autochthonous Corbicula fluminea was used to assess the sources and transfer of six trace metals (TMs) and fourteen Polycyclic Aromatic Hydrocarbons (PAHs) to the littoral-benthic biota of a large lake. The contaminant concentrations spatially varied with a value scale from 1 to 280 000 times along the lake littoral in both the sediment and clams. Multiple linear regressions were performed to explain the spatial variability of Corbicula fluminea contamination by considering both watershed and in-lake sources. The concentration of the sum of PAHs in clams was significantly correlated with sediment contamination, suggesting that PAHs contamination of the benthic biota mainly occur from the sediment. Most of the internal TM concentrations of clams were significantly correlated with stormwater drainage areas in the lake watershed, highlighting the importance of stormwater runoffs in the littoral biota contamination. The transfer of TMs and PAHs was assessed through the bioconcentration factor defined as the ratio of internal and sediment concentrations. As, Cd, Cu, Zn and light molecular weight PAHs were more bioconcentrated in C. fluminea than Pb, Sn and heavy molecular weight PAHs, suggesting differences in their bioavailability. This study underlines the relevance of using autochthonous organisms as bioindicators of lake littoral biota contamination concomitantly with sediment matrices, and illustrates the challenge of tracking pollution sources in lakes.

Use of fish otoliths as a temporal biomarker of field uranium exposure

This study aimed to determine uranium (U) pollution over time using otoliths as a marker of fish U contamination. Experiments were performed in field contamination (~20 μg L^-1: encaged fish: 15d, 50d and collected wild fish) and in laboratory exposure conditions (20 and 250 μg L^-1, 20d). We reported the U seasonal concentrations in field waterborne exposed roach fish (Rutilus rutilus), in organs and otoliths. Otoliths were analyzed by ICPMS and LA-ICP SF MS of the entire growth zone. Concentrations were measured on transects from nucleus to the edge of otoliths to characterize environmental variations of metal accumulation. Results showed a spatial and temporal variation of U contamination in water (from 51 to 9.4 μg L^-1 at the surface of the water column), a high and seasonal accumulation in fish organs, mainly the digestive tract (from 1000 to 30,000 ng g^-1, fw), the gills (from 1600 to 3200 ng g^-1, fw) and the muscle (from 144 to 1054 ng g^-1, fw). U was detected throughout the otolith and accumulation varied over the season from 70 to 350 ng g^-1, close to the values measured (310 ng g^-1) after high exposure levels in laboratory conditions. U in otoliths of encaged fish showed rapid and high U accumulation from 20 to 150 ng g^-1. The U accumulation signal was mainly detected on the edge of the otolith, showing two U accumulation peaks, probably correlated to fish age, i.e. 2 years old. Surprisingly, elemental U and Zn signatures followed the same pattern therefore using the same uptake pathways. Laboratory, caging and field experiments indicated that otoliths were able to quickly accumulate U on the surface even for low levels and to store high levels of U. This study is an encouraging first step in using otoliths as a marker of U exposure.

Heavy metals in tissues of scorpionfish (Scorpaena porcus) caught from Black Sea (Turkey) and potential risks to human health

Scorpionfish (Scorpaena porcus) is a demersal fish species commercially important for its of which meat is tough and delicious. The aim of this study was to determine heavy metal (Al, Cu, Ni, As, Cd, Hg, Pb, U) concentrations in this fish species which is traditionally consumed in the Black Sea Area and, to compare the concentrations of various toxic elements in different organs of the fish specimens (muscle, liver, gill, and skin). Within this scope, the mineralization was performed using microwave digestion system. Thirty-two scorpionfish caught from Sinop Inland Port during 2010 were analyzed. The heavy metal concentrations were determined with the method of inductively coupled plasma mass spectroscopy (ICP-MS). Verification of the method was demonstrated by analysis of standard reference material (NRCC-TORT-2 lobster hepatopancreas). After evaluation of the results, it was determined that the highest heavy metal accumulation was generally found in the liver. The maximum aluminum level and the minimum uranium level were found in the analyzed tissues. In terms of heavy metals, Al, Cu, Cd, and Hg showed a statistically significant difference between tissues (p < 0.05). It was determined that heavy metal concentrations obtained from the muscle tissues did not exceed the national and international recommended limits; and also it was found that daily intake amounts did not exceed tolerable daily intake amounts. Furthermore, in THQ based risk evaluation, the value 1 which is crucial for children and adults was not surpassed. In terms of public health, it was found out that there was not any risk in consumption of scorpionfish in the study area.

Exploring ecotoxicological fish bioassay for the evaluation of uranium reprotoxicity

Although reproduction in fish is known to be sensitive to metal exposure, few ecotoxicological studies have focused on the toxicological effects of metals. Because uranium (U) is naturally present in aquatic ecosystems (0.6-2 mg/L), freshwater organisms are subjected to chronic U exposure. Although new standardized assays are currently being developed to mimic realistic exposure conditions, they could be improved by taking into account the contamination that occurs throughout the life cycle of fish. The authors initially evaluated the effect of food (commercial flakes vs pure Spirulina) and ionic composition of the exposure medium on the reproductive performance of Danio rerio. The effects of U exposure on reproduction then were assessed 1) for the F0 adult stage at short exposure times (5 d, 20 d, and 40 d), and 2) for the F0 stage and the F1 generation after 200 d of exposure to control, low (20 µg U/L), and moderate (250 µg U/L) waterborne levels of U. Reproductive endpoints (reproductive success, fecundity, number of spawns, egg and larvae viability, and hatching) were measured mainly after the first spawn and after 10 d of cumulative spawns. The authors evaluated the plasticity of these endpoints and compared the effect of exposure conditions to identify the most relevant markers of the effect of U exposure on reproductive performance of D. rerio.

Biogeochemical behaviour and bioremediation of uranium in waters of abandoned mines

The discharges of uranium and associated radionuclides as well as heavy metals and metalloids from waste and tailing dumps in abandoned uranium mining and processing sites pose contamination risks to surface and groundwater. Although many more are being planned for nuclear energy purposes, most of the abandoned uranium mines are a legacy of uranium production that fuelled arms race during the cold war of the last century. Since the end of cold war, there have been efforts to rehabilitate the mining sites, initially, using classical remediation techniques based on high chemical and civil engineering. Recently, bioremediation technology has been sought as alternatives to the classical approach due to reasons, which include: (a) high demand of sites requiring remediation; (b) the economic implication of running and maintaining the facilities due to high energy and work force demand; and (c) the pattern and characteristics of contaminant discharges in most of the former uranium mining and processing sites prevents the use of classical methods. This review discusses risks of uranium contamination from abandoned uranium mines from the biogeochemical point of view and the potential and limitation of uranium bioremediation technique as alternative to classical approach in abandoned uranium mining and processing sites.

Relative importance of direct and trophic uranium exposures in the crayfish Orconectes limosus: Implication for predicting uranium bioaccumulation and its associated toxicity

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.

Determination of bioaccumulation of heavy metals and selenium in tissues of brown trout Salmo trutta macrostigma (Duméril, 1858) from Munzur Stream, Tunceli, Turkey

The objective of the present work was to determine the bioaccumulation of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), mercury (Hg), uranium (U) and selenium (Se) in gill, liver, and muscle tissues of the fresh water fish Salmo trutta macrostigma (Duméril, 1858) in Munzur Stream, Tunceli, Turkey. The highest concentrations of U (1.83 μg kg(-1)), Pb (119.84 μg kg(-1)) and Se (1.31 μg kg(-1)) were recorded in the gills of S. t. macrostigma. Concentrations of As (46.27 μg kg(-1)), Cd (109.19 μg kg(-1)), Hg (16.40 μg kg(-1)), Cu (18.19 μg kg(-1)) were recorded at highest levels in the liver. The results showed that there were significant differences in concentrations of As, Cd, Cu, Pb, Se, U and Hg in gill, liver and muscle tissue (p < 0.05). Heavy metals were within the edible parts of the investigated fish were in the permissible safety levels for human uses.

Uranium bioaccumulation in a freshwater ecosystem: impact of feeding ecology

The objectives of our study were: (1) to determine if there was significant uranium (U) bioaccumulation in a lake that had been historically affected by a U mine and (2) to use a combined approach of gut content examination and stable nitrogen and carbon isotope analysis to determine if U bioaccumulation in fish was linked to foodweb ecology. We collected three species of fish: smallmouth bass (Micropterus dolomieu), yellow perch (Perca flavescens) and bluegill (Lepomis macrochirus), in addition to several invertebrate species including freshwater bivalves (family: Sphaeriidae), dragonfly nymphs (order: Odonata), snails (class: Gastropoda) and zooplankton (family: Daphniidae). Results showed significant U bioaccumulation in the lake impacted by historical mining activities. Uranium accumulation was 2-3 orders of magnitude higher in invertebrates than in the fish species. Within fish, U was measured in operculum (bone), liver and muscle tissue and accumulation followed the order: operculum>liver>muscle. There was a negative relationship between stable nitrogen ratios ((15)N/(14)N) and U bioaccumulation, suggesting U biodilution in the foodweb. Uranium bioaccumulation in all three tissues (bone, liver, muscle) varied among fish species in a consistent manner and followed the order: bluegill>yellow perch>smallmouth bass. Collectively, gut content and stable isotope analysis suggests that invertebrate-consuming fish species (i.e. bluegill) have the highest U levels, while fish species that were mainly piscivores (i.e. smallmouth bass) have the lowest U levels. Our study highlights the importance of understanding the feeding ecology of fish when trying to predict U accumulation.

Are antioxidant and transcriptional responses useful for discriminating between chemo- and radiotoxicity of uranium in the crayfish Procambarus clarkii?

The main objectives of this study were to evaluate uranium (U) toxicity in the crayfish Procambarus clarkii at a low dose of exposure and to discriminate between the chemotoxicity and radiotoxicity of U. We conducted two sets of experiments using either 30 μg L(-1) of depleted uranium (DU) or (233)U, which differ from each other only in their specific activity (DU=1.7×10(4)Bqg(-1), (233)U=3.57×10(8)Bqg(-1)). The endpoints were oxidative stress responses and mitochondrial functioning in the gills and hepatopancreas, which were measured in terms of enzyme activities and gene expression levels. U accumulation levels were measured in different organs (gills, hepatopancreas, stomach, intestine, green gland, muscles, and carapace), and internal dose rates in the hepatopancreas were compared after DU and (233)U exposures. Significant U accumulation occurred in the organs of P. clarkii, and mitochondrial damage and antioxidant responses were detected. Despite the huge difference (21,000×) in the specific activities of DU and (233)U, few significant differences in biological responses were detected in P. clarkii exposed to these two pollutants. This finding indicates that the radiotoxicity was low compared to the chemotoxicity under our exposure conditions. Finally, genes expression levels were more sensitive markers of U toxicity than enzyme activities.

Effects of uranium on crayfish Procambarus clarkii mitochondria and antioxidants responses after chronic exposure: what have we learned?

We examined the impacts of Uranium (U) on mitochondria and on the response of antioxidants in the gills and the hepatopancreas of crayfish Procambarus clarkii after long-term exposure (30 and 60 days) to an environmentally relevant concentration (30 μg U/L). The expression of mitochondrial genes (12s, atp6, and cox1), as well as the genes involved in oxidative stress responses (sod(Mn) and mt) were evaluated. The activities of antioxidant enzymes (SOD, CAT, GPX and GST) were also studied. U accumulation in organs induced changes in genes' expression. The evolution of these transcriptional responses and differences between gene expression levels at high and low doses of exposure were also discussed. This study demonstrated that, after long-term exposure, U caused a decrease in antioxidant activities and induced oxidative stress. A possible ROS-mediated U cytotoxic mechanism is proposed. Expression levels of the investigated genes can possibly be used as a tool to evaluate U toxicity and seem to be more sensitive than the enzymatic activities. However a multiple biomarker approach is recommended as the perturbed pathways and the mode of action of this pollutant are not completely understood.

Effects of uranium uptake on transcriptional responses, histological structures and survival rate of the crayfish Procambarus clarkii

This work aims to investigate the accumulation levels and effects (transcriptional responses, histopathology and survival rate) associated with a wide range of dissolved uranium (U) concentrations (0, 0.03, 0.6, 4 and 8 mg/L of U) on adult male crayfish Procambarus clarkii during 4 (T4) and 10 (T10) days of exposure. The follow-up of the crayfish mortality showed that P. clarkii was highly resistant to U. Increasing waterborne U concentrations led to increasing bioaccumulation in key crayfish organs and increasing histological damages. U distribution in tissues was also evaluated using transmission electron microscopy and showed the presence of a detoxified form of U in the gill's epithelium in the shape of flakes. Expression levels of mitochondrial genes (cox1, atp6 and 12S gene) and genes involved in oxidative stress (sod(Mn) and mt) were examined together with the housekeeping gene 18S. atp6 and mt genes of P. clarkii were cloned and sequenced before analysis. Significant correlations were observed between U bioaccumulation and the down-regulation of both cox1 and sod(Mn) genes. This work provides a first U toxicogenomic and histopathological pattern of P. clarkii, identify U biomarkers and associate gene expression endpoints to accumulation levels. It also provides new insights into the mechanisms involved in U stress.

Internal distribution of uranium and associated genotoxic damages in the chronically exposed bivalve Corbicula fluminea

Uranium (U) internal distribution and involved effects in the bivalve Corbicula fluminea have been studied after direct chronic exposure (90 d, 10 μg.L-1). U distribution was assessed at the subcellular level (Metal Rich Granules -MRG-, pellets and cytosol fractions) in two main organs of the bivalve (gills and visceral mass). Micro-localisation was investigated by TEM-EDX analysis in the gills epithelium. DNA damage in gill and hemolymph samples was measured by the Comet assay. The 90-d exposure period led to a significant increase of U concentration in gills over time (× 5) and a large U quantity in subcellular granules in gills. Finally, a significant increase (× 2) in DNA damage was noted in exposed gills and haemocytes. This study shows that the accumulation levels and consequently the potential toxicity cannot be successfully predicted only on the basis of concentration in water or in tissues and subcellular fractions after chronic exposure.

Effects of dietary uranium on reproductive endpoints--fecundity, survival, reproductive success--of the fish Danio rerio

Exposure to metal-contaminated water has been shown to result in a number of reproductive abnormalities in adult and larvae fish, such as failure of oocyte maturation and teratogenic effects. Recently, dietary uptake of metals by fish has been recognized as a critical route of exposure, however, the mechanisms of metal uptake and toxicity are poorly understood and in need of further investigation. The objectives of the present study are to quantify uranium (U dietary transfers from spiked artificial diets) in Danio rerio tissues and embryos, as well as establish its effect on reproduction and embryonic development. Uranium's environmental prominence is currently increasing because of new mining and milling activities. Uranium concentrations range from 0.02 µg/L in natural waters to 2 mg/L. The focus of this study was to examine the trophic transfer and effects of U following exposure modalities (dose, exposure duration 1 to 20 d). Two different isotopes were used to distinguish between chemical and radioactivity toxicity of U. Results showed that U trophic transfer was low (0.52%). Uranium tissue distributions showed that accumulation occurred in digestive organs (liver, digestive tract) following dietary exposure. High levels of U were measured in the gonads (female in particular, >20% of relative burden). High U accumulation levels in eggs indicated maternal transfer of the contaminant. Moreover, U trophic exposure led to a reduction in reproduction success as a function of U accumulated levels. High U exposure conditions strongly reduced the total number of eggs (50%) and their viability at 10 d (reduction of the clutch number, low quality of eggs).