Evaluation of water column and sediment toxicity from an abandoned uranium mine using a battery of bioassays

Assessment of ecotoxicological effects of Fojo coal mine waste elutriate in aquatic species (Douro Coalfield, North Portugal)

Introduction: The exploitation of anthracite A in the Pejão mining complex (Douro Coalfield, North Portugal) resulted in the formation of several coal waste piles without proper environmental control. In 2017, a new pedological zonation emerged in the Fojo area, after the ignition and self-burning of some of the coal waste piles, namely: unburned coal waste (UW); burned coal waste, and a cover layer (BW and CL, respectively); uphill soil (US); mixed burned coal waste (MBW); downhill soil (DS). This study aimed to evaluate the toxic effects of 25 soil elutriates from different pedological materials. Methods: Allivibrio fischeri bioluminescence inhibition assay, Lemna minor growth inhibition assay, and Daphnia magna acute assay were used to assess the toxicity effects. Additionally, total chlorophyll and malondialdehyde (MDA) content and catalase (CAT) activity were also evaluated in L. minor. Results and Discussion: The results obtained from each endpoint demonstrated the extremely heterogeneous nature of soil properties, and the species showed different sensibilities to soil elutriates, however, in general, the species showed the same sensitivity trend (A. fischeri > L. minor > D. magna). The potentially toxic elements (PTE) present in the soil elutriates (e.g., Al, Pb, Cd, Ni, Zn) affected significantly the species understudy. All elutriates revealed toxicity for A. fischeri, while US1 and UW5 were the most toxic for L. minor (growth inhibition and significant alterations in CAT activity) and D. magna (100% mortality). This study highlights the importance of studying soil aqueous phase toxicity since the mobilization and percolation of bioavailable PTE can cause environmental impacts on aquatic ecosystems and biota.

Pollution status and risk assessment of trace elements in Portuguese water, soils, sediments, and associated biota: a trend analysis from the 80s to 2021

Pollution of water bodies and sediments/soils by trace elements remains a global threat and a serious environmental hazard to biodiversity and human's health. Globalization and industrialization resulted in the increase and availability of these substances in the environment posing unpredictable adverse effects to living organisms. To determine pollution status and risk contamination by trace elements, data available in the literature of the last 40 years on trace elements occurrence in three environmental matrices (water bodies, sediments/soils, and biota) from Continental Portugal were collected (about 90 studies). Data were compared to water and sediment quality guidelines to assess potential ecological risks. Most environmentally relevant hazardous elements include Zn, Cu, Cd, Pb, and As. Various studies found trace elements at levels higher than those considered safe by environmental guidelines. In surface waters, Al, Zn, Se, and Ag were found above aquatic life limits in about 60% of the reviewed papers, while Cu, Zn, and As exceed those values in more than 60% of mining waters. Hg and Cd in sediments from mining areas exceeded aquatic life limits and potential ecological risk showed extremely high risk for most of the elements. The data compiled in this review is very heterogenous, varying in terms of sampling schemes, trace elements analysed, and spatiotemporal settings. This heterogenicity leads to data differences that make meaningful comparisons difficult. Nevertheless, the compilation of scattered environmental spatial and temporal trace elements data, of either natural sources or human activity as well as the ultimate effect on biological systems, is of the upmost importance to broaden its knowledge, risk assessment, and implementation of mitigation measures.

Copper sulphate impact on the antioxidant defence system of the marine bivalves Cerastoderma edule and Scrobicularia plana

Anthropogenic activities, such as agriculture and industrial activities, are a main source of pollution contributing for the degradation of water quality and thus affecting the living organisms of aquatic systems. Copper is widely used at these practices being often released into the aquatic systems and may cause negative effects in its communities. This study proposes to determine the effects of copper in the antioxidant defence system of two size classes (big and small sizes) of Scrobicularia plana and Cerastoderma edule, two marine bivalve species with commercial interest. It was observed the behaviour activity of the organisms during the exposure to copper sulphate (CS) and was determined the enzymatic activities of glutathione-S-transferases (GST), glutathione reductase (GR) and glutathione peroxidase (GPx) (both selenium-dependent (SeGPx) and total (tGPx)) in the muscle tissue (foot). Lipid peroxidation (LPO) was evaluated through thiobarbituric acid reactive substances (TBARS) measurement in the foot. Changes in the behaviour and enzymatic activity were observed. Lipid peroxidation was observed at C. edule and S. plana big and small size classes, respectively, according to TBARS levels. The foot showed to be a good tissue to be used in biochemical analysis to detect the presence of toxicants.

Uranium toxicity to aquatic invertebrates: A laboratory assay

Uranium mining is an environmental concern because of runoff and the potential for toxic effects on the biota. To investigate uranium toxicity to freshwater invertebrates, we conducted a 96-h acute toxicity test to determine lethal concentrations (testing concentrations up to 262 mg L^-1) for three stream invertebrates: a shredder caddisfly, Schizopelex festiva Rambur (Trichoptera, Sericostomatidae); a detritivorous isopod, Proasellus sp. (Isopoda, Asellidae); and a scraper gastropod, Theodoxus fluviatilis (Gastropoda, Neritidae). Next, we ran a chronic-toxicity test with the most tolerant species (S. festiva) to assess if uranium concentrations found in some local streams (up to 25 μg L^-1) affect feeding, growth and respiration rates. Finally, we investigated whether S. festiva takes up uranium from the water and/or from ingested food. In the acute test, S. festiva survived in all uranium concentrations tested. LC₅₀-96-h for Proasellus sp and T. fluviatilis were 142 mg L^-1 and 24 mg L^-1, respectively. Specimens of S. festiva exposed to 25 μg L^-1 had 47% reduced growth compared with specimens under control conditions (21.5 ± 2.9 vs. 40.6 ± 4.9 μg of mass increase animal^-1·day^-1). Respiration rates (0.40 ± 0.03 μg O₂·h^-1·mg animal^-1) and consumption rates (0.54 ± 0.05 μg μg animal^-1·day^-1; means ± SE) did not differ between treatments. Under laboratory conditions S. festiva accumulated uranium from both the water and the ingested food. Our results indicate that uranium can be less toxic than other metals or metalloids produced by mining activities. However, even at the low concentrations observed in streams affected by abandoned mines, uranium can impair physiological processes, is bioaccumulated, and is potentially transferred through food webs.

Ecotoxicological bioassays of sediment leachates in a river bed flanked by decommissioned pesticide plants in Nantong City, East China

Traditionally, the toxicity of river contaminants is analyzed chemically or physically through river bed sediments. The biotoxicity of polluted sediment leachates has not caught our attention. This study aims to overcome this deficiency through a battery of biotests which were conducted to monitor comprehensive toxicity of sediment leachates for the Yaogang River in East Jiangsu Province of China, which is in close proximity to former pesticide plants. The general physical and chemical parameters of major pollutants were analyzed from river bed sediments collected at five strategic locations. The ecotoxicity analyses undertaken include overall fish (adult zebrafish) acute toxicity, luminescent bacteria (Vibrio fischeri) bioassay, and zebrafish embryo toxicity assay. Compared with the control group, sediment leachates increased the lethality, inhibited the embryos hatching and induced development abnormalities of zebrafish embryos, and inhibited the luminescence of V. fischeri. The results show that sediment leachates may assume various toxic effects, depending on the test organism. This diverse toxicity to aquatic organisms reflects their different sensitivity to sediment leachates. It is found clearly that V. fischeri was the organism which was characterized by the highest sensitivity to the sediment leachates. The complicated toxicity of leachates was not caused by one single factor but by multiple pollutants together. This indicates the need of estimations of sediment leachate not only taking into account chemical detection but also of applying the biotests to the problem. Thus, multigroup bioassays are necessary to realistically evaluate river ecological risks imposed by leachates.

Biogeochemistry of uranium in the soil-plant and water-plant systems in an old uranium mine

The present study highlights the uranium (U) concentrations in water-soil-plant matrices and the efficiency considering a heterogeneous assemblage of terrestrial and aquatic native plant species to act as the biomonitor and phytoremediator for environmental U-contamination in the Sevilha mine (uraniferous region of Beiras, Central Portugal). A total of 53 plant species belonging to 22 families was collected from 24 study sites along with ambient soil and/or water samples. The concentration of U showed wide range of variations in the ambient medium: 7.5 to 557mgkg(-1) for soil and 0.4 to 113μgL(-1) for water. The maximum potential of U accumulation was recorded in roots of the following terrestrial plants: Juncus squarrosus (450mgkg(-1) DW), Carlina corymbosa (181mgkg(-1) DW) and Juncus bufonius (39.9mgkg(-1) DW), followed by the aquatic macrophytes, namely Callitriche stagnalis (55.6mgkg(-1) DW) Lemna minor (53.0mgkg(-1) DW) and Riccia fluitans (50.6mgkg(-1) DW). Accumulation of U in plant tissues exhibited the following decreasing trend: root>leaves>stem>flowers/fruits and this confirms the unique efficiency of roots in accumulating this radionuclide from host soil/sediment (phytostabilization). Overall, the accumulation pattern in the studied aquatic plants (L. minor, R. fluitans, C. stagnalis and Lythrum portula) dominated over most of the terrestrial counterpart. Among terrestrial plants, the higher mean bioconcentration factor (≈1 in roots/rhizomes of C. corymbosa and J. squarrosus) and translocation factor (31 in Andryala integrifolia) were encountered in the representing families Asteraceae and Juncaceae. Hence, these terrestrial plants can be treated as the promising candidates for the development of the phytostabilization or phytoextraction methodologies based on the accumulation, abundance and biomass production.

Ecotoxicological assessment of flocculant modified soil for lake restoration using an integrated biotic toxicity index

Flocculant modified soils/clays are being increasingly studied as geo-engineering materials for lake restoration and harmful algal bloom control. However, the potential impacts of adding these materials in aquatic ecological systems remain unclear. This study investigated the potential effects of chitosan, cationic starch, chitosan modified soils (MS-C) and cationic starch modified soils (MS-S) on the aquatic organisms by using a bioassay battery. The toxicity potential of these four flocculants was quantitatively assessed using an integrated biotic toxicity index (BTI). The test system includes four aquatic species, namely Chlorella vulgaris, Daphnia magna, Cyprinus carpio and Limnodrilus hoffmeisteri, which represent four trophic levels in the freshwater ecosystem. Results showed that median effect concentrations (EC50) of the MS-C and MS-S were 31-124 times higher than chitosan and cationic starch, respectively. D. magna was the most sensitive species to the four flocculants. Histological examination of C. carpio showed that significant pathological changes were found in gills. Different from chitosan and cationic starch, MS-C and MS-S significantly alleviated the acute toxicities of chitosan and cationic starch. The toxicity order of the four flocculants based on BTI were cationic starch > chitosan > MS-S > MS-C. The results suggested that BTI can be used as a quantitative and comparable indicator to assess biotic toxicity for aquatic geo-engineering materials. Chitosan or cationic starch modified soil/clay materials can be used at their optimal dosage without causing substantial adverse effects to the bioassay battery in aquatic ecosystem.

Toxicity in semiarid sediments influenced by tailings of an abandoned gold mine

The mining district of El Triunfo (ET-MD) has an estimated 800,000 t of mine wastes scattered in the environment, contaminating the sediment with potentially toxic elements such as As, Cd, Pb, and Zn. In order to estimate the toxicity of the sediment to the adjacent biota, the aims of our study are to calculate the mortality and inhibition through bioassays, using sediment, and test organisms such as Daphnia magna and Selenastrum capricornutum (Pseudokirchneriella subcapitata), respectively. The D. magna mortality was 31 ± 12% and the S. capricornutum growth inhibition was 53 ± 24%. The contamination of the sediment determines the high mortality of D. magna and the high inhibition of S. capricornutum in the system, indicating risk for the biota in the contaminated system.

Toxicity assessment of the water used for human consumption from the Cameron/Tuba City abandoned uranium mining area prior/after the combined electrochemical treatment/advanced oxidation

The purpose of this work was detailed physicochemical, radiological, and toxicological characterization of the composite sample of water intended for human consumption in the Cameron/Tuba City abandoned uranium mining area before and after a combined electrochemical/advanced oxidation treatment. Toxicological characterization was conducted on human lymphocytes using a battery of bioassays. On the bases of the tested parameters, it could be concluded that water used for drinking from the tested water sources must be strictly forbidden for human and/or animal consumption since it is extremely cytogenotoxic, with high oxidative stress potential. A combined electrochemical treatment and posttreatment with ozone and UV light decreased the level of all physicochemical and radiological parameters below the regulated values. Consequently, the purified sample was neither cytotoxic nor genotoxic, indicating that the presented method could be used for the improvement of water quality from the sites highly contaminated with the mixture of heavy metals and radionuclides.

Depleted uranium disturbs immune parameters in zebrafish, Danio rerio: an ex vivo/in vivo experiment

In this study, we investigated the effects of depleted uranium (DU), the byproduct of nuclear enrichment of uranium, on several parameters related to defence system in the zebrafish, Danio rerio, using flow cytometry. Several immune cellular parameters were followed on kidney leucocytes: cell proportion, cell mortality, phagocytosis activity and associated oxidative burst and lysosomal membrane integrity (LMI). Effects of DU were tested ex vivo after 17 h of contact between DU and freshly isolated leucocytes from 0 to 500 µg DU/L. Moreover, adult zebrafish were exposed in vivo during 3 days at 20 and 250 µg DU/L. Oxidative burst results showed that DU increased reactive oxygen species (ROS) basal level and therefore reduced ROS stimulation index in both ex vivo and in vivo experiments. ROS PMA-stimulated level was also increased at 250 µg DU/L in vivo only. Furthermore, a decrease of LMI was detected after in vivo experiments. Cell mortality was also decreased at 20 µg DU/L in ex vivo experiment. However, phagocytosis activity was not modified in both ex vivo and in vivo experiments. A reduction of immune-related parameters was demonstrated in zebrafish exposed to DU. DU could therefore decrease the ability of fish to stimulate its own immune system which could, in turn, enhance the susceptibility of fish to infection. These results encourage the development and the use of innate immune analysis by flow cytometry in order to understand the effects of DU and more generally radionuclides on fish immune system and response to infectious diseases.

Uranium mining in Portugal: a review of the environmental legacies of the largest mines and environmental and human health impacts

The history of uranium mining in Portugal during almost one century has followed international demand peaks of both radium and uranium, which in turn were driven by medical, military, and civil applications. Nowadays, following price drop in the 1980s, mining activities decreased and ceased in 2001. The current challenge is to deal with environmental legacies left by old uranium mines, mainly located in Viseu and Guarda districts. In 2001, based on several radiological surveys carried out, the Portuguese government assumed the remediation costs of abandoned mine areas for environmental safety and public health protection. Detailed environmental and public health risk assessments were performed under the scope of studies both requested by the government and by funded research projects. It was found that the existing risks, due to radiological and chemical exposures to metals and radionuclide's, were particularly high at the old milling facilities and mines where in situ and heap leaching of low-grade ore occurred. The different studies, involving both humans and non-human species from different trophic levels, demonstrated the existence of effects at different levels of biological organization (molecular, cellular, tissues, individuals, and populations) and on ecosystem services. To mitigate the risks, the environmental rehabilitation works at the Urgeiriça mine complex are almost complete, while at Cunha Baixa mine, they are presently in progress. These works and environmental improvements achieved and expected are described herein.

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.

Use of diatom assemblages as biomonitor of the impact of treated uranium mining effluent discharge on a stream: case study of the Ritord watershed (Center-West France)

The rehabilitation of French former uranium mining sites has not prevented the contamination of the surrounding aquatic ecosystems with metal elements. This study assesses the impact of the discharge of treated uranium mining effluents on periphytic diatom communities to evaluate their potential of bioindication. A 7-month survey was conducted on the Ritord watercourse to measure the environmental conditions of microalgae, the non-taxonomic attributes of periphyton (photosynthesis and biomass) and to determine the specific composition of diatom assemblages grown on artificial substrates. The environmental conditions were altered by the mine waters, that contaminate the watercourse with uranium and with chemicals used in the pit-water treatment plants (BaCl2 and Al2(SO4)3). The biomass and photosynthetic activity of periphyton seemed not to respond to the stress induced by the treated mining effluents whereas the altered environmental conditions clearly impacted the composition of diatom communities. Downstream the discharges, the communities tended to be characterized by indicator species belonging to the genera Fragilaria, Eunotia and Brachysira and were highly similar to assemblages at acid mine drainage sites. The species Eunotia pectinalis var. undulata, Psammothidium rechtensis, Gomphonema lagenula and Pinnularia major were found to be sensitive to uranium effluents whereas Neidium alpinum and several species of Gomphonema tolerated this contamination. The relevance of diatoms as ecological indicator was illustrated through the changes in structure of communities induced by the discharge of uranium mining effluents and creates prospects for development of a bioindicator tool for this kind of impairment of water quality.

Sensitivity evaluation of the green alga Chlamydomonas reinhardtii to uranium by pulse amplitude modulated (PAM) fluorometry

Although ecotoxicological studies tend to address the toxicity thresholds of uranium in freshwaters, there is a lack of information on the effects of the metal on physiological processes, particularly in aquatic plants. Knowing that uranium alters photosynthesis via impairment of the water photo-oxidation process, we determined whether pulse amplitude modulated (PAM) fluorometry was a relevant tool for assessing the impact of uranium on the green alga Chlamydomonas reinhardtii and investigated how and to what extent uranium hampered photosynthetic performance. Photosynthetic activity and quenching were assessed from fluorescence induction curves generated by PAM fluorometry, after 1 and 5h of uranium exposure in controlled conditions. The oxygen-evolving complex (OEC) of PSII was identified as the primary action site of uranium, through alteration of the water photo-oxidation process as revealed by F0/Fv. Limiting re-oxidation of the plastoquinone pool, uranium impaired the electron flux between the photosystems until almost complete inhibition of the PSII quantum efficiency ( [Formula: see text] , EC50=303 ± 64 μg UL(-1) after 5h of exposure) was observed. Non-photochemical quenching (qN) was identified as the most sensitive fluorescence parameter (EC50=142 ± 98 μg UL(-1) after 5h of exposure), indicating that light energy not used in photochemistry was dissipated in non-radiative processes. It was shown that parameters which stemmed from fluorescence induction kinetics are valuable indicators for evaluating the impact of uranium on PSII in green algae. PAM fluorometry provided a rapid and reasonably sensitive method for assessing stress response to uranium in microalgae.

Evaluation of growth, biochemical and bioaccumulation parameters in Pelophylax perezi tadpoles, following an in-situ acute exposure to three different effluent ponds from a uranium mine

Mining activities invariably produce metal contaminated effluents. Depending on factors such as pH and metal concentration the toxicity of the effluent may vary. To assess the effects of three characteristically different effluent ponds from a deactivated uranium mine, with toxicologically relevant data, an in situ exposure with Pelophylax perezi tadpoles, was conducted. Tadpoles were exposed to the three effluent ponds, ranked by increasing order of metals concentrations (REF, M1, M2). Survival, growth, metal accumulation, antioxidant enzymes (catalase, glutathione peroxidase and glutathione reductase) and lipid peroxidation (LPO) were determined in tadpoles. As well, physical and chemical variables of the effluents were measured. Death percentage in the effluents was 3.17 (REF), 9.84 (M1) and 42.86% (M2) and was not coincident with metal accumulation which was highest in tadpoles exposed to M1, while metal contents in M2 tadpoles were quite similar to those recorded in REF tadpoles. However, high mortality in M2 was attributed to the extremely low pH (≈3.77). From the three effluents M2 tadpoles had the lowest growth and the antioxidant enzymatic activity was only affected in the case glutathione peroxidase (GPx) with significantly higher activity in M1, being in accordance with the highest accumulation of metals. LPO, usually associated with metal accumulation, had the following pattern M1>REF>M2. Overall, effluent toxicity in tadpoles exposed to M2 effluent seems to be primarily an effect of pH while in M1 toxicity is mainly owed to high metal concentrations. The effluent acidity seems to reduce metal accumulation probably due to damage in the integument, affecting ion uptake. The results obtained bring a better understanding of the toxicological processes that local P. perezi population is subjected to, mainly in the early life stages. Furthermore this study highlights the influence of pH in the toxicity of metal rich effluents.

Differential gene expression in Iberian green frogs (Pelophylax perezi) inhabiting a deactivated uranium mine

Iberian green frogs (Pelophylax perezi) were found inhabiting a deactivated uranium mine, especially an effluent pond, seriously contaminated with metals and radionuclides. These animals were previously assessed for oxidative stress parameters and did not revealed significant alterations. In order to better understand which mechanisms may be involved in the ability to withstand permanent contamination gene expression analysis was performed in the liver, through suppression subtractive hybridization (SSH). The SSH outcome in the liver revealed the up-regulation of genes coding for the ribosomal protein L7a and for several proteins typical from blood plasma: fibrinogen, hemoglobin and albumin. Besides their normal function, some of these proteins can play an important role as protective agents against oxidative stress. This work provides new insights on possible basal protection mechanisms that may act in organisms exposed chronically to contamination.

Effects of depleted uranium on oxidative stress, detoxification, and defence parameters of zebrafish Danio rerio

In this study, we investigated the effects of depleted uranium (DU), the by-product of nuclear enrichment of uranium, on several parameters related to oxidative stress, detoxification, and the defence system in the zebrafish Danio rerio. Several parameters were recorded: phenoloxidase-like (PO) activity, reactive oxygen species (ROS) production, and 7-ethoxyresrufin-O-deethylase (EROD) activity. Experiments were performed on adult and larvae D. rerio. Adult fish were exposed for 28 days at 20 μg U/L followed by a 27-day depuration period. Eggs of D. rerio were exposed for 4 days at 0, 20, 100, 250, 500, and 1,000 μg U/L. Results showed that DU increased ROS production both in adult and in larvae even at the low concentrations tested and even during the depuration period for adult D. rerio. DU also modified PO-like activity, both in the D. rerio adult and larvae experiments, but in a more transient manner. EROD activity was not modified by DU, but sex effects were shown. Results are discussed by way of comparison with other known effects of uranium in fish. Overall, these results show that the mechanisms of action of DU in fish tend to be similar to the ones existing for mammals. These results encourage the development and use of innate immune biomarkers to understand the effects of uranium and, more generally, radionuclides on the fish immune system.

Reanalysis of uranium toxicity data for selected freshwater organisms and the influence of dissolved organic carbon

The present study reanalyzed 46 existing uranium (U) chronic toxicity datasets for four freshwater species to generate consistent toxicity measures and explore relationships between U toxicity and key physicochemical variables. Dissolved organic carbon (DOC) was consistently the best predictor of U toxicity based on 10% inhibitory concentration (IC10) and median inhibitory concentration (IC50) values, with water hardness also being a significant co-predictor of IC50 concentrations for one species. The influence of DOC on acute and chronic U toxicity was further characterized using existing data for five species, and was found to vary depending on species, DOC source, and exposure duration (acute vs chronic). The slopes of the relationships between DOC and (normalized) acute and chronic U toxicity were modeled using cumulative probability distributions. From these, slopes were selected for which to correct acute or chronic U toxicity values or hazard estimates based on the aquatic DOC concentration. The fifth percentiles of these cumulative probability distributions for acute and chronic exposure data were 0.064 and 0.090, respectively, corresponding to a 6.4 and 9.0% reduction in U toxicity relative to the toxicity at the base DOC concentration for each 1 mg/L increase in DOC concentration (over the DOC range 0-30 mg/L). Algorithms were developed to enable the adjustment of U toxicity values and U hazard estimates, depending on DOC concentrations. These algorithms will significantly enhance the environmental relevance of water quality/risk assessments for U in fresh surface waters.

Assessment of liquid disposal originated by uranium enrichment at Aramar Experimental Center São Paulo--Brazil

This work presents a liquid disposal monitoring originated from uranium enrichment process at Aramar Experimental Center from 1990 to 1998. Assessment of uranium, fluorides, ammoniacal nitrogen, chemical oxygen demand, and pH measurements were made in water samples and compared with results achieved in other countries, as North America and India. The liquid disposal evaluation, generated by uranium enrichment process, showed low levels, considering most parameters established by Federal and State Legislation, aiming environmental pollution control. However, uranium levels were above the limits established by Conselho Nacional do Meio Ambiente, Environment Protection Agency and mainly by the World Health Organization.

Antioxidant response and metal accumulation in tissues of Iberian green frogs (Pelophylax perezi) inhabiting a deactivated uranium mine

Human mining activities tend often to generate greatly impacted areas which remain contaminated for long periods of time, giving rise to extreme habitats. Mining sites are usually characterized for the production of metal rich effluents with very low pH. In this work we analyzed physical and chemical parameters of water from a deactivated uranium mine pond (M) and a reference site (REF) as well as their metal content. Furthermore, we determined and compared metal accumulation in liver, kidney, bones, muscle and skin of Pelophylax perezi from REF with P. perezi from M. We also determined the enzymatic activities of glutathione-S-transferases (GSTs), catalase (CAT), glutathione reductase (Gred), and glutathione peroxidase (GPx; both selenium-dependent and selenium-independent) in liver, kidney, lung and heart. Additionally, lipoperoxidation (LPO) was also assessed in the same tissues via thiobarbituric acid reactive substances (TBARS) assay and lactate dehydrogenase (LDH) activity was determined in muscle. Our results revealed that the majority of metals were in higher concentrations in tissues of organisms from M. This trend was especially evident for U whose content reached a difference of 1350 fold between REF and M organisms. None of the organs tested for antioxidant defenses revealed LPO, nonetheless, with exception for liver, all organs from the M frogs presented increased total GPx activity and selenium-dependent GPx. However, this response was significant only for the lung, probably as a consequence of the significant inhibition of CAT upstream and to cope with the subsequent increase in H(2)O(2). Lungs were the organs displaying greater responsiveness of the anti-oxidant stress system in frogs from the uranium mine area.

Characterization and treatment of water used for human consumption from six sources located in the Cameron/Tuba City abandoned uranium mining area

The purpose of this research was the characterization and improvement of the quality of water used for human consumption of unregulated/regulated water sources located in the Cameron/Tuba City abandoned uranium mining area (NE Arizona, western edge of the Navajo Nation). Samples were collected at six water sources which included regulated sources: Wind Mill (Tank 3T-538), Badger Springs and Paddock Well as well as unregulated sources: Willy Spring, Water Wall and Water Hole. Samples taken from Wind Mill, Water Wall and Water Hole were characterized with high turbidity and color as well as high level of manganese, iron and nickel and elevated value of molybdenum. High level of iron was also found in Badger Spring, Willy Spring, and Paddock Well. These three water sources were also characterized with elevated values of fluoride and vanadium. Significant amounts of zinc were found in Water Wall and Water Hole samples. Water Wall sample was also characterized with high level of Cr(VI). Compared to primary or secondary Navajo Nation Environmental Protection Agency (NNEPA) water quality standard the highest enrichment was found for turbidity (50.000 times), color (up to 1.796 times) and manganese (71 times), Cr(VI) (17.5 times), iron (7.4 times) and arsenic (5.2 times). Activities of (226)Ra and (238)U in water samples were still in agreement with the maximum contaminant levels. In order to comply with NNEPA water quality standard water samples were subjected to electrochemical treatment. This method was selected due to its high removal efficiency for heavy metals and uranium, lower settlement time, production of smaller volume of waste mud and higher stability of waste mud compared to physico-chemical treatment. Following the treatment, concentrations of heavy metals and activities of radionuclides in all samples were significantly lower compared to NNEPA or WHO regulated values. The maximum removal efficiencies for color, turbidity, arsenic, manganese, molybdenum and nickel were 100.0%. Maximum removal percentage of Cu, F(-), V, Zn, (137)Cs, (226)Ra, (232)Th, (238)U were as follows: 98.0%; 82.7%; 99.9%; 95.6%; 75.0%; 76.9%; 80.0% and 99.2%. From the results presented it could be concluded that electrochemical treatment is a suitable approach for the purification of drinking water with complex mixture of contaminants, especially those with high turbidity and color.

Transfer modelling and toxicity evaluation of the effluent from an installation of cleansing and uranium recovery using a battery of bioassays

On July 7, 2008, a leak of effluent from an Installation of Cleansing and Uranium Recovery (Tricastin, France) led to the spillage of uranium in a stream. The acute toxicity of the effluent was evaluated, and compared to the toxicity of uranium nitrate in bioassays using several organisms: Chlamydomonas reinhardtii, Daphnia magna, Chironomus riparius and Danio rerio. A sediment bioassay was also performed on C. riparius using water and sediment sampled along the river. Results showed that effluent EC(50) 72 h was 0.65 mg U/l for algae and LC(50) 48 h was 1.67 mg U/l for daphnia, while values obtained for uranium nitrate were higher. The LC(50) 96 h of effluent to C. riparius was 22.7 mg U/l, similar to value for uranium nitrate; the sediment collected was not toxic to C. riparius larvae. The LOEC of effluent and uranium nitrate on HT(50) of D. rerio were similar (0.03 mg U/l), but larvae were more sensitive to uranium nitrate than to effluent. Our results suggest that other substances contained in the effluent could potentially be toxic to wildlife in association with uranium. In parallel, the modelling of the transfers based on uranium measurements in the surface water was used to fill data gaps and assess the impact along the river. These results provided an estimate of exposure conditions that occurred along the river. This approach allowed us to see that the risk to ecosystem during this incident was certainly low and concerned a short period of time, but it could have existed at least for some species.

Contamination by uranium mine drainages affects fungal growth and interactions between fungal species and strains

The presence of aquatic hyphomycetes has been reported for several heavy metal-contaminated waters. Tolerance probably is one adaptation to coping with heavy metals. To help clarify this issue strains of two species of aquatic hyphomycetes (Tricladium splendens Ingold and Varicosporium elodeae Kegel) were isolated from a reference stream and a stream contaminated with heavy metals and grown on malt extract agar prepared with reference and contaminated water to characterize colony morphology, growth rate, growth inhibition and interaction among species and strains. In V. elodeae the morphology of colonies differed between strains. Colony diameter increased linearly over time with growth rates being lower for strains isolated from contaminated than from reference streams (mostly for V. elodeae). Strains from the contaminated stream grew faster in medium prepared with contaminated water than in medium prepared with reference water, while for strains from the reference stream there was no significant difference in growth rates on the two media. In interacting isolates radial growth toward the opposing colony was generally lower than toward the dish edge. Percentage growth inhibition was higher for isolates in intraspecific interactions (13-37%) than in interspecific interactions (3-27%). However differences in growth inhibition experienced by interacting isolates were observed only in three cases out of 16. The difference between the percentage inhibition caused and experienced by a given isolate was highest in interactions involving isolates with distinct growth rates. Our results suggest that strains from the reference stream tolerate heavy metals while strains from the contaminated stream seem to be adapted to contaminated waters. We hypothesize that in natural environments fungal species-specific limits of tolerance to metal contamination might determine an abrupt or gradual response of the original fungal community to mine pollution giving origin to a poorer fungal community dominated by adapted strains with distinct functional efficiency.

Bait-lamina assay as a tool to assess the effects of metal contamination in the feeding activity of soil invertebrates within a uranium mine area

As part of the tier 2 of a site-specific risk assessment, this study was the first reporting an intensive in situ application of the bait-lamina assay; two exposure periods (7 and 14 days) were tested during four seasons in ten different sites, within a uranium mine area and at two different depths. The most contaminated sites (by deposition of sludge from the effluent treatment pond) were discriminated after 14 days of exposure because extremely low percentages of feeding activity were recorded. Previous sub-lethal ecotoxicological assays, already had demonstrated that the habitat function of these soils is compromised. Nevertheless, seasonality has proved to have a significant influence on responses. Thus to strength conclusions about the impact of contaminants, the in situ bait-lamina assay should be performed on different annual seasons, at least for temperate regions. It was also found that some environmental parameters (e.g. soil moisture and litter) can act as confounding factors in the bait-lamina assay.

Effects of uranium-contaminated sediments on the bioturbation activity of Chironomus riparius larvae (Insecta, Diptera) and Tubifex tubifex worms (Annelida, Tubificidae)

Freshwater sediments represent a compartment for accumulation of toxic substances, notably of metallic pollutants such as uranium. However, they also constitute a privileged habitat for many benthic macro-invertebrate species with important roles in the functioning of these ecosystems, particularly through their bioturbation activities. Uranium accumulation in sediments can thus have harmful effects on these organisms (e.g., developmental delay, malformations, mortality). The present study aimed to evaluate the consequences of these effects on the bioturbation activity of Chironomus riparius larvae and Tubifex tubifex worms. These two species, which are widespread in freshwater ecosystems, are characteristic of two different modes of bioturbation: bioirrigation and upward bioconveying, respectively. By quantifying the burial and redistribution of fluorescent particulate tracers (microspheres), sediment reworking induced by these macro-invertebrates was measured after 12d of exposure. Biodiffusion D(b) and bioadvection W rates, as well as several other parameters, were estimated to assess and compare the bioturbation activity of the two species, separately and in combination, between uncontaminated and uranium-spiked sediments. The results reveal that C. riparius larvae were more sensitive to uranium, but their bioturbation activity, even under uncontaminated conditions, had little effect on sediment reworking. Particle mixing was mainly induced by T. tubifex worms, which were only affected by uranium at high concentrations in the sediment. Finally, bioturbation by T. tubifex led to a high degree of uranium release from sediment to the overlying water, which highlights the crucial role of this mostly dominant species on uranium biogeochemical cycles at concentrations existing in naturally contaminated sites.

Benefits and limits of sediment toxicity tests as an aid to decision-making

With respect to the management of dredged sediments, a crucial issue is whether the removed materials (watered and/or processed) are disposed of or reused in an environmentally sound manner. In this context, the number of studies dealing with hazard or risk assessment has exponentially increased. This emphasis has resulted in the promotion and application of a very large variety of ecotoxicological tests. As a consequence, there is a clear need to highlight the scope and limitations of these tests for their appropriate selection and interpretation. In this paper we discuss the choice, implementation and interpretation of laboratory tests carried out on aquatic organisms at various levels of biological organization. We examine some experimental tools and methods in order to determine how suitable they are in regard to the objectives for which they are employed. To make this discussion more consistent our paper is based on results from research programmes conducted for governmental organizations and industrial partners. The Laboratoire des Sciences de l'Environnement (LSE) was involved with Cemagref de Lyon in a first methodological programme on risk assessment of scenarios of dredged sediment deposition. Another programme for a chemical company was implemented to assess the benefits of a physico-chemical treatment applied to contaminated dredged sediments in a scenario of reuse or deposit in gravel pits. Currently, the LSE is working on a programme of risk assessment for road sediments in valorization scenarios. From these programmes, we expose how single-species tests, as well as more complex bioassays and microcosm tests, can be used in an iterative step of risk assessment. Concerning microcosm tests, we also introduce a more realistic system that has been designed to simulate natural hydraulic conditions of gravel pits to assess the effects of toxicants on gravel pit aquatic biota during the sediment immersion phase and the sediment post-deposition phase (paper in preparation). The benefits of these ecotoxicological approaches are underlined, but limits are discussed with regard to several criteria: ecological relevance, realism, use for decision-making, cost and complexity of methods involved.

Use of a novel battery of bioassays for the biological characterisation of hazardous wastes

Four toxicity bioassays were used for the biological characterisation of nine hazardous wastes and extracts. This evaluation included conventional and novel bioassays, and combined in vivo and in vitro tests in order to facilitate the effect characterisation. This test battery incorporated different relevant taxonomic groups for the aquatic compartment and covered several ecotoxicological endpoints. The toxicity bioassays used for this characterisation were the acute immobilisation daphnia test, an acute toxicity test with larvae of Xenopus laevis, an in vitro test with the fish cell line RTG-2 comprising endpoints for cellular defence and viability, and finally the DR-CALUX assay to detect dioxin-like compounds. The aim of this study is to contribute to the development of a cost-effective battery of toxicity tests for the acute screening of hazardous and toxic wastes for the aquatic compartment. For this objective, the correlations between toxicity data derived from all bioassay were studied using a multivariate analysis, including the Principal Component Analysis. The results showed that Daphnia and Xenopus were effective assays to detect toxicity and they could be incorporated to a screening test battery. On the other hand, the toxicity results with the in vitro test RTG-2 showed that this test could be a good alternative to in vivo tests, demonstrating an acceptable sensitivity for toxicity detection and contributing other advantages as reducing assays cost and animal testing. Finally DR-CALUX test implemented the tests-batteries in the screening of hazardous wastes when there is a suspicious that dioxin-like compounds are presented in the samples.

The effectiveness of a biological treatment with Rhizopus oryzae and of a photo-Fenton oxidation in the mitigation of toxicity of a bleached kraft pulp mill effluent

Huge efforts have been made both in adopting more environmental-friendly bleaching processes, and in developing advanced oxidation processes and more effective biological treatments for the reduction of deleterious impacts of paper mill effluents. Even so, the success of such treatments is frequently reported in terms of chemical parameters without a proper evaluation of the effluent's toxicity mitigation. This is the first study reporting an exhaustive evaluation of the toxicity of a secondary bleached kraft pulp mill effluent, after either tertiary treatment with the soft-rot fungi Rhizopus oryzae or with a photo-Fenton oxidation, using a battery of freshwater species. As it has been reported the photo-Fenton/UV treatment has proved to be the most effective in reducing the colour and the COD (chemical oxygen demand) of the effluent. Nevertheless, extremely low EC(50) values were reported for almost all species, after this tertiary treatment. The treatment with R. oryzae was less effective in terms of colour removal and COD reduction, but proved to be the most promising in reducing toxicity.

Ecotoxicity of uranium to Tubifex tubifex worms (Annelida, Clitellata, Tubificidae) exposed to contaminated sediment

In freshwater ecosystems, sediments act as an accumulation compartment for metallic pollutants as uranium. However, they are also the habitats of numerous benthic macroinvertebrates that directly influence the structure and functioning of such environments. Consequently, these organisms could be affected by uranium. This laboratory study aimed to assess the ecotoxicity of uranium on Tubifex tubifex through 12-day exposure to contaminated sediment (0-5980 microg U g(-1) dry wt). At high concentrations (>599 microg U g(-1) dry wt), malformations were observed, and survival, biomass and burrowing activity were all reduced. This relative high resistance in polluted environments can be explained mainly by the implementation of several processes as autotomy, regeneration ability, increased production of mucus, a hormetic effect on biomass and a probable strategy for avoiding the contaminated sediment. This study represents the first assessment of uranium impact on T. tubifex at realistic concentrations in sediments near mining sites.

Histopathological changes and erythrocytic nuclear abnormalities in Iberian green frogs (Rana perezi Seoane) from a uranium mine pond

In spite of their sensitivity to anthropogenic stressors, adults of Rana perezi Seoane were found inhabiting effluent ponds from a uranium mine. Due to the presence of such organisms in this environment, it becomes of paramount importance to assess the damages induced by local contamination on these aquatic vertebrates, in order to integrate this information on a site-specific risk assessment that is being carried out in the area. To attain this purpose an ethically and statistically acceptable number of green frogs were captured in the mine pond (M) and in a pristine river (VR), a few kilometres from the mine. Bioaccumulation of metals and histopathological alterations were evaluated in the liver, kidneys, spleen, lungs and testes of the animals. Simultaneously, blood samples were collected for the evaluation of genotoxic damage on erythrocytes. Animals captured in the M pond showed significantly increased levels of Be, Al, Mn, Fe and U in the liver, as well as Pb and U in the kidney. The liver was the main target organ for the bioaccumulation of Be, Al, Fe and U. However, renal histopathologies were more severe than those of liver. The main tissue alterations recorded in animals from the mine were: a slight increase in melanomacrophagic centers (MMC) in liver, lung and kidneys; dilatation of the renal tubules lumen associated with tubular necrosis. A significantly higher number of erythrocytic abnormalities (lobed, notched and kidney shaped nuclei and micronuclei) were recorded in frogs from M than in frogs from VR, along with a significantly lower frequency of immature erythrocytes. Both observations suggested that the removal of abnormal blood cells might be compromised.

Characterisation of uranium(VI) sorption by two environmental fungal species using gamma spectrometry

Uranium(VI) sorption by two highly uranium-resistant air-borne fungi in a low-pH medium was measured by means of gamma spectrometry. Growth kinetics and stoichiometry of the two fungal species were also studied. Results show acceptable growth rates in synthetic medium with glucose and ammonia as carbon and nitrogen sources, respectively. Typical oxidative metabolism of carbohydrates was found. In vivo uptake of the radionuclide was negligible, but biosorption dry biomass presented a remarkable performance. The fungal strains showed potential for use in bioremediation.

In situ bioassay with Eisenia andrei to assess soil toxicity in an abandoned uranium mine

The goal of this study was to develop an in situ bioassay with Eisenia andrei, deploying it in several locations of an abandoned mining area. Our objectives were two-fold: (i) we intended to validate the in situ soil bioassay procedures, while (ii) providing ecologically relevant data to complement the ongoing risk evaluation based on laboratorial assays. To promote cost- and time-effectiveness, the in situ exposure was short (48 h) and the endpoints analysed included oxidative stress biomarkers and metal content in soil and organisms. The bioassay was carried out under different experimental conditions, simulating local (natural soil) vs. control conditions (LUFA soil), and irrigation with artificial rainwater vs. irrigation with diluted acidic effluent. Variation in the data was mostly due to soil type, rather than irrigation water, and substantial spatial heterogeneity was observed. Oxidative stress biomarkers did not fully work as sensitive parameters to environmental contamination. Earthworm metal burdens suggested a potential concern in terms of bioaccumulation of some metallic elements.

Acute and chronic toxicity of effluent water from an abandoned uranium mine

Inactive or abandoned mines represent a significant source of environmental, chemical, physical, and aesthetic impact. Among concerning situations, the occurrence of abandoned or semi-abandoned mine-associated ponds (for sedimentation of solids, for effluent neutralization, or for washing the ore) is a common feature in this type of system. These ponds are a source of contamination for the groundwater resources and adjacent soils, because they lack appropriate impermeabilization. The use of this water for agriculture may also pose chronic risks to humans. In Portugal, these problems have been diagnosed and some remediation projects have been developed. The purpose of our study was to evaluate the acute and chronic toxicity of water samples collected from the aquatic system surrounding an abandoned uranium mine (Cunha Baixa, Mangualde, Central Portugal). The present study focuses on the water compartment, whose toxicity was evaluated by means of standard toxicity assays using two Daphnia species (D. longispina and D. magna). Three different ponds were used in the characterization of the aquatic system from Cunha Baixa mine: a reference pond (Ref), a mine effluent treatment pond (T), and a mine pit pond (M). Metal analyses performed in the water samples from these ponds showed values that, in some cases, were much higher than maximum recommendable values established (especially Al, Mn) by Portuguese legislation for waters for crop irrigation. Acute toxicity was only observed in the mine pit pond, with EC(50) values of 28.4% and 50.4% for D. longispina and D. magna, respectively. The significant impairment of chronic endpoints, translated in reductions in the population growth rate for both species, gives rise to concerns regarding the potential risks for aquatic zooplanktonic communities, from local receiving waters, potentially exposed to point source discharges of the treated and nontreated effluent from Cunha Baixa uranium mine.