Multibiomarker toxicity characterization of uranium mine drainages to the fish Carassius auratus

Developmental toxicity in zebrafish (Danio rerio) exposed to uranium: A comparison with lead, cadmium, and iron

Populations of plants and animals, including humans, living in close proximity to abandoned uranium mine sites are vulnerable to uranium exposure through drainage into nearby waterways, soil accumulation, and blowing dust from surface soils. Little is known about how the environmental impact of uranium exposure alters the health of human populations in proximity to mine sites, so we used developmental zebrafish (Danio rerio) to investigate uranium toxicity. Fish are a sensitive target for modeling uranium toxicity, and previous studies report altered reproductive capacity, enhanced DNA damage, and gene expression changes in fish exposed to uranium. In our study, dechorionated zebrafish embryos were exposed to a concentration range of uranyl acetate (UA) from 0 to 3000 μg/L for body burden measurements and developmental toxicity assessments. Uranium was taken up in a concentration-dependent manner by 48 and 120 h post fertilization (hpf)-zebrafish without evidence of bioaccumulation. Exposure to UA was not associated with teratogenic outcomes or 24 hpf behavioral effects, but larvae at 120 hpf exhibited a significant hypoactive photomotor response associated with exposure to 3 μg/L UA which suggested potential neurotoxicity. To our knowledge, this is the first time that uranium has been associated with behavioral effects in an aquatic organism. These results were compared to potential metal co-contaminants using the same exposure paradigm. Similar to uranium exposure, lead, cadmium, and iron significantly altered neurobehavioral outcomes in 120-hpf zebrafish without inducing significant teratogenicity. Our study informs concerns about the potential impacts of developmental exposure to uranium on childhood neurobehavioral outcomes. This work also sets the stage for future, environmentally relevant metal mixture studies. Summary Uranium exposure to developing zebrafish causes hypoactive larval swimming behavior similar to the effect of other commonly occurring metals in uranium mine sites. This is the first time that uranium exposure has been associated with altered neurobehavioral effects in any aquatic organism.

Micronuclei in Fish Erythrocytes as Genotoxic Biomarkers of Water Pollution: An Overview

Freshwater and marine water bodies receive chemical contaminants from industrial, agricultural, urban, and domestic wastes. Eco-genotoxicity assays are useful tools to assess the cumulative genotoxicity of these pollutants. Fish are suitable indicators for biomonitoring of mutagenic and carcinogenic pollution.In this review, we present a complete overview of the studies performed so far using the micronucleus test in peripheral erythrocytes of fish exposed to polluted water. We have listed all the species of fish used and the geographical distribution of the investigations. We have analyzed and discussed all technical aspects of using this test in fish, as well as the advantages and disadvantages of the different experimental protocols. We have reported the results of all studies. This assay has become, for years, one of the simplest, fastest, and most cost-effective for assessing genotoxic risk in aquatic environments. However, there are still several factors influencing the variability of the results. Therefore, we have given indications and suggestions to achieve a standardization of experimental procedures and ensure uniformity of future investigations.

Chemical availability versus bioavailability of potentially toxic elements in mining and quarry soils

Abandoned mining and quarry areas are sources of potentially toxic elements (PTEs), through lixiviates or transfer processes of bioavailable fractions from mining wastes and tailings. In this study, earthworms (Eisenia fetida Savigny, 1826) were exposed for 28 days to two mining soils from a lead/zinc mine and two quarry soils from an old serpentine quarry. Despite their pseudo total metal contents, a previous characterization of these soils pointed out for a low chemical availability of PTEs. Therefore, a multibiomarker approach was used and the response of E. fetida to soils was assessed through the analysis of neurotoxic, oxidative stress, energy metabolism and DNA damage biomarkers (acetylcholinesterase, catalase, glutathione-s-transferase, lactate dehydrogenase, lipid peroxidation and DNA strand breaks). Metal bioaccumulation was also assessed to evaluate bioavailability and organism's exposure. Results showed that high contents of PTEs were recorded in the whole body of earthworms exposed to lead/zinc mine. However, the bioaccumulation factors for worms exposed to soils from both sampling sites were <1 due to the high PTEs contents in soils. Earthworms exposed to both types of soils displayed neurotoxic and energy metabolism effects. However, significant levels of oxidative stress and DNA damage were recorded only for earthworms exposed to lead/zinc mine soils. This study demonstrated that despite the low availability of PTEs showed by previous sequential chemical extractions, the results obtained from the direct toxicity assessment performed in this study, highlight the importance of a multibiomarker approach using soil organisms to provide a better evaluation of soils pollution.

Life history traits and genotoxic effects on Daphnia magna exposed to waterborne uranium and to a uranium mine effluent - A transgenerational study

Assessing the impact of uranium mining industry on aquatic ecosystems near mining areas is critical to ensure the long-term health and sustainability of ecosystem services. As so, a transgenerational study with Daphnia magna has been conducted to perceive to what extent intermittent discharges of uranium mine effluents into watercourses may impact the DNA integrity and life history traits of cladocerans. Organisms were exposed for 48 h to a 2% dilution of an uranium mine effluent (UME) and to a corresponding dose of waterborne uranium (WU) that, according to our preliminary studies, induces significant DNA damage in daphnids. After exposure, organisms were transferred to clean medium, where three successive generations were monitored for genotoxicity and other effects at the individual and population level. Despite some differences between WU and UME data, our results revealed that the negative impacts of the short-term exposure gradually disappeared after placing the organisms in clean medium. These results suggest that, under intermittent stress, daphnids are able to recover, since after the 3^rd brood release, DNA damage (measured as DNA strand breaks) is no longer observed and has no significant impact on the detectable life traits of offspring. Although our results indicate that populations of D. magna are not affected by intermittent and highly diluted discharges from uranium mining, aquatic systems under this kind of pressure should not be seen as hazardous-free. Future studies in this field are recommended and these should consider radionuclides in the water column, their accumulation in the sediments and also multiple life stages.

RIBE at an inter-organismic level: A study on genotoxic effects in Daphnia magna exposed to waterborne uranium and a uranium mine effluent

The induction of RIBE (Radiation Induced Bystander Effect) is a non-target effect of low radiation doses that has already been verified at an inter-organismic level in fish and small mammals. Although the theoretical impact in the field of environmental risk assessment (ERA) is possible, there is a gap of knowledge regarding this phenomenon in invertebrate groups and following environmentally relevant exposures. To understand if RIBE should be considered for ERA of radionuclide-rich wastewaters, we exposed Daphnia magna (<24 h and 5d old) to a 2% diluted uranium mine effluent for 48 h, and to a matching dose of waterborne uranium (55.3 μg L^-1). Then the exposed organisms were placed (24 and 48 h) in a clean medium together with non-exposed neonates. The DNA damage observed for the non-exposed organisms was statistically significant after the 24 h cohabitation for both uranium (neonates p = 0.002; 5 d-old daphnids p = <0.001) and uranium mine effluent exposure (only for neonates p = 0.042). After 48 h cohabitation significant results were obtained only for uranium exposure (neonates p = 0.017; 5 d-old daphnids p = 0.013). Although there may be some variability associated to age and exposure duration, the significant DNA damage detected in non-exposed organisms clearly reveals the occurrence of RIBE in D. magna. The data obtained and here presented are a valuable contribution for the discussion about the relevance of RIBE for environmental risk assessment.