Single Cell Analysis of Human Colonoids Exposed to Uranium-Bearing Dust

BACKGROUND

Uranium exposure remains an important environmental legacy and physiological health concern, with hundreds of abandoned uranium mines located in the Southwestern United States largely impacting underserved indigenous communities. The negative effects of heavy metals on barrier permeability and inhibition of intestinal epithelial healing have been described; however, transcriptomic changes within the intestinal epithelial cells and impacts on lineage differentiation are largely unknown.

OBJECTIVES

Herein, we sought to determine the molecular and cellular changes that occur in the colon in response to uranium bearing dust (UBD) exposure.

METHODS

Human colonoids from three biologically distinct donors were acutely exposed to UBD then digested for single cell RNA sequencing to define the molecular changes that occur to specific identities of colonic epithelial cells. Validation in colonoids was assessed using morphological and imaging techniques.

RESULTS

Human colonoids acutely exposed to UBD exhibited disrupted proliferation and hyperplastic differentiation of the secretory lineage cell, enteroendocrine cells (EEC). Single-cell RNA sequencing also showed more EEC subtypes present in UBD-exposed colonoids.

DISCUSSION

These findings highlight the significance of crypt-based proliferative cells and secretory cell differentiation using human colonoids to model major colonic responses to uranium-bearing particulate dust exposure. https://doi.org/10.1289/EHP13855.

Cinnamic Acid: A Low-Toxicity Natural Bidentate Ligand for Uranium Decorporation

Uranium accumulation in the kidneys and bones following internal contamination results in severe damage, emphasizing the pressing need for the discovery of actinide decorporation agents with efficient removal of uranium and low toxicity. In this work, cinnamic acid (3-phenyl-2-propenoic acid, CD), a natural aromatic carboxylic acid, is investigated as a potential uranium decorporation ligand. CD demonstrates markedly lower cytotoxicity than that of diethylenetriaminepentaacetic acid (DTPA), an actinide decorporation agent approved by the FDA, and effectively removes approximately 44.5% of uranyl from NRK-52E cells. More importantly, the results of the prompt administration of the CD solution remove 48.2 and 27.3% of uranyl from the kidneys and femurs of mice, respectively. Assessments of serum renal function reveal the potential of CD to ameliorate uranyl-induced renal injury. Furthermore, the single crystal of CD and uranyl compound (C9H7O2)2·UO2 (denoted as UO2-CD) reveals the formation of uranyl dimers as secondary building units. Thermodynamic analysis of the solution shows that CD coordinates with uranyl to form a 2:1 molar ratio complex at a physiological pH of 7.4. Density functional theory (DFT) calculations further show that CD exhibits a significant 7-fold heightened affinity for uranyl binding in comparison to DTPA.

Effects of diluted effluent on aquatic macroinvertebrate communities at the McClean Lake uranium operation in northern Saskatchewan

Diluted treated effluent from the McClean Lake uranium mill in northern Saskatchewan is released into Vulture Lake, which flows into the east basin of McClean Lake; this input could potentially cause a variety of disturbances to the aquatic systems. This study aimed to determine the potential effects of diluted effluent exposure (metals and major ions) on benthic macroinvertebrates in Vulture Lake and McClean Lake. Two monitoring locations located in Vulture Lake and eight in McClean Lake were used for collection water, sediment, and benthic macroinvertebrates. Complementary surface water bioassays were performed with larvae of the midge Chironomus dilutus using lake water from selected sites. Results indicated that total macroinvertebrate abundance and Margalef index (MI) did not follow the diluted effluent pattern. In addition, while the MI from artificial substrate samplers showed higher values in Vulture Lake and lower values at McClean Lake sites 4 and 5 (closer to effluent diffuser), the values recorded for sediment grab samples registered lower indices in Vulture Lake and higher values for sites 4 and 5. The final model from a Generalized Additive Modelling (GAM) approach suggested that electrical conductivity (EC), selenium (Se), and chloride (Cl) in water, and total organic carbon (TOC) and cadmium (Cd) in sediment are key variables that collectively may have influenced macroinvertebrate community composition at the study sites. Finally, across all test endpoints in the bioassays, exposure to lake water from Vulture Lake and McClean Lake had no statistically significant effects on C. dilutus.

Role of uranium toxicity and uranium-induced oxidative stress in advancing kidney injury and endothelial inflammation in rats

OBJECTIVE

Uranium exposure may cause serious pathological injury to the body, which is attributed to oxidative stress and inflammation. However, the pathogenesis of uranium toxicity has not been clarified. Here, we evaluated the level of oxidative stress to determine the relationship between uranium exposure, nephrotoxic oxidative stress, and endothelial inflammation.

METHODS

Forty male Sprague-Dawley rats were divided into three experimental groups (U-24h, U-48h, and U-72h) and one control group. The three experimental groups were intraperitoneally injected with 2.0 mg/kg uranyl acetate, and tissue and serum samples were collected after 24, 48, and 72 h, respectively, whereas the control group was intraperitoneally injected with 1.0 ml/kg normal saline and samples were collected after 24 h. Then, we observed changes in the uranium levels and oxidative stress parameters, including the total oxidative state (TOS), total antioxidant state (TAS), and oxidative stress index (OSI) in kidney tissue and serum. We also detected the markers of kidney injury, namely urea (Ure), creatine (Cre), cystatin C (CysC), and neutrophil gelatinase-associated lipocalin (NGAL). The endothelial inflammatory markers, namely C-reactive protein (CRP), lipoprotein phospholipase A2 (Lp-PLA2), and homocysteine (Hcy), were also quantified. Finally, we analyzed the relationship among these parameters.

RESULTS

TOS (z = 3.949; P < 0.001), OSI (z = 5.576; P < 0.001), Ure (z = 3.559; P < 0.001), Cre (z = 3.476; P < 0.001), CysC (z = 4.052; P < 0.001), NGAL (z = 3.661; P < 0.001), and CRP (z = 5.286; P < 0.001) gradually increased after uranium exposure, whereas TAS (z = -3.823; P < 0.001), tissue U (z = -2.736; P = 0.001), Hcy (z = -2.794; P = 0.005), and Lp-PLA2 (z = -4.515; P < 0.001) gradually decreased. The serum U level showed a V-shape change (z = -1.655; P = 0.094). The uranium levels in the kidney tissue and serum were positively correlated with TOS (r = 0.440 and 0.424; P = 0.005 and 0.007) and OSI (r = 0.389 and 0.449; P = 0.013 and 0.004); however, serum U levels were negatively correlated with TAS (r = -0.349; P = 0.027). Partial correlation analysis revealed that NGAL was closely correlated to tissue U (rpartial = 0.455; P = 0.003), CysC was closely correlated to serum U (rpartial = 0.501; P = 0.001), and Lp-PLA2 was closely correlated to TOS (rpartial = 0.391; P = 0.014), TAS (rpartial = 0.569; P < 0.001), and OSI (rpartial = -0.494; P = 0.001). Pearson correlation analysis indicated that the Hcy levels were negatively correlated with tissue U (r = -0.344; P = 0.030) and positively correlated with TAS (r = 0.396; P = 0.011).

CONCLUSION

The uranium-induced oxidative injury may be mainly reflected in enhanced endothelial inflammation, and the direct chemical toxicity of uranium plays an important role in the process of kidney injury, especially in renal tubular injury. In addition, CysC may be a sensitive marker reflecting the nephrotoxicity of uranium; however, Hcy is not suitable for evaluating short-term endothelial inflammation involving oxidative stress.

Perilla frutescens: A new strategy for uranium decorporation

Radionuclide uranium is a great threat to human health, due to its high chemical toxicity and radioactivity. Finding suitable uranium decorporation to reduce damage caused by uranium internal contamination is an important aspect of nuclear emergency response. However, the poor selectivity and/or high toxicity of the only excretory promoter approved by Food and Drug Administration (FDA) is an obvious disadvantage. Herein, we choose an edible natural product, the traditional Chinese medicine called Perilla frutescens (PF), which has wide sources and can be used as an excellent and effective uranyl decorporation. In vivo uranium decorporation assays illustrate the removal efficiency of uranium in kidney were 68.87% and 43.26%, in femur were 56.66% and 54.53%, by the test of prophylactic and immediate administration, respectively. Cell level experiments confirmed that it had better biocompatibility than CaNa3-DTPA (CaNa3-diethylenetriamine pentaacetate, a commercial actinide excretion agent). In vitro static adsorption experiments exhibited that its excellent selectivity sorption for uranyl. All those results findings would provide new research insights about natural product for uranyl decorporation.

[Research progress on uranium induced human renal injury and its risk prediction]

Uranium has both radiotoxicity and chemical toxicity. Low enriched uranium is mainly chemically toxic, the kidney is the target organ of uranium chemical toxicity. However, due to the differences among species and the mixed effects of chemical toxicity and radiotoxicity, the dose effect relationship of uranium is not clear, and the current standards in China do not provide chemical toxicity limits for uranium workplaces. This paper reviews the data of acute and chronic human uranium exposure, dose effect relationship and renal injury risk prediction literature at home and abroad, providing reference for the health protection of uranium workers and the establishment of chemical limits in uranium workplaces.

Exposure of Lemna minor (Common Duckweed) to Mixtures of Uranium and Perfluorooctanoic Acid (PFOA)

A variety of processes, both natural and anthropogenic, can have a negative impact on surface waters, which in turn can be detrimental to human and environmental health. Few studies have considered the ecotoxicological impacts of concurrently occurring contaminants, and that is particularly true for mixtures that include contaminants of emerging concern (CEC). Motivated by this knowledge gap, the present study considers the potential ecotoxicity of environmentally relevant contaminants in the representative aquatic plant Lemna minor (common duckweed), a model organism. More specifically, biological effects associated with exposure of L. minor to a ubiquitous radionuclide (uranium [U]) and a fluorinated organic compound (perfluorooctanoic acid [PFOA], considered a CEC), alone and in combination, were monitored under controlled laboratory conditions. Lemna minor was grown for 5 days in small, aerated containers. Each treatment consisted of four replicates with seven plants each. Treatments were 0, 0.3, and 3 ppb PFOA; 0, 0.5, and 5 ppb U; and combinations of these. Plants were observed daily for frond number and signs of chlorosis and necrosis. Other biological endpoints examined at the conclusion of the experiment were chlorophyll content and antioxidant capacity. In single-exposure experiments, a slight stimulatory effect was observed on frond number at 0.3 ppb PFOA, whereas both concentrations of U had a detrimental effect on frond number. In the dual-exposure experiment, the combinations with 5 ppb U also had a detrimental effect on frond number. Results for chlorophyll content and antioxidant capacity were less meaningful, suggesting that environmentally relevant concentrations of PFOA and U have only subtle effects on L. minor growth and health status. Environ Toxicol Chem 2023;42:2412-2421. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Integration of transcriptomics and metabolomics analysis for unveiling the toxicological profile in the liver of mice exposed to uranium in drinking water

Uranium is a contaminate in the underground water in many regions of the world, which poses health risks to the local populations through drinking water. Although the health hazards of natural uranium have been concerned for decades, the controversies about its detrimental effects continue at present since it is still unclear how uranium interacts with molecular regulatory networks to generate toxicity. Here, we integrate transcriptomic and metabolomic methods to unveil the molecular mechanism of lipid metabolism disorder induced by uranium. Following exposure to uranium in drinking water for twenty-eight days, aberrant lipid metabolism and lipogenesis were found in the liver, accompanied with aggravated lipid peroxidation and an increase in dead cells. Multi-omics analysis reveals that uranium can promote the biosynthesis of unsaturated fatty acids through dysregulating the metabolism of arachidonic acid (AA), linoleic acid, and glycerophospholipid. Most notably, the disordered metabolism of polyunsaturated fatty acids (PUFAs) like AA may contribute to lipid peroxidation induced by uranium, which in turn triggers ferroptosis in hepatocytes. Our findings highlight disorder of lipid metabolism as an essential toxicological mechanism of uranium in the liver, offering insight into the health risks of uranium in drinking water.

Maternal exposure to dietary uranium causes oxidative stress and thyroid disruption in zebrafish offspring

The contamination of uranium in aquatic ecosystems has raised growing global concern. However, the understanding of its chronic effects on aquatic organisms is limited, particularly with regards to transgenerational toxicity. In this study, we evaluated the maternal transfer risk of uranium using zebrafish. Sexually mature female zebrafish were exposed to 2 and 20 ng/g of uranium-spiked food for 28 days. The induced bioconcentration, thyroid disruption, and oxidative stress in both the adults (F0) and their embryos (F1) were further investigated. Element analysis showed that uranium was present in both F0 and F1, with higher concentrations observed in F1, indicating significant maternal offloading to the offspring. Meanwhile, an increased malformation and decreased swim speed were observed in the F1. Thyroid hormone analysis revealed significant decreases in the levels of triiodothyronine (T3) in both the F0 adults and F1 embryos, but thyroxine (T4) was not significantly affected. Additionally, the activities of antioxidant defenses, including catalase (CAT) and superoxide dismutase (SOD), and the expression of glutathione (GSH) and malondialdehyde (MDA) were significantly altered in the F0 and F1 larvae at 120 hpf. The hypothalamic-pituitary-thyroid (HPT) axis, oxidative stress, and apoptosis-related gene transcription expression were also significantly affected in both generations. Taken together, these findings highlight the importance of considering maternal transfer in uranium risk assessments.

A deeper understanding about the role of uranium toxicity in neurodegeneration

Natural deposits and human-caused releases of uranium have led to its contamination in the nature. Toxic environmental contaminants such as uranium that harm cerebral processes specifically target the brain. Numerous experimental researches have shown that occupational and environmental uranium exposure can result in a wide range of health issues. According to the recent experimental research, uranium can enter the brain after exposure and cause neurobehavioral problems such as elevated motion related activity, disruption of the sleep-wake cycle, poor memory, and elevated anxiety. However, the exact mechanism behind the factor for neurotoxicity by uranium is still uncertain. This review primarily aims on a brief overview of uranium, its route of exposure to the central nervous system, and the likely mechanism of uranium in neurological diseases including oxidative stress, epigenetic modification, and neuronal inflammation has been described, which could present the probable state-of-the-art status of uranium in neurotoxicity. Finally, we offer some preventative strategies to workers who are exposed to uranium at work. In closing, this study highlights the knowledge of uranium's health dangers and underlying toxicological mechanisms is still in its infancy, and there is still more to learn about many contentious discoveries.

Induction of lysosomal exocytosis and biogenesis via TRPML1 activation for the treatment of uranium-induced nephrotoxicity

Uranium (U) is a well-known nephrotoxicant which forms precipitates in the lysosomes of renal proximal tubular epithelial cells (PTECs) after U-exposure at a cytotoxic dose. However, the roles of lysosomes in U decorporation and detoxification remain to be elucidated. Mucolipin transient receptor potential channel 1 (TRPML1) is a major lysosomal Ca2+ channel regulating lysosomal exocytosis. We herein demonstrate that the delayed administration of the specific TRPML1 agonist ML-SA1 significantly decreases U accumulation in the kidney, mitigates renal proximal tubular injury, increases apical exocytosis of lysosomes and reduces lysosomal membrane permeabilization (LMP) in renal PTECs of male mice with single-dose U poisoning or multiple-dose U exposure. Mechanistic studies reveal that ML-SA1 stimulates intracellular U removal and reduces U-induced LMP and cell death through activating the positive TRPML1-TFEB feedback loop and consequent lysosomal exocytosis and biogenesis in U-loaded PTECs in vitro. Together, our studies demonstrate that TRPML1 activation is an attractive therapeutic strategy for the treatment of U-induced nephrotoxicity.

Response of Vicia faba to short-term uranium exposure: chelating and antioxidant system changes in roots

Uranium (U) phytotoxicity is an inherently difficult problem in the phytoremediation of U-contaminated environments. Plant chelating and antioxidant systems play an authoritative role in resistance to abiotic stress. To reveal the toxicity of U, the changes of chelating system, osmoregulatory substances and antioxidant systems in Vicia faba roots were studied after short-term (24 h) U exposure. The results indicated that the development of lateral roots and root activity of V. faba were significantly inhibited with U accumulation. Compared with the control, plant chelating systems showed significant positive effects after U exposure (15 - 25 μM). Osmoregulatory substances (proline and soluble protein) increasingly accumulated in roots with increasing U concentration, and O2- and H2O2 rapidly accumulated after U exposure (15 - 25 μM). Thus, the contents of malondialdehyde (MDA), a marker of lipid peroxidation, were also significantly increased. Antioxidant systems were activated after U exposure but were inhibited at higher U concentrations (15 - 25 μM). In summary, although the chelating, osmotic regulation and antioxidant systems in V. faba were activated after short-term U exposure, the antioxidases (CAT, SOD and POD) were inhibited at higher U concentrations (15 - 25 μM). Therefore, the root cells were severely damaged by peroxidation, which eventually resulted in inhibited activity and arrested root development.

Uranium: an overview of physicochemical properties, exposure assessment methodologies, and health effects of environmental and occupational exposure

Uranium is chemo- and radiotoxic element which can cause multifactorial health hazards. Natural and anthropogenic uranium contamination raises concerns about potential public health problems. Natural contamination plays a significant role with regard to uranium exposure in the general population, whereas anthropogenic contamination leads to occupational uranium exposure, particularly in nuclear industry workers. In this review, we present a state-of-the-art status concerning uranium-induced health risks with a focus on epidemiological findings of uranium processing and enrichment plant workers. We provide a general overview of physicochemical properties of uranium and analytical methods for measuring or monitoring uranium, describe environmental and occupational exposure scenarios, and discuss the challenges for objectively investigating risks from uranium exposure.

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

A combination of synchrotron-based elemental analysis and acute toxicity tests was used to investigate the biodistribution and adverse effects in Daphnia magna exposed to uranium nanoparticle (UNP, 3-5 nm) suspensions or to uranium reference (U_ref) solutions. Speciation analysis revealed similar size distributions between exposures, and toxicity tests showed comparable acute effects (UNP LC₅₀: 402 μg L^-1 [336-484], U_ref LC₅₀: 268 μg L^-1 [229-315]). However, the uranium body burden was 3- to 5-fold greater in UNP-exposed daphnids, and analysis of survival as a function of body burden revealed a ∼5-fold higher specific toxicity from the U_ref exposure. High-resolution X-ray fluorescence elemental maps of intact, whole daphnids from sublethal, acute exposures of both treatments revealed high uranium accumulation onto the gills (epipodites) as well as within the hepatic ceca and the intestinal lumen. Uranium uptake into the hemolymph circulatory system was inferred from signals observed in organs such as the heart and the maxillary gland. The substantial uptake in the maxillary gland and the associated nephridium suggests that these organs play a role in uranium removal from the hemolymph and subsequent excretion. Uranium was also observed associated with the embryos and the remnants of the chorion, suggesting uptake in the offspring. The identification of target organs and tissues is of major importance to the understanding of uranium and UNP toxicity and exposure characterization that should ultimately contribute to reducing uncertainties in related environmental impact and risk assessments.

PrsQ2, a small periplasmic protein involved in increased uranium resistance in the bacterium Cupriavidus metallidurans

Uranium contamination is a widespread problem caused by natural and anthropogenic activities. Although microorganisms thrive in uranium-contaminated environments, little is known about the actual molecular mechanisms mediating uranium resistance. Here, we investigated the resistance mechanisms driving the adaptation of Cupriavidus metallidurans NA4 to toxic uranium concentrations. We selected a spontaneous mutant able to grow in the presence of 1 mM uranyl nitrate compared to 250 µM for the parental strain. The increased uranium resistance was acquired via the formation of periplasmic uranium-phosphate precipitates facilitated by the increased expression of a genus-specific small periplasmic protein, PrsQ₂, regulated as non-cognate target of the CzcS₂-CzcR₂ two-component system. This study shows that bacteria can adapt to toxic uranium concentrations and explicates the complete genetic circuit behind the adaptation.

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

Micro- and nanoscopic X-ray techniques were used to investigate the relationship between uranium (U) tissue distributions and adverse effects to the digestive tract of aquatic model organism Daphnia magna following uranium nanoparticle (UNP) exposure. X-ray absorption computed tomography measurements of intact daphnids exposed to sublethal concentrations of UNPs or a U reference solution (U_Ref) showed adverse morphological changes to the midgut and the hepatic ceca. Histological analyses of exposed organisms revealed a high proportion of abnormal and irregularly shaped intestinal epithelial cells. Disruption of the hepatic ceca and midgut epithelial tissues implied digestive functions and intestinal barriers were compromised. Synchrotron-based micro X-ray fluorescence (XRF) elemental mapping identified U co-localized with morphological changes, with substantial accumulation of U in the lumen as well as in the epithelial tissues. Utilizing high-resolution nano-XRF, 400-1000 nm sized U particulates could be identified throughout the midgut and within hepatic ceca cells, coinciding with tissue damages. The results highlight disruption of intestinal function as an important mode of action of acute U toxicity in D. magna and that midgut epithelial cells as well as the hepatic ceca are key target organs.

Occurrence characteristics of uranium mineral-related substances in various environmental media in China: A critical review

The high demand and extensive exploitation of uranium resources resulted in the ubiquity and high detection levels of uranium mineral-related substances in various environment media in China. The potential adverse effects of uranium mineral-related substances on environment and human health have received extensive attention. Therefore, we reviewed the occurrence and spatial distribution of uranium mineral-related substances in various basins and environmental media in China to obtain an overall understanding. We collected information from over 70 papers reporting the occurrence and distribution of uranium mineral-related substances in multiple environments and 183 articles on the genesis of uranium deposits in China from 2001 to 2021. Then the occurrence of uranium mineral-related substances and corresponding correlation in different basins, environmental media and depth ranges were compared in detail. And this review assessed the uranium mineral-related pollution in China based on various environmental quality standards of China, EPA and WHO, and proposed the priority uranium mineral-related heavy metals and radioactive substances based on cluster analysis. This review showed that there were obvious differences in the occurrence characteristics of various uranium mineral-related substances in different environmental media, especially in the surrounding environment of sandstone type and hard rock type uranium deposits. These results will guide us to tackle the challenge of uranium mineral-related pollution in China. The correlation analysis of uranium mineral-related pollutants in different environmental media and the identification of priority pollutants will also provide instructions for us to control uranium mineral-related pollution. Finally, we put forward a series of urgent and practical suggestions on risk management and control of uranium mining according to the current situation of uranium mining environment in China, which is of guiding significance for the realization of "green uranium mining".

Does exposure to weathered coal ash with an enhanced content of uranium-series radionuclides affect flora? Changes in the physiological indicators of five referent plant species

Coal ash deposited in open landfills is a potential source of environmental pollutants due to the contained toxic element content. The weathered coal ash used in this study additionally contains enhanced activity concentrations of ²³⁸U series radionuclides. This study aimed to determine the physiological effects of enhanced ionizing radiation and toxic elements on five plant species (smilo grass, sticky fleabane, blackberry, mastic and pine tree) inhabiting the coal ash disposal site. Among the potentially toxic measured elements, contents of Sb, As and especially V significantly exceeded their respective levels at the control site, as well as the content of ²³⁸U and its progenies. Significant changes in photosynthetic pigments were recorded following chronic exposure to the plants growing on the coal ash site. Different responses were also observed in the plant species regarding the activity of catalase and glutathione-S-transferase (GST). The level of lipid peroxidation markedly increased in plants from the disposal site, except in blackberry, wherein GST activity was the strongest, indicating an important role of that enzyme in the adaptation to coal ash pollutants. The results of this study suggest that the modulation of the studied biochemical parameters in plants growing on coal ash is primarily species-dependent.

Environmental uranium exposures and cytokine profiles among mother-newborn baby pairs from the Navajo Βirth Cohort Study

The Navajo Nation was heavily mined for uranium (U) during the cold-war leading to a legacy of >1100 abandoned U mining, milling and associated waste sites. The Navajo Birth Cohort Study was initiated to assess the effect of non-occupational legacy exposure to U during pregnancy on birth outcomes and child development. We report that 92% of babies with detectable urine U at birth were born from mothers who had urine U concentrations greater than national norms during pregnancy, indicative of prenatal exposure to U. To assess immune alterations associated with U exposure on both mothers and babies, we investigated associations between cytokine profiles and maternal U and associations of these measures with cytokine profiles in babies. Effect sizes for the differences in cytokine profiles were more evident among babies than mothers. Overall, there were seven cytokines (IFN-γ, IL-1β, IL-2, IL-4, IL-10, GM-CSF, and TNF-α), for which the effect size for babies with higher than the national U concentrations was medium to large (ORs of 2.21 (1.08-4.52) through 1.71(0.76-3.83). In contrast, only three cytokines (IL-8, IL-12p70, and TNF-α) had effect sizes which almost reached medium strength (ORs of 1.64 (0.74-4.05) through 1.36 (0.65-2.87) in mothers with U above national norms. The effects of prenatal exposures to uranium and associated alterations in systemic immune responses resulting from U exposure could impact both maternal health as well as healthy child development through induction of inflammation, autoimmunity or other chronic diseases related to immune dysfunction that may affect long-term health.

Development of a Site-Specific Guideline Value for Copper and Aquatic Life in Tropical Freshwaters of Low Hardness

Copper (Cu) is a contaminant of potential concern for a uranium mine whose receiving waters are in the World Heritage-listed Kakadu National Park in northern Australia. The physicochemical characteristics of the freshwaters in this region enhance metal bioavailability and toxicity. Seven tropical species were used to assess the chronic toxicity of Cu in extremely soft freshwater from a creek upstream of the mine. Sensitivity to Cu was as follows: Moinodaphnia macleayi > Chlorella sp. > Velesunio sp. > Hydra viridissima > Amerianna cumingi > Lemna aequinoctialis > Mogurnda mogurnda. The 10% effect concentrations (EC10s) ranged from 1.0 µg/L Cu for the cladoceran Moinodaphnia macleayi to 9.6 µg/L for the fish M. mogurnda. The EC50s ranged from 6.6 µg/L Cu for the mussel Velesunio sp. to 22.5 µg/L Cu for M. mogurnda. Geochemical modeling predicted Cu to be strongly bound to fulvic acid (80%-99%) and of low bioavailability (0.02%-11.5%) under these conditions. Protective concentrations (PCs) were derived from a species sensitivity distribution for the local biota. The 99% PC (PC99), PC95, PC90, and PC80 values were 0.5, 0.8, 1.0, and 1.5 µg/L Cu, respectively. These threshold values suggest that the current Australian and New Zealand default national 99% protection guideline value for Cu (1.0 µg/L) would not provide adequate protection in freshwaters of low hardness, particularly for this area of high conservation value. The continuous criterion concentration predicted by the Cu biotic ligand model for conditions of low pH (6.1), low dissolved organic carbon (2.5 mg/L), low hardness (3.3 mg/L), and 27 °C was 0.48 µg/L Cu, comparable with the PC99. Consideration of the natural water quality conditions of a site is paramount for protective water quality guidelines. Environ Toxicol Chem 2022;41:2808-2821. © 2022 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2022 SETAC.

Cellular transport of uranium and its cytotoxicity effects on CHO-k1 cells

Uranium is a radioactive heavy metal and a significant public health concern; however, its associated underlying toxicological mechanisms remain largely unknown. In this work, the uptake and efflux processes of uranium in CHO-k1 cells were studied and the cytotoxicity effects were explored. It was found that both the uptake and efflux processes took place rapidly and half of the internalized uranium was expelled within 8 h. The uranium exposure caused a decrease of cell viability and adhesion ability in a dose-dependent manner and blocked the cell cycle at the G1 stage. In addition, gene expression analysis revealed relative changes in the transcription of metabolism related genes. Further studies revealed that the cytotoxicity of uranium could be alleviated by exposing cells to a lower temperature or by the addition of amantadine-HCl, an endocytosis inhibitor. Interestingly, after uranium exposure, needle-like precipitates were observed in both intracellular and extracellular regions. These findings collectively suggest that the cellular transport of uranium is a rapid process that disturbs cell metabolism and induces cytotoxicity, and this impact could be reduced by slowing down endocytic processes.

Assessment of metal exposure (uranium and copper) in fatty acids and carbohydrate profiles of Calamoceras marsupus larvae (Trichoptera) and Alnus glutinosa leaf litter

Physiological changes were explored in fatty acids (FA) and carbohydrate (CHO) composition in the shredder Calamoceras marsupus larvae (Trichoptera) and leaf litter (C. marsupus food) exposed to copper and uranium under natural and experimental conditions. We measured FA and CHO content in leaf litter and larvae specimens from reference and impacted streams, and exposed for 5 weeks to four realistic environmental concentrations of copper (35 μg L^-1 and 70 μg L^-1) and uranium (25 μg L^-1 and 50 μg L^-1). Regarding FA, (1) leaf litter had a reduced polyunsaturated FA (PUFA) content in metal treatments, s (14 to 33% of total FA), compared to natural conditions (≥39% of total FA). Leaf litter exposed to uranium also differed in saturated FA (SFA) composition, with lower values in natural conditions and higher values under low uranium concentrations. (2) C. marsupus had/showed low PUFA content under Cu and U exposure, particularly in high uranium concentrations. Detritivores also decreased in PUFA under exposure to both metals, particularly in high uranium concentrations. On the other hand, (1) microorganisms of the biofilm colonizing leaf litter differed in CHO composition between natural (impacted and reference) and experimental conditions, with glucose and galactose being consistently the most abundant sugars, found in different amounts under copper or uranium exposure; (2) CHO of detritivores showed similar high galactose and fucose concentrations in contaminated streams and high copper treatments, whereas low copper treatment showed distinct CHO profiles, with higher mannose, glucose, arabinose, and fucose concentrations. Our study provides evidence of metal exposure effects on FA and CHO contents at different trophic levels, which might alter the quality of food flow in trophic webs.

Calcium affects uranium responses in Arabidopsis thaliana: From distribution to toxicity

Uranium, a heavy metal and primordial radionuclide, is present in surface waters and soils both naturally and due to industrial activities. Uranium is known to be toxic to plants and its uptake and toxicity can be influenced by multiple factors such as pH and the presence of different ions. However, the precise role of the different ions in uranium uptake is not yet known. Here we investigated whether calcium influences uranium uptake and toxicity in the terrestrial plant Arabidopsis thaliana. To this end, A. thaliana plants were exposed to different calcium and uranium concentrations and furthermore, calcium channels were blocked using the calcium channel blocker lanthanum chloride (LaCl₃). Fresh weight, relative growth rate, concentration of nutrients and uranium and gene expression of oxidative stress-related genes and calcium transporters were determined in roots and shoots. Calcium affected plant growth and oxidative stress in both control (no uranium) and uranium-exposed plants. In shoots, this was influenced by the total calcium concentration, but not by the different tested uranium concentrations. Uranium in turn did influence calcium uptake and distribution. Uranium-exposed plants grown in a medium with a higher calcium concentration showed an increase in gene expression of NADPH oxidases RBOHC and RBOHE and calcium transporter CAX7 after uranium exposure. In roots, these calcium-dependent responses in gene expression were not observed. This indicates that calcium indeed affects uranium toxicity, but only in shoots. In addition, a clear influence of uranium and LaCl₃ (separately and combined) on the expression of calcium transporters was observed.

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.

Multigenerational Exposure to Uranium Changes Sperm Metabolome in Rats

Male infertility is a major public health issue that can be induced by a host of lifestyle risk factors such as environment, nutrition, smoking, stress, and endocrine disruptors. Regarding the human population exposed to uranium, it is necessary to explore these effects on male reproduction in multigenerational studies. The sensitivity of mass spectrometry (MS)-based methods has already proved to be extremely useful in metabolite identification in rats exposed to low doses of uranium, but also in human sperm. We applied this method to rat sperm over three generations (F0, F1 and F2) with multigenerational uranium exposure. Our results show a significant content of uranium in generation F0, and a reduction in the pregnancy rate only in generation F1. Based on principal component analysis (PCA), we observed discriminant profiles between generations. The partial least squares discriminant analysis (PLS-DA) of the 48 annotated variables confirmed that parental exposure of generation F0 (during both the preconceptional and prenatal periods) can have metabolic effects on spermatozoa for the next two generations. Metabolomics applied to epididymal spermatozoa is a novel approach to detecting the multigenerational effects of uranium in an experimental model, but could be also recommended to identify potential biomarkers evaluating the impact of uranium on sperm in exposed infertile men.

Delineating Effluent Exposure and Cumulative Ecotoxicological Risk of Metals Downstream of a Saskatchewan Uranium Mill Using Autonomous Sensors

There is increasing interest in using autonomous sensor technology to monitor aquatic ecosystems in real time and in employing such monitoring data to perform better ecological risk assessments. At seven locations in McClean Lake in northern Saskatchewan (Canada) that received diluted uranium milling effluent, we deployed sensor units to track effluent distribution and help predict potential biological effects on aquatic invertebrates. Water was also collected from each location on multiple occasions to measure major ions, dissolved metals, and routine water quality, and sediment was sampled to analyze total metals. The ecotoxicological risk to aquatic invertebrates was estimated using hazard quotients (HQs). The cumulative risk was estimated by summing the individual HQs, and the major ions risk was based on total osmolarity. The results indicated temporal and spatial variations in effluent exposure based on sensor electrical conductivity (EC) measurements in the McClean Lake East Basin. Individual HQs for water ranged from "moderate" (0.40-0.69) to "very high" (greater than 1) for silver, cadmium, arsenic, selenium, mercury, iron, and thallium. At all sites, major ions risk was less than 1. Individual HQs for sediment were "moderate" (0.40-0.69), "high" (0.7-0.99), and "very high" (greater than 1) for vanadium and cadmium. The cumulative risk in water and sediment for all metals combined was greater than 1 at some sites in Vulture Lake (which discharged into McClean Lake) and in McClean Lake itself. A more detailed estimation of the risks for aqueous selenium and arsenic (the only two metals that had good correlation with sensor EC data) indicated that their 90th percentile HQ values were less than 1 in McClean Lake, suggesting that these contaminants of concern do not represent a significant direct risk to aquatic invertebrate communities. Environ Toxicol Chem 2022;41:1765-1777. © 2022 SETAC.

Environmental and occupational health on the Navajo Nation: a scoping review

A scoping review was performed to answer: what environmental health concerns have been associated with adverse health outcomes in the Navajo Nation? The review focused on occupational and ambient environmental exposures associated with human industrial activities. The search strategy was implemented in PubMed, and two investigators screened the retrieved literature. Thirteen studies were included for review. Data were extracted using the matrix method. Six studies described associations between work in uranium mining and cancer. Six studies focused on environmental exposures to uranium mine waste and other metals, with outcomes that included biological markers, kidney disease, diabetes and hypertension, and adverse birth outcomes. One study explored occupational exposure to Sin Nombre Virus and infection. Most research has focused on the health effects of uranium, where occupational exposures occurred among miners and environmental exposures are a legacy of uranium mining and milling. Gaps exist with respect to health outcomes associated with current occupations and the psychosocial impact of environmental hazards. Other environmental exposures and hazards are known to exist on the Navajo Nation, which may warrant epidemiologic research.

Review of Knowledge of Uranium-Induced Kidney Toxicity for the Development of an Adverse Outcome Pathway to Renal Impairment

An adverse outcome pathway (AOP) is a conceptual construct of causally and sequentially linked events, which occur during exposure to stressors, with an adverse outcome relevant to risk assessment. The development of an AOP is a means of identifying knowledge gaps in order to prioritize research assessing the health risks associated with exposure to physical or chemical stressors. In this paper, a review of knowledge was proposed, examining experimental and epidemiological data, in order to identify relevant key events and potential key event relationships in an AOP for renal impairment, relevant to stressors such as uranium (U). Other stressors may promote similar pathways, and this review is a necessary step to compare and combine knowledge reported for nephrotoxicants. U metal ions are filtered through the glomerular membrane of the kidneys, then concentrate in the cortical and juxtaglomerular areas, and bind to the brush border membrane of the proximal convoluted tubules. U uptake by epithelial cells occurs through endocytosis and the sodium-dependent phosphate co-transporter (NaPi-IIa). The identified key events start with the inhibition of the mitochondria electron transfer chain and the collapse of mitochondrial membrane potential, due to cytochrome b5/cytochrome c disruption. In the nucleus, U directly interacts with negatively charged DNA phosphate, thereby inducing an adduct formation, and possibly DNA strand breaks or cross-links. U also compromises DNA repair by inhibiting zing finger proteins. Thereafter, U triggers the Nrf2, NF-κB, or endoplasmic reticulum stress pathways. The resulting cellular key events include oxidative stress, DNA strand breaks and chromosomal aberrations, apoptosis, and pro-inflammatory effects. Finally, the main adverse outcome is tubular damage of the S2 and S3 segments of the kidneys, leading to tubular cell death, and then kidney failure. The attribution of renal carcinogenesis due to U is controversial, and specific experimental or epidemiological studies must be conducted. A tentative construction of an AOP for uranium-induced kidney toxicity and failure was proposed.

Prenatal uranium exposure and risk for fetal neural tube defects: A case-control study in women living in a rural area of northern China

The adverse effects of uranium exposure on human health are well-known; less is known, however, regarding its association with congenital malformations. We conducted a case-control study to examine the association between prenatal exposure to uranium and risk for fetal neural tube defects (NTDs) using the concentration of uranium in placental tissue as an exposure marker in 408 NTD cases and 593 healthy controls. Uranium concentration was quantified with an inductively coupled plasma mass spectrometer. The odds ratios of NTDs for uranium exposure levels, categorized into quartiles, were estimated using logistic regression. The median concentration of uranium in the NTD group (0.409 ng/g) was significantly higher than that in the control group (0.218 ng/g). The risk for NTDs increased 2.52-fold (95% CI, 1.85-3.45) for concentrations of uranium above the median value for all participants. After adjusting for confounders, the risk for NTDs increased 1.36-fold (95% CI, 1.25-6.17), 1.77-fold (95% CI, 1.09-2.85), and 3.60-fold (95% CI, 2.30-5.64) for the second, third, and fourth quartiles of uranium concentrations compared to the lowest quartile, respectively. Prenatal exposure to uranium is a risk factor for NTDs in this population. Prospective studies are needed to further validate this finding.

Bioaccumulation characteristics and acute toxicity of uranium in Hydrodictyon reticulatum: An algae with potential for wastewater remediation

The bioaccumulation characteristics and acute toxicity of uranium (U) to Hydrodictyon reticulatum were studied to provide reference for further mechanism and application research. According to an analysis using visual MINTEQ software, the pH change caused by the photosynthesis of H. reticulatum leads to U remaining mainly in the species of UO₂(OH)₃^-. Fourier transform infrared spectrometer (FTIR) and transmission electron microscope (TEM) analysis showed that the bioaccumulation of U was related to the amino and carboxyl groups, resulting in cell wall damage. Using innovative cell staining microscopic observation techniques, U was mainly compartmentalized in vacuoles and pyrenoid; chlorophyll, soluble protein, dehydrogenase activity, and other physiological responses were closely related to the U stress concentration. Especially here, the change trend of the specific activity and specific growth rate of dehydrogenase was consistent, showing low concentration promotion and high concentration inhibition. Combined with the toxic response of the two, the half inhibitory dose for 72 h was determined to be about 30 mg L^-1. When bioaccumulation equilibrium is reached at 72 h, the maximum tolerance concentration of U without affecting the easy collection characteristics of the algae is 30 mg L^-1, and the maximum U bioaccumulation capacity was able to reach 24.47 ± 0.86 mg g^-1 by dry biomass.

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.

Adaptive Synthesis of a Rough Lipopolysaccharide in Geobacter sulfurreducens for Metal Reduction and Detoxification

The ability of some metal-reducing bacteria to produce a rough (no O-antigen) lipopolysaccharide (LPS) could facilitate surface interactions with minerals and metal reduction. Consistent with this, the laboratory model metal reducer Geobacter sulfurreducens PCA produced two rough LPS isoforms (with or without a terminal methyl-quinovosamine sugar) when growing with the soluble electron acceptor fumarate but expressed only the shorter and more hydrophilic variant when reducing iron oxides. We reconstructed from genomic data conserved pathways for the synthesis of the rough LPS and generated heptosyltransferase mutants with partial (ΔrfaQ) or complete (ΔrfaC) truncations in the core oligosaccharide. The stepwise removal of the LPS core sugars reduced the hydrophilicity of the cell and increased outer membrane vesiculation. These changes in surface charge and remodeling did not substantially impact planktonic growth but disrupted the developmental stages and structure of electroactive biofilms. Furthermore, the mutants assembled conductive pili for extracellular mineralization of the toxic uranyl cation but were unable to prevent permeation and mineralization of the radionuclide in the cell envelope. Hence, not only does the rough LPS promote cell-cell and cell-mineral interactions critical to biofilm formation and metal respiration but it also functions as a permeability barrier to toxic metal cations. In doing so, the rough LPS maximizes the extracellular reduction of soluble and insoluble metals and preserves cell envelope functions critical to the environmental survival of Geobacter bacteria in metal-rich environments and their performance in bioremediation and bioenergy applications. IMPORTANCE Some metal-reducing bacteria produce an LPS without the repeating sugars (O-antigen) that decorate the surface of most Gram-negative bacteria, but the biological significance of this adaptive feature was not previously investigated. Using the model representative Geobacter sulfurreducens strain PCA and mutants carrying stepwise truncations in the LPS core sugars, we demonstrate the importance of the rough LPS in the control of cell surface chemistry during the respiration of iron minerals and the formation of electroactive biofilms. Importantly, we describe hitherto overlooked roles for the rough LPS in metal sequestration and outer membrane vesiculation that are critical for the extracellular reduction and detoxification of toxic metals and radionuclides. These results are of interest for the optimization of bioremediation schemes and electricity-harvesting platforms using these bacteria.

Assessing the Toxicity of Mine-Water Mixtures and the Effectiveness of Water Quality Guideline Values in Protecting Local Aquatic Species

Six tropical freshwater species were used to assess the toxicity of mine waters from a uranium mine adjacent to a World Heritage area in northern Australia. Key contaminants of potential concern for the mine were U, Mg, Mn, and total ammonia nitrogen (TAN). Direct toxicity assessments were carried out to assess whether the established site-specific guideline values for individual contaminants would be protective with the contaminants occurring as mixtures. Metal speciation was calculated for contaminants to determine which were the major contributors of toxicity, with 84 to 96% of Mg predicted in the free-ion form as Mg²⁺ , and 76 to 92% of Mn predicted as Mn²⁺ . Uranium, Al, and Cu were predicted to be strongly bound to fulvic acid. Uranium, Mg, Mn, and Cu were incorporated into concentration addition or independent action mixture toxicity models to compare the observed toxicity in each of the waters with predicted toxicity. For >90% of the data, mine-water toxicity was less than predicted by the concentration addition model. Instances where toxicity was greater than predicted were accompanied by exceedances of individual metal guideline values in all but one case (i.e., a Mg concentration within 10% of the guideline value). This indicates that existing individual water quality guideline values for U, Mg, Mn, and TAN would adequately protect ecosystems downstream of the mine. Environ Toxicol Chem 2021;40:2334-2346. © 2021 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2021 SETAC.

Uptake and Toxicity of Respirable Carbon-Rich Uranium-Bearing Particles: Insights into the Role of Particulates in Uranium Toxicity

Particulate matter (PM) presents an environmental health risk for communities residing close to uranium (U) mine sites. However, the role of the particulate form of U on its cellular toxicity is still poorly understood. Here, we investigated the cellular uptake and toxicity of C-rich U-bearing particles as a model organic particulate containing uranyl citrate over a range of environmentally relevant concentrations of U (0-445 μM). The cytotoxicity of C-rich U-bearing particles in human epithelial cells (A549) was U-dose-dependent. No cytotoxic effects were detected with soluble U doses. Carbon-rich U-bearing particles with a wide size distribution (<10 μm) presented 2.7 times higher U uptake into cells than the particles with a narrow size distribution (<1 μm) at 100 μM U concentration. TEM-EDS analysis identified the intracellular translocation of clusters of C-rich U-bearing particles. The accumulation of C-rich U-bearing particles induced DNA damage and cytotoxicity as indicated by the increased phosphorylation of the histone H2AX and cell death, respectively. These findings reveal the toxicity of the particulate form of U under environmentally relevant heterogeneous size distributions. Our study opens new avenues for future investigations on the health impacts resulting from environmental exposures to the particulate form of U near mine sites.

Uranium (U) source, speciation, uptake, toxicity and bioremediation strategies in soil-plant system: A review

Uranium(U), a highly toxic radionuclide, is becoming a great threat to soil health development, as returning nuclear waste containing U into the soil systems is increased. Numerous studies have focused on: i) tracing the source in U contaminated soils; ii) exploring U geochemistry; and iii) assessing U phyto-uptake and its toxicity to plants. Yet, there are few literature reviews that systematically summarized the U in soil-plant system in past decade. Thus, we present its source, geochemical behavior, uptake, toxicity, detoxification, and bioremediation strategies based on available data, especially published from 2018 to 2021. In this review, we examine processes that can lead to the soil U contamination, indicating that mining activities are currently the main sources. We discuss the relationship between U bioavailability in the soil-plant system and soil conditions including redox potential, soil pH, organic matter, and microorganisms. We then review the soil-plant transfer of U, finding that U mainly accumulates in roots with a quite limited translocation. However, plants such as willow, water lily, and sesban are reported to translocate high U levels from roots to aerial parts. Indeed, U does not possess any identified biological role, but provokes numerous deleterious effects such as reducing seed germination, inhibiting plant growth, depressing photosynthesis, interfering with nutrient uptake, as well as oxidative damage and genotoxicity. Yet, plants tolerate U toxicity via various defense strategies including antioxidant enzymes, compartmentalization, and phytochelatin. Moreover, we review two biological remediation strategies for U-contaminated soil: (i) phytoremediation and (ii) microbial remediation. They are quite low-cost and eco-friendly compared with traditional physical or chemical remediation technologies. Finally, we conclude some promising research challenges regarding U biogeochemical behavior in soil-plant systems. This review, thus, further indicates that the combined application of U low accumulators and microbial inoculants may be an effective strategy for the bioremediation of U-contaminated soils.

Genotoxicity linked to occupational exposure in uranium mine workers: Granzyme B and apoptotic changes

BACKGROUND

Uranium mining and processing are an ancient occupation, recognized as being grueling and accountable for injury and disease. Uranium (U) is a radioactive heavy metal used in many industrial applications. It increases the micronuclei frequencies as well as chromosomal aberration and sister chromatid exchange in peripheral blood lymphocytes. Granzyme B and perforin are stored inside the leukocytes in secretory granules. These proteins are released outside the cells by a cell-to-cell contact under specific conditions for inducing apoptosis. So, this study investigated the potential health hazards with prominence on the biological effects of radiation exposure.

METHODS

A cross-sectional analytic research was conducted on Egyptian male mining field workers. Leucocytes' genotoxicity was evaluated using DNA fragmentation assay and comet assay. Furthermore, flow cytometric analysis of Granzyme B protein was done.

RESULTS

A significant increase in dead cells after dual acridine orange/ethidium bromide (AO/EB) fluorescent staining in radiation-exposed groups was noticed compared to control groups. Moreover, a significant increase in the fragmented DNA was evident in exposed groups relative to the control one. Granzyme B protein levels showed a significant increase concerning control.

CONCLUSION

A wide variety of adverse human health risks are considered a potential risk to Egyptian uranium miners. For employers working in both mining and processing fields, the most common molecular shift highlighted was the leucocyte damage in blood samples. To preserve the health of all employees, health education and administration of effective hazard management procedures are necessary.

Development of a Sublethal Chronic Toxicity Test for the Northern Trout Gudgeon, Mogurnda mogurnda, and Application to Uranium, Magnesium, and Manganese

Many international guidance documents for deriving water quality guideline values recommend the use of chronic toxicity data. For the tropical fish northern trout gudgeon, Mogurnda mogurnda, 96-h acute and 28-d chronic toxicity tests have been developed, but both tests have drawbacks. The 96-h toxicity test is acute and has a lethal endpoint; hence it is not a preferred method for guideline value derivation. The 28-d method has a sublethal (growth) endpoint, but is highly resource intensive and is high risk in terms of not meeting quality control criteria. The present study aimed to determine the feasibility of a 7-d larval growth toxicity test as an alternative to the 96-h survival and 28-d growth tests. Once the method was successfully developed, derived toxicity estimates for uranium, magnesium, and manganese were compared with those for other endpoints and tests lengths within the literature. As a final validation of the 7-d method, the sensitivity of the 7-d growth endpoint was compared with those of 14-, 21-, and 28-d exposures. Fish growth rate, based on length, over 7 d was significantly more sensitive compared with existing acute toxicity endpoints for magnesium and manganese, and was similarly sensitive to existing chronic toxicity endpoints for uranium. For uranium, the sensitivity of the growth endpoint over the 4 exposure periods was similar, suggesting that 7 d as an exposure duration is sufficient to provide an indication of longer term chronic growth effects. The sensitivity of the 7-d method, across the 3 metals tested, highlights the benefit of utilizing the highly reliable short-term 7-d chronic toxicity test method in future toxicity testing using M. mogurnda. Environ Toxicol Chem 2021;40:1596-1605. © 2021 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2021 SETAC.

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

The importance of incorporating kinetic approaches in order to gain information on underlying physiological processes explaining species sensitivity to environmental stressors has been highlighted in recent years. Uranium is present in the aquatic environment worldwide due to naturally occurring and anthropogenic sources, posing a potential risk to freshwater taxa in contaminated areas. Although literature shows that organisms vary widely with respect to susceptibility to U, information on toxicokinetics that may explain the variation in toxicodynamic responses is scarce. In the present work, Daphnia magna were exposed to a range of environmentally relevant U concentrations (0 - 200 µg L^-1) followed by a 48 h depuration phase to obtain information on toxicokinetic parameters and toxic responses. Results showed time-dependent and concentration-dependent uptake of U in daphnia (k_u = 1.2 - 3.8 L g^-1 day^-1) with bioconcentration factors (BCFs) ranging from 1,641 - 5,204 (L kg^-1), a high depuration rate constant (k_e = 0.75 day^-1), the majority of U tightly bound to the exoskeleton (~ 50 - 60%) and maternal transfer of U (1 - 7%). Effects on growth, survivorship and major ion homeostasis strongly correlated with exposure (external or internal) and toxicokinetic parameters (uptake rates, k_u, BCF), indicating that uptake and internalization drives U toxicity responses in D. magna. Interference from U with ion uptake pathways and homeostasis was highlighted by the alteration in whole-body ion concentrations, their ionic ratios (e.g., Ca:Mg and Na:K) and the increased expression in some ion regulating genes. Together, this work adds to the limited data examining U kinetics in freshwater taxa and, in addition, provides perspective on factors influencing stress, toxicity and adaptive response to environmental contaminants such as uranium.

Analysis of accumulation and phytotoxicity mechanism of uranium and cadmium in two sweet potato cultivars

The purpose of this study was to reveal the accumulation and phytotoxicity mechanism of sweet potato (Ipomoea batatas L.) roots following exposure to toxic levels of uranium (U) and cadmium (Cd). We selected two accumulation-type sweet potato cultivars as experimental material. The varietal differences in U and Cd accumulation and physiological metabolism were analyzed by a hydroponic experiment. High concentrations of U and Cd inhibited the growth and development of sweet potato and damaged the microstructure of root. The roots were the main accumulating organs of U and Cd in both sweet potato. Root cell walls and vacuoles (soluble components) were the main distribution sites of U and Cd. The chemical forms of U in the two sweet potato varieties were insoluble and oxalate compounds, while Cd mainly combined with pectin and protein. U and Cd changed the normal mineral nutrition metabolism in the roots, and also significantly inhibited the photosynthetic metabolism of sweet potatoes. RNA-seq showed that the cell wall and plant hormone signal transduction pathways responded to either U or Cd toxicity in both varieties. The inorganic ion transporter and organic compound transporter in roots of both sweet potato varieties are sensitive to U and Cd toxicity.

The response of the accumulator plants Noccaea caerulescens, Noccaea goesingense and Plantago major towards the uranium

Uranium (U) is a naturally occurring metal; its environmental levels can be increased due to processes in the nuclear industry and fertilizer production. The transfer of U in the food chain from plants is associated with deleterious chemical and radiation effects. To date, limited information is available about U toxicity on plant physiology. This study investigates the responses of metal-accumulating plants to different concentrations of U. The plants Noccaea caerulescens and Noccaea goesingense are known as metal hyperaccumulators and therefore could serve as candidates for the phytoremediation of radioactive hotspots; Plantago major is a widely used pharmaceutical plant that pioneers polluted grounds and therefore should not contain high concentrations of toxic elements. The experimental plants were grown hydroponically at U concentrations between 1 μM and 10 mM. The content of U and essential elements was analyzed in roots and leaves by ICP-MS. The amount of accumulated U was influenced by its concentration in the hydroponics. Roots contained most of the metal, whereas less was transported up to the leaves, with the exception of N. goesingense in a medium concentration of U. U also influenced the nutrient profile of the plants. We localized the U in plant tissues using EDX in the SEM. U was evenly distributed in roots and leaves of Noccaea species, with one exception in the roots of N. goesingense, where the central cylinder contained more U than the cortex. The toxicity of U was assessed by measuring growth and photosynthetic parameters. While root biomass of N. caerulescens was not affected by U, root biomass of N. goesingense decreased significantly at high U concentrations of 0.1 and 10 mM and root biomass of P. major decreased at 10 mM U. Dry weight of leaves was decreased at different U concentrations in the three plant species; a promotive effect was observed in N. caerulescens at lowest concentration offered. Chlorophyll a fluorescence was not affected or negatively affected by U in both Noccaea species, whereas in Plantago also positive effects were observed. Our results show that the impact of U on Plantago and Noccaea relates to its external concentration and to the plant species. When growing in contaminated areas, P. major should not be used for medicinal purpose. Noccaea species and P. major could immobilize U in their rhizosphere in hotspots contaminated by U, and they could extract limited amounts of U into their leaves.

Uranium(VI) toxicity in tobacco BY-2 cell suspension culture - A physiological study

For the first time, the physiological and cellular responses of Nicotiana tabacum (BY-2) cells to uranium (U) as an abiotic stressor were studied using a multi-analytic approach that combined biochemical analysis, thermodynamic modeling and spectroscopic studies. The goal of this investigation was to determine the U threshold toxicity in tobacco BY-2 cells, the influence of U on the homeostasis of micro-macro essential nutrients, as well as the effect of Fe starvation on U bioassociation in cultured BY-2 cells. Our findings demonstrated that U interferes with the homeostasis of essential elements. The interaction of U with BY-2 cells confirmed both time- and concentration-dependent kinetics. Under Fe deficiency, a reduced level of U was detected in the cells compared to Fe-sufficient conditions. Interestingly, blocking the Ca channels with gadolinium chloride caused a decrease in U concentration in the BY-2 cells. Spectroscopic studies evidenced changes in the U speciation in the culture media with increasing exposure time under both Fe-sufficient and deficient conditions, leading us to conclude that different stress response reactions are related to Fe metabolism. Moreover, it is suggested that U toxicity in BY-2 cells is highly dependent on the existence of other micro-macro elements as shown by negative synergistic effects of U and Fe on cell viability.

Bioaccumulation of uranium by Candida utilis: Investigated by water chemistry and biological effects

The bioaccumulation of hexavalent uranium (U(VI)) on Candida utilis (C. utilis) and its biological effects were investigated via batch and biologic techniques. The bioaccumulation mechanism of U(VI) and C. utilis were characterized by SEM, TEM, FT-IR and XPS. The batch results showed that C. utilis had a high adsorption capacity (41.15 mg/g wet cells at pH 5.0) and high equilibrium rate (~100% within 3.5 h). The analysis of intracellular hydrogen peroxides and malondialdehyde suggested that the growth of C. utilis was inhibited under different concentrations of U(VI) due to the abundant production of reactive oxide species. The activity of intracellular antioxidants (e.g., super oxide dismutase and glutathione) was significantly enhanced under U(VI) stress, indicating the anti-toxic effect of C. utilis cells under low U(VI) stress. These results indicated that C. utilis is an ideal biosorbent for removing radionuclides in environmental remediation.

Uranium inhibits mammalian mitochondrial cytochrome c oxidase and ATP synthase

As an emerging pollutant, uranium poses serious concerns to ecological and human health. The kidney has been established as a major deposition site and the most sensitive target organ for uranium poisoning, and the underlying toxicological mechanisms have been associated with oxidative stress and mitochondrial respiration. However, the identities of key molecular targets in uranium-induced toxicity remain elusive. In this study, we comprehensively evaluated the in vitro effects of uranium on ten critical enzymes in the mitochondrial respiration pathway and discovered that respiratory chain complex IV (cytochrome c oxidase) and complex V (ATP synthase) were strongly inhibited. The inhibitory effects were validated with mitochondria from human renal proximal tubule cells-the most affected renal site in uranium poisoning. The IC₅₀ values (around 1 mg/L) are physiologically relevant, as they are comparable to known kidney accumulation levels in uranium poisoning. In addition, these inhibitory effects could explain the well-documented uranium-induced reactive oxygen species generation and mitochondrial alterations. In conclusion, cytochrome c oxidase and ATP synthase are possibly key molecular targets underlying the toxic effects of uranium.

Multisystem combined uranium resistance mechanisms and bioremediation potential of Stenotrophomonas bentonitica BII-R7: Transcriptomics and microscopic study

The potential use of microorganisms in the bioremediation of U pollution has been extensively described. However, a lack of knowledge on molecular resistance mechanisms has become a challenge for the use of these technologies. We reported on the transcriptomic and microscopic response of Stenotrophomonas bentonitica BII-R7 exposed to 100 and 250 μM of U. Results showed that exposure to 100 μM displayed up-regulation of 185 and 148 genes during the lag and exponential phases, respectively, whereas 143 and 194 were down-regulated, out of 3786 genes (>1.5-fold change). Exposure to 250 μM of U showed up-regulation of 68 genes and down-regulation of 290 during the lag phase. Genes involved in cell wall and membrane protein synthesis, efflux systems and phosphatases were up-regulated under all conditions tested. Microscopic observations evidenced the formation of U-phosphate minerals at membrane and extracellular levels. Thus, a biphasic process is likely to occur: the increased cell wall would promote the biosorption of U to the cell surface and its precipitation as U-phosphate minerals enhanced by phosphatases. Transport systems would prevent U accumulation in the cytoplasm. These findings contribute to an understanding of how microbes cope with U toxicity, thus allowing for the development of efficient bioremediation strategies.

Terrestrial ecological risk analysis via dietary exposure at uranium mine sites in the Grand Canyon watershed (Arizona, USA)

The U.S. Department of the Interior recently included uranium (U) on a list of mineral commodities that are considered critical to economic and national security. The uses of U for commercial and residential energy production, defense applications, medical device technologies, and energy generation for space vehicles and satellites are known, but the environmental impacts of uranium extraction are not always well quantified. We conducted a screening-level ecological risk analysis based on exposure to mining-related elements via diets and incidental soil ingestion for terrestrial biota to provide context to chemical characterization and exposures at breccia pipe U mines in northern Arizona. Relative risks, calculated as hazard quotients (HQs), were generally low for all biological receptor models. Our models screened for risk to omnivores and insectivores (HQs>1) but not herbivores and carnivores. Uranium was not the driver of ecological risk; arsenic, cadmium, copper, and zinc were of concern for biota consuming ground-dwelling invertebrates. Invertebrate species composition should be considered when applying these models to other mining locations or future sampling at the breccia pipe mine sites. Dietary concentration thresholds (DCTs) were also calculated to understand food concentrations that may lead to ecological risk. The DCTs indicated that critical concentrations were not approached in our model scenarios, as evident in the very low HQs for most models. The DCTs may be used by natural resource and land managers as well as mine operators to screen or monitor for potential risk to terrestrial receptors as mine sites are developed and remediated in the future.

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.

Waterborne uranium causes toxic effect and thyroid disruption in zebrafish larvae

Uranium is a radioactive element that is widely present in aquatic environment. However, limited knowledge is available about the effect of uranium on thyroid system, which plays a key role in the development of animals. In this study, zebrafish embryos were exposed to different environmentally relevant concentrations of uranium (2, 20 and 100 μg/L) for 120 h. The bioaccumulation, developmental toxicities, changes of thyroid hormones (THs) and key genes related to the hypothalamic-pituitary-thyroid (HPT) axis in larvae were analyzed after exposure. Results showed that uranium could bioaccumulate in zebrafish larvae, with the bioconcentration factors ranging from 49.6 to 523. Consequently, significant developmental toxicities and changes in locomotor activities were observed with a concentration-dependent manner. The levels of triiodothyronine (T3) levels in larvae were substantially decreased, whereas those of thyroxine (T4) were increased in fish bodies. The levels of THs were regulated by the negative feedback loops through HPT axis related genes, most of which (NIS, Deio1, Deio2, TRα, TSHβ and UGT1ab) were significantly depressed after exposure to uranium. Our results suggest the potential toxicities and thyroid disruption of uranium on zebrafish, which would provide baseline data set for better understanding the impact of waterborne uranium on aquatic organisms and the associated mechanisms. This study also highlights the key role of thyroid disruption in the ecological risk assessment of uranium pollution.

Exogenous plant growth regulator alleviate the adverse effects of U and Cd stress in sunflower (Helianthus annuus L.) and improve the efficacy of U and Cd remediation

Plant growth regulators (PGRs) are widely used in agricultural activities and have the potential to improve plant growth and plant tolerance against metal stress. PGR-assisted phytoextraction is now an effective and inexpensive method for enhancing the plant removal of toxic metals from soil. In this study, we conducted experiments to determine the effects of PGR treatments on soil uranium (U) and cadmium (Cd) removal by sunflowers as well as their stress response to U and Cd contamination. We found that the plant growth was inhibited by combined U and Cd stress in sunflowers compared with that of the control; however, the application of exogenous PGR had reduced the combined U and Cd stress by stimulating photosynthesis, decreasing the levels of active oxygen and lipid peroxidation, and enhancing the activity of the antioxidant defence systems. Exogenous PGR also increased the uptake of U and Cd by sunflowers and therefore, improved their U and Cd remediation efficiency. Moreover, indoleacetic acid (IAA) was the most effective PGR at removing U and Cd in the soil; the U and Cd removal efficiency was 484.21% and 238.85% higher in the 500 mg L^-1 IAA application compared with that of the control without PGR application, respectively. Furthermore, none of the PGR treatments significantly influenced the available U and Cd contents in soil. Our results, therefore, may provide some detailed understanding on the technologies for the sustainable remediation of U and Cd contaminated soil by the combination of PGR treatments and phytoextraction.

A toxicological comparison between two uranium compounds in Artemia salina: Artificial seawater containing CaCO3

Uranium (U) mining is an aquatic environmental concern because most of these harmful compounds are discharged into freshwater, reaching the saline environment as the final destination of this contaminated water. Carbonates are present in ocean waters and are essential for benthic organisms, however they may influence the U-induced toxicity. Thus, the aim of this study was to compare the toxicity of uranium nitrate (UN) and uranium acetate (UA) in Artemia salina (AS), which is one of the leading representatives of the marine biota. The cultures of AS (instar II) maintained in artificial seawater containing CaCO₃ were exposed for 24 h to different concentrations of U compounds. The results showed that AS were more sensitive to UN (LC₅₀ ≈ 15 μM) when compared with UA (LC₅₀ ≈ 245 μM) indicating higher toxicity of this U compound. Calculated U speciation indicated that Ca₂UO₂(CO₃)₃ and (UO₂)2CO₃(OH)₃^- complexes predominated under our experimental conditions. The immobilization/lethality was observed after 9 h of exposure for both U compounds. However, only UN caused a significant decrease (≈40%) in the acetylcholinesterase (AChE) activity when compared with control. In order to observe preliminary toxicity effects, we evaluated oxidative stress parameters, such as catalase (CAT) activity, TBARS formation, radical species (RS) generation and cell membrane injury and/or apoptosis (CMI). In this study, we demonstrate that U compounds caused a significant decrease in CAT activity. Similarly, we also observed that UN increased TBARS levels in AS at concentrations 5 times lower than AU (10 μM and 50 μM, respectively). Furthermore, RS generation and CMI were enhanced only on AS treated with UN. Overall, the effects observed here were remarkably significant in AS exposed to UN when compared with AU. In this study, we showed different profiles of toxicity for both U compounds, contributing significantly to the current and scarce understanding of the aquatic ecotoxicity of this heavy metal.