Revealing the toxicity of monovalent and trivalent thallium to medaka fish in controlled exposure conditions

Thallium-induced neurocardiotoxicity in zebrafish: Protective role of adaptive UPR and DNA repair

Thallium (Tl) is a hazardous heavy metal widely used in industrial applications, leading to significant environmental contamination. Tl concentrations in surface waters can reach up to 1520 μg/L, exceeding safe limits and posing risks to aquatic ecosystems and human health. Monovalent thallium [Tl(I)] is highly stable and bioaccumulative, readily accumulating in aquatic organisms, plants, and the human food chain. Exposure to Tl has been associated with neurotoxicity, kidney dysfunction, and cardiovascular diseases, particularly affecting children and pregnant women, and may increase the risk of neurodegenerative diseases and cardiac arrhythmias. However, effective strategies to mitigate Tl toxicity remain lacking. This study establishes a zebrafish embryo model to investigate the toxicological mechanisms of Tl and evaluate the protective effects of IXA4, a selective XBP1 activator. Our results show that Tl exposure increases mortality, reduces hatching rates, impairs swim bladder development, and causes pericardial edema and brain abnormalities. Transcriptomic and qPCR analyses confirm that Tl induces endoplasmic reticulum (ER) stress and activates the unfolded protein response (UPR), key pathways involved in cellular toxicity. Co-treatment with IXA4 significantly improves survival rates and developmental outcomes by upregulating DNA repair genes, particularly in the nucleotide excision repair (NER) pathway, thereby reducing cardiac and neural damage. This study provides novel insights into the mechanisms of Tl toxicity, underscores the urgent need for stricter regulatory measures, and highlights IXA4 as a potential intervention for mitigating heavy metal toxicity in aquatic ecosystems.

The Impact of Thallium Exposure in Public Health and Molecular Toxicology: A Comprehensive Review

This review offers a synthesis of the current understanding of the impact of low-dose thallium (Tl) on public health, specifically emphasizing its diverse effects on various populations and organs. The article integrates insights into the cytotoxic effects, genotoxic potential, and molecular mechanisms of thallium in mammalian cells. Thallium, a non-essential heavy metal present in up to 89 different minerals, has garnered attention due to its adverse effects on human health. As technology and metallurgical industries advance, various forms of thallium, including dust, vapor, and wastewater, can contaminate the environment, extending to the surrounding air, water sources, and soil. Moreover, the metal has been identified in beverages, tobacco, and vegetables, highlighting its pervasive presence in a wide array of food sources. Epidemiological findings underscore associations between thallium exposure and critical health aspects such as kidney function, pregnancy outcomes, smoking-related implications, and potential links to autism spectrum disorder. Thallium primarily exerts cellular toxicity on various tissues through mitochondria-mediated oxidative stress and endoplasmic reticulum stress. This synthesis aims to shed light on the intricate web of thallium exposure and its potential implications for public health, emphasizing the need for vigilant consideration of its risks.

Thallium exposure interfered with heart development in embryonic zebrafish (Danio rerio): From phenotype to genotype

Thallium (Tl) is a rare trace metal element but increasingly detected in wastewater produced by coal-burning, smelting, and more recently, high-tech manufacturing industries. However, the adverse effects of Tl, especially cardiotoxicity, on aquatic biota remain unclear. In this study, zebrafish model was used to elucidate the effects and mechanisms of Tl(I) cardiotoxicity in developing embryos. Exposure of embryonic zebrafish to low-dose Tl(I) (25-100 μg/L) decreased heart rate and blood flow activity, and subsequently impaired swim bladder inflation and locomotive behavior of larvae. Following high-level Tl(I) administration (200-800 μg/L), embryonic zebrafish exhibited pericardial edema, incorrect heart looping, and thinner myocardial layer. Based on RNA-sequencing, Tl(I) altered pathways responsible for protein folding and transmembrane transport, as well as negative regulation of heart rate and cardiac jelly development. The gene expression of nppa, nppb, ucp1, and ucp3, biomarkers of cardiac damage, were significantly upregulated by Tl(I). Our findings demonstrate that Tl(I) at environmentally relevant concentrations interfered with cardiac development with respect to anatomy, function, and transcriptomic alterations. The cardiotoxic mechanisms of Tl(I) provide valuable information in the assessment of Tl-related ecological risk in freshwater environment.

Variation in the burden and chemical forms of thallium in non-detoxified tissues of tilapia fish (Oreochromis niloticus) from waterborne exposure

Thallium (Tl) is highly toxic to aquatic ecosystems, but information about its concentration and distribution characteristics in different fish tissues is limited. In this study, juvenile tilapia (Oreochromis niloticus) were exposed to Tl solutions with different sub-lethal concentrations for 28 days, and the Tl concentrations and distribution patterns in the fish non-detoxified tissues (gills, muscle, and bone) were analyzed. The Tl chemical form fractions, Tl-ethanol, Tl-HCl, and Tl-residual, corresponding to easy, moderate, and difficult migration fraction, respectively, in the fish tissues were obtained by sequential extractant approach. The Tl concentrations of different fractions and total burden were determined using graphite furnace atomic absorption spectrophotometry. Exposure-concentration effect determined the Tl burden in the fish tissues. The average Tl-total concentration factors were 360, 447, and 593 in the bone, gills, and muscle, respectively, and the limited variation during the exposure period indicates that tilapia have a strong ability to self-regulate and achieve Tl homeostasis. However, Tl fractions varied in tissues, and the Tl-HCl fraction dominated in the gills (60.1%) and bone (59.0%), switchover Tl-ethanol fraction dominated in the muscle (68.3%). This study has shown that Tl can be easily taken up by fish during 28-days-period and largely distributed in non-detoxified tissues especially muscle, in which concurrent risks of high Tl-total burden and high levels of Tl in the form of easy migration fraction, posing possible risks to public health.