Lead (Pb), due to its high toxicity and bioaccumulation tendency, is one of the top three pollutants of concern for both humans and wildlife and occupies second place in the Priority List of Hazardous Substances. In freshwater fish, Pb is mainly absorbed through the gills, where the greatest accumulation occurs. Despite the crucial role of gills in several physiological functions such as gas exchange, water balance, and osmoregulation, no studies evaluated the effects of environmentally relevant concentrations of Pb on this organ, and existing literature only refers to high levels of exposure. Herein we investigated for the first time the molecular and morphological effects induced by two low and environmentally relevant concentrations of Pb (2.5 and 5 μg/L) on the gills of Danio rerio, a model species with a high translational value for human toxicity. It was demonstrated that Pb administration at even low doses induces osmoregulatory dysfunctions by affecting Na⁺/K⁺-ATPase and AQP3 expression. It was also shown that Pb upregulates MTs as a protective response to prevent cell damage. Modulation of SOD confirms that the production of reactive oxygen species is an important toxicity mechanism of Pb. Histological and morphometric analysis revealed conspicuous pathological changes, both dose- and time-dependent.

Lead (Pb) is a non-essential, highly toxic, and persistent element widely recognized as one of the most concerning pollutants. It is listed on the Priority List of Hazardous Substances. Widespread environmental contamination from Pb is a serious issue for human health and wildlife. In fish, Pb mainly accumulates in the liver, which is a key component for metal detoxification and excretion processes. In this study, we investigated, for the first time, the morphological and functional injuries induced in zebrafish (Danio rerio) liver by two very low and environmentally relevant concentrations of Pb (2.5 and 5 μg/L) after 48, 96, and 192 h of exposure. We observed significant histological alterations in all the exposed samples, and it was demonstrated that the extent of injuries increased with dose and exposure time. The most common modifications observed were congestion of blood vessels and sinusoids, cytoplasmic vacuolizations, parenchyma dyschromia, and macrophage proliferation. Pb administration also resulted in a significant increase in lipid content and the upregulation of key genes that are involved in metal detoxification (mtf1) and the defensive response against oxidative stress (sod1 and cat). We show that even very low doses of Pb can disrupt liver morphology and function.

Lead (Pb) is a non-essential, highly toxic, and persistent element widely recognised as one of the most concerning pollutants, and it is listed in the Priority List of Hazardous Substances. Widespread environmental contamination from Pb is a serious issue for human health and wildlife. The liver, a key compartment for metal detoxification and excretion, is also the organ in which Pb mainly accumulates in fish. Herein, we investigated for the first time the morphological and functional injuries induced in zebrafish (Danio rerio) liver by two very low and environmentally relevant concentrations of Pb (2.5 and 5 μg/L) after 48, 96, and 192 hours of exposure. We showed significant histological alterations in all the exposed samples, also demonstrating that the extent of injuries increased with dose and exposure time. The most common modifications observed were congestion of blood vessels and sinusoids, cytoplasmic vacuolizations, parenchyma dyschromia, and macrophage proliferation. Pb administration also resulted in a significant increase in lipid content and the upregulation of key genes involved in metal detoxification (mtf1) and the defensive response against oxidative stress (sod1 and cat). We showed that even very low doses of Pb can disrupt liver morphology and function.

Unlike many other fungicides, strobilurins are applied several times during the growing season for prophylactic purposes, thus heightening the risk of environmental contamination. In the EU, the dimoxystrobin approval period lasted for 17 years. It has been classified as moderately toxic to birds and highly toxic to earthworms, and it is suspected to be carcinogenic to humans. However, it is still commercialized in several countries. The effects of dimoxystrobin are still largely underexplored, with only three studies reporting sublethal alterations in fish. Here, we evaluated for the first time the effects of dimoxystrobin on zebrafish liver after short-term exposure (96 h) to two sublethal and environmentally relevant concentrations (6.56 and 13.13 μg/L), providing evidence of morphological, functional, and ultrastructural modifications. We revealed severe alterations encompassing three reaction patterns: circulatory disturbance, regressive and progressive changes, which also showed a dose-dependent trend. Furthermore, we revealed that dimoxystrobin induced a significant increase in lipid content, a decrease in glycogen granules and affected the defensive response against oxidative stress through a significant downregulation of SOD and CAT. The information presented here demonstrates that the hazardous properties of dimoxystrobin may result from several pathological events involving multiple targets. Our results also emphasize the importance of the combined use of morphological, ultrastructural and functional investigation in ecotoxicological studies.

Lead (Pb) has progressively become ubiquitous due to widespread use. The liver represents a target of Pb toxicity due to its central role in metabolism and detoxification. The mechanisms of Pb hepatotoxicity have not yet been fully elucidated, although oxidative stress and iron dysregulation suggest the involvement of the ferroptosis pathway. It has been hypothesized that exposure to environmental Pb concentrations induces the activation of ferroptosis as a mechanism involved in Pb hepatotoxicity, an iron-mediated regulated cell death. To test this hypothesis, we exposed adult zebrafish to environmentally relevant Pb concentrations (2.5 and 5 μg/L), combining ultrastructural analysis (TEM) with the study of key markers of ferroptosis (GPX4, SLC7A11, NRF2, KEAP1 and ACSL4). The results demonstrated that Pb exposure induced dose-dependent and progressive mitochondrial damage in hepatocytes, characterized by loss of cristae and membrane rupture. At the same time, consistent with a ferroptotic molecular profile, increased expression of ACSL4, reduced levels of the protective factors NRF2, KEAP1 and SLC7A11, and altered expression of GPX4 were observed. Overall, our data collectively identify ferroptosis as a pathogenic pathway in Pb-induced hepatotoxicity.