Manganese toxicity
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Manganese Toxicity: Impacts and Mechanisms
Introduction to Manganese Toxicity
Manganese (Mn) is an essential trace element necessary for various biological functions, including enzyme activation and metabolic processes. However, excessive exposure to Mn can lead to toxicity, affecting both humans and plants. This article explores the mechanisms and effects of Mn toxicity across different systems.
Manganese Toxicity in Humans
Neurological Effects and Mechanisms
Excessive Mn exposure primarily affects the central nervous system (CNS), leading to a condition known as manganism, which exhibits symptoms similar to Parkinson's disease. Mn accumulates in specific brain regions such as the substantia nigra, globus pallidus, and striatum, disrupting the glutamine/glutamate-γ-aminobutyric acid (GABA) cycle and leading to neurotoxicity . This accumulation impairs dopaminergic and GABAergic neurons, causing cytoskeletal dysfunction and neurochemical imbalances 59.
Occupational and Environmental Exposure
Mn toxicity is often reported in occupational settings, such as welding, where inhalation of Mn-containing dust is common. Additionally, environmental exposure through contaminated drinking water has been linked to cognitive deficits in children, highlighting the vulnerability of developing brains to Mn toxicity 16. Symptoms include dystonia, bradykinesia, and speech disturbances, collectively termed "locura manganica" .
Treatment and Management
Current treatment options for Mn toxicity include chelation therapy with EDTA and supplementation with levodopa, although these are only mildly effective. Preventive measures, such as reducing Mn exposure in industrial settings and improving water filtration systems, are crucial .
Manganese Toxicity in Plants
Symptoms and Mechanisms
Mn toxicity in plants manifests through various symptoms, including chlorosis and necrosis, which vary widely among species. The toxicity disrupts photosynthesis and enzyme activity, primarily due to Mn's interference with other essential cationic metals 24. High Mn levels in soil, especially in acidic conditions, increase the risk of phytotoxicity .
Adaptive Mechanisms
Plants have evolved several strategies to cope with Mn toxicity, such as activating antioxidant systems, regulating Mn uptake, and compartmentalizing excess Mn into subcellular compartments like vacuoles and the endoplasmic reticulum . These mechanisms help mitigate the adverse effects and maintain plant health under Mn stress.
Environmental Factors
Environmental conditions, including light intensity, temperature, and soil composition, significantly influence Mn toxicity in plants. Wet soils rich in organic matter or those treated with acid-forming fertilizers are particularly prone to increasing Mn availability and toxicity 24. Climate change may exacerbate these conditions, necessitating further research and adaptive agricultural practices.
Cellular and Biochemical Impacts
Energy Metabolism Disruption
Mn exposure disrupts cellular energy metabolism by affecting iron-sulfur cluster and heme-enzyme biogenesis, leading to ATP synthesis impairment and energy deficiency. This disruption is a primary cause of Mn toxicity, as evidenced by studies on Escherichia coli and other model organisms .
Oxidative Stress
Mn-induced oxidative stress results from the generation of reactive oxygen species (ROS), which damage cellular components. However, merely suppressing oxidative stress does not fully restore cellular function, indicating that energy metabolism disruption plays a more critical role in Mn toxicity .
Conclusion
Manganese toxicity poses significant risks to both human health and plant ecosystems. In humans, it primarily affects the CNS, leading to neurodegenerative conditions similar to Parkinson's disease. In plants, Mn toxicity disrupts essential physiological processes, limiting growth and productivity. Understanding the mechanisms of Mn toxicity and developing effective mitigation strategies are crucial for managing its impact on health and agriculture.
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