Neurodegeneration

ASSOCIATION BETWEEN HEAVY METAL EXPOSURE AND PARKINSON'S DISEASE: A REVIEW OF THE MECHANISMS RELATED TO OXIDATIVE STRESS
Parkinson’s disease (PD) is a gradually progressing neurodegenerative condition that is marked by a loss of motor coordination along with non-motor features. Although the precise cause of PD has not been determined, the disease condition is mostly associated with the exposure to environmental toxins, such as metals, and their abnormal accumulation in the brain. Heavy metals, such as iron (Fe), mercury (Hg), manganese (Mn), copper (Cu), and lead (Pb), have been linked to PD and contribute to its progression.
Pyatha, Sarita et al. “Association between Heavy Metal Exposure and Parkinson's Disease: A Review of the Mechanisms Related to Oxidative Stress.” Antioxidants (Basel, Switzerland) vol. 11,12 2467. 15 Dec. 2022, doi:10.3390/antiox11122467

METALS AND NEURODEGENERATION
Once metals have accumulated in the nervous system, oxidative stress, mitochondrial dysfunction, and protein misfolding are the most common deficits associated with metal-induced toxicity. Once injured, neurons have to expend greater energy to synthesize neurotransmitters and maintain homeostasis. The increased burden combined with the neurotoxicity may lead to neuronal death. When some neurons are lost, the job has to be passed on to other neurons, initiating a vicious cycle of toxicity. Given that the nervous system does not regenerate as well as other systems do, the neurodegeneration and impairments usually become progressive with age, as typically seen in Alzheimer's disease and Parkinson's disease. 
Chen, Pan et al. “Metals and Neurodegeneration.” F1000Research vol. 5 F1000 Faculty Rev-366. 17 Mar. 2016, doi:10.12688/f1000research.7431.1