Arsenic is a metalloid element commonly found in geological deposits, and its various chemical compounds are known environmental contaminants. Biologically, it is a potent systemic toxin that interferes with essential metabolic pathways by mimicking other elements, such as phosphate or arsenic-binding groups on proteins. Exposure can occur through contaminated water or consumption of affected minerals, leading to acute or chronic poisoning. The toxic effects are varied, potentially impacting multiple organ systems, including the skin, kidneys, and nervous system. Modern research focuses on understanding the speciation of arsenic—the chemical form it takes—as toxicity levels and mechanisms differ drastically between inorganic and organic forms.