The chapter discusses the environmental occurrence, production, use, and human exposure to heavy metals such as arsenic, cadmium, chromium, lead, and mercury, and their toxic effects. These metals are naturally occurring elements with high atomic weights and densities, widely distributed in the environment due to industrial, domestic, agricultural, medical, and technological applications. Their toxicity depends on factors like dose, exposure route, chemical species, and individual characteristics. Arsenic, cadmium, chromium, lead, and mercury are classified as priority metals due to their significant public health impacts, including systemic toxicity and carcinogenicity. The chapter provides an analysis of their environmental sources, production, use, and potential human exposure pathways, as well as the molecular mechanisms of their toxicity, genotoxicity, and carcinogenicity. Each metal's unique properties and mechanisms of action are detailed, highlighting the importance of understanding these factors for effective risk assessment and management.The chapter discusses the environmental occurrence, production, use, and human exposure to heavy metals such as arsenic, cadmium, chromium, lead, and mercury, and their toxic effects. These metals are naturally occurring elements with high atomic weights and densities, widely distributed in the environment due to industrial, domestic, agricultural, medical, and technological applications. Their toxicity depends on factors like dose, exposure route, chemical species, and individual characteristics. Arsenic, cadmium, chromium, lead, and mercury are classified as priority metals due to their significant public health impacts, including systemic toxicity and carcinogenicity. The chapter provides an analysis of their environmental sources, production, use, and potential human exposure pathways, as well as the molecular mechanisms of their toxicity, genotoxicity, and carcinogenicity. Each metal's unique properties and mechanisms of action are detailed, highlighting the importance of understanding these factors for effective risk assessment and management.