A toxic substance is any material that can cause harm to living organisms through chemical reactions or interactions. These substances can be found in various forms, including solids, liquids, and gases. Common examples include heavy metals like lead and mercury, as well as certain chemicals used in industrial processes. Exposure to toxic substances can lead to health issues, ranging from mild irritation to severe illnesses or even death. Toxic substances can enter the body through different routes, such as inhalation, ingestion, or skin contact. Environmental sources of toxicity include polluted water, contaminated soil, and airborne pollutants. Understanding the nature and effects of toxic substances is crucial for public health and safety, as well as for environmental protection.