The dose makes the poison—even water can be toxic
Toxicity is how far a substance or mixture can harm an organism, a cell, or an organ. Snake venom has a no-effect dose; enough water can kill. Southern African bone arrows from 72,000–80,000 years ago were likely poison-tipped—toxicity as technology.
In toxicology, effect depends on dose: water can cause water intoxication at extreme intake, while even potent venoms have thresholds below which damage is undetectable. Toxicity is also species-specific, so animal-to-human comparisons need caution and safety factors. The Greek root toxikon once meant substances that kill or severely disable, tied to poisoned bows (toxon). Archaeologists think Paleolithic cultures widely treated arrows with poison; San communities of Southern Africa still craft beetle-and-plant tip mixtures that can stay lethal for months to a year.
Toxicity is often sorted into chemical, biological, physical, radioactive, and behavioural types. Pathogens are called pathogens more than toxicants; a single microbe can theoretically seed infection, while secreted products such as cholera toxin act as nonliving toxins—or venoms if from animals. Physical toxicants include inhaled asbestos or silica dust, corrosives that destroy tissue, asphyxiant gases that displace oxygen, and even excess water that dilutes vital ions. Radiation can damage organisms; behavioural toxicity names unwanted nervous-system effects of therapeutic drug doses.
Population risk is often summarized with metrics such as LD50. When data are thin, regulators compare similar chemicals and apply conservative safety factors—for example dividing a rat-safe dose by ten for humans, or by a hundred if the data come from fish. Mixtures such as gasoline or cigarette smoke complicate assessment because components interact. Global labeling schemes group physical, health, and environmental hazards; acute lethality is ranked in five categories from least to most exposure needed to kill. Skin corrosion must reach the dermis within four hours and not reverse in fourteen days; serious eye damage fails to reverse within twenty-one days.
Source: Toxicity
