In essence, toxicology is the science of poisons, toxicants, or toxins. A poison, toxicant, or toxin is a substance capable of causing harm when administered to an organism. Harm can be defined as seriously injuring or, ultimately, causing the death of an organism. This is a rather simplistic definition, because virtually every known chemical or substance has the potential for causing harm. The term toxicant can be a synonym for poison, or the term poison might be more appropriate for the most potent substances, i.e., substances that induce adverse effects at exposure levels of a few milligrams per kilogram of body weight (see later discussion). The term toxin usually refers to a poison derived from a protein or conjugated protein produced by some higher plant, animal, or pathogenic bacteria that is highly poisonous for other living organisms, e.g., botulinum toxins.
Toxicologist’s study the substances which are usually chemical compounds but may be elemental or complex materials. Radioactive elements, heavy metals (e.g., mercury or lead), or the packing materials used in food processing are examples of such substances. Food toxicology deals with substances found in food that might be harmful to those who consume sufficient quantities of the food containing such substances. On rare occasions, common foods are contaminated with unacceptably high levels of toxicants. Such substances can be inherent toxicants, substances naturally found in foods, or contaminants, which are substances that find their way into food either during the preparation or processing of such foods. Nutritional toxicology is the study of the nutritional aspects of toxicology.
Nutritional toxicology is related to and might even overlap but is not synonymous with food toxicology. Food toxicology emphasizes toxicants or toxins found in foods, whereas nutritional toxicology targets the interrelations that toxicants or toxins have with nutrients in the diet, which affect nutritional status. Nutritional toxicology can refer to the means by which the diet or components of the diet prevent against the adverse effects of toxicants or toxins. The fundamental concept of toxicology — the dose determines the poison — was based on the premise that all substances are poisons; there is none which is not a poison and the right dose determines the poison from a cure. Therefore, the premise that anything has the potential to be a poison if taken in a large enough doses dictates the scope of toxicology, which is to quantitate and interpret the toxicity of substances. Most toxicologists deal with exogenous compounds, or those compounds that are not part of the normal metabolism of organisms, i.e., xenobiotic or foreign compounds. Food and nutritional toxicologists deal with toxicants in food, the health effects of high nutrient intakes, and the interactions between toxicants and nutrients.