Toxicology studies chemicals, substances, and agents that negatively affect the health of humans and other living organisms. Toxicants are any substance, chemical, or agent that has a toxic effect. Some of the categories of toxicants are toxins (toxins are naturally produced by biological organisms), toxic elements such as some metals, metal ions, organometallics such as methylmercury, and metabolites. Toxins are toxicants that are naturally produced by biological organisms. Some examples of toxins are the botulinum toxin produced by clostridium botulinum, poisonous mushrooms, the tetanus toxin produced by clostridium tetani, mycotoxins from molds, the diphtheria toxin produced by corynebacterium diphtheriae, and toxins in harmful algae blooms such as red tide, for example. Teratogens are chemicals, substances, or agents that have an abnormal effect on an embryo or fetus. The embryo is sensitive during implantation and organogenesis, and the timing of exposure is important. Teratogens cause harm through various mechanisms such as alterations of mitosis, enzyme inhibition, mutation formation, and damage to chromosomes. An example of a common teratogen is alcohol. Ethanol exposure during pregnancy is associated with the characteristic facial abnormalities of fetal alcohol syndrome. Ethanol from alcoholic beverages crosses the placenta and interferes with neurogenesis, among other effects. And alcohol exposure during pregnancy increases the risk of childhood ADHD. There are many disorders that prenatal alcohol exposure is associated with, known as Fetal Alcohol Spectrum Disorders. Some toxicants are made more toxic by other substances. Potentiation is when a substance (chemical or other) that is not toxic in itself makes a toxicant more toxic. Additionally, when combined, some toxic substances become much more toxic, more than an additive effect, a synergistic effect. Synergism is when more than one toxicant comes together, and the result is something more toxic than simply adding their individual toxic effects together.

Reference:

Eaton DL, Shaffer RM. Basic Toxicology and Mode of Action of Toxic Substances. In: Boulton ML, Wallace RB. eds. Maxcy-Rosenau-Last Public Health & Preventive Medicine, 16e. McGraw Hill; 2022.