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What is poison – in forensic science
admin to Forensic Science  



Any substance capable of causing a toxic (harmful) response in an organism. In forensic science, detecting a poison is the responsibility of the medical examiner (ME) or pathologist, the toxicologist, and the forensic chemist. An oft-repeated phrase in toxicology is the dose makes the poison, which means that every substance can cause harm depending on how much is ingested. Even such familiar substances as water and table salt can cause death if sufficient quantities are ingested over a short period of time. The tox-icity of a poison is measured by a quantity called the LD50, lethal dose 50. The LD50 of a substance is that dose (based on body weight) that results in death for half of an experimental population such as laboratory rats or mice. For any given individual, the fatal dose of a poison will depend on general health, age, weight, and a number of other variables.

Poisons can be subdivided a number of ways. Biological poisons, broadly defined, are those obtained from living organisms such as bacteria or plants. Hemlock, strychnine, venom from snakes, and botulism are examples. Inorganic poisons include hydrochloric acid (HC1), cyanide (both salts and gaseous HCN), lye (sodium hydroxide, NaOH), ammonia, mercury, lead, thallium, and arsenic, which is perhaps the most notorious poison of all. Indeed, it was the prevalence of arsenic poisoning in the 18th and 19th centuries that was critical in driving the development of forensic toxicology. The term organic poisons usually refers to organic compounds including organic insecticides and pesticides such as DDT, toluene, and other petroleum distillates, and many drugs. Methanol (wood alcohol) poisoning can occur with homemade or adulterated liquors in which the methanol is substituted for ethanol. Of the gaseous poisons, carbon monoxide (cO), HCN, and forms of arsenic are the most familiar.

Poisoning can be accidental, suicidal, or homicidal. At a scene, the fact that the death has been caused by a poison may not be obvious, and so a thorough search of the area is required with attention focusing on empty containers, glasses, residues, and medication bottles. In homicides, food is a common means of administration. In Chicago in 1982, cyanide was placed into Tylenol capsules, resulting in the death of seven people. To date, no one has been convicted of the crime. In the wake of recent terrorist activity, there is increasing concern about mass poisonings of food, drugs, or water supplies, presenting a significant forensic and law enforcement challenge.