Poison is any substance that can harm or kill and Toxicology is the study of it. Forensic Toxicology study postmotem signs of the poisoning. The toxicity of a substance depends on the amount ingested, as well as the age, weight and state of health of the person who ingests it. Poison can be administered by ingestion, injection, or absorbed through the skin.
Some poisons, such as snake venom, is only dangerous if it is absorbed in the bloodstream. If poison is suspected at a crime scene the first step would be to take a sample from the victim, say from their bloodstream. As there would be other bodily fluids taken, the sample is treated to extract and purify the poison.
Some poisons can be extracted using organic solvents, such as ether or chloroform. Chromatography is a technique that separates the various compounds in a sample, and is very useful when it comes to identifying poisons. Nowadays chromatography is coupled with a technique called mass spectrometry.
Another way to identify poison is immunoassay. This is identifying antibodies made up for the foreign bodies in the blood, such as the poison. However this method is still being developed so is not widely used.
If a body suspected of poison has be exposed to nature and insects have been feeding off the body, there may be no or few soft tissues left. If the insects are still at the scene we can dissect them and extract the ingested tissues from their body. The poison may then be extracted from this.
Toxicology is the science of adverse effects of chemicals on living organisms. In general, a toxicologist detects and identifies foreign chemicals in the body, with a particular emphasis upon toxic or hazardous substances. A descriptive toxicologist performs toxicity tests to evaluate the risk that exposure poses to humans.
A mechanistic toxicologist attempts to determine how substances exert deleterious effects on living organisms. A regulatory toxicologist judges whether or not a substance has low enough risk to justify making it available to the public. A toxin is any material exerting a life threatening effect upon a living organism. Poisons are a subgroup of toxins.
Toxic materials exist in many forms (gaseous, liquid, solid, animal, mineral, and vegetable), and may be ingested, inhaled, or absorbed through the skin. Poisons generally enter the body in a single massive dose, or accumulate to a massive dose over time. Toxins work in minute quantities or low levels, requiring sensitive analytical instruments for detection.
Some toxins have medicinal value, but many produce irreparable damage. Some toxins have antidotes and others do not. Poisons can be combated by prompt treatment, and most organ damage (except for serious CNS injury) may be repairable. Whereas poisons are somewhat easily identifiable by their symptoms, many toxins tend to disguise or mask themselves.
A forensic toxicologist must consider the context of an investigation, in particular any physical symptoms recorded, and any evidence collected at a crime scene that may narrow the search, such as pill bottles, powders, trace residue, and any available chemicals. Provided with this information and samples with which to work, the forensic toxicologist must determine which toxic substances are present, in what concentrations, and the probable effect of those chemicals on the person.