Forensic toxicology
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Forensic toxicology is the use of toxicology to aid medicolegal investigation of death, poisoning, and drug use. Many toxic substances do not produce characteristic lesions, so if a toxic reaction is suspected, visual investigation may not suffice.
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.
Determining the substance ingested is often complicated by the body's natural processes, as it is rare for a chemical to remain in its original form once in the body. For example: heroin is almost immediately metabolised into morphine, making detailed investigation into factors such as injection marks and chemical purity necessary to confirm diagnosis. The substance may also have been diluted by its dispersal through the body; while a pill or other regulated dose of a drug may have grams or milligrams of the active constituent, an individual sample under investigation may only contain micrograms or nanograms.
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[edit] Samples
[edit] Urine
A urine sample is quick and easy for a live subject, and is common among drug testing for employees and athletes. Urine samples do not necessarily reflect the toxic substance(s) the subject was influenced by at the time of the sample collection. An example of this is THC from cannabinoid (for example, marijuana) use, which in heavy users can be detected in urine for up to 10 days following use. Note also that it can take as long as 8 hours until a given substance can be detected.
[edit] Blood
A blood sample of approximately 10 cm³ is usually sufficient to screen and confirm most common toxic substances. A blood sample provides the toxicologist with a profile of the substance that the subject was influenced by at the time of collection; for this reason, it is the sample of choice for measuring blood alcohol content in drunk driving cases.
[edit] Hair sample
Hair is capable of recording medium to long-term or high dosage substance abuse. Chemicals in the bloodstream may be transferred to the growing hair and stored in the follicle, providing a rough timeline of drug intake events. Head hair grows at rate of approximately 1 to 1.5 cm a month, and so cross sections from different sections of the follicle can give estimates as to when a substance was ingested. Testing for drugs in hair is not standard throughout the population. The darker and coarser the hair the more drug that will be found in the hair. If two people consumed the same amount of drug, the person with the darker and coarser hair will have more drug in their hair than the lighter haired person when tested.
[edit] Other organisms
Bacteria, maggots and other organisms that may have ingested some of the subject matter may have also ingested any toxic substance within it.
[edit] Other
Other bodily fluids and organs may provide samples, particularly samples collected during an autopsy. A common autopsy sample is the gastric contents of the decedent, which can be useful for detecting undigested pills or liquids that were ingested prior to death. In highly decomposed bodies, traditional samples may no longer be available. The vitreous humour from the eye may be used, as the fibrous layer of the eyeball and the eye socket of the skull protects the sample from trauma and adulteration. Other common organs used for toxicology are the brain, liver, and spleen.
[edit] Detection and Classification
[edit] Gas chromatography
Gas-liquid chromatography is of particular use in examining gases, or substances that can be heated to produce a gas. Volatile organic compounds fall into this category.
[edit] Detection of Metals
The compounds suspected of containing a metal is traditionally separated by the destruction of the organic matrix by chemical or thermal oxidation. This leaves the metal to be identified and quantified in the inorganic residue, and it can be detected using such methods as the Reinsch test, emission spectroscopy or X-ray diffraction. Unfortunately, while this identifies the metals present it removes the original compound, and so hinders efforts to determine what may have been ingested. The toxic effects of various metallic compounds can vary considerably.
[edit] Nonvolatile organic substances
Drugs, both prescribed and illegal, pesticides, natural products, pollutants and industrial compounds are some of the most common compounds encountered. Screening methods include thin-layer chromatography, gas-liquid chromatography
[edit] Miscellaneous
Venoms and other toxic mixtures of proteins or uncharacterised constituents are difficult to detect. Immunoassay may be the most practical means of detecting and measuring these highly potent and difficult to isolate substances, if antibodies can be grown against the active constituent. Most frequently, specific analytic procedures must be developed for each analyte of this type.
