Forensic toxicology

Forensic toxicology is the use of toxicologyto aid medicolegal investigation of death and poisoning. Many toxic substances do not produce characteristic lesions.

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: heroinis almost immediately metabolisedinto 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 gramsor milligramsof the active constituent, an individual sample under investigation may only contain microgramsor nanograms.

Samples

Urine

A urinesample is quick and easy for a live subject, and is common among drug testingfor 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 THCfrom cannabinoid(for example, marijuana) use, which can be detected in urine for weeks following use.

Blood

A bloodsample of approximately 10 cm³is 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 contentin drunk drivingcases.

Hair sample

Hairis 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 timelineof drug intake events. Head hair grows at rate of approximately 1 to 1.5 cma 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.

Other organisms

Bacteria, maggotsand other organisms that may have ingested some of the subject matter may have also ingested any toxic substance within it.

Other

Other bodily fluids and organs may provide samples, particularly samples collected during an autopsy. A common autopsy sample is the gastriccontents 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 humourfrom 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.

Detection and Classification

Gas chromatography

Gas-liquid chromatographyis of particular use in examining gases, or substances that can be heated to produce a gas. Volatile organic compoundsfall into this category.

Detection of Metals

A compound suspected of containing a metalis 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 spectroscopyor 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 effectsof various metallic compounds can vary considerably.

Nonvolatile organic substances

Drugs, both prescribed and illegal, pesticides, natural products, pollutantsand industrial compounds are some of the most common compounds encountered. Screening methods include thin-layer chromatography, gas-liquid chromatographyand immunoassay

Miscellaneous

Venomsand other toxic mixtures of proteinsor uncharacterised constituents are difficult to detect. Immunoassaymay 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 analyteof this type.

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It uses material from the http://en.wikipedia.org/wiki/Forensic+toxicology Wikipedia article Forensic toxicology.