Forensic toxicology

Forensic toxicology is the use of Toxicology to 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: 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.

Samples

Urine

A urine sample is quick and easy for a live subject, and is common among drug testing for employees and athletes

Blood

A blood sample of approximately 10cc is usually sufficient to screen for common toxic substances.

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 1.5cm 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 comsumed 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, maggots and 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

Detection and Classification

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.

Detection of Metals

A compound 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 an 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.

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 and immunoassay

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.