Forensic toxicology aids legal investigations through the study of poisons, substances that can harm or kill. The toxicity of a substance is dependent on various factors, including the amount ingested, and the age, weight, and health of the individual who ingested it. Poison can be administered by ingestion, injection, inhalation, or absorption, some of which are more dangerous that others. For example, some snake venoms are only dangerous if absorbed straight into the bloodstream. Toxic reactions can be one of three types. Pharmacological reactions cause injury to the central nervous system. Pathological reactions cause damage to the liver. And genotoxic reactions result in the creation of benign or malignant neoplasms or tumours. Though many toxins have antidotes, if levels of the substance reach a certain level, the effects may be irreversible. Pathological reactions can be reversed, though only if they are discovered early enough. Genotoxic and carcinogenic effects may take up to forty years to materialise, by which time it may be to late.
Forensic toxicology is utilised in most areas of a forensic investigation, though is particularly vital in suspicious deaths involving the suspected intake of some toxic substance. Drug testing methods employed are often used in cases of rape in which the victim has been slipped some kind of date-rape drug, rendering them unable to fight off their attacker while they are being sexually assaulted. Unfortunately many such drugs leave the system quickly.
An examination of the crime scene can often give investigators a clue as to what may have been ingested by the victim. Such evidence may include pill bottles, powders, trace residues and any other chemicals present.
The application of poisons has been a common method of murder for hundreds of years, though methods of detection have advanced in recent years. Initially one or more screening tests will be conducted in order to gain a general idea of what the toxin is. Common screening tests include physical tests (boiling point, refractive index), crystal test (treatment with a chemical reagent to produce crystals), chemical spot tests (treatment with colour-changing reagents), and chromatography (method of separating substance components). Following this, confirmation tests, such as gas chromatography and mass spectrometry may be conducted. Various chromatography methods are commonly used to separate the various compounds of a sample, allowing for the substance to be identified. Immunoassays can also be used to identify a poisonous substance by identifying the antibodies produced for the foreign substance. However this technique is still being developed and so is not widely used. In cases involving a corpse with little soft tissue present, insect analysis may be beneficial. Carrion feeding insects will most likely have ingested any toxic substances whilst feeding on the corpse. By dissecting and extracted the ingested tissue, further analysis may be able to identify the substance.
Hair is potentially an idea recording medium for long-term drug abuse. As chemicals are absorbed into the bloodstream they are transferred into the hair, where they may be stored. This can even provide a rough timeline of drug intake. Head hair grows at an approximate rate of 1 to 1.5cm a month, therefore cross-sections may be able to provide an estimation of when a substance was ingested.
Despite these techniques, the identification of toxic substances it is rarely straightforward. The body’s natural processes often complicate a substance, altering the chemical’s original form. For example, after ingestion, heroin is almost immediately metabolised into another substance and then metabolised further into morphine. Urine and blood samples are most commonly extracted for drug testing, though other bodily fluids and organs will suffice. The brain, liver and spleen are commonly used organs for this. While gastric contents are useful for the detection of undigested pills or liquids, such an analysis may not be useful hours after ingestion.
Though there is a vast array of toxin substances available, a selection are particularly common. Below are some regular poisons and their symptoms.
Acids: Characteristic burns around the mouth, lips and nose.
Aniline: Darkened skin around the face and neck.
Arsenic: Severe diarrhoea.
Atropine: Dilated pupils.
Bases: Burns around the mouth, lips and nose.
Carbolic acid: Strong odour of disinfectant.
Carbon monoxide: Cherry red skin.
Cyanide: Quick death, red skin, and a distinctive odour of almonds.
Food poisoning: Severe vomiting, diarrhoea and abdominal pain.
Metallic compounds: Diarrhoea, vomiting and abdominal pain.
Opiates: Pupil contraction.
Oxalic acid: Strong garlic odour.
Sodium fluoride: Convulsions.
Strychnine: Convulsions, lockjaw, a high pulse, and dark face and neck.