What is Forensic Toxicology?

What is Forensic Toxicology?

Forensic toxicology serves as an important tool for collecting and analyzing evidence in a crime-scene investigation. In this ScienceStruck article, we take a quick look at some of the basic aspects of this important field of criminal science.
ScienceStruck Staff
Last Updated: Mar 19, 2018
Forensic Toxicology

Forensic toxicology is the use of toxicology along with a few other disciples like analytical chemistry, pharmacology, and clinical chemistry in medico-legal investigations of death, poisoning, and drug usage. The main aim of this science is to help crime investigators obtain evidence, and accordingly interpret the results.

Forensic toxicology is not too concerned with the legal outcome of the investigation. As per the American Board of Forensic Toxicology (ABFT), this field includes the measurement of levels of alcohol, drugs, and other toxic substances in the biological specimens, along with the interpretation of the results in medico-legal contexts.

There are many areas of specialty within this field, the main one being autopsy (postmortem) toxicology. The American Academy of Forensic Sciences (AAFS) emphasizes that this field is highly collaborative in nature, as a forensic toxicologist often works in conjunction with law enforcement officers, forensic pathologists, forensic scientists, and other crime scene investigators.

The process of detection of drugs and other toxic substances present in the biological samples, takes place first by an initial screening, followed by a confirmation of the right compound, and lastly by the quantification of the compound. Both screening and confirmation are done using the different analytical methods.

Common Samples Collected in Forensic Toxicology

It is necessary that every analytical method in forensic toxicology is carefully tested with a predefined validation procedure to ensure correct and indisputable results each time. A testing laboratory involved in forensic pathology has to adhere to strict rules and policies, to ensure the best possible results along with the safety of every individual.

The choice of method for investigation and testing mainly depends on what substance is suspected, and the type of sample that is being tested. In biological samples, many complex factors like the matrix effect, metabolism, and conjugation of compounds have to be considered. Forensic toxicology also aims at finding out the compound statistics of the substances, along with their concentrations.

The following is a list comprising the typical biological samples which are taken for investigations, along with a short description of each one of them:
  • Urine: Urine samples provide quick and easy results for live subjects. It is most commonly used for drug-testing in employees and athletes. One disadvantage of urine samples is that, owing to the time it takes the body to metabolize and eliminate a toxic substance, it doesn't always reflect the toxic substances that the subject was under at the time of sample-collection.
  • Blood: A quantity of 10 cubic centimeter of blood is required to screen and confirm the presence of most toxic substances. Unlike urine samples, blood sample screening can provide the list of toxic substances present in the subject's body at the time of collection, and is hence ideal for testing the blood-alcohol content in drunken driving cases.
  • Oral Fluid: The layman term for oral fluid is saliva. However, oral fluid is a more appropriate term, as saliva is only a component of oral fluid. The concentration of the toxic substances present in the oral fluid is in parallel to that of the blood. The method of collection of oral fluids, being non-invasive, is gaining prominence in the collection of evidence in cases of drunken driving.
  • Hair: Hair is an important sample in the field of forensic toxicology, as it is capable of providing information about medium-to-long-term history of drug abuse. This is because, the chemicals in the bloodstream are transferred to the hair follicles, using which a rough timeline establishing the intake of drugs can be deduced. Hair grows at approximately 1.5 centimeters per month. So, cross-sections of the hair at different intervals can give a rough estimate of when the drug was ingested.
There are many other body fluids and even body organs that are collected during an autopsy, which can provide vital information to a forensic toxicologist. The most commonly collected samples are the gastric contents of the subject, which are very useful in the detection of undigested pills or liquids that were ingested just before the subject's death. This sample is however not useful in cases where the bodies are highly decomposed. Some of the other body parts that are used in an autopsy include the vitreous humor of the eye, brain, liver, and the spleen.