The forensic toxicologist deals mainly with providing information to the legal system on the effects of drugs and poisons. They are often very senior toxicologists who have gained a lot of experience in other areas of toxicology first, such as analytical chemistry.
Having gathered and evaluated the available toxicological evidence, they may attend court as an expert witness to describe and explain the evidence relating to the case. These can range from simple ‘drink-driving’ cases to fatal accident, suicide and murder investigations, where deliberate or accidental poisoning is suspected.
Forensic toxicologists use modern analytical procedures to isolate, identify and quantify drugs, endogenous compounds and poisonous substances in forensic samples. Often, only very small quantities of samples can be retrieved from a crime scene or the mortuary, and the sample matrix can vary widely – to include body fluids, plant materials and drug paraphernalia. Forensic toxicologists must assess the significance of these analytical data so as to identify relationships between exposure levels and clinical response. It is necessary to understand how the metabolism of a chemical can affect its concentration and pharmacological or toxic effects. It is also important to consider factors such as drug-drug interactions, tolerance, age-related effects, post-mortem redistribution and differences between individuals. It can be necessary for forensic toxicologists to conclude a probable cause of death in post-mortem cases.
Courts will often call a forensic toxicologist as an expert witness to report and explain the analytical results that they have been provided as evidence in the case, or to comment on the validity of data supplied by other laboratories. They are normally asked to give an expert opinion as to whether the measured concentration of a chemical could account for a toxic effect (or even death). They may also be able to suggest whether the level of exposure was consistent with normal use of the chemical, or if the level of exposure was excessive, indicating an accidental or intentional overdose.
Career opportunities for forensic toxicologists exist in both University and private forensic laboratories, and in specialist hospital medicine departments. With so many different types of legal case, forensic toxicology can provide a variety of scientific challenges.