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A Guide to Forensic Toxicology



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Many are often shocked when informed that a seemingly healthy person has died because of drug or alcohol overdose. Easy to go by undetected, these substances can often do more damage than one can imagine. It is the job of a forensic toxicologist to coax them out of their hiding places, following a highly classified approach.

Upon entering the body, drugs and alcohol will be distributed to all places where water is present and hence in theory traces of them can be found in locations including body fluids, tissues and organs.

Take alcohol for example, within minutes of consumption, it is absorbed into the bloodstream. The blood alcohol concentration then gradually builds up to a maximum, before eliminated by means of oxidation and excretion until the zero level is reached again.

Based on the fact that alcohol can be found in all parts of the body where water is present, there are actually various methods of finding out if someone has consumed alcohol. In post-mortem situation, when blood might not be available, the method of alcohol detection can be by examining water-rich organs such as the brain. Urine samples can also be taken, in both the living and the dead. What makes urine samples different to other detection methods is that urine can reflect consumption days, rather than mere hours before examination.

In a living person however, the preferred methods are usually blood tests and breath-tests. Among the two, breath-tests are considerably more convenient, and thus are more commonly used. The test measures the amount of alcohol in alveolar air, which is usually 1/2100 that of the alcohol in the blood.

Although rather handy, care must be taken during breath-tests to ensure that it is air from the lungs that is being measured. What to look out for are distractions such as alcohol present in the mouth, which can be caused by something as innocent as a recent rinsing with Listerine. Therefore, breath-test instruments are often installed with things called slope detectors, accepting breath sample only when there is no more or little change in breath alcohol concentration. The subject must also blow for a minimum time with a minimum breath flow rate.

When dealing with drugs, the toxicologist's job can sometimes be more difficult. The first thing to do would always be extraction and isolation of the drug, if any, from biological materials available. This is done on the observation that most drugs are either acidic or basic, meaning that they can be extracted by controlling the pH of the water solution in which the biological sample is dissolved into.

Then, procedures that follow would be screening and confirmation. By screening, the toxicologist is able to examine the specimens for a wide range of drugs within a short period of time. Common screening methods include thin-layer chromatography, gas chromatography and immunoassay. If the test result comes back as positive, the toxicologist would then proceed to do a confirmation test, with gas chromatography and mass spectrometry being the favoured methods.

What makes a toxicologist's job so hard is the fact that the toxicologist is always looking for minimal traces of the toxic agent consumed. This is because drugs and alcohol starts breaking down in the body the moment they are consumed. Therefore, often toxicologists have to be satisfied with even a nanogram of the drug. They must also be fully aware of metabolites of drugs as often those are found instead of the actual drug. Heroin for example, is metabolised almost immediately into morphine after entering the bloodstream. Toxicologist must also be aware of the effects of the same drug on different people, and the possible lethal effects of the combination of two drugs, both non-toxics on their own.

Assessing the presence of drugs in the body is actually a rather complicated and highly organised matter. Apart from having a solid base of scientific knowledge, one must never forget to keep an open mind, as well as a watchful eye, to all the bizarre possibilities.

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