Forensic toxicology is the study of poisons. toxicology is concerned with the chemical and physical properties of
toxic substances and their physiological effects on living organisms,
qualitative and quantitative methods for their analysis in biological and
nonbiological materials, and the development of procedures for the treatment of
poisoning. A poison may be regarded as any substance which, when taken in
sufficient quantity, will cause ill health or death. The key phrase in this
definition is “sufficient quantity”.
The ingestion of large amounts of
water over an extended period of time has been known to cause fatal electrolyte
imbalance. This seemingly bizarre behavior — ingestion of massive amounts of
water — is known as psychogenic polydipsia and occurs in certain forms of
schizophrenia. Conversely, minute quantities of arsenic, cyanide, and other
poisons may be ingested, causing no apparent toxicity.
“All substances are poisons;
there is none which is not a poison. The right dose differentiates a poison
from a remedy.”
The science of toxicology has
expanded to include a wide range of interests, including the evaluation of the
risks involved in the use of pharmaceuticals, pesticides, and food additives,
as well as studies of occupational poisoning, exposure to environmental
pollution, the effects of radiation, and, regretfully, biological and chemical
warfare.
The forensic toxicologist is
concerned primarily with the detection and estimation of poisons in tissues and
body fluids obtained at autopsy or, occasionally, in blood, urine, or gastric
material obtained from
a living person. Once the
analysis is completed, the forensic toxicologist then interprets the results as
to the physiological and/or behavioral effects of the poison upon the person
from whom the sample was obtained.
Establishing the cause of death
rests with the medical examiner, coroner, or pathologist, but success or
failure in arriving at the correct conclusion frequently depends upon the
combined efforts of the pathologist and the forensic toxicologist. Poisoning as
a cause of death cannot be proven beyond contention without toxicologic
analyses that demonstrate the presence of the poison in the tissues or body
fluids of the deceased. Most drugs and poisons do not produce characteristic or
observable lesions in body tissues, and their presence can be demonstrated only
by chemical methods of isolation and identification. If toxicological analyses
are avoided, death may be ascribed to poisoning without definite proof, or a
death due to poisoning may be erroneously attributed to some other cause.
The detection of alcohol,
narcotics, hallucinogens, or other drugs may substantiate the testimony of
witnesses as to the aggressive, incoherent, or irrational behavior of the
decedent at the time of a fatal incident. Conversely, negative toxicology
findings may dispel stories of the decedent’s drug use.Negative findings are
also significant in persons who should be regularly taking medications to
control pathological conditions.
It was traditionally believed
that if a body was black, blue, or spotted in places or “smelled bad” the
decedent had died from poison. Other mistaken ideas were that the heart of a
poisoned person could not be destroyed by fire, or that the body of a person
dying from arsenic poisoning would not decay. Unless a poisoner was literally
caught in the act, there was no way to establish that the victim died from
poison. In the early 18th century, a Dutch physician, Hermann Boerhoave,
theorized that various poisons in a hot, vaporous condition yielded typical
odors.
The murderous use of white
arsenic (arsenic trioxide) became so widespread among the general population
that the poison acquired the name “inheritance powder”. Given this popularity,
it is small wonder the first milestones in the chemical isolation and
identification of a poison in body tissues and fluids would center around
arsenic.
The 1800s witnessed the
development of forensic toxicology as a scientific discipline. In 1814,
Mathieiv J. B. Orfila (1787–1853), the “father of toxicology”, published Traité des Poisons — the first systemic approach to the studyM of the chemical and
physiological nature of poisons. Orfila’s role as an expert witness in many
famous murder trials, and particularly his application of the Marsh Test for
arsenic in the trial of the poisoner Marie Lafarge, aroused both popular and
scholarly interest in the new science. As Dean of the Medical Faculty at the University of Paris
The first successful isolation of
an alkaloid poison was performed in 1850 by Jean Servials Stas, a Belgian
chemist, using a solution of acetic acid in ethyl alcohol to extract nicotine
from the tissues of the murdered Gustave Fougnie. Modified by the German
chemist, Friedrich Otto, the Stas-Otto method was quickly applied to isolation
of numerous alkaloid poisons, including colchicine, conin, morphine, narcotine,
and strychnine; the method is still used today.
Most accidental poisonings occur
in the home. Children, due to their innate curiosity and adventurous nature,
may gain access to and ingest prescription. drugs, detergents, pesticides, and
household cleaners.
Accidental poisoning in adults is
usually the results of mislabeling, storage of a toxic substance in a container
other than the original one. As often as not, the improper container is an old
whiskey bottle! Arsenic, weed killer, strychnine, cyanide, cleaning solutions,
and numerous other deadly poisons have been eagerly and mistakenly drunk from
cider jugs and old whiskey bottles. Accidental poisonings may occur in industry
due to carelessness or mishaps which expose workers to toxic substances. While
the potential for accidental poisonings in industry is great, safety standards
and regulations and the availability of emergency medical services today
prevent industry from being a source of many fatal intoxications.
Drug abuse may involve the use of
illicit drugs such as heroin or phencyclidine; the use of restricted or
controlled drugs such as cocaine, barbiturates, and amphetamine; or use of
chemicals in a manner contrary to their intended purpose — such as inhaling
solvents and aerosol products.
Suicide is a common manner of
death in cases of poisoning. In general, about twice as many men successfully
commit suicide as women. However, twice as many women attempt to commit suicide
with poison as men. The most common suicidal agent is carbon monoxide, a gas
generated by the incomplete combustion of carbonaceous compounds. Automobile
exhaust contains a substantial concentration of carbon monoxide. Allowing a car
motor to run in a closed garage is the usual method used by those who commit
suicide with carbon monoxide. While cyanide, arsenic, and other well known
poisons may be occasionally used as suicidal agents, most deaths result from
prescription drugs. Persons suffering from depression and other emotional
disturbances usually have available a supply of potent and, if taken in excess,
deadly drugs to combat the symptoms of their psychological disorders. Today,
most suicidal poisonings involve multiple drug ingestion; usually three to
seven different drugs are ingested at one time.
Murder by poison most commonly
occurs within the home, and the physician will seldom suspect a bereaved
husband, wife, son, or daughter of poisoning another family member. Also, there
is rarely any symptom of poisoning which cannot equally well be caused by
disease. Vomiting, diarrhea, rapid collapse, and weak pulse, all symptoms of
arsenic poisoning, may also be due to a ruptured gastric ulcer or an
inflammation of the pancreas or appendix. Likewise, both strychnine and tetanus
cause convulsions. Contracted pupils and narcosis may be from narcotic drugs or
brain lesions. However, there are circumstances which render a diagnosis of poisoning
moderately certain. The onset and progression of symptoms to rapid death
immediately after eating or drinking indicate acute poisoning, since bacterial
food poisoning has a delayed onset of symptoms. Most poisons do not produce observable changes in body tissue;
hence, in many instances of poisoning, the value of the pathologist’s
examination of the body is establishing that death was not due to natural
causes or traumatic injury and that there is no evidence for cause of death
except from possible poisoning. In most cases, toxicological analysis produces
evidence for murder by poison. Biotransformation is a term used to denote the
conversion by the body of a foreign chemical to a structurally different
chemical. The new compound is called a metabolite. Biotransformation of a drug
or poison usually, but not always, results in formation of a physiologically
inactive substance which is more readily excreted from the body than the parent
compound. Evidence of heroin or cocaine use is indicated by the presence of
their respective metabolites, morphine and benzoylecgonine. Most gases of
toxicological significance are not detectable in autopsy specimens. However,
some may be isolated from blood or lung tissue by aeration processes. Usually,
air samples are collected at the scene of exposure. Steam
Volatile Poisons are isolated by steam
distillation. The sample (blood, urine, or
a tissue homogenate) is made acidic with hydrochloric acid or basic with solid magnesium oxide. A stream of steam is passed through the sample and the volatile poisons are distilled off in an aqueous
distillate. Poisons
distillable from an acid medium include carbon tetrachloride, chloroform,
cyanide, ethanol, methanol, phenols, nitrobenzenes, and yellow phosphorus.
Poisons distillable from a basic medium include amphetamine, aniline, meperidine, methadone, and nicotine. Metals are isolated from
tissue by destroying all the organic matter comprising the tissue. The tissue
may be destroyed by excessive heat (dry ashing) or by boiling with concentrated
acids or strong oxidizing agents (wet ashing). Various methods may be used to
identify specific metallic poisons remaining in the ash. Nonvolatile
Organic Poisons are usually present in tissues
only in minute quantities. Some drugs (e.g., barbiturates) may be directly
extracted from tissue homogenates by organic solvents. However, many compounds
are often separated from the bulk of the tissue matrix by preparing a
protein-free filtrate of tissue. This filtrate is then subjected to selective
extraction with organic solvents under varying conditions of acidity. Using
such techniques, drugs are isolated into five subgroups.
A color test is a chemical
procedure in which the substance tested for is acted on by a reagent which
causes a change in the reagent, thereby producing an observable color or color
change. Color tests may be used to determine the presence of specific compounds
or a general class of compounds. The procedures are usually rapid and easily
performed. The greatest utility of color tests in toxicology is the rapid
screening of urine specimens, as the urine may be analyzed directly without
time-consuming extraction procedures. An example of color test is the
“Trinder’s test” for the detection of salicylates in blood or urine. A reagent
of ferric nitrate and mercuric chloride is mixed with 1 ml of blood or urine;
if salicylates are present, a violet color is observed. As in all other
toxicology testing, the presence of salicylates must be confirmed by another
method of analysis. A positive Trinder’s test is observed for salicylic acid (a
metabolite of aspirin), salicylamide, and methyl salicylate. A false-positive,
that is the development of a color when no salicylate is present, may be
observed in urine of diabetic patients excreting acetoacetic acid and in
patients receiving high therapeutic doses of phenothiazine drugs.
Microdiffusion analysis is used
for the rapid isolation and detection of volatile poisons. A simple
microdiffusion apparatus consists of a small porcelain dish with two separate
compartments, an inner well surrounded by an outer well formed between the
periphery of the wall of the inner compartment and the higher outside wall of
the dish. The outer well is the sample cell, to which a small quantity, 1 to 5
ml, of blood, urine, or tissue homogenate is added. To the inner well an
“absorbent” is added. The absorbent is a reagent or solvent in which particular
volatile substances will readily dissolve. After the sample and absorbent are
added to the proper cell, the dish is sealed with a viscous sealant material
and a ground-glass cover plate. If allowed to sit at room temperature or gently
heated, the volatile poison will diffuse from the sample into the atmosphere of
the dish and be entrapped by the absorbent solution, which often is a color
reagent. As the poison is liberated from the sample, the toxicologist may
observe a color formation or color change in the absorbent in the inner well.
Chromatography is a separation technique. The components of a sample mixture
are distributed between two phases, one of which is stationary while the second
one, the mobile phase, percolates through a matrix or over the surface of a
fixed phase. The components of a sample mixture exhibit varying degrees of
affinity for each phase, and as they are carried along by the mobile phase, a
differential migration occurs. Some components are retained on the stationary
phase longer than others, producing a separation of the compound. The retention
of a component by the stationary phase depends on several factors, including
the chemical and physical nature of the stationary and mobile phases, as well
as the experimental conditions, such as temperature or pressure. It is
essential, therefore, that pure reference standards be chromatographed under the
same conditions as the unknown materials. Compounds are tentatively identified
by comparing their retention on the stationary phase with that of the reference
standards. There are many varieties of chromatographic analysis; however, only
the three most commonly applied by toxicologists will be briefly discussed.
These are thin-layer chromatography (TLC), gas liquid chromatography (GLC), and
high-performance liquid chromatography (HPLC). Spectroscopy concerns the
absorption or production of radiant energy. The absorption of radiation is a
characteristic of all molecules; however, the wavelength of the absorbed
radiation may vary from X-rays through ultraviolet, visible, and infra-red and
on to microwave and radio frequencies. The spectrophotometer used to measure
the absorption of radiant energy consists of a radiation source, a sample cell
through which the radiation passes, and a detector for measuring the absorption
of the radiation. The wavelengths most applicable to toxicological analysis are
the ultraviolet, visible, and infra-red. The commercial instruments used for
measuring the absorption of these forms of light may vary from simple
colorimeters, used to measure absorption in the visible range, to highly
sophisticated spectrophotometers employing monochromatic light and sensitive
electronics to detect, amplify, and record low levels of radiation. The
physiological effects of most drugs and poisons correlate with the
concentration in the blood and establish that absorption has taken place.
Therefore, blood concentrations are often the best indicators of toxicity;
consequently, blood is a most valuable specimen to the toxicologist.
Interpretation of blood or tissue
values may be divided into three categories: (1) normal or therapeutic, (2)
toxic, and (3) lethal. A normal value is that concentration of a substance
found in the general population and which has no toxic effect on the body. For
example, cyanide is usually readily identified as a highly poisonous chemical;
however, minute quantities of cyanide are generated following the ingestion of
certain foods. Also, small amounts of cyanide are generated and absorbed during
tobacco smoking. Therefore, small amounts of cyanide are a normal constituent
in the body and low concentrations are tolerated without toxicity. Many heavy
metals, such as arsenic, lead and mercury, which are not essential to normal
body functions, are present in the general population due to environmental
contamination.
The rate of
biotransformation of a substance is genetically controlled and is often subject
to significant individual variations. If several individuals are given the same
dose of drug per body weight, the blood concentration of each may vary greatly due to a
difference in their rates of biotransformation of the drug.
Acknowledgements:
The Police Department;
https://www.politie.nl/mijnbuurt/politiebureaus/05/burgwallen.html and a Chief Inspector – Mr. Erik Akerboom ©
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