Toxicology

• Author: D. P. Lyle
• Pages: 205-242

Toxicology 205

CHAPTER 12

TOXICOLOGY

Toxicology is the science of drugs, poisons, and toxins. The forensic toxi-

cologist is the scientist who deals with these substances and he, along with

the toxicology laboratory, are critical components of every crime lab. Since

drugs and poisons are often involved in accidental, suicida l, and homicidal

deaths, this science is critical to ma ny forensic investigations. The toxicolo-

gist is typically cha rged with analyzing unk nown substances, evaluating

drug involvement in abnormal behavior and responsibility for accidents,

assessing the role of drugs or poisons in the cause and manner of death,

and even testing employees in the workplace for illicit drugs.

You’ve no doubt heard the words poison, toxin, and drug, but what do

these terms actually mean? Are they simply dif ferent ways of saying the

same thing? Though you might think that a poison kills, a t oxin harms,

and a drug cures, these term s are indeed used almost interchangeably. The

reason is that what can cure can h arm, and what can har m can kill.

What Is a Poison?

If there are no real differences between a drug, a toxi n, and a poison, what

exactly is a poison? The basic definition of a poison is any substance that if

taken in sufficient quantities, causes a harmful or deadly rea ction. The key

206 Toxicology

phrase here is “sufficient quantities,” since anything and everything can be

a poison.

The toxicity of any substance depends upon how much and over what

time period it enters the body. Small amounts taken over a long period of

time, though they can accumulate and become deadly, usually cause little

harm, while a large dose ta ken all at once can prove deadly very quickly.

For example, arsenic is a deadly poison that if taken in suff icient amounts

can ki ll fairly quic kly, but did you know that you li kely have arsenic in your

body right now? If you’re a smoker, you have more than a little bit. The

same goes for the deadly poisons mercury and cyanide. These substance s

are in the environment and can’t be avoided, but they are in such small

quantities that they cause little if any real harm.

Even water and oxygen ca n be poisonous. How can these two life essen-

tials be deadly? If you drink too much water, it will severely dilute the

sodium and potassium in the blood and tissues of the body, damage the kid-

neys, and lead to coma and death. In fact, there’s a psychiatric syndrome,

often associated with schizophreni a and other psychiatric disease, ca lled

compulsive water drinking, in which massive amounts of water are con-

sumed and sometimes death follows. Pure oxygen, if breathed too long, will

irreparably damage the lungs and w ill also lead to death.

The same is true for prescription medications. The heart drug digi-

talis, which comes from the foxglove plant and has been used for over a

hundred years to treat heart fai lure and many types of abnormal heart

rhythms, is a deadly poison. Too much can lead to nausea, vomiting, and

death from dangerous changes in the rhythm of the heart. It’s ironic that it

can treat some abnormal heart rhythms while at the same time can c ause

other more deadly rhythms. It’s all about the dose. The right dose is medi-

cation; the wrong dose is poison.

Historical Perspective

Toxicology is a relative new science even though its roots date back nearly

200 years. As with most medica l and forensic scientific knowledge, the evo-

lution from basic science to practical usefulness takes time, sometimes cen-

turies. The typical pattern i s that a new basic science discovery will enter

Toxicology 207

the world of medicine and help resolve some medical problem and only then

enter the forensic arena, where it is applied to criminal investigations.

Arsenic is an excellent example, and the steps that led to a reliable test for

arsenic are indicative of how many toxicological procedures developed.

For centuries arsenic was a common poison, but there was no way to

prove it was the culprit in a suspicious death. Scientists first had to isolate

and then identify arsenic trioxide, the most common toxic form of arse-

nic, in the human body and only then could arsenic poisoning become a

provable cause of death. The milest ones in this development were a s follows:

• 1775: Swedish chemist Carl Wilhelm Scheele isolated arsenic by

employing chlorine, water, zinc, and heat to convert arsenic-contain-

ing substances into arsine gas. W hen this gas contacted a cold ves-

sel, arsenic would collect on the vessel’s surface.

• 1787: Similarly, Johann Metzger showed that if an arsenic-contain-

ing substance was heated with cha rcoal, a shiny, black “arsenic mir-

ror” would form on a cold plate held over the coals.

• 1806: Valentine Rose first showed that arsenic could be uncovered

in the human body when he treated the stomach contents of victims

of arsenic poisoning with potassium ca rbonate, calcium oxide, and

nitric acid, resulting in the production of arsenic trioxide. This could

then be tested and confirmed by Metzger’s test.

• 1813: French chemist Mathieu Joseph Bonaventure Orfila devel-

oped a method for isolating arsenic from dog tissues, proving that

ingested arsenic is distributed throughout the body. His book, Trea-

tise on General Toxicology, is considered by many to be the first toxi-

cological text and Orf ila the “Father of Toxicology.”

• 1821: Sevillas used similar techn iques to identify arsenic in the

stomach and urine of poisoned individuals. This is ma rked as the

beginning of the field of forensic toxicology.

• 1836: James Marsh developed an easier and more sensitive version

of Scheele’s original test , in which the “arsenic mirror” was collected

on a plate of glass or porcelain. The Marsh test beca me the stan-

dard and is the basis of the more modern method, the Reinsch test.