Toxicology (page 2)
Scope of Work
There are several areas of specialization within the
field, which offer a variety of career paths. One, postmortem
toxicology, involves the determination of the contribution
of drugs or other chemicals to the circumstances of the
death. The forensic toxicology laboratory contributes
a critical perspective to a death investigation, working
with a forensic pathologist, and scene investigators,
to determine which drug analyses or poisons are involved
(Figure 1). This is accomplished by performing tests on
body fluid and tissue samples received from the forensic
pathologist, and then assisting with the interpretation
of the findings. This effort requires knowledge of analytical
chemistry techniques, including instrument methods (Figure
2) utilizing gas and liquid chromatographic techniques,
mass spectrophotometry, UV-Visible spectrophotometry,
flame emission and absorption spectrophotometric techniques,
antigen-antibody immunoassay methods, as well as, traditional
qualitative and quantitative methods of analysis. An inquiring
mind is required, along with the ability to apply knowledge
of chemistry and pharmacology to solving real world puzzles.
(Figure 3).
Figure 2: Instrumental automation
as exemplified by the automated sampler which can extend
the work day and lead to increased case analysis and decreased
turnaround time.
Figure 3a: The ion source
in a mass spectrophotometer. Gas chromatography/ mass
spectrophotometry (GC/MS) is a technology that represents
a definitive means of identifying the presence of a substance.
Other forensic toxicologists work with law enforcement
agencies in the investigation of crimes in which an individual's
drug or alcohol use is an element of the crime or may
be a defense. This involves the same application of techniques
as in the death investigation setting, but typically deals
with lower concentrations of drugs, requiring greater
sensitivity of testing. The interpretation of the test
results in this area is the greatest challenge, applying
knowledge from clinical and medical studies, and experience
in the field, to give an opinion about the affects of
a drug or combination of drug on an individual at the
time of the crime or accident.
Workplace drug testing and forensic urine drug testing
has become an important aspect of employment and industries
with hazardous work conditions or jobs affecting the safety
of others. This aspect of forensic toxicology is usually
confined to the detection of specific drugs of abuse in
a large number of urine samples with some laboratories
performing tests on over 10,000 urine samples each day.
As with all of the forensic environments, there is a strong
emphasis of record keeping, chain-of custody documentation,
stringent quality control, and data management. The challenge
is to get the testing of such large numbers done as reliably
and efficiently as possible. Developments in this area
include the evaluation of specimens other than blood or
urine for drug testing, such as sweat, hair, and saliva.
Forensic toxicology testing also contributes in other
areas, as varied as wildlife crimes involving the poisoning
of animals, the use of drugs to facilitate sexual assault,
and drug use and doping in human and animal sports. In
all of the aspects of forensic toxicology, the interpretation
of the results is a consistent challenge. The results
obtained are determined by tests that are complex and
difficult for most juries and lawyers to fully understand
and appreciate. Therefore, the toxicologist must have
or develop the ability to describe the process involved,
the findings determined, and the relevant interpretation
derived in a straightforward and easily understood manner.
Figure 3b: A selective ion
monitored (SIM) graphic taken from a derivatized GC/MS
analysis. From this data the presence of a specific
drug metabolite, 6-acetylmorphine
(6-AM), is confirmed to be
present in an acute heroin death. 6-AM is a drug metabolite
which specifically documents heroin use.
