Transcript 10.4 – The Role of the Toxicologists

Toxicologists & Drug Analysis
Objectives

Describe techniques that
forensics toxicologists use to
isolate and identify drugs and
poisons.
Screening Tests

Use TLC, GC, Immunoassay
Immunoassay – very different
Based on specific drug antibody
reactions
Ability to detect small
concentrations
Best for detecting marijuana
Confirmation Tests

GC/MS
One step test of unequaled
sensitivity and specificity
Drug testing not related to
criminal matters
Drugs in Hair

Drugs remain in
 Bloodstream – 24 hours
 Urine – 72 hours
 Tested in Private labs, typical for workplace
screenings
 Hair nourished by blood flowing through capillaries near
root
 Drugs diffuse through capillary walls and become
permanently entrapped in hair’s protein structure
 Drug’s location becomes historical marker for delineating
drug intake
Heavy Metals

Group of poisons
Arsenic, Bismuth, Antimony, Mercury, Thallium
Reinsch Test
Dissolve body fluid or tissue in hydrochloric
acid solution then insert copper strip to solution
Appearance of silver or dark coating on copper
indicates presence of heavy metal
Confirm with inorganic analysis
Carbon Monoxide

One of the most common poisons
Primarily absorbed by red blood cells
Combines with hemoglobin to form
carboxyhemoglobin
Not enough hemoglobin left to carry
oxygen to tissues
Causes asphyxiation
2 Basic Methods for
Detection of CO

Spectrophotometric – visible spectrum
GC – liberates CO from blood
Calculate percent saturation
Greater than 50-60% = fatal
Fatal levels can be lower when in
combination with depressants
Arson Victim

High levels of carbon monoxide in
blood indicate that victim breathed in
products of fire and was alive when fire
began
Low levels = dead before fire started
Could have been placed there to destroy
evidence
Significance of findings

Interpreting results is the most
difficult chore
Blood concentration levels can be
used to estimate pharmacological
effects of drugs
Significance of findings

Before drawing conclusions, toxicologists
must consider other factors – age, physical
condition, drug history, tolerance
 Prolonged use can make an individual less
responsive to drug’s effects
 Additive or synergistic effects provided by
interaction of 2 or more drugs


Concentration in urine is poor indicator
because formed outside circulatory system
and drug levels can build up over long
periods of time
Drug can be found in urine 1-3 days after taken
and long after other effects have disappeared
Best used to corroborate other findings
Drug Recognition
experts (DRE)

1970s, LAPD developed and tested clinical
and psychophysical examinations that police
officers could use to identify and
differentiate between types of drug
impairment
Evolved into national program
Standardized methods
Not a substitute for toxicology testing
10.7 Questions
1. What is the difference between a screening test and a
confirmation test?
2. What are the three screening tests most widely used for forensic
toxicology? What is the confirmation test of choice?
3. Which of the following is not classified as a heavy metal?
A. Lead
B. Arsenic
C. Mercury
D. Thallium
4. Explain how inhaling carbon monoxide can cause death.
5. Name at least three factors in addition to blood concentration
levels that must be considered before drawing conclusions
about a subject’s drug induced behaviors.
6. Why is the concentration of a drug present in urine a poor
indicator of how extensively an individual’s behavior or state is
influenced by the drug?