Title: Forensic Toxicology
1Chapter 12
2Objectives
- Students should gain an understanding of
- The postmortem analysis performed by a
toxicologist - The many factors that make postmortem
toxicological information difficult to interpret - Alcohols effects on human performance
- The way in which alcohol is absorbed and
eliminated from the body - The measurement of blood alcohol concentration
(BAC) - Alcohol-related vehicle laws
3Introduction
- Postmortem analysis
- Investigates the presence of drugs, gases,
metals, and other toxic chemicals in human fluids
and organs - Determines their role, if any, in the death
- Human performance toxicology
- Measures the amount of alcohol or drugs in a
living persons blood or breath - Estimates their role in modifying human
performance or behavior
4Postmortem Toxicology (1 of 5)
- Begins with a case history of the deceased
- Includes age, sex, weight, medical history,
medication before death, autopsy findings, drugs
available to decedent, and interval between onset
of symptoms and death - Includes analyses for poisons as diverse as
prescription drugs, drugs of abuse, chemical
products, and gases
5Postmortem Toxicology (2 of 5)
- Collection of postmortem specimens
- All body fluids and organs in which chemicals
might concentrate are collected during the
autopsy. - Specimens should be collected before the body is
embalmed. - In cases of decayed bodies, analysis may be done
on bone marrow, fluid in the eye, or hair. - Maggots feeding on the corpse have been tested
for drugs and used as evidence.
6Postmortem Toxicology (3 of 5)
- Analysis of toxicology specimens
- The gastrointestinal tract is often analyzed
first, followed by urine. - Analysis focuses on the tissues of organs where
the concentration of drugs may be the greatest. - Specimens should be collected as soon as possible
after death. - Presumptive testing is performed first to detect
the presence or absence of drugs.
7Postmortem Toxicology (4 of 5)
- Analysis of toxicology specimens
- A positive immunoassay test leads to a
confirmation test (usually gas chromatographymass
spectrometry). - Each compound gives a characteristic fragment
spectrum. - A computer compares the samples spectrum to a
reference library. - The toxicologist tests for an inorganic substance
if the case study suggests poisoning.
8Postmortem Toxicology (5 of 5)
- Interpretation of toxicological information
- The toxicologist must determine how the poison
entered the body and whether enough poison was
ingested to cause death. - The highest concentration of poison is usually
found where it entered the body. - Toxicology analysis may be able to estimate when
the poison was dispensed.
9Human Performance Testing (1 of 3)
- Most common human performance tests are those to
determine if someone is driving a car under the
influence of alcohol or drugs - Amount of alcohol in a persons body is expressed
as blood alcohol concentration (BAC) - Studies have shown a direct relationship between
increased BAC and increased risk of accidents
10Human Performance Testing (2 of 3)
- Field sobriety testing assesses a drivers
degree of physical impairment - Interview with officer
- Preliminary examination
- Eye examination
- Divided attention psychophysical tests
- Vital signs exam
- Dark room exam
- Muscle rigidity exam
- Examination for injection site
- Suspects statements
- Opinions of evaluator
- Toxicology exam
11Human Performance Testing (3 of 3)
- BAC levels
- Low BAC alcohol affects cerebral function
- High BAC medullar function is affected
- BAC lt 0.06 sober
- BAC 0.35 coma
12Alcohol and the Law (1 of 2)
- 1939 first drunk driver law passed that used
BAC as a basis for determining sobriety (Indiana)
- 1943 researchers discovered that abstainers were
more sensitive to alcohol than moderate or heavy
drinkers - 1964 Grand Rapids Study
- Established the scientific foundation for per
se legislation, which triggers sanctions for all
drivers with a certain BAC - Validated the Breathalyzers effectiveness and
accuracy
13Alcohol and the Law (2 of 2)
- Legal limit for first per se laws was 0.15
- Individual states have passed their own laws and
strengthened DUI penalties - Citizen-advocacy groups, such as MADD, have
driven legislation - 1992 DOT recommended that all states adopt 0.08
as the legal definition of drunk driving
14Alcohol Metabolism (1 of 3)
- Absorption of alcohol into the body
- Ethyl alcohol is absorbed into the bloodstream
largely from the stomach and small intestine - Absorption produces BAC
15Alcohol Metabolism (2 of 3)
- Factors that influence the rate at which alcohol
enters bloodstream - Rate of gastric emptying
- Presence of food
- Concentration of alcohol taken in
- Type of beverage
- Rate at which alcohol is consumed
16Alcohol Metabolism (3 of 3)
- Elimination of alcohol by oxidationreduction
reaction - During elimination, alcohol is transported to the
liver, where enzymes catalyze the oxidation of
the alcohol. - The end product is sometimes more toxic than the
chemical being oxidized. - More than 90 of the ethyl alcohol that enters
the body is oxidized to acetic acid.
17Measurement of Blood Alcohol Concentration (1 of
2)
- Estimating the BAC from absorption-elimination
data - The most obvious way to measure intoxication is
to record the amount and type of beverage
consumed. - Analyses are often performed hours after an
accident, when metabolic processes have reduced
the BAC. - Toxicologists can use rates of absorption and
elimination to estimate the BAC at the time of
the accident.
18Measurement of Blood Alcohol Concentration (2 of
2)
- Estimating the amount of alcohol in the
circulatory system - Measurement of the concentration of alcohol in
the persons breath - Breath sample is easy to collect at the scene
- Direct chemical analysis of a blood sample
- Blood alcohol test is considered more reliable
19Breath Tests for Alcohol (1 of 3)
- Breathalyzer
- Includes two parts
- Instrument that calculates the BAC
- Attached mouthpiece that samples the breath
- Indirectly measures the amount of alcohol in a
persons breath by measuring the absorption of
light by potassium dichromate before and after
its reaction with alcohol - Must be continually replenished with fresh
chemical reagents
20Breath Tests for Alcohol (2 of 3)
- Intoxilyzer
- Measures the infrared radiation absorption in a
specific wavelength to confirm the presence of
organic chemicals - Detects only ethyl alcohol
- Requires suspect to blow into a mouthpiece to
give a sample
21Breath Tests for Alcohol (3 of 3)
- Alcosensor
- The alcohol fuel cell consists of a porous,
chemically inert layer that is coated on both
sides with a thin platinum layer. - Any ethyl alcohol present in the breath samples
is converted to acetic acid. - A microprocessor measures the electrical current
and converts the measured electrical current into
a BAC.
22Blood Tests for Alcohol (1 of 3)
- Gas chromatograph is the method of choice for
identifying BAC - Major drawback is the requirement of a blood
sample
23Blood Tests for Alcohol (2 of 3)
- Collection and preservation of blood from a
living person - Clean the skin with nonalcoholic disinfectant
- Remove blood with a sterile needle
- Add preservative to the sample
- Refrigerate the sample
- Collection of samples from a cadaver
- Collect blood samples from multiple sites or use
tissue samples other than blood
24Blood Tests for Alcohol (3 of 3)
- Gas chromatography analysis of BAC
- Ethanol has a retention time of 1.9 minutes.
- GC separates ethanol from acetaldehyde and
acetone, which reach the detector at different
times than ethanol. - A calibration curve is constructed that relates
the area under each peak to the concentration of
each component in the standard.
25Noninvasive Alcohol Testing
- Limitations of standard techniques
- Require handling of body fluids
- Require a compliant subject
- Can take hours for results or require subject to
be conscious enough to blow into the instrument - Touch-based instrument
- Uses near-infrared reflectance spectroscopy to
measure alcohol on the subjects skin - Measures alcohol levels in 90 seconds by shining
a beam of near-IR light on the forearm