Forensic Toxicology - PowerPoint PPT Presentation

1 / 25
About This Presentation
Title:

Forensic Toxicology

Description:

Chapter 12 Forensic Toxicology Objectives Students should gain an understanding of: The postmortem analysis performed by a toxicologist The many factors that make ... – PowerPoint PPT presentation

Number of Views:141
Avg rating:3.0/5.0
Slides: 26
Provided by: NCC102
Category:

less

Transcript and Presenter's Notes

Title: Forensic Toxicology


1
Chapter 12
  • Forensic Toxicology

2
Objectives
  • 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

3
Introduction
  • 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

4
Postmortem 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

5
Postmortem 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.

6
Postmortem 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.

7
Postmortem 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.

8
Postmortem 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.

9
Human 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

10
Human 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

11
Human 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

12
Alcohol 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

13
Alcohol 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

14
Alcohol 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

15
Alcohol 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

16
Alcohol 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.

17
Measurement 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.

18
Measurement 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

19
Breath 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

20
Breath 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

21
Breath 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.

22
Blood 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

23
Blood 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

24
Blood 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.

25
Noninvasive 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
Write a Comment
User Comments (0)
About PowerShow.com