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FORENSIC TOXICOLOGY. Chapter 6. Introduction. Toxicologists: detect and identify drugs and poisons in body fluids, tissues, and organs identify a drug overdose or monitor the intake of drugs

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  • detect and identify drugs and poisons in body fluids, tissues, and organs

  • identify a drug overdose or monitor the intake of drugs

  • work in crime laboratories, medical examiners’ offices, hospital laboratories and health facilities

  • measure the amount of alcohol or other abused drugs in the body for violations of criminal law


Toxicology of alcohol
Toxicology of Alcohol

  • Alcohol, or ethyl alcohol, is a colorless liquid normally diluted with water and consumed by many as a beverage.

  • Like any depressant, alcohol principally effects the central nervous system, particularly the functions of the brain.


Alcohol levels
Alcohol Levels

  • Appears in the blood a few minutes after it has been consumed.

  • Blood alcohol concentration slowly increases as it is absorbed from the stomach and the small intestine.

  • Once its complete, absorbed blood alcohol level reaches maximum.

  • The post-absorption period begins after maximum BAC is reached.

  • Alcohol concentration slowly decreases until level returns to a zero.


Absorption rates
Absorption Rates

Many factors can effect

alcohol absorption rates:

  • Time it takes to consume the drink

  • The alcohol content

  • The volume of the drink

  • Presence/absence of food in the stomach and the type of food

  • Gender

  • Body weight and height

  • Genetics


  • Is eliminated from the body through breakdown (oxidation) and excretion.

  • Alcoholic oxidation takes place in the liver.

  • Alcohol is excreted in breath, urine, and sweat.

  • Is measured as the quantity of alcohol present in the blood (BAC) or the alcohol content in the breath

  • The amount of alcohol exhaled in the breath is directly proportional to the alcohol concentration in the blood


Alcohol circulatory system
Alcohol & Circulatory System

  • Humans have a closed circulatory system containing heart, arteries, veins and capillaries

  • Alcohol is absorbed into the blood stream from the stomach and small intestines.

  • Some alcohol in the blood is carried to the liver where the process of alcohol-breakdown (oxidation) begins.


Alcohol circulatory system1
Alcohol & Circulatory System

  • Other blood, carrying alcohol, moves to the heart and is pumped to the lungs.

  • In the lungs, carbon dioxide and alcohol leave the blood and oxygen enters the blood in the air sacs known as alveoli.

  • There the carbon dioxide and alcohol are exhaled during normal breathing.

Breath testers
Breath Testers

  • Breath testers are designed to analyze a specific volume of breath.

  • The captured breath is exposed to infrared light.

  • The infrared light source allows the instrument to measure the (BAC) in the captured breath.

  • Other breath testing devices use fuel cells.


Portable breath testers
Portable Breath Testers

Many types of breath testers are designed to analyze a set volume of alveolar breath.

The captured breath is exposed to infrared light.

It’s the degree of the interaction of the light with alcohol in the captured breath sample that allows the instrument to measure a blood alcohol concentration in breath.

Field testing
Field Testing

  • Law enforcement officers use field sobriety tests to estimate physical impairment by alcohol.

  • The HGN (horizontal gaze nystagmus), walk and turn, and the one-leg stand are reliable psychophysical tests.

  • A portable, handheld, roadside breath tester can be used to determine a preliminary BAC.

  • A confirmation blood test is always performed


Confirmation blood testing
Confirmation Blood Testing

  • Gas chromatography is used to determine specific alcohol levels in blood.

  • Blood must always be drawn under controlled conditions by qualified personnel.

  • A nonalcoholic disinfectant must be applied before the suspect is stuck with a sterile needle.

  • The blood is collected in a glass tube that contains anticoagulant/preservative and refrigerated.


Alcohol and law
Alcohol and Law

  • The American Medical Association and the National Safety Council convinced the separate states to agree on an under-the-influence standard:

  • 1939 to 1964 the BAC was set at 0.15 %

  • 1965 the BAC was lowered to 0.10 %

  • 1972 BAC was lowered again to 0.08 %


Oklahoma university police bac calculator
Oklahoma University Police BAC Calculator

  • Web address:

    Theoretical BAC based on number/type drink, weight and hours drinking

Alcohol and law1
Alcohol and Law

  • In 2003, states adopted the 0.08 % “per se” level.

  • To prevent refusal to take a test for alcohol consumption, the National Highway Traffic Safety Administration recommended an “implied consent” law:

  • Adopted by all states by 1973, this law states operating a motor vehicle on a public highway automatically requires that the driver will submit for a test for alcohol intoxication or be subject to loss of the license.


Role of the toxicologist
Role of the Toxicologist

  • A toxicologist must be able to identify many drugs and poisons.

  • The toxicologist examines body fluids and/or organs for the presence of drugs and poisons.

  • If supportive evidence, such as the victim’s symptoms, a postmortem pathological exam, or analysis of the victim’s personal effects, the toxicologist is forced to use general screening procedures with the hope of narrowing thousands of possibilities to one.


Role of the toxicologist1
Role of the Toxicologist

  • The toxicologist is not dealing with drugs at the concentration levels found in powders and pills, having been digested and distributed throughout the body.

  • The body is an active chemistry laboratory - few substances enter and completely leave the body in the same chemical state.

  • Toxicologists must be prepared to assess the toxicity of the drug or poison.


Toxicology analysis
Toxicology Analysis

  • The forensic toxicologist must successfully detect, isolate, and specifically identify toxic drug substances.

  • Once the drug has been extracted from appropriate biological fluids, tissues and organs, the toxicologist can identify the drug.

  • Most drugs are either acidic or basic.

  • Identifying abused drugs requires two-steps:

    1) screening

    2) confirmation.


The screening step
The Screening Step

  • A screening test is used to provide a general classification of the

    drug(s) contained in a specimen

  • Screening tests must be verified with a confirmation test

  • The most common screening tests are: thin-layer chromatography

    gas chromatography



The confirmation step
The Confirmation Step

  • Gas chromatography/mass spectrometry the confirmation test of choice

  • GC separates the sample into its components

  • MS represents a unique “fingerprint” pattern that identifies the components.

  • The toxicologist may be required to state the effects of the drug(s) on the natural performance or physical state of the suspect/victim