chapter 10 forensic toxicology. what is forensic toxicology? the detection and identification of...

Chapter 10Chapter 10

Forensic ToxicologyForensic Toxicology

What is Forensic Toxicology?

• The detection and identification of drugs or poisons present in body fluids, tissues and organs.

The Biggest Culprit

• Alcohol is the most abused “drug” in the West and most likely the world.

• 40% of all traffic accidents are alcohol related.

• So the most numbers of samples sent to forensic toxicology labs are alcohol related.

What is Alcohol?• Organic compound • Carbon and hydrogen backbone with at least one

hydroxyl group (OH)• Many types, depending on the number of carbons

present• Humans consume Ethyl Alcohol or Ethanol

• Colorless liquid• Produced when yeast ferment grain, fruit and other vegetation such as potatoes

Toxicology of Alcohol

What happens to alcohol once it enters the body?

- Consumption / Ingestion- Absorption into bloodstream

- It then crosses the blood-brain barrier into neurons, affecting the Central Nervous System (CNS)

- Elimination - Oxidation (alcohol is changed to other products)- Excretion (alcohol is unchanged)

How do we measure alcohol levels?

• The most obvious measure of intoxication would be to see how much an individual has consumed

• This is impossible for a forensic toxicologist for several reasons:– He wasn’t present (Duh!)– Person’s body weight varies– Rate of alcohol absorption into bloodstream varies

• The Absolute (no pun intended) best way to check for intoxication would be to check brain tissue

• This is also impossible for obvious reasons – unless the person in question is dead.

This is your brain on ethanol

The next best thing

• So forensic toxicologists concentrate on blood.

• Blood circulates the consumed alcohol to ALL body tissues

• The concentration of alcohol in the blood is directly proportional to the concentration of alcohol in the brain

The Route Alcohol Takes

• Mouth Esophagus Stomach Small Intestine Bloodstream

• Alcohol is absorbed across the lining of the small intestine, into the bloodstream (some absorption can occur across stomach wall also)

• This happens within minutes of consumption • The blood concentration levels keep increasing as

more and more alcohol gets absorbed across S.I.

The path alcohol follows to your brain,

via bloodstream

The Rate of Absorption

Several factors affect the rate of absorption:

1. The amount of alcohol consumed

2. What was the alcohol content (or proof) of the beverage?

3. The rate at with it was consumed (1 beer over 1 hour, or 1 beer over 1 minute)

4. How much food was in the stomach?

You need to absorb this material!

• The longer it takes for all the alcohol consumed to be absorbed, the lower the peak alcohol concentration in the bloodstream.

• Food in stomach hinders/slows absorption

Empty vs. Full Stomach

After Absorption

• When all the alcohol is absorbed, its levels will be equally distributed in the “watery” tissues of the body (so not in fat, hair, nails, bones, etc.).

• If blood is not available (dead body) – a forensic toxicologist can work with other body fluids and tissues – Cerebrospinal fluid, vitreous humor, or brain

BAC – Blood Alcohol Concentration

• It is usually measured as mass per volume and expressed as a percentage.

• For example, a BAC of 0.02% means 0.02 grams of alcohol per 100 grams of an individual's blood, or 0.2 grams of alcohol per 1000 grams of blood.

• BAC can vary according to the person’s tolerance and metabolic rate

Can you tolerate it?

• Tolerance to alcohol varies from one person to another, and can be affected by such factors as genetics, adaptation to chronic alcohol use, and synergistic effects of drugs.

Metabolism

• The breakdown of chemicals, including alcohol

• The elimination of alcohol from the body depends upon the individual’s metabolism.

Elimination by Oxidation• Nearly all alcohol (95-98%) gets oxidized.• Oxidation – Ethanol is oxidized to produce carbon dioxide

and water• Oxidation occurs almost entirely in the cells of the liver.• Oxidation of ethanol is performed by an enzyme called

Alcohol Dehydrogenase in the following process.

(Acetaldehyde) (Acetic Acid)

The Acetic Acid is then oxidized further into CO2 and H2O

Rate of Ethanol Oxidation

• The rate of elimination via oxidation varies from individual to individual, depending upon their metabolic rate. Oxidation is also called “burn-off” and it reduces blood-alcohol concentrations.

Absorption must be complete in order for burn-off to reduce BAC levels.

Elimination by Excretion

• The 2% of ethanol that is not eliminated by oxidation is excreted through the breath, urine and perspiration.

• This excreted alcohol is not changed chemically – it remains ethanol.

Breath Dragon (Alveolar breath)• The amount of alcohol

exhaled in the breath is directly proportionate to the concentration of alcohol in blood.

• When air is exhaled, it contains CO2 and alcohol

• Hence the “Breathalyzer” Test

Alveolar Breath

Pulmonary Vein

Pulmonary Artery

Breathalyzer

• A breathalyzer (or breathalyser) is a device for estimating blood alcohol content (BAC) from a breath sample.

• “Breathalyzer” is a brand name and was originally made by Smith and Wesson, but now is a generic term used for all such devices.

• Measures alcohol found in alveolar breath.

Where’s the Proof?

• Alcoholic proof is a measure of how much ethanol is in an alcoholic beverage, and is approximately twice the percentage of alcohol by volume

• The proof number is twice the percentage of the alcohol content measured by volume at a temperature of 60 °F (15.5 °C). Therefore "80 proof" is 40% alcohol by volume, and pure alcohol is "200 proof".

What’s in a drink?

Legal BAC Levels

• The alcohol level at which a person is considered to be legally impaired varies by country.

• In the US the BAC limit is 0.08%

• However, drivers of commercial vehicles have a limit of 0.04%

• Sweden is one of the countries with the lowest level of 0.02%

When can you drink legally?

• As of 2007, all U.S. states have a minimum purchase age of 21. Unlike the states, Puerto Rico, the U.S. Virgin Islands, and Guam have a minimum purchase age of 18.

• In Mexico and Canada the drinking age is lower than 21, which encourages young people to go to these countries if they live near the border.

Normal brain of six week old baby The brain of a six-week old baby with “Fetal Alcohol Syndrome”

Field Sobriety Testing

• Horizontal Gaze Nystagmus

• Walk and Turn Test

• One Leg Stand Test

Horizontal gaze nystagmus

Horizontal gaze nystagmus

• The officer attempts to estimate the angle at which the eye begins to jerk

• "nystagmus" is medical jargon for a distinctive eye oscillation

• if this occurs sooner than 45 degrees, it theoretically indicates a blood-alcohol concentration over .05%.

• The smoothness of the eye's tracking the penlight (or finger or pencil) is also a factor, as is the type of jerking when the eye is as far to the side as it can go.

Walk and Turn

One leg stand

Collection and Preservation of Blood Evidence

• Must be drawn aseptically under medically accepted conditions

• An anticoagulant such as EDTA or potassium oxalate is added – to prevent clotting

• A preservative such as sodium fluoride is added to prevent bacterial growth

• Stored in refrigerator• Tested at a lab or medical facility

Other toxins in blood

• Narcotics (Heroine)

• Non-narcotic substances (Cocaine)

• Carbon Monoxide (CO)

• Heavy metals such as lead, mercury, arsenic, etc.

ACID vs. BASE Drugs

• Barbiturates and Aspirin (Acetylsalicylic acid) are acidic drugs with pHs lower than 7.

• Phencyclidine (PCP), Methadone, Amphetamines and Cocaine are basic drugs with pHs higher than 7.

Carbon Monoxide

• CO is a by product of combustion of organic materials (Gas, fires, etc.)

• CO has a greater affinity to hemoglobin than does CO2 or O2.

• CO + hemoglobin = carboxyhemoglobin• So once it is inhaled an enters the

bloodstream, it competes with O2 for hemoglobin.

• Too much CO kills – death by asphyxiation

The fate of other drugs in the bloodstream

• Heroin – gets converted into morphine once in the bloodstream

THE END