Toxicology is the study of the harmful effects of chemicals and toxins on living organisms. Forensic toxicologists play an important role in determining causes of death, especially in cases of suspected poisoning or overdose. They analyze samples like blood, urine, tissue, and hair to identify toxins and dose levels. Various factors must be considered like chemical properties, route of exposure, and individual vulnerability. Common toxins investigated include arsenic, cyanide, carbon monoxide, and heavy metals like lead and mercury. Breathalyzers and blood alcohol content measurements are used to prove alcohol intoxication.

1. Chapter 8 – Toxicology

2. Toxicology
the study of the adverse effects of chemicals
or physical agents on living organisms
Mathieu Orfila –father of toxicology

3. Forensic Toxicology
Postmortem—medical examiner or coroner
Criminal—motor vehicle accidents
Workplace—drug testing
Sports—human and animal
Environment—industrial, air, water, soil catastrophic, terrorism
Consumer – foods, cosmetics, over the counter drugs

4. Why we need forensics
toxicologists
Death unattended by a physician or occurring under
violent, unusual or sudden unexplained conditions
happens in approximately 20% of the population and
requires a medical/legal investigation

5. Forensic Toxicologist
☠ Determines if the toxin
☠ Caused the death – a lethal dose
☠ Contributed to death
☠ Caused impairment
☠ Explains behavior

6. If poison is suspected first step would be to take a
blood sample
Homicide poisoning mimics medical situations, a heart
attack or diabetic coma. This makes determining the
cause of death difficult.

7. Things to consider
Dosage
Chemical or physical form of the substance
Mode of entry into the body
Body weight and physiological conditions of the victim,
including age and sex
Time period of exposure
Presence of other chemicals in the body or in the dose

8. Toxicology Terms
Time of exposure
Chronic exposure – long period of time
Acute toxicity – immediate effects
Other chemicals/drugs in body
Synergism – combination exceeds individual effects
Antagonism – combination decreases individual effects
Chelating agent – cancels out the poison - antidote

9. Toxicity Classification

10. To Prove a Case
Prove a crime was committed
Motive
Intent
Access to poison
Access to victim
Death was homicidal
Death was caused by poison

11. Forensic Autopsy
Look for:
Irritated tissues
Characteristic odors
Mees lines—single transverse white bands on nails
Order toxicological screens
Postmortem concentrations should be done at the scene for
comparison.
No realistic calculation of dose can be made from a single
measurement.

13. Used for Analysis
Blood Liver tissue
Urine Brain tissue
Vitreous humor of eyes Kidney tissue
Bile Hair/nails
Gastric contents

14. Types of Poisoning
 Arsenic
 Cyanide
 Carbon Monoxide
 Ricin
 Lead Poisoning
 Mercury Poisoning

15. Arsenic
Claimed most victims
No odor, no taste
Fount in insecticides, pesticides and paints
Inhaled or swallowed – more than 90% absorbed into
blood

16. Cyanide
Rapid acting – kills in minutes
Used in photo processing
Colorless gas
Stops cellular respiration and ATP synthesis
Cells cant use oxygen

17. Carbon Monoxide
Colorless, odorless, tasteless
Faulty heating systems, car exhaust, fires
Absorbed through lungs

18. Ricin
Twice as deadly as cobra venom, two-tenths of a
milligram is a lethal dose.
Protein
Inhaled, injected, ingested
Potential terrorist – Al Queda
Death 36 – 72 hrs

19. Lead Poisoning
Lead compounds not highly poisonous, but chronic
exposure can lead to health problems
Lead based paints – banned in ’78
Tastes sweet
Still 38 million houses with lead paint

20. Mercury Poisoning
odorless, colorless, and tasteless
Disturbances in sensations ("pins and needles" feelings,
numbness) usually in the hands feet and sometimes around
the mouth
Lack of coordination of movements
Impairment of speech, hearing, walking
Muscle weakness, skin rashes, mood swing
Amalgam dental fillings
consume mercury-contaminated fish
exposed to spilled mercury

21. Alcohol
Alcohol appears in blood within minutes of consumption; 30–90
minutes for full absorption
About 5 percent is excreted unchanged in breath, perspiration, and
urine
Rate of absorption Signs of Alcohol Poisoning
Amount of alcohol consumed
Cold, clammy, pale, or bluish skin
The alcohol content of
the beverage Unconscious
Time taken to consume it Slow or irregular breathing
Puking repeatedly or uncontrollably
Quantity and type of food
present in the stomach
Physiology of the consumer

22. BAC – Blood Alcohol Content
Expressed as percent weight per volume of blood
Legal limit in all states is 0.08 percent
Burn-off rate of 0.015 percent per hour, but can vary

23. Henry’s Law
When a volatile chemical is dissolved in a liquid and is
brought to equilibrium with air, there is a fixed ratio
between the concentration of the volatile compound in
the air and its concentration in the liquid; this ratio is
constant for a given temperature.
THEREFORE, the concentration of alcohol in breath is
proportional to that in the blood.
1 ml of blood will contain nearly the same amount of
alcohol as 2,100 ml of breath.

24. Breathalyzer
Collects and measures alcohol content of breath
Breath sample mixes with 3 ml of 0.025 percent K2Cr2O7 in sulfuric
acid and water:
2K2Cr2O7 +3C2H5OH + 8H2SO4 → 2Cr2(SO4)3 + 2K2SO4 + 3CH3COOH + 11H2O
Potassium dichromate is yellow; as concentration decreases, its light
absorption diminishes, so the breathalyzer indirectly measures
alcohol concentration by measuring light absorption of
potassium dichromate before and after the reaction with
alcohol.