Toxicology Forensics Foster

• Substance that can cause injury
to the health of a living thing on
contact or absorption
– Usually reserved for naturally
produced substances that kill in
small quantities
Factors affecting Toxicity
1. Dosage- amount and frequency
2. The chemical or physical form of the
3. The mode of entry into the body
4. Body weight and physiological conditions of
the victim, including age and sex
5. The time period of exposure
6. The presence of other chemicals in the body or
in the dose
• Arsenic is a metal
– Rather insoluble in stomach acid
• As2O3 and extremely toxic As2O5
• Arsine AsH3 is a gas that can kill
• Small amounts of arsenic are good for you
and you are exposed to all the time
Factors (cont.)
• Lethal Dose
– LD50 refers to the dose of a substance that kills 50% of the test population,
usually within 4 hours
• Expressed in mg of substance per kg of body weight
• Chemical or physical form of the substance
– Solid, liquid …
• How it enters the body
– Blood, absorption…
• Body weight and physiological conditions of the
victim, including age and sex
– Larger doses are required for a big person
Factors (cont.)
• Time period of exposure
–Chronic exposure- exposure over a long period
of time
–Acute toxicity- effects almost immediately (hrs.
or days)
Violin markings
Factors (cont.)
• Presence of other chemicals in the body
– Synergism- combined effect of substances
exceeds sum of individual effect
– Antagonism- combined effect decreases
individual effects
– Chelating agent- stabilize or prevent the
precipitation of damaging compounds
Red Hourglass
Measuring Toxicity
Humans based on animal
LD50 (Rat, oral)
<1 mg/kg
Correlation to
Ingestion by 150-lb
Adult Human
a taste to a drop
1–50 mg/kg
to a teaspoon
50–500 mg/kg
to an ounce
500–5,000 mg/kg
to a pint
5–15 g/kg
to a quart
practically nontoxic
Over 15 g/kg
more than 1 quart
relatively harmless
To Prove a Case
Prove a crime was committed
Access to poison
Access to victim
Death was homicidal
Death was caused by poison
• Most abused drug in US
• ~40 % of accidents related to alcohol
• Tests
– Field
• One leg stand
• 9 step walk & turn
• Nystagmus–
– jerky eye
– Breath Analysis
– Blood Analysis