LD and LC Explained

What is LD50?

• LD stands for "Lethal Dose."
• LD50 represents the amount of a substance required to cause death in 50% of a group of test animals.
• Used to measure short-term poisoning potential (acute toxicity).
• Common test subjects include rats and mice.
• Expressed as the chemical dose per unit of body weight (e.g., mg/kg).
• Common administration methods: oral and dermal.

What is LC50?

• LC stands for "Lethal Concentration."
• Refers to the concentration of a chemical in air or water that causes death in 50% of test animals.
• Traditional experiments involve exposure over set periods (usually 4 hours).
• The LC50 value is determined for various durations based on legal requirements.

Why Study LD50?

• Different chemicals lead to various toxic effects, complicating direct comparison.
• LD50 tests provide a consistent measure of toxic potency through lethality testing.
• Allows researchers to compare different chemicals by observing lethality.

Origin of LD50

• Developed by J.W. Trevan in 1927.
• Provides a comparative measure for the potency of toxic substances.

Other Toxicity Dose Terms

• LD01: Lethal dose for 1% of the test population.
• LD100: Lethal dose for 100% of the test population.
• LDLO: Lowest dose causing lethality.
• TDLO: Lowest dose causing a toxic effect.

Acute Toxicity

• Refers to ill effects occurring shortly after exposure.
• "Relatively soon" can range from minutes to days (up to 2 weeks).

Conducting LD/LC50 Tests

• Typically performed using pure chemicals.
• Methods of administration include oral, dermal, intravenous, etc.
• Results expressed based on species, route of administration, and dosage.

Occupational Importance

• Inhalation (LC50) and skin absorption (LD50-skin) tests are relevant for workplace chemical exposure.
• Oral LD50 tests are more common but not always applicable to occupational settings.

Comparing LD50 Values

• Smaller LD50 indicates higher toxicity.
• Toxicity varies based on species, age, and exposure route.
• LD50 is not intended for long-term exposure assessment.

Examples

• Oral LD50 for dichlorvos varies across species and exposure routes.

Toxicity Classification Scales

• Hodge and Sterner Scale and Gosselin, Smith and Hodge Scale are commonly used.
• Provide different toxicity ratings and terms.

Applicability to Humans

• If toxicity is consistent across animal species, it likely applies to humans.
• Safety factors are applied due to variability and experimental uncertainties.

Using LD50 Values

• Aid in emergency response, safety equipment guidelines, transport regulations, exposure limits, and safety data sheets.
• Important to consider alongside other toxicity information, such as TDLO.

Note: LD50 is only an estimate for comparison.

Last revised: 2018-11-12