APES 8.12 Lethal Dose 50% (LD50)

Definitions and Concepts

• Dose Response Study:

  • A method that exposes model organisms to a chemical.

  • Independent Variable: Concentration of chemical (dose).

  • Dependent Variable: Response of organism (usually death or impairment).

• LD50 (Lethal Dose 50):

  • The dose that kills 50% of the test organisms.

  • Example: For mice exposed to arsenic, the LD50 is 13 mg/kg body mass, meaning 13 mg results in 50% mortality.

  • Measurements can be expressed as mass per mass (mg/kg), parts per million (ppm), or mass per volume (µg/dL).

ED50 (Effective Dose 50)

• Definition:

  • Refers to the dosage required for 50% of organisms to exhibit a measurable, non-lethal effect.

  • Examples: Infertility, paralysis, cancer.

  • Example with atrazine, a herbicide causing 50% infertility in frogs without resulting in death.

• Comparison with LD50 Graphs:

  • Same shape as LD50 curve but shifted right; higher doses result in non-lethal effects shifting to lethal outcomes as concentration rises.

Application of Dose Response Data

• Setting Acceptable Pollutant Levels:

  • Human studies are unethical; model organisms (like mice/rats) are typically used.

  • Safety Factor: Divide the calculated LD50 or ED50 by 1000 for human exposure levels (accounting for size and safety).

• Acute vs. Chronic Studies:

  • Acute Studies: Short-term studies, focused on immediate effects, limiting ecological consequence understanding.

  • Chronic Studies: Long-term studies examining the organism's full development from hatching to adulthood.