8.21 & 8.13: LD50 & Dose response Curve

Learning Objective:

  • Define lethal dose 50% (LD50)

  • Evaluate dose-response curves

Essential knowledge:

  • Lethal dose 50% (LD50) is the dose of a chemical that is lethal to 50% of the population of a particular species

  • A dose-response curve describes the effect on an organism or mortality rate in a population based on the dose of a particular toxin or drug

Dose-Response Studies & LD50:

Studies that expose an organism to different doses of concentrations of a chemical in order to measure the response (effect) of an organism

  • Independent variable = concentration of the chemical (added to food, water, or air)

  • Dependent variable = response measured in the organism (usually death or impairment)

LD50 refers to the dose or concentration of the chemical that kills 50% of the population being studied (EX: arsenic LD50 in mice = 13 mg/kg)

  • LD50 data is usually expressed as:

    • Mass (q. mg)/body unit mass (KG)

    • ppm - parts per million (in air)

    • Mass/volume (in water of blood

Dose-Response Curve:

The data from a dose-response study, graphed with percent mortality or other effect on the y-axis and dose concentration of chemicals on the x-axis

  • The lowest dose where an effect (death, paralysis, cancer) starts to occur is called the threshold or toxicity threshold

  • Dose-response curves are usually “s-shaped’ - low mortality of low doses, rapid increase in mortality as dose increases, level off near 100% mortality of high dos

ED50 & other Dose-Responses:

ED50 refers to the dose concentration of a toxin or chemical that causes a non-lethal effect (infertility, paralysis, cancer, etc.) in 50% of the population being tested

  • EX: the concentration of atrazine in water that causes 50% of frogs to become infertile

  • Same general “s-shape” as the LD50 dose-response curve, but at lower dose concentrations

Dose-Response Data & Human Health:

Dose-response studies for toxic chemicals are not done on humans: data from other mammals (mcie, rats0 are used to stimulate human toxicity

  • To determine maximum allowable levels for humans, we generally divide LD50 or ED 50 dose concentration by 1,000 for extreme caution

  • Acute vs. Chronic studies: most dose-response studies are considered acute since they usually only measure effects over a short period of time. They’re also isolated to a lab so they don’t measure ecological effects of organisms dying (trophic cascades)

  • Chronic studies are longer-term and follow developmental impacts

    • EX: study of fish from hatchlings to adults to study secual maturation