8.12/13 - LD50 And Dose Responsive Curve

Question 1

Dose Response Studies and LD50

Answer 1

• Studies that expose an organism to different doses of concentrations of a chemical in order to measure the response (effect) of the organism
• Independent variable = concentration of the chemical (added to food, water, or air)
• Dependent variable = response measured in org. (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 are usually expressed as:
  - mass (g, mg)/body unit mass (kg)
  - ppm - parts per million (in air)
  - mass/volume (in water of blood)

Question 2

Dose Response Curve

Answer 2

• The data from a dose response study, graphed with percent mortality or other effect on the y-axis and dose concentration of chemical on x-axis
• 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 at low doses, rapid increase in mortality as dose increases, level off near 100% mortality at high dosage

Question 3

ED50 and other Dose Requirements

Answer 3

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

Question 4

Dose Response Data and Human Health

Answer 4

• Dose-response studies for toxic chemicals are not done on humans; data from other mammals (mice, rats) are used to simulate human toxicity
• To determine maximum allowable levels for humans, we generally divide LD50 or ED50 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 sexual maturation