Minnesota Pesticide Applicator Practice Test

Which of the following LD50 ratings indicates the highest toxicity?

1. 50 mg/kg

2. 100 mg/kg

3. 200 mg/kg

4. 1000 mg/kg

The correct answer is: 50 mg/kg

The LD50 rating, or lethal dose for 50% of a test population, measures the toxicity of a substance. A lower LD50 value indicates that less of the substance is required to cause death in half the test subjects, demonstrating higher toxicity. In this case, a rating of 50 mg/kg signifies that a very small amount of the substance is lethal to half of the test subjects. This concentration reflects a highly toxic substance because it takes only 50 milligrams per kilogram of body weight to achieve that lethal effect. Conversely, higher LD50 values, such as those for 100 mg/kg, 200 mg/kg, and 1000 mg/kg, indicate progressively lower toxicity since larger amounts of the substance are required to cause the same lethal effect in half of the tested population. Thus, the 1000 mg/kg rating would be the least toxic due to the substantial amount required to reach the lethal dose. This relationship underlines why the 50 mg/kg rating corresponds to the highest toxicity.