Associate Certified Entomologist (ACE) Practice Exam

What is indicated by a higher LD50 value?

1. Higher toxicity of a substance

2. Lower toxicity of a substance

3. Equal toxicity across different compounds

4. Increased potency of a substance

The correct answer is: Lower toxicity of a substance

A higher LD50 value indicates a lower toxicity of a substance. LD50, or the lethal dose for 50% of the test population, is a standard measure used to assess the acute toxicity of substances. When the LD50 value is high, it means that a larger dose of the substance is required to be lethal to 50% of the studied population. This suggests that the substance is less toxic because it takes more of it to cause harm. Conversely, a lower LD50 value signifies higher toxicity, as it indicates that only a small amount is needed to cause lethality in half of the tested subjects. The concept of equal toxicity across different compounds is not implied by LD50 values, since these values can vary significantly among different substances. Similarly, increased potency is generally associated with lower LD50 values, indicating that less of a substance is needed to achieve a toxic effect. Thus, understanding the relationship between LD50 values and toxicity aids in assessing the risk associated with various chemicals and helps inform safe handling and exposure guidelines.