Texas FFA Nursery Landscape Practice Exam

Which LD-50 rating is considered most lethal to a human based on animal studies?

1. 945

2. 10000

3. 84

4. 1750

The correct answer is: 84

The LD-50 rating, or lethal dose for 50% of the population, is a key concept in toxicology that indicates the toxicity of a substance. A lower LD-50 value signifies that a smaller amount of the substance is required to be lethal, indicating higher toxicity. In this case, an LD-50 rating of 84 suggests that only a small dose of the substance is needed to reach lethal levels in half of the subjects tested. This is significantly lower than the other values listed. For instance, an LD-50 of 1750 indicates a higher threshold for lethality, suggesting that a larger dose is required to achieve the same lethal effect. Similarly, 945 and 10000 represent even greater amounts needed to cause death in 50% of the population. Thus, the LD-50 rating of 84 is considered the most lethal for humans, as it indicates that this substance is extremely toxic and poses a serious risk even in small quantities.