Texas Pesticide Applicator Practice Exam

What does a smaller LD50 value indicate about a pesticide?

1. It is more effective at lower doses

2. It is less toxic

3. It requires more chemical to be fatal

4. It is more poisonous

The correct answer is: It is more poisonous

A smaller LD50 value indicates that less of the substance is needed to achieve a lethal effect in 50% of a test population. This reflects a higher level of toxicity. Essentially, the lower the dose that can cause death, the more poisonous the pesticide is considered. Therefore, a pesticide with a small LD50 is significantly toxic and poses a greater risk of harm even at lower application rates. In contrast, a larger LD50 would suggest that a higher quantity is needed to achieve a lethal effect, which corresponds to being less toxic, thereby highlighting the importance of understanding LD50 values in assessing pesticide safety and usage in various contexts.