Texas Pesticide Applicator Practice Exam

What type of toxicity is indicated by a high LD50 value?

1. Highly toxic

2. Moderately toxic

3. Less toxic

4. Non-toxic

The correct answer is: Less toxic

The designation of toxicity in relation to LD50 (lethal dose for 50% of the population) is key in understanding how harmful a substance can be. A high LD50 value signifies that a larger dose of the substance is required to cause death in 50% of the test subjects, which suggests that the substance is less toxic. In terms of toxicity classification, substances with lower LD50 values indicate higher toxicity, as it requires less of the substance to reach lethal effects. Therefore, when one refers to a high LD50 value, it directly correlates to the understanding that the substance is generally safer at higher exposure levels, qualifying it as less toxic compared to those with lower values. Other options refer to varying degrees of toxicity that would be indicative of lower LD50 values. They don't align with the understanding of what a high LD50 relative signifies in the context of toxicity assessment. Thus, a high LD50 value is indeed indicative of a substance that is less toxic.