Texas Pesticide Applicator Practice Exam

What does LD50 mean?

1. Least Dose for 50% of test population

2. Lethal Dose for Fifty percent of animals exposed

3. Lowest Dose for 50% of effect

4. Long-term Dose for 50% survival

The correct answer is: Lethal Dose for Fifty percent of animals exposed

LD50 stands for "Lethal Dose for Fifty percent of animals exposed." This term is commonly used in toxicology to quantify the dosage of a substance that is required to kill half of a tested population of organisms, typically laboratory animals. The value provides a measure of the acute toxicity of substances, allowing researchers and regulatory agencies to assess the potential risks posed by chemicals, including pesticides, to non-target organisms, including humans. Understanding LD50 is crucial for appropriately determining safety levels for pesticide application, as it helps in evaluating the hazards associated with different chemicals. The lower the LD50 value, the more toxic the substance, indicating that a smaller amount of the substance can achieve a lethal effect. The other options do not accurately reflect the correct definition. While “Least Dose for 50% of test population” and “Lowest Dose for 50% of effect” might sound relevant, they do not specifically highlight the lethal aspect of the dose. "Long-term Dose for 50% survival" suggests a different concept, often related to chronic exposure, rather than the acute toxicity measured by LD50.