Which of the following statements best reflects how LD50 values are used to compare toxicity between chemicals?

• A. Lower LD50 always indicates higher toxicity.
• B. Higher LD50 always indicates higher toxicity.
• C. LD50 values are used to compare acute toxicity between chemicals.
• D. LD50 values measure chronic toxicity.

Answer: (C)

LD50 is the dose that kills 50% of a test population under a defined, short-term exposure. Because of that, its primary use is to compare how toxic different chemicals are in acute, or immediate, exposures. A smaller LD50 means the chemical is more acutely toxic—only a small amount is needed to cause death—while a larger LD50 means less acute toxicity. LD50 does not measure chronic or long-term effects, and values can vary depending on species, route of exposure, and experimental conditions. So the statement that best reflects how LD50 values are used is that they are used to compare acute toxicity between chemicals. The other ideas are off because they either invert the relationship, apply it to the wrong type of toxicity, or ignore the role of exposure context.