If a chemical has a very low LD50 value, which statement is true?

• A. It is less toxic
• B. It is highly toxic
• C. It requires a very high dose to kill
• D. It has no acute toxicity

Answer: (B)

LD50 is the dose that kills 50% of a test population. A very low LD50 means only a small amount is enough to be fatal, so the chemical is highly toxic in acute exposure. If the LD50 were high, it would indicate lower toxicity, and statements about needing a very high dose to kill or having no acute toxicity would contradict a low LD50. So the best interpretation is that the chemical is highly toxic.