How can you determine which substance is more toxic?

• A. The substance with a higher LD50 is more toxic.
• B. Toxicity cannot be compared between substances.
• C. Higher exposure duration always means more toxic.
• D. The substance with a lower LD50 is more toxic because less chemical is needed to kill the same number of subjects.

Answer: (D)

In toxicology, acute toxicity is often compared using the LD50 value, which is the dose needed to kill 50% of a test population under defined conditions. A smaller LD50 means the substance is lethal at a lower dose, so it is more toxic. So, if one chemical has a lower LD50 than another, it requires less of it to cause death in the same proportion of subjects, indicating higher acute toxicity.

Keep in mind that LD50 depends on factors like the route of exposure (oral, dermal, inhalation), the species tested, and the experimental setup. It measures acute lethality, not all possible harmful effects, and it doesn’t capture chronic toxicity, carcinogenicity, or non-lethal outcomes. Higher LD50 indicates lower acute toxicity, and comparing LD50 values should be done under comparable conditions.