Which statement is true about compounds with a high LD50?

• A. They are never hazardous
• B. They can still be hazardous
• C. They are always safe
• D. They are not related to hazard

Answer: (B)

LD50 is a measure of acute toxicity that tells us the dose needed to kill 50% of test animals. A high LD50 means the substance is less acutely toxic in that specific test, so it might seem safer at first glance. But hazard isn’t determined by this number alone. A chemical with a high LD50 can still cause harm through other routes or effects—such as irritating skin or eyes, causing allergic sensitization, or producing chronic problems like reproductive toxicity, carcinogenicity, or endocrine disruption. It can also pose environmental hazards or become hazardous with long-term or repeated exposure, even if its acute lethality is low. So, a high LD50 indicates lower acute toxicity, but it does not guarantee that the compound is free of hazards in real-world use.