What determines a pesticide's signal word?

• A. The highest measured toxicity among oral, dermal, or inhalation
• B. The lowest measured toxicity among routes
• C. The average toxicity across routes
• D. The pest target

Answer: (A)

Signal words reflect acute hazard to humans, and the driving factor is the most severe acute toxicity among exposure routes. To determine this, you compare the LD50 values for oral and dermal exposure and the LC50 value for inhalation. The route with the highest toxicity (the smallest LD50/LC50 value) determines the word shown on the label. If inhalation is the most dangerous route, that strongest hazard drives the signal word, even if oral or dermal toxicity is lower. This approach ensures the warning matches the greatest risk a user might encounter, reinforcing appropriate protective measures.