How are signal words for toxicity assigned?

How are signal words for toxicity assigned?

• A. Based on the lowest measured toxicity among routes
• B. Based on the highest measured toxicity among a single route
• C. Based on the highest measured toxicity, whether oral, dermal or inhalation
• D. Based on exposure duration only

Answer: (C)

Signal words on pesticide labels warn about acute toxicity by using the most severe route of exposure. The word is determined by looking at the highest hazard across oral, dermal, and inhalation routes—specifically the most toxic (lowest LD50 or LC50) value among those routes. If any route shows a higher hazard, the label uses the more protective word to ensure users are warned for the worst-case scenario, since exposure could occur by different routes in real-world use. It isn’t based on the lowest toxicity overall, nor on a single route’s toxicity alone, and it isn’t determined by exposure duration.