The fungicide chlorothalonil has an acute toxicity level of

• A. > 10,000 mg/kg as a dermal LD50
• B. < 10 mg/kg
• C. 100 mg/kg
• D. Unknown

Answer: (A)

Acute toxicity is described by the LD50 value for a given exposure route, which is the dose needed to kill 50% of exposed animals. A very high LD50 means the substance is not very toxic on contact. For chlorothalonil, the dermal LD50 is reported to be greater than 10,000 mg/kg, indicating it requires a very large dermal dose to cause lethal effects in half the test animals. That high number shows a very low acute dermal hazard.

The other options imply much greater toxicity (less than 10 mg/kg or around 100 mg/kg) or aren’t providing a measured value (unknown), which don’t align with chlorothalonil’s relatively low acute dermal toxicity. Therefore, the statement that its dermal acute toxicity LD50 is over 10,000 mg/kg best describes its hazard level.