5308
Chloracne is commonly observed in humans exposed to 2 , 3 , 7 , 8 - tetrachlorodibenzo - p - dioxin ( TCDD ) ; yet , the mechanism of toxicity is not well understood .
 Chemical: 2 , 3 , 7 , 8 - tetrachlorodibenzo - p - dioxin; Chemical: TCDD
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: 2 , 3 , 7 , 8 - tetrachlorodibenzo - p - dioxin; Chemical: TCDD