6719
Although the tumor - promoting effects of 2 , 3 , 7 , 8 - tetrachlorodibenzo - p - dioxin ( TCDD ) , coplanar polychlorinated biphenyls ( PCBs ) , and related compounds in liver tissue are primarily attributed to the activation of the aryl hydrocarbon receptor ( AhR ) , the underlying molecular mechanisms are still unclear .
 Chemical: 2 , 3 , 7 , 8 - tetrachlorodibenzo - p - dioxin; Chemical: TCDD; Chemical: polychlorinated biphenyls; Chemical: PCBs; Chemical: aryl hydrocarbon
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; Chemical: polychlorinated biphenyls; Chemical: PCBs; Chemical: aryl hydrocarbon