4849
Because TCDD blocks epicardium formation , but is not directly toxic to the epicardium once complete , we propose that inhibition of epicardium formation can account for the window of sensitivity to TCDD cardiotoxicity in developing zebrafish .
 TCDD, TCDD
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 TCDD, TCDD