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We also conclude that sources of the above four pollutants are similar but differ from the sources of polybrominated diphenyl ethers .
 Chemical: polybrominated diphenyl ethers
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: polybrominated diphenyl ethers