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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
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: polybrominated diphenyl ethers 
Answer:
 Chemical: polybrominated diphenyl ethers