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The headwater inputs generate chronic base flow concentrations of total mercury of about 1 , 000 ng / L , but most of the annual export of mercury from the system appears to originate farther downstream .
 Chemical: mercury; Chemical: mercury
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: mercury; Chemical: mercury