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Primary Leydig cells obtained from bank vole testes and the established tumor Leydig cell line ( MA - 10 ) have been used to explore the effects of 4 - tert - octylphenol ( OP ) .
 Chemical: 4 - tert - octylphenol
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
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Answer:
 Chemical: 4 - tert - octylphenol