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The study aimed to investigate the effect of occupational exposure to cotton dust on respiratory symptoms , ventilatory functions and pro - inflammatory cytokine levels ( tumor necrosis factor alpha , interleukin 6 and interleukin 1 beta ) .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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