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Arsenic ( As ) has been associated with multitude of animal and human health problems ; however , its impact on host immune system has not been extensively investigated .
 Chemical: Arsenic; Chemical: As
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: Arsenic; Chemical: As