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Apoptotic effect of arsenic in human mesenchymal stem cells ( hMSCs ) has been identified in our previous study ; the effects of arsenic on hMSCs remain largely unknown .
 Chemical: arsenic; Chemical: arsenic
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: arsenic