17501
However , these results also indicate very clearly that the observed exchange rate is negligible if samples are exposed to natural abundance of deuterium ( 0 . 0156 % ) in natural and laboratory environments before / during analysis .
 Chemical: deuterium
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: deuterium