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The aim of this work was to study the environment - reflecting short - term responses at different levels of organization of epipsammic diatoms from the R i o de la Plata estuary , Argentina that had been exposed to hexavalent chromium within experimental microcosms .
 Chemical: hexavalent chromium
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: hexavalent chromium