17640
A low level of placental PAH - DNA adducts was associated with an increased risk of NTDs ; this risk increased dramatically when a low adduct level was coupled with a high placental PAH concentration .
 Chemical: PAH; Chemical: PAH
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: PAH, PAH 
Answer:
 Chemical: PAH; Chemical: PAH