2964
Based on these studies , the frequency of spontaneous tail contractions at 26 hpf - a developmental stage with minimal AChE expression and activity - was significantly higher following exposure to paraoxon concentrations as low as 31 . 2 nM .
 Chemical: paraoxon
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: paraoxon