13343
The current study compares the effects of the three most common pH manipulation methods ( carbon dioxide , acid - base addition , and chemical buffers ) on acute Pb toxicity of a model fish species , Pimephales promelas .
 carbon dioxide, Pb
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 carbon dioxide, Pb