9420
Few studies assess the potential of ongoing sources of " fresh " polychlorinated biphenyls ( PCBs ) to aquatic systems when direct discharge to the environment has been eliminated .
 polychlorinated biphenyls, PCBs
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 polychlorinated biphenyls, PCBs