PCBs or biphenyl cannot provide energy for microbes, so they are primary energy and carbon sources. As stated before it takes months sometimes for microorganisms to activate their gene for dichlorine after the first exposure to PCBs. It has been proposed to use analogs to promote the activation of genes. However, even after the metabolic pathway is activated, the intermediates of the pathway create a bottleneck effect due to their toxicity. Also, there is the possibility that BP pathway leads to protoanemonin which is a dead-end metabolite that cannot be utilized by cells. Due to the high energy cost of this pathway, if no preferred energy source present in the system, cells will not activate this pathway.