However, you shall be careful when preparing a proper medium for the microorganisms you want to grow. What happens sometimes is that a particular xenobiotic turns out not to be lethal for some unwanted microorganisms. That can easily spoil the results. I'd first conduct some pilot research to ensure, whether the used xenobiotic does not serve as a source of carbon for other microorganisms.

The first thing is to decide which xenobiotics you are interested in. Your sampling sites will give you an indication regarding what types of xenobiotics your microbes are exposed to, hence which type of degrades you may find