Hopefully the group here has some suggestions on how this could be remedied.  

If it is an outside wall, then moisture from the exterior of the building is somehow getting inside.Have a mold remediation company look at the property.   

EPA has identified a remedy to address contaminated groundwater and that remedy is under design."

The owner was restricted by the municipality from renting it for any length of time and was called before a magistrate to determine remedy. 

If there was a security instrument that required a spouse’s signature to perfect it, that could be remedied in a similar manner but also adding a notary acknowledgment.Note: always provide the property location in order to receive accurate local feedback.

I'd like to talk to them before moving forward with the testing and remediation.”

I couldn't get a seller to remediate a buried oil tank, so let it go to a buyer who negotiated a 50K discount to waive.

Then, if you want to turn around and sell the property, how much would environmental remediation cost you when that tenant leaves?

Your lien remains in the same position as prior to the transfer and you still have all remedies available to you per your loan documents."

There are probably some local remediation companies out there that you could contact and get a general idea of the cost if you want to plan ahead.