Your contract probably says the seller is to maintain the home. The question comes up, was the mold there before, so the essentially maintained it or was it new. Assume it was new and the seller's didn't maintain the property. You can consult an attorney and pursue the seller's for a remedy, but remember they just did a short sale, so that implies they have a financial hardship. What could you get if you're successful?
Finally, the bank had no knowledge of the property they only agreed to release their lien for less than what is owed.
Ultimately you will need an attorney to review your contract and advise you. Did you close on the property? Are you rescinding your contract short of closing for a reason contained within the contract?