If the wood was sold for use in aquarium's, or you are sure that it is not soft wood,with possibly sap contained therein, then boiling and letting it dry outdoor's,or 1/2 cup of bleach to five gallon's of water and then drying it outdoor's should take care of mold.
Is another matter if this is wood collected near stream's,lake,wood's.
I have used such wood and it help's to know what type of wood,and what if any contaminates may have been used near where the wood was gathered.
With regard's to Lava rock, This pourus rock is rough on bellies,and barbel's, of fishes like loaches,pleco's, corydora's that scour over nearly every inch in the aquarium, while searching for food.
Would want smooth riverstones for these fishes if it were me.