Rinse them real well and pour a little bit of vinegar on top. If there is no reaction, the are probably ok. Then I would ld soak them in Clorox or ammonia solution and again rinse, rinse and rinse again.
As has been said, give them a good clean, you can pour boiling water on them in case there are are nasties lurking.
Some rocks can alter your ph, pop them in a bucket with some dechlorinated water & test the ph, leave them in the water overnight & test the ph again if all's well they can go in your tank.
I recently got some gravel from my driveway (for plant anchors also) - scrubbed, tested w/ vinegar, soaked in clorox solution, and then boiled. Later tested the water & it was ok. Tank water today tests ok as well.
I boiled for a total time of around 30 minutes, dumped the water out after the first time. Good thing I did that it was all dusty and who knows what on them. Second time water looked much cleaner. I'm not going to bother with cleaning solutions and risk getting in my tank. Thanks guys! I'm excited i've been wanting rocks like this I was shocked the dollar store had them. Perfect size bag for my needs for $1!