I doubt anything noticeable or hazardous to the tank leached. I have used this method in the past with great success. I buy a lot of rock on craigslist or get it donated from local guys who tore down their tank. I would never add any live rock to a tank no matter if it comes straight from the ocean or someone's tank. Let it soak in bleach for a week then scrub with a toothbrush and rinse and dry out. That is all. A couple months in the tank and it will be exactly like all the rest of the live rock you already have and will be free of any unwanted pests.