Not a stupid question at all and one I asked myself a few years ago. Based on what you learn, you might need to check into some sort of remediation before you start a veggie garden but too little information to make that call.
I sent samples to a lab for testing. A good lab will test for lead and other contaminants. It wasn't all that expensive but please know there is a good possibility that if you are in the US your extension office might provide this type of testing for free. I found out our local extension office tested for free after I paid an independent lab.
Did a quick search and found this-