This should not be a surprise to anyone over the age of 30. Remember all that unleaded gasoline? If you put lead into the gas and then you burn the gas, either that lead comes out the tailpipe or it stays in the car. Since the cars didn't keep getting heavier and heavier, we can safely conclude it went into the air. From there, because lead is actually kind of heavy, it fell onto the ground. Where it has stayed, because lead is not the most active of elements (in fact, that's part of the problem with lead, the rest being that apparently living things tend to confuse lead with other stuff like calcium. You can sort of see where that might lead to problems. Ahem).
In any event, I've known that you need to check for lead if you're going to garden. If you do find lead, the solution is simple and actually not that expensive: raised beds and soil you get from somewhere else (which you _also_ carefully test. Duh). You don't need a lot of depth for a garden, and there are in fact entire systems based on doing this for other reasons (square foot gardening springs to mind).
As a result, I find quotes like this a little insulting:
"lead is surprisingly prevalent and persistent in urban and suburban soil"
Only surprising to people whose parents didn't stop them from ever eating the berries growing along the road. Because they were laden with lead from gasoline exhaust. Cars went everywhere people went, so it should surprise no one that everywhere people have been for a few decades has a lot of lead sprinkled about.
Still, it is probably good to get the word out, to people who hadn't heard already.