If it weren't all on the margins of the leaves I would agree that it's chemical and I still wouldn't rule it out but those leave look exactly like a broad leaved container plant the had the roots briefly go dry. The way they're situated on that grade, the roots on the sidewalk side would go dry first. If that's the case, keep'em wet and they'll recover.
I have to wonder though, what's under that little gray strip of mulch running parallel to the sidewalk... a trench perhaps?