Weed killer

Today when I came home for lunch there was a young man spraying weed killer on weeds growing along the side of the building. One weed he sprayed was directly in front of the steps going down to my front door. Then it rained this afternoon. I am sure that the rain water picked up some of the poison from the weed killer and spread it on the areas that my roommate and I, and any guests we may have, too, walk on to get to the apartment. I really don't want weed killer, even diluted weed killer, on my carpet. My hands were full, but my shoes still came off as soon as I came in the door!