I think they would be fine. I have them in various places around the yard, including the chicken run. I would worry more about pesticides and chemical sprays than contamination by the chickens. Even if they are away from the coop they are still open to wild birds and other animals passing through. I just rinse, like I do everything from my garden, before using.
The coop is in my small closed backyard no chemicals or pesticides on my part... but i do have neighbors I have pollinator gardens on the other side of my yard so no spraying if any kind.