Oxolic acid, pheromone lures to capture mites, Queen pheromone boosters, synthetic brood pheromones, Formic acid, and a host of other things are from time to time, are mentioned as "natural". I've heard that the acids are "natural" due to them being produced on some level in nature, and so the rationale is that huge quantities, are also considered "Natural". Arsenic is natural, as well as salt. Both in high enough amounts can kill. Both are needed for life. But even lower amounts cause damage in many forms, once you go above the limits found naturally. Definition of a pollutant: A pollutant is any naturally occuring substance that is in the wrong place or is found in excess. Seems many thing we place in the hive and try to justify it's use, can be classified as a "pollutant". And many times, pollutants are found to be a danger in so many ways. Something to think about.