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It is also worth pointing out the fact that no levels are demonstrated to be safe; one only demonstrates what causes harm. If no harm is noticed at some level, that does not guarantee that no harm has occurred. This is the way with scientific studies of safety; they look for harm, and if none is found, it is generally considered to be safe, but it is never actually proven to be safe, and normally, over time, the testing gets better so that harm is noticed with lower amounts of the thing tested. This applies to contaminants in food and water and other such matters as well.