There isn't?
We know the rate of mesothelioma in people with no known occupational exposure, but we have very little quantitative data about how much a given amount of asbestos exposure might increase one's risk. The disease takes decades to develop after exposure.
There are an infinite number of things that don't exist and that we don't have any evidence of. It is nice if we can positively disprove them, but that is not necessary to justify disbelief.