That is a 1980 pamphlet, not a scientific paper. OP is right -- there is a lower limit of acceptable asbestos exposure that is not well known. All the asbestos

That is a 1980 pamphlet, not a scientific paper. OP is right -- there is a lower limit of acceptable asbestos exposure that is not well known. All the asbestos-related mesothelioma cases were from workplace exposure for an extended period (more than two months). Furthermore, there are two major forms of asbestos that have widely varying effects. Chrysotile has been shown to not be harmful in small doses. (That's the stuff that you'll find in popcorn ceilings installed prior to 1974.) "Inhalation toxicity studies of chrysotile at non-lung overload conditions demonstrate that the long (>20 µm) fibers are rapidly cleared from the lung, are not translocated to the pleural cavity and do not initiate fibrogenic response." Reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3581056/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3581056/