A surprising finding was the very low exposure threshold for an observed increase in risk. For the diseases overall in men, the threshold band was 2.0–29.2 ug/m3-years of cumulative silica exposure, and 2.0–10.7 ug/m3 of mean silica exposure, with two-thirds of cases occurring at mean exposures below 18.1 ug/m3. By contrast, the cited European silica exposure limit is 100 ug/m3.

These data are therefore compatible with a cumulative exposure and latency effect in autoimmune disease. This does not, however, exclude the possibility of more than one silica dosing mechanism in the induction of these diseases.

For SLE and small vessel vasculitis in men, there was arguably no dose-response trend beyond the ‘any silica’ threshold. This raises the question of a potential confounder associated with dusty job status other than dust exposure per se.