The issue with significant exposure to MDF is not just the dust but the chemical components, the main one being formaldehyde which is a know carcinogen.
Wood dust has a nominal Australian OHS exposure level based on Oak and Beech of 5 ppm for softwoods and 1 ppm for hardwoods but this does not include MDF which is 0.5 ppm. A new standard of 0.1 ppm has been talked about for some time. No one knows the toxicity of Australian timbers (not enough stats) but if anything they are likely to be worse than oak and beech.