First, low level of radioactivity are ok. It depends on the type. Actually, the higher ones like gamma are not so bad because the tend to go right through the body.
Beta seems to be the worst as it can get through skin and stopped somewhere inside the body.
Not sure which is relevant here. If it is really just a little over the background its no big deal. More importantly, I suspect are toxic effects from inhalation. Silica grains can cause silicosis but this is largely mechanical blocking of air passages in the lungs. I would guess the same could happen for a great number of metal oxides if they are small enough to easily get into the air and into air passages, something like a few micron particle size.