  Dust particulate fallout on materials in use for rare-event searches is a
concerning source of radioactive backgrounds due to the presence of naturally
occurring radionuclides K-40, Th-232, U-238, and their progeny in dust. Much
effort is dedicated to inform radioactive backgrounds from dust and evaluate
the efficacy of mitigation procedures. A great portion of such effort relies on
fallout models and assumed dust composition. In this work, an ICP-MS based
methodology was employed for a direct determination of fallout rates of
radionuclides and stable isotopes of interest from dust particulate at the
SNOLAB facility. Hosted in an active mine, the SNOLAB underground laboratory
strives to maintain experimental areas at class 2000 cleanroom level. This work
validates the mitigation procedures in place at SNOLAB, and informs dust
backgrounds during laboratory activities. Fallout rates of major constituent of
the local rock were measured two to three orders of magnitude lower in the
clean experimental areas compared to non-clean transition areas from the mine
to the laboratory. A ca. two order of magnitude increase in stable Pb fallout
rate was determined in an experimental area during activities involving
handling of Pb bricks. Increased K-40, Th-232, and U-238 fallout rates were
measured in clean experimental areas during activities generating particulate.
