Estimates of fiber emission by Canadian and U.S. households

We estimated the extent of microfiber shedding during laundry by households in Canada and the U.S.A. using the average microfiber loss by weight (131 mg per kg of textile per wash) and count (514,400 microfibers per kg of textile per wash) by all synthetic fabrics in this study. Data was converted using the average weight of a domestic laundry load (4 kg). Natural fabrics (i.e. cotton and wool), as well as blends containing natural fibers, were excluded from this estimate.

The annual total household release of synthetic microfibers from laundry in Canada was estimated using a total of 14,072,080 households [29], and an average of 218 laundry loads per year per household [30]. For the U.S.A., annual synthetic microfiber release from laundry was estimated using a value of 127,586,000 households [31] and an assumed 300 laundry loads per household per year [32]. To estimate microfiber emission via municipal wastewater, we assumed a 95% retention in facilities based on data from studies of primary, secondary, and tertiary wastewater treatment plants [18, 19]. These estimates consider the proportion of domestic wastewater that is untreated or collected into household septic tanks in Canada [33] and the U.S.A. [34].