The University of Georgia Cooperative Extension reports that, “around 30 to 40 percent of the contaminants inside your home are brought in from outdoors.”1 The EPA recommends removing shoes to reduce the amount of lead that gets tracked into the home.2 An EPA study has also found that taking your shoes off at the door can reduce the presence of commonly-used herbicides in the household.3
1 Pamela R. Turner, September 2015, “Leave it at the Door: A Guide to Reducing Contaminants in Your Home,” Circular 1070 (Formerly HACE-E-81), extension.uga.edu/publications
2 EPA “Protect Your Family from Sources of Lead,” https://www.epa.gov/lead/protect-your-family-sources-lead#soil
3 Marcia G. Nishioka, Hazel M. Burkholder, Marielle C. Brinkman, and Robert G. Lewis. 1999. Distribution of 2,4-Dichlorophenoxyacetic Acid in Floor Dust throughout Homes Following Homeowner and Commercial Lawn Applications: Quantitative Effects of Children, Pets, and Shoes. Environ. Sci. Technol. 33 (9):1359–1365.