Migration of contaminated soil and airborne particulates to indoor dust

Abstract

We have developed a modeling and measurement framework for assessing transport of contaminated soils and airborne particulates into a residence, their subsequent distribution indoors via resuspension and deposition processes, and removal by cleaning and building exhalation of suspended particles. The model explicitly accounts for the formation of house dust as a mixture of organic matter (OM) such as shed skin cells and organic fibers, soil tracked-in on footwear, and particulate matter (PM) derived from the infiltration of outdoor air. We derived formulas for use with measurements of inorganic contaminants, crustal tracers, OM, and PM to quantify selected transport parameters. Application of the model to residences in the U.S. Midwest indicates that As in ambient air can account for nearly 60% of the As input to floor dust, with soil track-in representing the remainder. Historic data on Pb contamination in Sacramento, CA, were used to reconstruct sources of Pb in indoor dust, showing that airborne Pb was likely the dominant source in the early 1980s. However, as airborne Pb levels declined due to the phase-out of leaded gasoline, soil resuspension and track-in eventually became the primary sources of Pb in house dust.

FIGURE 1

Conceptual diagram depicting the movement of contaminated soil and airborne particulates into a residence, subsequent mixing with organic matter in floor dust, redistribution indoors via resuspension, and removal by cleaning and exhalation with building air. The variables are defined as: CLN is the first-order particle removal rate from floors due to cleaning activities, R is the resuspension rate of floor particles to indoor air, D_f is the rate of dust fall to floors, F_om is the flux of organic matter onto floor surfaces, T_s is the rate of soil track-in on footwear into a residence, Ach is the air exchange rate, and v̄_r and v̄_o are the mean deposition velocities for resuspended particles and outdoor-derived air particles, respectively.

FIGURE 2

Reconstruction of the contributions of outdoor air Pb to total Pb in floor dust for three scenarios of soil track-in to Sacramento residences.

FIGURE 3

Sensitivity analysis of the parameters controlling the (a) predicted level of As loading on floors for Midwest residences and (b) the concentration of As in dust fall. Model responses are determined for low and high values of input parameters, as described in the Supporting Information.