Pathways of lead contamination in households include lead-based paint, lead contaminated dust, and lead contaminated soil. The Brigham and Women's Hospital longitudinal lead study investigated the relationship between infant blood levels from late pregnancy to two years of age and lead levels in environmental media. Environmental media sampled and analyzed for lead included dust from floors, furniture surfaces, and window sills, soil, tap water, and interior air.
Multiple regression models were fitted to the data to determine the relationship between exterior and interior levels of lead, and childhood blood-lead levels. Soil and other environmental lead sources may directly affect blood-lead levels by ingestion or inhalation pathways, and indirectly through their contribution to house dust or other environmental media. Bornschein and his co-workers have proposed the use of structural equation models for determining both the direct and indirect effects of lead levels in the environment on blood-lead levels. Structural equation models fitted to the data suggested a pathway of lead from soil to the dust on the window sill to the dust on the floor to childhood blood.