Heavy metal capture and accumulation in bioretention media were investigated through the use of a one-dimensional filtration equation for paniculate metals, advection/dispersion/ adsorption transport equations for dissolved metals, and sequential extractions. Predicted spatial profiles and partitioning patterns of captured metals were compared to data derived from a bioretention cell in the District of Columbia. Zinc, lead, and copper profiles showed a high surface accumulation, significantly decreasing with the media depth. Surface street particle-enriched areas had the highest heavy metal levels, demonstrating a close relationship between capture of metals and runoff particles. Sequential extractions suggested that most captured metals were of anthropogenic origin. Soluble-exchangeable bound metals from the sequential extraction correlated well with predicted aqueous dissolved metals; the more strongly associated metal fractions correlated with modeled runoff and media paniculate metals. A simple risk evaluation indicated that lead isthe limiting metal in bioretention accumulation. On the basis of information collected in this study, a shallow bioretention cell design is suggested for systems with a focus on metal capture.
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