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Under acidic conditions in the stomach of humans, the nature of phases in contaminated solids significantly influence lead (Pb) release and bioaccessibility. This study focused on Pb solid-phase speciation and release kinetics and the relationship between the two. Contaminated soil and waste materials from a Pb mining and processing site contained 279-7770 and 495-83400 mg/kg total lead (Pb t ), of which 47-76% and 38-55%, respectively, were extractable (MgCl 2 + NaOH + EDTA). Release rates were measured with a stirred-flow reactor under simulated gastric conditions at a pH of 1-3 and at temperatures of 278-328 K. During the first 10 min, Pb release rates at 297 K and pH 1 were high (53 and 31 mg (g of Pb t ) -1 min -1 , soil and waste, respectively), and most samples released >50% of Pb t within the first 10 min. Between 10 and 60 min, Pb was generally released at lower rates (11 and 3 mg (g of Pb t ) -1 min -1 , soil and waste, respectively). Lead release kinetics and solid-phase speciation indicate that Pb is present in at least two different solid phases. A kinetic model representing two simultaneous first-order reactions suggested the presence of a fast and a slow reacting pool; corresponding half-lives were in the range of 1 and 10 min, respectively.

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