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TECHNICAL REPORTS

Heavy Metals in the Environment

Decreasing Lead Bioaccessibility in Industrial and Firing Range Soils with Phosphate-Based Amendments

^a Dep. of Civil Engineering, 208 Harbert Engineering Ctr., Auburn Univ., Auburn, AL 36849
^b Environmental Sciences Div., P.O. Box 2008, Oak Ridge National Lab., Oak Ridge, TN 37831-6038
^c Dep. of Geological and Environmental Sciences, Stanford Univ., Stanford, CA 94305

^* Corresponding author (mark.barnett{at}auburn.edu).

Received for publication August 13, 2008. In–situ stabilization using phosphate (P) amendments, such as P-based fertilizers and rock, are a potentially cost-effective and minimally disruptive alternative for stabilizing Pb in soils. We examined the effect of time (0–365 d), in vitro extraction pH (1.5 vs. 2.3), and dosage of three P-based amendments on the bioaccessibility (as a surrogate for oral bioavailability) of Pb in 10 soils from U.S. Department of Defense facilities. Initial untreated soil bioaccessibility consistently exceeded the U.S. Environmental Protection Agency default value of 60% relative bioavailability, with higher bioaccessibility consistently observed at an in vitro extraction pH of 1.5 vs. 2.3. Although P-based amendments statistically (P < 0.05) reduced bioaccessibility in many instances, with reductions dependent on the amendment and dosage, large amendment dosages (approximately 20–25% by mass to yield 5% P by mass) were required to reduce average bioaccessibility by approximately 25%. For most amendment combinations, reductions continued to occur for periods up to 1 yr, indicating that the observed reductions were not merely experimental artifacts of the in vitro extraction procedure. Although our results indicated that reductions in Pb bioaccessibility with P amendments are technically feasible, relatively large amendment masses were required to achieve relatively modest reductions in bioaccessibility. The cost and potential environmental implications of adding such large amounts of P may limit the practicality of in situ immobilization for some Pb-contaminated soils, industrial and firing range soils in particular.

Abbreviations: B_A, amended bioaccessibility • B_U, untreated bioaccessibility, C_A, amended cleanup level, C_U, untreated cleanup level • DI, deionized • DoD, U.S. Department of Defense • PBET, physiologically based extraction test • RP, rock phosphate • TIC, total inorganic carbon • TOC, total organic carbon • TSP, triple-super-phosphate • Vol, VolCanaPhos