Environ. Sci. Technol. 1996, 30, 761-769
Lead Release from Smelter and Mine Waste Impacted Materials under Simulated Gastric Conditions and Relation to Speciation UBALD G. GASSER,† WILLIAM J. WALKER,‡ R A N D Y A . D A H L G R E N , * ,† ROBERT S. BORCH,§ AND RICHARD G. BURAU† Department of Land, Air, and Water Resources, University of California, Davis, California 95616-8632, Science and Engineering Analysis Corporation (SEACOR), 1734 34th Street, Sacramento, California 95816-7004, and Department of Geology, University of California, Davis, California 95616-8632
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 (Pbt), of which 47-76% and 38-55%, respectively, were extractable (MgCl2 + 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 Pbt)-1 min-1, soil and waste, respectively), and most samples released >50% of Pbt within the first 10 min. Between 10 and 60 min, Pb was generally released at lower rates (11 and 3 mg (g of Pbt)-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.
Introduction The chronic and acute toxicity of Pb to humans has been known for several centuries (1, 2); however, environmental * Corresponding author voice mail: 916-752-2814; fax: 916-7521552; e-mail address:
[email protected]. † Department of Land, Air, and Water Resources, University of California. ‡ SEACOR. § Department of Geology, University of California.
0013-936X/96/0930-0761$12.00/0
1996 American Chemical Society
issues concerning Pb remain a subject of debate (3-5). Lead uptake by humans, especially by young children, is generally dominated by particle ingestion (oral-gastrointestinal pathway), but respiratory and dermal uptake may also occur (6, 7). With young children, the Zn > Pb), (ii) carbonates (Ca-Mg > Fe > Pb), and (iii) sanding slag. Iron oxides, principally goethite and ferrihydrite, are formed during iron sulfide oxidation under the Eh/pH conditions of the residential soils. Altered pyrites and sphalerites, containing up to 40 mol % of Fe, generally have weathering rinds of iron oxides. While Pb concentrations range from nondetectable to 50 mg/kg in sulfide minerals (exclusive of galena inclusions in pyrites), Pb
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Total element concentration.
soil soil soil soil soil soil soil soil soil
S1 S2 S3 S4 S5 S6 S7 S8 S9
a
tailings tailings slag mine waste mine waste smelter ash/soil mixture
type
W1 W2 W3 W4 W5 W6
sample no.
b
35 108 78 62 77 nd 56 nd 83
3 14 54 6 5 nd 3 nd 79 nd
