Environ. Sci. Technol. 1998, 32, 3825-3830
Toxicity Characteristic Leaching Procedure Fails To Extract Oxoanion-Forming Elements That Are Extracted by Municipal Solid Waste Leachates KIM HOOPER,* MILAD ISKANDER, GURMAIL SIVIA, FATIMA HUSSEIN, JOHN HSU, MERLYN DEGUZMAN, ZENAIDA ODION, ZAIDA ILEJAY, FRED SY, MYRTO PETREAS, AND BARTON SIMMONS Hazardous Materials Laboratory, California Department of Toxic Substances Control, 2151 Berkeley Way, Berkeley, California 94704
U.S. EPA and state regulatory agencies rely on standard extraction tests to identify wastes that have the potential to contaminate surface water or groundwater. To evaluate the predictive abilities of these extraction tests, the Toxicity Characteristic Leaching Procedure (TCLP), the Waste Extraction Test (WET), and the Synthetic Precipitation Leaching Procedure (SPLP) were compared with actual municipal solid waste leachates (MSWLs) for their ability to extract regulated elements from a variety of industrial solid wastes in short- and long-term extractions. Shortterm (18 and 48 h) extractions used MSWLs from a variety of California landfills. Long-term sequential extractions (4884 days) simulated longer term leaching, as might occur in MSW landfills. For most regulated elements, the TCLP roughly predicted the maximum concentrations extracted by the MSWLs. For regulated elements that form oxoanions (e.g., Sb, As, Mo, Se, V), however the TCLP underpredicted the levels extracted by the MSWL. None of the standard tests adequately predicted these levels. The results emphasize the need for better standardized techniques to identify wastes that have the potential to contaminate groundwater with oxoanion-forming elements, particularly arsenic.
Introduction The Toxicity Characteristic Leaching Procedure (TCLP) (1) was adopted by the U.S. EPA to identify wastes that have the potential to contaminate groundwater with a number of regulated elements based upon disposal in a municipal solid waste landfill. The inaccuracy of TCLP, however, in predicting extraction of elements from wastes (especially alkaline wastes) by landfill leachates is a gap in the federal regulation of hazardous waste (2). Earlier, California adopted the Waste Extraction Test (WET) to help identify wastes that may contaminate groundwater (3). The principal difference between the two tests is the choice of anions used to simulate the leaching properties of municipal solid waste leachates (MSWLs). Acetate, used in the TCLP, has been found often * To whom inquiries should be addressed; phone (510)540-3499; fax: (510)540-2305; e-mail:
[email protected]. 10.1021/es980151q CCC: $15.00 Published on Web 10/21/1998
1998 American Chemical Society
TABLE 1. Elements Regulated in Hazardous Wastes regulated element
symbol
antimonya arsenica barium beryllium cadmium chromiuma,b cobalt copper lead mercury molybdenuma nickel seleniuma silver thallium vanadiuma zinc
U.S.
Sb As Ba Be Cd Cr Co Cu Pb Hg Mo Ni Se Ag Tl V Zn
California X X X X X X X X X X X X X X X X X
X X X X X X X X
a Elements that form oxoanions and polyanions (8). is regulated separately in California.
b
Chromium(VI)
TABLE 2. Experimental Design treatment
extraction fluid
volume waste extraction (mL) (g) period
MSWL blank
MSWL
500
0
MSWL (1:10)
MSWL
500
50
MSWL (1:10) + CO2 MSWL (1:20)
MSWL
500
50
MSWL
500
50
MSWL (1:20) + CO2 WET blank WET (1:10) TCLP blank TCLP (1:20) SPLP blank SPLP (1:20)
MSWL
500
50
500 500 1000 1000 1000 1000
0 50 0 50 0 50
citrate 0.2 M citrate 0.2 M acetate 0.1 M acetate 0.1 M sulfate/nitrate sulfate/nitrate
18 h to 84 days 18 h to 84 days 18 h to 84 days 48 h to 84 days 48 h to 84 days 48 h 48 h 18 h 18 h 18 h 18 h
replacement volume, (mL)a 50 50 50 100 100 50 50 100 100 100 100
a For long-term extractions only; 10% aliquots of extractant solution were analyzed at each sampling interval.
in MSWLs. Citrate, used in the WET, is reported to be animportant chelator of toxic metals (4). In a study that extracted MSW ashes with acetate, the WET, and MSWL, the WET generally extracted more than did the other leaching tests (5). A third extraction test, the Synthetic Precipitation Leaching Procedure (SPLP) (6), does not have a specific regulatory application, but simulates the extraction of elements from wastes by percolating rainfall. As shown in Table 1, California regulates 17 elements in solid waste (7), and the U.S. EPA regulates eight elements (1). Six of the regulated elements form oxoanions (8) (Table 1), and may behave differently than the other regulated elements. Recently, California reviewed its hazardous waste regulations. As part of this effort, studies were undertaken to compare the amounts of regulated elements extracted from wastes by the TCLP, WET, SPLP, and MSWLs to VOL. 32, NO. 23, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3825
TABLE 3. Concentrations (mg/kg) in Wastes and Composites short-term solid waste Ag Al As Ba Be Ca Cd Co Cr Cu Fe Hg Mg Mo Ni Pb Sb Se Tl V Zn a
long-term
burn ash, BA
composite, CO
mine tailings, MTa
NAb 10100 229 157 8.58 6190
