chlorinated hydrocarbon data relevant to this study. At DGA, Edwin Williams contributed to instrument calibrations, Eric Grosjean provided support in the field operations and in data reduction, Fabrice Grosjean assisted in data reduction, and Denise Yanez prepared the draft and final versions of the manuscript. Registry No. PAN, 2278-22-0; CH3CC13, 71-55-6; CpCl,, 127-18-4.
Literature Cited National inventory of potentially toxic pollutants. Superfund Amendments and Reauthorization Act, Title 111, US. Environmental Protection Agency, Washington, DC, 1989. Zurer, P. Chem. Eng. News 1989,67(49),4-5. Rasmussen, R. A.; Khalil, M. A. K. Sci. Total Environ. 1986, 48, 169-186. Rasmussen, R. A.; Khalil, M. A. K. Science 1986, 232, 1623-1624. Shikiya, D.; Liu, C.; Nelson, E.; Rapaport, R. The magnitude of ambient air toxics impact from existing sources in the South Coast Air Basin. Revision Working Paper No. 3, Planning Division, South Coast Air Quality Management District, El Monte, CA, 1987. Barnstable, H. G.; Rogers, D. P.; Shorran, D. E. Atmos. Environ. 1990,24B, 137-151. Miller, D. F.; Shorran, D. E.; Moffer, T. E.; Rogers, D. P.; White, W. H.; Macias, E. S. J . Air Waste Manag. Assoc. 1990,40, 757-761. Hisham, M. W. M.; Grosjean, D. Southern California Air Quality Study: Toxic Air Contaminants, Task I, Final Report to the California Air Resources Board, Agreement A832-152, DGA, Inc., Ventura, CA, Jan 1990.
(9) Lawson, D. R. J. Air Waste Manag. Assoc. 1990, 40, 156-165. (10) Hisham, M. W. M.; Grosjean, D. Environ. Sci. Technol. 1991,25, 857-862. (11) Hisham, M. W. M.; Grosjean, D. Abstracts of Papers, 198th National Meeting of the American Chemical Society, Miami Beach, FL, Sept 10-15,1989 American Chemical Society: Washington, DC, 1989; ENVR 69. (12) Hisham, M. W. M.; Grosjean, D. Atmos. Environ. 1991, Z A , 1497-1505. (13) Grosjean, D.; Wilhns, E. L., II; Hisham, M. W. M. Removal of pollutants by carbon and permanganate-alumina filtration systems in museums: a case study. Final report to the Getty Conservation Institute, DGA, Inc., Ventura, CA, Sept 1990. (14) Williams, E. L., 11; Grosjean, D. Inland Areas Air Quality Study: A One-Yenr Survey of Ambient Levels of Aldehydes, Nitric Acid and Peroxyacetyl Nitrate (PAN) in Palm Springs and Perris, June 1989June 1990. Final report to the South Coast Air Quality Management District, DGA, Inc., Ventura, CPL,Nov 1990. (15) Williams, E. L.; Clrosjean, D. Atmos. Environ. 1990,24A, 2369-2377. (16) Grosjean, D.; Parniar, S. S.; Williams, E. L. Atmos. Enuiron. 1990,24A, 1207-1210. (17) Rasmussen, R. A. Chlorinated Hydrocarbon data during SCAQS. Dept. of Environmental Sciences, Oregon Graduate Institute, Beaverton, OR, 1987. (18) Redgrove, M., California Air Resources Board Technical Services Division, Sacramento, CA, personal communication, 1989. Received for review January 8,1991. Revised munuscript received June 17, 1991. Accepted June 25, 1991. This work has been supported in part by the California Air Resources Board, Sacramento, CA, Agreement A832-152, The Getty Conservation Institute, Marina del Rqy, CA, and the South Coast Air Quality Management District, El Monte, CA.
COMMUNICATIONS Interaction of Quicklime with Polychlorobiphenyl-Contaminated Solids David L. Sedlak, Kirk E. Dean, David E. Armstrong, and Anders W. Andren" Water Chemistry Program, University of Wisconsin, Madison, Wisconsin 53706
Introduction A recent press release (I) from the United States Environmend Prokction Agency (u.s.EPA) stated that the application of quicklime (CaO) to soils at a polychlorobiphenyl- (PCB-) sik in significant decreases in PCB concentrations. ~~b~~~~~~experiments on the interaction of quicklime and PCBs performed by a u.s, EPA contractor(2) led to the conclusion that the observed losses were attributable to an abiotic chemical reaction. Results of the laboratory experiments did not indicate either a specific reaction mechanism or the identity of the constituents present in quicklime responsible for catalyzing the reaction. Furthermore, the experiments did not fully disprove the possibility that physical processes, such as volatilization, were responsible for the observed losses. The EPA Risk Reduction Engineering Laboratory in Cincinnati, OH, is performing fur1036 Environ. Sci. Technol., Vol. 25, No. 11, 1991
ther experiments with quicklime (3),and their preliminary results suggest that Physical Processes may be The possibility that quicklime could provide a Simple, effective m a n s of removing PCBs from contaminated soils would have profound implications for waste treatment, and further examination of this phenomenon is merited. The hydration of quicklime (reaction 1) is a highly exothermic reaction, and relatively high temperatures can be reached in quicklime-amended soils. For example, CaO + HzO
-
Ca(OH)2
(1)
hydration of a sample of commercial grade quicklime with a small quantity of water results in temperatures of 80-90 "C within several minutes. Increased temperatures in quicklime-amended soils could cause PCB losses through either the effect of temperature on abiotic reaction rate constants or enhanced volatilization.
0013-936X/91/0925-1936$02.50/0
0 1991 American Chemical Society
Abiotic degradation reactions of PCBs at temperatures below 100 "C have been reported previously (4-6). The oxidation of PCBs has been observed in the presence of a ruthenium tetroxide catalyst a t temperatures between 50 and 70 "C (4). Reductive dehalogenation and ring cleavage have been achieved with a palladium catalyst and sodium hypophosphite a t temperatures between 50 and 90 "C (5). Although the catalysts and conditions used in these laboratory experiments probably do not exist in quicklime-amended soils, it has been suggested (2) that some impurity in commercial quicklime formulations catalyzes a similar abiotic reaction. Elevated temperatures in CaO-treated soils may also affect the physical partitioning of PCBs between soil, water, and air. Measured Henry's law constants, particle/water partition coefficients, and particle/air partition coefficients are all strongly temperature dependent, and high temperatures favor partitioning into the vapor phase in such three-phase systems (7).The partitioning of PCBs at temperatures above approximately 40 "C has not been studied in great detail; however, theoretical considerations imply a continuation of the trends observed at lower temperatures. In view of the uncertainty of the previously reported results (2) and the potential benefits of the quicklime treatment, we performed experiments to discriminate between losses by volatilization and degradation. The effect of quicklime was evaluated under two sets of conditions. First, losses were measured in quicklime-treated suspensions of diatomaceous earth/sand, under conditions similar to those described in a previous report (2). Second, treatment of PCB-contaminated soil with quicklime was simulated. Measurements were made of the parent PCB congener and possible degradation products in the solid, liquid, and gas phases following treatment.
Materials and Methods To facilitate analysis of losses and possible degradation products, we used a specific PCB congener, 2,2',4,4'tetrachlorobiphenyl (TCB). Previous experiments with PCB mixtures ( 6 ) indicate that tetrachlorobiphenyl congeners will be intermediate in reactivity with hydroxyl radicals and no significant variability in reactivity has been observed between PCB congeners undergoing other abiotic reactions ( 4 , 5 ) . Purified TCB and I4C-labeledTCB were obtained from Ultra Scientific (North Kingstown, RI) and from Sigma Chemical Co. (St. Louis, MO), respectively. Diatomaceous earth (Celite 521) and analytical grade CaO (99.95% purity) were purchased from Aldrich (Milwaukee, WI). Millipore Milli-Q water was used in all experiments. Commercial grade quicklime was obtained from The Western Lime and Cement Co. (West Bend, WI). Results from analysis of the commercial quicklime by ICP spectroscopy are included in Table I. PCB-spiked solids were prepared by adding the appropriate amount of 2,2',4,4'-TCB (14C-labeled and unlabeled), dissolved in ether, to a glass beaker containing a 2:l (by mass) mixture of diatomaceous earth/sand. Initial TCB concentrations on the solids were approximately 100 mg/kg. The ether was allowed to slowly evaporate for 12 h at room temperature prior to the start of an experiment. To extract TCB and possible nonpolar degradation products, samples (10 mL) were collected from the diatomaceous earth/sand suspensions. The samples were extracted in isooctane/acetone using a high-energy sonication probe (8). TCB and possible volatile degradation products in the gas phase were collected on Tenax-TA resin traps. The
Table I. Results from Analysis of Commercial Quicklime Sample by ICP Spectroscopy
element arsenic beryllium cadmium chromium cobalt copper lead lithium aluminum calcium iron
concn, ppm 37.7 19.1 2.6 13.7 16.2 7.4 16.9 2.2
element
Trace Components manganese molybdenum nickel potassium selenium sodium zinc magnesium
Major Components, 70of Total 0.203 magnesium 34.25 phosphorus 0.125 sulfur
concn, ppm 135.1 3.2 15.4 48.9 39.4 140.1 4.1 33.93 21.58 0.223 0.306
traps were extracted by elution with 15 mL of acetone and then 80 mL of hexane at a rate of 2 mL/min. Extracts were concentrated to 10 mL prior to analysis. After completion of experiments under simulated field conditions, Soxhlet thimbles containing quicklirneamended solids were placed into Soxhlet extractors and extracted with a 1:l mixture of hexane/acetone for 16 h. Extracts were dried by elution through Na2S04and adjusted to a volume of 50 mL prior to analysis by GC/MS. All solvent extracts were analyzed for TCB by GC/MS (Hewlett-Packard 5890/5970) with a DB-5 capillary column (J&W Scientific, Folsom, CA). TCB concentrations were quantified using the selective ion monitoring (SIM) mode with 2-chlorobiphenyl as an internal standard. Samples were also analyzed qualitatively for reaction products using the scan mode ( n / e 40-550). 14C in solvent extracts was quantified by liquid scintillation counting (Packard Instruments, Model 1900CA) in Optiflour scintillation cocktail. The production of 14C02was monitor d by analysis of the Carbosorb solution after completion of the experiment. Two milliliters of Carbosorb cocktail was added to 10 mL of Permaflour scintillation cocktail and the resultant mixture was counted on a liquid scintillation counter. The amount of labeled TCB used in these experiments was sufficient to detect mineralization of less than 1% of the total TCB initially present. The possible production of volatile degradation products was evaluated using a cold trap. The walls of a glass impinger were coated with hexane and immersed in a liquid nitrogen bath. The cold trap was sampled by removal of the impinger from the liquid nitrogen and addition of 5 mL of hexane. The hexane was immediately counted on a liquid scintillation counter. Chloride concentrations were measured at the conclusion of the reaction using a chloride-specific electrode (Orion Model 971700).
Results and Discussion Suspension Experiments. Suspensions of diatomaceous earth/sand (33.3 g/L) were used in the first series of experiments. These experiments were performed in an attempt to replicate the conditions under which PCB losses were previously reported (2). The suspensions were prepared by adding quicklime to the spiked solids in the experimental device illustrated in Figure 1. To minimize losses of TCB and possible degradation products to surfaces in the reactor, all parts (with the exception of a Teflon-coated magnetic stir bar) exposed to the suspensions or the air in the headspace were constructed of glass, and only brass fittings and valves were Environ. Sci. Technoll., Vol. 25, No. 11, 1991
1937
Three-way Valve
0
P u r i f i e d Air-
0 Blank 0 P u r e CaO I
Flgure 1. Experimental device used in suspension experiments.
0
Table 11. Final Mass Balance for TCB in Suspension Experiments
experiment
traps
blank analytical CaO commercial CaO
81 81 65
% TCB recovered" suspension headspace
2 2 10
total
4 3
87 86
6
81
used. In addition, all headspace surfaces were heated with insulated heating tape, controlled by a voltage regulator. Preliminary experiments demonstrated that such measures were essential to avoid losses of TCB to surfaces in the headspace. Despite these precautions, small amounts of TCB (3-6'70 of the total amount present) partitioned to the headspace surfaces, necessitating hexane extraction of the headspace surfaces and valves at the conclusion of the experiment. The experiment was started by adding 450 mL of water, through a three-way valve, to 15 g of TCB-spiked diatomaceous earth/sand and 7.5 g of quicklime. For the blank treatment (no CaO), the pH of the water was adjusted with NaOH to the same values (12.1) as the suspensions containing quicklime. Following addition of water, the suspension was heated to 90 "C with a heating mantle and purified air was purged through the -200-mL headspace a t a rate of 20 mL/min. Air from the headspace was passed serially through two Tenax-TA resin traps. The second trap usually contained less than 2'70 of the total mass of TCB found in the first trap. The air was then passed through a midget impinger containing 10 mL of Carbosorb cocktail to trap 14C02.The air was then passed through a glass cold trap containing hexane, which was cooled with liquid nitrogen. Flow rates were monitored using a soap bubble meter connected downstream of the impinger. Suspension samples and traps were analyzed after 30 min and a t 1-h intervals for 5 h. Suspension samples (10 mL) were withdrawn into a volumetric pipet modified to fit onto the sampling port with a brass Swagelock fitting. The distribution of TCB in the suspensions and on the traps is shown in Figure 2. Most of the TCB volatilized from the suspensions and was recovered on the resin traps. Approximately BO-85% of the total TCB added was accounted for at the conclusion of the experiments on the traps, the headspace surfaces, and in the suspension (Table 11). Losses of approximately 15% of the total TCB added were observed in all of the experiments (including the Environ. Sci. Technol., Vol. 25, No. 11, 1991
2
3
4
5
Time ( h o u r s )
" Expressed relative to amount TCB added.
1938
1
Flgure 2. Distribution of TCB in suspension and on traps for suspension experiments. Filled symbols indicate suspensions: hollow symbols indicate resin traps.
experiment without CaO). The losses were most likely attributable to incomplete extraction of headspace surfaces and volatilization occurring during sampling. Volatilization rates from the suspension containing analytical grade CaO and the blank experiment were nearly identical. The suspensions prepared from commercial grade CaO exhibited slower volatilization rates, which may have been attributable to enhanced sorption of TCB on organic materials, or other impurities in the commercial quicklime. Aside from consistent mass balances between the different experiments, several other observations suggest that volatilization rather than abiotic degradation was responsible for TCB loss from the suspensions. Products of TCB degradation, either partial degradation or complete mineralization, were not detected. These include the following. (1)Nonpolar degradation products, produced through either hydroxylation or dechlorination of TCB. 2,2',4,4'TCB was the only compound detected in GC/MS scans of the solvent extracts. In addition, analysis of 14Cin the solvent extracts agreed with results from the GC/MS analysis (mean difference between 14Cand GC/MS analyzed TCB was less than 2.0% for each experiment). (2) Volatile degradation products, produced through ring saturation and/or cleavage. 14C was not detected above background levels in any of the samples collected from the cold trap. (3) 14C02,produced through mineralization of TCB. 14C was not observed at concentrations above background in any of the samples collected from the Carbosorb impinger. (4) Increased chloride concentrations, produced through dechlorination and/or mineralization. Chloride concentrations in samples from the suspe~~sions ranged from 0.15 to 0.25 mM. The sensitivity of the chloride-specific electrode may not have been adequate to detect small increases in chloride, but no trend was observed in concentrations between the experiments. These results demonstrated thait volatilization was the mechanism responsible for TCB loss under these conditions. After 5 h at 90 "C, TCB did not degrade in the presence of quicklime. Enhanced volatilization of TCB from suspension may explain the results reported previously. Although EPA's contractor (2) did not detect a
Table 111. Effect of CaO and Water on the Loss of 2,2',4,4'-TCB from Spiked Diatomaceous Earth/Sand Mixtures conditions4 % CaO
% H20
1
0
2 3 4 5 6
18 36 36 36 67
66 25
expt
0
50 100 100
max temp, OC 23 34 23 37 30 56
TCB recovered concn, pg
re1 % b
452, 406 416 408, 345 393 367 460, 344
92 90, 85 87 81 102, 85
"Percent CaO and percent water added expressed on a mass basis relative to the total mass of solids. "ecovery expressed relative to blank experiment performed at the same time.
significant amount of PCB in traps attached to the outlet of his experimental system, a significant amount of volatilization from the suspension may have occurred. Our experiences in the design of the experimental system suggest that unless the headspace above a suspension is heated, and only glass and metal parts are used, PCBs will partition strongly to surfaces. Simulated Field Conditions. Experiments with heated suspensions of PCB-contaminated materials may not adequately simulate conditions occurring when quicklime is applied to contaminated soils and sludges. The water content of quicklime-amended soils hydrated under field conditions is significantly lower than that of the suspensions, and volatilization could occur from dry particles warmed through the transmission of heat from elsewhere in the soil column. In addition, it is unlikely that temperatures as high as 90 "C will be reached under field conditions, or that elevated temperatures will be sustained for long time periods. Conditions more closely resembled those occurring in soils were simulated to evaluate the potential for volatilization and/or abiotic degradation of PCBs in the presence of quicklime. These experiments were performed (without external heat) by adding very small amounts of water (
